Doors off vne
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Doors off vne
In the limitations section of the 206 manual and placarded inside the aircraft there is a vne of 69 kias with the front doors off. One of the reasons given in the flight manual is cyclic reversal.
Has anyone ever experienced this condition or know of any instances of cyclic reversal showing up in flight?
Has anyone ever experienced this condition or know of any instances of cyclic reversal showing up in flight?
I flew a 206 on attachment with the Australian Army with the doors off, and certainly cruised around at normal speeds. On one trip it was the only time that I've felt a little apprehensive about flying: 10000 ft, no doors and light turbulence
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I think it's more to do with the possibility of air pressure building up in the cabin and causing problems. In the AStar I'm told the speed restriction is to stop the front windows blowing out.
Phil
Phil
The doors-off Vne in the 206 is there because:
When the interrupted airflow around the fuselage reaches the horizontal stabs (inverted airfoils to create a down force on the tail), the angle of attack on the stabilizers is not constant, and therefore, nor is the lift created by them. At high speeds, the nose can pitch down and, depending on c/g and Hd, aft cyclic limits may be reached.
The term 'cyclic reversal' was a poor choice, and does not mean that pulling back makes the helicopter pitch down, as some have surmised.
Window and cabin integrity are not factors in the 206 doors-off Vne.
When the interrupted airflow around the fuselage reaches the horizontal stabs (inverted airfoils to create a down force on the tail), the angle of attack on the stabilizers is not constant, and therefore, nor is the lift created by them. At high speeds, the nose can pitch down and, depending on c/g and Hd, aft cyclic limits may be reached.
The term 'cyclic reversal' was a poor choice, and does not mean that pulling back makes the helicopter pitch down, as some have surmised.
Window and cabin integrity are not factors in the 206 doors-off Vne.
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Not an expert at all but looking at the other posts and trying to simplify it, maybe it goes like this -
In normal forward flight the horizontal stab. looks like this ' - ' and because it is inverted generates the required down force to keep the a/c level.
If you take the doors off (quite heavy and at quite a forward station) the CG is now back and the horizontal stab. now attacks the air like this ' / ' and therefore generates an up force pushing the nose down.
all of these things 1 aft CG
2 horiz stab pushing up
3 HZ then becoming more level and pushing down
leads to instability in pitch
I GUESS
In normal forward flight the horizontal stab. looks like this ' - ' and because it is inverted generates the required down force to keep the a/c level.
If you take the doors off (quite heavy and at quite a forward station) the CG is now back and the horizontal stab. now attacks the air like this ' / ' and therefore generates an up force pushing the nose down.
all of these things 1 aft CG
2 horiz stab pushing up
3 HZ then becoming more level and pushing down
leads to instability in pitch
I GUESS
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The reason is quite simple.
On the bell 206A, at very light weight and aft CG, with the doors off, the aircraft has negative static stability - ie when you start from 60 knots, you have to push the stick forward to go faster, but when you stabilize at 70 knots the stick will be slightly farther aft than at 60.
Negative static stability was not permitted by the regulations, but the choice of words is awful - stick reversal is not a term that is used anywhere else, and leads one to think that if you are in that situation that pushing forward on the stick will bring the nose up, which of course is patently wrong.
The Canadian Air Force did some tests on the Bell 206BII, which is heavier and when fitted with radios and an interior has a more foreward CG. They did tests to 100 knots and found the handling acceptable.
Because of commonality, and a desire to keep costs down, the doors off supplement from the Bell 206A has been kept.
But I often wondered if some lawyer wasn't going to take Bell to the cleaners over the 'stick reversal' term.
On the bell 206A, at very light weight and aft CG, with the doors off, the aircraft has negative static stability - ie when you start from 60 knots, you have to push the stick forward to go faster, but when you stabilize at 70 knots the stick will be slightly farther aft than at 60.
Negative static stability was not permitted by the regulations, but the choice of words is awful - stick reversal is not a term that is used anywhere else, and leads one to think that if you are in that situation that pushing forward on the stick will bring the nose up, which of course is patently wrong.
The Canadian Air Force did some tests on the Bell 206BII, which is heavier and when fitted with radios and an interior has a more foreward CG. They did tests to 100 knots and found the handling acceptable.
Because of commonality, and a desire to keep costs down, the doors off supplement from the Bell 206A has been kept.
But I often wondered if some lawyer wasn't going to take Bell to the cleaners over the 'stick reversal' term.
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Thanks for the input. I can say from experience that I have had the 206 to 110 kias with the front doors off and it didn't fall out of the sky. Sorry for the delay some of us have to work!!
