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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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afterburner
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PostPosted: Fri Feb 13, 2009 7:13 pm    Post subject: Reply with quote

veeany wrote:
I am going to stick my neck out now and suggest that your Bell man is mistaken. I will report back shortly either way.

You many have well done that. He's one of the Bell engineers who were involved in certification, and regardless of how the situation is explained for the R-44, I'll stick to his explanation for now. (although it does sound silly)

The Robinson is a whole new ballgame. They have more special rules and explanations than I can keep in my head. It's a bird of another feather, and I would rather not get mine plucked, so I don't fly them.

Laughing
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Last edited by afterburner on Fri Feb 13, 2009 7:17 pm; edited 1 time in total
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PostPosted: Fri Feb 13, 2009 7:16 pm    Post subject: Reply with quote

veeany wrote:
Sarah is it worth spliiting this thread up and leaving the Colin Mcrae stuff where it was and giving the Doors Off / Stick Reversal stuff a new one with a link to it ?


I agree. We need to split this off now. We are way off the original thread.

Good idea Veeany.

Ab
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PostPosted: Fri Feb 13, 2009 7:26 pm    Post subject: Reply with quote

Veeany et Al....

I just got a call from Technical Support at Robinson. The Vne restriction applied for doors off is strictly for safety. They do not want anything being pulled outside of the cabin. In addition, any arms or legs which are extended outside the cabin above that speed could be severely injured.

TS at Robinson has heard nothing of any cyclic reversal problem applicable to the doors off in the R-22 or 44.

Right from the mouth of Robinson. !

Hey, I don't make this stuff up.

gotta go now.... Helicopter
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PostPosted: Fri Feb 13, 2009 10:02 pm    Post subject: Reply with quote

Consider the topic split!

By the way according to Dick Sanford the R44 doors off VNE is indeed for safety and not structural reasons. Apart from the potential injury resulting from sticking an appendage out the door opening, if a rear seat is unoccupied the seat actually starts lifting up on the hinge and the seatbelts seriously flap and start thrashing you!

I have witnessed this taking photos from the back of an R44 where the pilot was flying close to doors off VNE (100kts). It was painful, cold and very windy and probably the only time I've been in a helicopter where I've wished the flight would hurry up and be over!

Sarah
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PostPosted: Fri Feb 13, 2009 10:26 pm    Post subject: Reply with quote

WhirlyGirl wrote:
Consider the topic split!

...in a helicopter where I've wished the flight would hurry up and be over!

Sarah


Burn her at the steak! Just kidding!
Sorry for hijacking the mcrae thread and thanks for splitting it and giving me the glory (or is it the blame?) Very Happy

Look what i've started... dead interesting isn't it.

So let me see if i've got this right.
the AS350B suffers from servo-transparency also called stick reversibility.
the B206A with doors off can suffer from stick reversal, but this is a bad description of a handling characteristic (a valid one) hence the lower Vne but not the same as servo-transparency . (in case you weren't sure)
the R44 doesn't suffer from stick reversibility or stick reversal but has flappy seats and with doors off like the 206 has problems with the SSI.

SSI = Seat to Stick interface - i.e. people and associated junk.

Glad we cleared that up Very Happy
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PostPosted: Fri Feb 13, 2009 11:37 pm    Post subject: Reply with quote

Close but not a cigar. I will go over this one more time. The Bell 206A has a lower Vne doors off for safety only! It has nothing to do with stick reversal, or servo-transparency, of which it suffers neither.

We expect it to be an aerodynamically complicated explanation, but it is not. Sometimes we do things simply because it is safer.

Now where did I put that door?.... Helicopter

Post amended to avoid a duel at sundown. Laughing
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PostPosted: Sat Feb 14, 2009 12:42 am    Post subject: Reply with quote

WhirlyGirl wrote:
By the way according to Dick Sanford the R44 doors off VNE is indeed for safety and not structural reasons.


Interesting, as the safety course I took was hosted by Dick, as you know. Strange then how I would make a note as I did... oh well, it's too long ago to remember exactly!
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PostPosted: Sat Feb 14, 2009 1:36 am    Post subject: Reply with quote

James T Lowe wrote:
Interesting, as the safety course I took was hosted by Dick, as you know. Strange then how I would make a note as I did... oh well, it's too long ago to remember exactly!


