Dear Mr. Soule,

Thank you for your letter of July 26, 1995. I think it was the summer of 1952 vacationing here at Lake Placid that I first realized it would be interesting to make a maple seed that went up, and I made two that worked, one with an Infant Torpedo, the other with a Torpedo junior. One of these models, I forget which, is still somewhere the woods nearby.

Both models had flat plate airfoils and balance arms, and they used the gyroscopic precession of the propeller to twist them into positive pitch.

The fall following I went to England as a graduate student in nuclear physics, and once there built more models. These used little .5cc (also 0.46 and .0.7cc) "Diesel" (more properly compression-ignition) engines, which were marvelously convenient to run, no battery, no wires, but a nasty stench of half -burned ether.

I soon learned that a wing with a large unstable center of pressure travel with angle of attack made an unstable model. Flat plate airfoils were satisfactory, and so were cambered wings with little tailplanes set at a negative angle of incidence. So also was a cambered wing flown with Hiller paddles set at a large positive angle of attack. This model once flew away with its engine running. A lady on its flight path reported that she had seen it but said, "I couldn't see who was in it." I explained that no one was in it, and she said again, "I couldn't see who was in it." You have heard of the bulldog tenacity of the English.

I had my name and address on this model, but even so heard nothing for a long time. I got a letter eventually. The delay had resulted because the model had landed in the back yard of a blind man who lived with his retarded son. Evidently the back yard was inspected either infrequently or ineffectively.

I flew at Cambridge's designated model-flying field, Stourbridge Common, which had both thistles and cows. This made for interest when an engine did not run right and one had to dive out from under the settling model and avoid both thistles and cow pies.

At this point each model had a hole in it at about its center of gravity, and I supported it on a headless nail driven into the end of a stick that I held over my head while it was spinning up to speed. Very interesting was the time I got the engine running with exactly the right degree of feebleness so the model would hover in ground effect at a height of about two feet. It settled from launching height to cruising attitude, drifted across the common with the wind, contoured down the bank of the river Cam, across the river two feet off its surface, up the other bank, across some grass, a path and more grass, and finally hit a wall-like board fence. It climbed five feet or so up the fence on the deflected air before it hit.

I have seen models do strange and wonderful things, but nothing quite like that low-attitude tour. Once I put three castering wheels on the same model and it took off from a Macadam path on the common.

About that time that I took my models to Aeromooleller, which was then in Watford. There I met Harry Hundleby, Ron Moulton and Vic Smeed. It was Moulton with whom I dealt. That same day we went out into the country and, in the gloom and chill of an English winter afternoon, Ron took the picture of my models and me that appeared in the Aeromooleller article. He used flash to supplement the daylight. I remember having tea with Ron and I think Harry in a cheerfully depressing (an English specialty) hole in the wall in Watford.

It was Aeromdeller people, not I, who first hand-launched the models. A twist of the wrist was all it took.

Between the time I went to Aeromodeller and the summer of 1954 1 got the models to carry fuselages with a primitive swash plate. This plate applied enough cyclic pitch via rubber bands to make them fly slowly and majestically forward, but not enough to upset the inherent stability of the rotor.

I made one cross-shaped fuselage that I connected with strings to a cross I held in my hand. This let me guide the model like an upside-down marionette. Tilting the bottom cross applied cyclic pitch. I would start the engine, hand launch the model with a flip and catch the bottom cross as the lines pulled it up off the ground.

A bit later, Deboorne Piggott and 1, the Wrong Brothers, built a model, 1.1 feet from engine end to wingtip, which was powered by an ED Racer of 2.5 cc. The wing was solid balsa and 69 inch span by 3-inch chord. The model screwed its way upward through the air like an apple corer through an apple, but it was weak and soon broke on a landing. Making airplanes larger makes them more efficient and less rugged.

A Jetex-powered model rose from the floor of the ground floor corridor of the Austin Wing of the Cavendish Laboratory and filled the corridor with evil-smelling smoke.

Back in the USA more models followed. I discovered that by tilting the motor arm up with respect to the wing I could get marginal stability with a cambered wing and no stabilizer. One of those models flew away in a thermal. I remember seeing it spinning overhead, engine off, getting smaller and smaller.

