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#41
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Best place for CG along roll axis
how much elevator control force is
available with and without trim being set. It depends on the system. For example, if you have a trim tab, the tab is reducing the amount of force needed to go one way, while increasing the force needed to go the other way; the net effect is the position of zero force (corresponding to the trimmed airspeed) is different. The elevator "wants to" be in a certain position, and if that position is (say) near the nose-up limit, then it will take less stick force to go to the full nose up elevator position. In the case of an auxilliary elevator, the nose itself is moved by the added forces that the auxilliary elevator provides. This does change the angle of attack of the regular elevator, but only to the extent that it is "trailing", not to the extent that it needs to provide any extra force to move the tail (and thus the nose). The elevator will trail in (say) the somewhat nose up position (corresponding to the trimmed airspeed), and less travel will be available in the nose up direction. It will take less force to get there however, since the neutral position is already trailing somewhat nose up. Other systems have their own methods, but if you see it here, you should be able to figure it out there. IT is possible that a fly-by-wire system could be designed without trim, relying on brute force instead (and using software to give the stick feedback, if desired). In this case, the force the pilot feels is arbitrary (up to the software designers) and the force on the elevator is just what it would be were you to muscle the elevator around. "Trimming" would move the elevator just like the stick would, and you'd be left with less travel in one direction and more in the other, but mainly because "you're already there". but it still reduces control in one direction. Could be a big issue during landing during gusty crosswind conditions, or during takeoff when unexpected turbulence is encountered. Well, yes, but this is taken into account when they designed the airplane. Every limit, when encountered, will be (...er) limiting. The aircraft is designed so that those limits are outside the normally expected flight regieme, and gusty crosswinds are part of that regieme. Alas, airplanes are not really tested for this; the "demonstrated crosswind component" is not considered a limit - it is just the maximum crosswind that happened to occur when they test flew it (or maybe test flew it for FAA demonstrations). Jose -- "Never trust anything that can think for itself, if you can't see where it keeps its brain." (chapter 10 of book 3 - Harry Potter). for Email, make the obvious change in the address. |
#42
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Best place for CG along roll axis
Mxsmanic,
So if someone tosses a bag in the back, or if the person next to you weighs more or less than 170 lbs, you redo the calculations? Yes. It's not rocket science. In fact, it's one of the key things you learn when really flying. -- Thomas Borchert (EDDH) |
#43
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Best place for CG along roll axis
Thomas Borchert writes:
Yes. It's not rocket science. In fact, it's one of the key things you learn when really flying. It would be interesting to know how many pilots actually bother. -- Transpose mxsmanic and gmail to reach me by e-mail. |
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