special feature
The simplicity of flight
P A N E L   T H R E E
Finesse & Power
For the horizontal flight of a plane,
the thrust of the engines is equal to the drag, while the lift is equal to the weight. The ratio of lift to drag is known as the finesse.
For a jumbo jet the finesse is 15
at cruising speed.
If the engines were to run out of fuel at a height of 12km, a jumbo jet could rely on its finesse to glide 180km to a landing.
v = velocity
w = weight (lift)
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The Equations of Flight
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How powerful do the engines need to be?
Power is the energy expended in an action. We calculate the power required to achieve flight like this: velocity by drag
drag = w ÷ finesse
= 300 tonnes ÷ 15
= 20 tonnes (200,000 newtons)
So, the power required
= v x drag
= 250 x 200,000 newtons
This represents 50,000 kilowatts