Catapult Research Paper

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Aircraft Catapult
Military aircraft are often required to operate from very short runways, such as aircraft carriers, where the runway length is too short to allow the aircraft to take off conventionally under its own thrust. An aircraft can only take-off once it produces a lift force greater than its weight in order to accelerate vertically. From the Lift equation:
L=1/2 C_L ρAV^2
Where L is the Lift force, C_L the lift coefficient, ρ the air density,A wing surface area and V the velocity. [1] The only variables the can easily be changed without reconfiguring the aircraft is velocity and as such in order to decrease the take-of distance, take-off velocity must be reached in a shorter time period and hence the aircraft acceleration during the
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This equates to 88.45MJ of energy using the equation W=Fx.
The required energy output of the catapult system must be variable. Smaller, lower mass aircraft will require less force to be exerted by the catapult to reach take-off velocity as compared to heavier aircraft with higher take-off velocities. There is a danger of over stressing the aircraft airframe if the exerted forces are too great and consequently reducing the aircraft lifespan.
Steam Catapults
Currently, aircraft carriers with catapult launch systems all use steam catapults. These catapult systems consist of two cylinders mounted below the runway surface. A piston in each cylinder is connected to a shuttle which is free to move in a track along the runway centreline. An aircraft taking off is locked on to the shuttle and then throttles its engines to take-off thrust. Any movement is prevented by a holdback bar. Valves are then opened which release steam into the cylinders, pushing both pistons and propelling the aircraft and shuttle assembly along the track. The hold back bar is disengaged when the steam valves are opened. The aircraft reaches its take-off speed in a much shorter distance due to the force exerted by the catapult. Once the aircraft has taken-off and the piston moved past a steam pressure switch, the steam valves are closed and exhausts
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Ford class aircraft carriers. [9] In this design the aircraft is accelerated by a linear induction motor where the applied force and acceleration can be varied accurately. This allows for smoother acceleration as compared to steam catapults and permits very light aircraft such as UAV to be launched off of aircraft carriers, a feat which it not possible with standard steam catapults. Linear induction motors work similarly to a standard induction motors except that the stator has been un-winded and runs the length of the track. The rotor, instead of being spun around its central axis is rather pulled along the stator by a moving magnetic field. Similarly, the linear induction motor of the EMALS [10] consists of two 100m parallel stators with a rotor built from permanent magnets moving between the stators. The stators are built from sections and only the section next to the rotor is energized at a given moment, reducing power consumption. Furthermore, Hall Effect sensors provide real-time feedback of the rotor velocity and thus the velocity profile during launch can be closely matched to that required of the launching

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