Water soaked plywood is surprisingly cheap and effective. Let it soak
overnight, mount it shortly before your test. Easy, disposable, should last
for several tests per piece.
Evan Daniel
On Sep 12, 2016 10:52 AM, "Ben Brockert" <wikkit@xxxxxxxxx> wrote:
I'm glad to hear the test went off fairly well.
Those mud daubers are certainly a pain. A good fifteen minutes of
every day's testing on a stand in Alabama was going through the
checklist uncovering and recovering various vent lines.
I used graphite plates for the flame redirectors on the tube rocket
launches at Armadillo, but they are kind of pricey, fragile, and
difficult to hold. For the 500lb engine testing at Masten we burned
through a lot of concrete pavers, which are cheap and replaceable but
throw off molten concrete. At Moonex I just used a big stainless pipe
elbow off McMaster, but it was peroxide monoprop so the thermal
environment was easier.
The farther the deflector can be from the nozzle the easier of a time
it has, but the wider the hot plume is.
The big boys mostly use refractory brick and special mixes of concrete
to deal with the conditions. If you do go for concrete, dry porous
concrete mixes survive longer than wet poured ones, aim more for
cinder block than driveway consistency.
Water sprays are less useful than you'd think, the exhaust just cuts
right through them. Adds a nice fog to the exhaust plume though.
On Mon, Sep 12, 2016 at 9:31 AM, Robert Watzlavick
<rocket@xxxxxxxxxxxxxx> wrote:
The dewar was at 20 psi in this case. Now I have to clean out the LOXtank
and all the plumbing since some crumbs may have made it downstream. Ihave
a LOX filter but it was upstream of this particular line. Lessonlearned!
rocket@xxxxxxxxxxxxxx>
-Bob
On 09/11/2016 11:53 PM, Andrew Burns wrote:
Re. the mud daubers, from experience spiders can hold about 5 psi quite
comfortably...
Andrew
On Mon, Sep 12, 2016 at 2:49 PM, Robert Watzlavick <
wrote:tube
Oh, and I forgot the real excitement that happened. The one 3/8 inch
gotI forgot to cap off that was sitting in my garage the past two months
atclogged by mud daubers. I opened the dewar and the tank wouldn't fill
valveall. It took a lot more effort than I expected to clean it out.
-Bob
On 09/11/2016 09:45 PM, Robert Watzlavick wrote:
I finished up the last of the water and LN2 cold tests I planned for my
250 lbf LOX/kerosene rocket. The goals for the tests were:
1. Test an alternate LOX loading scheme to reduce the tank ullage -
Ben's suggestion worked great. After filling, I closed the LOX vent
improvedfirst, waited a few seconds, then closed the LOX fill valve. This
seconds.the pressurization time of that tank from 2 seconds to around 0.6
psi whenAlso, the helium pressure only dropped about 200 psi instead of 400
I waspressurizing the tanks.
2. Adjust the pressure regulator setpoints - The Aqua 1247 regulators
I'm using have quite a bit of droop under the flow rates I'm using so
flow.able to tweak them statically to give the desired pressures under full
effectiveDuring the run, the pressures drop a bit which will change the
themixture ratio from around 1.87 at the start of the run down to 1.81 at
is aend. The LOX pressure falls off faster during the run even though it
discussedlower pressure (340 psi) than the fuel (500 psi). We previously
thethis and I believe it is due to the cooling of the helium as it enters
reduced theLOX tank, probably not due to absorption in the liquid.
3. LOX insulation on tank and fill lines - I used 1/2 inch rubber pipe
insulation on the LOX tank (in 4 sections) and fill lines which
thinner.fill time from 8 minutes down to about 4 minutes. The Aerogel/Pyrogel
option looks like a better alternative for the tanks since it is
3500An alternative would be to use 1/4 or 3/8 inch thick pipe insulation.
4. Helium pressure vs. run time - In my previous tests using 2200 psi
helium, I wasn't even able to get 10 seconds of run time. By using a
ablepsi supply cylinder along with the tank ullage technique above, I was
about 17to load the onboard tank to about 2500 psi and that was enough for
on 10seconds of runtime, more than enough for a first flight. I'm planning
slowseconds or less but I want enough helium in the tank to account for
throughleaks during pad operations.
5. Sticky LOX vent valve - I wrapped the LOX vent valve in a 4x6 inch
poly bag with appropriate cutouts and ran a slow stream of nitrogen
do theit to displace all the ambient air. The idea was to prevent ice from
forming on the valve body and then dripping back into the bearing on a
subsequent fill operation. This worked as expected so I'll probably
up.same thing to the LOX fill valve and main valves. It also keeps
condensation from dripping on to the servos when the LOX tanks warms
do a
Thanks everyone for your suggestions and advice. The next steps are
tohot fire with the rocket strapped down so I'm looking for ideas on how
verticalhold down a lightweight stringer-based vehicle (no skin yet) for a
two oftest. I don't have a launch rail here so I was thinking of gripping
was tothe four stringers and clamping them to my test stand. Another idea
and usetie into the engine/frame bracket somehow to handle the thrust loads
unplannedguy wires to keep the top of the vehicle pointing upwards. An
videolaunch would definitely not be a good thing! I could also use some
suggestions on how to safely redirect the exhaust so I can still take
used.and pictures during the firing. I've seen curved or angled plates
-Bob
