Boeing 777 Flare difference with Forward CG and Aft CG
Thread Starter
Joined: Mar 2009
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From: Planet Earth
Boeing 777 Flare difference with Forward CG and Aft CG
Hello Everyone,
Anyone with expertise in aerodynamics out here? Can you please tell me how different the flare feels on a B777 with a forward CG (lets say 23%) and with an aft CG (lets say 35%)? Am looking for elevator response (quick vs sluggish) and similar. Thank you very much!
Best regards!
Anyone with expertise in aerodynamics out here? Can you please tell me how different the flare feels on a B777 with a forward CG (lets say 23%) and with an aft CG (lets say 35%)? Am looking for elevator response (quick vs sluggish) and similar. Thank you very much!
Best regards!
Joined: Dec 2001
Aviation Qualifications: ATPL
Posts: 3,766
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From: GA, USA
I don't fly a 777 but I'd like to think physics don't change with airplane type.
What I don't know if artificial 'feel' systems differentiate between forward and aft cg.
I would assume it 'feels' the same just aircraft response is slightly slower or faster.
What I don't know if artificial 'feel' systems differentiate between forward and aft cg.
I would assume it 'feels' the same just aircraft response is slightly slower or faster.
Joined: May 2017
Posts: 66
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From: San Diego
Forward CG is slightly more sluggish in pitch up. Think about the physics, for example, put a huge lead weight (or an obese pilot!) in the cockpit, then try to pitch up. The tail will need do apply more moment to the CG to raise the nose, requiring a greater tail deflection. Flare is a pitch up command, so the tail has to deflect more on the forward CG case. ... Fly-by-wire moves that tail fast so you may never notice the difference though.
Whats really interesting is the main gear sinks more during flare with a forward CG since the tail has to apply more downward force. (Non-minimum phase control.) This means you can slam the mains into the ground harder than usual if you flare late!
Whats really interesting is the main gear sinks more during flare with a forward CG since the tail has to apply more downward force. (Non-minimum phase control.) This means you can slam the mains into the ground harder than usual if you flare late!
Joined: Apr 2006
Posts: 416
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From: uk
Edging towards 9000 hrs on all the 777 variants from 200 to 300 ULR. tbh I have never noticed a difference! Though the landing/flare characteristics between RR powered versions and GE90s is significant. Residual thrust, ground effect and wing span differences play a huge part.
My biggest issue is the controls oscillating in manual flight!!
My biggest issue is the controls oscillating in manual flight!!
Joined: Sep 2003
Posts: 462
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From: Sand pit
Have flown with Cg very forward, and very aft... very little difference and assume it has lot do do with fbw artificial feel?
The md-11 was a different airplane at extremely light vs heavy weights but 777 is very consistent at different weights and cg
The md-11 was a different airplane at extremely light vs heavy weights but 777 is very consistent at different weights and cg
Joined: Feb 2009
Posts: 379
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From: Seattle
777 Pitch Control not a function of CG
The C*U pitch control law implemented on the 777 does not involve any adjustments as a function of airplane CG. During approach / landing column input generates a pitch rate (i.e., C*U) command. Near the ground the flare compensation function requires slight column pull to maintain pitch attitude such that pilot input during flare is nominally a pull until main gear touchdown followed by relaxing the pull to lower the nose gear.
The relatively consistent response across a range of CG values comes from C*U seeking to deliver the same pitch rate for a given column input regardless of CG.
The relatively consistent response across a range of CG values comes from C*U seeking to deliver the same pitch rate for a given column input regardless of CG.
