New scratch build - Slipstream

I've started my next scratch build. This one I'm calling "Slipstream". It will be 79" tall, 3" diameter, and have a single 29mm motor mount. This will also be my first zipperless design. So far I've just been working on the wood parts - fins, centering rings, baffle, etc. One of the fins was slightly warped, so I clamped them to a flat surface, hoping it will relax a bit.

I cut out the 1/8" plywood rings with a 3-1/2" hole saw, then trimmed them to size on my wood lathe. For the center hole, I used the closest hole saw I had, then sanded it to fit with my Dremel.

One of the rings will be the baffle for the zipperless coupler. I made a pattern on my computer and used it as a guide for drilling the holes.

I marked each hole location with an awl, then drilled them with a 5/16" bit. The two half moons are for the baffle in the motor mount tube.

I epoxied the eyebolt to the coupler baffle, and epoxied the baffle into the coupler. I cut a piece of plastic pipe to use as a spacer so the baffle would be level in the coupler. I also epoxied the first half moon baffle into the motor mount tube.

Got the baffle epoxied into the coupler, and the half moon baffles epoxied in the motor mount tube. I also epoxied the upper centering ring to the motor mount tube.

qquake2k said:

I epoxied the eyebolt to the coupler baffle, and epoxied the baffle into the coupler. I cut a piece of plastic pipe to use as a spacer so the baffle would be level in the coupler. I also epoxied the first half moon baffle into the motor mount tube.

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Epoxy is great for holding that nut to the eye bolt. If it ever does start coming loose, you're hosed. Something that is cheap insurance is to take a hammer and give a few good wacks to crush the threads sticking out of the nut before you epoxy them. Even if the epoxy breaks loose, the eyebolt still won't unscrew from the nut.

Handeman said:

Epoxy is great for holding that nut to the eye bolt. If it ever does start coming loose, you're hosed. Something that is cheap insurance is to take a hammer and give a few good wacks to crush the threads sticking out of the nut before you epoxy them. Even if the epoxy breaks loose, the eyebolt still won't unscrew from the nut.

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You know, that's a good idea. I've done that before in other applications, but never thought about using it here.

Got the fin slots cut out, and did a test fit. I've never done upswept fins before, I think I like them!

In my one other 29mm rocket, I've just used masking tape for motor retention. But I decided to put tee nuts in this one just in case I decide to do something else. Better to have them and not need them, than need them and not have them...

The coupler is 6" long. Should I leave 3" of it sticking out, or only 2"? My thinking is that 2" will be enough to hold it together during flight, but have less drag when the upper section ejects at apogee.

Also, the upper body tube is 34" long. I definitely don't need all that space for the parachute and shock cord. Should I put a bulkhead in the upper tube to take up some of the space? That would leave less volume that the ejection charge has to pressurize.

Great build so far,can't wait to see the finished look with paint.You know now I have to go build one of my own.Can't let the wife in on this,the rocket will just appear one day in the basement.Love that rocket magic.Good luck on the rest of your build.

qquake2k said:

The coupler is 6" long. Should I leave 3" of it sticking out, or only 2"? My thinking is that 2" will be enough to hold it together during flight, but have less drag when the upper section ejects at apogee.

Also, the upper body tube is 34" long. I definitely don't need all that space for the parachute and shock cord. Should I put a bulkhead in the upper tube to take up some of the space? That would leave less volume that the ejection charge has to pressurize.

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well, i won't hurt to put a bulk head in, and i will reduce the chance of a failed separation.
best to ground test the design before first flight, esp with the baffle.

really liking your build.

Gillard said:

well, i won't hurt to put a bulk head in, and i will reduce the chance of a failed separation.
best to ground test the design before first flight, esp with the baffle.

really liking your build.

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I know about ground testing with dual deploy rockets. But how would I ground test this one? It will be using motor deploy.

qquake2k said:

I know about ground testing with dual deploy rockets. But how would I ground test this one? It will be using motor deploy.

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i ground tested a motor deploy rocket last weekend - it was an uscale of a gemini DC using port vented rear deployment.

heres what we did,

made a small parcel of BP around an estes ingitor using making tape.
placed that in the motor mount with the ends of the ignitors sticking out.
made an end cap to seal the end of the motor mount, and then fastened that to the rear motor mount ring (we had t nuts in the ring like yours)

it worked we, and we were able to get the amount of BP just right after 3 tests (first was far too energetic)

its worth doing if you are concerned about deployment in large airframes, better to find out on the ground as it's less problematic than having a failed deployment a few 1000 feet up.

Is there a way to find out how much black powder comes with Aerotech reloads and in single use motors?

