# Torque

JTH First Officer

Hi, could anyone explain what torque is, specifically in relation to planes? I've checked out a Wikipedia article on it but it seems really complex 😳

I've already heard different references to torque in the aviation world. I once heard that torque was the reason that my plane veered to the right as it was taking off down the runway. But ony my B1900D, torque is a little gauge that seems to measure engine power.

So if anyone could explain the mystery that is torque, it would be much appreciated! Thanks a lot, JTH 🙂

PH First Officer

Power can be measured in units of torque. Now for the guages in TP torque is used as opposed to manifold pressure/RPM. It is a measure of power.
Torque used in the context of sending you off the runway again is power. If you were able to hold the propeller of an aircraft still (please don't try!) and the wheels were off the ground the aircraft would spin around...now because the wheels are on the ground the force of the spinning moment causes the aircraft to veer...add to this the slipstream from the prop deflecting the rudder...you end up heading towards the grass!

JTH First Officer

Thanks. What's the difference between torque and RPM?

crash_deplane Trainee

Torque is rotational force, usually expressed in pound feet or newton meters. Applying a force at the end of a lever creates rotational force, hence torque. For example, with a long wrench handle you create lots of torque. RPM is revolutions per minute, which is rotational speed. The product of torque and rotational speed is power, so it takes more power to create lots of torque at a high RPM than it does at a low RPM. In the case of the propeller, torque is the force turning the propeller, and the tachometer is showing how many RPM the propeller is spinning at.
-Dave

Don Wood Guest

The explanation of torque has been covered. However, that is not what causes an airplane to veer during takeoff roll. Instead, it is a property of the angles of the propellor blades resulting in asymetrical thrust and is called P-factor.

P-factor only exist when an airplane is at a positive angle of attack. That is the reason that the yawing effect on takeoff is much more pronounced in high-power tail wheel aircraft than it is in tricycle gear aircraft, although it still occurs on front-wheel a/c.

Basically, at a positive angle of attack, the angles of the propeller result in a greater angle of attack on the downward side of the prop rotation than on the upper. Since the greater angle produces greater thrust, the a/c tends to yaw in the direction the prop is turning. This occurs in flight also but is much less noticeable on takeoff since you see the effect on the a/c's track along the runway. In the air, you just apply a little rudder pressure and barely notice it. Again, the greater the power of the engine, the more it will occur both in takeoff and in flight.