letter from EAA

[carlschneider]

I have flown my gyro at oshkosh the last 38 years. The last five years I have manned the PRA booth. The is a letter I got from the EAA.


Carl

This is not the first time that this has been an issue during our show.EAA does not consider this to be acceptable business activity. We ask that something is done to extinguish this type of business conduct at future EAA events. If this type of business continues,EAA will take appropriate action.

The following is the letter that EAA received.

I believe that you should be made aware of something that happened at the EAA AirVenture 2005. The reason I have taken wo long to send this note is that it took this long for me to cool off enough to put the event into words.

On Sunday, July 31, the last day of the EAA, I decided to tour the ultra-lite area with two other RAF 2000 owners. As you know, there are several representatives of the gyroplane industry that have a footprint on the ground in that area so we were interested in visiting with them. That said the area would most certainly be a stop on the list of prospective purchasers of the RAF 2000.

We most naturally stopped at the PRA's tent, since all three of us are members of that association. At least two of us were wearing RAF pilot caps. After reading the caps, the fellow manning the booth came towards us shaking his finger at us and indicating that there were a lot of deaths as the result of RAF 2000 gyroplanes.[I remember reading an artical in the PRA Rotorcraft Magz. that somewhat slammed the RAF for fatalities. In reviewing a few of the examples given in the article,I noticed that the pilots were not certified in class or category to be flying an RAF 2000. I considered the data flawed at best, and ignored it.]

Each of us tried to reason with the PRA representative. Certainly he must be aware that the RAF 2000 is the most successful gyroplane kit on the Market, and certainly he should not publicly slander another vender at the EAA. We all believe that training and certification leads to safe flights. He didn't agree.
Wne-by-one we gave up and walked away to enjoy what was to that point a fantastic experimental avaition event.

This encounter could only be viewed as very negative and upsetting to any enthusiast of the RAF gyroplane. My guess is that RAF's sales will be probably where impacted by the presence of the PRA representative at the EAA AirVenture 2005.

I just wanted to let you know what is taking place on the EAA grounds.

Jim


I very well rember them---they attacked me when I was packing to go home. They lie---I'm done.

Does anyone else want to man the PRA booth in '06?

Carl

[Chuck Roberg]

I don't know what to say Carl. Sounds like the EAA does not care about stable aircraft.

I can understand why your frustrated. Sorry your going to give up the PRA booth. I'd like to hear a little more about your side of the story.

[Heron]

Carl
Don't give up, you are precious!
can I have that jerk's address or phone number?
I may have a few words to say to him.
Next year lets have a sandwich shop there an the RAF sandwich will be . . .boloni of course! :D
But dont be upset
Heron

[C. Beaty]

When Carl says the RAF stooges lied, they lied. But that shouldn’t surprise anyone familiar with RAF business practices.

Several years ago, when Norm Jackobson was operating the old Rotorcraft Conference, Don LeFluer offered to lay some money on him for “Internet Services” if he would pull all posts critical of RAF products.

Norm of course told him where he could put his money and then got threatening letters from Don’s lawyers.

*****************************

From the wording of the letter supposedly submitted by the “offended” individuals, it is clear that it was composed by RAF Marketing.

[Chuck_Ellsworth]

I also have been the recepient of a threatening letter from RAF's lawyer.

It of course was bluff, because I have enough evidence to back up my allegations of dishonest buisness practices by RAF that they never followed up.

However no one should ignore threats of legal action from anyone because it can be very , very expensive trying to defend yourself.

The gyroplane community has a very serious problem that just never seems to end with this infighting about stability or the lack thereof.

What everyone should do is ask how many companies are selling products that keep this issue front and center.

Chuck E

[Adam H]

Maybe I'm being naive here but I didn't see anything in the letter that said this was a complaint from RAF, the letter said it was three guys, two of whom were RAF owners, wearing RAF hats. The question in my mind is whether this is a couple random RAF guys making this accusation or actually an RAF conspiracy... That is what we're saying, right?..that RAF (the company) so hates the PRA that they sent a false letter to the EAA accusing someone at the PRA tent of bad mouthing RAF and giving these three guys a hard time. If that is the case then wow, that is really low. Carl, maybe you could give a little more background to this story before we all jump to conclusions. Do you remember three RAF guys coming into the tent at all? Who attacked you when you were leaving?.. and by attacked do you mean they were yelling at you?

[KenSandyEggo]

Gee, I have one too. Maybe we should form a club. If everyone who has one sent me $100 in dues, I could by myse.....I mean the club a car. Then once a year, anyone who comes to Charlotte could drive it for a 1/2 hour. I'll volunteer to keep the oil changed and the car washed the rest of the year. We'll put the title in my name so you guys don't get sued.

[PW_Plack]

Chuck R,

I don't think this has anything to do with EAA's stand on safe aircraft. I'm not sure you could even make a statistical case that the RAF is less safe than other gyros on a fatality-per-hours-flown basis. If EAA took this seriously enough to accuse Carl of this action without getting his side of the story, it suggests to me that the letter came from someone at RAF, a major AirVenture client.

Carl, if this in fact never happened, I hope you responded.

[C. Beaty]

Carl, you do need to respond to the three stooge’s letter to the EAA.

My speculation is that someone you had explained CLT to went to the RAF booth and began asking why the RAF-2000 did not have CLT or a horizontal stab.

Don LeFleur realized his sales would be hurt if prospective buyers knew the facts so sent his 3 stooges down to hassle you and pick a fight.

That letter to the EAA has his handprints all over it:

“I remember reading an artical in the PRA Rotorcraft Magz. that somewhat slammed the RAF for fatalities. In reviewing a few of the examples given in the article,I noticed that the pilots were not certified in class or category to be flying an RAF 2000. I considered the data flawed at best, and ignored it.”

“Certainly he must be aware that the RAF 2000 is the most successful gyroplane kit on the Market, and certainly he should not publicly slander another vender at the EAA. We all believe that training and certification leads to safe flights.”

I don’t know whether you made the spelling errors in retyping or if Don threw in a couple of misspelled words as a disguise. Whatever the case, those are Don’s words.

[Timchick]

It sounds like those guys (if they did actually read an article in PRA) went to Carl looking for a fight. Unfortunately, RAF has more pull and influence than the the PRA with the EAA.

[carlschneider]

Adam and all

I do not rember the exact words but the three of them came to the PRA tent making fun of my gyro. One was very aggressive. Janie was behind the tent and even before they opened their mouths, she thought they were looking for a fight.

One of them was real civil and we had a good conversation after two of them left.

EAA did not ask for my side of the story,they just said we had to get along at the convention.

Over the years, after having the thrust line issue explained to them, several people said they were going to get their money back from RAF. I suppose Don didn't like that.

Carl

[Doug Riley]

Back to Ron Awad's point. This isn't 1992. Carl's story proves that point. The present situation is not one of individual homebuilders who simply have different takes on a debatable technical issue. That may have been the case 15 years ago, but it just no longer is.

RAF is engaged in a systematic and very aggressive disinformation campaign, launched for its own financial gain (or maybe survival). The campaign is conducted by every means OTHER than rational debate: technical double-talk, personal attack on very reputable aviation people, intimidation through legal threats, muzzling of government-licensed flight instructors through financial coercion and intentional isolation of new customers from sources of the truth. (That last tactic is a favorite of cults of the Jim Jones variety, BTW.)

Meanwhile, the physics of RAF's design problem is high-school level stuff. Push on something off center and it spins. We have world-class engineers and physicists (some with PhD's) explaining this material to us. We have the results of a British government-sponsored study. We have Sport Pilot test criteria compiled painfully by worldwide consensus of test pilots, engineers and designers -- with RAF's own participation and consent. Most embarrassing for all of us, we have Cierva's own patent, claiming centerline thrust as a stability innovation, circa 1932.

All of these authorities point us in the same direction. Still, RAF tries to slither around them, deny their authority or just intimidate them into shutting up.

Once you begin advocating "peace at any price," you've as good as signed yourself into slavery. To hold onto your integrity, sometimes you just have to draw the line, right HERE, right NOW. At some point, you have to say, even to your best friend, that our friendship ENDS if you persist along an immoral and destructive path. It is not worth splattering the bodies of innocent people just to get more folks to attend your chapter corn roast.

If that rips the "community" apart, then the community is a corrupt one and shouldn't exist.

[automan1223]

You cannot argue numbers. The facts are what they are.

EAA needs to understand that safety over profit is where they should follow the pointer on the moral compass. Not harass the only rotorcraft org about promoting safety !

Jonathan

[Dean_Dolph]

Carl, who signed the letter from the EAA? If the PRA BOD isn't going to respond then it is likely that one of us will and that might not be a good idea! Then again........ In either case an EAA contact is needed.

[Heron]

Guys . . .Is PRA really this insignificant in this matter?
Heron

[GyroRon]

Doug I agree with what you said. I think RAF the company is scum. But let us focus our powers on the company itself and do something.

[karlbamforth]

I think RAF the company is scum.

Ron, I know you are an outspoken individual, but please try to refrain from making comments like this.
It doesn't help anyone, it lowers poeples opinion of you and it certainly doesn't help the gyro community as a whole.

To everyone.
If we are ever going to improve the reputation of the gyro community we have to be civil and adult about what we say. We have to have facts and be able to prove them.
It really doesn't matter how important the subject, ranting, raving, swearing and name calling will simply discredit everything that is said. We will just be viewed as a bunch of wierdo hooligans out to kill ourselves, ohh hold on a minute thats what they think already.

[Chuck_Ellsworth]

Well Karl.. each to his own opinion. and as to this.

" Quote:
Originally Posted by GyroRon
I think RAF the company is scum. "

Ron is only telling it like it is.

It is those with their heads buried in the sand who do not understand.

Chuck E.

[Heron]

I could not do anything secret or wrong because I am always visible and loud . . .and I like it that way! :D
Ron is just fine and my opinion is that RAF is not part of us and will never be, unless it changes hands . . .hmmm there is a thought . . .PRA should buy RAF and . . . .ok . . .ok . . .
Heron

[Rick Whittridge]

I smell Canadian Bacon!

[Aussie_Paul]

.....All this politically correct s**t is not helping the world, let alone the gyro movement.

The are times when someone has to stand up and be counted. I did this in Oz several years ago, and paid a price by upsetting a number of people.

The fatality rate of HTLMs at that time was quite horrendous, (the AC era) and I was peeved that I was lumbered in with a dangerous pecies of pilot and aircraft.:eek:

At a flying a few weeks ago I see most gyros close to CLT sporting effective h/stabs.:D

I have done my job and the gyroplane discussion in Oz is focused in the right direction now. yes there is always a bit opf bitching etc buy that is of no cosequence in the whoile sachem of having gyropl;anes respected in the aviation arena. I am not lookng for a pat on the back just stating facts. This action cost me dearly financialy and in the degredation of some personal relationships, BUT a relationship so fragile is not worth getting upset about.

