AIRCRAFT CARBURETOR AIRSCOOPS on FUEL-AIR and Their Effect METERING in Flight 420087
THE design of a carburetor airscoop involves:
Location of the intake opening to receive full air-speed ram and exert minimum drag (which involves knowledge and experiment as to the external air flow around the airplane); and
Conducting the intake air to enter the carburetor with uniform pressure across its stream with minimum turbulence, and minimum loss of impact pressure (which involves the study of internal air flow).
In general, the two main objectives, maximum ram and minimum disturbance of carburetion, go hand in hand and have the same structural requirements.
An analysis is given of the principles of fuel-air metering, by measuring the air velocity differential through air orifices of fixed size, and transmitting this differential, corrected for variations of air density, to secure corresponding fuel flow differential through selected fuel orifices. A description is then given of the departures from steady full-stream air flow encountered in flight service, and the manner in which these affect air-speed metering.
Methods are given for detecting, measuring, and curing disturbances from these sources.
Recommendations also are given for improved warm and cold air control, for protection against ice formation in the intake system, by eliminating the variable ram differential between cold and warm air flow which exists with most current scoop designs.
In conclusion, the need is emphasized for freer cooperation between the airplane, engine, and carburetor engineers; and for recognition in our procurement procedure of the need for preliminary check tests in actual flight, on prototype airplanes, of the design and characteristics of not only the scoop and carburetor, but also all other engine accessories whose functioning may be affected by differences between flight and ground-test conditions.