Thrust

E80 Static Motor Test

Spring 2009

Forces on a Rocket

http://www.grc.nasa.gov/WWW/K-12/rocket/rktth1.htmlhttp://www.grc.nasa.gov/WWW/K-12/rocket/rktth1.html

The Question

• In the event of a crash landing of your rocket, what will be the effect on the instruments inside the rocket?

(Translation)

• What is the velocity of impact?

• What is the impulse response of the rocket structure?

Solid rocket engine

Specific impulse

Static Motor Test

Static Motor Test

Static Motor Test

0T e e e eqF mV P P A mV

final initial

burn burn

m m mm

t t

,T averageeq

FV

m

Thrust Analysis

KINETICS(Non equilibrium processes)

Fuel Burn Rate

m

THERMODYNAMICS(Equilibrium processes)

Exit conditions from nozzle

ePeV

Kinetics of Solid Fuel Combustion

4 4 2 3 3 2 2( ) ( ) ( ) ( ) ( ) ( )6 10 4 2 3 12s s s g g gNH ClO Al Al O AlCl N H O

burnsfuel VAm

ntburn kPV

!!!!!!ENERGY

Thermodynamics of Flow Processes

212

constant ( )

constant ( )

AV mass balance

h V energy balance

Isentropic Flow through Nozzles

21dA A

MadV V

0dA

dV

0dA

dV

0dA

dV

For subsonic flow (Ma<1)

For supersonic flow (Ma>1)

For sonic flow (Ma=1)

Isentropic Flow of Perfect Gas Through Converging-Diverging Nozzle

12

1

2* 2

11

1

21

e

e

e MaMaA

A

Isentropic Flow of Perfect Gas Through Converging-Diverging Nozzle

12

1

2* 2

11

1

21

MaMaA

A

Rocket thrust summary

E80 Static Motor Test Lab

1. Calibrate Load Cell2. Measure Thrust Curve of Rocket Motor3. Measure Average Mass Flow Rate4. Compute combustion pressure assuming

isentropic nozzle flow. Model burn rate of rocket fuel.

5. Estimate the impact velocity of your rocket.