The world wide gyro industry is heading in a much better direction safety wise than it has for quite some time. The internet is a tool that proven to be a very effective tool.

As I said above, eventually a stand has to be made by individuals, clubs, associations, legislators, and companies.

I am passionate about gyroplanes, and about stability in whatever aircraft you fly.

How quickly we achive our goals of acceptance in the aviation community will depend on how long it takes for people, clubs, associations, legislators, and companies to take a stand.

I hope that the intent of this post has been conveyed by my inadequate writing style.

Aussie Paul.:)

[mcbirdman]

Doug You have expressed the problem that has been brewing for years. You addressed the overall problems and how it trickles down to individual experience with AMAZING clarity. It is clear that the positioning through advertising and swaying people from asking the questions they won't answer has resulted in sales that are still being made without people having all the information. Then people who are verbal about their losses and frustration are labeled or asked to sit on the sideline while they show up with their flawed machines and lack of real changes. You hit it so clear from a wide point of view all the way down to how they are working at the grassroots level. I am afraid that your post may get lost in the other words of support for Carl. Carl, I am sorry you are getting flak now from them. Doug WRITE (right) on !

Doug R says :"Back to Ron Awad's point. This isn't 1992. Carl's story proves that point. The present situation is not one of individual homebuilders who simply have different takes on a debatable technical issue. That may have been the case 15 years ago, but it just no longer is.

RAF is engaged in a systematic and very aggressive disinformation campaign, launched for its own financial gain (or maybe survival). The campaign is conducted by every means OTHER than rational debate: technical double-talk, personal attack on very reputable aviation people, intimidation through legal threats, muzzling of government-licensed flight instructors through financial coercion and intentional isolation of new customers from sources of the truth. (That last tactic is a favorite of cults of the Jim Jones variety, BTW.)

Meanwhile, the physics of RAF's design problem is high-school level stuff. Push on something off center and it spins. We have world-class engineers and physicists (some with PhD's) explaining this material to us. We have the results of a British government-sponsored study. We have Sport Pilot test criteria compiled painfully by worldwide consensus of test pilots, engineers and designers -- with RAF's own participation and consent. Most embarrassing for all of us, we have Cierva's own patent, claiming centerline thrust as a stability innovation, circa 1932.

All of these authorities point us in the same direction. Still, RAF tries to slither around them, deny their authority or just intimidate them into shutting up.

Once you begin advocating "peace at any price," you've as good as signed yourself into slavery. To hold onto your integrity, sometimes you just have to draw the line, right HERE, right NOW. At some point, you have to say, even to your best friend, that our friendship ENDS if you persist along an immoral and destructive path. It is not worth splattering the bodies of innocent people just to get more folks to attend your chapter corn roast.

If that rips the "community" apart, then the community is a corrupt one and shouldn't exist.

--------------------------------------------------------------------------------
Last edited by Doug Riley : Today at 07:48 AM.

[PW_Plack]

Carl,

I'd like to know who at EAA sent this thing, if only so I can accurately describe the letter when I decline to renew my EAA membership this year.

[Doug Riley]

I beat'cha to it, Paul W.!

[carlschneider]

Paul

The letter came from the office of Rebecca Blake at the EAA headquarters.

You can get there telephone number on the back of your EAA card.

Carl

[Dean_Dolph]

Anyone see a way to organize a gyro stability truth group to present the facts where ever RAF sets up camp?

I would not like to see it affiliated with anyone but if this happened I wonder what the FAA and RAF's reaction would be. I've never been to Osh so don't know what the layout is or how it is managed so this might not be possible.

[bartc150]

How about a banner advertising this forum. I recently thought of this at a light sport aircraft show in Sebring.

[Timchick]

I like the t-shirts idea with the phrase "Friends don't let friends fly unstable Gyros" and loiter around the RAF booth.

[Dean_Dolph]

I like the t-shirts idea with the phrase "Friends don't let friends fly unstable Gyros" and loiter around the RAF booth.Hey, there you go! And on the back you could put 'Ask me what an unstable gyro looks like" or something less obvious like "Ask Me What Makes a Gyro Stable". I guess it would be invite trouble to put a RAF silhouette on the front and a silhouette of a stable gyro on the back and/or the Rotary Forum web address.

Edited too add - This should invite attention where ever a person walks at an aviation event. In fact it might have more impact than just loitering around the RAF camp and inviting trouble. That is not to say that people couldn't pass the RAF display frequently. Since I would bet that RAF monitors this Forum, do you think they will take counter measures and contact EAA in order to head anything like this? Hey, that would be good in a way since they would start to acquire a cry baby reputation.

[Harry_S.]

Edited too add - This should invite attention where ever a person walks at an aviation event. In fact it might have more impact than just loitering around the RAF camp and inviting trouble. That is not to say that people couldn't pass the RAF display frequently. Since I would bet that RAF monitors this Forum, do you think they will take counter measures and contact EAA in order to head anything like this? Hey, that would be good in a way since they would start to acquire a cry baby reputation.


Dean; I am in no manner, whatsoever, upholding nor defending RAF Marketing. But IMO, the statement above is a bit juvenile...it seems to me that WE are acquiring the cry baby reputation...if you want to call it that.

Doug R. has a more sensible/logical approach to reaching RAF Marketing.

.

[Timchick]

The EAA can't do anything against anyone if it's just a bunch of individuals. We may not want to tie it to this forum and give the forum a black eye but if enough individuals did something it would be neat. Maybe Phil can whip up some t-shirts for us.

[Dean_Dolph]

Dean; I am in no manner, whatsoever, upholding nor defending RAF Marketing.Maybe not but it sounds like it.But IMO, the statement above is a bit juvenile...Juvenile? Hey at my age I've been called worse and juvenile actually sounds good! ...it seems to me that WE are acquiring the cry baby reputation...if you want to call it that.Why? Just because we keep repeating the facts?Doug R. has a more sensible/logical approach to reaching RAF Marketing.

. There is no denying that Doug admirably always presents his thoughts concisely (to bad I can't!) and with inherent value. That is not to say that there are not multiple ways to achieve a goal and I don't think any of them need to be dismissed without consideration. There is always more than one way to get there from here.

[PW_Plack]

Guys,

You can't confront RAF with the facts until you have some. This whole thing goes nowhere until actual standardized stability testing is conducted on the various kits, allowing legitimate comparisons.

Jim Mayfield made an offer, about two years ago when he was at GBA, to run the whole series of tests on any other company's machines for costs, which were about $4000 at the time. I can imagine several reasons, some legitimate, why other companies might not want to acept the offer.

This will probably have to be done by an independent, outside organization with no agenda. PRA at the very least lacks the money to do it. EAA won't have the interest. Any grant writers out there with a little spare time?

[Vance]

I have not had a positive outcome when I have offered unsolicited advise.

I have not done well with confrontation.

I understand the gravity of the situation, but that does not cause me to believe that a previously unsuccesful stratagy will suddenly work.

I do not have the answer because I am confused.

Thank you, Vance

[Dale Young]

Scum sounds acurate to me Ron. If I allowed my best friend to drive drunk, I'd be labeled an A$$H4le. Let alone put someone in a position that they think that they are safe, when I know that they actually are not!!!

[gyroblackwell]

Guys (and gals)...

I will bring up this Letter at the Bensen Days BOD meeting. I will request that a motion be made to respond to this threat, and I will ask other Board members to help.

Yes the PRA BOD can and will do something about this.
In a formal letter to the EAA rep. that sent the notice. I am also an EAA member and will voice my opinion also. I was at the convention along side Carl for most of the event. I never heard any RAF bashing. Only talking up CLT, and The benefits of the newer designs.

I will personally write a letter voicing my disapproval of the RAF bullies and they're back-stabing methods.

I will Defend as I have the right to do, those that are being falsely accused.

I thought Airventure 05 went really well, and enjoyed hanging out with Carl. Would hate to see the PRA booth band from this event.

[gyrogreg]

I much appreicate all that Carl does and has done for gyros - including his work at Oshkosh and including his passion to make gyros safer! Carl told me about this thread last week, and I'm just catching up. Got something to say, but hope this doesn't dig me a time consuming hole:

First, I do not remember any article in Rotorcraft mag that specifically comments on RAF. Maybe there have some that have, but I don't remember them. I do know that RAF feels like some of the articles myself and others have written were directed at RAF, but I have been careful to keep all my discussions as objective and generic and educational as possible. But, if someone feels the shoe fits them, they may feel a little pressed by some of my articles. We even went so far as to "sanitize" our original NTSB accident report (originally submitted to FAA at their request with full disclosure of the specific makes and models listed) by labeling the various brands and models as "A", "B", "C", etc. I don't agree that the PRA or Rotorcraft mag has specifically pointed fingers at RAF - it may have pointed fingers at gyroplane configurations and poor aerodynamics, but not at specific models!

However, the forum has had no such PC conduct. RAF misplaces the blame on the PRA for the heat they pointedly get on this forum. Even though many of you disagree, the PRA is expected to be the glue or agent to improve the safety of our sport. To do that, the PRA needs to try to keep communications open and constructive. Frankly, it is convenient for some in their "defensive" positions to attribute the bashings they get on the forum as an excuse to not participate in constructive efforts or dialogue at all!

I do believe that part of the big problem we gyro people have is respect and credibility by others - FAA, EAA, etc. The FAA and EAA read these forums, and frankly get a lot of "lobbying" by some pointing out all the foment and disagreement. Frankly, the trash talk is not helping our credibility at all! The defensive and protective postures the finger pointing puts people in is not constructive - it just continues to extinguish any real dialogue and participation to change the accidents and fatalities and the poor respect for our sport.

I first ran into this several years ago when we went to petition the FAA Rotorcraft Directorate in Ft. Worth to allow gyroplanes in the LSA rules. They wanted no part of it, mostly they said, because all the arguing among us (and the often technically immature blaming and finger pointing) convinced them the problems could not be solved - and they did not even want to try to solve our problems.

Believe me, some of the immature trashing on this forum and other places has not helped us bring important portions of the community together, and it paints the gyro community, in the eyes of the FAA, EAA and others, as impossibly immature and unsalvageable. It has sometimes taken superhuman efforts to even get these orgs to lend us an ear.

