How does total impulse compare between the older motor and the present
design?Barry Jolly Sent from my Sprint Tablet.
-------- Original message --------From: William Claybaugh
<wclaybaugh2@xxxxxxxxx> Date: 7/12/19 15:09 (GMT-05:00) To:
arocket@xxxxxxxxxxxxx Subject: [AR] Re: Vacuum processing of solid propellant A
careful review of the history of design changes on my two-stage shows that the
increase in performance from circa 150 km to around 200 km was caused both by
the measured increase in density of the vacuum post processed propellant but
also by the near simultaneous discovery of a modified BATES grain design that
pushed volumetric loading to a little above 86% from a previous about 80%.After
reviewing that history and some additional work I’ve identified a monolithic
grain design that gives 83.5% loading in the upper stage and 85% in the lower
without erosive burning concerns. That is now the baseline and, using the
slightly denser propellant, sims to about 200 km, including 7 lbsm of
ballast.BillOn Thu, Jul 11, 2019 at 10:10 PM William Claybaugh
<wclaybaugh2@xxxxxxxxx> wrote:David:To be clear, I’m open to there being
something wrong somewhere in the simulations; I’m not claiming this two-stage
will do more than 150 klicks when asked by non-professionals.If there is
something wrong in the sim, I’ve yet to find it...but the results are hotter
than I expected during initial design. But then I’ve managed over the last two
years to stuff about 12% more propellant into it than I initially thought
possible.BillOn Thu, Jul 11, 2019 at 10:00 PM David Summers <dvidsum@xxxxxxxxx>
wrote:Btw, thanks for all this. It sounds like most of the performance gain is
design specific, as in given a fixed design this change makes a large
improvement. Still fascinating!-DavidOn Thu, Jul 11, 2019, 5:54 PM William
Claybaugh <wclaybaugh2@xxxxxxxxx> wrote:Troy:It’s late on this side of the
lake; I’ll shoot you the most current files tomorrow my time.BillOn Thu, Jul
11, 2019 at 9:48 PM Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx> wrote:Bill,
Troy: The two test to date were, as before, near 400 psia and near 750 psia;
the 500 psia Isp is an estimate coming out of Burnsim based on the measured Isp
at the two pressures. The “estimate” part is fine, so long as you appreciate
that to claim that the same propellant in a denser form produces a different
specific impulse than the lower density equivalent can only be truly verified
by conducting 2 instrumented static tests measuring both delivered total
impulse and pressure curves that closely match for a true apples to apples
comparison. That implies that the Kn ratio profile likely needs to be adjusted
between the 2 tests to accommodate the reduced mass discharge rate for the
reduced density propellant, but also (conversely) for the difference in burn
rate (normally increased for lower density resulting in an increase in
discharge & flow rates). Suboptimal densities often influence the burn rate
exponent too which can further complicate the comparison or at least achieving
useful comparable pressure curves. Where I’m coming from (in terms of specific
impulse) is the ultimate comparison is to say I can achieve x isp with this
density and I can achieve y isp with that density both in their optimum
configuration ie. expansion ratios matched as best as possible to the
conditions and structural margins likewise. In a dynamic sense, it does make
sense that the higher density / slower burning propellant will ultimately
achieve a higher specific impulse due it working for a longer time at a higher
altitude, but I’m not sure if this was factored into the simulations? The 7
second trajectory average increase for the second stage (compared to the
previous “air processed” propellant) is coming out of the trajectory sim and
the estimated 2.5 second gain (at 500 psia) that I assume reflects the higher
aluminum content; I don’t see how density can have an effect on Isp. Well,
yeah, that makes more sense. I’m happy to share the motor files and RASAero
file if you’d like to look them over. I’m happy to look over them, up to you
Bill. Cheers,Troy Bill On Thu, Jul 11, 2019 at 7:39 PM Troy Prideaux
<troy@xxxxxxxxxxxxxxxxxxxxx> wrote:So, just to be clear, the comparison
measurements were all done and measured at *very* similar pressures (*measured
pressures*) not implied similar pressures based on identical Kn profiles? Also
(just to be clear), your implied increase in specific impulse of the upper
stage (7 sec) is entirely based on porosity reduction or is that also
incorporating the additional metal influence. Regards, Troy From:
arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On Behalf Of ;
William ClaybaughSent: Friday, 12 July 2019 11:22 AMTo:
arocket@freelists.orgSubject: [AR] Re: Vacuum processing of solid propellant
Troy: The slightly increased Isp is measured in static tests at 2.5 seconds.
