Rocket Propulsion Contents Review Types of Rockets Examples

Rocket Propulsion Contents: • Review • Types of Rockets • Examples • Whiteboards © Microsoft Encarta

Rocket Propulsion So far we have: Impulse = F t = m v F = Force (N) t = Elapsed time (s) m = Mass (kg) v = Change in velocity (m/s)

Rocket Propulsion So: • F = engine thrust • t = time to burn fuel • m = mass of fuel burned • v = exhaust gas velocity F t = m v

Which Rocket Accelerates faster? A Demo – F 14 B

Rocket Propulsion If we re-arrange this formula: m v = F t t t

Rocket Propulsion You get F = Engine thrust (N) F = m v m = Fuel burn rate (kg/s) t t Where: v = Exhaust velocity (m/s)

Rocket Propulsion Solid Fuel Engine: © Microsoft Encarta

Rocket Propulsion Solid Fuel Engine: Thrust of the Engine: F = m v t • Big v means big F • Big v also means lots of pressure • Danger Will Robinson! © Microsoft Encarta

© Estes

Lookout! m =. 5 kg, F t = 20 Ns F t = m v 20 Ns =. 5 kg v v = ? (x 2. 237 for mph) © Estes

Impulse – Area under F vs t graph F 100 N t 5. 0 s Impulse is area under = (40 N)(6. 0 s) = 240 Ns

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What is the impulse? F 100 N t 5. 0 s Average F = 70 N, t = 8. 0 s, Impulse = (70 N)(8. 0 s) = 560 Ns W

What is the impulse? F 100 N t 5. 0 s Impulse = (40 N)(3. 0 s) + (70 N)(5. 0 s)= 470 Ns W

What is the impulse of the D 12 engine? Impulse = (10. N)(1. 73 s-0. 11 s) + (28 N-10 N)(0. 42 - 0. 21) = 19. 98 Ns (about 20 Ns) 20 Ns W

Rocket Propulsion Liquid Fuel Engine: • How do you keep it from tipping? • Why the “steam” coming off? © Microsoft Encarta

Saturn V Rocket - Apollo missions Escape Tower Command Module L. E. M Third stage Second stage First stage Saturn V Animation (Flash in IE)

Rocket Propulsion Example 1: A rocket burns fuel at a rate of 1. 2 kg/s, with an exhaust velocity of 1250 m/s. What thrust does it develop? F t = m v v = 1250 m/s m = 1. 2 kg t = 1 s (F)(1 s) = (1. 2 kg)(1250 m/s), F = 1500 N

Rocket Propulsion Example 2: A model rocket engine develops 12 N of thrust with an exhaust velocity of 718 m/s. What is its fuel burn rate? F t = m v F = 12 N v = 718 m/s m = ? kg t = 1 s (12 N)(1 s) = m(718 m/s), m =. 0167 kg Burn rate =. 0167 kg/s

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A certain rocket engine burns. 0352 kg of fuel per second with an exhaust velocity of 725 m/s. What thrust does it generate? F t = m v F(1 s) = (. 0352 kg)(725 m/s), F = 25. 5 N W

The Saturn V’s first stage engines generated 33. 82 MN of thrust (33. 82 x 106 N) with an exhaust velocity of 2254. 7 m/s. What was its fuel burn rate? F t = m v (33. 82 x 106 N)(1 s) = m(2254. 7 m/s), m = 15, 000 kg Burn Rate = 15, 000 kg/s W

A D 12 engine generates 11. 80 N of thrust burning fuel at a rate of. 0143 kg/s. What is the exhaust velocity? F t = m v (11. 80 N)(1 s) = (. 0143 kg) v, v = = 825. 2 m/s W

A model rocket has a total mass of 235 grams, 145 grams of which is fuel. The engine burns the fuel in 2. 74 s, with an exhaust velocity of 890 m/s. What thrust does the engine generate? F t = m v F(2. 74 s) = (. 145 kg)(890 m/s), F = 47. 1 N W

A model rocket has a total mass of 235 grams, 145 grams of which is fuel. The engine burns the fuel in 2. 74 s, with an exhaust velocity of 890 m/s. What are the initial and final rocket masses? F = 47. 1 N Uh, initial =. 235 kg Final =. 235 kg -. 145 kg =. 090 kg . 235 kg and. 090 kg W

A model rocket has a total mass of 235 grams, 145 grams of which is fuel. The engine burns the fuel in 2. 74 s, with an exhaust velocity of 890 m/s. What is the initial rocket acceleration? F = 47. 1 N mo =. 235 kg, m =. 090 kg, <F>=ma (hint) <47. 1 N - (. 235 kg)(9. 8 m/s 2)> = 2 (. 235 kg)(a), a=44. 8 N/. 235 kg=191 m/s initial = 191 m/s/s W

A model rocket has a total mass of 235 grams, 145 grams of which is fuel. The engine burns the fuel in 2. 74 s, with an exhaust velocity of 890 m/s. What is the final rocket acceleration? F = 47. 1 N mo =. 235 kg, m =. 090 kg, <F>=ma (hint) <47. 1 N - (. 090 kg)(9. 8 m/s 2)> = 2 (. 090 kg)(a), a=44. 8 N/. 090 kg=514 m/s final = 514 m/s/s W