I know some of us are so very passionate - that we might sometimes get carried away beyond constuctive comments. But, I ask you to keep in mind what others might think when they see immature and non-constuctive name calling and finger pointing. Carl has put out money and time and energy and stress to try to educate people (at Oshkosh and otherwise) on the advantages of gyros and how to get there. If it helps, I also do not think this letter had been provoked by Carl. (I have been the focus of other such similar "letters" that are likely not what they claim to be.) I do appreciate that the current environment certainly can drive any side to less constructive approaches. When the gyroplane community is percieved as a mature and credible entity, maybe the EAA and FAA and others would put more effort into coorperation with us. But, believe me, they have not totally had a complimentary perception of us - understandable if you review some things they might see on these forums! For my part, what they see from the real PRA will be credible and constructive and inviting of open dialogue.

Please try to be part of the solution, rather than part of the problem!

Thanks for your attention - Greg

[Heron]

Greg
I only care about what I think of others, not what they think of me!
SEcondly:
Is there any other place or group, involved in gyros, that is more close together than this Forum? I would like to be part of it, if they take me of course . . .
And if the main organizations that should be guiding us through the hardships and get us to better times, are making decisions based on chit chat . . .then we are in deep s**t, excuse my french.
Why do you blame others for our shortcomings, didn't this people before us do their best?
Maybe there are other reasons for the slump, like bad management and lack of marketing strategies.
It seems to me that RAF is playing the game of influence, like in pressuring some not so strong minds to cave in and leave them alone to do what they want.
Or so I think . . .
Heron

[Doug Riley]

Greg, I know that you know why people lose patience. Many, many times the technically knowledgeable folk (yourself included) have behaved well. They've written cool, polite and organized presentations of their analyses of PIO, PPO and related stability problems and solutions.

These presentations have been scholarly without being stuffy. They've cited other authorities, they've cited history, they've cited basic high-school physics. They've related the theory to our collective real-world experiences. They've pointed out why certain appealing but incorrect theories are flawed.

And they've done it over... and over... and over again. I'm amazed that you and the others have the patience to keep repeating the same material year after year.

The response from the RAF crew has been the same every time. One of them will engage for a first pass. Once the logical give-and-take gets precise, however, they're gone. Trot out the triangle rule for adding vectors and you'd think you'd shown sunlight on a vampire. Dead silence. Total disengagement.

The next thing we see in the cycle is either some new personal outrage -- the EAA letter for example -- or another PPO fatality. The cycle begins anew. Going by memory alone, the period of this cycle looks to be around 4-6 months.

A live joint seminar, with a blackboard and an audience, by the best technically-astute defender of the RAF position and one of the mainstream thinkers, might finally get to the bottom of this.

I do think it's disingenuous of the FAA and EAA to give equal credence to reasoned positions and (given the above cycle) to what appears to be flat-earthism. That's PC-ism run amok. With all their learning and technical resources, surely they can follow the simple physics and figure out who's right. It just isn't that complicated.

[Chuck_Ellsworth]

" I do think it's disingenuous of the FAA and EAA to give equal credence to reasoned positions and (given the above cycle) to what appears to be flat-earthism. That's PC-ism run amok. With all their learning and technical resources, surely they can follow the simple physics and figure out who's right. It just isn't that complicated."

Doug, now that RAF Marketing has a former FAA specialist on their team maybe there will be a reasoned position supported with known physics to bring credibility to their claims that the RAF 2000 is safe, stable and suitable to be used as a primary trainer and sold to the public.

Chuck E.

[Harry_S.]

Maybe not but it sounds like it.


Boy...Never let it be said that I'm in RAF Marketing's corner. Please enlighten...where have I ever stated that I endorse RAF Marketing?

Many times I have said that I like *MY RAF Machine* as I have it configured. I certainly don't see that as an endorsement for the company, (Marketing.) Do you?


Cheers :)

[PW_Plack]

Greg,

You're telling us that the rantings of frustrated everyday citizens on an internet forum are derailing the efforts of the sport's official representative body? That's a little like saying the police won't investigate my mother's murder because the next-door neighbors can't agree whether a .22 round could be lethal.

Your post is headed "Talk facts, not trash!" What facts are we to quote? RAF posts big sales numbers, and to many prospective gyro buyers, that speaks louder than theoretical talk of CLT and H-stabs.

We have no incidents-per-hour stats on RAF, or any gyro, because nobody knows how many are flying, or how many hours they're being flown. That leaves us with the need to scientifically demonstrate the effect of design factors on stability, which nobody seems to be able to get done. I respect you, and appreciate the time and effort you've spent on this issue, but we're stalemated until someone can raise the money to do actual testing to allow comparisons among various gyroplane models.

If there were facts to talk about, much of this bickering would be gone. The people who deny the laws of physics would be shown clearly to be flat-earthers, and the rest of us could just send HTML links to those who obviously hadn't got or understood the news.

[PW_Plack]

Greg,

That's a sad commentary on the state of the FAA. Approval of LSA standards would not impose anything on RAF. They could continue to make their kits the same way they always have, and the decision would be left to the marketplace. RAF has even approved the standards! What's left to do?

Your post is headed "Talk facts, not trash!" What facts are we to quote? RAF posts big sales numbers, and to many prospective gyro buyers, that fact speaks louder than theoretical talk of CLT and H-stabs.

We have no incidents-per-hour stats on RAF, or any gyro, because nobody knows how many are flying, or how many hours they're being flown. That leaves us with the need to scientifically demonstrate the effect of design factors on stability, which nobody seems to be able to get done. I respect you, and appreciate the time and effort you've spent on this issue, but we're stalemated until someone can raise the money to do actual testing to allow comparisons among various gyroplane models.

If there were facts to talk about, much of this bickering would be gone. The people who deny the laws of physics would be shown clearly to be flat-earthers, and the rest of us could refer newbies to real numbers. Until then, the most credible members of our community are still from a community many consider to be a bunch of eccentrics. (To put it mildly.)

[chuter]

I'm going to stick my head up above the trench for minute.

Even though most on this forum might not agree with Mr. Weaver's views on stability, I believe he has represented gyroplanes positively while in the FAA. I believe we have a more acceptable image thanks to his enthusiasm, and that gyros are coming out of the mysterious-death-machine image they've had for so long. I believe the FAA now sees them more as a legitimate sport aircraft.

Of course others like Greg Gremminger deserve a lot of credit in this area also.

I also agree with those on this forum that have suggested the smart-ass name-calling gets us nowhere.

I think we have a good opportunity at this time; there's been a hint of dialogue between an RAF representative and CLT proponents on this forum, I hope it keeps up and this crap can somehow come to an end soon.

[Gary_in_Orygun]

I'll start out my thoughts by saying we should change: "Friends don't let friends fly unstable Gyros" to "Friends don't let friends fly unstable gyros without all the facts and precautions." I don't think we should get into telling people what kind of experimental aircraft they can and cannot fly. (or should and should not fly).

But we should continue to find an acceptable voice of authority that can deliver the gyro-stability physics; a voice that is not biased and that people respect. NASA came to mind when I suggested this before. Any gyro-manufacturer or dealer that spouts a particular stability theory that does not agree with other manufacturer/dealers can be suspect, regardless of how correct they are.

I hope that our PRA BOD can find a good ear at EAA to express the other side of the story regarding the EAA letter that was mentioned here.

My suggestion is that we continue to work on getting the stability facts straight, accepted by most, and diseminated. Other issues will fall into place or off the map if we succeed on those points. No need for any name calling.

[Heron]

Is the future of Gyroplanes hanging on this issue?
Is RAF more important than all of us?
thanks
Heron

[gyrogreg]

Greg,

That's a sad commentary on the state of the FAA.

Paul, nobody said the FAA isn't in a sad state of affairs when it comes to gyroplanes - Marty Weaver's influence aside! We are a small entity and mostly a thorn in their busy side! The Sport Pilot part of the FAA, partly due to Marty's efforts, has been fairly supportive of gyro interests in the PILOT side of the fence. BUT, the the Rotorcraft Directorate in FT Worth has jurisdiction over the AIRCRAFT side of the house - standards, etc. That is our ongoing and persistent challenge with the FAA. That is the main reason we don't have SLSA gyroplanes. But, there are also persistent challenges for gyroplanes with other parts of the FAA, such as the people who write the test standrds and tests. Ever take a gyroplane specific FAA written test - it's archaic, and, IMHO, presents even dangerous practices - traditional, but dangerous. The FAA is a beaucratic challenge - but, with Marty's past and hopefully future help, we will continue to make progress - thanks to efforts in the name of the PRA!

Approval of LSA standards would not impose anything on RAF. They could continue to make their kits the same way they always have, and the decision would be left to the marketplace. RAF has even approved the standards! What's left to do?

Surprise, RAF DID approve the gyroplane ASTM standards!!! With a lot of smoozing with RAF - in spite of heavy RAF bashing - RAF agreed to join and work on the ASTM gyroplane committee. They actually hired a professional aerodynamic engineer! This person worked actively and constructively with the whole subcommittee - for well over a year! In the end, he suggested good criteria on many areas in the standard. But, stability was the committee's, and his, toughest challenge. In the end, he and RAF agreed to the "RESULTS" standards for stability. This means that the standard, as for all aircraft standards and by FAA edict, did not specifiy an particular configuration (HS, prop thrustline, color, etc.). The standard sets the criteria on the results of standard (and mostly very easy) flight testing. Unfortunately, we did lose some participants on the committee who could not live with not REQUIRING a HS and CLT! But, practically, the standard does not care how a design achieves the RESULTS criteria, it only cares that the flight tested results are met. This is the same as ANY aircraft standard - look at Part 23 for certificated airplanes - does not require a HS - but does require specific static and dynamic stability results! The deal breaker was the HS stab issue! It is undesireable and unacceptable to the FAA to "prescribe" a specific design or configuration - and RAF would have balked if we had tried! The bottom line is RAF did sign on to the standard and the stability results criteria, and I do believe they do feel they can meet the standard - with the stabilator? But, strangely, that engineer no longer works there! But, I have not seen any flight test results, and I am highly dubious that they can meet the full stability criteria with their current offerings. I'm just waiting to see someone actually do the flight testing and report the results!

The ASTM standards for LSA can impose some pressures on RAF, even though the RAF 2000 does not meet LSA definition for its weight! Especially for the stability issues, when people start to understand the criteria and ask the pertinent questions and expect the right answers, even producers not selling under LSA rules may feel the market pressures to satisfy their customers. That is why we are spending so much effort in trying to educate the gyro community on these standards. The informed consumer will be a safer consumer. The informed pilot will make safer decisions!


