Models + Marquardt = Ramjets
September 1949 Air Trails

September 1949 Air Trails

Table of Contents These pages from vintage modeling magazines like Flying Aces, Air Trails, American Modeler, American Aircraft Modeler, Young Men, Flying Models, Model Airplane News, R/C Modeler, captured the era. All copyrights acknowledged.

As with most careers in technology fields, many of the most successful and imaginative people engaged in some lesser form of the craft as a hobby in their younger years. Burt Rutan, famous for his canard airplane designs and as founder of Scaled Composites with its SpaceShipOne suborbital craft, is a very familiar example of that. Roy Marquardt, a Caltech graduate who initially worked for Northrop Corporation, is not quite as well-known; however, his aerospace company, Marquardt Aircraft Company, was widely regarded for its founder's "outside-the-box" thinking with his unique jet-powered designs. The Whirlijet shown in this 1949 issue of Air Trails magazine was likely the motivation for the JETicopter Jetex engine powered model distribute in the early 1950s by American Telasco. Marquardt's ramjets typically had no moving parts except for the fuel pump, and could run on low octane gasoline. The U.S. Air Force funded many research projects.

Models + Marquardt = Ramjets

By Don Downie

Once he built model airplanes - good ones too! Now he builds "flying stovepipes," those trans-sonic ramjet engines that make headlines every time a new story is released.

Everything about Roy Marquardt is jet-propelled. His experimental helicopter, the Whirlijet, is the first of its kind in the world. He even has a jet-propelled pipe lighter.

Head man of a 26-acre aircraft plant with over 175 employees and $2,500,000 in military orders for jet engine research, young Marquardt gives much of the credit for his success to model building.

"Model building is the finest way I know to demonstrate ideas found in books and magazines. There are probably as many wrong ideas as right ones, but the up-and-coming enthusiast who combines reading and research with his model building will learn a lot about aviation, just as I have," says Marquardt.

He should know, for Roy Marquardt began his aviation career at the age of 12, teaching model-building at the "Y" in Burlington, Iowa. In high school he was largely responsible for building two gliders; a primary job that he cracked up himself and a secondary sailplane that was barely completed because of slim finances when the banks closed in 1933. Everyone was broke in those lean years, so they all resumed building inexpensive model airplanes.

Marquardt won the Mississippi Valley model contest; sweepstakes for 1937, with an 8-hour, 50-mile flight from East St. Louis, across the river and on toward central Missouri. Plans for his plane, the Rizer Rider, were printed in Air Trails later that year.

Life was just one blue-ribbon contest after another until Marquardt came West and entered the California Institute of Technology for graduate study in aeronautics. Even then he took time out from his slide rule work to win the 1939 California State contest in Taft. Since that time, however, his model building has been restricted to engineering research scale-downs and helicopter models.

To fill in a meager income during school years, Marquardt taught advanced mathematics and worked on the wind tunnel staff at Cal-Tech until he received both his Bachelor and Master degrees in aeronautical engineering there.

After college came a job in the aerodynamics department at Douglas Aircraft and a two-year stretch at nearby Northrop where the former model builder was in charge of one of the first Navy research contracts in jet propulsion. He moved to the University of Southern California as director of aeronautical research and persuaded USC to take a contract from the NACA for jet helicopter research. Next came the Marquardt Aircraft Corporation and later the Whirlijet.

"The helicopter itself was almost incidental," says Marquardt. "It grew out of a test stand for these pulse-jet engines, a modified V-1 buzz-bomb power plant, but the helicopter worked out so successfully that we hope to go ahead with a contract to perfect it.

"Actually, over 90% of our work is in the research and development of ramjet motors for military planes and drones. We built the 20-inch 'stovepipe' for the Martin Gorgon IV and the 30-inch wing-tip jet engines for the Lockheed F-80. Beyond that, our ramjet business is classified as a military secret."

The 30-inch jet, already successfully test-flown on the F-80, is 11 feet long. The smaller 20-inch engine has been flown on the F-51, F-82, F-83 and the F7F. All that security regulations permit is the statement that "at its design speed, this engine develops greater thrust than the largest available American turbojet. It is sufficient to power a large pilotless aircraft or a small fighter."

The Gorgon IV, built by Martin Aircraft and powered with a 20-inch, seven-foot Marquardt ramjet engine, has just been announced by the Navy. Since the ramjet has no static thrust and therefore cannot take off under its own power, tests at Point Mugu in California were made with the Gorgon IV taken aloft and released from a specially modified Northrop Black Widow. Other than a fuel pump, these engines have no moving parts and operate on 80 octane gasoline.

In comparing the various types of jet engines, Marquardt says, "at design speeds, the ramjet has a specific fuel consumption per pound of thrust of about four times that of a turbojet engine and about one-fifth that of a rocket engine. This high fuel consumption at subsonic speeds necessarily limits the application of ramjet engines to very short periods of time where the light weight of the engine more than makes up for its high fuel consumption.

