Quote from Allan Lupton:
"We were always puzzled that the Trident was no noisier with three Speys than the 1-11 was with two, until we had closer contact with the Weybridge opposition post-nationalisation. They told us that the 1-11's air-driven CSD was responsible - and I presume that the "hush-kit" did not include that in its scope."
The 1-11's CSDSs definitely produced a horrendous noise on engine start-up, but would they have made any difference after that?
(For those not familiar, a CSD provides a constant-speed drive for the AC generator, which enables the frequency of the AC to be maintained at the standard 400 Hz (if you're lucky!). It's driven mechanically from the engine's accessory gearbox. However, on the 1-11 the two units also incorporated a turbine which enabled them to be turned by the air used for engine start. Most other a/c had dedicated air-starter units on each engine, but the 1-11's CSDS was used to turn the engine via its accessory gearbox. So it combined the two roles. The drive shaft was a bit fragile, having a tendency to shear - particularly during a cold start, and particularly if the pilot was "milking" the HP fuel-cock to avoid exceeding the maximum EGT while the engine struggled to accelerate to idle r.p.m.. When that happened, you had also lost the generator on that engine. As oldchina says, it could also get stuck.)
Last edited by Chris Scott; 21st Feb 2017 at 10:19.