Consider this airplane in a full power vertical dive at (a) 30,000 and then (b) 20,000 ft. Prove that at these two altitudes the airplane cannot reach Mach l.

1. From the data shown in Fig. 6.2, estimate the value of the Oswald efficiency factor for the Lockheed C-141A. The wing aspect ratio of the C-141A is 7.9. 2. Since the end of World Warn, various claims have appeared in the popular aviation literature of instances where powerful propeller-driven fighter airplanes from that period have broken the speed of sound in a vertical, power-on dive. The purpose of this problem is to show that such an event is technically not possible. Consider, for example, the Grumman F6F-3 Hellcat, a typical fighter from World War II. For this airplane the zero-lift drag coefficient (at low speeds) is 0.0211, the wing plan form area is 334 ft2, and the gross weight is 12,44llb. It is powered by a Pratt and Whitney R-2800 reciprocating engine that, with supercharging to an altitude of 17,500 , produces 1500 horsepower. Consider this airplane in a full power vertical dive at (a) 30,000 and then (b) 20,000 ft. Prove that at these two altitudes the airplane cannot reach Mach l.

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