Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!gem.mps.ohio-state.edu!tut.cis.ohio-state.edu!att!cbnews!military From: oplinger@ra.crd.ge.com (B. S. Oplinger) Newsgroups: sci.military Subject: Re: Rotary engine airplane troubles Message-ID: <10671@cbnews.ATT.COM> Date: 27 Oct 89 03:29:33 GMT References: <10577@cbnews.ATT.COM> Sender: military@cbnews.ATT.COM Organization: General Electric Corp. R&D, Schenectady, NY Lines: 90 Approved: military@att.att.com From: oplinger@ra.crd.ge.com (B. S. Oplinger) [mod.note: While the first sentence is incorrect, as shown in another of today's postings, this article does a good job of explaining all these different engines. - Bill ] Rotary engines and radial engines are indeed much different. I'll try to give a much simplified description (as in a wwI aircraft, in ground vehicles and later airplanes, the fixed part of the engine may vary) of the differences. A typical engine has a fixed case which holds the engine parts (block) and looks like (pardon the ASCII graphics): cylinders || || || || \/ \/ \/ \/ ________________________ <---- fuel/exhaust on the top here | | | | | | ___ | ___ | ___ | ___ | | |_| | | | | | | | | | | | | | | | | | | | | --|-----|- ---|-----|--+-------- shaft (energy provided) |________________________| [mod.note: You need a ring job. 8-) - Bill ] It is broken up into cylinders, each of which has a fuel input and a piston. The fuel is premixed with oxygen (carburated, hence a carburator) and pumped into the cylinder. The piston compresses it and then an ignitor (spark plug) causes it to burn. The pistons are placed on a shaft in a staggered manner so that as the gas expands the piston pushes the shaft and other pistons compress the fuel, it explodes, pushes the piston, etc for a self repeating cycle. Note: all of the energy is at right angles to the shaft. [mod.note: (this is habit forming !) Note that fuel-injected engines do not pre-mix fuel and air, but inject the fuel directly into the cylinder. - Bill ] A radial engine, on the other hand has the shaft fixed and the piston placed in a star shaped pattern around the shaft (at least in airplanes) kinda like this: \ / \ / --- o --- the 'o' is the shaft( looking on end) / \ / \ All of the fuel, lubrication, exhaust is based on the natural tendency of thing to fly outward. The fuel is fed into the center of the engine. It is then fed into each cylinder and when burnt, the exhaust gases flow outward. Bolt the propellor onto the engine block and when the block turns, the propellor turns. If you think about the mass being moved here you will quickly see why it was so easy to turn the plane to the left. (Think about the physics experiment where you stand on a turntable, someone hands you a spinning bicycle wheel. When you turn the wheel from horizontal to vertical, the platform turns. Same thing here) Rotary engines on the other hand, do away with the piston in the cylinder approach. Instead they use a cam. The simplest description I can come up with is: Imagine a football. Place it in a home trash can (you know the round kind with a lid) which has been cut as tall as the football is round. Now if you turn it there is a half-moon kinda space on each side of the football and no space at the points (shink you picture of the diameter of the trash can if necessary). Now, dent the trash can so that it is no longer round. The half-moon space will now grow and shrink. At the point where it is the largest, cut a hole for a fuel injector. At the point it is the smallest, cut a hole for a spark plug and an exhaust. If you imagine a bunch of these stacked on top of each other and a shaft running from top to bottom, you have a rotary engine. The energy provided by the expanding gasses is applied more efficiently to the shaft. The cam turns and so does the shaft, unlike a piston engine where you must convert up and down to around and around. This should make a smoother running more efficient engine. In practice, it is difficult to maintain (as a buddy with a RX-7). brian oplinger@crd.ge.com [mod.note: Wankel rotaries are now being considered for light aircraft, because of their favorable power-to-weight ratios. Oh, and some followups may be more appropriate to rec.autos.tech. - Bill ]