Sub-Min Contrail L800 Build

So I guess I have to ask first, is it against the rules to post a thread in here documenting the exact replication of a Contrail L800 motor as well as the build of the rest of the rocket that attaches to it? There is no fancy rocket science going on here, I just measured the components of a motor and am replicating it out of raw material. I should also note that I'm not trying to infringe on Contrail as this rocket will never be sold or even given away, I'm just doing it sort of as a class project and also to see if I can. Also we bought a Contrail motor for this purpose so they actually made a sale off of this endeavour. If a friendly mod can give me the okay I'll post the build photos and openrocket files but withhold all exact dimensions of the guts and any of the fancy math. I promise it is super pretty and will probably be one of the shiniest rockets to ever grace this forum.

You might find that the motor that you build as a copy will possibly be regarded as an uncertified motor if you intend using it in a rocket launch, or even testing it. This might be in the experimental category. Additionally, although I’m not familiar with the the laws in the US, there may be some intellectual property issues.

ArchitectOfSeven said:

So I guess I have to ask first, is it against the rules to post a thread in here documenting the exact replication of a Contrail L800 motor as well as the build of the rest of the rocket that attaches to it? There is no fancy rocket science going on here, I just measured the components of a motor and am replicating it out of raw material. I should also note that I'm not trying to infringe on Contrail as this rocket will never be sold or even given away, I'm just doing it sort of as a class project and also to see if I can. Also we bought a Contrail motor for this purpose so they actually made a sale off of this endeavour. If a friendly mod can give me the okay I'll post the build photos and openrocket files but withhold all exact dimensions of the guts and any of the fancy math. I promise it is super pretty and will probably be one of the shiniest rockets to ever grace this forum.

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Homemade motor parts relegate your motor to research. You may fly research motors at Tripoli Research Launches as long as you are a member of Tripoli and certified at least Level 2.
As far as forum rules, I’m no authority.

It's meant for flight and testing at FAR so it doesn't have to comply with Tripoli or NAR rules. If I can get an official mod permission that would be great but otherwise i guess i need to get access to the experimental section and post it there. I still will post the process not including the motor if anyone is interested.

ArchitectOfSeven said:

It's meant for flight and testing at FAR so it doesn't have to comply with Tripoli or NAR rules. If I can get an official mod permission that would be great but otherwise i guess i need to get access to the experimental section and post it there. I still will post the process not including the motor if anyone is interested.

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I am interested. Sounds like a cool project.

View attachment HybridCompDev.ork

Well I don't want to disappoint and I actually want a little input on the recovery solution so here is my current openrocket design.

The issue with the recovery is figuring out how to safely eject a drogue and main separately from a shared space. I'm thinking about using two seperate avionics bays, one directly above the motor and responsible for drogue ejection and one in the tip of the cone that is responsible for main deployment. Deployment method is to eject the cone and drogue at apogee, drop like a relative rock to 500 ft and then blow the main out of a foil/tape sealed tube inside the nose cone. My first question is what could go wrong and what do you suggest? I could try to do a coupler but it might be a little hard to safely pull off because the forward body tube is aluminum tubing.(this was to make the connection with the motor stronger and more stable) Another alternative is I just pop the main at apogee with redundant altimeters and just depend on the shoelace express and a gps module to find it later.

HED, pop a furled main at apogee then unfurl down low?

Alright motor is complete so I'm off to the races on the rest of it. The plan is to polish and wax the outside once I'm ready to put it all together because with this rocket the motor IS the airframe. Again if anyone here can offer any advice on how to pull off deployment I'd be grateful. I have sort of an idea of what might work but ideas are definitely welcome.

dhbarr said:

HED, pop a furled main at apogee then unfurl down low?

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Like with some sort of tender descender?

Impressive work!

ArchitectOfSeven said:

Like with some sort of tender descender?

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Jolly Logic chute release? A custom heavier duty version, though.

For a rocket this heavy I would seriously consider full redundant dual deployment.

Check out the deployment system in Purdue University hybrid rocket at

https://www.google.com/url?sa=t&rct...A_Tsohas.pdf&usg=AOvVaw05XzVy8Cq6t8s7uILgsa-8

ArchitectOfSeven said:

Like with some sort of tender descender?

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Or a cable cutter.

You could deploy a drogue, drop quickly, then cut a cable to allow the drogue to pull out a d-bagged main.

Prairie Twister makes an extremely small cutter, some folks like a hotwire, I've seen testing on just using an ematch to melt a zip tie. Lots of deploy-and-a-half solutions, if you have a mentor or advanced peer nearby I'd try it their way.

Voyager1 said:

Impressive work!



Jolly Logic chute release? A custom heavier duty version, though.

For a rocket this heavy I would seriously consider full redundant dual deployment.

Check out the deployment system in Purdue University hybrid rocket at

https://www.google.com/url?sa=t&rct...A_Tsohas.pdf&usg=AOvVaw05XzVy8Cq6t8s7uILgsa-8

Click to expand...

