Gravity is the Main Source of Energy for a Heavier Than Air Aircraft

Gravity is the Main Source of Energy for a Heavier Than Air Aircraft

If one were to truly think about the energy consumption of an aircraft flying thought the air, one would quickly realize that dramatically less energy is consumed than would be expected.

When a plane is flying, say straight and level, the thrust generated from its engines must continuously transfer enough energy to overcome drag and create lift. The lift created must continuously counteract the gravitational weight of the craft. This would also be the case if the aircraft were pointed vertically and acting more as a rocket.

Very few aircraft are equipped or capable of sustained powered vertical flight (steady speed or even acceleration)--most if not all are fighter aircraft. The energy consumption of an aircraft in vertical flight is enormous and as a result is usually used in short bursts.

Now if an aircraft in straight and level flight should consume approximately the same amount of energy as one in vertical flight, what constitutes the difference?

I state that gravity is the additional energy source and also serves as the PRIMARY energy source of an aircraft.

Thursday, March 24, 2011

Gliding and Glide Ratio

An aircraft at altitude and without power should free fall to terminal velocity. The aircraft's wings and their corresponding design and shape is the reason that it does not.

When a plane looses power it will be pulled down vertically and fall. This movement can then be used to cause airflow over the wings which will result in lift being generated. The resulting lift and forward movement will dramatically reduce fall and allow the aircraft to land. This is called the glide-ratio--i.e. the ratio of un-powered forward movement to vertical descent (forward to down). In this mode, an aircraft's only source of power is gravity.

A fully loaded 747-400 weighs about 875,000 lbs and has a glide ratio of about 17 to 1--moves 17 units forward for every unit down. Therefor a 747 without power at 36,000 feet (6.82 miles) can fly forward about 115 miles before having to land/crash.

Realife examples:
British Airways 747 glides to out of dust cloud to engine restartBA 747
Airbus A330 flew about 19 minutes without power and landed safely: Airbus A330
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