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could not be entirely dismissed. In 1955 the best readily available metals were less than ideal for airframes and skins that might be subjected to very high temperatures. To counter this the USAF hoped to partly over- come the problem by dumping excess heat into the central fuel tanks. The powerplant proposed for this aircraft was a very sophisticated RFGT. Under devel- opment by Orenda Engines (Avro Canada’s jet engine division), it was based on the ear- lier design for Project Y. This second-genera- tion RFGT drew air through upper central inlets for VTOL operation and front-facing upper and lower inlets for forward flight. An air bearing was used to support the compres- sor/turbine wheel and the combustion cham- bers were coupled to a reheat system, which ducted gas to a fairly complicated arrange- ment of exhaust vents. Controlling the aircraft in flight would have been achieved by the selective direction of exhaust gases and bending the jet flow by means of the Coanda Effect. Pitch and roll was regulated by the annular nozzles and the rear exhausts were responsible for yaw con- trol. A second approach to flight control was considered. This used a shaped ring sur- rounding the edge of the entire aircraft, which acted as a selectively regulated Coanda exhaust system. This appears to have been developed from the system used on the smaller research aircraft and it may have been seen as the simpler solution. Unfortu- nately, wind tunnel tests showed that this design created excessive drag at supersonic speeds and the lower air intake ceased to function properly in level flight because exhaust gases were flowing across the bot- tom of the aircraft. Anumber of modifications were proposed which included the use of two small louvred exhaust vents positioned in the upper aerofoil to improve directional con- trol, but the idea was finally dropped. By 1956 the USAF is known to have expressed serious concerns about the relia- bility and combat survivability of the RFGT engine. It had always been know that without engine power this kind of aircraft would be impossible to fly and an emergency landing would be out of the question. Frost’s team accepted this concern and set about DIRECTION OF ROTATION DIRECTION OF ROTATION 65 Project Y2 Silver Bug aircraft concept illustration. USAF A cross-section of the radial flow gas turbine engine used in Project Y2 aircraft. USAF Project Y2 Silver Bug cross-section of bearing design. USAF Canada’s Cold War Saucers