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Small vehicle work, Big vehicle work, Mass flow test

January 28 and February 1, 2003 meeting notes

January 28 and February 1, 2003 meeting notes



Small Vehicle Work


We did all the body wiring this week – over 100 CPC crimp connections.




We are currently running lines for:


Four differentially throttled engine valves, with two lines for the servo drive (switches polarity for direction) and three lines for the pot feedback.

One master cutoff valve with the same wiring as the engine valves.

One solenoid control with two lines for the CO2 drogue ejection.  We might consider adding another of these for redundancy.

Two release latches with two lines each for the main chute release.  This is redundant.

A shielded cable for the tail camera.


We still have several free lines for future expansion.  We will probably also be adding a pressure transducer plumbed into the CO2 system so we can know for sure the drogue ejection system is ready.


I could have reduced the total number of lines by making all of the valve pots share the same +5V / ground signal, and the recovery actuators could have shared grounds, but I decided it was easier to just run separate wires.  I don’t have a firm opinion on this call yet.


Having all this wiring does make me consider possibly moving the electronics to an insulated box at the base of the vehicle, which could eliminate all the cabling on this vehicle, but for the manned vehicles we would have to run a bunch of lines back up for pilot control and display, so it would probably just balance out there.



Big Vehicle Work


The vendor that we had expected to do the carbon fiber filament winding on our big tank has backed out, and a couple more inquiries hasn’t turned anything up yet.  Does anyone know a composite shop that can wind a 63” x 144” pressure vessel (we can provide the liner)?


Our stand-in fiberglass tank will be here in a couple weeks.  It will have the same mass we are targeting the carbon tank for, but half the volume (shorter).  We will be able to do all the flights possible without a launch license with that tank, so we don’t really need the carbon tank for quite a while yet, but I wouldn’t mind having it sitting in a corner for when we are ready to use it.


The hatch reinforcement and sealing lip will be done next week.  This is necessary before we do a crush cone drop test, otherwise it would likely buckle where the hole in the cabin is.  We have shrunk the hatch a little bit, to a corner-rounded 24” x 30”.  The extra reinforcement weight is proportional to the hatch size, and we also want the hatch to be able to hinge down onto the tank end, which it can’t do if it is much taller.


The first full size crush cone (>7’ tall!) will be done next week.  We are going to test this before ordering any quantity.  One point worth noting is that we had originally asked for full seam welds inside and out, with the outer surface ground smooth.  We later realized that having a fat weld on the outside really doesn’t hurt us much, because we will have the entire vehicle sprayed with thermal insulation for the fast flights.  Dropping the inner seam weld and grinding saves a good chunk of fabrication cost.


We debated doing a cabin pressurization test with the boilerplate tank end, but we decided that cutting it out after we have sealed it all up with RTV would be a pain, so we will just wait until we bond the cabin to a real tank for the test.


Matt made an updated rendering of our current X-Prize vehicle design, and to give it a really good sense of scale, he composited it into a real photo of us working at the launch attempt in Oklahoma:




One change I am currently thinking about is arranging for the launch stand to grab the engine pods somehow, instead of requiring its own set of hardpoints on the tank bottom.


Flow Sensor


We tested our S-Mass coriollis mass flow sensor on Saturday.  We are starting to use some really large plumbing for this, with 2” flanges, fittings, and pipe / hose throughout.  The sensor reads up to 25 kg/s mass flow, which equates to a monoprop enging of nearly 7000lbf thrust.  The response rate seems good, so this will allow real-time Isp measurement during engine runs.




The sensor is very picky about not having any trapped gas.  We had to fiddle with it quite a bit to get it working, and we aren’t yet completely sure of the right procedure to guarantee that we can start a test run properly.  It wouldn’t be a problem if we loaded the tank with vacuum, but the fiberglass tank can’t handle that.


For testing, we had an ugly chain of reducing fittings to go from a 2” NPT to a 1” NPT to a ½” NPT to a manual ball valve.  The flow was obviously very turbulent on exit, but it was still a little surprising that with 250 psi behind it, only 5 kg/s of water would flow through a ½” ball valve under those conditions.  There is really something to be said for flanged connections over threaded connections, and we will probably have to start paying more attention to smooth plumbing flow as we try and get more performance.


We galled a 5/8” stainless bolt in one of the flanges, and had to cut it off.  I hate using anti-seize on fasteners near something that may have peroxide sitting in it for moderate amounts of time, because it always makes a mess that seems to get everywhere, but stainless galls so easily that you really do need to.




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