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Ground Cooling and Flight Tests of an Airplane Equipped with a Nose Blower Engine Cowling

Flight and und-cooling tests were conducted with a Northrop
attack airplane Air Corps designation, A-lTA) to detemine the
merits of a nose-blower engine cowling designed and built at the
N.A.G.A. Laboratory. The chief object of the tests was to deter-
mine the cooling characteristics" of the nose blower, particularly
for ground and low-speed operation. 0f secondary interest was
the effect on the speed or drag of the airplate.

The tests showed that the nose-blower oowling was definitely
smerior to the N.A.C.A. cewling from the standpoint of ground
cooling, since the engine was operated at full throttle for
15 minutes with cylinder temperatures well below the recommended
limit. Although there was a slight decrease in speed with the
nose blower for the particular installation tested, the results
of the speed tests were really inconclusive as regards the possi-
bili ties of improved high-speed performance. The nose-blower
cowling was definitely more powerful as a blower than it need have
been for satisfactory ground cooling, and. consequently the power
absorbed was excessive.

IMIRODUUEION

During the past year, the N.A.G.A. conducted experiments in
the 20-foot tunnel on several cow-ling models intended to improve
the cooling of radial engines at low airspeeds and torednoe the
drag. Tests were made on a wing-duct system, described in refer-
ence l, which showed that improved cooling could be obtained if
the wing were sufficiently thick to accommodate efficient entrance
ducts. Several blower systems for 'use when wing ducts are not
practicable are described in references 2 and. 3 in which the air
is drawn in through entrances located in the wing roots, in the
side of the cowling, and‘in the nose of the cowling These systems
showed promise of fulfilling the requirements set forth, so fwther
tests with an engine appeared to be advantageous for further
developing the systems and demonstrating their qualities.

A Northrop attack airplane (Air Corps designation, A-l'lA) was
borrowed from the Air Corps early in 1939 to carry out further the
cowling experiments in flight. I:I.‘he nose blower type, described in
2

reference 3, was selected for the first experiment because itm

the easiest to install, and, if it proved. successful, it would. have
the greatest imediate application.

'Ehe chief object of these tests vas to determine the cooling
characteristics of the ceilings. It was realized that there was
little chance for increasing the speed. of this airplane by any
improvmente in the nose shape because the drag contributed by the
NA.C.A.'ccwlin3 is only a mall part of the dragof the entire
airplane.