Sparrowhawk Tailwagging????

[GyroRon]

Not that I had seen this myself - I admit I wasn't watching them too closely - but the word on the streets is that the Sparrowhawks basically are always hunting in yaw, that they aren't rock solid in yaw like most other gyros. It was said that at Mentone everyone noticed that the sparrowhawks all appeared to be wagging their tails as they took off and flew by, while the RAF guys flew straight and true.

Anyway anyone here have much experience with the Sparrowhawk and care to comment?

[Walker]

I've flown in "Ruby", an AAI modified RAF that is up here in Washington. It was rock solid in ALL axis; pitch, yaw, roll. My only negative comment I had at the time was that I felt the rudder springs were too heavy. It took a lot of pressure to make a rudder input. Now, the cabin on Ruby is an RAF cabin. I don't know if the wider (and squarer - is that a word?) cabin of the Sparrowhawk has any noticable yaw hunting tendencies.

Walker

[GyroRon]

From what I heard the tail wagging is in the true Sparrowhawks not the Modified RAF's.

[mcbirdman]

Yes Ron,

I didn't want to say anything but when we were at mentone but we definately noticed it and discussed it. We saw it also on the high speed passes. At first I thought they were actually trying to Wag them to the croud as they passed by. Then we started watching and sure as heck. They were doing that whenever they were close enough to see.

I will tell you from what I saw, and if I could see it on the ground easily.... If my machine was doing that it would drive me crazy! I saw it as a huge negative but I also know what would fix it but people wont do it. It is obvious that putting the tail back on a longer frame would result in a more stable machine. I know people don't want to do things that make sense to me for what seems to me odd reasons. However - I wouldn't want to get the kind of ride we were seeing. Someone that was standing in our group said he rode in it and it definately was occillating back and forth. Actually I am surprised that this took this long to be mentioned.

It may have to do with how forward/where the vertical axis pins are placed along the tail towards the leading edge / center of lift. I don't know but I know it would not be such a sensitive problem if they weren't already working with a such duck tail in the beginning... And I am sure it can be worked out. I just am not sure I would be demonstrating it when something has to be changed that you can even see from the ground. It looked like it was swinging 10 degrees to the left and to the right. Can you imagine trying to keep a compass heading? Pointing yourself within 20 degrees of your required heading? Or even trying to read the compass anyway? I want them to do well and again, I am sure it will be fixed. They have done so much already, this is probably a realitively easy fix.

[Aussie_Paul]

From my limited tall tail experience, I find that an open frame single seat or one with a pod (not cabin) seem to be ok with the tall tail. Once you start getting more surface area out the front the yaw problem seems to sneak in. Engine stopped, unless you keep more than efficient glide speed the rudder can be quite useless. A bit like a Raf.

Ron, a scenario, the engine stopped and at minimum airspeed to allow you to stop and drop the Dominator in the last foot using the Dominators u/c advantages. How effective would the rudder be?

Just some thoughts.

Aussie Paul. :)

[Brent_Brown]

Not very but at 0 airspeed what good is the rudder?

[Udi]

I felt some yaw when I was flying the AAI modified RAFs (one of them was Ruby) during gusty conditions in Buckeye. It was my impression that the gyro was tracking true to into gusts - which is the result of strong static stability in the yaw axis. My single place Air Command is doing the same. It is not the lack of yaw stability, but rather maybe excess of it.

A smaller rudder, located further back, would improve this "problem" by increasing the dynamic stability while maintaining static stability. A flying arrow does not change its direction with every gust.

Increasing the gyro MOI would also tend to reduce the sensitivity of the machine to horizontal gusts.

This may be a case of too much of a good thing is not always be good.

Udi

[Chopper Reid]

[QUOTE=Aussie_Paul]From my limited tall tail experience, I find that an open frame single seat or one with a pod (not cabin) seem to be ok with the tall tail. Once you start getting more surface area out the front the yaw problem seems to sneak in. Engine stopped, unless you keep more than efficient glide speed the rudder can be quite useless. A bit like a Raf.

