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QUOTING a comparison of the radial engine with a star fish, the author compares the frontal areas of radial and V-type engines and shows how air can be applied to the cylinders of in-line engines to secure efficient cooling with minimum parasite drag. Advantages of upright and inverted engines are contrasted in various respects; and engine-mountings, cylinder design and valve gears are discussed. Difficulties that have been encountered in gearing in-line engines having less than 12 cylinders are mentioned, and a simple method of gearing is proposed in which the elasticity of a relatively long propellershaft is utilized. The paper concludes with a comparison of the production problems of radial and in-line aircraft engines.

It is stated that in cases where cylinder distortion produces exhaust valve leakage, the problem of valve burning becomes one of considerable difficulty. A flexible exhaust valve seat, which apparently conforms to the valve and produces a tight seat even though the cylinder head be distorted, has been designed and tested. Apparently complete sealing of the valve was secured in a cylinder known to be subject to exhaust valve seat distortion. This result indicates that heat dissipation through the seat is not of major importance when a tight seal of the valve is secured. The use of flexible inserts may remove some present limitations on cylinder design.