B1C17L1011
Topic Author
Posts: 96
Joined: Fri Jun 29, 2001 12:42 am

Turboprop Throttles

Sun Jun 30, 2002 7:10 am

I'm I correct in assuming that on most turboprops, the turbine and the propeller turn at a constant speed while the throttle merely adjusts the propeller pitch. Please give me some insight.

B1C17L1011
 
JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: Turboprop Throttles

Sun Jun 30, 2002 7:33 am

On any constant speed prop airplane the thrust levers control power output, and the prop levers allow selection of prop RPM.

The thrust levers only control the angle of the prop indirectly by way of the prop govenor to the extent needed to keep a constant RPM. The angle of the balde will change by way of the prop govenor when the thurst levers are moved the RPM will not.

The power turbine, and the prop only turn at the same RPM on a direct drive turboprop. Some turboprops are gear driven.

Does this help?

JET
 
B1C17L1011
Topic Author
Posts: 96
Joined: Fri Jun 29, 2001 12:42 am

RE: Turboprop Throttles

Sun Jun 30, 2002 1:37 pm

Yes, Thanks JET
In addition I would like to know; How are the thrust levers and the prop levers adjusted in relation to each other. Are the prop levers infinitely variable, or do they have specific settings? Also, are most large turboprop aircraft of the "constant speed" type.
 
JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: Turboprop Throttles

Sun Jun 30, 2002 2:20 pm

The theory behind a constant speed prop is that it allows you to pick a specific engine RPM for a specific job.

For climb a high RPM, and a low blade pitch are preffered for best performance.

For cruise a low RPM high blade pitch is preffered for efficiency.

The props are always adjusted before the thrust levers for a power increase, and after for a power decrease.

The rule to remeber is props in front of throttles..... to prevent an overspeed situation.

For example the 1900C I used to fly... we would get the climb numbers for the conditions off the sun visor where they were printed for quick reference.

We would have a torque value, and a RPM for given ambient conditions.

If we wanted to climb you push the props foward to the desired RPM, and then push the power up to the torque values as long as it didn't exceed any otherr engine limitations of course.

The the prop levers can set an infinetly variable RPM between "ground fine" and full foward.

All turboprops are constant speed.

JET

 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Turboprop Throttles

Sun Jun 30, 2002 8:52 pm

This explanation should probably be in an FAQ somewhere...

The modes and procedures of operation vary a lot between different aircraft and power plants though.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Metwrench
Posts: 715
Joined: Fri Aug 17, 2001 11:25 am

RE: Turboprop Throttles

Tue Jul 02, 2002 11:46 am

Speaking for TPE-331's, The prop governor maintains RPM. It does by so varying the pitch of the prop. Advance the power lever, the engine fuels "up" and tries to increase in RPM. The prop gov responds by increasing pitch which slows down the RPM. Meanwhile the increased fuel flow is allowing the prop to provide more positive thrust.

RPM is selected by the position of the "speed lever". Basically, there are 3 positions; ground idle (72%); Take Off 100%; Cruise 97%. The only time the speed lever is used is to transition between modes of flight.
 
Android
Posts: 79
Joined: Thu Jun 27, 2002 2:42 pm

RE: Turboprop Throttles

Tue Jul 02, 2002 1:58 pm

On the Dash-8 The Power Lever (PL) controls the engine RPM in the forward power range and controls Blade angle in the idle thru reverse "Beta" range.
Engine RPM and Prop RPM in Beta by the Fuel Control-HMU/MFC and the Engine Control Unit(ECU) fuel Schedule.The Condition Levers(CL) are used to set Prop RPM in the forward thrust range and provide manual prop feathering and fuel on/off control for Engine Start/shutdown.
Takeoff on the Dash-8 Props are set to Max (1200 RPM) and then brought back to usually 1050 on the climb and 900 during cruise for cabin comfort.
Then usually during final approach they are brought back to 1200 for better response and possible go-around.Power is adjusted to airspeed rate of descent as required
The New Dash-8 400 uses full electronic Engine and Prop controls (Throttle by wire).
Cheers
Andy
Dash-8 Rep
 
MDCJets
Posts: 163
Joined: Wed Apr 18, 2001 10:06 am

RE: Turboprop Throttles

Tue Jul 02, 2002 2:31 pm

If you have FS2K or FS 2002, get to know the King Air 350, and read the pilot handbook. It tells how prop condition and throttle levers should be used.
 
broke
Posts: 1299
Joined: Wed Apr 24, 2002 8:04 pm

RE: Turboprop Throttles

Tue Jul 02, 2002 10:51 pm

Turboprop powered aircraft have two operating modes, Beta and flight. In the Beta mode, which is on the ground, the engine speed is variable according to power lever (not throttle, those are for reciprocating engines) angle. In flight the propeller is in the constant RPM mode and the propeller angle is varied by changing the power lever angle. Most later turboprops are totally constant speed, i. e. once you go into the flight mode on take-off the prop RPM is constant. On Rolls-Royce Dart powered airplanes, there is a different prop RPM for different flight modes, i.e. climb, cruise, descending. These airplanes are more difficult to ground run after engine changes and while trouble shooting in order to determine if the engine prop combination are operating OK.

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