THRP-1

[G_T]

Sorry about the color balance of the last pic. In any event you can see the core is not smooth but substantially smoothed.

Gerald

 

[G_T]

The fuel grain core repair job looks fine. It smoothed out a touch more with more spinning. It's quite smooth at the injector end, where it will matter the most. The region in front of the injectors typically consumes slightly more fuel web.

On to making the igniter from hell...

Doubled pyrodex with a fitted ematch bahaves like a little rocket motor. I've used a variation of this that is less directional to light N and O motors.

Here I'm using three of these. They are epoxied into the preheater liner with 5 minute epoxy. Each will blast flame down the core of the fuel grain. An injector fits between each of these. Two of the injectors start out with stubby plug tubes sticking out, and the remaining injector gets the fill line. The line line and the plugs will get fiberglass sleeving except perhaps a quarter inch near the injectors.

I haven't made the modified thermite paste that is going to be added next. It took me longer than expected to make the pyrodex part of this igniter. This certainly isn't a production method! Too time consuming.

The modified thermite epoxy paste is going to be interesting. I'm looking forward to the static test.

For scale, this is a section of 54mm LE phenolic liner that plugs into the bottom of the coupler.

I think for the static test I'm going to have to epoxy on a base of some sort, to simulate the metal wall that resides on one side.

Historically, the first burn used some split pyrodex pellets glued onto a solid fuel grain. It dumped half the nitrous before it got going. The second burn used lots of BKNO3 for preheater. That also dumped lots of nitrous before it got going. But once it started to burn it was up to full thrust acceptably quickly. This motor is very hard to light.

Gerald

 

[G_T]

Added...

I might decide to flip the preheater so it points the flame away from the nozzle. That would guarantee the whole collection of pyrogen lights quickly, before the nitrous has a chance to quench it.

Static test of the preheater tomorrow (Ok, today. It's late).

Gerald

 

[G_T]

Getting the GSE together...

Gerald

 

[G_T]

Video of preheater test. Good test of the wireless GSE. As for the preheater, not quite what I'm aiming for. The coating process producing the modified thermite essentially cancels a lot of the thermite reaction and slows it down a couple orders of magnitude. Notice how the thermite portion continues to burn and actually only really gets going its best after the initial combustion is completed? It is nowhere near fast enough.

I'm not showing it, but we tried a small batch of the modified thermite. An ematch wouldn't ignite it. It took a BKNO3 augmented ematch to light it. The combustion wasn't a thermite reaction but instead it was just burning the Mg. It left behind a copper, magnesium, and potassium oxide ash. Way too cool and way too slow. It's a dud.

It appears my process of coating the Mg separately from the CuO is way too effective. It ends up that the Mg burns (there are some other things in there) but the CuO is substantially uninvolved. So it isn't thermite, just a really crappy pyrogen. It is even hard to light!

I'll be keeping the pyrodex part of the preheater design, since that has the desired burn rate and instant-on behavior, but replacing the modified thermite with BKNO3/NC to punch up the heat. There won't be time to static test the new version, so it will have to do.

Gerald

 

[G_T]

UFO - Unidentified Frying Object

One thing about prep of this motor. I don't like lots of extra tubes coming out the nozzle. That makes a mess and I don't like the degree to which it can choke the nozzle before getting blown out. I prefer a cleaner arrangement.

The first burn of this motor, I used a long piece of tubing that went from one injector on out the nozzle, made a big loop, then went back in to plug into another injector. So there were effectively three lines each a quarter inch, going through the nozzle. These were taped together to form a bundle.

The second burn - flight last year at URRF - I made short sections of tubing with the ends fused closed. That was heat gun work and very gentle work with a mini torch. Made a few failures getting the two good ones made. Then boiled them for stress relief. I had lots of trouble with outgassing when heating, forming little pinholes. Very fiddly. But, it worked. I used a microscope for inspection to make sure they didn't have any micro pores.

This year for the third burn I have a new batch of tubing. I couldn't get this batch to fuse up. It wanted to form more pinholes and I couldn't get it to flow over smoothly on the surface. I gave up.