Very well said Paul, and its great that this tall tail thing stuck right up next to the prop is getting some airplay. Its been my thoughts all along that the tail has to be further back to get it in the airflow when the engine stops. At least your design Paul, has the tail where it should be. If it was such a great idea to have a tall tail stuck right behind the prop, why doesnt FW have the tail right behind the cab and save all that metal in having a tail boom sticking back. ! :)

[GyroRon]

Chopper, Aussie Paul, you guys need to try a Dominator. I recently added a clutch to my gearbox and have been practicing vertical decents with the prop stopped, Still have plenty of rudder control even at below flying speed. With the prop turning and some airspeed it takes only a hint of rudder deflection to make the gyro yaw hard one way or the other. With no prop blast and minimal airspeed the deflection needed can be quite a lot but still no problems.

No offense meant but it just seems you guys in Aussieland are still about 20 years behind the USA in gyroplane design and accepted practices.

[GyroRon]

McBirdman, apparently alot of people have noticed it and have talked about it for a while and no one has wanted to bring it up here for discussion on the forum. I heard about it from someone who was at Mentone and saw it. I figure it is better to get it out in the open and discuss it - if there is or isn't a problem - than for Sparrowhawks rep to get tarnished as it seems it has been quietly doing. The person I heard this from was looking to buy a Sparrowhawk till he saw the tail wagging, now he is considering another brand that was also flying at Mentone straight and true.

[Chopper Reid]

Ron,
I'm sure that if I was a social flier then I would most definately be looking at a Sparrowhawk canopy or a modified RAF, something comfortable 2 seat, out of the wind with doors for winter comfort, however, for what I do, I need a tough "antiquated gyro" that is going to be able to operate out of spots that were never intended for use to takeoff on, economical, designed to last and need very little maintenace. Fortunately for me, that very gyro is built just a few miles from home. Best of all is that this design of gyro is one that has in excess of 50,000 hours of "out there working in the outback" reliabilty built into it!
Your "Dominator" gyro would probably not last one week or even less on the 'strips" I have to be able to use. :D A 2 stroke engine is a "definate no go" item too!
We are probably all of 20 years behind you guys Ron :) but one area that we do lead you guys in is actual gyro hours flown .Its not uncommon to find here in Australia guys with over 3,000 hours up.
Your pod Ron is one which allows a good airflow past it so the tail in an engine out experience is going to have good authority unlike the RAF and Sparrowhawk pods.
Surely Cessna and Piper didnt get stability wrong Ron ??? :eek:

[GyroRon]

I wouldn't be able to compair my dominator with a RAF or Sparrowhawk cause I have only been up twice in a RAF and never in a Sparrowhawk. Only know that my Dominator has no problems.

I also don't see how you could think there is that much difference between the gyros you guys fly and a gyro like a Dominator. They are all built pretty much the same except for the thrustline and tail group. Mine can get off the ground in about as short of a space as I have ever seen ANY gyro get airborne and I also have a nice soft suspension which could only be better than the rigid axles alot of the older designs use. I agree that if I were to be flying a gyro day in and day out racking up thousands of hours a year, a Rotax 912 or maybe Subaru would be the only way to go. A two stroke can be just as dependable, but as fast as you guys put on the hours, you would be constantly doing engine maintance - or else having failures, which must have been what happened since you guys know not to use them.

[GyroRon]

And on a cessna or Piper even with the tail WAY back there, you still have to deal with P factor and prop torque. Just as you do with a gyro with the short tail WAY back there. A gyro with a full span tail does not require fancy footwork to keep it going straight no matter the power setting.

[mcbirdman]

Ron, you are right. about first part and also about p factor/torque prop. I found out exactly how much torque roll you get in the winter when you gun the engine on a go around. If you hit it too hard at once you can feel like you just hit a huge side gust. (152) That is why smooooothhhhh in on the throttle. And what I was talking about wasn't just a little on the the sparrowhawk. Have you ever seen a hopped up car gun it on grass? the side to side as it is trying to move forward? Reminded me of that all while it was flying over. We said what the heck are they doing and they kept doing it.

