I started with the sustainer fins. I've been planning how to do these for some time. The foil is hard to get right as the leading angle is less than 1 degree. I've had really good luck in the past making ply fins with veneer birch and balsa so I figured a way to create the fins from built up thin layers with a skin layer. The skin is scored at the edges between planes.
Nice project! The real thing has a great Flame-to-rocket ratio
Good luck getting the staging to work out. As they say, high-power staging isn't twice as hard, it's 10x as hard (and keep adding zeroes for subsequent stages)
The sustainer is LOC 2.14" tube. The fin can/nozzle area is almost exactly the diameter of the coupler tube.
I got started on the fin can setting a CR to the leading edge of the fin tabs, using a coupler to make sure it's square to the airframe. Then glued in a motor tube using a temporary rear CR to center it.
Angled fin slots are marked and cut. I'll glue in each fin before cutting the next one in order to keep the tube from getting out of round since the cut will extend to the end of the tube.
Also got started on the tailcone. It's 1/32 birch ply, will need plenty of filling and sanding.
4 fins in place. Next is the slotted fin can which will need internal fillets for strength since it will support the interstage coupler. Then I'll start building out the tailcone/interstage.
Glad you guys are following along, I'll carry on then!
Added a centering ring down inside the fin can coupler material, up against the aft ends of the fin tabs for strength. Used screws as temporary handles to dry fit and eventually glue it in place.
Worked on the tailcone. Here I have some scrap airframe and coupler that I'll dry fit the cone onto to glue the centering into the back of the cone. I've sanded the edge of the CR to match the cone angle.
And the CR glued in place. Starting to look like a cone type thing!
A third CR went on the end of the coupler for strength where the airframe extension will go. The cone will go on followed by the airframe extension. Another temporary CR will keep it straight.
So far the Cg is well ahead of the Cp so I will be moving the location of the electronics bay further aft to reduce overstability. I'll have it just far enough forward to accommodate a 6GXL motor.
The tail cone should meet flush with the fin can so it needs some filler to smooth out the joint. I marked the edge where they should meet with masking tape and filled. After drying I sanded up to the edge and cleaned up some more after removing the tape. After the pics I filled the gaps behind the fins using the angles I'd already sanded as guides.
The electronics bay is pretty standard design. For a rocket this size I use #6 threaded rod. Will have a rotary switch for power and a slide switch to shunt the igniter.
Thanks Dave, the first pic is the flight I'll be modeling. It was a test flight with a shorter sustainer than flights loaded up with instrumentation.
Got a first coat of primer on the business end of the sustainer. I love how the first coat of primer unifies the look of all the various materials. Looking good so far, plenty of sanding, filling, and priming from here.
Sanded down the first coat of primer with 220 and filled some low spots.
Extended the motor tube about 3/4 inch and glued on the Estes retainer. I had made the interstage extension a bit longer than anticipated, and I like the motor retainer sticking out a bit so I can easily tape the igniter lead to it.
Then got the connectors on the leads. I like to use these PC board header type connectors here. I have a batch of ematches soldered to PC header pins ready to go in my launch box so at the field I just plug and tape.
The connection to the ebay is similar but the molex equivalent. A harness can be made up and keyed with male and female contacts. The connection isn't locking but the contacts have a pretty strong tension so it won't disconnect until the airframe separates and pulls them apart. The connectors are carefully soldered in addition to crimped because they will take some abuse.
The LOC nose cone is a bit long, and actually doesn't really start to taper for a couple inches past the base. I was able to cut a couple inches out for a more scale shaped nose.
Above shows where I made the cut. Then I cut off the shoulder. A few minutes with the dremel and I epoxied it back together.
Pic with new nose cone. Bottom section has second coats of filler, primer, and sanded to 220.
Watching with great interest! I love sounding rockets and have a small collection of different Black Brants. My next big scale build will probably be another BB.
Installed a centering ring about 10" below the nose cone. I like to do this as an anchor point as well as holding the chute up by the nose cone so it doesn't slide to the bottom during boost.
Alright got the black on yesterday. The black brant should be flat black but I went with a satin sheen because it will be a lot tougher. Flat will show every scuff and scrape. I plan on flying this a lot. Don't tell anyone.
It's hard to get the fin angles with the camera but here's the best I could do with the lamp at a good angle.
While the paint dried I sewed an octagonal parasheet with spill hole.
This evening I drilled a couple holes in the switch ring for the rotary switches. Upper stages will have a power switch and an igniter disconnect switch.
They do kind of stick out like a sore thumb but at least they'll be rotated toward the back (either side of the rail). Safety is paramount so I find a really dummy-proof system at the pad is important for the safety of a complex rocket. There's always someone who needs to offer "assistance" which can lead to distraction. I hate monkeying with tape, wires, etc. out at the pad.
Getting some paint on it. Starting to look like a black brant.
Wiring up the electronics bay. Decided to go with a second rotary switch instead of a slide switch for the motor igniter. Soldered leads to the switches, will mount them in the band, then make the connections.
