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AN extensive study of oil foaming has brought Mr. Pigott to the following conclusions: 1. All suction-side resistance of either pressure or sump pumps must be reduced as much as possible. 2. Velocities in suction piping should be kept below 5 fps at all points. Bends that cannot be eliminated should be long radius. Valves and other restrictions must be avoided. 3. Spur-gear pumps can be improved by optimum exposure of teeth on the suction side, use of side pockets, and reduction of clearance. Without help, these pumps still won't be good enough for the highest altitudes. 4. Oil tank pressurizing will provide boost for the pressure pump. 5. Centrifugal boosters are useful, except with cold oil or with much aeration. For the pressure pump, the booster should be located directly at the oil tank, and for the scavenge pump, at the sump. Both must be drowned, no lift. 6.

WHILE the centrifugal supercharger is excellently suited to aviation service and to relatively constant-speed, diesel-engine service, Mr. Pigott states, it is not of value for cases of considerable variation in speed where full boost is required at all speeds. The Roots-type blower, the author says further, has had a justified development for low-pressure boost, but is not valuable for compression ratios much in excess of 1.6 because it has no adiabatic compression. The vane-type supercharger, while it has an adiabatic compression, as so far developed appears to the author to be somewhat complex in structure, requires internal lubrication, and has not yet shown satisfactory efficiency compared to other types. The Elliott-Lysholm screw-type and the new P. L. internal-gear type appear to him, however, to give great promise for satisfactory supercharging at the higher pressures beyond the range of the Roots type, and appear to be the best present line of development.