Preliminary Model Tests of a Wing-Duct Cooling System for Radial Engines, Special Report

Wind-tunnel tests were conducted on a model wing-nacelle combination to determine the practicability of cooling radial engines by forcing the cooling air into wing-duct entrances located in the propeller slipstream, passing the air through the engine baffles from rear to front, and ejecting the air through an annular slot near the front of the nacelle. The tests, which were of a preliminary nature, were made on a 5-foot-chord wing and a 20-inch-diameter nacelle. A 3-blade, 4-foot-diameter propeller was used. The tests indicated that this method of cooling and cowling radial engines is entirely practicable providing the wing of the prospective airplane is sufficiently thick to accommodate efficient entrance ducts , The drag of the cowlings tested was definitely less than for the conventional N.A.C.A. cowling, and the pressure available at low air speed corresponding to operation on the ground and at low flying speeds was apparently sufficient for cooling most present-day radial engines.