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HeliTorque :: View topic - Doors Off VNE / Cyclic Stick Reversal
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HeliTorque Forum Index » Flight Dynamics

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Doors Off VNE / Cyclic Stick Reversal Goto page Previous  1, 2, 3, 4  Next
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Jen
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PostPosted: Sat Feb 14, 2009 7:21 pm    Post subject: Reply with quote

occasion1 occasion9 occasion5 occasion7

Happy birthday!

This site has some great smilies Laughing
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PostPosted: Sat Feb 14, 2009 7:49 pm    Post subject: Reply with quote

On the subject of VNE's, how come the R44 has a max autorotation VNE but the R22 doesn't?

Sarah
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Heliwhore
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PostPosted: Sat Feb 14, 2009 9:24 pm    Post subject: Reply with quote

I'm just throwing this out there, follow me if I make enough sense:

All helis have a Vne in auto, this would be the speed at which the disk gets tilted so far into the oncoming airflow that we start to lose the required autorotational force, and hence lose RRPM.

The R44 has a large horizontal stabiliser which puts the aircraft in a more nose down position than the 22 in autorotation(ie descent). This nose down would allow more control input in the forward plane which would allow you to exceed the Vne.

The R22 on the other hand may run out of control input and therefore automatically restrict you to a lower speed. I don't know this for sure, but if anyone does it would be interesting to know.
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Last edited by Heliwhore on Sun Feb 15, 2009 2:49 pm; edited 1 time in total
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haggishunter
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PostPosted: Sun Feb 15, 2009 12:27 pm    Post subject: Reply with quote

As we know in autorotation if we select an accelerative attitude initially we see RPM reducion as we are reducing disc loading. After a short time RPM will begin to increase with speed as the AoA reduces causing less rotor drag/increase size of driving region. This will only occur up to apoint as the AoA will become so small that the driving region will start to reduce.

I guess the R22 simply will reach power-on Vne first prior to any effects of high speed autorotation becoming apparent.

But that is a good question and I have never had anyone ask me that!

Now heres a question. Does anybody here fly a non-UK registered R22 in the UK?

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PostPosted: Sun Feb 15, 2009 1:27 pm    Post subject: Reply with quote

Truthfully, I do not know, but it will come down to the rotor inertia exhibited by the R22 as opposed to the R-44. The blades on the R22 will stop on a dime if you do not watch the rotor rpms. Decay is rapid, but not so in the R44. I believe that the R44 having a higher rotor inertia, can operate in auto-rotation over a much wider speed range.

I will gladly make a call to Robinson on Monday if someone sends me a PM to remind me.

I have to call Bell as well on the "doors off" Vne and stick/cylic reversal thread question as well.

My phone bill will be cheaper.

Glad to do it.

gotta go... Helicopter
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PostPosted: Sun Feb 15, 2009 1:37 pm    Post subject: Reply with quote

Quote:
Does anybody here fly a non-UK registered R22 in the UK?


I would have to check my log book but I am sure I have done in the past...

W.[/quote]
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PostPosted: Sun Feb 15, 2009 1:37 pm    Post subject: Reply with quote

Both sensible theories. I guess we could ask Robinson themselves...

No I haven't flown a non-UK R22 in the UK. Why?

Sarah
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PostPosted: Sun Feb 15, 2009 1:56 pm    Post subject: Reply with quote

Just curious how much the control sensitivity increases by when flying close to Vne (G-reg 92 kias Vno). Have been close to Vne for a few moments but never for a continuious period of time.
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PostPosted: Sun Feb 15, 2009 2:53 pm    Post subject: Reply with quote

Used to flog around Oz at whatever the thing would give me. Generally 95-96kt. Didn't notice anything unusual or any particular sesitivity.

Also remember Vno is only a recommended limit. We are allowed to exceed with caution and only in calm conditions.
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PostPosted: Sun Feb 15, 2009 5:17 pm    Post subject: Reply with quote

HaggisHunter wrote:
Just curious how much the control sensitivity increases by when flying close to Vne (G-reg 92 kias Vno). .


I do not believe there will be any noticeable change in sensitivity up to Vne in most copters.

Actually, look at it another way. As you exceed Vne, blade stall will occur and control sensitivity decreases. As the retreating blade stalls, the copter starts to become unstable, stick shakes at the onset, and eventually (in a counter rotating system), copter rolls off to the left and nose pops up abruptly.

There will be some safety margin in the Vne speed I suspect, but because I am a very conservative pilot who always "flies the numbers", I can't speak from actually experiencing the condition.

heliwhore wrote:
Also remember Vno is only a recommended limit. We are allowed to exceed with caution and only in calm conditions.

As for Vno, it is a recommended speed to keep you out of trouble for sure. Above that speed, things can happen for various reasons: aerodynamic, mechanical, etc. It is the "region of risk" to be taken seriously.

I do not "test" recommended speeds but choose to respect them.

gotta go.... Helicopter
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PostPosted: Sun Feb 15, 2009 5:43 pm    Post subject: Reply with quote

AB,

Just for your info the UK CAA added a 92 kias Vno to the R22. Their reasoning "significant increase in control sensitivity".

Hope you're well and the wind has calmed down!

HH
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PostPosted: Sun Feb 15, 2009 6:40 pm    Post subject: Reply with quote

HaggisHunter wrote:
AB,

Just for your info the UK CAA added a 92 kias Vno to the R22. Their reasoning "significant increase in control sensitivity".

Hope you're well and the wind has calmed down!

HH


Yes, it should have been there from the start. Operating at Vno WILL increase sensitivity. It is "inverse thinking" from my explanation of Vne. We had been speaking of control sensitivity as it approaches Vne.

As you depart away from Vne and fly at Vno or less, control sensitivity will not suffer degradation, and thus "increases". (so to speak Laughing )
It depends from which end you look at the horse. Laughing Laughing

Thank you....I am well. Wind has calmed a bit, so I'm flying my kite today. Laughing

gotta go now.... Helicopter
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PostPosted: Sun Feb 15, 2009 7:01 pm    Post subject: Reply with quote

Hmmm, wrong end of the stick me thinks....

Anyways, I can vouch that I've noticed no marked difference in sensitivity through Vno up to 96kt. I'm sure the CAA is quite rightly keeping us away from Vne where there very well could be a change.

This said, the Vno recommendation is there in the UK, and it's there for a reason, whatever that might be.
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PostPosted: Sun Feb 15, 2009 9:13 pm    Post subject: Reply with quote

Heliwhore wrote:
Hmmm, wrong end of the stick me thinks....

Anyways, I can vouch that I've noticed no marked difference in sensitivity through Vno up to 96kt. I'm sure the CAA is quite rightly keeping us away from Vne where there very well could be a change.

This said, the Vno recommendation is there in the UK, and it's there for a reason, whatever that might be.


I think it was a good idea of the CAA to institute a max Vno speed for the R-22.

Laughing
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Last edited by afterburner on Sun Feb 15, 2009 9:53 pm; edited 3 times in total
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PostPosted: Sun Feb 15, 2009 9:16 pm    Post subject: Reply with quote

Retreating Blade Stall has never been demonstrated in the R22, not to say it can't happen. But during certification test pilots were not able to get the aircraft fast enough to see the onset of RBS. Source - RHC Safety Course.

HH
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