So I did something different. Not sure if it is a good idea or a stupid idea. Time will tell!

I took a length of the new tubing and applied a bit of bending load. While this was held I used a micro heat gun to briefly warm the compression side of the curve over about a half inch length of the tubing.

I repeated this quite a number of times until I had a V shape of the correct angle to align with the injectors' convergence angle (these are impinging injectors, and the angle really should have been greater). Then I warmed the sides a bit more and gently warmed the back of the curve.

I didn't heat the back until the shape was made, since I didn't want to thin the tubing.

Anyway it didn't bubble or pinhole. But the surface isn't as smooth as I would like. This tubing is slightly different than the last batch. I think it is higher quality tubing but less moldable.

Not that I trust it...

So I took about a half dozen Viton beads and softened them in acetone. When soft I used the flat end of a round toothpick and rammed three down each side and packed them into the pointy end of the V. Then I took a little of the remaining Viton-containing acetone solution and painted over the less than smooth surfaces of the V.

Viton is reasonably compatible with nitrous, at least for this sort of fairly short exposure. I'm hoping if there were any microscopic pin holes or flaws, the viton will plug it up long enough that it won't be an issue.

Next I took a length of fiberglass insulation sleeve and worked it around the V, taping the ends closed with strips of masking tape. Then the rest of the acetone and Viton solution was used to rubberize the fiberglass.

If you look at the photo post-installation, you'll note there is a band at the end of each injector which is not protected from flame. These bands are where I want the tubing to soften from the preheater so the nitrous can blow the tubing apart.

I'll leave a similar unprotected band on the fill line.

Unfortunately doing it this way means I need to put a hook into the fill line for clearance. I didn't really think about this problem when I decided to go this route. At least it only needs a slight hook.

Gerald

 

[G_T]

I lightly warmed and increased the bend on an end of the coil of tubing so it will go into the third injector just fine.

Plumbing work...

Holley 16226NOS 6AN-660 BOTTLE adapter, to go between the CGA-660 valve on the B50 cylinder and the Contrail BFV and purge manifold system. https://a.co/d/azXFRXO (the link Tom from Contrail sent me).

Contrail BFV valve assembly stored conveniently in a Seahorse 58 portable waterproof dry box that I also picked up on Amazon. Nice box for the price and a good fit for the assembly.

Nitrous Outlet 4AN stainless steel braided hose, with Nitrous Outlet 1/8NPTx4AN adapter 00-01904-B, with Contrail sourced Fast Injector 1/4 line to 1/8 NPT.

Contrail sourced 1/4" fill line.

Gerald

 

[G_T]

I'm working on the flight preheater. It will use pyrodex as in the static test, which generate little rocket flames towards the forward bulkhead. That part worked very well in the static test. The additional pyrogen is being replaced with BKNO3-V with a 3mm web to attempt to achieve a 1s burn time for the preheater.

I used BKNO3 and pyrodex last time around as part of the preheater, along with essentially a solid propellant. There was only a fraction as much pyrodex, and the BKNO3 I made was slower than it should have been because of something I did in the processing. Last year's arrangement would not have achieved the instant-on behavior of this year's preheater, courtesy of 6 pyrodex pellets and 3 ematches.

So even with just the pyrodex there is already a fair bit of gas generation and a lot of heat. The addition of BKNO3 this time around is to boost the temperature some more and to give a bit more gas generation. The extra gas generation is to make it so that when the nitrous injectors clear and start jetting nitrous, they will do so into a pressurized combustion chamber rather than an unpressurized one. This will reduce the initial flow rate so it won't be as much greater than normal combustion flow rate as was the case last time. That reduces the refrigeration rate from the nitrous injection, which should help make it a fair bit easier to light.

The pyrodex burn rate is pressure dependent. It will burn faster in this situation than was the case in the atmospheric pressure static test. However BKNO3-V has a burn rate that hardly varies over a wide pressure range. That makes it a safer pyrogen addition.

I was going to use BKNO3-NC but the higher burn rate should not be needed. I hope! And BKNO3-V is a bit safer.

