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Estes A8 engines thrust curve change?

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John Crane

Feb 1, 2021, 11:44:05 PM2/1/21
Does anyone know if Estes changed the thrust curve of the A8 engines?
A tech doc from the 70's shows only a spike for boost. Today's website
shows a spike followed by a flatter sustaining thrust like the B and C

Was the 70's doc incorrect, or was that how they made them in the 70's?


DH Barr

Feb 2, 2021, 9:21:59 AM2/2/21
Couldn't speak to whether or not the 70's version was correct, but there have been several adjustments in measurement and design over the years.

John Crane

Feb 2, 2021, 1:24:13 PM2/2/21
The question arose when I tried to update the thrust curve data for my
Model Rocket Performance program.

The experimental data in Estes TR-11 shows well-built Alpha rockets
reaching 116m on average with A8-5 engines. My program calculates this
within +-2m using the original spike curve.

However, when I upgraded the thrust data for the 'new' A8-5 engines, I
get 154m. Off by more than 32%.

Since the program works well for other engines; I think it's a data
issue and not the code.

Which leads me to believe old A8 engines had only boost thrust and not
sustainer thrust.

I guess for now, I'll just keep both old and new A8 engines in the database.


David Schultz

Feb 2, 2021, 7:13:41 PM2/2/21
I dug up an Estes publication ("The Classic Collection") which has a
copy of TN-1 in it. It shows a thrust curve for the A8 that matches that
for the B4 except for that long tail. Peak thrust of about 13N and all
done in 0.3 seconds.

So it is possible that they really were made that way. The B4 would just
be an A8 with extra BP for some end burning action.

When and why that changed I have no idea. The test data on the NAR web
site says it was collected in 1995 so sometime before then.

David Schultz
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