Monday, November 19, 2018

0.018" matters...

I had a batch of end caps machined for the Carbon tube tank.
This was 4" outer, 0.035 metal liner 0.009  poly bag, and 0.004 gap.
This was all carefully measured and tested, it works well...

I thought I could reuse these end caps in the 4" 035 wall tube, alas I neglected to account for the bag.
The 0.009 on both sides or 0.0018 in diameter is enough that the caps don't seal correctly.....
Grumble Grumble....
I could line the aluminum tube with the bag and continue....


Not a huge deal, but I thought I had enough for 3 sets of flight hardware, now I have zero...
I need to machine new ones...

So even with the loose fit, I thought I'd assemble the tank and  hydro test one.
The end cap retention failed at 420PSI. The cap retaining screws failed in shear.
In hind sight I did not use enough screws, according to the screw stress calculations they should have failed at 390 psi.


So all in all its nice to actually be building and assembling hardware again.

So Mariellen's garden got its first dose of hydro test water, in about 4 years.

Wednesday morning update...
Rebuilt the test tank, used more screws, hydro ed
to 600 PSI without failure.






2 comments:

Robert Clark said...

I wonder if you could do a flight to the 100 km von Karman for suborbital space before doing a fully orbital rocket. Even this is sufficiently challenging that there has been a $1 million prize competition established for a flight to this altitude for a single stage liquid-fueled rocket by a university team.

Accomplishing this altitude can be made easier by using both carbon fiber for the propellant tanks and an aerospike nozzle. Amateur rocketeers working with solid rockets have been building their own carbon fiber casings for a while now. You can probably purchase one at the 4” diameter you need.

Surprisingly, an actual test of an aerospike nozzle still hasn’t been done at near vacuum conditions despite the fact the aerospike has been known of since the 60’s. The highest it has been tested is about 30,000 feet where the air density is still 1/3rd that at sea level. But even getting to 100,000 feet the air density is 1/100th that at sea level where the performance will be at near the vacuum levels. So even getting to this altitude will be a significant.advance in testing the aerospike.

Bob Clark

Monroe said...

I can machine you some caps if you want.