The additional flight performance is increasing altitude in the sim. The
baseline 231 seconds (at 500 psia) is measured in over 100 static tests of the
“air processed” propellant. I have to date only two tests of the slightly
denser version but those tests imply 233.5 at 500 psia. (Note that the vacuum
propellant is 10% Al rather than the baseline 7.2%). I’ll be doing more test w/
more vacuum degassing time once the desert cools some (read: November); those
tests will be at around 400, 700, and 1000 psia and should provide a better
reality check. For now, that is the data I have to plow into the sims. I
should add that changes in grain design—the effect of a longer first stage burn
having been noted—are also in play here. My very most recent modeling has
extended the booster burn to 11 seconds while adding 3% more propellant
(smaller core); that pushes altitude from 210km to near 230km. I should also
note that 90+ % of the dry mass is weighed; only the payload and ballast are
not currently measured. Bill On Thu, Jul 11, 2019 at 6:59 PM Troy Prideaux
<troy@xxxxxxxxxxxxxxxxxxxxx> wrote:Bill, fair enough. It sounds like a pretty
tenuous chain of assumptions, but it does shed light on the difference. I’m
curious on how you arrived at the assumption that the denser propellant would
deliver a noticeable increase in specific impulse? I can understand how that
can occur in small motors where you might expect noticeable deviations in
pressure from varying surface area exposure, but for a large motor? Troy From:
arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On Behalf Of ;
William ClaybaughSent: Friday, 12 July 2019 10:14 AMTo:
arocket@freelists.orgSubject: [AR] Re: Vacuum processing of solid propellant
Troy, David: Let me be the first to agree that sims are just sims and reality
awaits. I too was surprised by the seemingly large change and have spent some
time trying to understand it: First this is a two stage rocket and the effect
of higher propellant fraction is accordingly magnified in a way we don’t see in
a single stage. Second, the propellant is not just denser, it is also
slightly higher performance, a trajectory average of about four seconds for the
first stage and around seven seconds for the upper stage (which lights at
around 40k feet and burns out above 75k feet); this appears to be a significant
second order effect. Lastly, the propellant is slightly slower burning (because
of fewer voids). When optimized w/ my 2-DOF sim the longer burn in the first
stage (10 seconds instead of eight) produces a much lower MaxQ which—in the
sim—produces a notably higher burnout velocity and altitude. When the coast
between burns is adjusted (was 21 seconds, now 12) because of the higher and
faster booster burnout the upper stage gains almost a Mach number in burnout
velocity (was Mach 5.2, now 6.1). Then it gets tricky: the upper stage
violates the two-caliber rule above Mach 5.25. It looks like seven pounds of
ballast behind the nose tip take care of that but it does not look like the
aluminum fins survive the ride. I’m currently looking at titanium leading
edges for the upper stage fins. I don’t know if the sims are reliable (but the
program has a long history of accuracy); I’ll probably be flying one of the
upper stages early next year and then we’ll get a better idea of what to
expect. Let me also address a favorite topic, the cost benefit: this has cost
about $350 in out of pocket infrastructure investment (a vacuum tight lid for
the mixing bowl w/ view port). Everything else—including the vacuum pump,
gauges, and lines—was already in hand. Bill On Thu, Jul 11, 2019 at 5:35 PM
David Summers <dvidsum@xxxxxxxxx> wrote:That is fascinating! Is your propellant
mass fraction unusually high? I can't think of another reason for that result,
and I'd like to understand it better. Thanks! -David Summers On Thu, Jul 11,
2019 at 1:15 PM William Claybaugh <wclaybaugh2@xxxxxxxxx> wrote:David: In
flight simulations of my two-stage, stuffing 3% more propellant into the same
volume raises the peak altitude from a tad over 150km to 210km in the most
recent runs. Bill On Thu, Jul 11, 2019 at 4:47 PM David Summers
<dvidsum@xxxxxxxxx> wrote:Hoping to take this on a learning tangent: Why take
all the effort to get a few percent higher density? I'd imagine that it
translates to less than 3% higher performance, so wouldn't a simpler process
with a few percent larger chamber be more optimal? What am I missing? Or is it
just a why not go for perfect kind of thing? Thanks! -David Summers On Thu,
