15th Apr 2012, 21:44
Modern turboprops operate with the turbine running at full speed at all times. Power is varied by controlling prop pitch; when the prop blades are set at an angle that demands more power for the turbine to keep running at full speed, more fuel is proved to the turbine, etc.
Question: did turboprops always operate this way--Viscounts, say, and anything that preceded them? In other words, were there ever "throttlable" turboprops?
16th Apr 2012, 01:55
It's been 28+ yrs since I've flown one
but I don't think PT-6's run at full speed all the time.
16th Apr 2012, 04:46
In a fixed wing usually a PT6 works with throttle/torque controlling percentage power and a separate pitch working on governer like a recip. Later model stuff has single lever operation.
16th Apr 2012, 13:01
The Rolls Royce Dart is a single spool engine with an adjustable constant speed prop.
The throttle controls the rpm between 11000 and 15000 by adjusting the PCU and also most of the fuel required via the FCU. There is also an electrical Fuel Trimmer that controls the rest of the fuel required via a mechanical linkage to the FCU.
In operation the engine idles at about 7000 rpm. As the throttle is advanced slowly the rpm increases until at 11000rpm the prop. starts to govern. (minimum constant speeding).
As the throttle is advanced further the rpm increases as a direct result of lever position until max of 15000 is achieved.
When power is reduced after take off, the throttle is retarded to give the required rpm and the fuel trimmer is reduced to give the required TGT for climb and then cruise power.
Typical climb 14500 rpm 750 TGT
Typical cruise 14200 rpm 730 TGT.
These are for the HP Herald with RDa 7-532 IIRC.
If you listed to Pink Floyd's "On the run" from "Dark side of the moon" you can hear a Viscount with the increase in rpm during take off.