Planelover From United States of America, joined Dec 2001, 321 posts, RR: 0 Posted (11 years 2 months 2 weeks 18 hours ago) and read 1820 times:
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.
Flyf15 From , joined Dec 1969, posts, RR: Reply 1, posted (11 years 2 months 2 weeks 18 hours ago) and read 1792 times:
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 From United States of America, joined Dec 2001, 321 posts, RR: 0 Reply 2, posted (11 years 2 months 2 weeks 15 hours ago) and read 1756 times:
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?
Shaun3000 From United States of America, joined Mar 2002, 445 posts, RR: 0 Reply 3, posted (11 years 2 months 2 weeks 10 hours ago) and read 1722 times:
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 From United States of America, joined Nov 2001, 199 posts, RR: 0 Reply 4, posted (11 years 2 months 1 week 6 days 23 hours ago) and read 1723 times:
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.
Planelover From United States of America, joined Dec 2001, 321 posts, RR: 0 Reply 5, posted (11 years 2 months 1 week 6 days 12 hours ago) and read 1709 times:
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.
Jsuen From United States of America, joined Aug 2001, 211 posts, RR: 0 Reply 6, posted (11 years 2 months 1 week 5 days 23 hours ago) and read 1696 times:
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).