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Jet Propulsion

Lecture - 30

Ujjwal K Saha, Ph. D.Department of Mechanical Engineering

Indian Institute of Technology Guwahati

Prepared underQIP-CD Cell Project

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Rocket Engines

Ariane 5Space Shuttle Columbia

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A rocket propulsion system not only provides the propulsive force but also means of controlling its flight path by redirecting its thrust vector to provide directional control. This is known as Thrust Vector Control (TVC).

Thrust Vector ControlThrust Vector Control

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to change a flight path/trajectoryto rotate a vehicle or change its attitude during flightto correct for deviation from the intended pathto correct for thrust misalignment.

Reasons for TVC

Pitch/Yaw -Simple deflection of thrust vectorRoll – Rotary vanes/separate nozzle.

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Control of Thrust Vector

Pitch Yaw Roll

Pitch Moments: Nose up/down Yaw Moments: Move left/rightRoll Moments: Roll/turn sideways

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Choosing a TVC MethodChoosing a TVC Method

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TVC Methods:TVC Methods:

1. Gimbaled Engine:In this case, the engine has a hinge or a gimbal(a universal joint) that allows rotation about its axis – that is the whole engine is pivoted on a bearing.

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2. Flexible Laminated Bearing:

3. Flexible Nozzle Joint:

The swiveled nozzle changes the direction of throat and nozzle. It is similar to gimbaled engine. The main drawback in using this method is the difficulty in fabricating the seal joint of the swivel since the swivel is exposed to extreme high pressure and temperatures.

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4. Jet Vanes: Jet vanes are small airfoils located at the nozzle exit plane, and behave like ailerons or elevators on an aircraft, and cause the vehicle to change direction. This control system causes a loss of thrust (2 to 3 %), and erosion of vanes.

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5. Jetavators: The system has rotating airfoil shaped collar, and gives an unsymmetrical distribution of gas flow. This provides a side force thereby changing the direction of flight.

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6. Jet Tabs: The system has tabs rotated by hydraulic actuators. Power is supplied from compressed nitrogen. Usually, this type of TVC methods are used in military missiles.

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7. Side Injection: A secondary fluid (gas or liquid) is injected into the exhaust stream to deflect it and thereby changing the thrust vector. The gas is either vented from the main combustion chamber or from an auxiliary gas generator. For liquids, catalyzed monopropellant (e.g., hydrazine, nitrogen tetra-oxide) is used.

8. Vernier Rockets: These are small auxiliary rocket engines, and can provide all attitude control, or just roll control for single engine stages during the main engine burn, and means of controlling the rocket after the main engine shut off.

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TVC Methods & ExamplesGimbal

or hinge

Flexible laminated bearing

Flexible nozzle joint

Jet vanes Jetavator Jet tabs Side injection

Small control thrust

chambers

Four rotating aerodynamic vanes in jet

Sealed rotary joint

Nozzle is held by ring of alternate layers of elastomerand metal

Universal joint suspension for thrust chamber

Rotating airfoil-shaped collar gimballednear nozzle exit

Four paddles rotate in and out of hot gas flow

Secondary fluid injection on one side at a time

Two or more gimbaled auxiliary thrust chambers

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• TVC needs an onboard power source during flight• Two basic implementations - Recirculating & Blowdown• Recirculating

– Working fluid (oil, electricity, gas) is recirculated in a closed loop system

– Ex: Hydraulic pump, Electric generator, gas compressor– Pros - Never runs out (until onboard power supply

does, which usually means the end of the flight anyway); easier pre-flight testing

– Cons - Heavier, more complex• Blowdown

– Working fluid is dumped overboard after use– Ex: Hydraulic accumulator, Electric batteries, gas

pressure vessel, thrusters– Pros - Lighter, simpler– Cons - Limited duration (must estimate total fluid

requirement, add margin)

TVC Power Supply Categories

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References1. Hill, P.G., and Peterson, C.R., (1992), Mechanics

and Thermodynamics of Propulsion, Addison Wesley.

2. Oates, G.C., (1988), Aerothermodynamics of Gas Turbine and Rocket Propulsion, AIAA, New York.

3. M.J.L.Turner, (2000), Rocket and Spacecraft Propulsion, Springer.

4. Sutton, G.P. and Biblarz, O., (2001), Rocket Propulsion Elements, John Wiley & Sons.

5. Zucrow, M.J., (1958), Aircraft and Missile Propulsion, Vol. II, John Wiley.

6. Barrere, M., Jaumotte, A., Veubeke, B., and Vandenkerckhove, J., (1960), Rocket Propulsion, Elsevier.

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