Lecture 4

Lecture 4 - Lecture 4 Aircraft Propulsion D.Toohey Image...

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Lecture 4 Aircraft Propulsion Image Courtesy of USAF 96 D.Toohey
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Aircraft Propulsion Systems 4 main categories – Piston Engines • Otto and diesel cycle engines • Normally drive propellers – Jet engines • Turbojets • Turbofans • Turboprops • Pulse jets • Ram jets – Rocket engines • Very high specific fuel consumption • Only practical for hypersonic applications – Electric motors • Quiet • Problems with energy storage Image Courtesy of NASA 97 D.Toohey
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Piston Engines Overview • T: Thrust • V: Velocity • P AV : Power Available • BHP: brake-horse- power, also called shaft- horse-power, SHP η p : Propeller efficiency P AV = η p BHP ( ) = TV 98 D.Toohey
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Piston Engines Overview A piston engine produces work by turning a propeller. It does not generate thrust directly. Power generated by engine is converted into propulsive power by the propeller. Propellers will never be able to convert all engine power into propulsive power. We can relate the ratio of propulsive power (power available to the aircraft) to the engine power by the propeller efficiency. In this class we 1often assume constant propeller efficiency. When this is true, how do P AV and thrust vary with velocity for a constant BHP (Constant throttle setting, constant altitude, temperature)? 99`q` D.Toohey
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Four stroke Otto Cycle 1. Intake stroke 2. Compression Stroke 3. Power Stroke 4. Exhaust Stroke Constant volume heating P V 4 1 2 3 100 D.Toohey
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Factors Affecting Power Output of Piston Engines Fuel to Air ratio – Too rich and combustion may not be complete – Too lean and combustion might not take place Max RPM – Increasing RPM will increase power output, but there are limits. – Max values for typical engines are 2200 to 3500 RPM Temperature – At higher air temperatures (hot day) the SHP will decrease Altitude – As altitude increases, power output decreases 101 D.Toohey
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Altitude Effects on Power Output Charge per stroke – Quantity of air in introduced to cylinder controls amount of heat released. – Depends on the intake pressure, also called the manifold
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This note was uploaded on 02/02/2011 for the course MAE 154s taught by Professor Tooney during the Spring '09 term at UCLA.

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Lecture 4 - Lecture 4 Aircraft Propulsion D.Toohey Image...

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