A jet airplane is a feat of engineering. It is amazing that such a big, clunky thing on the ground can be so elegant and efficient in the air. An airplane is meant to fly and not rattle along on the ground. The four forces that govern flight are drag, thrust, weight, and lift. Drag is an aerodynamic force that resists the forward motion of the airplane. Everything on an airplane, like the tail and rudders, interacts with the surrounding air during flight and contributes to drag. Thrust is the force that moves the airplane through the air. The engines on an airplane provide thrust to counteract drag. The third force is weight and is the action of gravity on the airplane. Finally, the fourth force is lift. Lift is the force that moves the airplane from the ground into the air. There are several factors that contribute to lift, including the size and shape of the airplane. The wings of the airplane provide for much of the lift. At takeoff, as the airplane speeds down the runway, the movement of air over and under the wings provides enough lift to overcome the force of weight and cause the plane to fly off the ground. Another factor that contributes to lift is the velocity (forward speed) of the airplane. Increasing velocity means more air flowing over, under, and around an airplane's wings. Moving air creates air pressure, and further, slower air produces higher air pressure while faster air produces lower air pressure. Because of the shape of the wing, the air moving beneath the airplane wing is slower than the air moving over the wing, which results in a difference in pressure and thus lift.
When an airplane speeds down the runway, it eventually reaches the velocity when speed of the air over the wings is high enough that the forces of lift and thrust are greater than the forces of weight and drag, and the airplane takes off into the air. However, the key here is that the airplane has to accelerate down a runway of a certain length to get to the velocity needed to achieve the required lift to take off. What happens when the runway is not long enough? At major airports, runways can range between one to three miles long. Can an airplane take off safely on a short runway? The answer is yes, and you can see fighter jets taking off on short runways on naval aircraft carriers that would normally take longer runways to get airborne.
An aircraft carrier is a warship that acts as a seagoing airbase. During war or military exercises, the job of the aircraft carrier is to deploy and recover naval aircraft. But aircraft carrier runways are less than 1000 feet longβnot the one to three miles that are required to get a plane up the in the air normally. How does a fighter jet on an aircraft carrier reach the velocity required to fly? Airplanes on aircraft carriers use a catapult to reach the velocity required for lift to overcome the force of weight. This is called catapult-assisted takeoff (CATO). Figure 1 shows a jet fighter flying off of the U.S.S. Intrepid.
Figure 1. This image is of an aircraft carrier that used catapult-assisted takeoff to help jets take off.
What is a catapult and how does catapult-assisted takeoff work? A catapult is a device that is used to fling projectiles great distances. It is a compound machine made up of several simple machines. There are various types of catapults, but they all operate on the principle of stored energy. The projectile is flung when the stored energy is released. In aircraft carriers, the catapults are comprised of two pistons, each sitting in a cylinder which lie parallel and next to each other. The cylinders are embedded in the aircraft carrier's deck, and the pistons are attached to a shuttle, an apparatus that sits on the surface of the deck, which is then attached to the jet. When a jet is ready to take off, its front wheels are attached to a slot in the shuttle with a towbar and a holdback bar is attached to the back of the wheels and the shuttle. The pistons are locked into place, and cylinders are filled with steam to a preset pressure. The pilot turns on the jet's engines to develop thrust, and then, the pistons are released. The holdback bar falls away, and the jet is hurled forward. At the end of the runway the towbar pops off, and the jet is released. Watch the video below to see a catapult-assisted takeoff of a fighter jet.
In this aerodynamics science project, you will investigate catapult-assisted takeoff using a model airplane. Can you confirm that a catapult, even in a much smaller model, will affect the flight? How does the catapult-assisted takeoff affect the accuracy of the flight?
Test Condition
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Distance Trial 2
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Distance Trial 5
Fly without launcher
Fly with launcher
| Fly with launcher and throw |
Test Condition
Distance
Trial 1
Distance
Trial 2
Distance
Trial 3
Distance
Trial 4
Distance
Trial 5
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Trial 6
Distance
Trial 7
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Trial 9
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Trial 10
Fly without launcher
Fly with launcher
Fly with launcher and throw
Test Conditions
Fly without launcher
Fly with launcher
Fly with launcher and throw
Equation 1.
