[AR] Re: Intertank coupling design
- From: Ben Brockert <wikkit@xxxxxxxxx>
- To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
- Date: Sat, 12 Oct 2013 16:00:57 -0600
On Fri, Oct 11, 2013 at 6:17 PM, Robert Watzlavick
<rocket@xxxxxxxxxxxxxx> wrote:
> Thanks for the suggestions. The tank walls only need to be around 0.05 or so
> to take the 500 psi load with a 1.5 FS. I went with 1/8 wall instead of 1/16
> because I figured it would have better tolerance to handling damage and also
> be easier to true up round.
>
For reference, Stig and Stiga were 1/8", and they were 15.25"
diameter. I don't think I ever took video of it because I was usually
lifting, but the normal way we uprighted the things was to hook straps
to the crane all the way at one end, manually pick up the other end 20
or however many feet away, then crane up the strap end as quickly as
possible while walking the engine end.
What I'm saying is that it was super sturdy even unpressurized at that
diameter, so a much smaller rocket with the same wall thickness is
going to be nearly indestructible when it comes to handling damage.
I'd be surprised if it was round enough away from the jaws to be able
to turn down the OD and keep a consistent thickness. While I'm not
anti-optimization in the way John is, I would say that turning down
the tanks is a waste of time for this first effort.
> Your point about the joint strength in general is well taken. I need an
> estimate of the flight loads ideally. Since its not actively controlled, they
> should be small except for weather vaning right after launch.
>
For a finned rocket the highest aerodynamic load is when the fins come
off. There's been a long history of unguided liquid rockets flying out
of the Lucerne test sites, going transonic near the very end of their
burns, and ripping the fins off and going sideways. So I'd put more
effort into making sure the fins stay on (and, if composite, stay
laminated) than doing complex things at other junctions in the rocket.
Ben
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