Orthodrome
13th Dec 2014, 13:44
Good evening all of you,
I've recently done some research in this forum as well as in the www and some public 737-specific material but there is one particular issue that I am still having trouble to understand concerning the tabs mounted to the 737 ailerons and elevators:
As for the aileron-mounted tabs I found out that they are for the purpose of "manual reversion" in case of HYD A+B FAIL or dual ENG FAIL. This would mean we had to refer to them as "servo tabs" or "control tabs" (phraseologies vary for one and the same thing as we know...).
1. In the case of manual reversion, how will these tabs be operated? Are they coupled directly to the control cables that otherwise would operated the hydraulic valves?
2. In case of normal operation, will the aileron tabs be fixed relative to the ailerons? Then how is the transition to the control cable coupling achieved in order to move the tabs in case of manual reversion?
I've read some "theories" of chaps calling them "Balance Tabs" which wouldn't make a lot of sense to me during normal operations (why should fully powered hydraulic flight controls need a classic balance tab?)
As for the elevator tabs I assumed they behave just like the aileron tabs (servo function in case of manual reversion, otherwise during normal ops fixed relative to the elevator) until I found this picture in another thread on that topic: http://www.b737.org.uk/images/ngelevtabs.jpg
So how do the elevator tabs behave during normal operation?
-As classic balance tabs? (which would yield the question why are they needed on a fully powered hydraulic FCS?)
-fixed relative to the elevator? (which doesn't seem to be true looking at the picture noted above)
-as anti-balance tabs during flight with flaps extended (to compensate for airflow changes due to altered wing downwash?!)
Maybe some 737 guy out there could help me answer those questions, I hope they haven't been too confusing.
I've recently done some research in this forum as well as in the www and some public 737-specific material but there is one particular issue that I am still having trouble to understand concerning the tabs mounted to the 737 ailerons and elevators:
As for the aileron-mounted tabs I found out that they are for the purpose of "manual reversion" in case of HYD A+B FAIL or dual ENG FAIL. This would mean we had to refer to them as "servo tabs" or "control tabs" (phraseologies vary for one and the same thing as we know...).
1. In the case of manual reversion, how will these tabs be operated? Are they coupled directly to the control cables that otherwise would operated the hydraulic valves?
2. In case of normal operation, will the aileron tabs be fixed relative to the ailerons? Then how is the transition to the control cable coupling achieved in order to move the tabs in case of manual reversion?
I've read some "theories" of chaps calling them "Balance Tabs" which wouldn't make a lot of sense to me during normal operations (why should fully powered hydraulic flight controls need a classic balance tab?)
As for the elevator tabs I assumed they behave just like the aileron tabs (servo function in case of manual reversion, otherwise during normal ops fixed relative to the elevator) until I found this picture in another thread on that topic: http://www.b737.org.uk/images/ngelevtabs.jpg
So how do the elevator tabs behave during normal operation?
-As classic balance tabs? (which would yield the question why are they needed on a fully powered hydraulic FCS?)
-fixed relative to the elevator? (which doesn't seem to be true looking at the picture noted above)
-as anti-balance tabs during flight with flaps extended (to compensate for airflow changes due to altered wing downwash?!)
Maybe some 737 guy out there could help me answer those questions, I hope they haven't been too confusing.