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Given:
T-38A weighing 10,000 lbf and flying at 20,000 ft
From Fig. P1.1, the maximum Mach number with afterburner ("Max" thrust curve) is M≈1.075. From Table 1.2b, the standard day speed of sound at 20,000 ft is 1036 94 ft/s. Using the definition of the Mach number as MV/a (the instructor may have to give this definition to the students since it is not found in Chapter 1), the velocity is:
V=Ma (1.075) (1036.94 ft/s)=1114.7 ft/s
The maximum lift-to-drag ratio, (L/D), occurs at the point of minimum drag. D850 lhf. Assuming that the airplane is in steady, level, unaccelerated flight, IW=10,000 lbf, and:
(I/D) 10,000/bf/850lbf=11.76
The Mach number where this occurs is M≈ 0.53. The minimum velocity of the aircraft under the given conditions is M 0.34 and is due to the buffet (or stall) limit.
1.2)
Given
T-38A weighing 10,000 lbf and flying at 20,000 ft with "Mil" thrust at M = 0,65
From Eqn. 1.1, the total energy of the aircraft is: E=0.5mV+mgh
The mass of the airplane is given by Eqn. 1.2. m=W/g=10,000lbf/32.174 ft/s² = 310.81 slugs
As in Problem II the velocity of the airplane can be found as
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