I am working on a project that is a mid/high power rocket. The diameter is 2.60 inch and has a removable MMT to allow for 29mm, 38mm, and 54mm motors. The length will be between 5 and 6 feet.

I have 4 goals for this project:

1) To learn dual-deployment electronics
2) Have it go supersonic
3) Return safely to the earth
4) Certify L1

Up to this point I have built only one mid-power rocket, an AeroTech Initiator.

From time to time I will post my progress. The fun is in the journey and I figure there will be a lot of “fun” on the way.

There are basically 5 major segments:

1) Fin Can
2) Drogue Bay
3) Avionics Bay
4) Main Bay
5) Nose Cone

This is my own design and not a kit, which means I am going slow and deliberate and thinking through each step. I didn’t want to build a huge rocket just to have it fail. If it does fail then it is a smaller loss (although a loss is a loss). Regardless, I have already learned a lot.

I dub this design Excalibur.

Greg

The fin can for this project is finished regarding construction, and is in the process of being prepped for paint.

The airframe is 2.60 inch OD purchased from Giant Leap. It is a heavier wall construction than standard model rocket tubing. I wrapped two layers of 5 oz fiberglass to give it more strength. After laminating the tube, I cut it to a 16 inch length. Afterwards I squared the ends of the tube.

This rocket utilizes a four-fin design. The fins are surface mounted instead of through-the-wall (TTW) construction. The surface mounted fins were to accommodate multiple motor mount sleds, for 29mm, 38mm, and 54mm motors. The fins are 1/8” plywood with solid carbon rod leading edges and tubular carbon rod trailing edges epoxied in place. The fins were tack attached with CA, while two foam board templates were holding the fins in place. Once the fins were in place, I used a mix of Aeropoxy adhesive epoxy and Kevlar pulp to form the structural fillets. I used Aeropoxy Light filler and a PVC coupler to make a smooth and consistent aero fillet. I then added a layer of 5 oz carbon fiber to the fins. Typically this is not required, but since this will fly (hopefully) in the transonic realm, it is needed to give the fin extra rigidity to combat fin flutter.

The fin can is a “zipperless” design, so the coupler will be suggested to a lot of stress, and is likely the “weak link” of the design. For that reason I added 2 wraps of fiberglass and 1 wrap of carbon fiber to give it an extra strength factor. I chose a 316 stainless steel U-bolt from McMaster Carr. The properties 316 SS are better than 304 SS, and much better than standard carbon steel to resist corrosion. That is why 316 SS is used inside the human body and in marine applications. I attached a birch plywood cap with the same kind of mix I used for the structural fillets. I added brass strips, which were drilled to accommodate the 3 x 2-56 Nylon screws which will serve as sheer pins.

All in all I am pretty much pleased with the fin can. The only thing that I am not very happy about is that it will weigh in at about 1000 grams, which is about half of my launch weight budget. If I had to do it over again I think I could cut almost half the weight off by simply using carbon fiber for the tube. But this is a learning process, and I am learning I have a truck and not a sports car. Hopefully it is a tough truck!

Finally, this is my first rocket which will use rail buttons and not lugs. Rather than glue the buttons to the airframe, I surface mounted two nuts to accommodate the buttons near the fore and aft section of the fin can. For the top lug I added a second nut inside the airframe. This is typically not done, so it was a little risky. After I glued them, I had concerns about the alignment and whether or not they were within the tolerances of the launch rail. So I ordered a 3 foot section of launch rail so I could check things. The rail came and it turned out that it was within tolerances. The buttons felt very secure, as well. When I had the fin can hanging horizontally on the rail, it reminded me of an AIM-9 Sidewinder (even though tip mounted rails are rotated 90 degrees away from the aircraft).

Now I have to figure out what to work on next, the airframe or the avionics bay. Hmmm.

Cheers
Greg

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Well I finished what I call the gross paint effort on the fin can. I now have the major coverage on the fin can, which was accomplished with rattle-can spray paint. The white paint is Rustoleum Gloss White, Professional. I would paint a light coat, wait about 7 minutes, then put on another coat. I liked how that paint performed. The gloss black is a Rustoleum product as well. It only performed so-so. I might use it again or I might not. For the coupler I was going for a chromate green, as an homage to the internal areas of WWII aircraft. That was actually Krylon avocado, and it performed pretty well. I then added the rail buttons. So far I think it is slowly matching the vision I have for it.

