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Vehicle work, new catalyst packs

July 30 and August 3, 2002 Meeting Notes

July 30 and August 3, 2002 Meeting Notes

 

Vehicle Work

 

We got a tremendous amount of work done this week.  We are nearing completion of two full vehicles.

 

The seated lander should be flying again next week.

 

We straightened the bent frame by wedging it between the trailer and Joseph’s tractor, and running a floor jack under the middle until it straightened out.  Russ gave it a quick paint job.

 

The foam pad legs have been replaced by wire rope isolators directly underneath the main frame triangulation points.  The small vehicles worked fine with legs sticking horizontally out from the vehicle, but the big vehicles were constantly bending the legs on even fairly mild landings, so we are getting rid of the concept.  Initially, the vehicle was designed so that it could be placed upside down without intruding on the pilot, but given how readily the legs bend, that never would have provided protection anyway.  The wire rope isolators (from www.enodine.com) that we have on right now don’t have much travel (about 1.5”), but the basic technology is almost ideal for a VTVL vehicle, because they absorb shock in all three axis.  We may wind up getting some custom ones made, because the ones with larger compression strokes are way too stiff for our needs.

 

All of the engine mounts are now positioned so that the nozzles are above the frame.  After ruining two sets of nozzles all around in our big crashes, we are now trying to protect them a lot better.

 

The tube vehicle is going to take a couple more weeks before it is ready to fly.

 

Gem City metal spinning (www.gcmetalspinning.com) will have our nosecones ready by the end of next week.  They aren’t going to fit perfectly, but we will fill in the gap with foam, and it will work for this initial vehicle.  I am hoping that custom filament winding is reasonably priced for future vehicles.

 

We bought a new parachute and deployment bag from Butler Parachutes (www.butlerparachutes.com).  We will be cutting the nosecone and fabricating the “escape tower” rocket system for pulling the parachute next week.

 

We made some little 45 degree angle reflectors to mount on the side of the rocket so we can have the laser altimeter and a video camera up near the top of the vehicle.  I bought some first-surface laser mirrors for this, but our hand tests are somewhat inconclusive on if this works with the altimeter or not.  We will get it properly mounted and tested soon.

 

Russ took apart the battery pack for the laser altimeter so we can hook it up to be powered by the main vehicle power supply.  Annoyingly, it needs 6v power, which means we need to add another power converter.

 

We decided that the little 1” motors are not going to be sufficient control authority for the tube vehicle.  If it was perfectly balanced, they would probably be sufficient, but they wouldn’t be able to cope with even a 2” offset in the center of gravity with the main engine at full throttle.  We can statically balance it that well by balancing the vehicle on the engine bell, but a gust of wind could probably cause the peroxide to slosh enough to get it out of range.  We are rebuilding it for the 2” engines, which will give 4x the control authority.

 

We added a 1.5’ extension at the top that the nosecone will be attached to.  This allows us to have a platform just for the parachute system, and attach the altimeter and video camera underneath it, with clearance above the electronics box.

 

New Catalyst Packs

 

I traded some email recently with Arvil Porter ( www.arvilporter.com ), who is one of the old time rocket dragster builders, as well as the guy building the rocket motors for Brian “rocketguy” Walker.  He made some points about even pack compression and not needing anti-channel rings later in the motor, so, since we needed to build a set of four 2” motors for the tube, we experimented with a new packing sequence.

 

Our previous 2” motors had the following sequence:

 

2 ACR (anti-channel-ring) spacers at the top to allow the peroxide to spread out

6 stainless screens as spreaders

ACR

10 sets of one stainless screen with two silver screens

ACR, press to 1500 psi gauge indicated (about 900 psi on the pack)

10 sets of one stainless screen with two silver screens

ACR, press

10 sets of one stainless screen with one silver screen

ACR, press

14 sets of one stainless screen with one silver screen

press, retaining plate

 

A total of 50 stainless screens and 64 silver screens.

 

We weren’t using a solid spreading plate because it probably introduces a bit more latency for pulsed engines, but not having a solid plate to press against does keep the pack from being as evenly compressed.

 

We had resorted to the doubled silver screens before we had a press gauge, so it was possible that they weren’t really needed with proper compression, which would give the pack less opportunity to loosen with time.

 

I was pressing on the ACR because I was using a hollow tube (a 1” engine, actually) to compress the screens, and it wouldn’t bear on the center anyway.

 

The new pack experiment was:

 

2 ACR as spacers

Solid spreading plate with 29 0.060” holes, which should not be a pressure drop compared to the main engine jet

6 stainless screens as spreaders

10 sets of one stainless screen with one silver screen

press to 2000 psi guage indicated (about 1200 psi on the pack), using a full plate to get even pressure

ACR

10 sets of one stainless screen with one silver screen

press, ACR

10 sets of one stainless screen with one silver screen

press, ACR

10 sets of one stainless screen with one silver screen

press

10 sets of one stainless screen with one silver screen

press

10 sets of one stainless screen with one silver screen

press, retaining plate (it took quite a bit of force to screw the nozzle on)

 

 A total of 66 stainless screens and 60 silver screens.

 

There are a few other points of note for this test set:  I exclusively used the 1 7/8” bore spiral rings as ACR, while the earlier engines used 2”, which wrapped around to a triple layer at the crossing point, taking up more depth.  The 1 7/8” don’t exert as much force on the wall, but sit flatter.  We are also using isopropal alcohol in our ultrasonic cleaner now, while previously we were using methanol.

 

All tests were with the 1/4" ball valve instead of a solenoid.

 

We did the initial break in run with two liters of peroxide at 300 psi initial, with a 0.080” jet.  The first brief opening of the ball valve let a liquid slug of peroxide come all the way out of the engine, as is common with fresh screens.  After that cooked off, the second pulse was perfectly clear, and running out the remainder was perfectly clear and smooth, making 32 pounds of thrust.

 

The next run was at 600 psi.  The warmup pulse was almost instantly clear, and the run was a perfectly clean and smooth 49 pounds.

 

The next run increased the jet size to 0.120”, and we skipped the warmup pulse altogether.  Thrust rose to 119 pounds, and was still perfectly smooth, but thrust was now decaying proportional to the tank pressure, indicating that the metering jet was no longer the primary restriction.

 

We then made a long duration run with about six liters of peroxide, again skipping the warmup pulse.  It ran for 22 seconds, staying perfectly smooth, even as the pressure and thrust decayed.

 

To see if the long run had made any permanent changes in the pack, we did other things for a couple hours to allow it to cool back down to room temperature.

 

We did another two liter run at the end of the day.  We gave it a warmup pulse, but it probably didn’t need it.  The run was again perfect.

 

I suspect that this packing arrangement would work fine, and have a lower pressure drop, with 20 mesh silver screens, as opposed to the 32 mesh screens we use.  With the current arrangement, the maximum thrust is lower than with the looser packing, but it is probably justified for the excellent catalyzation.  I mistrust engines that aren’t jet restricted, because it is easy to have them go rough after things settle in, so we will probably put a 0.100” jet on these motors for the tube vehicle.  We’ll see how these behave after a few hundred seconds of run time.

 

 

 

 

 

 





 






 
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