Did you write this Dennis?  :)

Do you now think it might be worth solving the problems? :)


Paul Lamar

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Technical Correspondence — April 2002
continued...     2 of 3



Compound Glory

Recently I read about the remarkable Wright R-3350 Turbo-Compound aircraft engine
that had three turbocharger-like turbines that were connected via clutches
directly to the crankshaft. In its final form this engine produced 3700 bhp
from its 18 cylinders, up from 2700 bhp of the original Cyclone. Has this
technique ever been tried on auto engines? It seems that a V-type engine
with a turbine off each bank of cylinders plus a mechanically driven
supercharger would really be something.
P. Houston
Ottawa, Ontario, Canada

No doubt the R-3350 was one of the greatest aircraft piston engines to ever
swing a prop, and, interestingly, neither Wright, nor arch rival Pratt & Whitney,
nor any of several other aircraft engine builders worldwide, employed
turbo-compounding on other engines. The technique, which apparently is
unique to the big Cyclone, came along at the dawn of the turbine age, and
thus the end of large-displacement piston-engine development. Wright Aeronautical
calculated the Turbo-Compound feature was worth 550 bhp on the R-3350, which
was also centrifugally supercharged.

Several aspects of turbo-compounding do not lend themselves to automotive use.
It's mechanically complex, with most of the disadvantages of turbocharging
(costly turbines, heat retention, packaging problems, exhaust obstruction),
plus the mechanical intricacies found around the crankshaft. All told, the
Turbo-Compound feature added 540 lb. to the R-3350. Furthermore, it seems
doubtful the always-varying rpm of an auto engine is suited to the geartrain
and clutches, whereas the big Cyclone was employed in multi-engine aircraft
where relatively few rpm changes were encountered.

Finally, while your blown and Turbo-Compound V-type engine would clearly
thunder out plenty of power, no doubt even greater power could be realized
without the complexity of turbo-compounding, which is one way of recouping
energy otherwise lost as exhaust heat. Turbocharging is another such method.
In fact, the current F8F Bearcat air racer, Rare Bear, employs a
non-Turbo-Compound R-3350. It is boosted by centrifugal supercharging
and nitrous-oxide injection, but the exhaust runs freely to the atmosphere.



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