The VDT, or "variable discharge turbine," was proposed as an
accessory to the
Pratt & Whitney R-4360 and
Wright R-3350 radial engines as a means of increasing power. The system used a variable
nozzle for the engine's
turbosupercharger exhaust which could constrict flow and create
jet thrust from the nozzle. Like the
turbo compound its intent was to recover lost energy that would otherwise just be vented overboard.
In tests it was quite successful and was slated for use on the
Convair B-36C,
Boeing XB-54, and
Republic XR-16/XF-12. None of these projects panned out however.
Convair had trouble with high altitude cooling of the R-4360 VDT engine, owing to the necessity of changing the original
pusher configuration to a
tractor configuration. The
Air Force would have had to build wider
taxiways for the XB-54, and the
Boeing B-52 was in development anyway, and the Air Force chose to order
RB-52's rather than the XR-16. Development of the engine was cancelled as well and the Variable Discharge Turbine faded into
obscurity.