Vertical CG limitations?
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vertical CG
I
I believe that the now delayed A380F was to have the upper deck lowered approx 4" with reference to the pax version, to allow the use of large cargo pallets on the upper deck. The need here was to increase the available, combined total floor loading towards 10kg/square m. The flight control's authority to cope satisfactorily with the range of vertical CG was not in question IIRC.
I know you don't want to hear it but I can't help myself. I agree with MFS etc; the lift on the tailplane is negative in most civilian aircraft. If you wish to improve the SFC in the cruise, an aft CG will allow a reduction in trim drag on the tailplane. An aft CG will also help with the RTOW / Vspeed calcs.
If you wish to go even further but still shy away from exotic flight control systems such as the F16, then a reduction in the static margin will do even better (health warning on this though).
Under wing engines, amongst other things, allow the pylons by which they are attached to act as vertilons and the 'jet upset' recovery proceedure adopted by both BAC and AI (Mike C was the Boeing tp; I can't recall the AI tp) does call for the thrust to be reduced in the extreme nose high/low IAS situation
Actus
I believe that the now delayed A380F was to have the upper deck lowered approx 4" with reference to the pax version, to allow the use of large cargo pallets on the upper deck. The need here was to increase the available, combined total floor loading towards 10kg/square m. The flight control's authority to cope satisfactorily with the range of vertical CG was not in question IIRC.
I know you don't want to hear it but I can't help myself. I agree with MFS etc; the lift on the tailplane is negative in most civilian aircraft. If you wish to improve the SFC in the cruise, an aft CG will allow a reduction in trim drag on the tailplane. An aft CG will also help with the RTOW / Vspeed calcs.
If you wish to go even further but still shy away from exotic flight control systems such as the F16, then a reduction in the static margin will do even better (health warning on this though).
Under wing engines, amongst other things, allow the pylons by which they are attached to act as vertilons and the 'jet upset' recovery proceedure adopted by both BAC and AI (Mike C was the Boeing tp; I can't recall the AI tp) does call for the thrust to be reduced in the extreme nose high/low IAS situation
Actus
Last edited by actus reus; 14th June 2008 at 12:36. Reason: typo
Joined: Feb 2007
Posts: 434
Likes: 9
From: Darwin, Australia
Re: LA-4 amphibian.
I am of the impression that the elevator trim on an LA-4 is set up to overcome the high thrust line. I recollect something to do with the size and rigging of the horizontal stabilizer trim tabs and location relative to the propeller wash causes the aircraft to pitch nose down on a power reduction (ie engine failure) despite the high thrust line. The cost I understand is cruise speed - I've heard of pilots using a bungee on the control column in cruise to reduce the trim tab offset resulting in a faster cruise.
Can anyone confirm or dispel this?
I am of the impression that the elevator trim on an LA-4 is set up to overcome the high thrust line. I recollect something to do with the size and rigging of the horizontal stabilizer trim tabs and location relative to the propeller wash causes the aircraft to pitch nose down on a power reduction (ie engine failure) despite the high thrust line. The cost I understand is cruise speed - I've heard of pilots using a bungee on the control column in cruise to reduce the trim tab offset resulting in a faster cruise.
Can anyone confirm or dispel this?
Joined: Feb 2005
Posts: 4,581
Likes: 0
From: flyover country USA
The trim drag must be considerable. See:
http://cdn-www.!!!!!!!!!!!!!!/aviatio.../1/1257166.jpg
http://cdn-www.!!!!!!!!!!!!!!/aviatio.../1/1257166.jpg
