Boeing ailerons
 

Noticing paxing the other day,(763) staring at the trailing edge, the inboard aileron doing all of the work in cruise. No surprises there. What did surprise me was that the outboard aileron did not come into play until we were rolling onto final and pretty much everything was dangling out.

At what speed does the outboard aileron lockout and/or reengage?

Looked in the 744 flight manual and it mentions "high speed" and "low speed". Very specific that!

------------------
Those who restrain desire do so because theirs is weak enough to be restrained.
William Blake

There are TWO things involved here - flaps and airspeed. When the aircraft is 'clean' and speed above approx. 238 kts, the outboards are locked out. If either the aircraft is 'dirty' or the speed is below 238, the outboards bcome active; stops Red Arrow type roll rates at cruise speeds. :) :)
This is for the 744, BTW. The 76 may be different.

Cornish Jack,
Is preventing rapid roll rates the primary reason for locking the outboards? I always thought it was to prevent stresses and bending in the wings?

Aileron lockout for the 747-400 is when speed exceeds 238 KIAS AND with the flaps up. If you leave flaps at 1, speed will exceed 238 KIAS before aileron lockout occurs, and will only occur once flaps are up. Sort of makes flying on 2 engines on one side a bit easier???
Also with speed decreasing the aileron lockout occurs at 232 KIAS activating the little suckers once again OR when the flaps go to 1. Good luck.

Looking for the 767 stuff as well.....but unfortunately I only have a general Boeing produced ops manual for the 767 which does not give all this good stuff.


[This message has been edited by FLUFFY SHOES (edited 19 January 2001).]

NIMBUS,

The outboard ailerons are locked at high speeds to prevent wing-tip twisting and the resulting aileron reversal!

The aileron lockout on the 767 is based only on flaps not speed. The outboards unlock when the flaps aren't up.

763 Outboard aileron lockout is controlled by the SAMs (stab. trim aileron lockout modules)with speed inputs from the DADCs.The SAMs constantly receive mach no. and computed airspeed signal (Vc) from the DADCs with lockout occuring at--
Vc > 275knts
Mach 0.5-0.58 and Vc>235knts
Mach>0.58
The SAMs also lock out certain flight spoilers as well (4,5,8,9) when the outboard ailerons are locked out.

Gas Path gives the formula. Tom Cat gives the official reason. Seems like all the Boeings do it but differ in the method.

Does anyone remember the reason for the 'Aileron Upset' on the Vickers (or BAC)VC10? The ailerons were tipped upwards when the flaps were extended and faired off when the flaps were fully up. It was suppposed to provide wing bending load relief in some way.

**********************************
Through difficulties to the cinema

Blacksheep....
Probably the best people to answer your query would be H.M. flying club as they still operate the '10.
I do know that the L1011 had a similar system but the aileron deflection was when the flaps were up! they were also active for bending relief. It was only fitted to the -500 model as it had a greater wingspan (approx 18ft overall??) and meant that the structure didn't need strengthening.

"The aileron lockout on the 767 is based only on flaps not speed."

I believe this is correct (unlike the 744, there is only one thing which will lock/unlock the ailerons... other than the BITE test that is ;) ).

On the 744, there is something known as lock/unlock hysteresis. Lock/unlock depends on whether the aircraft is accelerating or decelerating (so my 744 training notes tell me):

"The ailerons will lock when the "Group A" LE Flaps are retracted and either the airspeed is above 238kts or the mach number is above .53. They will unlock when the Group A LE Flaps are not retracted or airspeed is below *232kts* and mach number is below .51. I guess this is to prevent the ailerons unlocking and locking rapidly if your speed is somewhere between these values (and, perhaps, turbulence is causing your airspeed to fluctuate).

Rgds.
Q.

Blacksheep,
Also in the Airbus A340 and A330, the ailerons deflect upwards to reduce wing loading, but not when flaps are extended. Infact when the flaps are extended they deflect downwards (aileron droop) to increase lift.

QAVION,

The B767-300 Aileron lockout is operated by an electrical actuator that aligns the the pivot points of the aileron quadrant input and output cranks. Thus, when locked out, rotation of the input crank produces no output crank movement. The left and right electric actuators are driven by two Stabiliser Trim/Aileron Lockout Modules (SAM) with one operating both ailerons and the other in standby. A logic cross-feed provides automatic selection of the controlling SAM (usually the Left.) Each SAM is fed with CAS data from its on-side Digital Air Data Computer via ARINC429 data bus. The controlling SAM generates discrete lock commands to both outboard aileron lockout electrical actuators and monitors actuator position for fault annunciation and control switching decisions.

The lockout is done to a speed schedule as follows:

1. Vc > 275 Kts CAS
2. Mach No. in the range 0.5M to 0.58M AND Vc equal to or greater than 235 Kts CAS

OR

3. MachNo. equal to or greater than 0.58M

The schedule contains a threshold hysteresis band of 0.2M/6 Kts CAS Vc to provide for recomputation lag time. Actuator Lock/Unlock time is 15 seconds.

The Flaps are not involved in any way whatsoever.

**********************************
Through difficulties to the cinema

Blacksheep ... you are a legend. Thankyou. Got any info on the 767-200 lockout?

Wow...thanks all.

Legend? Aw, I'm all embarrassed now! I only cribbed from my LAE course notes... :)

**********************************
Through difficulties to the cinema

The 707 did the same and it was dependant on flap position. Flaps up, ailerons locked.
The VC10 and L-1011-500 did it for wing stress relief and drag reduction.