We have no incidents-per-hour stats on RAF, or any gyro, because nobody knows how many are flying, or how many hours they're being flown. That leaves us with the need to scientifically demonstrate the effect of design factors on stability, which nobody seems to be able to get done. I respect you, and appreciate the time and effort you've spent on this issue, but we're stalemated until someone can raise the money to do actual testing to allow comparisons among various gyroplane models.

If there were facts to talk about, much of this bickering would be gone. The people who deny the laws of physics would be shown clearly to be flat-earthers, and the rest of us could refer newbies to real numbers. Until then, the most credible members of our community are still from a community many consider to be a bunch of eccentrics. (To put it mildly.)

I agree, we need data to put the arguing to rest. But I don't agree that this requires a lot of money or expertise or equipment. There is no reason that any pilot, at least moderately familiar in their gyro, can't go out on a calm evening and test most of the stability criteria on their gyro! It does not take any money! It does not take any special equipment - unless you want to wire in a tape recorder to your helmet to record the results and data as you fly. This would take no more than 20-30 minutes to do at one loading data point (for single eaters, this is probably all you need!)

I have published the procedures many times on this forum and in Rotorcraft and they are currently published on the PRA website. I don't know why the reluctance to test different gyros and report the results! I often demonstrate testing all three static stability criteria in just a few minutes in my gyroplane. (To do this testing at all load arrangements in my Magni tandem would take a few flights at different loads - but just a few minutes each flight.)

I have one caveat to this testing by the regular gyro Joe! We don't propose that you conduct any DYNAMIC stability testing. If your gyro is prone to PIO - which you don't know - you have to actually approach divergent response (PIO) to verify the potential exists. In other words, only an experienced test pilot should test for PIO. BUT, the STATIC flight testing is easy and simple and and safe and very telling! In fact, if the Static stability criteria are met - and a a substantial HS is employed to do so - as is probably necessary to meet the criteria anyway - the gyro is probably very not-prone to PIO. There are some technical aerodynamic factors that suggest that achieving the static stability criteria with a substantial HS assures isolation from PIO tendencies. We don't know this for sure, so, for this we will need to see more full data from manufacturers that actually do some DYNAMIC flight testing! But, if the gyro is G-Load statically stable, it is highly unlikely that it can buntover, and is probably very not-prone to PIO if it has a reasonable HS!

I have been trying to find time for a supplement to my latest Rotorcraft articles addressing these tests and static pitch stability. I guess I just need to do this. I will develop and publish a datasheet to test and report static stability pitch flight testing results. I had hoped some people might report some testing results to help evolve a standard datasheet and procedures a bit more, but I'll just put something together with my own testing experience. The datasheet would be valuable to enter the results in a database and eventually isolate some correlations and confirmation of the criteria and procedures.

I see if I can post a draft of the datasheet soon - for your peer review!

- Greg Gremminger

[PW_Plack]

Greg, I hear you, but all your work leads to a dead-end if you don't get someone impartial to do the test flights, and record the data. RAF's "test flights" are likely to result in "science" like this, from their product bulletin in 2000:

Horizontal Stabilizer: The RAF 2000 Gyroplane was tested by the factory with a Horizontal Stabilizer. It was found to have some adverse flight characteristics evident during the testing and there was a consequential crash of the test aircraft in 1996...

[gyrogreg]

Greg, I hear you, but all your work leads to a dead-end if you don't get someone impartial to do the test flights, and record the data. After reading the results of RAF's "test flights" with a horizontal stabilizer, you're going to put their internal LSA test results into comparisons, and call it settled?

We hear this all the time! And it has been discussed from day 1 of the LSA rules. The FAA designed the LSA rules to be self-certified with written "Letters of Compliance" from the manufacturer. No manufacturer can dare to lie if they don't want to be hung out to dry if someone catches them! And, these tests are designed that anyone check the factory claims. There is no way any manufacturer is going to get away lying about test results when anybody can conduct the tests on any gyro to verify the factory claims.

We are encouraging purchasers to ask informed questions, and to require the manufacturer give them a "Letter of Compliance" to the standard. The "Letter of Compliance" is mandatory for the sale of SLSA aircraft. But, that is no reason a customer can't require one from any manufacturer for any gyro or kit. An informed customer asks the pertinent questions such as "does this meet the ASTM standards?" - or at least, "does this meet the stability criteria in the ASTM standard?". This gives the customer all the power. If the manufacturer will not provide a "Letter of Compliance" with the sale, smart informed customers should look elsewhere. But, if a manufacturer lies about meeting the criteria, in writing, they are hung out to dry by any lawyer that want's to have that model tested to see if it does or does not meet them.

There will be plenty of opportunity for impartial individuals, even for partial individuals to conduct the testing - not just the factory. You can conduct the test. Even a person partial to a certain manufacturer, completely duped by that manufacturer's PR, can test their gyro easily - no reason not to! I doubt they can remain partial if their testing does not confirm what the factory assured them in the "Letter of Compliance". If one customer insists on and gets a "Letter of Compliance" from a certain manufacturer, that manufacturer is hung out to dry if he lied! In fact, it will be even easier for an "informed" customer to have the demo pilot demonstrate and explain the static stability tests on the demo ride - you will not be able to fake that with an informed customer!

Now I don't say a manufacturer has to meet all the criteria in the standard. But if we educate the consumer, they should know enough to insist that the product at least meets the important criteria of flight stability - including roll and yaw! The customer should at least get a "Letter of Compliance" that says what criteria in the standard that model does or does not meet - if it doesn't meet it all. I would urge the customer to make sure it meets at least the stability criteria - if it doesn't meet some less critical criteria of the standard, that's the customer's choice - it probably won't kill them. But, if the "Letter of Compliance" says it meets the stability criteria, and that owner tests it, or God forbid, a lawyer has it tested for a lawsuit, that manufacturer is hung out to dry!

What I'm hoping for, and what the FAA is counting on, is that we will have enough data from enough owners of the various models, that if a manufacturer is lying about their test data, it would be readily apparent in the data.

The criteria in the standard, especially the important static stability criteria in the standard is easy to test. These are results objective testing that do not require instrumentation or subjective judgenebt - it either passes or it fails! - and no other documentation is actually needed even for SLSA sales - other than the "Letter of Compliance". If we can get numbers of people to conduct and report the flight test results - maybe everyone ought to test their gyro to see what it's safe limits are - and we put that data together in a database for public review - it will look awful funny when nobody's data agrees with the manufacturer's data! All we are looking for is an informed public requiring at least certain important compliance with the standard - and then lots of individual test data that either confirms the factory's data, or makes the factory data stand out as a lie!

As for RAF, I have been told that they actually purchased around $50K of flight test instrumentation and recording equipment just for flight testing. They didn't need to, but they did. One thing about the RAF factory, they do excellent mechanical and QC work. Their documentation is complete. If they use their test recording equipment, it would be very hard to fake that! If I were a customer, I would certainly want to see the test documentation, even if it is just a standard test data sheet available to anyone! I would certainly insist that the demo pilot demonstrate and explain the static stability test - can be easily done in a short 15 minute flight! But, in any case, anyone that lies about the flight test results will be found out pretty quick when it doesn't repeat for that model in the field.

Here's another aspect of all this! Stability is not just black and white. Almost assuredly, any gyro will have speed/power/loading ranges where they meet the stability criteria. So that gyro can be said to be "stable" in at least some operating range. Where they will tend to fail the stability tests are at some extremes or combinations of the operating range - such as above a certain higher airspeed where, say, G-Load stability goes neutral and then unstable at a higher speed. Above that speed, where the gyro becomes G-Load statically unstable, it can buntover! This should identify the operating range, or Vne of that gyro. As you conduct the flight tests, you test it at incrementally higher speeds or combinations of speed/power to see where it starts to go statically unstable. At any rate, I could argue that almost any gyro is "stable". But, I would have to qualify that as to the operating range within which it is stable and protected from buntover, etc. This serves two purposes - the factory should identify and publish the safe operating range - not just say Vne is 125 mph because the engine can push it that fast - if it goes G-Load unstable at 75 mph! Secondly, the pilots of such machines can easily and safely verify these numbers so they at least know what their safe flight envlelope really is.

The key to all this is education. We purposefully made the static criteria where flight tests very easy and simple and safe to do. As we get people to understand these tests and what they really tell us, then we will have smarter operators who make better decisions about flying. If I know the gyro I fly in is G-Load unstable above 75 mph, therefore capable of a buntover ("PPO" for those who think in terms of high thrustlines), then I will not fly above 75 mph!

At any rate, this has been all discussed early on when the FAA said "you must do something about all the fatalities, or we will, and you won't like it!" The FAA create a performance standard! FAA feels strongly, as do I, that market pressure from informed customers and pilots insisting on the aircraft they buy meeting certain standards criteria, will take care of any lying manufacturers. And, if that doesn't work, even a not-so-smart lawyer can take care of them for good - their tails (pun intended) are hanging out if they lie. If they know they really don't meet the criteria, rather than lie about it, they would be better off to just admit they don't! Then let's see how many sales they make! This is all intended to use an informed market to influence safer gyros!

But, I am a bit frustrated that not many are actually testing their gyros - its just too easy, and actually fun to do! I don't know why everyone thinks it is so hard to do! I demonstrate the basic flight tests with every new student I take out flying - the first hour of flight! The reaction: "That's all there is to it?!" But, I will put out a test data sheet for collecting and reporting the data. I'll keep it real simple! If necessary, I'll conduct forums at the conventions and fly-ins, maybe even at Bensen Days in a few weeks to get people to test their gyros. then, you could go right out to a demo pilot and say show me how this does! Whether or not informed pilots influence safer manufactured gyros, we WILL improve gyroplane safety when individuals identify their gyro's own safe operating envelope. And from the test data, it may actually be easy to make some simple adjustments or mods to extend that safe operating envelope on that gyro!

Anyone that want's to test their gyro now, if you don't understand the procedure and explanation in my last series of articles, call me and I will talk you through them - it's too easy to not do and not know what the safe limits of your gyro really are! My number is 573-883-3541.

[chuter]

Greg,

Can you post a link to the testing steps? I just spent a while trying to find them on the PRA site with no luck, and I don't have all my magazines.

Thanks,

[Friendly]

Michael, I believe Greg has it on his web page.
Greg, maybe we could get some videos of the testing. Maybe this is something the PRA could offer on their (our) web site and mag.

[chuter]

Ahhh, found it here:
http://www.magnigyro.com/USA/feature_articles/envpart5.pdf

Thanks

[PW_Plack]

Greg, I think I understand, but I can't say it makes sense to me.

For the results to be meaningful to me, especially after this much controversy, someone independent of the kitmaker needs to test all the major kits in a uniform fashion, so they can be compared apples-to-apples. It doesn't need to be the FAA, but it would be great if it were PRA, or a major university.