I'm considering adding a thick ring of Mg/NC paint at the nozzle end of the preheater to provide a very hot burning oxidizer hungry section just waiting for the first hint of nitrous to flare up with lots of extra heat but very little gas.

Not a simple preheater. If this doesn't work I don't know what will.

Gerald

 

[rocket_troy]

Just be wary of adding sizable amounts of anything with extremely high pressure exponents like NC or pyrodex. The last thing you need is substantial blowback into the tank on ignition. It's one of those things I'd put in the "worked last time, but doesn't mean it'll work next time" category although chilling the N2O a bit does mitigate the risk significantly.

TP

 

[G_T]

This NC is mononitrocellulose lacquer not double or triple base smokeless. It doesn't provide enough oxidation potential to handle itself, let alone handling a Mg addition. I think the resulting combination (Mg rich with NC as a binder) won't have much gas generation potential at all. It's mostly Mg. Now using NC that is fully nitrated would fit under the "bad plan" label!

The pyrodex of course does have a notable exponent. I'm expecting the burn rate to increase when the oxidizer flow starts. I want it to. I don't think I've overshot (famous last words). But the proof will be in a few days.

For future versions of the motor I'm changing injector design. These three fat streams are too hard to light. I'll go showerhead or something else that breaks up the flow much better, and hopefully come up with a design that does progressive flow startup.

I am gambling on pretty nearly instant start this time around (about 1/2 second delay is my target). If it doesn't work that way, then the motor won't light. The preheater will be done, unlike the version in the static test. The nitrous will just quench the heat since at full flow it has near 1.5MW of cooling power.

That's different than the slow burn igniters used in the last two tests which were practically guaranteed to eventually get the motor lit, just by being tenaciously resistant to being fully put out.

-----

I trimmed all the loose threads from the TAC-1 drogue chute. They were interfering with the nosecone fit. One thread would potentially jam the nosecone. So it got a haircut.

Gerald

PS - Please keep the questions, comments, precautions, observations coming! Each makes me question and reevaluate what I'm doing and that is a good thing. I appreciate it!

Any questions about any part of this are very welcome! I'll do the best I can to answer.

 

[G_T]

Grain weighed. Weighing afterwards will show how much fuel was burned.

-----

I put about 2g of Mg/NC paint (low in NC, mostly there as a quick cure binder to make the paint) in the preheater towards the nozzle end of the BNKO3. This is just to the nozzle side of the injectors, to give greedy decomposing nitrous something to bite into in the first fractional second of combustion.

I've been thinking on a problem I created. The original design was for a solid propellant grain to be cast into the preheater liner. This would have only a thin web. I did this as part of the first two preheaters - and of course it didn't work. Not nearly energetic enough.

This time I didn't do that. As a consequence, there is a notable step down from the precombustion chamber diameter to the grain core diameter. Not a problem per-se, but the problem comes from the resulting rapid erosion of a good percentage of the fuel web right at the end of the precombustion chamber. This will result in the fuel burning out at the injector end before the end of the burn. That is bad... very bad.

At the nozzle end it wouldn't be the same problem. The atmosphere would be reducing there. But at the injector end, it is very strongly oxidizing as well as being pretty hot.

Solution in the picture. I'm using a mixing cup as a temporary mold to cast a fuel ramp, rather like the convergent section of a nozzle. Hopefully it works. In the interest of the time I don't have, I'm going to use a blend of 5 minute epoxy (wish I had 15 minute on hand; laminating resin is too slow), wax that I'll pulverize, and an opacifier/catalyst. I don't have the time to mess with the HTPB/wax/... blend that is the actual fuel grain. Anyway the mix will still qualify as hybrid fuel and the regression rate should be similar.

Gerald

 

[G_T]

Turns out I did have some usable 15 minute epoxy. But I couldn't make it work with the wax I had on hand. Had to substitute. Oh well. It will work, just not as well.

Gerald

 

[G_T]

That sorta kinda worked. Picture is how it looks installed. I'm somewhat tempted to install it for real and transport it that way. It's about as protected as it would get. I'd just have to grease the outside of the liner.

You can see the tripled pairs of pyrodex pellets, the two injectors with the stubbed V shaped plug with a bit of fiberglass on it, the one open injector for the fill line, the brownish blobs of BKNO3, and some of the Mg paint above those blobs. I don't know how to make it more enerjetic than this without risking blowing it up. What a PITA. If this doesn't work I don't know what would. At least I'm finally done with everything related to the motor that doesn't happen at the field.

I've replaced the screw switches that gave me problems last flight, and soldered most of the connections. But I still have to deal with the Raven's collection of wires to the switch. I find wiring Ravens less fun than other boards, though they tend to be reliable. I'll post a pic when I'm done with it. But it won't be tonight.

I'd packed the main chute late last year so I won't be showing that this time around. It's the same as last time so look for those pics.

Gerald

 

[G_T]

Last flight I used these screw switches, but didn't really like them. They come loose too easily - or can go the other direction and turn themselves on. Not ideal.

So I repurposed it!

Actually, what I really wanted was the green screw connector on the other side. Somewhere around here I have a box of these connectors, but I couldn't find them. I'm sure I put them some place perfectly logical - at the time.

Here's the deal. A Raven altimeter, which incidentally uses common positive, requires one side of each ematch, as well as one terminal from the board, to go to a switched positive voltage source. So I'm repurposing the old screw switch as a convenient board mounted connector strip. I chopped a copper tack and soldered it across the terminals so the sides connect to each other. Then I sawed off excess board with a hacksaw, and epoxied the board down.

Now the ematch leads can connect to a convenient screw terminal for the + side of the connection. The - side connects to the Raven.

Note those two white blocks with Allen head screws in the top on the second picture? Those are the new arming switches for the altimeters that I showed unmounted a while back. I like them so far.

I have the altimeter board swung out so you can see the Raven. The other side of that board has the RRC3. When I'm done prepping I tie that side of the board down with a pair of black zip ties. It is a convenient arrangement where I can clip and hinge out board(s) as needed. It's what I call a cage bay. 3 allthread rods give a lot of flexibility in arranging boards.

Gerald

PS - Because I made the mistake of epoxying the ematch wires down in the preheater, I'm going to clip all the wires short and twist together. Then I'll wrap on leads at the field to go to the pad. The leads will separate at the wrap, rather than having the ematch wires hanging out the nozzle as the rocket flies away! That would hurt nozzle efficiency.

 

[G_T]

Now at URRF. Fingers crossed. Not sure if I'll launch tomorrow or Saturday.

I have some more pics, but probably won't be posting until I get back home. Hopefully somebody can take some decent video. I didn't bring anything suitable for that, and will be busy at the control box.

Gerald

 

[pugachu]

Now at URRF. Fingers crossed. Not sure if I'll launch tomorrow or Saturday.

I have some more pics, but probably won't be posting until I get back home. Hopefully somebody can take some decent video. I didn't bring anything suitable for that, and will be busy at the control box.

Gerald

Good luck on your flight!

 

[G_T]

Thanks!

Once I get my flight off and recovered (presuming; fingers crossed) and ditto the other flights in our group, I'll have plenty of nitrous on hand. If someone wants to launch something on a contrail or compatible hybrid and has the motor and the rocket, and the fill line and adapter if not 1/4", I'll sell nitrous at what I paid for it (unfortunately pricy) and I have the GSE.

Gerald

 

[OzHybrid]

Thanks!

Once I get my flight off and recovered (presuming; fingers crossed) and ditto the other flights in our group, I'll have plenty of nitrous on hand. If someone wants to launch something on a contrail or compatible hybrid and has the motor and the rocket, and the fill line and adapter if not 1/4", I'll sell nitrous at what I paid for it (unfortunately pricy) and I have the GSE.

Gerald

Try buying Nitrous in Australia. Then you'll know what pricey is.....
Good luck with the flight.

 

[G_T]

Thought I'd go ahead and post a few more pictures from before this weekend's flight attempt. These were taken during the prep.

I have some more pics of the electronics bay to post but not this weekend.

Friday was relatively rained out. I didn't figure there was time before the rain got in so didn't even try.