Jolly logic is sold out so scratch that. Perhaps I could make a custom version but i would have preferred to use the logic board from an original. Another issue with those things is going to be additional cost which is butting up against the classes budget limitation. I'm trying to MacGyver something out of materials I have on hand which includes a 3d printer, aluminum tube, round stock, and possibly duct tape and/or chewing gum. I think I might be onto something that allows me to use the body volume a little more efficiently.
View attachment 345100
View attachment 345101

My current plan is to merge these two designs into something like this:

The way it would work is to deploy the drogue out of the nose cone at apogee and retain the av bay with large shear pins(4 4-40 nylon screws is my first rough estimate) and then use a fairly powerful charge to blow the main at 500ft. This arrangement allows me to run two stratologgers redundantly to improve reliability. The two major things I have to be really careful about with this design is making sure the pins are strong enough to survive drogue shock and then have a strong enough charge to cut them for main deployment. Also if that charge is a little hot I'm wondering how the shock cord would fare. I should probably note that the body tube is aluminum so high pressures are not a concern.

What do you think?

That sounds like basically a reverse head end deployment. Though switch the drogue and drogue charge such that it pushes the drogue out. Also will this have tracking of some sort? If so then maybe pop the main up higher to be able to get a signal to tracking purposes.

0011001100 said:

That sounds like basically a reverse head end deployment. Though switch the drogue and drogue charge such that it pushes the drogue out. Also will this have tracking of some sort? If so then maybe pop the main up higher to be able to get a signal to tracking purposes.

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I'm putting a cheap gps tracker in it that only pings out a location once a minute or so to the cell phone network. I could set the main to pop a little higher if it would help at least pick out a direction before it falls in a ditch and loses signal or whatever. Good call on the charge location. I'll fix that in a moment on the CAD model which I should post fairly soon.

Just a side comment and you probably know already, but just in case:

The tank portion of the hybrid - you need to clean that for oxygen service. Or at least, clean very well with acetone or other good grease solvent, followed by second cleaning with denatured alcohol to remove any traces of acetone etc, then DO NOT TOUCH. For assembly, you need to use Krytox grease. Don't substitute. Also some types of O-rings are not compatible with nitrous. Nitrous is a solvent. Contaminants - such as organics, acetone, finger oil, non-fluorinated grease, etc - sensitize the nitrous rendering it MUCH easier to ignite, and lowering the detonation threshold. For the commercial Contrail motor, those details were already handled. But for EX you have to take care of them yourself.

Gerald

G_T said:

Just a side comment and you probably know already, but just in case:

The tank portion of the hybrid - you need to clean that for oxygen service. Or at least, clean very well with acetone or other good grease solvent, followed by second cleaning with denatured alcohol to remove any traces of acetone etc, then DO NOT TOUCH. For assembly, you need to use Krytox grease. Don't substitute. Also some types of O-rings are not compatible with nitrous. Nitrous is a solvent. Contaminants - such as organics, acetone, finger oil, non-fluorinated grease, etc - sensitize the nitrous rendering it MUCH easier to ignite, and lowering the detonation threshold. For the commercial Contrail motor, those details were already handled. But for EX you have to take care of them yourself.

Gerald

Click to expand...

This is very much EX so that is on me and any and all advice relating to oxidizer safety is welcome. Thank you for the cleaning advice I'll follow that to the letter. I think we already have the Krytox and I will double check on the o-ring compatibility.

The bulk of the CAD is done for recovery and "payload".
What do y'all think? Obviously the U-bolts will be cut down and there should be a few radial screws that I neglected to add out of laziness. McMaster solidworks files are not always easy to modify without screwing things up...

Well its been a little bit but a huge amount of work has happened and gone into this thing. Basically yesterday we *sort of* finished the rocket and ran the motor through a static fire and had everything prepped for ejection testing and flight over at RRS(next door to FAR). Unfortunately the sister rocket of this build(from another class team) which has essentially the same motor tested really low on thrust due to incorrect fuel grain selection so we scrapped the ejection test and flight attempt and just opted to complete the static fire. The motor burned nicely on liquid for about 10 seconds and sputtered a little flame from gas for another 10 or so. The impulse came back at roughly 3500N-s, peak thrust at 500N, and average around 225N. That was only half the average thrust we expected(although total impulse was close to the 3800N-s expected) so cancelling the flight was a given. I'm going to put up a massive update here for now and then when updates or improvements are made I will document as well if you want to see it.

So here we go:

Here is another picture of the completed motor broken down into pieces. I may have made a joke or two relating this to the rocket having good reception or having plenty of bars :eyeroll:



And here is the front part of the rocket that I can truly say is my design and is something that I am pretty proud of.
Here we are printing the electronics housing in the back left as well as a wind tunnel scale model that fell over in the printer and failed to print. Perhaps we can try again on that part if we add a support or something.

And here is the finished housing and the nose cone shoulder that it drops into.

Here it is in place.


This is the nose cone shoulder/avionics bay components and pictures of it assembled. It should match the solidworks model from the previous post fairly exactly of you want to see a cutaway of how it goes together.






