The General Motors Research Laboratories X-250
by Kimble D. McCutcheon
Published 22 Aug 2015; Last Revision: 1 Oct 2021
27 Mar 2016 — Survivor Section Added; 12 Jul 2016 — PT-19A Images Added
1 Oct 2021 — More Flight Testing History
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Shortly after the General Motors Corporation (GM) purchased the Allison Engineering Company on 1 Apr 1929, the General Motors Research Laboratories (GMRL) began work on a series of 2-stroke U-cylinder engines that featured dual cylinders joined by a common combustion chamber. The two pistons were connected to the crankshaft in a way that produced different port timings for the intake and exhaust pistons. This was typically done by phasing the crankpins at small angles (10° ~ 20°). If the proliferation of patents covering this U-cylinder scheme is any clue, this was a popular concept in the 1920s and early 1930s. GMRL continued to work with this concept through the 1930s and into the mid-1940s, eventually creating a 200 hp radial with four cylinder pairs called the X-250. |
| GMRL X-250 Cutaway on Display at the Henry Ford Museum (Robert F. Pauley Collection) |
GMRL X-250 Cutaway on Display at the Henry Ford Museum (Robert F. Pauley Collection) |
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