The alternative, waiting for it to demonstrated in a liability lawsuit, seems like bad planning.

[gyrogreg]

- independant stability testing - It doesn't need to be the FAA, but it would be great if it were PRA, or a major university.

I agree it would be best if an independant tester conducted the tests - maybe in the future - maybe even the PRA. But, until someone is able to take on that responsibility, i think the best way is just for everyone to become familiar with this and do it! Once people start doing it, they will see it is no big deal. I will see if we can hold some forums on it - and have people go out and do it right away. It would be fun at an event, over the PA system, to communicate wiht a pilot and talk them through the short tests and let them report the results right on the radio to the crowd. That would be fun!

Links to the procedure:
The envpart5.pdf (http://www.magnigyro.com/USA/feature_articles/envpart5.pdf) article is part of an older series of articles - although it is all still valid the procedures I am suggesting are not properly detailed in this particular article.


A new series or articles specifically addressing the ASTM gyroplane standards on stability and the procedures for static pithc stability testing has been published in Rotorcraft magazine over the past 5 issues. We, the PRA, would like for people to support the PRA (with your membership dues), so we are reluctant to provide the magazine material completely on the WEB - wouldn't have any members, just wait a month to read it for free on the PRA website. But, we have been posting this series of articles in the PRA Safety web page (http://www.pra.org/index.php?module=fatcat&fatcat[user]=viewCategory&fatcat_id=28&module_title=article&MMN_position=25:25) section of the PRA website. Currently, we have posted only the first 2 parts of this series of 6 parts. I have just sent the last 4 parts to the webmaster to post - so they should be posted soon. Take a look at the first two parts, the others should be available soon as well.

I will also soon post the full set of these articles on my Magni FEATURES (http://www.magnigyro.com/USA/features.htm) web page.

As I said, I hope to also soon publish a simple flight test data sheet for these static stability tests. I will probably post that in draft form on a thread on this forum for some per review, comments and advice.

- Thanks, Greg

PS: I am happy to provide this information to anyone who needs it - and we are doing so for free because it is important to the safety of our freinds! But, if you are not currently a member of the PRA, please consider joining to help support efforts like these. Nobody earns any money from this stuff, but my loyalties are with the PRA, and I think it is important for anyone flying gyros to support the PRA and help keep it be more able to affect safety and be viable as a representative and advocate for out sport.

[ahancock]

I would just like to see some RAF owners do the static stability tests and post them on the forum. I see posts from RAF owners who like their machines and consider them safe, but so far, none of them have posted test results.
Alan

[mcbirdman]

Paul and Greg - exactly. If they put a mechanism on there that makes it easier to fly but masks the edge of control just to pass the tests as described then a machine that is actually much more dangerous could pass the test with a bandaid but still have some serious hidden defects by comparison. IE Stabolator. jtm

It seems more like a way to pass the test to gain credibility without using the knowledge to eliminate the hidden problems.

[Doug Riley]

There is a possibility that the standard tests won't smoke out PPO tendency in cases where the aircraft is PPO-prone but is equipped with a control-system "stabilator."

The tests (presumably to avoid asking anyone to risk suicide) don't mandate that you deliberately induce zero G at full throttle and see what happens. Instead, they are intended to smoke out designs in which the rotor thrust line is in front of the CG. This can normally be detected by pulling extra G's just as well as by reducing G's below 1.0.

The control-system vane MAY be able to suppress this symptom. Here's a possible scenario:

During the test turn, if the rotor thrust line is ahead of the CG, the increased rotor thrust will tends to pull the nose up. In a no-HS machine, this will require the addition of forward stick pressure to maintain airspeed. With the stabilator, however, if the pilot holds the stick still in the turn, the nose-up rotation will give the stabilator a positive angle of attack. This, in turn, will supply the forward stick pressure. The pilot doesn't have to.

A rotor-based stabilization setup works during higher G operation because rotor thust increases, thereby adding control power. The essence of low G, however, is low rotor thrust and reduced control power. The stabilator is only effective if there's control power. Thus, the stabilator may look OK in the high-G tests, but still "lose it" in a genuine low-G event.

Therefore, Jim McN may have a valid point about the stabilator hiding the edge of the cliff. Greg Gremminger has probably explored gyro pitch-stability testing in more (scary) detail than anyone else alive. Maybe he could comment on how valid this concern is.

[Heron]

Doug :
Is it possible to have those scenarios drawn for better understanding?
Is there going to be a Forum about this at BD?
thanks
Heron

[Hognose]

Jim and guys --

If I understand Greg's set of tests properly, and I *think* I do, if the RAF passes the test with the addition of Duane Hunn's Rotor Stabilator, then it passes the test -- period. If the machine passes the test, it's stable enough to be safe.

My personal opinion is that the the stabilator has more of an influence on control loads than anything else. It adds feedback to the control system and makes large control displacements progressively more difficult -- that, IMHO, can only be positive for safety. Again, I have not personally spoken to Duane about the stabilator and what he was trying to do with it, and I want to hear from him personally what he has in mind... I will catch up with him at one of these shows, I'm sure.

The test is not something that is subject to "cheating." In a way, you're "cheating" on stability when you use a forward offset of the rotor thrust vector to ensure that the aircraft is stable in normal operation. Some high-thrustline gyros do that. But the test for G-load stability, as I understand it, deals with that. Yes?

All six parts of Greg's ASTM articles are posted on his website at the link he gave. The sixth part contains the G-load stability test, which is simplicity itself. Greg's article on "Misconceptions" is a must-read, also.

cheers

-=K=-

[Doug Riley]

Hognose:

Not quite. Obviously, G changes (which are really AOA changes) can be in either direction away from normal -- up or down. The version of the test that I've seen looks for the aircraft's reaction only to an INcrease of G load above 1.0. It does not test for reductions to fractional G load, or zero G load.

The underlying assumption is that the aircraft's reactions will be symmetrical either side of one G. If the rotor thrust line is ahead of the CG, that fact will show up in the plus-G test as a reversal of stick pressure gradient, and that's all you need to know.

Usually that will make sense. I'm suggesting, however, that the control vane MAY make the aircraft's reactions asymmetrical. The vane MAY be able to produce a normal stick pressure gradient in plus-G tests. If it can do this, it will do it by manipulating the rotor thrust's direction. You can't get the same stable results with the vane in zero G conditions, however, because there IS no rotor thrust. Asymmetry.

Zero G can be preciptated by a downdraft, with no causitive control input by the pilot. The vane will be useless in such a situation. No rotor thrust, no control. The tilt of the rotor head is irrelevant during zero G. That in itself isn't necessarily deadly, of course, unless it unleashes a PPO caused by high thrustline.

Greg Gremminger actually went out and tried to PPO his Magni by throwing the stick hard forward. The HS seems to have prevented PPO, to judge by Greg's apparent continued presence among us.

It would be unfortunate if we had to test all gyros that way, though. Some would flunk. A vane attached to the rotor head system cannot prevent PPO.

I don't know if the RAF that PPOed most recently -- the one in Quebec in December -- had a stabilator. Maybe someone else does. Michel had many friends in the gyro group up there.

[JByrd]

[QUOTE=Doug Riley]Hognose:

Some would flunk. A vane attached to the rotor head system cannot prevent PPO.

QUOTE]

Some gyro configs have flunked for sure.

Fully agreed with your assessment. In my opinion, if anything, these rotor-head vane/short wings are a de-stabilizing influence by moving the center of lift forward (bad) somewhat negating the pitch stabilizing effect of the horizontal plane of the tail. Some people do will not agree however that horizontal tails are necessary at all.

My argument is why not attach them to the nose boom for a mini-canard effect and try that out?

I should not say things like that... Someone might take my somewhat sarcastic remark seriously and get thoroughly hurt for sure.

I would not want to try to fly a pogo-stick. The vanes look cool though. I would not get into a machine that had them.

Jim

[Hognose]

Doug, working backwards through your post:

I'll ask Jim Logan about Michel's gyro. Jim was adamant that Michel should not have been soloing that gyro without more dual, despite Michel's other gyro experience. (Let alone, instructing in it. According to my recollection of what Jim told me, Michel had eight hours time in type, and all his other gyro time was in machines that were less than half the gross weight.

If Greg tried to PPO his Magni, I'm surprized. He seems so sane when you meet him! Personally I would not "throw the stick forward" in any rotorcraft, but maybe I'm just a wuss.

In the "Misconceptions" document, Greg makes the point that the "zero-G event" we talk about is really a notional construct that we use to simplify the physics. The unload on the rotor saps it of rotating energy long before it gets to zero, and there can still be significant but sub-1.0 G on the rotor when it does one of the Bad Things we usually associate with bunting over: strikes the airframe, loses RRPM irretrievably, loses rigidity.

My instinct is that what the rotor stabilator does in the 1.0 (unaccelerated flight) to 2.0 (60º bank) range it will do in the 1.0 to 0.5 or so range also. Below some factor nothing anybody can do for you except buy flowers.

cheers

-=K=-

[gyrogreg]

Doug and Hognose - very interesting topic - I love mind games! First let me suggest I do not like the term "PPO-prone". I would rather refer to "buntover-prone". Any gyro can buntover - no matter whether it is "Pushed over with Power", or not. All that is really necessary is a pitch reaction to G-Load disturbance that increases that disturbance in the same direction. This is most easily visualized by the RTV forward of the CG. "PPO" is a specialized form of a "Buntover" that has been popularized because it may be more easily visualized and described for high TL gyros. But, that description is incomplete, because not all of the static pitching moments are actually considered. The reason I do not like the term "PPO" is that many people assume they will have no problem if they do not have a high prop thrustline to "Push" the nose over! In reality, the RTV forward of the CG, in a decreasing rotor thrust condition, is initiating a "bunt over" - whether it is can be described as a PPO is just symantics! Don't assume a gyro can't buntover just becasue it can't "push over"! Likewise it is just as erroneous to assume a gyro can "PPO" becasue it appears to have a HTL!

Also, it has been often suggested that even the visualization of the RTV aft of the CG for a G-Load stable condition is an over-simplification. The rotor aerostatics itself, it is suggested, can actually make the pitch reaction to a G-Load disturbance be in the restorative direction - even if the CG is exactly on the RTV and is not helping - as may be the case in a truly CLT and CLD (Centerline Drag) condition. It has been argued that positive G-Load stability can be achieved in a gyroplane even if the RTV is physically exactly aligned with the CG - as many people erroneously assume is assured in a CLT gyro! The test actually verifies aircraft reaction to G-load deviation, which includes the rotor effects with the RTV/CG effects - and even "stabilator" effects. Even for a gyro with the CG aligned exactly on the RTV, with rotor effects, the G-load static reaction could still be in the stable restorative direction. One might say the CG is "effectively" forward of the RTV because the G-load reaction of the airframe (and therfore rotor) is proper. It would be hard to prove exactly where the real CG is relative to the RTV, but the test can ceertainly determine if the "effective CG" is properly forward of the RTV - producing positive G-Load stability!

