what forces act on an airplane to keep it at a level altitude?

Answer 1

The force of gravity (its weight) is always acting on the plane and is pulling it down towards the ground.

Additionally, when the plane is flying, there is a lifting force which acts upward on the plane due to the difference in pressures as air travels over the wings.

Since these two forces (weight and lift) are the only ones which act in the vertical direction during level flight, they must be equal in magnitude but act in opposite directions so as to cancel each other out. When the force of lift equals the force of gravity, the net upward/downward force equals zero and the plane does not accelerate...it flies level.

There can, of course, be additional forces acting on the plane (for example, due to the engines thrusting it forward, ...), but these forces act perpendicular to lift and weight and thus do not effect the plane's vertical motion (so the plane might be accelerating forward, but still flying at a constant altitude).

Answer 2

There are lots of little forces acting on an airplane, but if you want the main ones that keep it at a level altitude, then there are two:
1. the weight of the airplane due to gravity (pulling it down)
2. aerodynamic lift from the wings (pushing it up)

Gravity we're all familiar with: any mass is attracted by another mass. In and near the earth, the earth itself pulls masses like rocks and airplanes downwards. The bigger the mass, the more force (we call this its weight).

Aerodynamic lift from the wings (or airfoils, as they're called) happens because of their shape and the angle they're at as they go through the air. The air that goes over the wing is forced to move faster than the air underneath the wing. Faster air has lower pressure than slower air. Thus, there's a force of pressure pushing on the wing upwards from beneath.

When the aerodynamic lift force balances the weight of the plane, it stays at a level altitude.

Answer 3

Four forces act on a plane: Thrust (delivered by the engine); Drag (the friction caused by moving the plane through the air); Weight (same in the air as on the ground); and Lift (provided by the wings as the air flows over them). When thrust equals drag, the plane maintains speed; when thrust is greater than drag, the plane accellerates. When lift is greater than weight, the plane rises; when lift and weight are equal, the plane maintains level flight; when lift is less than weight, the plane descends. Not all the vectors of these forces are exactly opposite each other. For example, the weight vector points directly from the center of mass of the plance to the ground, but the lift vector is typically angled backwards a little, so that it can be broken out into components that are perpendicular and parallel to the weight. As the whole lift vector increases, the part countering weight increases, but so does the part countering thrust, making it harder to go faster.

Answer 4

Gravity acts downward. Lift caused by the flow of air over the wings acts upward and finally Newton's first law of motion is in effect when the aircraft jet engines are on. As the air is sucked into the engines and expelled out the back the aircraft is accelerated forward. This force is called thrust.

Answer 5

I don't think that there are any such forces for level flight. It is the job of the pilot or autopilot to check on the altimeter all the time and adjust the control surfaces to get a zero rate of climb.

Answer 6

Lift and gravity
Thrust and drag

Answer 7

Thrust, drag, lift and gravity.