Bryan Becker
Topic Author
Posts: 327
Joined: Fri Mar 02, 2001 12:38 pm

Gas Turbine Horse Power

Tue Mar 06, 2001 10:25 am

Does enyone know how to convert pounds of thrust to horse power I'd like know how to find out. My friend says that drag racers have more horse power. I'd realy like to find out if it is true Thanks!!!!! Smile
 
242
Posts: 495
Joined: Tue Oct 24, 2000 1:10 pm

RE: Gas Turbine Horse Power

Tue Mar 06, 2001 11:25 am

Well, I don't have a conversion formula for you, but here's some numbers on a P&W 1800 turbo shaft engine found on the EMB-120, a 33 seat regional aircraft that weighs in at about 25,000 pounds at max takeoff weight.

Spinning at 30,000 rpm, this little engine produces 1800 horsepower and a whopping 77,000 foot pounds of torque. These figures are for EACH engine.

After working on these engines for a few years, I just can't look at a "high performance" reciprocating automotive engine without laughing.
 
Aerotech
Posts: 254
Joined: Sun Jul 09, 2000 10:44 am

RE: Gas Turbine Horse Power

Tue Mar 06, 2001 11:35 am

Oh, let me talk to your friend. Hes takling about tourque, not horsepower. The equation is simple. IT's 2 horsepower to one pound of thrust. So, for example, a dragster has 5,000 H.P., while a 747 (with 250,000 lbs. of thrust) has 500,000 H.P. So he can stick that in his pipe and smoke it. MY dad is the same way. And, just for reference, the Space Shuttle (or at least, the two booster rockets at launch) produces 7 million pounds of thrust, which is 14 million horespower.
 
dynkrisolo
Posts: 1825
Joined: Mon Feb 12, 2001 12:12 am

RE: Gas Turbine Horse Power

Tue Mar 06, 2001 11:46 am

Thrust is a measure of force. Horsepower is a measure of power or rate of work which is the product of force and velocity. Without knowing the velocity, comparing thrust and horsepower is totally meaningless.
 
timz
Posts: 6120
Joined: Fri Sep 17, 1999 7:43 am

RE: Gas Turbine Horse Power

Tue Mar 06, 2001 12:03 pm

Power is force (or thrust, let's say) times speed. It so happens that at a speed of 375 statute miles per hour, the horsepower equals the force-- if force is measured in pounds. At 750 miles per hour the horsepower would be twice the force in pounds, and so on.

So if a 747 flew at 750 mph, and if it had a thrust of 250,000 lb at that speed, then it would be generating 500,000 hp. But 747 cruise thrust (at 35,000 ft altitude) is maybe 50,000 lb at maybe 550 mph, so cruise horsepower is something like 75,000.

242, dunno which decimal point you misplaced-- is it really 70,000 lb-ft of torque? If so, it couldn't be at 30,000 rpm, since that combination adds up to 400,000 hp.
 
Bryan Becker
Topic Author
Posts: 327
Joined: Fri Mar 02, 2001 12:38 pm

RE: Gas Turbine Horse Power

Tue Mar 06, 2001 12:09 pm

Thanks so much now that I know that I'm the one who is right Smile
 
Guest

RE: Gas Turbine Horse Power

Tue Mar 06, 2001 12:11 pm

HP=((thrust in pounds)x(speed in knots))/375

if my memory is correct
 
timz
Posts: 6120
Joined: Fri Sep 17, 1999 7:43 am

That's True, Except...

Tue Mar 06, 2001 12:33 pm

If it's 375 that appears in the denominator then speed must be in statute mph, not knots.
 
Aerotech
Posts: 254
Joined: Sun Jul 09, 2000 10:44 am

RE: 242

Wed Mar 07, 2001 7:32 am

Are you sure that's 70,000? I mean, the Herk only has 88,000.
 
242
Posts: 495
Joined: Tue Oct 24, 2000 1:10 pm

RE: Gas Turbine Horse Power

Wed Mar 07, 2001 7:47 am

Yep, straight out of the P&W maintenance manual.
Seventy seven thousand foot pounds of torque at the output shaft of the RGB.
 
timz
Posts: 6120
Joined: Fri Sep 17, 1999 7:43 am

RE: Gas Turbine Horse Power

Wed Mar 07, 2001 12:16 pm

If you specify the horsepower (1800) and the torque (77,000 lb-ft now?) the speed has to be 123 rpm. Zat sound right? If it doesn't, either the torque or the horsepower has to be off.
 
avt007
Posts: 1989
Joined: Mon Jul 10, 2000 4:51 am

RE: Gas Turbine Horse Power

Wed Mar 07, 2001 1:57 pm

Back when I worked on CV580s, my favourite instrument was the horsepower indicators(not torque!). The index was 0-4, and it was labelled "HPx 1,000"!
More numbers; the PW123 (Dash 8) is rated at 2380 hp.
 
Aerotech
Posts: 254
Joined: Sun Jul 09, 2000 10:44 am

RE: Gas Turbine Horse Power

Wed Mar 07, 2001 3:34 pm

Something has to be off. A C-130 has about 4,700 S.H.P. per engine, and 22,000 ft.lbs. of torque. Dare I say there was a type-o in the P&W maual?
 
Guest

RE: Gas Turbine Horse Power

Wed Mar 07, 2001 10:00 pm

The Allison T56A-15 (C-130H) produces 4910 eshp and its Max torque is 19,600 inch pounds of torque. I am currently studying to be a high power ground runner on type.
 
timz
Posts: 6120
Joined: Fri Sep 17, 1999 7:43 am

RE: Gas Turbine Horse Power

Thu Mar 08, 2001 1:49 am

Aerotech says 4700 shp, 22000 lb-ft, which implies 1100 rpm; 777_sandbag says 4910 eshp (maybe 4500 shp?), 19600 lb-inches, which implies something like 15,000 rpm. So one is gearbox output and one is input?
 
242
Posts: 495
Joined: Tue Oct 24, 2000 1:10 pm

RE: Gas Turbine Horse Power

Thu Mar 08, 2001 6:44 am

One of the reasons I retained this little tidbit of information onr the P&W 1800 is that it seemed abnormally high. I'm assuming that this value is at the prop flange, however, the torque probes are at the rear of the engine. The wording in the manual states that when the torque gauges in the cockpit read 100%, this equals 77,000 ft/lb of torque. I no longer work on this aircraft, otherwise I'd scan the page to show you all.
 
Guest

RE: Gas Turbine Horse Power

Thu Mar 08, 2001 11:40 am

The T56 compressor/turbine spins at 13810 rpm and the prop turns at 1020 rpm.
 
Aerotech
Posts: 254
Joined: Sun Jul 09, 2000 10:44 am

RE:777_sandbag

Thu Mar 08, 2001 3:22 pm

As you may know, many limits (not just power) imposed by the maufacturer are there for longevity, and safety reasons. However, I have talked to a C-130 (H2) pilot here at Elmendorf A.F.B. who has personally had them up to 22,500. The maintenance crews actually painted a red line on the torque guage on the line between 22 and 23.
 
Guest

RE: RE:777_sandbag

Thu Mar 08, 2001 5:17 pm

I would love to know what TIT was reached to achieve 22,500 in-lb. At 1077 deg c we normally have trouble reaching 19,600. It would have been interesting to do a borescope on the turbine and have a look at the mag plugs.

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