There were little models and medium-sized models, but no big models. There was a model that ROWed with floats and a model that ROWed without floats. The latter floated on the buoyancy of its wing with hydroskis to lift it out of the water once it started to spin. There were models that carried suspended payloads, and a model where the suspended load ran the throttle, so the model hopped along, bouncing the payload on the ground. Each time it hit, the throttle would open.

There were models stabilized with a "stop sign," a vertical surface mounted above the center of rotation and oriented so as to apply stabilizing cyclic pitch if the model began to fly sideways. Because stop sign stabilization goes as the square of sideways speed the flight has a wobbly sort of stability. By combining stop-sign stability with wing camber instability, which is first power, the model can be made to fly in steady forward flight, but this is a good way to break it because the landings are also in forward flight.

Some models had reversed rotation and pusher propellers. One of these, with a stop sign, was launched by holding it by the balance arm and throwing it like a boomerang. This is the most complicated way I know of to make a boomerang that does not come back.

The reversed rotation models were built with the idea of using them to launch boomerangs, spinning, at high attitude so I could see if the boomerangs were stable in autorotation. This never -worked, because I could not get the carburetion right in the high centrifugal field that resulted from a rate of rotation high enough so the boomerang would not stall when released.

I am not a boomerang expert. Indeed I do not fully understand why the standard method of warping an MTA (maximum time aloft) boomerang works. But work it does. Good MTA boomerangs now fly away in thermals. Indeed HLG people have talked about ways to exclude boomerangs from HLG competitions,

Then there were the "Together-Messes," each a powered model and a glider on opposite ends of a string that revolved around each other like a double star. I later read of two combat models' doing this after getting their lines tangled together. I never got the stabilization of together Messes straightened out. When they were stable I did not know what I had done right. They tended toward limit-cycle stability, the orbiting pair as a whole flying in circles.

In Red's Hobby Shop (of blessed memory) in Wheaten, MD, I once saw on display a "monocopter" (flat plate airfoil Charybdis) made by Djau (for Django Rinehart? -- actually Joe) Carter of Vienna Virginia. I have known Joe ever since. Joe has made many monocopters. He likes minimum performance so the models rise slowly. He also likes long flights. After the Nationals at Springfield a few years ago Joe launched a monocopter with a giant tank. It was a calm day with a low overcast, into which the model disappeared, and from which it later reappeared, still within the confines of the launch field.

Joe and I went to an informal conference on Charybdis-type helicopters held by Professor of aero engineering Gabriel Bohler of Catholic University. There was a proposal for a man-carrying version, which I and I think Joe regarded as insane. It was like my fuselage-equipped models, and the propeller seemed too close to the pilot's head.

Deedless Research Inc. advertised a Charybdis in American. Aircraft-Modeler. It has reverse rotation. The gyroscopic precession of its propeller will reduce its collective pitch. I have one of the kits but have not built it.

Ben Buckle in England used, or proposed to use, a Charybdis to lift a photo-taking model out of jungle clearings, and Stephen Morris, then of Stanford U., built at least one Charybdis and other all-rotating helicopters. Morris has a flying wing model that flies as a normal airplane and then converts to a maple seed for an autorotating vertical descent.

I made one rubber-powered model that I remember, and one with a C02 engine. The latter soon broke its supply line with fatigue. The combination of the model's rotation and a turning, heavy, two-blade propeller caused ferocious vibration. This is true to a lesser degree with internal combustion-powered models. With a three-blade propeller a model vibrates less. It also makes less noise, because any vibration is fed into the wing and makes it broadcast like a loudspeaker.

I have enjoyed reading about people's experiments with these models. The models seem to me to be totally innocent -- good fun and no practical applications I do not remember any contact from the record breakers. They just went ahead and flew -- and good for them.

That is all that occurs to me about charybdes (charybdises?). I have written other letters on the subject, and when I get back to Bethesda I will try to remember to send you copies of them. Thanks very much for your letter. It has been a pleasure to go through my memories to answer it.

Happy flying,

/s/

Charles W. McCutchen