Attention Turboprop Pilots

[flyin74]

Can you Turboprop pilots please explain what Torque is? What does it measure?

[Tinstaafl]

Torque is a turning force ie how much rotational 'push' there is.

[Flight Detent]

Hi,
I can remember back to my Lockheed P3 days when I was really into turboprops. (had to be!)

Torque is measured in that acft by something called a 'torquemeter' (funny enough), it was mounted in the output shaft of the engine, before the reduction gearbox.
All it did was measure the amount of twist of a specific shaft section, and indicated it via a 40 tooth alignment setup.

It was indicated in SHP (Shaft Horsepower) and was reasonably accurate.
It was also a constant speed engine, very powerful and reliable, allowed up to 4600 SHP, with up to 5,300 SHP for short periods!

Cheers:ok:

[rotornut]

Torque in turboshaft engines in helicopters is expressed as a percent, with 100 percent being the maximum allowable, at least in the Bell 206 Jetranger. If you exceed 100 percent you are "overtorquing" which could damage the engine.

Also in turbine helicopters, the engine and rotor speeds remain constant through the use of a governor. As the pilot increases the pitch of the blades through the collective, the torque required will also increase as the blades require more power to maintain their speed due to more induced drag.

Torque is measured in foot-pounds in the English system. The simplest definition I have heard is that torque is "twist force" as opposed to straight line force.

Hope this sheds some light on the subject.

[GearDoor]

In the GE CT-7 used in the Saab 340, the Np shaft (propellor shaft) has a set of teeth on both the forward end and the aft end. As the shaft rotates, sensors monitor the rotary motion at both ends, similar to an anti-lock braking system. As power is applied, a measureable twist, or torque is to the Np shaft and is measured by the two sensors as an out of phase difference between the front and rear teeth. This difference is proportional to torque and is expressed in percent.

In a PT-6 engine, oil pressure is measured in the propellor hub and is presented to the pilot as either a percent of maximum, or in foot-lbs of torque. I'm not sure exactly the mechanical/hydraulic workings of this system.

[Dockjock]

Torque is to the turboprop as
Manifold Pressure is to the piston.

Sort of, mostly.:ok:

[RatherBeFlying]

When handpropping, torque in foot-pounds is the product of the distance of the hands from the propshaft centre in feet times the force in pounds exerted on the propellor.

Sufficient torque on a piston engine will result in a start and futile exercise on a PT6:O

[the road atlas]

Can also be expressed in "pounds" on the gauge on some PT6 instulations.

[the road atlas]

Can also be expressed in "pounds" on the gauge on some PT6 instulations.

[Captain Phaedrus]

...and remember, careless torque costs lives!

On a more serious note, torque on the gauge is a very accurate indication of power being put into moving the aircraft along - a much better idea of what is going on than, say, N1 on a jet. Whereas a jet engine will often still show a 'healthy' N1 after failure, a failed turboprop will not produce torque.

[Stan Evil]

Torque is a measure of the ability to twist something so the torque required to turn a propellor (or helicopter rotor) is a measure of the effort being put into moving the air with the prop and so the effort in moving the aircraft forwards (or upwards). I've avoided words like thrust and power because they aren't the same thing - the rate of producing torque (ie Newton metres per second) is in fact power as torque shares the same units as work.

One of the confusions regarding torque is the units it is apparently measured in on some aircraft. Torque's real units are ft pounds or Newton metres. However, at least one PT-6 powered aircraft I've flown has its torque gauge calibrated in PSI! The reason for this is that the device for measuring torque in many engines relys on twisting a shaft with a helical gear on the end. The helical gear makes the shaft push into its bearing which is oil filled and so it compresses the oil and this pressure has a direct relation to torque. To be honest, the gauge could just as well be calibrated in cabbages as long as you know how many cabbages is max torque etc.