The Forces on an Airplane

Four Main Forces

Lift, Weight, Thrust, and Drag

Weight, Lift, Thrust, Drag

Weight

Thrust

Lift

Drag

Weight is a force that is directed toward the center of the Earth. The magnitude of the weight depends on the mass of all the airplane parts, fuel, and any payload on board. A major problem in flying is trying to overcome weight. This is done by lift.

Lift overcomes the downward force caused by weight and gravity. Lift is generated by the wings and the forward motion of the airplane.

Thrust is generated by the engines on the airplane. Paper airplanes don’t have continuous thrust, so they fall to the ground. For the plane to move forward, the thrust force must be greater than the force made by drag.

The force of drag is caused by air resistance, and is affected by the shape and velocity of the aircraft. Would a box shaped airplane have a large or small drag force? How do you know?

Forces Affect Each Other

• Forces acting in the same or opposite directions have an affect on one another.

• Thrust is used to overcome drag, while lift overcomes the weight of the aircraft.

Can This Plane Fly?

Weight = 8,000 Newtons

Lift = 5,000 Newtons

Would this plane be able to fly?

Raise your hand!

How Do They Fly?

• The design of the wing (an airfoil) causes air over the wing to move faster than the air under the wing. This creates a high pressure system under the wing. This is Bernoulli’s Principle!

• The high pressure underneath the wing creates lift. What direction is the lift force in?

Remember this?

Bernoulli’s Principle

• The toilet paper unrolled because of Bernoulli’s Principle. Air moves very fast over the top of the toilet paper, creating a high pressure system under the paper, allowing it to move forward and stay level.

This guy LOVES Bernoulli’s Principle!

Different Types of Airplanes

Airplanes made for speed

Planes made for stealth bombing by the military

Amphibian Airplanes

Paper airplanes

Paper Airplanes

• Now, you get to make a paper airplane.

• Try and make one with a design that will allow maximum flight time and distance!

• If you throw it in the classroom, you will not be allowed to participate. We will just be building them today.