Why the "Horse Power" is not used to measure the output of jet engines?

Question

Why they always use "Pound" to measure the thrust, and is there a way to convert from lb>>hp?

Answer 1

Horsepower does refer to work done, as indicated in an answer above. I forget the exact formula, but it has to do with torque and RPM of the engine. This makes sense for a piston engine, or a jet engine that turns a prop (turboshaft or turboprop) because the amount of power available directly relates to how much "oomph" the engine puts into a rotating prop to pull the engine through the air.

Jet engines have torque and RPM, but they use this torque and RPM to compress the incoming air to feed the combustion chamber, not to pull the engine through the air. The output of a jet is measured in pounds of thrust, because that is what matters - the amount of "push" out the back end.

It would be nice if the world used a common measure for the two types of engines, but since we started with piston engines and at the time everybody understood HP as a measure of power, it stuck. Then along came the jet, and they realized that the thrust (in pounds) was what mattered.
Rarely, you see pounds of thrust for propeller aircraft (which is basically the pounds of air that the prop pushes backwards.)

It really doesn't make much sense to try and compare the two types of engines because they have such different applications. Since most prop aircraft are compared with other props, they use a common set of units. The odd time that you compare a prop with a jet, it is kind of like comparing a sailboat with a canoe.

If you MUST try to compare them, there is a very rough conversion that allows you to compare. The problem is that the equation changes as forward speed increases, because the propeller efficiency changes, but at static (takeoff) conditions, a propeller produces something like about 8.5N thrust per kW of input power......huh?.....let me convert that to US units.....about 1.5 lb of thrust per HP.

Answer 2

It is not as effective as pounds of thrust. Horse power usually denotes a mechanical movement (ie. with linkage), as where the output on a jet engine is fast and some hot air movement. I do not know of any way to convert the two measurements.

Answer 3

Horsepower is defined as the amount of work to lift a weight of 33,000lbs, a height of 1foot for 1 minute, so HP is defined as work.
Jet engines do not produce work unless there is a Rotor hub (helicopters) or a Propeller hub (airplanes) attached to it, otherwise it will only accelerate a big mass of air and will push itself forward, so that's why they are rated in LBS of thrust.

Answer 4

There is a simple answer. At approximately 450 mph, 1 pound of thrust equals one horsepower. As speed increases above that, the engine produces more than a 1:1 thrust. Please bear in mind that this is just a ballpark figure.

Answer 5

HP is a measure of work done. So yes, if you know the weight of the aircraft and it's top speed, you can ballpark HP. I don't have the formula on hand. And because it dosent use any IC engine(s) it dosnt need any cylinder, nither pistons and hp is used only ther is a presence of cylinder or pistons

Answer 6

HP is a measure of work done. So yes, if you know the weight of the aircraft and it's top speed, you can ballpark HP. I don't have the formula on hand.

Answer 7

N1 & EPR are turbine parameters that infer power output.

Answer 8

With a couple of excellent replies above, no point in repeating it. Try this link for conversions

http://www.sengpielaudio.com/ConvForce.htm

Answer 9

maybe the pounds are used because of quick comparison to the aircraft's weight:)