What I think is actually important from a "BUNTOVER" perspective is that the inherent pitch reaction (from any mechanism) is in the G-Load restorative direction. "Buntovers" happen when a decreasing G-Load causes the rotor to pitch forward and futher reduce the G-load - a self-building, or "positive feedback" condition - a "buntover-prone" condition.

Quebec "buntover" accident: To my recollection, the pictures of this yellow gyro in the parade before the accident did not show a stabilator. I may be wrong. My thoughts on that accident, if this gyro did not have a stabilator, and the one he trainind in (Duane's) did, the pilot's reactions were not trained for his gyro! If the yellow gyro did have a stabilator, I think this might suggest the gyro was still G-Load unstable. Could someone search the forum and find the parade pictures?

Stabilator: I am not sure the G-Load test would "hide" the basic G-Load unstable condition when a Stabilator is employed. I don't think we can be sure until tests are actually done! But, here are some thoughts:

The stabilator and it's components actually have mass and inertia - so that may have some dynamic effect in a G-load disturbance such as a downdraft as to what pitch control force might be applied to the rotor. A sudden downdraft would suddenly "drop" the aircraft (flight path change) - and the inertia of the stabilator could cause the rotor to pitch more nose-down - further decreasing rotor load - divergent DYNAMIC pitch input.

But, the downdraft should cause the stabilator to try to aerodynamically pitch the rotor nose-up - corrective direction trying to stop a buntover! So, the DYNAMIC effect of the stabilator is questionable in my mind. The static tests DO NOT assure good DYNAMIC stability. I think actual DYNAMIC flight testing must be done on any gyro that does not employ a good size (volume) HS.

Can the G-Load test identify if a stabilator equiped gyro is "buntover - prone"?: I think it can!

I think the static G-load reaction will be symetrical about the 1G point for small deviations in G-load (from 1G). A buntover does not require zero G to progress into a buntover. A buntover only requires that a decreasing G-load results in rotor pitching to decrease the rotor load even more. It's the positive feedback rapid progression to less and less G-load that is the buntover. So, I tend to think the actual zero G condition, at which all control power is lost, is well after the fate is sealed. My suggestion is that the G-load static stability test, done in the safe, positive G direction, would reflect symetrically if it were (could be done) in a statically reduced G condition! So, if the test indicates postiive G-load stability, it would indicate a G-load restorative response in the moderate reduced G condition - G-Load stable.

Doug, your suggestion that, in the G-load test under a bit more than 1G in the turn, the increased AOA on the G-load unstable airframe AND stabilator will apply a stabilator induced forward force - providing forward stick force "hiding" the forward pilot force that would identify G-Load instability. Therefore, with no forward force required by the pilot, the conclusion would be that the gyro is at least not G-load unstable! I think I've followed your scenario!

But, the G-load test requires that BOTH aft PRESSURE and aft stick POSITION be present to (maintain airspeed and) verify G-Load positive stability. (My head hurts from this hard thinking! But) I am thinking, that because the airframe, in reaction to RTV forward of the CG, would actually be in a nose-higher AOA, the stabilator would have to be moving the stick forward - even though, by your reasoning, the pilot would have to apply no, or maybe even aft stick pressure. The force might be neutral or aft, but the stick would still be further forward - not satisfying the criteria! (My head is still hurting!) G-load instability revealed!

Maybe another way of thinking is what would the gyro do in the banking turn if the stick is held STATIONARY through the test. When the stick is held stationary, the stabilator can have no effect, and the true G-load reaction on the airframe can be uncovered. For a G-load stable craft, one that reacts with a nose-down condition - in the restorative direction - to the increased Gs in the turn, the fixed-stick airspeed would increase. This is because the forward CG is pulling the nose lower and the rotor follows the airframe and the gyro speeds up! The opposite would be true in the fixed-stick condition for an unstable gyro (with the "effective" RTV forward of the CG.) Inherently slowing down in the fixed-stick condition in a turn is an indication that the pitch reaction of the gyro to G-load is in the divergent, or agravating direction. (For a decreasing G-load, the G-load would further reduce due to the more nose-down airframe reaction of the forward RTV. - My head still hurts!) This fixed stick test is just a different way of conducting the same test - but instead of stick force and position, you are looking for a changing airspeed. In a fixed stick banking turn, the airspeed should inherently increase - to reduce the rotor AOA and try to reduced the increased G-Load. (Now I have gotten everyone's head hurting!)

I do think we need test data to verify these concepts more precisely, but this is partially the reasoning that the standard requires both stick PRESSURE and POSITION, in the banking turn to maintain original trimmed airspeed - to verify positive G-load stability.

In development of this criteria in the standard, it had been suggested that we really only needed to verify stick position to verify G-load stability (or instability). This may be true. But, it is inherently confusing if the direction of required stick position were in the opposite direction from the actual force applied on the stick. That was reason enough to require both stick POSITION and FORCE be in the same direction!

(An aside: In the testing, how can we measure stick position - without spending a lot of money on instrumentation? This works really well: Use a retracting tape measure. Tape the release trigger tight so the tape can be moved in and out. Mount the tape meaure on the panel so the tape can be extended out and held with your fingers on the stick as you fly. (I used double sided tape to stick the tape measure to my instrument panel. Then, holding the end of the tape against the stick as you fly, you can measure actual stick position on the tape as it retracts and extends from the tape measure body. You can actually record stick position from the tape measurement.)

[Udi]

I agree with Greg - a stab-less RAF with a stabilator would require the stick to move forward to maintain airspeed in a turn. The stabilator would indeed help stabilize the rotor vs. G-load, but since the RTV is passing fwd of the CG, the airframe will pitch nose up and the stick move forward.

Also, it has been often suggested that even the visualization of the RTV aft of the CG for a G-Load stable condition is an over-simplification. The rotor aerostatics itself, it is suggested, can actually make the pitch reaction to a G-Load disturbance be in the restorative direction - even if the CG is exactly on the RTV and is not helping - as may be the case in a truly CLT and CLD (Centerline Drag) condition. It has been argued that positive G-Load stability can be achieved in a gyroplane even if the RTV is physically exactly aligned with the CG - as many people erroneously assume is assured in a CLT gyro! The test actually verifies aircraft reaction to G-load deviation, which includes the rotor effects with the RTV/CG effects - and even "stabilator" effects. Even for a gyro with the CG aligned exactly on the RTV, with rotor effects, the G-load static reaction could still be in the stable restorative direction. One might say the CG is "effectively" forward of the RTV because the G-load reaction of the airframe (and therfore rotor) is proper. It would be hard to prove exactly where the real CG is relative to the RTV, but the test can ceertainly determine if the "effective CG" is properly forward of the RTV - producing positive G-Load stability!
I am one of those who are suggesting the above. Furthermore, I am suggesting that a HTL gyro in which the RTV is passing somewhat fwd of the CG may still exhibit positive static stability IF (and only if) it has a very effective stab installed. The reason for that is the steeper lift curve of the stab vs rotor lift curve. I do not believe the RTV must pass behind of the CG for a gyro to be safe and stable. The proof is in the pudding - gyros with large and effective stab (e.g. Magni, SH) exhibit positive stability even at low airspeed, where the airframe AOA is positive vs. airflow. In these conditions, the stab is LIFTING. When the stab is lifting, the RTV is most likely passing fwd of the CG. Both Jim Mayfield and Greg G. have told me their machines have passed the stability tests at low airspeed, with a high nose attitude. This is a proof that a gyro can be stable with the RTV passing fwd of the CG (but the condition is a LARGE AND EFFECTIVE STAB).

Udi

[PW_Plack]

The stabilator's response in standardized stability tests is interesting to predict, but I have a much simpler hope for it.

The RAF stabilator will be a little like having Dofin, Duane or Jim handling the other stick. It can't cut the throttle for you, but it will very quickly supply a cyclic input in the correct direction to save your butt at the start of what might otherwise be a catastrophic aerodynamic event. Perhaps that will be enough to keep some of these newly-soloed career ATPs out of trouble long enough to learn the machine's habits.

[gyrogreg]

The stabilator's response in standardized stability tests is interesting to predict, but I have a much simpler hope for it.

The RAF stabilator will be a little like having Dofin, Duane or Jim handling the other stick. It can't cut the throttle for you, but it will very quickly supply a cyclic input in the correct direction to save your butt at the start of what might otherwise be a catastrophic aerodynamic event. Perhaps that will be enough to keep some of these newly-soloed career ATPs out of trouble long enough to learn the machine's habits.

Paul - my thoughts only, I have not seen any engineering or data on any of this, just mind games:
I don't think we can know whether the stabilator would worsen the risk of buntover, or lessen it. Aerodynamically, it might be understood how it could increase the rotor AOA under a reduced G disturbance. But, it also has mass / inertia. Under a strong enough sudden reduced G disturbance, its inertia might tend to further reduce the rotor AOA and G-load - destabilizing! In a strong G-load disturbance, it could be a "race" between these two opposite effects - and with the airframe pitching rapidly and divergently from the aft CG. I don't think we know which would win, or at what G-load disturbance rates the total effect of the stabilator would be in the restorative direction and at what rates it might be in the divergent direction.

This is a DYNAMIC effect - admittedly not tested by the static tests. I do not think DYNAMIC testing is safely conducted by other than professional test pilots. I do believe that the stabilator has at least one beneficial stability effect - maybe more! The stabilator increases the stick forces for the pilot. In other words, stronger stick feedback forces, I believe, can discourage the pilot from over-reactive stick inputs. But, that doesn't stop the wind from doing something too far! And I can't say this would actually improve dynamic stability by causing a longer natural oscillation period or stronger pitch damping. This just might prevent or discourage such over-reactive pilot input that might otherwise sustain PIO.

And, the stabilator has limits to what it can do:

If the pilot restricts stick movement, or forces the stick against the stabilator reaction, any good effect of the stabilator is prevented!
The stabilator can only work in the range between cyclic stops. If it hits the rear stop, in restorative reaction perhaps, once it hits the stop, no further rotor AOA input can be made - by the stabilator, or by the pilot! At some high pitching rate, such as what might initiate a buntover, I think the cyclic has a good chance of "bottoming out", and further restorative action stops!

