Speaking of Cf from the nozzle, for long burn time single stages, there’s a
staggering amount of theoretical altitude available from dialling up the
expansion area of nozzle exit according up RASAero II which raises the question
of flow separation and how much one can tolerate in a relatively small and
stout nozzle during the early phases of flight?
Re: the CF tubing. I’m wondering if you even want an optimised for pressure
vessel tube? Wouldn’t the end retention be the ultimate limitation (the
Achilles Heel) of utilising a composite tube? Depending on your retention
method, it might be beneficial to have more axial support than optimal for
pressure vessels? Apparently you can achieve at least an 800MPa tensile
strength from plain woven (90 deg weave) CF-Epoxy composite and up to >1200 if
using an optimal epoxy. Say, you can achieve 800MPa (multi-directional) with a
non-optimized composite tube from hoop in particular – that gets you on par
with Grade 5 Ti with the benefits of lower mass?
Troy
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On ;
Behalf Of John DeMar
Sent: Wednesday, 12 January 2022 11:21 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: fiberglass conduit
Bill,
Another approach is to add more propellant (length or diameter, and grain
design) and stay with aluminum. 10% more APCP is cheaper than a titanium
casing. Also, optimize the Cf from the nozzle.
Madcow tubing is made by Curtis Turner (Performance Rocketry) in PA. The CF
tubing for HPR airframes is not intended to be a pressure vessel. He will make
custom tubes with higher-temp epoxies or even phenolic. But... he is unreliable
when dealing with individuals.
I have a 3000 PSI hydrostatic tester, GP model HT1.5-3000:
https://www.gpequip.com/products/electric/electric-high-pressure-testers
If anyone needs a casing or tank tested, just holler. No charge, or a small
voluntary fee if more involved. Either proof testing or destructive testing. I
tend to make a small version of a design with new materials and see what it can
do. Then proof test a full-scale article.
-John DeMar
Las Cruces, NM
On Tue, Jan 11, 2022 at 4:49 PM William Claybaugh <wclaybaugh2@xxxxxxxxx
<mailto:wclaybaugh2@xxxxxxxxx> > wrote:
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
<mailto: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
<mailto: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
<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.
