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Turboprop Throttles  
User currently offlineB1C17L1011 From United States of America, joined Jun 2001, 96 posts, RR: 0
Posted (12 years 2 months 4 days ago) and read 4512 times:

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

8 replies: All unread, jump to last
 
User currently offlineJETPILOT From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 1, posted (12 years 2 months 4 days ago) and read 4501 times:

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


User currently offlineB1C17L1011 From United States of America, joined Jun 2001, 96 posts, RR: 0
Reply 2, posted (12 years 2 months 3 days 18 hours ago) and read 4459 times:

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.


User currently offlineJETPILOT From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 3, posted (12 years 2 months 3 days 17 hours ago) and read 4460 times:

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



User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 4, posted (12 years 2 months 3 days 11 hours ago) and read 4438 times:

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.
User currently offlineMetwrench From United States of America, joined Aug 2001, 750 posts, RR: 2
Reply 5, posted (12 years 2 months 1 day 20 hours ago) and read 4363 times:

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.


User currently offlineAndroid From Japan, joined Jun 2002, 80 posts, RR: 0
Reply 6, posted (12 years 2 months 1 day 17 hours ago) and read 4348 times:

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


User currently offlineMDCJets From United States of America, joined Apr 2001, 175 posts, RR: 1
Reply 7, posted (12 years 2 months 1 day 17 hours ago) and read 4339 times:

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.

User currently offlineBroke From United States of America, joined Apr 2002, 1322 posts, RR: 3
Reply 8, posted (12 years 2 months 1 day 9 hours ago) and read 4316 times:

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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