And that it too bad about the guy reconsidering. The other one has too many failing/cheap parts on it that should be replaced to make it worth it. I would rather get the sparrowhawk and let them figure out the tail. Realitively minor compared to the things they have already tackled.
Take care,
jtm

[ventana7]

I have about 20 hours in 2 different AAI modified RAF's. I never noticed any yaw or hunting or wagging problems in normal flight. In gusty conditions I deffinately felt the wag or hunting but that is to be expected and a moment after the gust past the gyro continued flying straight and true. It was never a problem.

I flew Ruby - Randy Coplen's machine and also really disliked the stiff rudder response but the other machine I flew did not have this problem at all so I am sure it is something that can be fixed.
I have not flown a true Sparrowhawk so cannot comment on its tail wagging.

Rob

[pwendell]

I wonder why somebody didn't simply ask the AAI folks about the (perceived) problem. I know that both Steve and Terry were at Mentone. AAI has never been anything but honest and forthcoming. Jim would have it no other way. I'm sure most of you remember the landing gear problems they had last year as well as the training accident before that, which had nothing to do with the aircraft. They stepped up and told truth.

Like Rob, I haven't yet flown the Sparrowhawk, but I do have 60 hours in 3 different modified RAFs. Last winter and this summer I've had the pleasure of flying in some pretty turbulent air caused by thermals -- 115 degrees will produce some rising air -- and low level wind shear. The aircraft will point its nose into the relative wind in a gust. This can be simply countered with a little pedal, if you like, or it will correct itself as soon as the gust passes or you pass through the shear zone. Controllability, even for a low time student, is never an issue. Pitch excursions, even is quite rough air, are also quite minor and will self-correct, although more experienced pilots will probably choose to correct them with slight pressure before the aircraft does.

Last winter Terry and I spent a lot of time working on my takeoffs and landings. The weather was pretty unusual for AZ and almost every week for about two months the surface winds would start off very light, but just a few hundred feet off the ground the winds could be a good 15-20MPH or more. As a mission would progress the winds would sink slowly to the surface. This type of low level wind shear can make short final pretty interesting, but after only a short time I had little trouble establishing and maintaining a stabilized approach through the shear zone, even when it was 50ft off the ground. The aircraft inspires confidence even in changing conditions close to the ground.

The Subaru engine does provide quite a bit of torque so, even with the tall tail, left cyclic and right pedal are necessary to keep the aircraft flying straight as it leaves the ground on takeoff. If the pilot misjudges the amount of control input necessary, the tail will definitely occillate and/or the aircraft will drift off the center line for a few moments. I've made more than a few takeoffs like that:) It ain't pretty, but it isn't dangerous.

The modified RAF seems to me to be an excellent trainer with very neutral and predictable handling characteristics. If anyone has any questions about the qualities of the Sparrowhawk, I encourage them to simply ask the folks at AAI rather than gossip. If anyone has any questions about training in or flying the modified RAF, I'll be happy to answer them honestly and share my experiences both good and bad.

[Mayfield]

Thanks Ron, James, Udi, Brian and others for participating in the thread.

Those of you that know me understand that I’ll do my best to answer your questions as honestly and straightforwardly as I can.

Udi hit it pretty much right on. The SparrowHawk is very stable in yaw statically. That is: it will tend to align itself with the relative wind. It has an extremely powerful vertical control surface and as such, will react to very small wind direction changes by attempting to point the nose into the wind.

I’m going to have to go a little far afield here so please bear with me as I dish up some food for thought.

Since I seem to be able to organize my thoughts best in small bites, I’ll try to put discrete ideas in numbered paragraphs:

1. There are essentially two types of control surfaces. Fixed stabilizer with movable control surface and “all flying.” Each of these types has certain advantages and (since every Ying must have a Yang) certain disadvantages.

2. Both types work by producing lift in the desired direction.

3. With a fixed stabilizer/movable control surface the pilot, in the case of a rudder, varies the direction and amount of lift produced by changing the camber of the stabilizer/rudder combination. Just like a flap on a wing changes the amount of lift produced at a given speed.

