[AR] Re: Intertank coupling design
- From: Robert Watzlavick <rocket@xxxxxxxxxxxxxx>
- To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
- Date: Sun, 13 Oct 2013 17:10:19 -0500
I'm only truing up the tank ends where they attach to the bulkheads, not over
the whole tank length. The tubing as-delivered was 0.120 (1/8 nom.) and I was
able to still have 0.105 left after turning down the OD and ID.
Indestructible will be good for my first liquid attempt. Initial performance
estimates are only about 15k ft since it will be heavy and have a short burn
but that's fine for now.
On Oct 12, 2013, at 17:00, Ben Brockert <wikkit@xxxxxxxxx> wrote:
> 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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