Spiral descent in an RAF

[dragonflyerthom]

I would like to know if what I have heard is true. Is the spiral decent going right in a RAF impossible to get out of?? Maybe some of the other RAF pilots can answer this question. If it can be gotten out of what is the correct inputs to do this?

[StanFoster]

Thom: When we were talking on the phone..I wasnt meaning to say that it was just the RAF...its any gyro with rotors that turn the standard way.

Someone please correct me if what I told Thom needs any correction, but basically I told him that you can get in a predicament in a high speed spiral descent with no power on....as if you were trying to descend in a cloud and you got your gyro in a dive...power off...and a right spiral. Stupid situation but we have to set up a scenario...

So in this power off dive thats spiraling to the right, you are diving at VNE and are right at retreating blade stall. You cant push the stick forward to as this just makes the speed go higher making the retreating blade stall worse. You dont want to add any more right stick as you already are spiraling to the right. You cant add back stick since that makes the retreating blade stall worse...and if you add left stick...that also makes the retreating blade stall worse.

How to get out of this predicament? Someone please chime in...of course the best answer is not to find yourself in such a stupid situation.

Stan

[Doug Riley]

Stan, aft stick reduces the cyclic pitch of the retreating blade in a gyro with a rotor that spins CCW viewed from above.

Some thinkers advise against right pirouettes (= a rudder spin while doing a vertical descent). If the spindle is in any poisition other than perfectly straight-up when you do this maneuver, the spindle is moving in a "stirring" path in the middle of the rotor disk. This feeds a continuous cyclic pitch change into the rotor. The cyclic pitch change is more abrupt when the gyro is spinning to the right than when it's spinning to the left. In the left spins, the rotor is "running away" from the stirring spindle.

In practice, the spin is unlikely to be fast enough to cause a problem if it's done with zero airspeed. A fast rudder reversal WITH AIRSPEED is much more violent and may cause an excessively quick cyclic change that the rotor can't follow.

A gyro with a large H-stab located directly under a short rudder may lose rudder authority in a power-off vertical descent.

[gyromike]

A gyro with a large H-stab located directly under a short rudder may lose rudder authority in a power-off vertical descent.


I notice this on my Bensen Doug.
I'm guessing the stab blankets the rudder and it's hard to start a pirouette and keep it going.

The Dominator though, does it with ease.

[Doug Riley]

Yes, even the big stretched tandem Dom twirls nicely, Mike. Nicer still, it stops when you tell it to.

Rudder blanketing is one of a couple reasons that a keel-mounted HS isn't ideal.

On re-reading Thom's post, though, it sounds as if he and Stan are talking about a tight, fast, coordinated, power-off descending spiral, not a vertical twirly thing. In the fast-spiral case, fuselage pod effects are apt to be at their maximum. That may account for a tendency to get stuck in a spiral.

[Chris Burgess]

dragonflyerthom, Short answer, No

14 CFR 91.13
14 CFR 91.303
14 CFR 91.307 (c)&(d)

And I still don't see any of this in the Practical Test Standards:(

"Push your aircraft's limits and you may find and exceed your own"

Final Comment here, "Don't play with an aircraft that is not a Toy"

[dragonflyerthom]

The reason this subject was brought up was from the ROC 2006 vid that I watched. I was aware that this is an advanced maneuver and was just curious as to the reason and the inputs to get out of it. Guess my FW training was kicking in. You are right and that is probably why it is called a death spiral. I know that some of the Dom's and Air Commands do it. I have enough limits on my RAF at present without putting some more on it.

[Doug Riley]

Thom, it's an interesting quirk of rotorcraft that they don't have the same kind of spiral instability that FW craft do. A FW plane tends to try to tighten a spiral because the outside wing is going faster than the inside one. You can get into a "death spiral" when you can't see the ground and your butt/inner ear decide that the centrifugal effect feels like a climb instead of what it is -- a turn.

Your rotor blades experience the same outside-inside airspeed difference. It's at a maximum when the blades are at 9 o'clock-3 o'clock. However, because of the 90-degree phase lag in the rotor's precession response, this difference results in a slight nose-up tendency (= more rotor blowback) instead of an overbanking tendency.

Strangely, this is true for both a left and a right turn.

[Harry_S.]

"Push your aircraft's limits and you may find and exceed your own"

Final Comment here, "Don't play with an aircraft that is not a Toy"



Well stated, Chris.