An effective HS is not limited as this. At any time the aircraft is pitching, even at a severe pitch angle, the HS provides a restorative moment opposing that pitch moment. And it is doing so by a cube factor to the rate of pitching! This HS restorative effect does not "bottom out" at some severe pitch or cyclic angle. The pilot cannot restrict or prevent this action with cyclic input. If the pilot cyclic input is in the helpful direction, the HS is helping the pilot. If the pilot cyclic reaction is in the wrong direction, the HS is opposing the pilot input at a proportionally higher effect!

So, I don't know how we can really say for sure how any device, other than a HS will improve stability safety. Unfortunately, all the paper and mind games probably can't say definitively. A professional test pilot might be able to do the dynamic testing to say definitively. Unfortunately, accident reports might be the most definitive! (Anyone reach any conclusions about whether the Quebec accident gyro had a stabilator, and whether this was a buntover?)

Udi,
One thought on low speed static stability. I tend to think that, at low speeds, where the nose is high and perhaps the RTV is actually forward of the CG, the pendulum effect also contributes to the static pitch stability. At higher speeds, the other aerodynamic effects overpower the pendulum effect - and therefore the high speed aerodynamics must be arranged to provide the static stability.

I agree that the stab vs, rotor lift curves might provide a powerful stabilizing effect for gyros that have a good HS - especially at low airspeeds. But, my suggestion that "pendulum effect" is a contributor at low speeds originates from the fact that we seem to have no stability accidents or issues at low speed - even for gyros that don't have a HS! I suspect that might be because the pendulum effect might present such a very slow natural oscillation rate that the pilot is much more able to "keep ahead" of any disturbances. This may be more related to the DYNAMIC stability of the aircraft at slow speeds as well to any static stability provided by the pendulum at low speeds. At higher speeds, the pitching rates from such powerful aerodynamic forces might be the predominant contributor to both static and dynamic stability (or instability).

- Just my thoughts (my head stopped hurting this morning though! So these thoughts might not be even less coherent this morning!) - Greg

[Doug Riley]

Greg -- Yes, if you can monitor stick position accurately, you can look beyond the masking pressures supplied by the stabilator. The stabilator necessarily works by moving the stick. And as long as your stability pass-fail criteria include both a non-reversing stick pressure gradient AND a non-reversing stick POSITION gradient, the test may tell you what you need to know.

I agree also that the stabilator will continue to work at fractional G's -- up to a point. That point is the problem. Where is it?

Picture a sudden entry into a sharp downdraft, perhaps of the rough thunderstorm-driven variety. If this downdraft is enough to reduce the rotor instantly to a zero-lift AOA, then the rotor thrust vector is for the moment irrelevant. The RTV isn't pulling anymore. If the aircraft has a high thrustline or airframe aerodynamics that create a nose-down torque in these conditions, then nose down she will. In the absence of rotor thrust, the stabilator and any trim spring in the system will both pull the rotor head back, as long the pilot allows them to. The rotor will precess to the new orbit commanded by this motion. That back-tilt will obviously tend to restore positive rotor AOA, positive G and rotor thrust.

But will it succeed? Timing is everything, as usual. The rotor does not tilt back instantly. The spindle takes a measurable time to get there. The rotor takes an additional interval to follow. If, meanwhile, there are moments trying to flip the gyro forward, the flip will have progressed to a certain angle by the time these intervals are over.

Here's the point: If the gyro has nosed over enough in those intervals so that, when the rotor head hits the rear stop, the rotor AOA is still zero or nearly so, you're done. The limits of the stabilator (or anything else that tries to stop pitchover using the rotor) have been reached and exceeded. The amount by which the frame needs to nose down for this to be the case is only 10-15 degrees.

IOW, there's a critical set of conditions in which a rotor-based strategy for preventing a pitchover won't work. These conditions include, most importantly, some force that provides the pitch-over torque. This is most often the propeller in a HTL configuration but the right (that is, wrong) airframe config could do it, too.

Responsible gyro pilots should object in the strongest possible terms to a blanket statement that ANY gyro can bunt over. This implies, falsely, that there is something inherent in gyros or rotorcraft that makes them prefer to be upside down. It further implies, falsely, that there is no truly safe gyro -- all of them are more or less trying to flip all the time, and good design merely makes the odds a little less bad. If that were true (it isn't), then the FAA would be right to deny Sport Aircraft treatment to gyros permanently.

Greg, I'm pretty sure that's not what you mean, but it's what people often take away from this kind of discussion. That's a shame. Sooo... once more, for the record:

There is NOTHING whatsoever inherent in a gyroplane rotor that tends to make the aircraft try to invert. Bunt, or pushover, or whatever else you want to call it, is not a peculiarity of rotary-wing lifting devices at all.

It is an unstable AIRFRAME that causes these flip-over crashes. Put fixed or flex wings on an unstable airframe, and the FW craft will bunt over, too. (Check out John Moody's famous PPO in his Easy Riser FW ultralight at Oshkosh, around 1978.)

"Unstable airframe" does not mean anything quite as simple as prop thrustline above CG, though that's by far the most serious current source of gyro instability. A modestly HTL craft can be stable with an appropriate H-stab. OTOH, pontoons can make even a LTL craft unstable. You must consider all the forces on the frame that might push/pull it over, and make sure they are countered by a device just as reliable as these forces themselves are.

Greg, I think that's your point in generalizing about pitch-over accidents.

(Note that, if your design DOES arrange the various frame forces so that they remain balanced in zero G, you can sail through short-duration zero G's in your gyro with no bunt -- not even any nose movement. Longer-duration zero G's (more than a second) are apt to slow the rotor down too much and should be avoided.)

P.S.: The RAF gyro in the parade photo was the one that crashed in the Midwest in July, not the one that crashed in Quebec in December.

[Udi]

Greg, I have two questions regarding your last post. 1. I always thought the stab dynamic response to pitch rate was linear, assuming of course, the stab lift curve is linear vs. AOA, for a given range. What makes the dynamic response a cube of pitch rate? 2. Would you elaborate on the pendulum effect? Did you mean to say the gyro MOI becomes more significant at low airspeeds? Since the gyro is free to rotate in space I can't see how it can be considered a pendulum.

Udi

[gyrogreg]

Doug,

You're right about my comment about "any gyro". I certainly didn't mean that ALL gyros are inherently always trying to flip over! You probably explained it right, and I will be more careful in using that language if people take that to mean that all gyros are inherently unsfe.

I firmly beleive that there is nothing inherent in the rotor that makes ALL gyros unsafe! It is truly the combined aerodynamic effects of the rotor with the airframe. I believe that gyos can be configured to be nearly perfectly safe, with few inherently dangerous attributes and some very significant safety and control attributes that no other aircraft has.

I guess my less literal meaning in my comments is that some gyro configurations that are popularly thought to be perfectly safe, may not be so in every instance or flight configuration. Ie. - the unqualified bias for CLT (often dangerously confused with LTL) gyros and the unqualified bias against ALL HTL gyros. In either case, there certainly are configuration issues that could result in a buntover for any of these. And, in either case, there probably are configuration characteristics that could be implemented to to make LTL, HTL and CLT configurations nearly perfectly safe!

Udi,

I am probably in technmically murky waters on my end on these two questions you bring up. I don't know that I am able to answer these with the aerodynamic credibility it takes - maybe others can clarify more. But, I'll try briefly:

HS dynamic response: The HS has a static linear reswponse - restorative moment proportional to AOA (pitch) displacement. However, DYNAMICALLY, when the HS would say, be accelerating upward, the lift changes on the HS are changing as lift would be changing on increasing airspeed on a wing - I beleive the lift on a wing is a function of the cube of the airspeed!. The aerodynamic forces on the HS as the gyro is accelerating in pitch, would be increasing at a rate proportional to the cube of the rate of change in the airflow change on the HS.

Now, I can't claim this is right -0 I really have not had time to investigate this in depth. But, I do know that the DYNAMIC stabilizing effects of the HS require more than just a first order, purely linear change in HS lift vs. AOA (or airframe pitch angle.) If the restorative process of the HS were simply proportional to the AOA of the airframe, dynamically, the HS would provide no pitch damping - the gyro wouild naturally oscillate in pitch - never damping from the HS contribution! This simple first order, simple proportional contribution is essentially the same as a spring would provide. I learned this when I was working on modeling the pitch reactions of a gyro on an Excel program - my sort of spreadsheet integrator working with small changes in factors - another subject! But, this showed me that simply relying on the proportionate lift of the HS would result in nothing better than an undamped oscillation when excited by a step function (wind gust).

This was where I realized the HS dynamic damping effect relied on it's vertical velocity and acceleration to provide the out-of-phase damping moment to "damp" the oscillation. This recent discussion provoked me to thinking that this HS changing AOA, and its changing velocity relative to that HS vertical movement, might be providing those out-of-phase damping moments proportional to the cube of the actual airspeed change - which in a dynamic pitching action is the rate at which a buntover may be progressing. I have not,a nd probably will not ahve time to run any equations on this untli a less busy season. I may be wrong in the cube function - it may cancel one factor out in the equations somewhere. But, Iwould bet the dyanmic pitch restorative moment provided by the HS will be foudn to be at least a square function advantage over the other STATIC moments that are would be accelerating a gyro nose-down in a buntover event. Greater minds than mine will have to tell me how this all works - I just know that a HS does provide a "damping" action, and this cannot be explained by the static forces on the HS from simply its AOA at any given point. The "damping action requires an out-of-phase HS moment change. And this out-of-phase comes from it's velocity /acceleration component of lift - which are out-of phase to the actual pitch angle - damping forces. (My simple mind sees this analogeous to a child pumpin their legs in the right phase to slowdecreas, or "dampen" their cycles on a swing!

Pendulum effect at slow airspeeds: Again, I'm not a sure I can derive this mathematically - maybe someone else could. Chuck describes the gyro as a pendulum on a much longer arm that the rotor to CG arm. The natural "swing" of this pendulum would be relative to the mass of the gyro and the length of that moment pendulum arm. However, the natural osciallations of the gyro at higher speeds where the effects of aerodynamic and thrust moments are much greater, the important inertial element is the MOI of the gyro - and the moment arms and aerodynamic forces on the airframe. I presume this cannot be easily broken down into separate issues - at low speed the "pendulum effect" MAY be more in control, and at high speed, the aerodynamic moments on the MOI will be more in control.

I hope greeater minds than mine might be able to explain this better. But, it seems evident to me that we have fewer pitch stability related issues at low speeds, and more issues at higher speeds when the aerodynamic forces and moments are more prevelant!

