Spektor
5th Jun 2005, 16:48
Hi, guys,
I am trying to prepare for an Interview with Cathay Pacific, and have come across the following two questions in the gouge:
1. Why are [outboard] ailerons locked out at high speeds? I believe I have that one answered - twisting loads, aileron reversal etc.
2. How is it done on B-747, A-340? Need help with this one, for I have not got a clue.
Thank you in advance any info you could share.
Spektor.
spannersatcx
5th Jun 2005, 18:37
747 classic Outboard Aileron Lockout Mechanisms ___________________________________
A. An outboard aileron lockout mechanism is located in each wing to isolate the outboard ailerons from the lateral control system during high speed flight. The mechanism consists of a housing, cable quadrant, input crank, output crank and a series of levers and links, that, when in certain positions, will either transmit or prevent the transmission of motion from the control wheel to the aileron power package. The lockout mechanism is electrically controlled by an actuator installed on the mechanism housing.
B. With the trailing edge flaps fully retracted, the pivot point of the mechanism is aligned with the center of rotation of the aileron control quadrant, point A. In this configuration the quadrant cannot transmit motion. When the flaps leave the full up position the electric actuator repositions the lockout mechanism to separate the pivot points. With these points separated the mechanism will then transmit motion to the
aileron power package.
The outboard aileron electric lockout actuator provides the input to the aileron lockout mechanism. The actuator consists of a 28-volt dc reversible motor controlled by limit switches within the actuator, and an actuator shaft. During operation the actuator shaft will travel 2 inches between limit switch actuations. The shaft cannot be adjusted.
Electrical power to the actuator is provided from the OUTBD AIL LOCKOUT circuit breaker on electrical circuit breaker panel (P12) through a switch actuated by the outboard trailing edge flap power package located in the wheel well.
The 744 is similar in operation and principle except it's logic is slightly different as there is an actual speed input as well -
Operation of an outboard aileron is prohibited by a lockout mechanism when the group A LE flaps are fully retracted and either the airspeed is above 238 knots or the mach number is above 0.53M. To operate on outboard aileron, the group A LE flaps must be partially extended or the airspeed is below 232 knots and mach number is below 0.51 M.
A340 -
Two inboard and outboard ailerons are provided on each wing ; two electrohydraulic servocontrols actuate each aileron.
In manual roll control mode, the aileron control is performed from the side sticks which send electrical signals to the Flight Control Primary Computers (FCPC) and Flight Control Secondary Computers (FCSC).
The computers elaborate command orders to the servo controls, depending on the different control laws.
At high speed (Vc higher than 190 kts in CLEAN CONF), the outboard ailerons are servoed to zero.
In AP mode and in certain failure cases, the outboard ailerons are used up to 300 kts.
When the RAT is extended, the outboard ailerons are not used, associated servo controls being swiched to the damping mode in order to minimize the hydraulic consumption.
On ground, with hydraulic systems not pressurized, the ailerons may or may not droop down to the servocontrol stop depending on the scatter of bearing and seal friction.
NOTE: There is no aileron trim control.
These are taken from the Boeing and Airbus manuels, hope that helps.:\
Spektor
5th Jun 2005, 18:55
Mr. Spannersatcx
Priceless stuff! Thank you, Sir!
Spektor.
Good replies spannersatcx.
Just to add on the 747 SP its a function of airspeed and not the flaps.
230 kts. is the majic number.