4. An “all flying” tail, on the other hand, varies the direction and amount of lift produced by changing the angle of attack of the entire control surface.

5. Fixed stabilizer/movable rudder controls have a tendency to go to zero camber when the pilot stops pushing on a pedal. Put another way, when the pilot stops pushing, the surface goes back to streamline position. They give increasing force feedback to the pilot with an increase in airspeed or an increase in deflection. Unfortunately they are heavier and more complex than “all flying” surfaces.

6. An “all flying” tail as found on the dominator, the SparrowHawk, or the stabilator on Piper Cherokees does not by itself have any self centering characteristics nor does it provide force feedback to the pilot. Just like the fixed stab/movable rudder device, the pilot must put in and hold pedal pressure as long as he wants to fly the aircraft in a yawed state. The difference is that with an “all flying” tail, hinged at the center of pressure (~25% chord), The control surface (by itself) will not recenter.

7. Different manufacturers have used different methods to ensure automatic recentering and force feedback. The Air and Space 18A, which also uses a center mounted, all flying tail, employs large centering springs in the tail cone. The RAF Stability augmentation kit equipped aircraft use centering springs. Dominator and the current SparrowHawk use an anti-servo tab, as does the Piper Cherokee.

8. For those not familiar, an anti-servo tab is a small surface attached to the trailing edge of the all flying surface. The trailing edge, of the anti-servo tab, deflects in the same direction as the trailing edge of the master surface. This essentially changes the camber on some of the master surface area, which provides force feedback to the pilot and automatically recenters the all-flying surface when pedal pressure is released.

9. The big advantage of all flying surfaces is that they are lighter and simpler than hinged surfaces.

I know this is a long post. Please bear with me just a little longer. I understand you have asked me what time it is and I’m telling you how to build a clock. I think the members of this forum, for the most part, want to know the “why” of things as well as the “what.”

Just a few more of the numbered paragraphs. I’m getting old, and if I don’t number my thoughts I’ll get lost.

10. Unlike fixed stab/movable surface devices, which will “auto-center” even with substantial slop in the rigging, an “all-flying” surface will not. Springs or anti-servo tabs are used to provide centering force, but if the rigging to the rudder, and to the anti-servo tab, is not tight the “all-flying” surface will not stay centered. The nose will wander.

11. Udi: The SparrowHawk is statically and dynamically stable in yaw. Full pedal deflection/release testing shows 1.5 cycles to full damping.

12. I offer the following thought: Arrows do indeed point into the relative wind when they fly. An arrow fired into a crosswind, that has a velocity of any significant percentage of the arrow's forward velocity, will fly a curved path partly because the arrow's surfaces are fixed. I do not however disagree with you. The MOI of a typical arrow is pretty high.

13. During testing I have, in varying wind conditions, conducted engine out, with propeller stopped, testing to touchdown. In calm winds, or with a head wind, they have been conducted to zero ground speed touchdowns. In crosswinds, we test, engine off/prop stopped to twice the crosswind component velocity (X-wind component of 5 knots equals a 10-knot touchdown speed). I suspect I could trim a little off of that but have elected not to until I get younger. Remember that if the engine is running you can land at zero ground speed as long as V-stab sees “airspeed greater than X-wind component.

14. These comments, that I am grateful you all posted, are essentially “Field Service Difficulty” reports. I will deal with them as such. For now all end users will be asked to check their rudder cable and anti-servo tab cable for tightness. Terry Eiland has tightened his and seems to be having acceptable performance. (Terry independently thought his way through the cable tension idea without any assistance. Thanks Terry).

15. “All-flying” control surfaces have been used for years with great success. They must be rigged properly and the pilot must be aware of the "all-flying" tail characteristics. The easiest thing to do is to keep just a little pressure on both pedals.