[Doug Riley]

Greg: I agree fully w/ respect to LTL gyros. Check out the original (i.e. British) 1928 Cierva patent on CLT, recently posted by Chuck Beaty in one of the RAF discussions. In it Cierva specifically states that he developed CLT to get away from what he thought were undesirable flight qualities of LTL!

I think the best current understanding of this issue is actually the one that the Brits are adopting -- keep the thrustline close to the CG/CM, then fine-tune with a HS. That's pretty much what Cierva had in mind, too. We're still re-inventing the wheel.

I do think that an UNCOMPENSATED* HTL is more dangerous than an UNCOMPENSATED LTL of the same magnitude. The LTL produces airframe movements with throttle adjustments that are in a stable direction; admittedly, these movements may be excessive and require damping or manual trimming. That's where the HS comes into play.

An uncompensated HTL creates unstable frame movements with throttle adjustment 100% of the time. In this case, the HS has more work to do than in the LTL gyro. The HS must not just damp, but overcome and actually REVERSE the moments created by the engine thrust. You know from the Magni, and I know from the Gyrobee, that this can be done with a well-designed HS if the HTL is modest... so we have to keep it that way!

* By "compensated" I mean equipped with a device such as a HS that gets the rotor thrust line back at least to the CG for all power settings and permitted airspeeds. A HS often must have a specific incidence setting, size, and location to achieve this result.

[gyrogreg]

I do think that an UNCOMPENSATED* HTL is more dangerous than an UNCOMPENSATED LTL of the same magnitude. ---
An uncompensated HTL creates unstable frame movements with throttle adjustment 100% of the time.

Your last post well said! - an uncompensated HTL creates a less stable and more unsafe situation whenever it is at high power or high speed. This is because both prop thrust and airframe drag are producing destabilizing nose-down moments that move the RTV to or froward of the CG. I would not say this is the case 100% of the time, but it is likely the case any time the gyro is flown at higher airspeeds, and other conditions such as a low or negative G maneuver. But, apparently (from "pendulum effect"?) just about any gyro configuration does not present control or stability issues at low and moderate airspeeds, with or without power.

On the other hand, an uncompensated LTL, likely presents a less stable and less safe condition only when it might be at low power and HIGHER speeds. The lack of prop thrust on a LTL would no longer enhance stability by forcing the CG further forward of the RTV. AND if the gyro has aerodynamics, such as a lot of draggy stuff below the CG and/or an enclosure/windscreen that forces the nose to fly lower (RTV further forward) at higher speeds, the uncompensated LTL can actually be statically unstable at that low power, high airspeed condition - possibly even capable of a buntover! (Picture a gyro with floats in the extremed!) But, this condition and risk is only presented in such LTL configuration at times when it is flown at higher airspeeds and low or no power - not 100% of the time. This same configuration may however present such a sudden unstable condition upon sudden power reduction or loss, as to present the pilot with sudden control difficulties that could initiate either PIO or buntover reactions. But, again, this risky situation does not happen a large percentage of the time.

I don't think anyone could argue with the British approach - moderate prop thrustline offsets and a good HS. But, are they even talking about the HS requirement? - I have not heard that! I do not agree that their logic and determination of this guidance is well founded in basic aerodynamics. They have come to this conclusion based on flight testing of a VPM-16 to verify a computer model that, from what I understand of their studies, does not place appropriate weight on the effective use of a HS, nor on the significant issues of airframe aerodynamic drag and pitching moments. But, like a lot of people, there is a strong tendency to try to reduce these principles into easily understood, but simplified cook-book recipes! It's not that easy, for instance, I would not choose to fly any gyro who's prop thrustline is within their 2 inch criteria (if you could even design it to be there and stay their reliabily), if it did not have an effective HS to balance even this minor offset! And, Dynamic stability is another issue that is not addressed at all by prop thrustline only. And judging by the British prohibition to even add a HS to an existing gyro in Britain, I'd say they either don't have a full understanding of how to make a gyro safe, or have other motives to supress gyros in Britain!

[Udi]

I have created a little sketch to illustrate how the stab is creating a damping force about the pitch axis. Look at the first sketch. The oval shape is the stab (sorry, I couldn't draw a better airfoil). The gyro is flying at 60 mph with the stab parallel to the relative airflow. When the gyro starts pitching nose up or nose down (in the picture it pitches nose down, tail up), the stab is moving vertically up or down. The vertical movement of the stab is changing the relative direction of the airflow the stab is seeing, resulting in a change in the stab angle of attack. In this example, the stab is moving up at a rate of 10 fps, which is a pretty fast rate.

The vectors to the left of the stab are showing what the "new" relative wind looks like. The up movement of the stab at 10 fps results in a change of AOA from 0 to 6.5 degrees (before the stab AOA vs. direction of flight had a chance to change). Note that the relative airspeed is changing very little from 88 fps to 88.6 fps - less than 1%. Only the AOA is changing.

The **change** in AOA is directly proportional to the pitch rate - not the pitch angle. In other words, a pitch rate of 5 fps will cause a change in AOA of 3.25 degrees, half of the change in AOA resulting from a pitch rate of 10 fps. The lift that is generated as a result of the pitch rate is always opposite to the direction of the movement.

Obviously, as the nose is pitching down, the stab AOA relative to the direction of flight will change too, but that AOA is the static stability part of the stab action. Damping is occurring only due to **pitch rate**. This calculation shows that damping is a linear function of pitch rate, assuming the lift provided by the stab is a linear function of AOA (this is a good assumption as long as we stay away from the stall zone).

I don’t think I am describing it very clearly, but it’s the best I can do.

This sketch can also explain why stab damping is a square function of the stab distance from the CG. The vertical speed of the stab is directly proportional to the distance of the stab from the CG (think about the circumference of a circle - 2 pi r). When the stab is mounted twice as far from the CG, it's vertical speed will also be twice as fast, for the same angular pitch rate. This is linear. BUT - the stab moment arm is also double when you move it back, so the net result is 2x2=4 -- a square of the distance.

This dynamic response is very interesting when you think about it. Stab damping happens not only when the tail is moving AWAY from center, but also when the tail is moving back to center. See the second sketch for example. Say the nose has pitched 10 degrees down (and the stab 10 degrees up) and stopped. Due to the negative AOA of the stab, the stab will be pushing the nose back up. Due to the damping force, the stab would be resisting the nose-up movement, as explained above.

If the stab is moving down (back towards center) at a rate of 10 fps - this pitch rate will reduce the stab AOA by 6.5 degrees, to oppose the direction of the movement. This means the damping AOA takes away from the static AOA. At some point, when the gyro pitch angle relative to the direction of flight is about 6.5 degrees nose down, damping force will cancel out the static force and the net stab force will actually be zero! As the stab attitude goes below 6.5 degrees the net stab force will be opposite to the direction of the movement. This is good because this force will help stop the nose up pitch rate and reduce overshoot (hence damping).

Once you see how simple and clever this stab pitch damping business really is, it is very hard to understand why some people/companies resist so much incorporating a stab into their designs.

Udi

[Vance]

I love it when you fellows talk like that. I have this unreasonable fantasy that some day, through repetition of the principles, I will grasp the concept.

Thank you Udi, this helps me to understand you embracing a long moment arm.

I am still confused, but that is another way of telling that I am still breathing.

Thank you Greg, your way of describing things is certainly the oppisite of the reasoning behind the letter.

Thank you Doug, your explanations are always so grounded, I am very gratefull for the knoledge you so generously share.

Thank you, Vance

[Heron]

We may have to copy and paste all of this and get it embeded on our gyro minds . . .
thanks
Heron

[gyrogreg]

Udi, I figured we could count on you for some deeper insight into this dynamic effect. I now think I understand why you have been suggesting that the further back the HS, even for the same HS volume, the dynamic stability is improved. I did not really follow the reasoning before, but now I think I understand better!

So, this argues that the the further back tails, such as the Littlewing, the stronger the dynamic damping. So, for a desired HS volume, if you have the choice between putting a smaller area HS further back, or a larger HS closer to the prop, you would be better off dynamically (PIO stuff) to chose the smaller area farther back.

The "gap" we have in stability testing is that we are recommending that non-test pilot types do not conduct DYNAMIC testing for safety reasons. This might seem to leave a "hole" in our recommendation to conduct the STATIC tests only. We have been suggesting that, if static stability is achieved through the use of a HS, then for good assurance that there would also likely be good DYNAMIC stability, use at least the same "volumne" HS as far aft as you can - within reason for your configuration. The LW does this in spades.

So, I take it that you do refute my earlier suggestion that the HS "balances" other pitching moments with a "cube" function advantage. What do you think: Is the HS restorative effect simply a phase shifted first order effect, or, is it a square or cube function?

For instance, in the case of a gyro that is flying with the RTV forward of the CG experiencing a down draft: How does the nose-down pitching acceleration form the CG/RTV relationship compare with the nose restorative acceleration? Is it just out-of-phase so as to provide damping, or is a square or cubed advantage over the simple CG/RTV moment.

It would be nice if we could get some handle on how, from HS placement aft, we might assure that a gyro that exhibits good static stability (the three tests) would also be acceptable from a PIO susceptibility standpoint?

[Udi]

What you are calling "the restorative effect", Greg, is the sum of both the static force and the dynamic force. Both are linear functions. The static force is a linear function of pitch angle and the dynamic force is a linear function of the first derivative of the pitch angle - the pitch rate. If you want to put it in mathematical terms (where is Raghu when you need him), I guess you may describe the total "restorative force" with a first order differential equation.

One more interesting fact to note - even though lift is a square function of airspeed, stab pitch damping is not (because one must divide the pitch rate by airspeed to derive the damping AOA - then multiply by airspeed squared to derive lift). It is not completely linear, but very nearly so. The static force, however, is a square function of airspeed. So, the static/damping ratio is approximately linear with airspeed. This means that a gyro that has a stab that is marginally damping at 60 MPH may not be adequately damped at 100 MPH.

Udi

[gyrogreg]

I have started a new thread to suggest a DRAFT datasheet for conducting the Static stabilty flight tests.

Please visit the Gyro Static Pitch Test datasheet (http://www.rotaryforum.com/forum/showthread.php?p=104706#post104706) thread.

Thanks, Greg Gremminger

[Lspav8r]

I cant believe noone asked me to join in the frey. Im hurt.:argue: Oh well When I get smart I will add my two or three or four or five cents to this mess. I love a good fight. Just kidding.

Has this issue been dealt with finally? If there is a big push to be a part of Airventure I assume this has been handled and the issue is over?

I did notice that this year the RAF Africa contingent wasnt at Airventure. Damn, and I even bought a shirt form them in 2008:noidea: But hey I had no idea there was a problem with the RAF machine at the time so dont accuse me of sleeping with the enemy.:noidea::rip: