Introduction to Jet Propulsion

1
Introduction to Jet Propulsion

• P M V Subbarao
• Professor
• Mechanical Engineering Department

Strong and Reliable Muscles for the Aircraft
2
Global Momentum Analysis
3
Momentum Equation
Vac
Vjet
pinlet
pexit
Newtons Second Law of Motion
Reynolds Transport Theorem
4
For a frictionless flight, pressure forces are
only the surface forces
Steady state steady flow
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Pressure Thrust
Momentum Thrust
At design cruising conditions Pressure thrust
is zero.
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Generation of Thrust The Capacity
Thrust
f Fuel-air ratio
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Dynamic Equilibrium Cruising Vehicle
For a cruising vehicle
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Drag on Aircraft
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Generation of Lift
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Drag Coefficient of an Air Craft
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Generation of Lift
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Drag Coefficient of an Air Craft
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Lift - to - Drag Ratio
Flight article Scenario L/D ratio
Virgin Atlantic GlobalFlyer Cruise 37
Lockheed U-2 Cruise 28
Rutan Voyager Cruise4 27
Albatross 20
Boeing 747 Cruise 17
Common tern 12
Herring gull 10
Concorde M2 Cruise 7.14
Cessna 150 Cruise 7
Concorde Approach 4.35
House sparrow 4
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Minimum Drag Coefficients Minimum Drag Coefficients Minimum Drag Coefficients Minimum Drag Coefficients Minimum Drag Coefficients
Aircraft Type Aspect Ratio CDmin
RQ-2 Pioneer Single piston-engine UAV 9.39 0.0600
North American Navion Single piston-engine general aviation 6.20 0.0510
Cessna 172/182 Single piston-engine general aviation 7.40 0.0270
Cessna 310 Twin piston-engine general aviation 7.78 0.0270
Marchetti S-211 Single jet-engine military trainer 5.09 0.0205
Cessna T-37 Twin jet-engine military trainer 6.28 0.0200
Beech 99 Twin turboprop commuter 7.56 0.0270
Cessna 620 Four piston-engine transport 8.93 0.0322
Learjet 24 Twin jet-engine business jet 5.03 0.0216
Lockheed Jetstar Four jet-engine business jet 5.33 0.0126
F-104 Starfighter Single jet-engine fighter 2.45 0.0480
F-4 Phantom II Twin jet-engine fighter 2.83 0.0205 (subsonic) 0.0439 (supersonic)
Lightning Twin jet-engine fighter 2.52 0.0200
Convair 880 Four jet-engine airliner 7.20 0.0240
Douglas DC-8 Four jet-engine airliner 7.79 0.0188
Boeing 747 Four jet-engine airliner 6.98 0.0305
X-15 Hypersonic research plane 2.50 0.0950
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Propulsive Power or Thrust Power
Measure of compactness of a jet engine
Specific Thrust S
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Measure of fuel economy
Thrust Specific Fuel Consumption TSFC
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Aviation Appreciation
Propulsion Efficiency
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Jet Characteristics

• Quantities defining a jet are
• cross-sectional area
• composition
• velocity.

Of these, only the velocity is a truly
characteristic feature and is of considerable
quantitative significance.
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Jet Characteristics of Practical Propulsion
Systems
System Jet Velocity (m/s)
Turbofan 200 - 600
Turbojet (sea-level, static) 350 - 600
Turbojet (Mach 2 at 36000 ft) 900 - 1200
Ramjet (Mach 2 at 36000 ft) 900 - 1200
Ramjet (Mach 4 at 36000 ft) 1800 - 2400
Solid Rocket 1500 2600
Liquid Rocket 2000 3500
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Nozzle Steady State Steady Flow
in
jet
First Law
No heat transfer and no work transfer No Change
in potential energy.
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Combined analysis of conservation of mass and
first law
A SSSF of gas through variable area duct can
interchange the enthalpy and kinetic energy as
per above equation.
Consider gas as an ideal and calorically perfect.
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Isentropic expansion of an ideal and calorically
perfect gas.