THE TURBOCRAFT U-22
ADVERTISEMENTS for the U-22 Model Aircraft Engine began appearing in the July 1965 men's crafts magazines and hit the aircraft modeling community like a bombshell.
Mr. R.G. Britt, of Turbocraft Engineering Corporation, of 308 70th Ave. N. , Myrtle Beach, S. C. was offering the first fully functional gas turbine engine for $189.50. It measured 2-3/4" in diameter, x 12" in length, with a dry weight of 30 oz. Its long cylindrical shape looked ideal for realistic model jet aircraft propulsion.
It promised 8 pounds of static thrust @ 48,000 RPM with a single-stage centrifugal compressor, an 8-chambered combustion section, and a single-stage impulse turbine. Thrust was variable via a fuel flow valve, and could be increased to 10 pounds (with afterburner.) Suitable fuels were listed as "aviation gasolines, butane, propane, naptha, nitromethane, methanol, acetone, and ether".
The U-22 required a pressurized fuel system. The system should be capable of delivering liquid fuel under a pressure of 80 to 100 pounds per square inch into the injector fuel port located near the front on the engine air intake.
There were two options. The U-22A was a set of full scale enginering drawings, and a parts list with a price sheet for $5.00. The U-22D was a complete construction kit for $750.00. For either engine, a 1/5HP 20,000RPM starter motor was available for $39.95.
With 46 years of hindsight, the U-22A was the better bargain. In all those years, I know of only three working U-22A engines; two of mine, and one built by a friend in the U.S. Army who had unlimited tools at his disposal.
One look at the fading "$5 blueprints" told me that there was insufficient information to build a working engine. Most notably, the combustion chambers were 8 CO2 tubes! I wrote to Britt over and over, and in time slowly received technical & operating specifications, engine operating information, and test data. I even had him send another set of plans because after three months my first set had faded out! I set about trying to get the thing to work, feeling fortunate that I had only lost $5.00 and some postage in the venture. In the interim, the dozens of $750 kit buyers made such a legal clamor they forced Britt out of business, and I never heard from him again.
THE PROBLEMS:
1. Very few engines could achieve ignition in all 8 combustion chambers. The solution I discovered was "cross-over tubes"; these are little tubes welded to the middle of each combustion chamber, so that although each chamber had its own spark plug, ignition in one chamber lit the adjacent chambers, and then the entire engine. In my second engine, I used cross-over tubes with just two spark plugs to keep down the weight and it worked just as well.
2. At 48,000 RPM there isn't sufficient compression to start (or run) the engine with liquid fuels. Propane works, but a propane tank is not something you would put in a model airplane. And that's what most people wanted the U-22 for.
CONCLUSION
Britt's U-22 project may have started out with good intentions, but somewhere along the line, when he saw that it wasn't working, he probably felt that he had put so much money into it, he just went ahead and promoted the thing anyway.
