Aircraft Production Board,
Washington, D. C.
Gentlemen: At your request we have made a careful study of the aircraft motor situation and hasten to submit our report as follows:
In order to get this report in your hands promptly we have condensed it as much as possible and have covered the essentials only.
In view of the fact that there are a number of good motors for training-machines available, we have disregarded this type of motor and have confined our attention strictly to the high-efficiency, low-weight per horse-power type, such as is necessary at the front.
In order that any motors that are built by this country may be of any value when received at the front, it is, of course, absolutely necessary that their efficiency be brought up to or a little beyond the best now available in Europe. This, of course, made it necessary for us to know just what has been accomplished in Europe. The French and English Commission has enabled us to obtain this information by answering our questions very clearly and completely.
From information obtained from these gentlemen and from other sources, we believe that the Loraine Dietrich is the coming motor in Europe. This motor has not been built in large quantities as yet, but some thirty had been constructed and carefully tested out at sea-level and also at about 6,000 feet elevation. The important facts about this motor are as follows:
Eight cylinders: 120 mm. bore by 170 mm. stroke.
Cylinders made of steel with water-jackets welded on. Motor is direct-driven and develops 250 horse-power at 1,500 r. p. m., and 270 horse-power at 1,700 r. p. m. The weight of the bare motor is 240 kilos, or approximately 528 pounds, while the weight of the motor complete with radiator and water is 305 kilos, or 671 pounds. There seems to be a reasonable doubt regarding the exact weight of the bare motor, as while the French Commission gave us the figure of 528 pounds, information from other sources indicates a weight of 552 pounds; probably some intermediate figure is more nearly correct, but in any event the motor gives a horse-power for approximately two pounds of weight when figured at its maximum output of 270 horse-power.
After obtaining this information and considering the matter very carefully, we next investigated the matter of testing such a motor, as we knew that a motor of this type could not be run at full power for long periods of time without developing serious trouble. Here again the French Commission gave us valuable information. They stated that in using a motor of this type it is only run at full power for short periods of time while climbing or fighting, and that all other times it is run at speeds 200 to 300 r. p. m. slower. In view of the fact that the motor is built to run under these conditions, it is, of course, necessary to test it under similar conditions, and they stated when trying out a new model of motor it is their practice to mount a propeller which will just hold the motor down to maximum speed under full throttle. The motor is then run for fifty hours, in periods of six to eight hours each, but the motor is not run up to full speed for more than a total of ten hours during this entire period, nor is it run more than thirty minutes at any single time under this condition. The other forty hours’ running is under throttled conditions, turning the same propeller 200 to 300 r. p. m. less than maximum speed.