Aviomania's Agrinio Antics

"Cyclic stall" theres a new one for me, Can you explain this a bit further birdy, what is it?, and what does it do?
Its wen the cyclic pitching rate your askn of the blades is airodynamicaly higher that is possable at a given rrpm.

my rpms stay low with a big rotor and 40hp! my cyclic response stays slow!
Thats a little bit different Red. Youll bump the teeter stops before youll stall.

Thanks David. I still want to see you flying a genesis thought!!!
Dont wurry Nik, if one went past ere, it wouldnt leave here a virgin.

birdy said:

"Cyclic stall" theres a new one for me, Can you explain this a bit further birdy, what is it?, and what does it do?
Its wen the cyclic pitching rate your askn of the blades is airodynamicaly higher that is possable at a given rrpm.

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So If im Sitting in the air all fat and happy, hanging off me prop (moving very slowly with full tap on) and decide im outta here and put her into a turn, i could come across cyclic stall if i input the turn too fast? What will i feel/hear?

All_In said:

It's seems I missed a few posts, sorry if I missed any others please remind me.

If I'm mistaken please correct me. I'd rather know the truth than be right.

When I asked the 4 other manufacturer's if they had financing or have a pay as you build plan. They all said no. Soon after I became an Agent for Aviomania we created and offered a $2,500.00 sub-kit pay as you build option.
Since then at least one other manufacture has now offered a $5,000.00 pay as you build option for their ultralight only. This is an example regarding how competition helps all of us.

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I remember when I would dream of owning a gyro and ordered the Brock catalog. I thought I could start building one because Mr. Brock sold the KB2 in sub kits. Of course his business was closed. I know star bee has sold various frame kits and individual components. Maybe you are the first. Dominator sells components of their machines. I just did not understand what your were meaning by first.

Who ever took this video really did an outstanding job of keeping the gyro in focus and with very little shake. They deserve some credit as the gyro was really moving a lot of directions and lots of altitude changes.

Do you have a close up of the mech prerotor at the head? In the video it appears the cable housing has come loose from the Bendix fixture. But it may be the way it is made, I can't tell. It is noticeable at the end of the video.
Good luck with the sales!

What will i feel/hear?
Depends on alota things Trent.
If you were hangn off the prop and did a hard peddle stomp without 'circling' the stick, youd more likely just bump the stops, or feel pitching inertia resistance, coz youd be feedn a big disc attitude change with low rrpm.
Cyclic stall can happen if you fight this stick movement.

Cyclic stall can happen at any rrpms, but generaly at the slower end if at all. [ askn the disc to change attitude faster than it airodynamicaly can]

Stalling is pretty unlikely, but you wont miss the sound if you do it.

Friendly said:

Do you have a close up of the mech prerotor at the head? In the video it appears the cable housing has come loose from the Bendix fixture. But it may be the way it is made, I can't tell. It is noticeable at the end of the video.
Good luck with the sales!

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Looks like its the trim spring doing a bit of rattling, I don't think its the prerotator

birdy said:

...
If you were hangn off the prop and did a hard peddle stomp without 'circling' the stick, youd more likely just bump the stops, or feel pitching inertia resistance, coz youd be feedn a big disc attitude change with low rrpm.
Cyclic stall can happen if you fight this stick movement.

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Hi birdy, if you mean to say that when standing on the prop at low airspeed and lowish rrpm you turn around the quickest by stomping on the rudder (best use the one in the direction the rotor is turning) and letting the stick do whatever it needs to do (i.e., keep a light grip on it but don't stop it from wandering) then you're "spot on" as you'd say

Just be aware that your nose will be pointing right steep downward and the stick will want to move in a semi-circle from the rear center to near the front stop. Don't fight it. Be prepared to lose some altitude, don't immediately be hauling back on the stick either or else you'd ask too much in too little time from the rotor.

-- Chris.

What Birdy calls cyclic stall is also known as precession stall.

That’s when a rotor blade is called upon to develop more lift than it can in order to tilt (or precess) the rotor.

Precession stall makes a bang like a shotgun being fired. It comes from a stalled blade slapping the air. It’s likely to be the last sound the pilot or an unstable gyro ever hears.

High inertia, slow rotors are more prone to precession stall than low inertia, fast rotors.

Hi Chuck,

Hmm this has got me thinking now about a previous accident now. you say it would be the last sound to hear, why so? will the rotors pretty much be unload and fall out of the sky? Why only on an unstable gyro?

An unstable gyro, one with propeller thrust line well above the CG and with insufficient horizontal stabilizer has all the requirements to become a rotary lawn sprinkler or yo-yo once the rotor stalls.

Also applies to gyros that rely upon rotor thrust to balance propeller torque. They can become roll axis yo-yos.

(best use the one in the direction the rotor is turning)
Dun proper Chris, it dont matter which way you stomp, coz theres should be no or minimal cyclic action.
I do it alot, hangn there, waitn for 'it' to make the first move, and it trys to duck past. Ill go from 45* nose up at 0IAS to 90* nose down ina second, either way.


What Birdy calls cyclic stall is also known as precession stall.
Thanks mate, i knew i could count on you to make sence of wot im thinkn.

you say it would be the last sound to hear, why so?
Accordn to CB Trent, i hada little stall incident a few years ago, http://www.rotaryforum.com/forum/showthread.php?t=8427 , but it was only for a coulpa cycles, and under different circumstances, so im still ere.

Thanks for the link birdy i'll have a gander,

Gotta go and fart arse around with me blades (larkin) later on set em up this morning and for the life of me can't get em trackin right, hopefully i'll get em sorted out before tomorrow, wanna go for a fly for Terry since it'll be a year tomorrow since he died in his gyro, which nearly make me wonder if he precession stalled his rotors along with how his gyro was setup all wrong but we'll never know.