16. Based on the input I have received I will:

a. Determine optimum rigging tension for the rudder and tab cables.

b. Revisit anti-servo tab size and geometry.

c. Explore the desirability and feasibility of installing rudder cable tensioning springs in the cockpit area. I hope I do not find them necessary, but will do whatever is required.

We will fix what ever we need to fix.

Thanks for your patience everyone. I’ll try to answer (less long-winded) any further questions on this subject. I recognize that the SparrowHawk is far from perfect. My staff (who should get the credit) and I will continue to improve the product. I am very content though. A couple of years ago we on the conference were discussing fatal PPOs. Now we are discussing irritants. We (all of us) have come a long way.

Respectfully submitted

Jim Mayfield

[darrellwittke]

Jim, your post was most informative and lucid. Good luck with getting the message out for Sparrowhawk owners to recheck and adjust their cable tension. Thanks for being open and willing to hear criticism (slight as it may be.)

[Aussie_Paul]

........"A couple of years ago we on the conference were discussing fatal PPOs. Now we are discussing irritants. We (all of us) have come a long way."

Most of us certainly have. :D

Well posted Jim. ;)

Aussie Paul.:)

[GyroRon]

Jim I hope you understand I wasn't trying to bring this up to bash Sparrowhawks. I think what I did, and what you did - per your reply above - will surely shut up the bad talk that has been whispered around since Mentone.

My guess is it needs a much larger anit servo tab, the one on the Dominators is just barely big enough and they are small machines compared to the S.H. A Piper Cherokee If I recall correctly has it's anti servo tab running the whole length of the Horizontal Stab.

[Mayfield]

Ron,

I did not interpret your comments as bad mouthing. As I stated, we are operating using a "Field Service Difficulty Report" (FSDR) system to drive quality/product improvement. We analyze every FSDR we receive. Some I can not easily fix. I think we can fix this one.

My guess (and I hate guessing) is that we will end up tweaking the anti-servo tab.

Also, I did not fully respond to James's and Brian's comments in my last post:

1. James/Brian: Brian said words to the effect of stating that fixed wing aircraft do not have a great bloody tail just behind the cabin. I concur. The biggest driver on location of the tail is being able to have adequate rotor clearance while still having adequate tail volume. The second driver is being able to build a structure light enough to not screw up CG and strong/rigid enough to support the tail loads and transmit those tail loads to the CG without bending or resonating. This is easier with a short boom.

2. I also did not fully discuss Udi's ideas. I'll give it some thought.

For now, I think we need to ensure that the cables are rigged properly and that we understand the different characteristics of an "all-flying" surface.

R/S
Jim

[mcbirdman]

As the tail goes back further the longer the arm and thus the smaller the need of the tail as it becomes more effective. This means it is easier to move the tail back. The secondary advantage is that the tail farther back is exposed to airflow better - especially if there is an engine out.

Since the horizontal plane doesnt change incedence I am not sure why you are trying to make it move also. The vertical plane sounds like it would have less problems if only a portion of the surface moved. If there was a tailpost of sort it would provide a rigid mounting surface that could be coupled to the airframe better (rigid) to answer the problem of weight and strength that occurs with simply trying to mount a flying tail further back. The tailpost provides the strength, the ability for increased length and would not have to be as big or heavy as it would be more efficient and physically smaller.

I guess that is what I am thinking. With increased frontal and side area it might benefit from an even slightly longer tail rather than using the old design as a reference.

I do wish you increased sucsess. jtm It is fun seeing you overcome these hurdles and provide a positive alternative to a similiar design that seems to feel there is no room for improvement.

[Mayfield]

Thanks again James. Hurdles, while not necessarily fun, are inevitable. We, in my opinion, can learn a lot about a person or a company by how they handle the hurdles.

I'm going to try to answer your questions:

James said: "As the tail goes back further the longer the arm and thus the smaller the need of the tail as it becomes more effective."

Ans: That is certainly true. The practical problems in structure are pretty big. We weigh and balance and try to find an acceptable engineering compromise. There are times that I wish I could have done things differently within practical constraints.

James said: "The secondary advantage is that the tail farther back is exposed to airflow better - especially if there is an engine out."