Cheers :)

[StanFoster]

Doug-As to be expected from you, another excellent post. Tell me though , since you reread my post, I would like to change the scenario to a LEFT TURNING power off-descending spiral with the retreating blade just about to stall -at VNE. I had the right spiral wrong as your comment that a left cyclic input would reduce the pitch thus improving the situation. So-a left turning descending spiral at VNE-power off, has me thinking that any more backstick would make matters worse by bringing on retreating blade stall. Any forward stick would increase the speed past VNE. Left stick would make the spiral worse, and right stick would increase the pitch of the retreating blade thus stalling it. Is this not then being in the corner of a box with no way out? THANKS Stan

[Doug Riley]

Well, Stan, back stick still will de-pitch the retreating (left) blade. So that's a good thing.

Of course, gyro rotor blades don't stall all at once. The inner portion of the retreating blade is always stalled. The stalled area spreads outward as you go faster, as flapping/blowback cranks more cyclic pitch into the retreating blade to compensate for its lower airspeed. (The retreating blade's airspeed is its rotational (tangential) speed MINUS the gyro's forward airspeed.)

LESS of the retreating blade stalls the slower your forward speed. In a turn, the two blades have, in effect, different "forward" speeds because the retreating blade is on the inside of the turn. So less of the retreating blade will be stalled in a left turn at airspeed X than in straight-line flight at airspeed X.

What you're asking boils down to whether it might be possible to go so fast in a left spiral that the retreating blade stays sufficiently unstalled to operate normally as long as you're turning -- while at the same speed in a straight line, the whole retreating blade would stall.

You might be able to gin up a set of numbers on paper that would reach this result. It seems pretty unlikely in reality to me, though. A tight enough turn to raise these issues would be so steeply banked that the blade's forward airspeeds woudl go back to nearly identical (at 90 deg. bank, these speeds ARE identical). Such a tight turn also would the load up the rotor, increasing its RPM and lessening the relative effect of the inside-outside blade speed difference as a percentage of total blade airspeed.

It would be prudent to slow down a bit with a little back stick (or actually a little release of forward pressure) and be gentle with your high-stick input when coming out of a screaming left spiral. If you insist on getting into one in the first place.

[PW_Plack]

Stan,

I'd bet you have lots of room above VNE before you risk destructive blade flap in flight. I'd expect the rotors to keep working to 140 or 150 MPH.

If you're 40 or 50 per cent past VNE, well...you made some poor choices!

[birdy]

Is the spiral decent going right in a RAF impossible to get out of??
Simple answer, no.
If it was, i woulda made alot of holes with the wasa.;)
This thread has wandered a bit from your orgional question tho.
In a 0 AS virtical decent, you have to be carefull to not let the machine slip backwards, coz things can get very confusing and messy real quick. Specialy in a RAF with its cab and usless rudder.
If you want to spin in a controled way, you need either a little forwad AS or some thrust to control it with.[ airflow over the rudder]
But if you have no power on and plenty of AS, then you'll have good rudder effect. To a point.
If you go too fast, or turn too sharply, then as Doug said, your go'n to be askn too much of the rotors, BUT, long before you get to this point, the rotors will be telln you your getn too keen, and the feed back it sends will only be ignored by a fool.

With my ever increasing personal altitude ceiling [ now bout 1000'] i get to play more with the decents of every kind, and i'm not dead yet :) .

The best ones i'v tryed are the virtical side slip spirals, with the keel at near 90*. Good fun and the blades make a hell of a noise :) .

[Doug Riley]

Vertical side slip spirals? Birdy, is that a slip in which you slip your way around a circle? Allow a little yaw toward the direction of slip but not enough to coordinate the turn?

[Aussie_Paul]

[I]The best ones i'v tryed are the virtical side slip spirals, with the keel at near 90*. Good fun and the blades make a hell of a noise :) .

90* to what Birdy?

Aussie Paul. :)

[birdy]

Vertical side slip spirals?
I did post an explination Doug, but wen i re read it, i realised it wasnt appropriate information for a public forum, so i delieted it.

[Doug Riley]

...but I got it before it disappeared. I was picturing something different anyway.

[GyroRon]

Death Spiral......

If there is footage on a ROC video of a gyro doing a death spiral then it must have been me. :)

John Stevens gave that manuver the " Death Spiral " nickname, to me it seems like a harmless and easy trick to do though.

The way I do the trick is usually I begin with at least 1000 feet AGL altitude and bring the gyro into a vertical decent or at least a slow forwards speed decent.

Then, I allow the nose to drop fairly low to build up airspeed.... usually 60-70 mph and then at that point I pull the stick back hard and also to the right.

Once this happens the gyro will slow rapidly and do a tight banked turn and the rotors speed up dramatically. As the airspeed bleeds off I let up on the back stick pressure and allow the nose to drop but still have alot of right stick input held in.