I do plan to throw on some trim paint and more details. But I don’t want to go hog wild, since this is more of an experimental airframe than something I want to show off. And because I would feel bad if it crashed!

I have also been seasoning tubes for rolling carbon fiber cloth. If all goes well, then I may have the rest of the airframe sometime soon. The next big sub-project is the av bay, followed by the pistons.

It is interesting that a few years ago when I was building modrocs (and I still like to do that) that doing this was something that I had no desire to do. But I think my desire changed when I saw the abject disappointment of a family that lost their rocket that flew on a G motor. From then on I thought one of the best ways to get a rocket back (and to avoid the heartache) was to use lower thrust, or make the jump to dual-deployment. Hopefully I will find out later this year if I did my “homework” and things work as advertised.

Greg

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I've never messed with HP or electronics like this.

If your fin can is closed up, how does it deploy? Is there a transmitter/receiver pair or wire jacks that will pull free?!?

That is a very good question.

I plan not to use an ejection charge in the motor, so when motor burnout is complete it will have done its job.

Between the fin can and the nose cone, there are three tube sections. The tube above the fin can is the drogue bay, which houses the drogue chute. The tube above the drogue bay is the avionics bay (aka, av bay, electronics bay, e-bay) which houses the flight electronics. Finally, above the av bay is the main bay, which houses the main chute.

There is a small altimeter unit in the av bay that has a barometric sensor. Prior to launch, you flip switches to determine at what altitude you want the main to come out. While the rocket is mounted on the rod/rail you activate the unit. The altimeter is wired to two separate black powder charges, one in the drogue bay side and the other on the main bay side.

At launch, the altimeter "senses" that it is moving and gets ready for apogee. At apogee, when the barometer readings go static (more or less), electrical current is sent to the drogue BP charge by a special wire called an e-match (electrical match). This is essentially the same kind of wire that professional pyro technicians use at fireworks displays to launch the firework from its mortar tube. The BP charge fires an the expanding gas separates the airframe joint, just like on a modroc. With drogue chute, you want to target about a 50 ft/sec rate of fall. That speed minimizes drift while not causing a whole lot of shock on your rocket when the main deploys.

At the predetermined altitude, the main charge will fire when the barometer detects that altitude and out goes the main chute. Hopefully, it will land gently near the pad!

Greg

Kinda like when Windows 95 came out, plug & pray!

I think the "butterfly factor" will be quite large that day!

Greg

I made some decals for this project to dress it up a bit. I wanted something that fit the paint scheme and suggested a NASA launch vehicle, so I used the shuttle as a guide.

I used Bare Metal Chrome for the metallic accents on the fin TE. I cut out a size larger than required and stuck it on after removing the self-adhesive backing. I used a Q-Tip to burnish it smooth. I made a small template of clear Mylar of the shape I was going for and used a sharp hobby knife to cut the foil and removed the excess foil with tweezers.

I played with the scale and placement on a CAD program, then when everything looked like it fit I put them on inkjet decal paper. I sprayed 4 light coats of Krylon Gloss Acrylic Crystal Clear, waiting about 30 minutes or so between coats. And waited over 24 hours before attempting the decal application. My rule is to wait at least 24 hours or until the odor has pretty much stopped.

When I remember, I apply alcohol to degrease the surface. I used distilled water (I had it handy because of the small fish bowls close by) with just a touch of dishwashing soap. Nothing else was used to help set the decal other than dabbing with or using the capillary action of a paper towel to help coax out the extra water.

Whew! This was a lot of work, but I like the way it came out.

Greg

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Looking great so far, love the decals, truly spices it up some .

2.6" host mount was popular back in the day, should allow the single motor options you mention, plus dual or triple 29mm, and 4 x 24mm , etc.... although the fin can section is too short for a 2.5" RATTworks K240


keep posting, looks great .

~ AL

I would have made the fin can a bit longer to take bigger motors if your planning on 38mm and 54mm motors.