Ans: Although most cabin gyroplanes have the blunt body drag of a refrigirator, and the SparrowHawk is certainly no exception, our tufting shows pretty good flow over the H-stab and the V-stab power off and power on.

James said: "Since the horizontal plane doesnt change incedence I am not sure why you are trying to make it move also."

Ans: Structural simplicity and weight James.

James said: "The vertical plane sounds like it would have less problems if only a portion of the surface moved."

Ans: A fixed stabilizer/movable control surface is, as you state, a great solution if weight and complexity are not issues.

James said: "If there was a tailpost of sort it would provide a rigid mounting surface that could be coupled to the airframe better (rigid) to answer the problem of weight and strength that occurs with simply trying to mount a flying tail further back. The tailpost provides the strength, the ability for increased length and would not have to be as big or heavy as it would be more efficient and physically smaller."

Ans: Again James, everything you say is true. The problem is not only weight, although that is a big one. The problem is the tail boom. A single boom, unsupported laterally, would have to be very, very stiff to prevent it from resonating in flight. A fixed tail post would form a nice box structure vertically. For lateral loads, however, it is about as long as it can be without starting to suffer fatique wise.

James said: "I do wish you increased sucsess."

Ans: Thank you James. It is appreciated.

James said: "jtm It is fun seeing you overcome these hurdles and provide a positive alternative to a similiar design that seems to feel there is no room for improvement."

Ans: There is a lot of room for improvement. Improvements will be based, in large part, by feedback from the field. Although fun, it is also my duty to produce the safest aircraft I can. I, and my team, which really includes all of you, will do our best.

R/S
jim

[Udi]

Jim,

I know the SH is stable in yaw. My thinking was that maybe the static component was too strong. When I fly a C-152, I don't get this kind of quick yawing into side gusts, even at slow airspeeds. Why is the difference?

Clearly, the C-152 is heavier than the SH, but not by much. Normal gross weight with only one pilot is only 1500 lbs. The bigger difference is in the weight distribution (MOI). Another big difference is in the distance of the vertical stabilizer from the CG.

Although, as you said, you have adequate dynamic stability, an even higher dynamic stability would tend to slow down the reaction speed of the vert. stab. to horizontal disturbances. Static stability is linear with the distance from the CG, while dynamic stability is exponential. This is my explanation why a C-152 may "plow" through horizontal disturbances without hunting, while short-coupled gyros (aircraft) don’t.

I don't even know that this is a real problem - I am just trying to theorize why we see these differences. By the way – I had similar thoughts while flying in a Boeing 747 over the Atlantic. We were flying through some amazing horizontal gusts. The whole aircraft was thrown sideways, but I felt very little yawing…

Udi

[Mayfield]

Udi,

Thanks. I'm targeting rigging as the most logical culprit right now. I'll know more after some testing this week.

I am beginning to think (but do not yet know for certain) that any cable slack will allow an all flying surface to hunt.

I hope to do some static experiments by disconnecting the cables, vectoring air into the tail at different angles and watching the response.

Then we will reconnect the cables and continue the experiment with different cable tensions.

One elegant solution would be to get rid of the current cable within sheath set up and use a well tensioned, continuous loop system with phenolic pulleys.

I'll try to keep folks posted.

jim

[mceagle]

From my point of view, it is great to see a manufacturer addressing perceived problems and rectifying where necessary. All too often, manufacturers will take a high horse stand and refuse to admit to a possible fault. (sound familiar?)
Top of the class Jim and the team at AAI.

[mcbirdman]

Jim,



Static stability is linear with the distance from the CG, while dynamic stability is exponential. This is my explanation why a C-152 may "plow" through horizontal disturbances without hunting, while short-coupled gyros (aircraft) don’t.

Udi

I like that. It is like the difference of an arrow and a bolt ( short arrow ). One is less affected by the wind. In this case it seems that it matters even more to have everything tuned in a "short" situation.

