rcav8r
7th Jun 2006, 04:40
Hello,
I pose a rather trivial question. On multi-engine ac, is it easy to keep the throttles in sync when moving them? 747s for instance, have four levers to contend with, are minute differences in lever angle insignificant during application of thrust?
Rainboe
7th Jun 2006, 10:05
Completely. You need an appreciable difference to feel it. The engines have electronic units that help stabilise thrust settings, though not align them. Jets don't need any synchronisation to stop the rythmic sound you get with piston engines, and minor thrust differences are not very effective. You still try and line them up as well as you can to ensure you have correct power settings.
Intruder
7th Jun 2006, 10:16
Not quite true, Rainboe...
In the 744, the EECs (Electronic Engine Controls) synchronize the engines as well as control the N1, as long as the autopilot is engaged. Also, as long as the thrust levers are within about a half knob of each other, the same N1 is commanded for all 4 engines.
In the 742, however, it is a different story completely. On the runway the engines are stabilized at 70%, and the relative thrust lever positions noted. That relative setup is retained up to T/O thrust, with the FE doing final adjustments as required.
Also, jet engines DO need synchronization to minimize beat frequency vibrations. The closer the engines are to the fuselage, the more notable the beat freqs become.