Sometimes when too much information is being absorbed, the human mind "couples" things together in a mental string in "pieces", and at other times, we "interpret" what we hear or see to the level of our own understanding. This can result in knowledge that in and of itself is correct, but not when the mind "co-joins" them.

It happens to everyone. As always, the "truth is out there" ....
(or rather in here....the forum that is) Laughing

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PostPosted: Sat Feb 14, 2009 3:40 am    Post subject: Reply with quote

As far as I remember the R44 POH does not mention control reverse. Many years of doors off photo and filming in the R44 and have never suffered any problems. I agree with WG, more for pax comfort and safety I reckon. Stand to be corrected though.

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PostPosted: Sat Feb 14, 2009 6:07 am    Post subject: Reply with quote

Call me boring, its my birthday I can't sleep so I got up and thought I'd take a closer look at this for the 206 only,

I've never seen anyone mention cyclic stick reversal other than about a jetranger but it wouldn't surprise me if people had historically (wrongly) grouped the R44 along with the 206 because both have reduced Vne when the doors are removed.

I have current (according to the revisions on the Bell website) copies of the B206A, B and BIII flight manuals each and every one of them makes reference to 'cyclic stick reversal' or' reversal of cyclic fore aft stick position gradient', in relation to operating the aircraft with the doors off.

In the A model there is a warning in the limitations section.
In the B model there is a warning in the flight manual supplement with associated limitiations.
In the BIII model there is a warning in the limitations section once again.

How Bell chose the Doors Off Vne I guess we will never know, that seems to be the source of at least two conflicting opinions both with sources at Bell. Lets agree to disagree on that one, at the end of the day its a limit so we have no choice.

What is unquestionable is that Bell cite in their flight manuals a need to not exceed the figures they set due to the 'cyclic stick reversal' issue previously mentioned, so yes all civilian 206s are subject to the limitation and Bell make a point of telling you why in the flight manual.

[Hearsay Starts]
A bit of further research which is mere hearsay turns up that the negative static stability criteria in the certification requirements that were in force when the 206 was certified where full of things that really affect fixed wing more than rotary, and that the effects that are felt in the 206 when operating with negative static stability and cyclic stick reversal most pilots would not even notice , but because the criteria were in the requirements they had to be obeyed.

Further hearsay from a pilot who cited the factory school and their description of how this was documented is that the airflow over the horizontal stabiliser is affected by turbulent air caused by having the doors off and that this causes a nose pitch down moment which is then countered by moving the cyclic back slightly and thats the root cause.

The last two snippets are merely hearsay and I can't prove them.
[Hearsay Ends]

The flight manuals are in the aircraft go and take a look.

I will do some research on the original issue of servo transparency in the AS350 and report back probably tomorrow.
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PostPosted: Sat Feb 14, 2009 11:39 am    Post subject: Reply with quote

Happy Birthday Vee!

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PostPosted: Sat Feb 14, 2009 12:14 pm    Post subject: Reply with quote

Thank you.
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PostPosted: Sat Feb 14, 2009 1:20 pm    Post subject: Reply with quote

#Birthday
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PostPosted: Sat Feb 14, 2009 3:54 pm    Post subject: Reply with quote

veeany wrote:
The flight manuals are in the aircraft go and take a look.


I did, and it is in there. I know Bell calls it stick/cyclic reversal in the manual, but it is not a true representation of what they are trying to explain.

However, my Rep at Bell will be getting a nasty call from me on Monday morning. He insisted that the 206 does not suffer from either. Although I have never had it do that, it urks me that I cannot get a proper answer from them. I depend on their information.

Thanks Vee.

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PostPosted: Sat Feb 14, 2009 4:48 pm    Post subject: Reply with quote

Vee....
Forgot to wish you a Happy Birthday. Best wishes and safe flying always.

Quote:
How Bell chose the Doors Off Vne I guess we will never know, that seems to be the source of at least two conflicting opinions both with sources at Bell. Lets agree to disagree on that one, at the end of the day its a limit so we have no choice.


I guess not, but as you so succinctly pointed out, the Vne speeds are there. The why and how we may never know for sure.

Ours is not to question why, but simply to do and fly.

Have a great day! Cheers! #Birthday hello2
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