[Doug Riley]

Jim Mayfield, I imagine you're familiar with the Dominator anti-servo tab mechanism. The tab is actuated by a slotted metal strip, sliding over a fixed pin projecting up from the tail tube. It's elegantly simple, light and cheap, but it's also not prone to developing freeplay as a cable setup is.

[birdy]

Your a good,respectable man Jim. :)

The standard RAF virtical tail is too small,simple.
When landing one up and no power,I'm on full left peddal at the flare to stop my weight yawing it to the right. :mad:
But as Jim said,every ying has a yang. ;)
When fly'n in a crosswind that is gusting stronger than your airspeed,then a slightly sluggish reaction can mean not git'n dizzy from the constant 90 degree yaw changes.Altho ,it's much worse [more sluggish]with the doors on.With the doors off,the peddals become mear foot rests,just like the ferel. :D

Just simple observations of a SCG. :o

[murraybarker]

Gyro Ron, Not all Aussie gyro pilots are 20 years behind in idea's. I, and others have been flying low thrustline/tall tail gyro's for about 14 years now.The notion that a dominator style woul not last long while mustering is crap.A freind of mine did many thousands of hours doing just that untill he broke his back in a motor bike accident.(While mustering). If the gyro is built properly it will last as long as any other design.I have never had a problem with tall tail in any cenario. Engine stoped,vertical decents,vertical decents while spinning(which I do at air displays).even though it is close to the prop the one on my two seater is 6 feet tall.Think about it. Im sure if the musterers out there could fly a dominator for a while they would never go back to the old style, been there done that.

[GyroRon]

Murry, sounds like I will have to exclude you from my statement. How about a pic of your machine

[murraybarker]

Ron, The idea is slowly spreading down here. When the first tall gyro was built here in 1990 everyone was horified. We got comments like "It will tip over while taxiing,you need a ladder to get into it etc etc". I'm sure Ernie got the same comments a few years before that. The thrustline on this Gyro isnt as low as we usualy make them but it's not to bad. Iv'e seen Gyro's all over OZ and you seem to get the same styles in the same area,and because they all seem to fly sucessfully there's no thought of trying new designs.

[GyroRon]

Murray, nice machine! And sooner or later when more of your fellow Aussies have had a chance to get past the tallness of the machine and it's looks and fly one, you will see a radical change in what Aussies consider a good gyroplane. Once your in the seat and in the air flying, how tall it is or how it looks makes no difference. A good flying and stable and safe machine is just simply better.

[Cobra Doc]

I can't say noticed any "Yaw hunting" when I flew with Jim Mayfield. The only tail wagging was on my part and intentional. Maybe AAI's gyros are just rigged better? I did notice the pedals were a bit heavy, but it only took a couple of turs to get used to it. On the day we flew there was a stiff but steady breeze out of the north. The breeze was just under 15kts and I was able to track straight down I-10. With that much crosswind and 80kts (or was it mph?) forward, obviously I wasn't heading down the highway but I tracked true. I also taped my wife's flight with Steve McGowan. Looking back at the tape, the white gyro flies true no matter who is on the controls.
Maybe gyro pilots have the same affliction Pitts pilots have that Budd Davisson describes as "Dancing Feet". I've noticed the same tail wagging in short couple airplanes with relatively low time pilots, meaning low time in make and model.

[Hognose]

Like Rob Dubin I have only flown the AAI-mod RAF (with AAI's Terry Brandt, for one whopping hour) and did not observe any unusual yaw or "tail wagging." Rudder was not needed for normal turns and there was no correction needed; it was useful for landing in a mild x-wind.

I'd be interested to hear what Terry (or even more so, Jim Mayfield) has to say about this. I have sat in the "true" Sparrowhawk and the cabin is much roomier and more comfortable than the RAF version. The RAF version has (IMHO) better "styling," which is fine if you plan to put the thing in your garden and admire it, but the "boxy" AAI has much more room, and the seats are way better than the RAF seat-tank (not to mention easily adjustable -- a big deal for instructional users), so it's a much nicer cabin for those of us who plan to actually fly.

