The Mightiest V-1710 Was a Turbo-Compound
by John Leonard
| Thanks to the generosity of the Rolls-Royce Heritage Trust Allison Branch, Inc., the AEHS is pleased to reprint a series of John Leonard's feature articles from the Allison Branch newsletter. The Rolls-Royce Heritage Trust is one of the world's great engine information resources. Memberships are reasonably priced and provide a number of benefits. For more information, see the Rolls-Royce Heritage Trust web pages under the home page Links tab. |
The first V-1710 produced 750 hp. By the beginning of World War II it was producing 1,050 hp, then 1,125, then 1,325, and late model P‑38s got 1,475. But engineers recognized that there was a lot of energy going out the exhaust pipes.
An attempt to recover some of this energy resulted in the turbocompound V-1710 shown at the bottom of the page. It was identified as the V-1710‑E22 by Allison, and as the V-1710‑127 by the government. A turbocompound engine collects all of the exhaust gasses and runs them through a turbine, with all of the power generated going back into the crankshaft and ultimately to the propeller. It differs from a turbosupercharged engine, which uses exhaust gas energy to increase the pressure of incoming air. Work on this engine began in about 1944 and continued until 1946, when Allison asked that it be cancelled because turbine engines had greater promise. It was the first successful turbocompound engine, and probably one of only three to ever be built. This engine was designed to power the XP-63H, which, as it turned out, never flew. The V-1710‑E22 had a military rating of 2.320 hp, and a War Emergency Rating with water/alcohol injection of 3,090 hp.
The most successful turbocompound engine was a version of the air‑cooled, 18‑cylinder, two‑row radial Curtiss-Wright R-3350. This engine had three turbines, each fed by six cylinders, that were geared to the crankshaft. The normal version produced 2,700 hp and weighed 2,850 lbs. The turbocompounded version produced 3,500 hp and weighted 3,440 lb. This engine was used on the Douglas DC‑7 and some versions of the Lockheed Constellation. The other turbocoupound engine is the Napier Nomad, which was built in England. It was a 12‑cylinder, horizontally opposed, liquid cooled, valveless, 2‑stroke cycle Diesel engine with a 3‑stage turbine. It reached flight test but not production.
The Allison engine collected the exhaust gas from all 12 cylinders and routed it to the turbine at the rear of the engine through two exhaust tubes. The shaft from the turbine ran through the center of the first stage supercharger impeller, back to the engine and put its power directly into the crankshaft. The turbine could not be connected to the supercharger impeller because the supercharger was driven by a variable speed transmission, which did not run at a fixed speed ratio with respect to either the crankshaft or the turbine. Since this engine was to power a P‑63, it used an extension shaft and a remote gearbox attached to the crankshaft at the front of the engine at lower left in the picture below. This engine represented quite an advancement over the original 750 hp engine.
Copyright © 2001 Rolls-Royce Heritage Trust Allison Branch, Inc.
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