View Full Version : Thrust conversion to Horsepower

22nd Jul 2001, 00:42
OK...this has stumped everyone in Essex so far, can someone...

...give me a conversion for thrust (a force) to horsepower/watts (power) for jet engines?

e.g. the B737 has 20/22k engines (20/22,000 pounds of thrust).
What is that in layman's terms?

22nd Jul 2001, 01:35
Only a partial answer I'm afraid. Don't have my conversion tables with me & damned if I can remember them.

Power = Thrust x TAS

22nd Jul 2001, 03:53


25th Jul 2001, 22:46
This site will provide the calculator required to convert ft.lbs. into horsepower or watts of energy , while it doesn't give the actual formula it will calculate the equation for you.
Hopefully this will be of use to you. The software download is free,and it is most usefull. http://www.angelfire.com/on3/theclan/download.html
or this one:

[ 25 July 2001: Message edited by: Dragonspet ]

26th Jul 2001, 19:16
OK, thanks for all the replies, BUT...

I must be being thick here, but all the conversions I've seen relate to the TAS Of the aircraft for engine power.

Now, if a car has a 100bhp engine, it is a 100bhp engine, whether the car is at 100mph or parked in the drive.

Are we saying the engine only putting out a few bhp at the start of the T/O roll (a few knots), and only at maximum power at 420kts in the cruise?!

A little help please?!..

27th Jul 2001, 15:40
Dear Forum readers

Thrust and horsepower cannot be directly compared because, by definition, power is a force applied through a distance in a period of time. All the power produced by a jet engine is consumed internally to turn the compressor and drive the various engine accessories. The jet engine does not develop any horsepower in the normally accepted sense but supplies only one of the terms in the horsepower formula. The other term is provided by the vehicle in which the engine is installed. To determine the thrust horsepower the following formula is used

net thrust x velocity of plane(mph)
THP= -------------------------------------

If an airplane is flying at a velocity of 375mph and developing 4000 lb of thrust the THP will be
4000 x 375
THP=------------ = 4000

at 375 mph each pound of thrust will be converted to one horsepower, and for each speed of the airplane there will be a different thp. At 750 mph this 4000 lb thrust jet engine will produce 8000 thp.


piston broke
30th Jul 2001, 22:22
In some book I once read - perhaps the Whittle story, someone (Churchill?) asked how many HP the original Whittle engine produced. Boffins applied slide-rules and decided that the 1000-ish lb thrust equated to 1000HP, which was deemed sufficiently impressive in a prototype that approval was given for continued funding and development.

Hardly a scientific suggestion, but is it roughly valid?

2nd Aug 2001, 19:41
It gets off the ground - let it go

D Beaver
4th Aug 2001, 00:19
piston broke

I think it's in "Not Much of an Engineer" by Stanley Hooker. Fascinating book about his experiences with the Merlin, Whittle's jets, Avon, Orpheus, Olympus, Pegasus and RB211, etc. The anecdote about the thrust to HP is in there (although I think it refers to Lord Hives, not Churchill) and an excellent Appendix with details. If anyone wants a copy, try www.abebooks.com (http://www.abebooks.com) (usual disclaimer - 1. I'm a satisfied customer, 2. My kids work there! ;) )

[ 03 August 2001: Message edited by: D Beaver ]