Cheers,

When an unstable gyro tumbles out of the air, witnesses often report hearing what they believe to be an explosion; a “loud bang.”

That’s precession stall; the engine is tumbling the machine head over heels faster than the rotor can produce enough lift to follow. I’ve heard it; sounds to me like a 12 gauge shotgun being fired. It’s similar to slapping the water with a canoe paddle turned broadside.

which nearly make me wonder if he precession stalled his rotors along with how his gyro was setup all wrong but we'll never know.
Thought that mite have been the incident you were thinkn of.
Was talkn to 'the boss' bout it and I would be lean'n more towards torque roll initialy.
No dout the blades woulda stalled at sum point, but thats not wot caused the bingle im thinkn.
But yeh, rong bloke, rong machine and rong time.

And CBs discripton; It’s similar to slapping the water with a canoe paddle turned broadside. is spoton the sound.
It’s similar to slapping the water with a canoe paddle turned broadside.

Just as an asside CB [ and not wantn to hijac your thread Dinoa], but iv been mean'n to ask for ages bout the blades i 'stalled'.
As you could imagine, i hada good look [ bout 10 secs] at the blades wen i landed, but i was lookn for contact evidence at the tips. But a while later i did find that the straps [ bar to blade cheek plates] hada 'bruise' on their trailing side. Like a slight ripple, as if theyd hit sumthn at speed and kinked the straps at the point between the bar and blade.
Id never hit anythn with them, and cant see how a stall coulda stressed um this way, but cant think wot else woulda dun it. They still flew fine.
Wot would bruise a strap like this?

[ and before you ask to see a pic of um, they are the totaled ones i fixed by smackn um one the ground wen turning too low. ]

birdy said:

Dun proper Chris, it dont matter which way you stomp, coz theres should be no or minimal cyclic action.

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I still think that yawing the ship around in the direction the rotor turns would minimize any risk of getting into a precession stall. Particularly if you're marginal on rudder authority or you're timid in stomping on the peddal.

-- Chris.

Chris, your only rotating on the bolt, theres no cyclic. [ well, there shouldnt be] . Wen your nose high at min AS, the rotor is close to virtical. Wen youv dun your 180* stomp, your near 90* nose down, and the disc is still near virtical. Hasnt hardly moved.
If your useing the rotor to turn [ bank] then for sure, theres alota cyclic happen'n.

If theres any limiting facter, itd be which way you torque roll.
With my 912, its left side high, so iv less left stick travel, so turning with the rotor has me closer to the stop than against.
Rite stomps are faster n easier coz of this.
Wen i do a left stomp, im know im near the left stick control limit.

birdy said:

Chris, your only rotating on the bolt, theres no cyclic. [ well, there shouldnt be] . Wen your nose high at min AS, the rotor is close to virtical. Wen youv dun your 180* stomp, your near 90* nose down, and the disc is still near virtical. Hasnt hardly moved.
.

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David.. that depends on your Gyro. A HTL gyro will be as you described.. the engine is trying to put the nose down so you are using the rotor to keep it up.

on a CLT design such as the Genesis the engine thrust is applied at the CM so the rotor is only ~8-9* deferent from the frame angle and the stick position is at neutral position (P factor and aerodynamic effect of the tail have some offset from neutral).

So... hard ruder turns with the genesis are easy especially if you are flying with a light grip on the stick.

on 1:30 in the video you can see a recovery with 45* right ruder. the result is a slight nose down attitude with a slight bank ( this is the recovery planed to use if i had engine failure at low alt.).

at 2:47 is a ruder recovery as you described with 180 degrees ruder turn. that puts you on a 45* nose down attitude and is the recovery planed when i have engine failure above 50 feet.

normally an engine failure gives you couple of seconds of prop usage ( the prop does not stop from 2100 +rpm to 0 in a split second.... generaly....). if the failure is electric the prop takes about 2 seconds to stop. some times the loss of power is gratual.... So..... using the prop airflow to help you turn is a good practice... in my case right ruder!!!.

With the genesis since the stick position is in the center and engine torque is effectively reduced, precession stall is avoidable especially with a light grip on the stick.

Friendly said:

Do you have a close up of the mech prerotor at the head? In the video it appears the cable housing has come loose from the Bendix fixture. But it may be the way it is made, I can't tell. It is noticeable at the end of the video.
Good luck with the sales!

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That is the trim spring. The prerotator flex shaft attachment is not visible from this angle.

birdy said:

Just as an asside CB [ and not wantn to hijac your thread Dinoa], but iv been mean'n to ask for ages bout the blades i 'stalled'.
As you could imagine, i hada good look [ bout 10 secs] at the blades wen i landed, but i was lookn for contact evidence at the tips. But a while later i did find that the straps [ bar to blade cheek plates] hada 'bruise' on their trailing side. Like a slight ripple, as if theyd hit sumthn at speed and kinked the straps at the point between the bar and blade.
Id never hit anythn with them, and cant see how a stall coulda stressed um this way, but cant think wot else woulda dun it. They still flew fine.
Wot would bruise a strap like this?

[ and before you ask to see a pic of um, they are the totaled ones i fixed by smackn um one the ground wen turning too low. ]

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A rotor with a stalled blade can flail around and do crazy things.

Bottom line: I don’t know what gave your blade straps a permanent wave.

Birdy, Chuck, Chris, Nicolas, I'm learning a lot of new things here!!! Thank you so much for the input!!!