M092 a écrit:
Sauf, qu'en pilotage manuel, sur Boeing (contrairement à Airbus), la roue de trim ne fonctionne QUE lorsque le pilote agit sur le switch de trim électrique du manche... Mais sa rotation ( silencieuse, comme sous pilote automatique) a pu passer inaperçue...
J'ai lu dans les pages précédentes que sur les 737, l'avion se trimait tout seul, même en manuel, c'est le STS.
Je crois qu'il compense le déplacement des volets, l'augmentation de la poussée moteur et/ou la variation de vitesse.
Donc même en manuel, c'est normal d'entendre ou de voir la roue de trim tourner.
J'ai trouvé ça sur le net:
Speed Trim System (STS)An electrical stabilizer trim input automatically controls certain aircraft attitude conditions when undergoing large thrust changes in the lower speed region, such as takeoff and go-around. These conditions require high thrust settings and are especially present with a low weight aircraft and a relatively aft center of gravity where the aircraft wants to “nose up”. The STS supports the crew during these conditions when manually controlling the aircraft without the use of an autopilot by an opposite stabilizer trim, commanding a nose down force by use of the autopilot trim.
STS activates:
– Between 100 KIAS and Mach 0.60 (fading to zero after M 0.68)
– 10 secs after takeoff
– 5 secs after releasing trim switch(es)
– N1 >60%
– Autopilot disengaged
– Trim required
A short manual trim selection overrides the speed trim and will inhibit it for around 10 seconds, just in case that the speed trim inadvertently provides an incorrect input.
The SPEED TRIM FAIL light Illuminates amber:
– accompanied by the FLT CONT annunciator and MASTER CAUTION with a failure of the STS
– after RECALL is pushed together with the FLT CONT annunciator and MASTER CAUTION but extinguishes when Master Caution System is reset with a single FCC channel failure.
The stabilizer speed trim itself (not to be confused with STS) depends on flap position as it is most needed with the flaps extended around the takeoff and landing phase.
When the flaps are up, the low speed trim moves the stabilizer at 0.2 ups (units per second) and when the flaps are extended the high speed trim moves the stabilizer at 0.4 ups.
This stabilizer speed trim is available during autopilot operation, than stabilizer trim speed changes when the flaps are up to 0.09 ups and when the flaps extended to high speed of 0.27 ups.