Ben,
You gave me an interesting idea. I tried #2 below previously and it
worked OK as a fuel tank but it was quite a bit heavier than I wanted,
mainly because the end cap was flat and thick and had to accommodate the
o-ring seal. A hole down the center would have been used for passing
tubes and wires through the tank.
http://www.watzlavick.com/robert/rocket/rocket1/photos/dsc_9168m.jpg
http://www.watzlavick.com/robert/rocket/rocket1/photos/dsc_9167m.jpg
I don't have any welding capability yet I was thinking of a variant on
it where you still have the through bolts but it is sealed with a small
weld bead at the ends, far enough away from the bolts that the HAZ
doesn't impact the strength. So basically use the weld just for sealing
and let the bolts take the load. Stat-O-Seals could be used to seal
around the bolts, although for cryo use, you might need something
better, like a tiny spring energized seal or just a metal crush washer.
I'd like to find a way to make propellant tanks be part of the airframe
since they're nice and thick already.
-Bob
On 8/4/20 2:49 PM, Ben Brockert wrote:
Rereading your message this is probably more specific than what you're
asking, but I already wrote it, so...
There's basically three ways to hold bulkheads and nozzles in a
cylindrical tube without sticking out too much (like a bolted flange
would):
1) Circlips. You have a thick walled tube, you put a groove in it that
holds a circlip. The bulkhead goes in and is kept from popping out by
loading the circlip. Away from the groove you can turn the tube down
if you want to optimize weight. This is more common in aluminum motor
casings.
2) Through bolts. Bulkhead goes in, and is bolted in place from the
outside. You have to do the math right on what the bolts can hold in
shear. This also weakens the wall of the tube, but possibly not as
much as the circlip approach if the bolts are strong and distributed
well, usually in multiple rings.
In both case 1 and 2 the parts are commonly sealed with o-rings and
can be disassembled. Additional sealant can be used but makes
disassembly harder.
3) Welding. On whichever end you don't need to reopen, or both if you
can cast the fuel in place through the nozzle, all the components are
welded. More common in solids or liquid thrust chambers than hybrids.
A flat bolted flange will work, and is probably fine if the diameter
of the rocket body is larger than the diameter of the rocket motor
assembly. But flat bolted flanges as shown in the presentation are
usually only used in test stand engines, not ones for flight. I guess
I don't know what yours is for, so maybe that's fine. It is fairly
common to have a bolted flange on the top of a liquid rocket engine
thrust chamber, but they tend to be much more optimized with one part
threaded (so that the bolt circle can be closer to the wall) rather
than the nut and bolt approach shown in the presentation.
Do you have a mechanical engineer on your project? They are very
useful. Worth their weight in snickers and coffee.
On Tue, Aug 4, 2020 at 8:10 PM Jack Hanna <jackhannaofficial@xxxxxxxxx> wrote:
And i'm back with some more potentially "stupid" questions about the general
design of a hybrid, focusing on the good ol' bulkheads today
: - I assume the design is similar to this, with the two peices pushing
together with an o-ring in the middle to create a seal.
- What o-rings can handle the pressures / temps / low temps of working with
nitrous / paraffin?
Continuing on with that, - how do you attach it the the outside body of the
rocket? Just thinking out loud would it be some sort of rivet or bolt on each
side of the chassis, or are there other ways?
- Similar to that, how do you keep the fuel in place, or do you not? Are
there out of body rivets or what do you do to keep the inside bits secured to
the outside?
- What materials are usually made for the body of the combustion chamber, ones
that can handle the heat and pressure?
https://www.slideshare.net/RichardHorta/flare-cdr-presentation - this is what ;
i'm using as a reference for this stuff