"Actually, you can build a model plane to fly at 20 mph with a ramjet engine. The main problem would be in designing the correct fuel nozzles, and I don't recommend that any but the most energetic model builders take a crack at it. We get into enough trouble with these big ramjets and we have a lot more background than the average basement model fan."

The Whirlijet is the first known flyable pulse-jet helicopter. This 29-foot helicopter has an eight-inch pulse-jet engine on the tip of each blade. Marquardt and his staff of engineers, which includes such well known modelers as Don Justice and "Joe" Weathers, did both the basic design and development of these 15-pound "engines."

There is no need for a tail rotor on the Whirlijet since there is no mainrotor torque except for bearing friction. The main advantage of this unusual design is its light weight. On the conventional helicopter, nearly half the gross weight goes into power plant, gear boxes, clutches, tail-rotor and linkage. On the Whirlijet, the power plant comprises only five percent of the total weight, but fuel consumption is roughly four times that of the conventional craft.

For short hops of under an hour in the air, the pulse-jet 'copter figures out on paper to be a more efficient load-carrying vehicle than its present competitors, according to the designers. It will lift twice the pay load for the first hour of flight of any similarly sized helicopter.

The pulse-jet engine is an explosion-type power plant having reed-like valves in the air inlet while the ramjet is a continuous-burning engine. No other power source is required for the Whirlijet since fuel and ignition are supplied to the pulse-jet engines through integral lines within the blades.

Since the Whirlijet was designed primarily as a flying test stand, little consideration was originally given to its utility as an aircraft. When pilot Bill Davis first flew the ship, he found the hovering and forward flight characteristics unexpectedly stable. Designers credit this stability to the mass of weight of the jet engines at the extreme tips of the rotor blades and point out that many conventional helicopters carry weights in the tips of their blades for added stability. To date, only low altitude flights have been made in the Whirlijet and no accurate performance data is available.

The pulse-jet engines on the Whirlijet are started by pumping fuel into the combustion chamber, igniting the mixture with a spark plug and then holding a nozzle from an outside air compressor in the nose of the engine until resonance occurs. Resonance in a pulse-jet engines is similar to resonance in a church pipe organ where sound waves (explosion waves in the engine) go down the tube and bounce back as a new wave is started. The explosions of a pulse-jet engine are timed to the length of the tube, just as the tone of the pipe organ is determined by the length of the pipe. Just as the organ pipe amplifies the noise, the pulse-jet engine amplifies the thrust.

Once resonance occurs, the stream of compressed air is removed and the rotor is freed for rotation. In a finished model, a built-in starting system would include an air compressor and a tank within the fuselage with transmission lines inside the rotor blades. A rotary seal, similar to that now used for the fuel system, would carry compressed air to the rotor-tips.

The Whirlijet weighs 1,000 pounds and has wood and steel rotors with a laminar flow NACA 8-H airfoil. Cyclic pitch control is conventional while directional control is obtained from a single rudder hinged about a 450 inclined axis. The control system and landing gear are from a Sikorsky R-6 helicopter.

Like all good model builders, Marquardt is an opportunist. During the early development of the ramjet engine he now produces, there were no adequate test laboratories. A ramjet cannot be tested in a trans-sonic wind tunnel because it contaminates the air-stream with its exhaust gasses. Actual flight-testing is expensive and accurate results are hard to calibrate, so Marquardt and Bob de Vault, another former modeler, contracted with the Kaiser Steel plant at Fontana, California, to use their blast furnace blower for an air supply. It proved to be the best compressed air reservoir in the area and is still being used for research purposes. A large line was tapped into the compressor to shoot a steady stream of air into the mouth of the ramjet engine at speeds up to 1,000 mph and accurate readings were no problem to obtain.

While teaching at USC, Marquardt built up his pint-sized research plant at Venice, California, and recently leased the 100,000-square-foot Timm hangar on the Metropolitan Airport at Van Nuys in the San Fernando Valley.

In addition to their ramjet engine business, they also manufacture radio loudspeakers and industrial mufflers. Their muffler business is coming in very handy for this new company since they can eliminate most of the noise from their experimental jet engines with Marquardt-built mufflers.

"It's been a long haul from those first model' building days' at the 'Y' in Burlington," reminisced Marquardt as he selected a pipe from the large stand on his desk and lit it with his jet lighter. A sign on his desk says "The Chief," and refers to this 31-year-old, 6'1" ex-model builder who now weighs 240 pounds and "likes to eat just about anything."

"Actually, we look on these sub-sonic jet engines more or less as toys. If he could get past the guard at the gate, the guy who draws 'Buck Rogers' could get some real ideas out here."

Posted January 31, 2022