- Thrust
**Thrust**is a reaction force described quantitatively by Newton's Second and Third Laws. When a system expels or acceleratesmass in one direction the accelerated mass will cause a proportional but opposite force on that system.**Examples**A

fixed-wing aircraft generates forward thrust when air is pushed in the opposite direction of flight. This can be done in several ways including by the spinning blades of apropeller , or a rotating turbine pushing air out the back of ajet engine , or by ejecting hot gases with arocket engine . The forward thrust is proportional to themass of the airstream multiplied by thevelocity of the airstream. Reverse thrust can be generated to aid braking after landing by reversing the pitch of variable pitch propeller blades, or using a thrust reverser on a jet engine.Rotary wing aircraft andthrust vectoring V/STOL aircraft use engine thrust to support the weight of the aircraft, and vector some of this thrust fore and aft to control forward speed.A

motorboat generates thrust (or reverse thrust) when the propellers are turned to accelerate water backwards (or forwards). The resulting thrust pushes the boat in the opposite direction to the sum of themomentum change in the water flowing through the propeller.A

rocket 's mass is propelled forward by a thrust force equal to, and opposite of, the time-rate of momentum change of the exhaust mass accelerated from the combustion chamber through the rocket engine nozzle. This is the exhaust velocity with respect to the rocket, times the time-rate at which the mass is expelled, or in mathematical terms::$mathbf\{T\}=frac\{dm\}\{dt\}mathbf\{v\}$ where:

***T**is the thrust generated (force); some texts use the symbol F_{th}

* $frac\; \{dm\}\; \{dt\}$ is the rate of change of mass with respect to time (fuel burn rate);

***v**is the exhaust velocity.Of course, for a launch the thrust at lift-off should be more than the weight, and with a fair margin, because a "slow launch" would be very inefficient.

Each of the three

Space shuttle main engine s can produce a thrust of 1.8 MN, and each of its two Solid Rocket Boosters 14.7 MN, together 39.4 MN. Compare with the mass at lift-off of 2,040,000 kg, hence a weight of 20 MN.By contrast, the

simplified Aid for EVA Rescue (SAFER) has 24 thrusters of 3.56 N each.In the air breathing category, the AMT-USA AT-180 jet engine developed for

radio-controlled aircraft produce 90 N (20 Lb_{f}) of thrust. [*cite web*] The GE90-115B engines fitted on the

url = http://usamt.com/Mel/comm/comm_products.html

title = AMT-USA jet engine product information

accessdate = 2006-12-13Boeing 777 -300ER, recognized by theGuinness Book of World Records as the "World's Most Powerful Commercial Jet Engine," have a tested thrust of 569 kN (127,900 lb_{f}).**References****ee also***

Aerodynamic force

*Gimballed thrust , the most common thrust system in modern rockets

*Thrust-to-weight ratio

*Thrust vectoring

*Tractive effort

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