question
Thread Starter
Joined: Jul 2002
Posts: 358
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From: australia
question
if you take off in a single engine prop aircraft with a c of g aft of the c of p and find that full fwd stick won't stop the nose from rising, will a reduction in power help or will the reduced airflow over the elevator worsen the situation? Also, how will different flap positions affect the situation?
PS I'm not planning on experimenting but have recently read of someone who found themselves in this situation!
PS I'm not planning on experimenting but have recently read of someone who found themselves in this situation!
Moderator
Joined: Feb 2000
Aviation Qualifications: CPL
Posts: 14,480
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From: UK
Well my brief opinion over breakfast...
I'm not sure I fully understand what you mean by CP in this context, I suspect that you actually mean CG aft of the aft CG limit?
As a situation, what you describe seems feasible, the subsequent actions are very dependent upon aircraft design.
For example, if you've got a type with a very high thrustline, then power will probably help - alternatively with a very low thrustline then cutting the power will help - this is just all about moments about the vertical CG.
Wash over the tailplane is a less clear issue - but lets say you have got a lot of propwash over the tailplane. In that case, increased power should make the tailplane ,more effective and may aid the pilot in getting the nose down.
Flaps - not sure, I've seen flaps both stabilise and destabilise an aeroplane in pitch (both high-wing / low tail aeroplanes). I'm sure there's some theory out there which describes what SHOULD happen, but my experience it's never as simple as theory would have you believe for which reason I'll pass on that one.
G
I'm not sure I fully understand what you mean by CP in this context, I suspect that you actually mean CG aft of the aft CG limit?
As a situation, what you describe seems feasible, the subsequent actions are very dependent upon aircraft design.
For example, if you've got a type with a very high thrustline, then power will probably help - alternatively with a very low thrustline then cutting the power will help - this is just all about moments about the vertical CG.
Wash over the tailplane is a less clear issue - but lets say you have got a lot of propwash over the tailplane. In that case, increased power should make the tailplane ,more effective and may aid the pilot in getting the nose down.
Flaps - not sure, I've seen flaps both stabilise and destabilise an aeroplane in pitch (both high-wing / low tail aeroplanes). I'm sure there's some theory out there which describes what SHOULD happen, but my experience it's never as simple as theory would have you believe for which reason I'll pass on that one.
G
Thread Starter
Joined: Jul 2002
Posts: 358
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From: australia
Cheers Ghengis,
What I meant was the center of pressure. Your post was all good 'food for thought' though, thanks. I am pretty sure the a/c was a low wing but not sure on the thrust line. I'll have a re-read and see if I can find out.
Cjam
What I meant was the center of pressure. Your post was all good 'food for thought' though, thanks. I am pretty sure the a/c was a low wing but not sure on the thrust line. I'll have a re-read and see if I can find out.
Cjam
Joined: Jun 2002
Aviation Qualifications: PPL
Posts: 5,106
Likes: 323
From: east ESSEX
I would suggest if you got/ get airborne in a configuration where the CofG is beyond the aft limit, then you do not make any large/ sudden inputs on any controls/ change power gently /dont alter flaps/gear. The aircraft will be close to being unstable longitudinally, and could diverge in pitch, nose-up/down.
Fly very gently around and get it on the ground
Lateral/directional stability will also be affected, so it must be flown carefully,as balanced as possible and as smoothly as possible. Most a/c will be able to cope with the CofG behind the aft limit; they will have been tested , and normal limits will be inside those boundaries.
Then, back on the ground, go back and do the calcs. again!!!
Fly very gently around and get it on the ground
Lateral/directional stability will also be affected, so it must be flown carefully,as balanced as possible and as smoothly as possible. Most a/c will be able to cope with the CofG behind the aft limit; they will have been tested , and normal limits will be inside those boundaries.
Then, back on the ground, go back and do the calcs. again!!!
Morning Calm
Joined: Jul 2002
Posts: 12
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From: Farnborough
Well, one way to get the nose to drop is to roll on bank. Some years ago an A300-600 got airborne with c of g aft of the limit, and the pilot, having run out of other ideas (elevator/stabilizer/flaps), applied 40 degrees of bank and flew around in circles until the fuel could be transferred to remedy the problem. Sounds bizarre, but it saved the day. Of course, if this doesn't work then you're probably headed for a spin!
Just goes to show how important the trim sheet is.............
Just goes to show how important the trim sheet is.............