I know AT 38mm loads come with 1.6g of FFFFg, but I'm not sure about the 29mm HP. I think (but I'm not positive) that the 29mm hobbyline and the SU hobbyline F and G motors come with 0.9 grams.

Hello,

Here is a quote from PML about RecoveryComponents FAQ (link https://www.publicmissiles.com/images/PMLRecoveryComponentsFAQ.pdf see p4).

The following will give you an idea of how much ejection charge BP is commonly
supplied with various size motors:
• G: 0.7g
• H: 1.4g
• I: 2.0g
• J, K: 2.1g

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You should have used a 38mm MMT! so you can fly with a lot more motors configurations.
Those fins are looking cool!

When I ground test it, should the rocket be standing up or laying on its side?

qquake2k said:

When I ground test it, should the rocket be standing up or laying on its side?

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lying on it's side, with plenty of space on either end.

Does this look like it will work? I put the tip of an Estes igniter into a drinking straw, and sealed it with hot glue. I put the powder in, folded over the top, and wrapped it with cellophane tape. That's 1/8 teaspoon of FFFg Pyrodex, which as far as I can tell, is approximately 1/2 gram. I have an electronic scale that measures grams, but not fractions of a gram. I figure this will be a good starting point. I'll try one outside the rocket to see if it works, and if so, how big the bang is.

looks very neat.
much more professional than the masking tape job my friend and I did.

let us know how it worked.

qquake2k said:

Does this look like it will work? I put the tip of an Estes igniter into a drinking straw, and sealed it with hot glue. I put the powder in, folded over the top, and wrapped it with cellophane tape. That's 1/8 teaspoon of FFFg Pyrodex, which as far as I can tell, is approximately 1/2 gram. I have an electronic scale that measures grams, but not fractions of a gram. I figure this will be a good starting point. I'll try one outside the rocket to see if it works, and if so, how big the bang is.

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That looks like it would work great for Black Powder. I'm not so sure it will work with Pyrodex.

The Pyrodex usually has to be contained much better to get it to fully burn and give consistent ejections. You might want to cover the whole thing, including the folded end, with a couple of layers of electrical tape. Don't use masking tape. The electrical tape stretches and keeps everything contained for just that little bit longer before bursting.

If you want to test the consistency of the Pyrodex, make up 5 charges with the exact same amount. Set up the rocket with just the nose cone. Make sure the fit is consistent. You might want to do this in the shade or on a cloudy days so heat doesn't affect the nosecone fit. Fire all five charges and measure the distance the nose cone goes each time. You might be surprised at the variation.

Handeman said:

The Pyrodex usually has to be contained much better to get it to fully burn and give consistent ejections. You might want to cover the whole thing, including the folded end, with a couple of layers of electrical tape. Don't use masking tape. The electrical tape stretches and keeps everything contained for just that little bit longer before bursting.

If you want to test the consistency of the Pyrodex, make up 5 charges with the exact same amount. Set up the rocket with just the nose cone. Make sure the fit is consistent. You might want to do this in the shade or on a cloudy days so heat doesn't affect the nosecone fit. Fire all five charges and measure the distance the nose cone goes each time. You might be surprised at the variation.

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You're right, it wasn't very energetic. I tried a 1/2 gram charge and a 1 gram charge, and they were about the same. Due to my nephew Wes' photography skills, you can see why. It blew the bottom of the straw apart, but didn't burn all the powder. I'll try wrapping the packet in electrical tape next time.

And I can't set the rocket up to eject the nose cone, because of the zipperless design. I'll have to see if it can eject the upper section of the rocket.

Yep - that's the problem with pyrodex used in rocketry. BP tends to all burn, even when not contained very well, but pyrodex needs more containment.

cjl said:

Yep - that's the problem with pyrodex used in rocketry. BP tends to all burn, even when not contained very well, but pyrodex needs more containment.

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Unfortunately, Pyrodex is all I can get locally. The guy at the gun shop said that they'd have to have an underground concrete bunker to sell black powder in California.

I tried another one, this time wrapped in electrical tape. Much better result. The first video is the unwrapped charge, and the second video is the wrapped charge. The camera didn't pick up the much louder bang from the second charge, but trust me, it was much more energetic.

https://www.youtube.com/watch?v=bZ240PFiFKI

https://www.youtube.com/watch?v=3Us97N7Oq-o

Bought a cool little scale at Harbor Freight. It's a tiny little thing, but perfect for weighing black powder. You have to print out the page and take it in to get the sale price in the store.

https://www.harborfreight.com/1000-gram-digital-scale-97920.html

Got the fins epoxied on. Next it's internal and external fillets.

I discovered the first of two major mistakes. I cut the fin tabs too short.

And after I had epoxied the bulkhead in the upper body tube, I discovered my second major mistake. Can you guess what it was?