Pulsejet Flight Video

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G91 flying

Post by dynajetjerry » Tue Jan 15, 2008 9:24 pm

As many others have said, your model and flying are very impressive and deserve much praise. In the U. S., the flying of such models is rare because of the lack of suitable sites and restrictive (but reasonable,)regulations. However, Bruce Tharpe and some of his friends have built and flown many successful p-j RC models in the desert areas of Nevada; he sent me very interesting videos of some of them.
Bruce's fuel systems make use of a pressurizing system much like yours except that he also employs a Cline "fuel controller" (Jim Cline's description,) to permit wild aerobatics. In fact, he has published much of his technology in hobby magazines.
During my employment at Curtis in 1953-54, I developed a rigid tank system that also required a controller, though its tank would not have permitted much maneuvering. I made use of a modified "Jim Walker" Regulator(TM) on a small p-j to permit operation but it was of limited success due to insufficient development. Pressurization was like yours and that feature worked quite well. The engineer in charge (Paul A. Frank, my boss,) talked to Russell Curtis about it and they agreed to stop such work. That was many years before the advent of the Tigerjet and similar designs. Curtis also stopped all our work on a small Dyna-Jet.
In fact, the only thing we fully developed during my 1 1/2 years there was the still-produced Dyna-Fog, Jr.
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Re: Pulsejet Flight Video

Post by nitro » Tue Jan 11, 2011 5:31 am

All control line pulse jet flyers know about pressured fuel tanks off the combution chamber.N,A,S,S is the group on this subject.With no valve about 4psi is about it.I have read in Big Pulse jets 17psi is normal if a one way valve is used.For RC Planes this is not needed though.

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Re: Pulsejet Flight Video

Post by Mark » Tue Jan 11, 2011 3:57 pm

In that Russian book there is a diagram with two manometers illustrating two taps, one on either side of the combustion chamber just forward of the neck. The valve is a single leaf or petal and depending on which way it is orientated, the manometer either indicates a pressure or vacuum in the liquid filled U-shaped devices. In the drawing, the valves are very close to the engine so I would guess they are made of metal. There is one article I read that said the Dynanet intake experiences a backflow just before the valves can snap shut. It only travels an inch or so before being reingested, helping to mix the fuel and air even more. Maybe this doesn't happen as much at high air speeds or at all with some designs, I'm just going by the literature out there. Another article says at high speeds, pulsejet valves stay open and they become poorly running ramjets. Conversely, in another book, perhaps Foa's, states that subsonic ramjets benefit from pulsating combustion and the line between valveless pulsejets and subsonic ramjets is blurred, but I digress.
I guess the reeded pressure tap in reverse is just acting like a typical intake valve would, trying to draw in air on the low pressure phase. On the surface and in conclusion, it seems funny to have a single spot provide you pressure or vacuum depending on your wants and needs.
I wonder what losses you would get or the curve on a graph the greater the distance the tap from the engine in both cases? I suppose the diameter of the tubing would also be a factor.
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