John:
I was running out the door and that last post is too curt: the cost /
benefit trade is not between tubes plus liner (as I appear to have
suggested) but rather between existing and delta performance:
For my specific vehicle the existing design is good for about 70k feet;
planned “Gen 2” changes will raise that to about 75k feet w/o changing the
tube and at no net increase in cost. Going to a Ti tube appears to result
in about 80k feet at an additional total launch cost of about 10%; going to
near maximum performance CF increases launch costs by about 40% while
performance goes to about 84k feet (the CF vehicle appears to be too light
and thus draggy but increasing mass does not appear to increase altitude,
instead, burnout velocity is reduced).
I’m already using Titanium in the current nozzle and will use it much more
extensively in the “Gen 2” nozzle; I’ve no special fear of working with it
and have access to shops with decades of experience if I can’t machine a
part myself.
For me, the remaining question is whether an existing CF tube (Mad Cow
offers 6” by 60” at around $700) could be fitted w/ a liner and offer
slightly higher performance than Ti at a similar cost. That requires doing
a hydro test to find out what pressure that tubing can handle.
Bill
On Tue, Jan 11, 2022 at 3:18 PM William Claybaugh <wclaybaugh2@xxxxxxxxx>
wrote:
John:
If performance is all and no cost too high, than carbon fiber is certainly
the answer.
I’ve priced a professional grade carbon fiber tube with liner at about 10x
the cost of aluminum; Titanium, OTOH, appears to cost about 3x. Carbon
fiber saves a bit less than 60% of the aluminum tube weight while Titanium
saves at least 30%, possibly 50% once optimized: the cost benefit clearly
favors Ti over either Al or CF.
Bill
On Tue, Jan 11, 2022 at 3:08 PM John DeMar <jsdemar@xxxxxxxxx> wrote:
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>
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] *On Behalf Of *Troy Prideaux
*Sent:* Wednesday, 12 January 2022 8:24 AM
*To:* 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 ;<arocket-bounce@xxxxxxxxxxxxx>] *On
Behalf Of *William Claybaugh
*Sent:* Wednesday, 12 January 2022 5:11 AM
*To:* 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> 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>
wrote:
maybe of interest for airframes and solid motor builders-
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.
