One of the major factors is the fact that the Tee Dee .020 cost so much it has now become a museum piece. The engine has clearly become unobtainable from a monetary factor and parts support. It certainly is beneficial that Bernie has plugs now for .020 engines, but some of the major components needed for the Tee Dee aren't and probably won't be made available. I suppose for those that own this engine it makes a great choice. Ken

               I totally agree Larry, I truly believe it may have been Cox's best engine they made. More parts have recently become available, but these engines for those who don't own them are ridiculously expensive. Ken

Actually, the Tee Dee .020 is much sought after for certain FF events where it is the only game in town.  This accounts for the high prices and scarcity. 

The Cox RTF engine has about the same power and fuel consumption, though a bit more weight, and represents a great alternative.   Your Bipe is a nice design, and I would not want it to fail because of engine unavalibilium.