And of course the nose cone itself after the layup and waiting to cure. my teammates did most of the work on this one and it came out really good, especially considering this os the first time any of us had ever tried doing it. The process was making a 3D printed mold, waxing it like 6 times, and hoping for the best when it came to removal. We had intended to use the party balloon method that Air Command uses to separate their parts from male molds but we couldn't find a large enough balloon in time. In the end we tossed it in an oven at 80c and knocked the mold out by hitting the tip with a hammer. In that case it helped that we intended to have a machined tip on it to begin with.


More coming in the next few slides...

Here are a few more pictures of the nose cone and how it all came together:






Next post is the full recovery layout

Alright well here is the recovery plan as I had it ready to go yesterday. The laundry consisted of a 24" drogue that was basically pressure packed into the nose cone and a 48" main that was equally vigorously packed into the body tube as seen on the left. Separation points are both located at the avionics coupler, the nose cone going first and then the main and avionics bay being ejected at 700ft.

Here is the connection to the front of the motor. 1/4" chromoly steel rod that just slips through a hole in the side of the motor/body coupler. Seems to work nice so far.

Connection inside the nose cone. A small u-bolt set into an 1/8" aluminum plate. The plate is held above by a small section of the nose cone mold that was set in by CA glue. Below the plate is another section of the mold that is attached by 4 screw placed from the outside.

Here is the StratologgerCF side of the electronics. Things are disconnected because I had to take it out and didn't remember to take a picture until after everything was unplugged.

And here is the Raven Featherweight 3 that I already had that is acting as both a main phase redundancy as well as the backup igniter for the charges.


Actual ejection and ignition consisted of duel 0.7g charges of BP in the nose housed in plastic tubes capped with e-matches and hot glue. The lower charge is a duel charge of 1.8g of BP with the same construction method. Each tube had a e-match on each end so a total of 3 igniters are possible to connect(For these altimeters at least. 4 possible connections if I switch out the stratologger for something with backup channels) for each charge set. Maybe this feels a little like overkill but I watched the other team do their testing and some of the charges only chuffed instead of exploding properly so I opted to make the charge itself redundant. Also the backup charge was going to be somewhat larger in case the first one failed for whatever reason.

So here is the fin can post. Fins were water jet cut out of 1/8" aluminum plate and mounted in a section of aluminum tubing machined to a wall thickness of 1/8". Attachment was through setting the base of the fin into a shallow alignment groove, setting it up in a pair of alignment jigs we made, and welding them on. After that was complete I covered the welds with a fillet of metal epoxy that can out pretty decent. The edge bevels never happened because we ran out of time and the sleeve itself wound up being too short due to general materials shortage but the handy thing about it being a fin can is I can just switch it out with a new one at any time.

Here is the picture of it coming together.

First time the motor was stacked together.


First time the forward body and avionics coupler were stacked on.

First time the hole thing was roughly stacked and started to look like a real rocket.


And here is the sister rocket that I mentioned in a previous post. Just a quick shout out to their team for helping my team out in getting this thing built. Idk if John will ever read this but if you do you are awesome.

Okay and here is a nice picture of the completed rocket.


And as a little bonus here is the rocket on the test stand over at Reaction Research Society and a youtube video of the test fire.


https://youtu.be/T0IOVLufbxE

Makes me want to fly my M Contrail motor again. That thing screamed like a banshee then the sound echoed off the treeline. Awesome.

Dave A said:

Makes me want to fly my M Contrail motor again. That thing screamed like a banshee then the sound echoed off the treeline. Awesome.

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Do it
Btw, how many burns are these nozzles good for?

Burned 2 so far and the nozzle looks pretty good.

I have seen with my EX M hybrid, where the fuel contains a substantial percentage of wax, the nozzle gets a wax film. It is likely the wax film is present during the burn, and boiling off as it flows through the convergence section and throat. That appears to be providing substantial nozzle cooling. In my motor's example, the nozzle looked completely new under a coat of wax after a burn. When I was up to the motor after the static test at Battle Park, the aft end of the motor was nowhere near as hot as a solid motor would have been and the tank end was cool. Depending on the fuel used in ArchitectOfSeven's EX motor, a similar liquid film cooling of the nozzle might be occurring. So for mine at least, I'd say it is good until I drop it.

Dave, I'm in Centreville.

Gerald

Thanks for the info on the nozzle durability.

Next thing I've been trying to figure out but don't have a particularly solid method to quantify is shear pins. The nose cone shear pins do not seem too difficult. It needs to mostly just stay put during flight so I gave it 4 #2 nylon screws around the base(deployed by 0.9g of BP). The main pins, however, are a little bit of a different story. They need to take the shock load of a normal drogue deployment and NOT break but shear properly when the main charge goes off. For the moment I set it up for 4 #4 nylon screws which means I need at least a 1.8g BP charge to break them loose. Does anyone here have lots of experience with this sort of arrangement and particularly, does anyone know how to estimate the shock load from drogue deployment so I can do this better?

IIRC, the rule of thumb is about 30G. So if your forward section in front of the shear pins weighs 5 pounds, then you want it to shear out at not less than 150 pounds force.

In a high speed horizontal deployment, you'll still deploy the main in all likelyhood. But for most other scenarios, the front will stay attached upon drogue deployment.

Gerald