Thrust to HP

[taxicabdriver]

I was just curious if anyone can fill me in on how pounds of thrust equates to horsepower. I know that its more, but not sure how much more.

 

[norskman2]

Depends. Here's what the beanie-heads at NASA say:

A perfectly efficient 2 horsepower engine would deliver enough power to generate 100 pounds of thrust at a velocity of 11 feet/sec. Suppose we increase the speed to 22 feet/sec. We would now cover the 110 feet distance in 5 seconds. The work would still be 11,000 foot-pounds (100 pounds of thrust for 110 feet). But the power required is now 2200 foot-pounds per second, or 4 horsepower. Increased horsepower lets you fly faster with the same amount of thrust, or it lets you generate more thrust at the same velocity.

http://wright.nasa.gov/airplane/powr.html

 

[AvJunke]

Got that one on a 135 oral once. At sea level, it's basically a one to one ratio. As you ascend you have to account for all the changing variables, but that is your basic answer.

 

[Bluto]

They are totally different measures of two totally different things. Thrust is a force. No velocity is required or implied by thrust. Horsepower is a measure of the rate at which work is done. In other words, Power is a force applied over a given distance in a given period of time.

To convert from thrust to Horsepower the equation:

HP = [Thrust (pounds) X Velocity (knots)]/ 325 (375 if you use MPH instead of knots)

Works pretty well.

For a simple rule of thumb:
At 325 knots, (or 375 MPH) 1 lb of thrust is roughly equal to 1 horsepower.

Altitude has nothing to do with it, with the exception that depending on engine type, thrust will generally vary with altitude.