Today I hit a couple snags which wasted about 2 1/2 hours. I had to wire a pair of electrical plugs on some cords. Simple job, right? Well the plugs I picked up at the hardware store must have been designed by some CAD whiz that had never wired anything. Stupidest design I've ever seen. I'll be re-doing them when I get home. 5 minute job, over a half hour to jury rig it to substandard level.

Second snag was the tether. It worked fine back home in testing, but at the field the pin wouldn't go in all the way and engage the ball bearings. I never did figure out why not. But I ended up having to strip the electronics bay half apart to get it working. Hopefully everything is back together correctly at the field! I think so...

But it ended up late when we were out to load the rocket. We didn't have a pad with the right rail out at the away cells (1010 for this one), and the wind had picked up. I decided to scrub for the day. Unless anything unforseen happens (who am I kidding; it's a rocket launch) the attempt will be first thing in the morning. The winds at ground and altitude are predicted to be a fair bit less. That's a good thing. A number of rockets got treed today, and should could go higher than any other at this launch, if it works.

Gerald

 

[G_T]

I haven't forgotten this thread! It's been a busy week though so I haven't gotten back to it. I'll get some more pics posted this weekend and try to catch this thread up to date soon.

Here the modified TD-2 tether and the Peregrine CO2 system are prepped.

I had left them assembled too long before cleaning last time around. I ended up using a fine pumice wheel in a micromotor to repolish a section inside the Peregrine tube where some corrosion had hit the aluminum. Of course the little steel parts needed cleaning as well.

I talked about it quite a number of posts back, but the aluminum press fit cap on the TD-2 was necessary at least on my unit when it is misused by mounting it to a bulkhead in this fashion. If the tension was off-axis on the tether pin (not installed in this picture) it would jam rather than release when under load. The aluminum piece is simply an alignment guide so the pin cannot pull off-axis. The jamming was the circular depression for the balls being of a coincidentally bad dimension to match the thickness of the top aluminum plate. Tilted, it would hook quite solidly there. Now it would also probably shake loose almost immediately on a flight given the gyrations of a rocket on descent, but I thought it better not to trust to that. Hence the cap.

It's a press fit, and not coming off without considerable persuasion!

Gerald

PS - BTW, both of these units are expected to be exhaustless into the electronics bay side, and that has been my experience. I just threw a shroud around the CO2 system since that's the one with a little black powder in it, and I had the shroud. So if it does vent a little inside, the shroud will filter the gasses and help protect the electronics. Again, this would not be a normal event and has never happened in my experience at least.

 

[G_T]

Prepped electronics bay.

Gerald

 

[G_T]

That's as far as it got. Went out Saturday to launch, but needed a different rail. I called it due to time and approaching storm. Went out Sunday to launch, and the lower rail guide broke.

I hit a deer on the way to the launch and had to stop quite quickly. Stuff in the car got shaken around quite a bit. I suspect something impacted or heavily loaded the guide. It didn't break off at that time. But on the rail, ready to be raised a second time, it just sort of broke without being loaded. It must have been just barely hanging on.

So no launch

I even had it upright on the rail and pressure tested it, before letting out the pressure and lowering it to turn on the video camera. It's probably a good thing it failed just sitting there horizontal, rather than on the launch.

Anyway, rather disappointing.

Gerald

 

[OzHybrid]

That's as far as it got. Went out Saturday to launch, but needed a different rail. I called it due to time and approaching storm. Went out Sunday to launch, and the lower rail guide broke.

I hit a deer on the way to the launch and had to stop quite quickly. Stuff in the car got shaken around quite a bit. I suspect something impacted or heavily loaded the guide. It didn't break off at that time. But on the rail, ready to be raised a second time, it just sort of broke without being loaded. It must have been just barely hanging on.

So no launch

I even had it upright on the rail and pressure tested it, before letting out the pressure and lowering it to turn on the video camera. It's probably a good thing it failed just sitting there horizontal, rather than on the launch.

Anyway, rather disappointing.

Gerald

At least you didn't make the nitrous equivalent of dry ice. It's very expensive.... I'm sure you'll be good at the next go. A man's gotta know his limitations...... Clint Eastwood.