THE effect of the aircraft-engine intake system on the design of other engine components is here related by Mr. Doman, who applies his findings particularly to a series of 4¼ x 3½ horizontally opposed aircooled engines.
Valve sizes were varied to obtain the maximum size of inlet valve without appreciable restriction of the flow through the exhaust valve, and at the same time that would provide a strong bridge in the cylinder head between the valve openings.
Care must be taken that restrictions to flow are not created in the intake port. “The intake port,” Mr. Doman says, “is probably the most critical item in the whole induction system as far as affecting power output.”
In horizontally opposed engines, the carbureter is usually mounted on the oil pan underneath the engine, despite the objections that the carbureter interferes with the streamline of the undercooling and, if a retractable nose wheel is used, the most suitable location brings the nose wheel into the cowl where the carbureter is located.
One solution has been a “runner” type of manifold, which the author applies to 4-, 6-, and 8-cyl horizontally opposed engines. At present, this type does not give as uniform mixture distribution as the system with individual pipes, but Mr. Doman is confident that this disadvantage will be overcome with more intensive research work.