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Chapter 9: Problem 113

A sail plane with a lift-to-drag ratio of 25 flies with a speed of 50 mph. It maintains or increases its altitude by flying in thermals, columns of vertically rising air produced by buoyancy effects of nonuniformly heated air. What vertical airspeed is needed if the sail plane is to maintain a constant altitude?

Short Answer

Expert verified
The necessary vertical airspeed to maintain a constant altitude is 2 mph.

Step by step solution

01

Without Thermals

Firstly, discuss the scenario when the sailplane is not flying in thermals. The vertical speed of sailplane \( V_d \) (descent rate) without thermals is calculated by dividing the horizontal speed \( V_h \) by the lift-to-drag ratio \( R \). The formula is given by: \( V_d = V_h / R\)
02

Substitute given values

Substitute the provided values into the formula. Given that \( V_h = 50 mph \) and \( R = 25 \), we find: \( V_d = 50 / 25 \) = \( 2 mph \)
03

Conclusion

Conclude that when the sailplane is flying in thermals, the vertical airspeed must be at least the descent rate of the sailplane without thermals. Thus, the necessary vertical airspeed is \( 2 mph \).

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