boatgeek
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- Dec 27, 2014
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TRF newbie here asking for design comments on a new scratch rocket. Here's the scoop:
Just after WWII, my great-grandfather was working as a commercial photographer in the LA area. He was hired by the Starkist company to take pictures of their tuna and make a promotional movie. As you can see from the picture below, these were the days when fishermen's lives were pretty cheap and the sea was a limitless resource. That really is four guys with bamboo poles standing on a grating outside the boat yanking one several-hundred-pound tuna over the rail.
I fell in love with that fin shape for a rocket, especially the lower pectoral fin in the picture. On the other hand, I knew that an 8:1 aspect ratio would make it awfully hard to keep the fin attached to the body tube. So after some tracing, a little judicious scaling in AutoCAD and a trip through OpenRocket, we have this design:
The motor mount is 29mm since I have a 3-grain Cesaroni kit with spacers and a couple of single-use motors hanging about. The bulkhead/centering ring near the front of the motor mount will likely become a bulkhead with a hole to stop forward movement of the larger casings. I've had trouble with recovery harness attachment on MD rockets, so the body tube is 38mm, with TTW fins laser cut from 1/8" plywood. It's good to have a friend with a laser. Stability is kinda high for the 1-grain/disposable motors at over 2.5 calibers, but I want to be able to launch it on low-thrust 3-grain motors, ideally some of the longburns like the Mellow or G/H54 Red Lightning. I also expect the CG to move aft a bit to account for epoxy and fillets around the fin can and motor mount. The overall rocket is about 30" long, although it's possible I'll go with a 34" piece of LOC tubing for the body tube. Less cutting that way. The launch lug shown is for drag purposes. I expect to launch on 1010 rail buttons at club launches in WA.
On to the questions:
Do you see any fatal (or non-fatal) flaws in the design I should address?
Would it be a good idea to put in a coupler a little above the fin can so that I could add a dual deploy and/or access the recovery harness root for maintenance/repair?
Is it going to be impossible to work between the 29mm and 38mm tubes?
Does anyone do non-BP dual deploy systems (springs, co2, etc.)?
I'll be back with pictures as I build. Thank you!
Note: These pictures came in really tiny. Is there an easy way to adjust that?
Just after WWII, my great-grandfather was working as a commercial photographer in the LA area. He was hired by the Starkist company to take pictures of their tuna and make a promotional movie. As you can see from the picture below, these were the days when fishermen's lives were pretty cheap and the sea was a limitless resource. That really is four guys with bamboo poles standing on a grating outside the boat yanking one several-hundred-pound tuna over the rail.
I fell in love with that fin shape for a rocket, especially the lower pectoral fin in the picture. On the other hand, I knew that an 8:1 aspect ratio would make it awfully hard to keep the fin attached to the body tube. So after some tracing, a little judicious scaling in AutoCAD and a trip through OpenRocket, we have this design:
The motor mount is 29mm since I have a 3-grain Cesaroni kit with spacers and a couple of single-use motors hanging about. The bulkhead/centering ring near the front of the motor mount will likely become a bulkhead with a hole to stop forward movement of the larger casings. I've had trouble with recovery harness attachment on MD rockets, so the body tube is 38mm, with TTW fins laser cut from 1/8" plywood. It's good to have a friend with a laser. Stability is kinda high for the 1-grain/disposable motors at over 2.5 calibers, but I want to be able to launch it on low-thrust 3-grain motors, ideally some of the longburns like the Mellow or G/H54 Red Lightning. I also expect the CG to move aft a bit to account for epoxy and fillets around the fin can and motor mount. The overall rocket is about 30" long, although it's possible I'll go with a 34" piece of LOC tubing for the body tube. Less cutting that way. The launch lug shown is for drag purposes. I expect to launch on 1010 rail buttons at club launches in WA.
On to the questions:
Do you see any fatal (or non-fatal) flaws in the design I should address?
Would it be a good idea to put in a coupler a little above the fin can so that I could add a dual deploy and/or access the recovery harness root for maintenance/repair?
Is it going to be impossible to work between the 29mm and 38mm tubes?
Does anyone do non-BP dual deploy systems (springs, co2, etc.)?
I'll be back with pictures as I build. Thank you!
Note: These pictures came in really tiny. Is there an easy way to adjust that?