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Pilot53

777 FBW Turns

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According to the fcom the FBW system on the 777 corrects for the up elevator and rudder needed to maintain altitude and coordination in a turn up to 30 degrees.  However I find myself needing to compensate quite a bit with up elevator to maintain altitude unless the bank angle is changed very slowly.  Is this accurate?  On the real aircraft does this system only work for very slow bank changes?


Mike Iacovetta

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My understanding is that FBW changes for SP1 were extensively based on actual aircraft performance.  Trim changes are not as fast as possible bank changes so yes, you are probably seeing correct behavior.  RSR said best to forget there is a FBW system because in the end it ends up flying like a Cessna... not at all same control laws as an Airbus.


Dan Downs KCRP

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RSR said best to forget there is a FBW system because in the end it ends up flying like a Cessna... not at all same control laws as an Airbus.

That's good advice, however the control laws aren't that different to Airbus for flying inside the flight envelope. Envelope protection is applied differently but you should never be in that situation in normal flying. The yoke with artificial feel is of course different to a sidestick with spring feel but the control laws themselves are fundamentally similar. In roll there is very little difference, it's a roll rate demand. In pitch the main difference is the addition of trim reference speed.

 

Going back to the OP's question, they are right, pitch should be maintained up to 30 deg bank. I've seen it demonstrated clearly in a 777 simulator. When I tried it in the PMDG 777 I had mixed success but I think that's because I have a joystick and it's hard to separate pitch and roll inputs. Pitch attitude will only be maintained if you make no pitch input. When I've managed a pure roll input with no pitch input then pitch attitude has stayed level in the turn.

 

The essence of the Boeing FBW design is to make the controls feel like a conventional aircraft but with certain simplifications such as automatic trim and pitch and roll attitude hold. Therefore it's best to forget the FBW when manually flying. Let it work for you rather than thinking about what it should do.


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Even more well said stuff :-)

 

The FBW has been discussed in enormous length before....so I will keep it short this time.

 

let me just say that pitch correction during turns works in the PMDG777.

When you start your roll in the PMDG777 you will have to correct pitch though otherwise the airplane will fall into the turn. (same with a yoke or stick).

But once you have stabilized the turn (be it level or with a certain sink rate) it will stay right at the bank and pitch you want. Quite stable....very much like the real one.

 

Only the roll entry is more easy in the real 777, but there is a little price difference too.


Rob Robson

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