The ground mode sensor comprises a Weight on-Wheels sensor that detects When the main landing gear is bearing Weight, thus indicating that the landing gear is in contact With the ground.
The takeoff mode sensor preferably comprises an engine speed sensor operable to detect When any of the aircraft's engines is operating above a predeter mined speed. This alloWs the control unit to distinguish betWeen a takeoff condition at Which the engines Will be operating at a relatively high speed (e.g., greater than 60 percent fan speed) and a taxi condition or landing rollout at Which the engines typically operate at a relatively loW speed (e.g., less than 60 percent fan speed).
In order for the control unit to provide an immediate unlock signal to the auxiliary strut in the event of a refused takeoff (RTO), the takeoff mode sensor preferably also comprises a thrust lever sensor operable to detect When any of the thrust levers for the aircraft's engines is advanced beyond a predetermined limit, Which indicates a throttled-up condition. Thus, if an RTO occurs during a takeoff roll and the thrust levers are chopped back to idle (i.e., beloW the predetermined limit), the auxiliary strut is immediately unlocked so that the load on the landing gear is evenly distributed to all Wheels for maximum braking efficiency.
The takeoff mode sensor preferably also comprises a ground speed sensor operable to detect When the aircraft is traveling above a predetermined ground speed. In this manner, the control unit is able to distinguish betWeen a takeoff roll and, for instance, a ground test of the engines in Which the engines may be operating at a high speed. Thus, the auxiliary strut can remain unlocked unless the aircraft is actually rolling doWn the runWay at an appreciable speed. Preferably, the control unit is operable to unlock the auxiliary strut upon expiration of a predetermined time period folloWing liftoff of the aircraft from the ground. Liftoff is indicated by a change of state of the signal from the Weight-on-Wheels sensor.
The auxiliary strut has the capability of assuming two different lock-up lengths, one optimiZed for landing and one optimiZed for takeoff. In this manner, a greater amount of bogie beam rotation can be alloWed on landing so that touchdoWn loads are absorbed and damped by the auxiliary strut before the strut locks up.