planelover
Posts: 313
Joined: Sat Dec 22, 2001 1:22 pm

Choppers With JSF Configured Engines?

Wed Oct 02, 2002 5:04 am

Hey all,
I was checking out a little cut-away of a JSF. The JSF's lift fan is spun from a shaft running into the front of the engine, and the engine also produces thrust out the back of the engine. My question is this, could a chopper use the same type of setup? On the chopper, you could replace the turbo-shaft with a jet engine that has a shaft to main blades being driven off the front of the engine and use the engine's thrust to provide most of the forward motion. You could probably fly at least 300mph.

Well, that's my question based on my little (or no) knowledge.  Smile/happy/getting dizzy

Have fun.  Smile/happy/getting dizzy
PL

 
flyf15
Posts: 6633
Joined: Tue May 18, 1999 11:10 am

RE: Choppers With JSF Configured Engines?

Wed Oct 02, 2002 5:42 am

Helicopters already are powered by jet engines. Thats what a turboshaft is...a jet engine with a power drive coming off the front of it. Also, a turbofan is what the JSF has, a turbojet with a fan on the front of it.

Choppers (at least with current technology) can't fly too much faster than they already do.
 
planelover
Posts: 313
Joined: Sat Dec 22, 2001 1:22 pm

RE: Choppers With JSF Configured Engines?

Wed Oct 02, 2002 8:09 am

Thanks Flyf15. I understand the basic design of turboshaft (which is the same thing as a turbine, right?), turbojet, and a turbofan. I guess I thought there was more difference than what there really is between a turbofan/jet and a turboshaft. Do turboprops blow a lot of exhaust out of the exhaust duct(s) on the side(s)? Why can't choppers use the trust from the jet to help provide forward thrust? Do those choppers (sorry forget what they are called) that don't have a tail rotor direct engine thrust out of the boom or does the boom have a small rotor inside of it?
Thanks again.
Have fun.  Smile/happy/getting dizzy
PL
 
shaun3000
Posts: 439
Joined: Thu Mar 14, 2002 4:10 pm

RE: Choppers With JSF Configured Engines?

Wed Oct 02, 2002 1:28 pm

Turboprobs do not have near the exaust (nor the exhaust temperature) as regular jet engines. Why? All the energy is used to turn the propellor. Same goes for a helicopter. But it's still nothing to laugh at.
 
UPS763
Posts: 195
Joined: Wed Nov 14, 2001 7:00 am

RE: Choppers With JSF Configured Engines?

Thu Oct 03, 2002 12:18 am

Planelover,
Rotor dynamics and cabin structures often have more to do with speed limitations than engine power. Even the difference between in the piston powered R44 and the turbine powered B206 is relatively small. Then when talking about twin engined jet helicopters like the Twin Star, it only cruises between 5-15 kts faster then its single engined sibling. Your question though was to vector thrust out of the rear of the engine also, this would also not work because the speed would be to fast, remember a helicopters Vne is based upon retreating balde stall.

matt
 
planelover
Posts: 313
Joined: Sat Dec 22, 2001 1:22 pm

RE: Choppers With JSF Configured Engines?

Thu Oct 03, 2002 11:26 am

Thanks you all. This is all very interesting. I don't quite understand why turboprops don't have as much exhaust as a jet. Do they run at a much lower RPM? Could someone elaborate on that a little bit?
Thanks, have fun.  Smile/happy/getting dizzy
PL
 
jsuen
Posts: 204
Joined: Tue Aug 14, 2001 2:36 pm

RE: Choppers With JSF Configured Engines?

Fri Oct 04, 2002 12:13 am

Think about it this way. If you just hooked your car engine to a big fan, you would move quite a bit of air. However, your car engine is hooked to your transmission and your wheels. The exhaust from your tailpipe hardly produces thrust at all, yet the engine is producing the same amount of energy (in theory).

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