I have my technician ham radio license now (KD5LUY), so I am
going to pick up some two meter handheld radios for the telemetry soon.
If there is a better band for it, someone let me know. Transmitting
telemetry over the family radio handheld systems I have isn't technically
Darin brought the accelerometers, but we don't have circuits
for them yet. He will be looking into the eval boards, or just building it from
I talked to FMC again about the 90%. They have it
available right now, but they will have to do the site inspection before they
will let us buy it. They are going to want to see the following things at our
facility: good supply of water, clean siphons or pumps for transfer, a
safety shower, good ventilation, and disposal plans. Russ, you may
need to take point on getting that done at your site. The FMC guy may be
up here next week for other work, so we will probably meet with him even if we
don't have everything in place yet.
Russ confirmed the silver screen order from the Indian
company, but we don't have a delivery date yet.
Phil brought in a big rocket that could hold our flight
tank. It is still open for discussion whether we are going to modify one
of Phil or Neil's rockets or build one from scratch for the peroxide motor.
Neil: if you sent the valve catalog person to the address on
my business card, that was our old building. See if you can grab a few
catalogs for the next meeting.
I brought in two NOS valves for us to experiment with.
Both valves are in the $100 to $200 range, each.
The cheater solenoid is a normally closed solenoid that
draws 7 amps at 12v.
The remote bottle valve is a switched valve that can be
rapidly set open or closed, and stays that way without any further power.
The not-very-scientific test of blowing through the valves
showed the RBV to be noticeably more restrictive than the solenoid, as well as
We discussed using the solenoid for the launch valve by
including a small battery pack with the rocket, but it was considered important
to make sure that the tank stays vented after the flight. The solenoid
would draw the battery down fairly quickly, then leave the tank closed.
If there was residual peroxide that got at all contaminated, the tank could
pressurize if we didn't get to the rocket quickly.
Until proven unworkable, the plan is to use the remote
bottle valve as our launch valve on the engine. The three wires will be
connected to exposed lugs on the outside of the rocket, which will be connected
to our launch system with alligator clips. We can pulse the valve open
and closed to warm the catalyst pack before the full power launch.
I also brought a handful of braided stainless teflon hoses
and fittings from Earl's. The braids are a bit of a pain to work with,
and I am wondering if we can just use the teflon core in cases where we aren't
worried about hose damage. Does anyone know if the braid's strength
contributes to the line pressure rating, or is it all from the hose?
I still don't fully get the reasoning behind which fittings
are AN, pipe, or CG.
We pulled apart the engine we got from Juan. It is a
nice looking piece of work.
Interestingly, the catalyst pack is not just pure silver
screens, but includes some other types of screens at the entry side, and
interspersed through the pack. Possibly getting the peroxide flowing into
the screen pack before it touches any catalyst is a good thing.
We haven't had a check valve between the launch valve and
engine in any of our previous discussions. With the engine below the
tank, a check valve is needed to prevent an overpressurizing chamber from
blowing back into the tank and draining more peroxide in. That could happen
if we had a very undersized nozzle, and would be "bad". On the
VTVL platform with the engines above the tank level, there wouldn't be any
drain/siphon effect, but it would probably still be a good idea.
Both valves are straight through flow. The current
bottle manifold has a 90-degree outlet, but if we machine our own bottle
connector, we could rigidly connect the tank to the T for the fill valve to the
launch valve to the check valve to the engine. The current manifold is
nice for the test stand with the manual valve, pressure gauge, and blow-off
valve, but it would be dead weight in the rocket, and would require some
flexible line going from the bottle outlet to get back in the centerline.
We need to make some brackets to hold the motor on the test
Resolved: the vacuum catch tank should be large enough
to serve as the purge tank. It will take longer to draw the vacuum, but it
avoids a possible fuck-up scenario of someone accidentally overflowing the
catch tank by dumping the entire flight tank into it, and it saves us extra
valves and lines for a dedicated purge system.
We hadn't addressed this in previous discussions, but we
need to make sure that none of fill system is ever left in a closed
position. The decision was to make the vacuum / purge valve an open/close
valve instead of a momentary, and add an explicit purge step to the fill
checklist after disconnecting from the flight tank.