At this time I add in a little right rudder as well and just hold the controls, adjusting back pressure and side pressure to keep the speed from building.... meanwhile the nose is pointed VERY low, almost seems like the nose is pointed straight down.

Due to the way this manuver is done, the rotor stays loaded and RRPM is higher than what you see in cruise and to me the gyro seems perfectly safe and under control during this manuver. It is a cool way to loose altitude, and of course the rotors make all kinds of pops and choppy sounds!

[Doug Riley]

I think we have two different sources for the same name here.

The scary videos they show you in FW ground school refer to the "death spiral" that a pilot without instrument training gets into when he loses sight of the ground.

Olympic figure skaters have a "death spiral" move that's part of the "couples" routine.

If I understand Ron's description, his rotor (being a round wing) is doing what a rotor would do in a regular coordinated spiral -- namely, directing some of its thrust toward the center of the spiral to make the force that sustains the turn -- but the airframe just happens to be pointed a different way than usual, thanks to cross-controlling. Is that it, Ron?

[GyroRon]

Controls aren't crossed when I do this manuver. Right rudder, right stick, and back stick, nose pointed nearly straight down, gyro spirals around and around.

If the gyro did what it does in this move, with the nose still pointed at the horizon, the gyro would be doing barrel rolls.

[C. Beaty]

What Ron is describing is a tight corkscrew spiral dive with a bit of rudder input to keep it tight. I don’t think there’s any danger in that but it would be nice to have a rotor flap angle indicator.

What the RAFers seem to be concerned about is pirouettes where, due to the area of the cabin, there’s insufficient rudder and to make matters worse, the spiral slipstream off the prop, acting on the half-height rudder, increases the spin rate in one direction.

A full span tall tail would solve that problem along with a host of others.

[dragonflyerthom]

I was just on youtube and found this little video that has Thai music and was video in Spain. As you will notice it is a stock RAF 2000

http://www.youtube.com/watch?v=LibtnVJ1JoM&feature=PlayList&p=47791BC3703C879E&index=20

Imagine that. He did a gyro decent also

Here is another of a magni I believe in the U.K

http://www.youtube.com/watch?v=9yKiQCGCM4o

[Chuck_Ellsworth]

When looking up at an RAF flying over head and seeing that big cabin with that thin keel and only the vertical fin and rudder and no H.S. shure looks weird.

It makes me nervous thinking about it.

[OzyRuss]

Is the spiral decent going right in a RAF impossible to get out of??
Simple answer, no.
If it was, i woulda made alot of holes with the wasa.;)
This thread has wandered a bit from your orgional question tho.
In a 0 AS virtical decent, you have to be carefull to not let the machine slip backwards, coz things can get very confusing and messy real quick. Specialy in a RAF with its cab and usless rudder.
If you want to spin in a controled way, you need either a little forwad AS or some thrust to control it with.[ airflow over the rudder]
But if you have no power on and plenty of AS, then you'll have good rudder effect. To a point.
If you go too fast, or turn too sharply, then as Doug said, your go'n to be askn too much of the rotors, BUT, long before you get to this point, the rotors will be telln you your getn too keen, and the feed back it sends will only be ignored by a fool.

With my ever increasing personal altitude ceiling [ now bout 1000'] i get to play more with the decents of every kind, and i'm not dead yet :) .

[Quote]The best ones i'v tryed are the virtical side slip spirals, with the keel at near 90*. Good fun and the blades make a hell of a noise :) .


Just to get me head around this.........

Keel at 90 degrees, vertical side slip spirals..............

Puts mast on the horizontal, puts blades pure vertical.......Machine is spiraling down vertically.........from 1000ft

Yea right............you is smokin sum real good weed there :violin:

[Aussie_Paul]

Russ, I think Birdy changed "weed" brands and this lot is stronger!!!:rapture: :rapture:

Aussie Paul. :)

[birdy]

So Russ n PB, wots so hard to understand???

[OzyRuss]

With you all the way, right up to the moment of turning the ignition key.

After that it gets too far fetched [ too Holywood blockbuster stuff ].........:noidea:

Machine layin on it's side, blades vertical,machine spiraling as it drops vertically..............yea right

[Aussie_Paul]

90 degrees to what was my question Birdy.

Aussie Paul. :)

[Steve McGowan]

Death Spiral......

If there is footage on a ROC video of a gyro doing a death spiral then it must have been me. :)

John Stevens gave that manuver the " Death Spiral " nickname, to me it seems like a harmless and easy trick to do though.

The way I do the trick is usually I begin with at least 1000 feet AGL altitude and bring the gyro into a vertical decent or at least a slow forwards speed decent.

Then, I allow the nose to drop fairly low to build up airspeed.... usually 60-70 mph and then at that point I pull the stick back hard and also to the right.

