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MILNET Brief
  Jet Engines




Jet engines, or more properly, turbine engines, are based upon the idea of a central shaft connected to canted blades mounted like a wheel, one at the front and one at the rear. These wheels are called turbines. The front turbine is called the compressor, and its job is to take air into the engine, and compress it to high pressures. A combustion chamber area takes this compressed air, adds fuel to it, and the fuel ignites. The fuel and air mixture provides a rearward thrust, which blows out the back, as well as turns the rear turbine. The turning rear turbine rotates on the central shaft, and thus spins the front turbine bringing in more air.


At some point this process reaches a point where an equilibrium is met, and the engine will produce no more power per RPM.


Thus designers have added other devices to increase the thrust as need, for example, an afterburner, which injecrts raw fuel (at dangerously prodigious rates) directly into the outlet area. The afterburner gobbles fuel at alarming rates, so pilots do not select the afterburner for normal cruise, relying upon this additional thrust only for takeoff and high dash capability and then usually for only short moments to create acceleration.


Another more efficient technique is to add larger turbines at the front which blow air by the outside of the engine, cooling as well as providing high "bypass" air at the rear for additional thrust. These are called turbo-fan engines.

More modern aircraft and engines are designed with thrust to weight ratios that allow the aircraft to cruise at supersonic without the necessity to use the afterburner.

The table below lists a few of the U.S. military jet aircraft engines used, with a navigational link that jumps down to an image of that engine located below the table:

Aircraft
 Engine Manufacturer
 Engine Designation
F-100, F101, F-102, B-52, U-2, KC-135
 Pratt & Whitney Aircraft
 J-57
F-104, F-4
 General Electric
 J-79
SR-71
 Pratt & Whitney Aircraft J-58
DC-10 Extender and add-on to other refueling aircraft
 Pratt & Whitney Aircraft PW4000
F-16, F-15
 General Electric
 GE-F100
PW-F100
F-18
 General Electric
 F400-GE-400/402
F-22
 Pratt & Whitney Aircraft
 F119-PW-100
C-5
 General Electric
 TF-39

Note:  Some engines are dual sourced, that is, P&WA may supply the first round of engines, but the military has second sourced to GE, or visa-versa.  This keeps the engine manufacturing industry balanced and ensures the military is not at the mercy of a single source.


Illustrations/Drawings/Photos













Pratt & Whitney F100 Engine Used in F-15 Eagle and F-16 Fighting Falcon (USAF)





GE F100 Engine Used in F-15 Eagle and F-16 Fighting Falcon (USAF)




GE F404-GE-F400 Engine Used in A/F-18 Hornet (U.S. Navy and Marines)





Pratt & Whitney F119-PW-F100 Engine
Powers the USAF F-22 at Supercruise (supersonic without engaging afterburner)



Also features a "vectored thrust" nozzle which points the engine's thrust according to flight control inputs



GE J-79 With Afterburner
(F-104 Starfighter and F-4 Phantom II)



P&WA PW4000 TurboFan Jet Engine


Used on  Boeing 767-200, Airbus A330-200
and USAF/NATO Military In-Air Refueling Aircraft



GE TF-39 Engine used on the giant C-5A Military Transport
Sources:
  1. An Introduction to Air Breathing Engines - A  Primer, Aircraft Engine Design.com, Jack D. Mattingly, 2006, AIAA
  2. J57 Turbojet Engine, Pratt & Whitney Aircraft
  3. J58 Turbojet Engine with Afterburner, Pratt & Whitney Aircraft
  4. F100 Jet Engine, Pratt & Whitney Aircraft
  5. PW4000 Jet Engine, Pratt & Whitney Aircraft
  6. F119 Jet Engine, Pratt & Whitney Aircraft
  7. GE Aviation, Military Jet Engines
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