The Dyna-Jet is one of many small pulsejet engines that can power model airplanes
During the final days of World War II, the German Air Force built and flew a small but powerful pulsejet-powered cruise missile known as the "V-1." Because of its characteristic engine noise, the V-1 was often called the "Buzz Bomb."
Following World War II, small pulsejets for model airplanes emerged in the United States (Dyna-Jet, MiniJet), Japan (Tiger Jet), and elsewhere. Among the many brands and models of small pulsejets were the PJ-31, Minijet, Dyna-Jet, Marquardt MA-16, Saunders-Roe pulsejets, SNECMA "Valveless Resojet," M.E.W. 307, Tiger-Jet L-1 and M-1, Ogawa O.S. Type II, Jaggers Juggernaut, Decojet, BMW RT.2000, Brauner, Victoria MD.1, Hagiwara's Eureka jet, SAAB J35, and other PJ-31, Minijet, Dyna-Jet, Marquardt MA-16, Saunders-Roe pulsejets, SNECMA "Valveless Resojet," M.E.W. 307, Tiger-Jet L-1 and M-1, Ogawa O.S. Type II, Jaggers Juggernaut, Decojet, BMW RT.2000, Brauner, Victoria MD.1, Hagiwara's Eureka jet, and the SAAB J35.
The Russians were designing and building very advanced engines as well. In fact, the Russian (actually Soviet) pulsejets were produced in far greater variety of sizes, designs, and models than anywhere else. Early Russian pulsejet models broke many speed records:
1948: 110 kph
1953: 264.776 kph
1955: 275.004 kph, and 301 kph
Since those days long ago, pulsejet-propelled models have gone much, much faster.
Pulsejets operate by reaction-propulsion, which is more similar to rocket power than a conventional jet engine. Pulsejets are usually long, tubular devices with an air and fuel inlet at the front. Just inside this inlet there is some kind of simple one-way valve that permits air and fuel to enter, but closes when the combustion chamber pressure increases (forcing exhaust to flow out the tail, and producing power).
Pulsejets operate by a repeating cycle:
Air and fuel enter the combustion chamber tube
A spark plug (at start) or the hot chamber ignites the fuel/air mixture
The fuel/air explosion forces the front inlet valve closed, creating high pressure in the chamber
The hot exhaust thrusts out the rear end of the chamber tube
Forward ram air pressure plus sharply decreased chamber pressure enable the valve to open again, and the cycle repeats as a rapid series of explosions in the tube
The pulse cycle is typically between 100 and 200 cycles per second, and the result is a very noisy operation that quickly makes the combustion chamber tube red hot. The sound of even a small pulsejet engine is remarkable and quite intolerable, far exceeding 130 dB levels. Pulsejet-powered models are quite unwelcome in many places, for obvious reasons.
Pulsejet valves are the key to successful operation, and the Russians came up with dozens of unusual concepts, including (besides the usual "daisy" flapper valves, like in the DynaJet) triangular and trapezoidal flappers, multi-flappers, multi-spring flappers, and several unusual valve seats.
A small but fairly comprehensive introduction to pulsejets for aeromodelling is the classic "Jets and Models Guide." Another is "Russian Pulsejet Engines and Pulsejet-Powered Model Airplanes." These texts provide illustrations, charts, and plans that explain how each engine operates, and how to maintain them.
We carry a selection of pulsejet technical books, including some from NACA/NASA, in our eBay Store.