Once this happens the gyro will slow rapidly and do a tight banked turn and the rotors speed up dramatically. As the airspeed bleeds off I let up on the back stick pressure and allow the nose to drop but still have alot of right stick input held in.

At this time I add in a little right rudder as well and just hold the controls, adjusting back pressure and side pressure to keep the speed from building.... meanwhile the nose is pointed VERY low, almost seems like the nose is pointed straight down.

Due to the way this manuver is done, the rotor stays loaded and RRPM is higher than what you see in cruise and to me the gyro seems perfectly safe and under control during this manuver. It is a cool way to loose altitude, and of course the rotors make all kinds of pops and choppy sounds!

Ain't that what the naked girls do in the booby bars on the poles..:wacko:

Yall scaring hell outta me,, whats it anyhoo...:noidea:

I never done nothin like that... I do like watchin the girls doin it..:flame:

Thatswhat Ya mean huh RON !!!!:blabla:

[birdy]

Machine layin on it's side, blades vertical,machine spiraling as it drops vertically..............yea right:confused:
Were did ya hear bout that little trick Russ????
News to me.

90 degrees to what was my question Birdy.
Use your imagination PB. Wots it usualy not at 90* to?
[ and its nuthn like wot Russ is thinkn of, buggered if i know wot Russ is thinkn of.]
I think Russ has seen too many movies ;) .

[OzyRuss]

Is the spiral decent going right in a RAF impossible to get out of??
Simple answer, no.
If it was, i woulda made alot of holes with the wasa.;)
This thread has wandered a bit from your orgional question tho.
In a 0 AS virtical decent, you have to be carefull to not let the machine slip backwards, coz things can get very confusing and messy real quick. Specialy in a RAF with its cab and usless rudder.
If you want to spin in a controled way, you need either a little forwad AS or some thrust to control it with.[ airflow over the rudder]
But if you have no power on and plenty of AS, then you'll have good rudder effect. To a point.
If you go too fast, or turn too sharply, then as Doug said, your go'n to be askn too much of the rotors, BUT, long before you get to this point, the rotors will be telln you your getn too keen, and the feed back it sends will only be ignored by a fool.

With my ever increasing personal altitude ceiling [ now bout 1000'] i get to play more with the decents of every kind, and i'm not dead yet :) .

[Quote]The best ones i'v tryed are the virtical side slip spirals, with the keel at near 90*. Good fun and the blades make a hell of a noise :) .

Last time i checked me keel was leval [ horizontal]......90* now puts me keel pure vertical, puts me mast now to horizontal, puts me blades now vertical...........now me gyro is dropping vertically....i got sumin wrong here or what

[dragonflyerthom]

I don't think this is something a low time pilot like me needs to know. I just hope I never get into a situation where I will find out. Birdy you put a lot of trust in your abilities and I am glad you are around to tell the tales. Scary isn't it Russ.

[GyroRon]

Steve, your right! I would much rather experience that kind of Death Spiral than the gyro kind! In the words of Martin Lawrence... You so Crazy! ;)

[gyromike]

90º of yaw to the flight path, Birdy?

[Aussie_Paul]

Machine layin on it's side, blades vertical,machine spiraling as it drops vertically..............yea right:confused:
Were did ya hear bout that little trick Russ????
News to me.

90 degrees to what was my question Birdy.
Use your imagination PB. Wots it usualy not at 90* to?
[ and its nuthn like wot Russ is thinkn of, buggered if i know wot Russ is thinkn of.]
I think Russ has seen too many movies ;) .

Birdy, I don't have time for your guessing games as to how your mind works. :(

I prefer facts rather than me having to use my imagination which may be wrong. :noidea:

Aussie Paul. :)

[birdy]

Russ and PB, if you realy want to know ,PM me, coz as Thom said, its not appropriate for a public forum. I'v already posted an explination, then deleted it after readn it coz it dont belong in public.

90º of yaw to the flight path, Birdy?
I dont think theres a gyro in the world that could do that Mike ;) .

, I don't have time for your guessing games as to how your mind works.
I can assure you PB, my mind is way outa your league.:lol:
As i said, i posted, then deleted, but if your interested, it aint rocket science to figure out.:noidea:

This sorta info is communicated on a need to know basis, and you dont NEED to know.:rant:

[Aussie_Paul]

A simple question Birdy, 90 degrees to what??

Aussie Paul. :)

[birdy]

And a simple answer PB, you dont need to know.:)
Dont like your own medicin ay Paul?

At least i was askn a ligit question, but you refused to answer it.[ coz you couldnt ;) .]

[birdy]

Thought as much PB, i can read you like a book:).