Resolved: don't worry about plumbing a second nitrogen tank
in the fill cart to handle a tank running out with the engine not fully
pressurized, instead add a check of the bottle pressure to the checklist before
hooking it up to the engine.
The mil-spec quick connect fitting was very cool, and should
work out great for the fill connection. We have a couple, but we don't
know exactly where we could get more.
If we can only find a 400psi nitrogen regulator right now,
we can live with it, but we will eventually want 1000psi capability for
The vacuum source is an open question right now. The
existing vacuum pump works fine, but requires a lot of AC power. Various
options were discussed.
Idea: can one of those little cigarette lighter
powered tire pumps be cannibalized into a vacuum pump?
Cart to hold everything
12V car battery for power
Water bucket with lid
Four port manifold (quick connect, vacuum, peroxide,
Nitrogen check valve
Momentary pushbutton for nitrogen solenoid.
Peroxide check valve (very soft spring for vacuum draw
Momentary pushbutton for peroxide solenoid.
Peroxide transfer tank
Vacuum catch tank (five gallon water jug)
Vacuum gauge for catch tank
Vacuum solenoid (use remote bottle valve so it can be left
Two position momentary switch for bottle valve.
We might share the check valves by teeing the peroxide and
It would be best to have the nitrogen and vacuum valves
right at the filling manifold to minimize the chance of any peroxide draining
into the lines during filling, but the solenoids are too heavy to just hang off
the quick connect. We might want to consider some semi-rigid support for
When we go to a flight tank without a pressure gauge, we
will need a pressure gauge on the fill manifold. We may just take the one
off the flight tank.
The game plan
Next week we should complete the fill cart, and we should
get several practice runs loading and blowing water through the engine on the
test stand (without the catalyst pack). That might even register a bit on the
load cell. If all is right with the universe, we may even blow our
remaining concentrated peroxide through the engine for a short bit of thrust.
We should plan on several short runs, and several full
flight load runs on the test stand once we have our drum of 90%.
We need to prepare the peroxide rocket. What
electronics do we want to run? Probably an off-the-shelf altimeter for
recovery, but we can also include my GPS telemetry system and Darin's
accelerometer systems. We need our own big launch rail.
We can test several things at the HPR launch this
month. I should have my GPS telemetry system (If I don't have the
telemetry working yet, I'll just log the data to a basic stamp for analysis),
and it would be nice if we could fly the experimental rocket on a certified
motor before we try it with the peroxide motor. It might even make sense
to launch it with the flight tank filled with water to more closely simulate
the flight conditions.
Get the waiver for an experimental launch in November and
fly the peroxide rocket a few times. If we have done everything right, we
should be able to just put it back on the rail, roll the fill cart up to it,
and run through the fill procedure to get it ready for flying again.
An interesting thought: a later "smart" rocket
with a micro controller and some more valves could use residual tank pressure
to do parachute ejection. After the peroxide has blown out, it could
close it's launch valve to retain the nitrogen pressure. When it wants to
eject the parachute, it could open a different solenoid to vent the nitrogen
behind an ejection piston. Peroxide drips might be a problem, and
it might just be simpler and safer to have a separate little cold gas tank for
ejection, but it would definitely be nice to get rid of the black powder
Another "smart" option would be to experiment with
optimal engine thrust curves instead of just snapping to wide open and staying
Post launch, the effort will turn towards the VTVL platform.
Testing pulse-width modulation of engine solenoids and
searching for better computer controllable proportioning valves. Russ is
checking on the electronics needed to switch the solenoids with a logic level
Building engines from scratch. We may build some
100-300 lb thrust motors that we could launch the big rocket with, but my push
is to figure out the motors we will use for the VTVL system. Those will
probably only be 10-20 lb motors, because there will be four of them on the
vehicle, and we don't want it to generate much more thrust than the platform
weighs, since we will be targeting tethered hovering and control behavior.
Building the VTVL platform. The current idea is to use
an inner tube as "landing gear" (later untethered flights may launch
from water), and have the four little engines spread high and far, so the
exhaust plumes are as far from the ground and body as we can manage.
We will see how controllable it is with a purely manual
joystick and throttle interfaces, but before we untether it we will want gyros
and range sensors giving good instrumentation, and possible an auto-pilot.