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SHP Vs Lbs Thrust  
User currently offlineParapente From United Kingdom, joined Mar 2006, 2149 posts, RR: 11
Posted (8 years 4 months 6 days 14 hours ago) and read 15803 times:

Prop engines are measured in Shaft horse power. Fan engines are measured in Lbs of thrust. The 2 are different. How does one compare the relative thrusts of 2 engines. Is there a formula?

3 replies: All unread, jump to last
User currently offlineJetMech From Australia, joined Mar 2006, 2726 posts, RR: 52
Reply 1, posted (8 years 4 months 6 days 12 hours ago) and read 15791 times:

Quoting Parapente (Thread starter):

Check out this thread and see if your answer is there  Smile .

Engine Power (by LH748i Nov 6 2007 in Tech Ops)

Regards, JetMech

JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2620 posts, RR: 25
Reply 2, posted (8 years 4 months 6 days 11 hours ago) and read 15781 times:

Strictly speaking it is engines which develop shaft power which are measured in SHP. Aircraft jet engines don't so are measured in thrust units.

It is easy enough to convert power to thrust, or vice versa, but you need to know propeller efficiency as well. You could fit a more efficient propeller onto an engine and get more thrust from it, but the power output of the engine would be the same.

The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineBuzz From United States of America, joined Nov 1999, 697 posts, RR: 20
Reply 3, posted (8 years 4 months 5 days 13 hours ago) and read 15685 times:

Hi Parapente, Buzz here. There are conversion formulas, we used to grind through them when I was going to college. I haven't used them in years... So for an accurate answer, see what JetMech, and Jetlagged have posted.

For a very rough approximation, 60% of the horsepower is more or less the pounds of thrust. Of course, it makes a difference if you're at cruise speed (and altitude), or waiting at the end of a runway and hoping you have enough power to take off. (grin) Propellers are more effective at low speed - move a larger mass of air more efficiently.
Those little Bede BD-5's with the tiny jet engine worried me - can it get up to flying speed before the end of the runway?


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