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The Flight of an Aircraft Involves Complex Principles of Physics, from Aerodynamics to the Force Necessary to Overcome Gravity. During Takeoff, an Airplane Needs to Consume a Significant Amount of Energy to Reach Sufficient Speed and Generate Lift.
When you are flying in an airplane, have you ever wondered how much energy is spent to keep it in the air? Although it seems like a simple question, it hides a complex concept of physics that has everything to do with the aerodynamics of flight.
Let’s understand what happens behind this in an easily comprehensible way.
The Exchange of Energy — Lift vs Drag
The engines of an airplane are responsible for propelling the aircraft forward. However, much of that energy does not go directly to keeping the airplane in the air.
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It is used to overcome drag, the air resistance that pushes the airplane backwards while it moves forward.
Lifting, which is what keeps the airplane in the air, does not consume energy directly for forward movement.
The problem is that to generate lift, the airplane ends up creating additional drag, known as induced drag, which causes the airplane to lose speed and efficiency.
The Role of Induced Drag
The big question lies in induced drag, being a side effect of generating lift.
When the airplane gains altitude, it needs to overcome the air and create lift, but this generates extra resistance.
Depending on the speed and altitude of the flight, induced drag can account for up to 80% of the total drag during moments like takeoff or landing, when the airplane’s speed is lower. Even in cruise flights, this percentage remains between 30% and 40%.
This means that of all the energy supplied by the airplane’s engines, a large part is used solely to combat drag and keep the airplane in the air, without moving forward.
Therefore, energy loss occurs primarily in combating induced drag.
How Engineers Try to Minimize This Loss
Aviation engineers have various strategies to reduce the energy loss caused by drag.
One of the most common methods is using high-aspect-ratio wings, like those found on gliders. Long wings create less drag per unit of lift, making flight more efficient.
Another trick used is wingtips, small vertical fins located at the tips of the wings. They help reduce air vortices, which are a major source of drag.
Furthermore, modern airplanes use supercritical wings, designed to improve aerodynamic efficiency at high speeds, such as those of commercial jets.
And there are even more advanced designs, such as aircraft with blended wing-body, which optimize energy use by significantly reducing air resistance.
How Much Energy Is “Lost”?
Although lift itself does not consume energy directly, the production of induced drag is what makes a difference in flight efficiency.
On average, between 30% and 50% of the total thrust of the airplane is used to combat aerodynamic drag, with a large part of it coming from induced drag due to lift.
So the next time you are flying at 35,000 feet (approx. 11 km), remember that a significant portion of the fuel burned is not just pushing the airplane forward but also helping to keep it in the sky.
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