I am not sure what the tail number of the plane I flew with Terry at Fond du Lac was. I thought it was more stable, but as maneuverable, as Dofin Fritts's unmodified RAF. In my opinion alone, the higher cost of the AAI kit is justified by the higher quality of the parts and improvements throughout the design. Interestingly, the delta in costs is about equivalent to the cost of the AAI stability and control augmentation kit for the RAF 2000. (Which gives you CLT but does not change your rotor head and blades). Ken J's plane, if I remember right, has the AAI kit and the rotor upgrades, both.

A lot of guys say they saw this gust-induced yaw from the ground. Anybody experience it from inside the plane?

cheers

-=K=-

[twistair]

Guys,

After our first test flight I wrote that we didn't see any yaw at S/L flight. Having now much more flying hours in SH I can tell that it yaws at IAS 120 and higher. Don't know still what is the reason(s) - it may be a result of assembly or something else. I'm really curious in finding the reason so we'll continue testing after we put our SH on skiis (yes, gentlemen, there is already -10 C here and 10" snow covers the field).
I can also add that calibrating airspeed indicator we found that it shows ~20 kmh more than it is in reality: 100 kmh IAS is actually 80 kmh TAS. Thus we didn't see any yaw at 80 kmh TAS but it appears at 100 kmh TAS. And become uncomfortable at 130-135 kmh TAS. Again, I still don't know where the real reason for yawing lays.

This small video shows the thing. Don't mention camera vibrations - it's not aircraft but simply me getting cold :)

SparrowHawk Yaw3 (http://delta.wtr.ru/files/shyaw3.mpg) (mpeg, ~ 2.5 Mb)

[Doug Riley]

Just a guess: A large portion of the vertical fin may be in turbulent air when it's flying directly behind that boxy pod. Only when the aircraft starts to sideslip a few degrees does the fin receive clean air and begin producing a centering force. So the nose oscillates. The wake turbulence would tend to get worse as airspeed increased.

[twistair]

But, Doug,

The tail is in the propwash stream - isn't it permanently well mixed and turbulent? I've heard that standard RAF2000 cannot fly straight - it yaws too and it was told earlier that it is due to airflow detachment from cabin sides. If memory serves, it was a short article in Rotorcraft some years ago and it also described simple way to decrease yawing at RAF by installing turbulators at cabin sides. These turbulators were made on ideas used on gliders to stabilize laminar flow border on wing. Could you comment this?

[Doug Riley]

The propwash will tend to have the characteristics of the inflow. This is good if the inflow is simple and straight; the outflow will tend to be so, too. The outflow's direction will be influenced by the inflow's direction (which is why an immersed fin or HS can work). If the inflow is turbulent (air flowing in swirls in all directions) so, too will be the outflow. That's why pusher props located behind big cabins make so much noise. The "detachment" of the flow is what leads to the turbulence -- so it's another way of talking about the same effect. "Attached" flow is more nearly laminar and detached flow is turbulent.

[twistair]

Thanks, Doug,

Things become clear when explained so clearly.

[pwendell]

I've got about 3 hours in the Sparrowhawk prototype, N4132R, with an injected EJ25. Compared to the AAI modified RAF it is much more comfortable. It flies very well. I experienced no adverse yaw in straight and level flight up to 85MPH indicated. That is as fast as I flew. The performance with the EJ25 is great, although throttle control is definitely more touchy than what I'm used to. The fuselage tends to fly a little flatter during climb out and approach than the modified RAFs I've flown, so the sight picutre is a bit different. With the EJ25 it really wants to get off the ground NOW, so it requires more forward pressure earlier than the modified RAFs to keep it from lifting off too early.

Other than my intial takeoff (thank you Steve) and a little trouble with throttle control, I found the Sparrowhawk very easy to fly and MUCH more comfortable. I have only ever flown AAI modified RAFs before.

[KenSandyEggo]

I have had my modified gyro up to about 95 m.p.h. and I have never noticed any yawing. That would be about 109.25 knots, I think....wait, that would be 80.75 knots.....no, knots are higher.......crap.