Jul 11, 2019 at 12:41 PM Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx> wrote:If I
vaguely recall (I could be mistaken) it was Mark Spiegl (?) who 1st mentioned
this process here about maybe 15 odd years ago. If I recall he was utilising
this process as an amateur and achieving some pretty good results. Troy From:
arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On Behalf Of ;
Anthony CesaroniSent: Friday, 12 July 2019 6:31 AMTo:
arocket@freelists.orgSubject: [AR] Re: Vacuum processing of solid propellant
Not with traditional solid constituents and configurations and I’ll leave it at
that. One technique that does have some merit is centrifugal casting. In this
example you have more energy at your disposal to consolidate the solid loading
in the absence of proper vacuum processing equipment. The propellant mix is
prepared and post degassed using vacuum, turnover and vibration as usual. The
prepared propellant is then transferred into the motor case or casting tube
with a cap on one end. The case is then closed with a cap on the remaining open
end and the whole affair is spun, longitudinally in a spin fixture or a lathe
equipped with explosion proof electrics (I’m sure). The case is spun at
moderate speed until the propellant cures. After the propellant has cured, a
section through the propellant will show very high solid consolidation with a
resin rich condition on the ID surface. The next step is to use your explosion
proof lathe to bore out the excess resin on the ID and you will have an
extraordinarily high solids loaded propellant grain remaining. Some
experimentation is required to optimize the particle morphology and the speed
should be optimized to produce the most consolidation while minimizing the
migration of the smaller diameter particles. To optimize the process further,
one end of the case should be supported by a roller steady and the dam on that
end should have an opening to allow the slow and well placed transfer of the
propellant into the case while it’s spinning instead of putting the whole mess
in there at the beginning. This actually works and you can achieve some
impressive densities using this method. Anthony J.
CesaroniPresident/CEOCesaroni Technology/Cesaroni
Aerospacehttp://www.cesaronitech.com/(941) 360-3100 x101 Sarasota(905) 887-2370
x222 Toronto From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx>
On Behalf Of Edward WranoskySent: Thursday, July 11, 2019 3:43 PMTo:
arocket@freelists.orgSubject: [AR] Re: Vacuum processing of solid propellant Is
there any sort of VARTM like process for manufacturing propellant? Edward On
Mon, Jul 8, 2019 at 8:39 AM William Claybaugh <wclaybaugh2@xxxxxxxxx>
wrote:Uwe: Yeah, as Anthony observed it is air trapped on the solids that
produces the problem. The AP is tri-modal (200, 400, 600 micron) and mixed via
a sieve on-site, lots of opportunity for air to entrain in that process. The Al
is 5 micron and picks up air rather like a sponge. Wetting it and degassing
might help some but the subsequent final mixing w: the AP is going to introduce
air. I’m thinking the strategy is going to be to post processing degas a set of
samples (5 minutes, 10, 15) and compare density gain per step. That should
offer a guess as to what can be achieved before the mix sets up. Bill On Mon,
Jul 8, 2019 at 12:18 AM Uwe Klein <uwe@xxxxxxxxxxxxxxxxxxx> wrote:Am 07.07.2019
um 19:59 schrieb William Claybaugh:> Uwe:>> For safety we can’t mix the Al & AP
together;reminds me of the special 3 outlet can used forchemically silvering
mirrors back when. :-)Hmm.create separate airless pastes with each component as
a first step?Delayed wetting of solids always introduces air.> processing
usually> proceeds by mixing the liquids (including catalyst), adding the
aluminum> to the liquid mix w/ careful hand stirring), then folding into the
AP> followed by final mixing.>> Bill>> On Sun, Jul 7, 2019 at 11:37 AM Uwe
Klein <uwe@xxxxxxxxxxxxxxxxxxx> <mailto:uwe@xxxxxxxxxxxxxxxxxxx>> wrote:>>
Am 07.07.2019 um 18:39 schrieb William Claybaugh:> > Does degassing the
liquid components before mixing help or does the> > subsequent mixing just
reintroduce air?>> Use mixing machinery where the mixing implements don't
break the> surface. i.e. avoid "whipped cream" effects.>> Any fine
grained solids will need degassing after they> have been immersed in but
not fully wetted by fluid components.> IMU no way around it.>> Mix
solids superficially, evacuate, add liquids on top.> return pressure to
normal.> Then start mixing ( top mentioned prerequisites apply :-)>>>
Uwe>>
