Question about turbo props

[zasca]

PDT had a chick dig the good vibes on a dash so much her mother threaten to sue the airline... true story

 

[IBNAV8R]

niiice.

 

[CutEmUp]

If your going to split hairs on me torque as it relates to turboprops, is the tendency for a shaft to rotate about a specific axis. This is measured on some aircraft by the actual amount of deflection or twist of the shaft that occurs under load and displayed as a % of maximum.

Obviously torque is not the same unit of measure as power just as EPR is not a measure of power but a ratio or pressures. As I said in my previous post torque % is what is primarily used in the Saab to set a desired amount of power (100% torque is about 100% power).

Is 100% torque=100% power @ 50% RPM?...No.

 

[CutEmUp]

Torque IS power in the purest sense. Assuming a prop could even turn with zero torque it would be incapable of producing any force without a torsional load. Pick an engine. zero torque = zero power = zero thrust.

In every turboprop I have flown, torque is the PRIMARY measurement of power. Of course, I've never flown a turboprop with a fixed pitch prop. (pitch-locked notwithstanding). While most piston aircraft and jets don't measure torque, it is nonetheless there and part of the power/thrust equation.

Now, I have heard of some aircraft capable of flight without torsional force from the powerplant. They're called gliders (and balloons)

0 torque = 0 power...wrong. If you have 0 power then you will have 0 torque, but this equation is not symmetric. How much power is being applied to a shaft if has 1000Nm of torque on it at 0 RPM?...0. Back to statics and dynamics class.

 

[mesaba13]

Send out an emergency alert to all turboprop operators:

"Do not look up % torque on the manufacture charts to determine takeoff power setting. A genius pilot on FI has pointed out that we have been doing it wrong all these years. In the future the operator needs to convert the appropriate % torque values to equivalent Horsepower (or watts) and utilize that for all operations. Horsepower gauges are in the process of being installed in all aircraft. Per ICAO requirements Watts will eventually be the official power setting used."

ex: "Set 2400 horsepower" or "Set 36000 Watts"

 

[CutEmUp]

Send out an emergency alert to all turboprop operators:

"Do not look up % torque on the manufacture charts to determine takeoff power setting. A genius pilot on FI has pointed out that we have been doing it wrong all these years. In the future the operator needs to convert the appropriate % torque values to equivalent Horsepower (or watts) and utilize that for all operations. Horsepower gauges are in the process of being installed in all aircraft. Per ICAO requirements Watts will eventually be the official power setting used."

ex: "Set 2400 horsepower" or "Set 36000 Watts"

So, these power setting charts you speak of don't indicate a specific prop RPM to use? I would suspect that if you tried to takeoff at 100% torque at minimum RPM you wouldn't get the "power" you had hoped for.

There are actually airplanes that do show a "power" gauge. A Cirrus has a constant speed prop and one lever to control both throttle and RPM. The computer figures out the power required and sets the RPM and MP accordingly.

This really just gets back to what someone asked about the airplane getting louder before landing. The RPM is increased so that maximum power is available in the event of a go around. 100% torque is always available with a push of the power lever (uh oh, its called a power lever) but this won't relate to 100% power unless you are at 100% RPM (condition levers max), but you already knew that.

 

[CutEmUp]

http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm

 

[mesaba13]

Oh thanks for clearing that up, that's why I set the CL's levers to max before takeoff and landing several thousand times.

Its pretty simple: if you want more power for a given CL setting you increase the power lever position. How much do you increase it? You reference the % torque gauge which is the primary way turboprop pilots set power.

Do you start these kind of debates in the cockpit as well?

Co-pliot: "Go around set power"

CutEmup: "Ah its not actually called power its torque, you know statics, dynamics, I went to engineering school"

Co-pilot "Okay but that is a mountain in front of us so set something"

 

[CutEmUp]

Its pretty simple: if you want more power for a given CL setting you increase the power lever position.

So, you are saying that power is contingent to CL setting (RPM) AND power lever position (torque)? Very good...progress.

 

[CutEmUp]

You reference the % torque gauge which is the primary way turboprop pilots set power.

Yes, but I make sure that the RPM is at the desired setting too. Otherwise, the power isn't set, is it?

 

[Count Dracula]

I betcha flying a 4 day with some of you is like a never ending root canal.

 

[kf4amu]

Good god this makes me embarrassed to fly a dash

 

[zasca]

Oy... Speechless

 

[RJLoser]

I always loved the guys that would slam the CL or "speed levers" in the Jetstream forward on you prior to landing. Nothing like throwing out the anchor.

 

[AntiJedi]

I always loved the guys that would slam the CL or "speed levers" in the Jetstream forward on you prior to landing. Nothing like throwing out the anchor.

Do that on the Bro, and you might lose control of the prop altogether.