I am familiar with tip jet powered helicopter experiments. Is there any aircraft that use/used this mode and would it be useful to use a tip jet driven prop on aircraft instead of piston or turbine power?
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3 Answers
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There was a study done on the use of tipjets in civilian aircraft in the 1950's, if I can find the source I'll edit it into this answer. In any case, the conclusions from that study were as follows:
Because of the fundamental inefficiency of subsonic ramjet propulsion, a tipjet-powered propeller "engine" in the 100 to 150 horsepower-equivalent range was completely uncompetitive with piston power. The fuel flow rate required to run the tipjet prop was excessive.
The tipjet-prop plane had extremely limited range if carrying the same amount of fuel as the piston plane, and no useful load if it carried enough fuel to match the range of the piston plane.
answered Apr 22, 2020 at 2:45
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$\begingroup$ I would think having the mass of jet engines at the ends of propellor blades (which run at 5-8 times the RPM of a helicopter rotor) would create horrendous gyroscopic effects, while having a jet (or pieces thereof) come off would create enough vibration to destroy the airframe. $\endgroup$– jamesqfApr 22, 2020 at 4:24
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1$\begingroup$ true. also, if one jet flames out, the whole shebang goes out of balance. Tipjets are really only good for converting fuel into noise and hot air. $\endgroup$ Apr 22, 2020 at 4:31
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$\begingroup$ And could tip jets be powered by a conventional engine, through pneumatic linkage of some sort with compressor? There was some helicopter concept back in the 80's that worked in a similar way. $\endgroup$– OpusciApr 22, 2020 at 12:52
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1$\begingroup$ Hiller helicopters explored this extensively in the 1950's and '60s. Look up hot cycle tipjet and cold cycle tipjet. $\endgroup$ Apr 22, 2020 at 17:37
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Only experimentally, such as the CL400 tip ramjet experiments. It doesn't really work because if one quits, your airplane turns into a pinwheel due to the long arm of the thrust source from the yaw axis unless the wings are very short. Not literally a pinwheel, but it'll want to roll over and crash pretty bad. If they were out on the tips of wings with the kind of span you need to cruise efficiently at high altitude (as opposed to a stubby winged fighter), you'd need a rudder the size of Wisconsin to be able to control it single engine in a low speed departure climb.
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3$\begingroup$ I think the OP means jet engines on the tips of the propellors, not on the wingtips. $\endgroup$– jamesqfApr 22, 2020 at 4:19
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Ludwig Wittgenstein investigated the technology while at Manchester University, UK, and even took out a patent. But his experiments in the lab and on a local railway track came to nothing and he never built an aeroplane. He later became famous as a philosopher.
The idea has been revisited now and again ever since, but I never hears of a plane actually flying with a tipjet-driven propeller.
