Absolutely. Such an analysis is worth considering when you’re seriously
entertaining the idea of something like a Karman Line attempt.
There are also some practical fabrication advantages with Ti – it’s much easier
to weld compared to Al-Alloy and I don’t think you need to retemper post
welding and you don’t need to mix in different grades of alloy to weld like you
do with something like 6061.
Having a material that’s quite weld friendly does open up retention and fin
options that aren’t really a consideration for Al-Alloys.
On the flip side, it’s a very hard material and things like fins might need
to be send out to a capable shop for subtractive work if that’s required.
Troy
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On ;
Behalf Of John DeMar
Sent: Wednesday, 12 January 2022 9:08 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: fiberglass conduit
The other factor with aluminum is that the tensile strength reduces quickly
with increased temperature. At 150C, aluminum derates by ~20%. Using this
limitation and applying a safety margin of 1.5, the useful operating pressure
is only around 800 PSI (for Troy's example comparison). Countering that issue
with more insulation reduces the volume loading. So, we get a decrease in total
impulse caused by lower chamber pressure and/or lower volume loading.
But, aluminum is cost effective in both material and machining. This is
important when iteratively improving a propellant formula and grain design (and
the launch vehicle)... more tests, more flights, to iron out everything. If the
motor efficiency becomes "the thing" to improve, I think it's worth putting
effort into the mass ratio via alternative casing materials and insulation
schemes. Without thinking too hard, and by looking at where others have gone
for solids professionally, composite casings are the end results of the
improvement process.
-John DeMar
Las Cruces, NM
On Tue, Jan 11, 2022 at 2:29 PM Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx
<mailto:troy@xxxxxxxxxxxxxxxxxxxxx> > wrote:
The quick comparison I did a year or 2 ago:
Tube Material Comparison
Material
OD
Wall
Density
Yield Str
Max Press
Max Pressure
Wt
Capacity
(mm)
(mm)
(g/cc)
(Mpa)
(Mpa)
(Psi)
(Kg/mtr)
(m^3/mtr)
6061-T6
152.4
3.175
2.7
241
10.04
1456
4.02
0.0168
Ti-6Al-4V
152.4
1
4.43
880
11.55
1675
2.11
0.0178
316 SS
152.4
2
8
290
7.61
1104
7.56
0.0173
Troy
From: arocket-bounce@xxxxxxxxxxxxx <mailto:arocket-bounce@xxxxxxxxxxxxx>
[mailto:arocket-bounce@xxxxxxxxxxxxx ;<mailto:arocket-bounce@xxxxxxxxxxxxx> ] On
Behalf Of Troy Prideaux
Sent: Wednesday, 12 January 2022 8:24 AM
To: arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
Subject: [AR] Re: fiberglass conduit
Bill,
I’ve only looked at it regarding some numbers – not pricing. I was assuming
it to be much more costly than that so I never bothered investigating it
further. It certainly is appealing in particular for something like a hybrid
tank where you can weld heavier ends on for non protruding coupling. For a
tank, the thinner wall not only reduces dry weight per unit section, it also
increases wet mass loading per given section. The same would apply to a solid,
and you can probably reduce your liner margin somewhat – especially for
regressive pressure profiles as the material will handle much more heat than
AL-alloys for even more additional wet mass loading.
Troy
From: arocket-bounce@xxxxxxxxxxxxx <mailto:arocket-bounce@xxxxxxxxxxxxx>
[mailto:arocket-bounce@xxxxxxxxxxxxx] On Behalf Of William Claybaugh
Sent: Wednesday, 12 January 2022 5:11 AM
To: arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
Subject: [AR] Re: fiberglass conduit
John:
Have you or anyone you know ever looked at Titanium tubing? I’m finding that
0.050” wall 6” outside diameter tube can be had for around $700 per 60” length
vs. about $240 for an aluminum tube at 0.125” wall.
That would come in at about two-thirds the weight of the aluminum tube, saving
three pounds or about 10% of the current dry mass of my 6” motor. It would
require going to button head fasteners rather than countersunk so drag would go
up some but that weight savings appears to be worth an about 10% altitude gain
and thus might be worth the extra $500 per flight.
Bill
On Tue, Jan 11, 2022 at 9:17 AM John DeMar <jsdemar@xxxxxxxxx
<mailto:jsdemar@xxxxxxxxx> > wrote:
The phenolic looks interesting as a motor casing. They spec axial tensile
strength but not radial. 60% the weight of aluminum but only 17% the tensile
strength. There goes the weight advantage unless one adds a carbon fiber
overwrap. And hydrostatic tests it. Still, there's the issue of attaching
closures to the tubing... appropriate adhesive, plus pinning, plus insulation.
-John DeMar
Las Cruces, NM
On Tue, Jan 11, 2022 at 8:16 AM James Fackert <jimfackert@xxxxxxxxx
<mailto:jimfackert@xxxxxxxxx> > wrote:
maybe of interest for airframes and solid motor builders-
championfiberglass.com <http://championfiberglass.com>
has glass epoxy and phenolic epoxy conduit in 3/3" to 8" sizes, three wall
thicknesses, 10 foot lengths
lots of coupling anf fitting options
even split clamp over repair/reinforcement tubes.
should be reasonable prices since its a commercial product.