## Thrust Augmentor Calculation Help

Moderator: Mike Everman

grant_gibson45
Posts: 4
Joined: Sun Mar 02, 2008 2:31 pm

### Thrust Augmentor Calculation Help

Hi,
I am new to the forum, although I have read many of the posts on here, and I know the subject of thrust augmentors comes up quite alot. However I need help fairly soon as I am writing up my university dissertation.

I have dimensions of a converging-diverging augmentor however I have 2 main questions.

How can I predict the thrust increase obtained from the augmentor because I tried working from first principles assuming 1-D isentropic flow, but I don't know the temperature of exhaust gas and velocity at exhaust exit to calculate mach no.

Secondly, I have devised an experiment to investigate the optimum distance from the exhaust tip to the throat of the augmentor and I am supposed to say that students would measure peak thrust against distance from exhaust tip to the throat of the augmentor. Then compare the results they got with a theoretical calculation. But can this "optimum" distance be calculated theoretically ? Is there in fact an optimum distance or am I missing something here.

I really hope someone can help as I am stuck at this point in my write up, because I obviously need to know the maximum thrust output to safely design a clamp.

Cheers

Grant

Al Belli
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Joined: Thu Oct 09, 2003 10:36 pm
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Location: Pennsylvania - USA

### Augmentor calculations

Hi,

See Bruno's post on thrust augmentors in the FAQ section of this site.

You can expect 1.8 to 2 times thrust augmentation.

Al Belli

WebPilot
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### V-1 exhaust gas velocity at startup ...

Hi Grant,

You are living a bit 'on the edge', eh?
Grant wrote: How can I predict the thrust increase obtained from the augmentor
because I tried working from first principles assuming 1-D isentropic flow,
but I don't know the temperature of exhaust gas and velocity at exhaust
exit to calculate mach no.
I can help you a little bit.

F. Shultz-Grunow did the calculation for the V-1.

He did not plot this in his paper, but I did, here:

You may wish to visit my thread, Dimensionless Space and Time.

I cannot help you with the thrust augmentor, because I do not believe
in them. At startup they may help, but then they just create a lot of drag
as the vehicle accelerates to higher velocities.

Then, it's better to just 'jettison' them.

Good Luck with your defense.