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Name: Rachel
Status: student
Grade: 9-12
Country: Australia
Date: Summer 2012


Question:
How does the wingspan of a plane affect the ability of the hang time? What is the best way to achieve a longer hang time?



Replies:
Hi Rachel,

I am not sure what you mean by "hang time" with an airplane. I'm going to take a guess that you are talking about the ability of the airplane to stay aloft by gliding alone. For an airplane with an engine not producing power, it can be considered as a glider. Glider (also called sailplane) performance is characterized by a few numbers. One of them is the minimum sink rate. That is the rate at which the glider loses altitude assuming it is flown in the best possible way. A glider pilot will tend to fly at or near the minimum sink airspeed while thermaling (flying in upward moving warm air) in order to achieve the best performance.

The aspect ratio of the wing directly effects its lift and drag. It does this by affecting the production of wing tip vortices. Wing tip vortices both reduce the lift of the wing and increase the drag, both of which negatively impact the minimum sing rate. These vortices occur only at the wing tip, so their relative effects can be reduced by making the wings very long and thin. This is why you see gliders with very long thing wings compared to powered airplanes which tend to have shorter, wider wings.

Regards, John C. Strong


Hi Rachel,

Well, you have got me there! I am mystified by your term "hang time". This term is not used in the field of aerodynamics. Maybe you are referring to how far a plan can glide?

If so, as a general rule, long narrow wings tend to result in greater lift and less drag, resulting in a longer distance covered when gliding.

Perhaps you can re-submit your question with more detail.

Regards, Bob Wilson



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