Rocket Propulsion
Contents:
Review
Types of Rockets
Examples
Whiteboards
Microsoft Encarta
Rocket Propulsion
So far we have:
Impulse = Ft = mv
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
Ft
=
mv
Which Rocket Accelerates faster?
Demo F14
Rocket Propulsion
If we re-arrange this
formula:
mv = Ft
t
t
Rocket Propulsion
You get
F = mv
t
Where:
F = Engine thrust (N)
m = Fuel burn rate (kg/s)
t
v = Exhaust velocity (m/s)
Rocket Propulsion
Solid Fuel Engine:
Microsoft Encarta
Rocket Propulsion
Solid Fuel Engine:
Thrust of the Engine:
F = mv
t
Big v means big F
Big v also means lots of
pressure
Danger Will Robinson!
Microsoft Encarta
Estes
Lookout!
m = .5 kg, Ft = 20 Ns
Ft = m v
20 Ns = .5kg v
v = ? (x 2.237 for mph)
Estes
Impulse Area under F vs t graph
100 N
5.0 s
Impulse is area under = (40 N)(6.0s) = 240 Ns
Whiteboards
1|2|3
What is the impulse?
100 N
5.0 s
Average F = 70 N, t = 8.0 s, Impulse = (70 N)(8.0 s) = 560 Ns
560 Ns
What is the impulse?
100 N
5.0 s
Impulse = (40 N)(3.0 s) + (70 N)(5.0 s)= 470 Ns
470 Ns
What is the impulse of the D12 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
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?
Ft = mv
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?
Ft = mv
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
Whiteboards
1|2|3|4|5|6|7
A certain rocket engine burns .
0352 kg of fuel per second with an
exhaust velocity of 725 m/s. What
thrust does it generate?
Ft = mv
F(1 s) = (.0352 kg)(725 m/s),
F = 25.5 N
25.5 N
The Saturn Vs 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?
Ft = mv
(33.82 x 106 N)(1 s) = m(2254.7 m/s),
m = 15,000 kg
Burn Rate = 15,000 kg/s
15,000 kg/s
A D12 engine generates 11.80 N of
thrust burning fuel at a rate of .
0143 kg/s. What is the exhaust
velocity?
Ft = mv
(11.80 N)(1 s) = (.0143 kg)v,
v = = 825.2 m/s
825.2 m/s
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?
Ft = mv
F(2.74 s) = (.145 kg)(890 m/s),
F = 47.1 N
47.1 N
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
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 )> =
(.235 kg)(a), a=44.8 N/.235 kg=191 m/s2
2
initial = 191 m/s/s
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 )> =
(.090 kg)(a), a=44.8 N/.090 kg=514 m/s2
2
final = 514 m/s/s
