THE importance of obtaining complete information on the operation of engines in the airplane over the entire flying range, particularly in the case of the high-speed airplane, if we are to obtain the most effective airplane possible, is emphasized by Mr. Wiegand.
Mr. Wiegand sets up certain characteristics of aircraft engines that affect carburetion. These are:
Since the engine operates on air, the carburetor must meter the fuel in proportion to the weight of air burned, which has a direct relation to indicated horsepower output.
Engine air consumption and, therefore, fuel consumption, bear no fixed relation to brake horsepower or brake specific fuel consumption.
Since the carburetor meters on the basis of airflow, there is no fixed relation between carburetor metering and brake specific fuel consumption.
The aircraft carburetor has certain functions, which can be summarized as follows: It should meter and mix fuel in a selected proportion to the weight of air consumed by the engine; provide fuel-air ratios for all flight operations; incorporate an acceleration system that will allow the pilot to open and close the throttles at any rate, load, altitude, and frequency; meter satisfactorily with many types of fuel systems and air systems at any airplane attitude.
If such severe conditions are to be met, it is obvious the highest skill is required. Even when the best techniques of today are followed, it cannot be expected that the present carburetors can meter to closer limits than ±5% over the entire engine operating range.
“Considering the variables involved,” Mr. Wiegand concludes, “the quality and functional performance of present carburetors are considered satisfactory from a practical operating standpoint, and with further cooperation of the aircraft, carburetor, and engine manufacturers, should continue to improve in a normal manner.”