flyguy614
Matt Dahle Photography
- Joined
- Apr 6, 2022
- Messages
- 23
- Reaction score
- 41
Hi all!
I'm new here, my name's Matt, and I recently broke the H motor world record. I thought it might be fun to make a quick post on the design of the rocket, and some future improvements to be made!
A unique (in my opinion) part of the design is that the tailcone is permanent, and the fins are mounted to it. I wanted to put the fins as far back as possible to be able to make them as small as possible while still having a stable rocket. I thought it'd be a fun and clever design consideration to work around, and it ended up working out really well. The rocket uses an H13 with no thrust ring, and the motor gets loaded in the front. The shock cord is kevlar line, which is tied in a loop on the body-tube end. the loop goes around the H13 longitudinally, and ties/wraps once around the nozzle to make sure it doesn't slip up around the motor. The kevlar around the motor creates a good friction fit for the motor in the body tube, it takes a good 60lbs+ to get the motor in or out. With the maximum thrust peak on the H13 being about 10lbs, it's a light and reusable way to retain the motor for this purpose! It also is what holds the shock cord in place, no need for an eyebolt, bulkhead, epoxy, etc.
The avionics go in the nosecone, and are held in by yet another kevlar string. This kevlar string is epoxied into the top of the nosecone, and is tied around a 3D printed coupler that fits into the bottom of the nosecone. Once tied, you tie the other end of the parachute's shock cord to that loop, and voila! You've got a rocket.
Note: I ended up finding out later that I probably could've made my fins a little bit smaller than they were, but I think I'll keep them that size to keep the stability with it being such a small and dense rocket.
I thought it'd be funny to write on the rocket in crayon, and call it "unfinished cardboard tube."
We found out that it wasn't weathercocking when I launched it again a couple days later. In zero wind, it did the same exact thing but in a different direction. Relative to the rocket, it could've been the same direction, as I didn't pay much attention to what the orientation of it was when I put it in the tower. But when plotted out, their flight paths to apogee look almost identical, with the second flight not being as good as the first. The second flight ended up reaching an apogee of around 14,870 or so. Also worth noting that the second flight's landing seemed to be a bit harder, as some of the fillets' adhesion broke from the fins. This is probably partly due to me having rushed the fillets. Glad they worked out fine on the first launch, but definitely worth having some better fillets (amongst other fixes) next time.
Thanks for reading!
I'm new here, my name's Matt, and I recently broke the H motor world record. I thought it might be fun to make a quick post on the design of the rocket, and some future improvements to be made!
Build
The rocket is a minimum diameter cardboard H13 build with carbon fins, a styrene nosecone, a 3d printed tailcone, and lots of 100lb kevlar line. I used an EasyMini on Apogee Redundant mode for charges, and a Featherweight Tracker for tracking. The chute is a 9" nylon chute.A unique (in my opinion) part of the design is that the tailcone is permanent, and the fins are mounted to it. I wanted to put the fins as far back as possible to be able to make them as small as possible while still having a stable rocket. I thought it'd be a fun and clever design consideration to work around, and it ended up working out really well. The rocket uses an H13 with no thrust ring, and the motor gets loaded in the front. The shock cord is kevlar line, which is tied in a loop on the body-tube end. the loop goes around the H13 longitudinally, and ties/wraps once around the nozzle to make sure it doesn't slip up around the motor. The kevlar around the motor creates a good friction fit for the motor in the body tube, it takes a good 60lbs+ to get the motor in or out. With the maximum thrust peak on the H13 being about 10lbs, it's a light and reusable way to retain the motor for this purpose! It also is what holds the shock cord in place, no need for an eyebolt, bulkhead, epoxy, etc.
The avionics go in the nosecone, and are held in by yet another kevlar string. This kevlar string is epoxied into the top of the nosecone, and is tied around a 3D printed coupler that fits into the bottom of the nosecone. Once tied, you tie the other end of the parachute's shock cord to that loop, and voila! You've got a rocket.
Note: I ended up finding out later that I probably could've made my fins a little bit smaller than they were, but I think I'll keep them that size to keep the stability with it being such a small and dense rocket.
Pain
This is the rocket after a paint job. This rocket in particular ended up weighing about 80g dry, about 290g wet. Unfortunately, I was putting the motor into this rocket the day before I left to Black Rock, and grabbed/pushed too hard in the wrong place. I ended up crumpling the rear end. I had some thick tube left over, and elected to rapidly build another bottom half using it instead of using thin tube. The thick tube rocket was not polished and not as aerodynamic as the first one. It was also a bit heavier, weighing in at 99g dry and 309g wet, but at least I had a rocket.I thought it'd be funny to write on the rocket in crayon, and call it "unfinished cardboard tube."
Launch
Anyway, I launched it from a tower I designed out at UROC's UR NUTS launch at Black Rock. Unfortunately, it went pretty sideways about 40ft AGL. It was positively stable, so it flew straight after that, but why it did that was a mystery. We thought it was weathercocking at first, but we found out later that it does that in zero wind as well. At maxV, it was going 917ft/s up, and 439ft/s sideways. Regardless of this, it still reached an apogee of 15,257' AGL. I certainly think it could reach 17k if it went reasonably straight up, but that's hard for a rocket like this.We found out that it wasn't weathercocking when I launched it again a couple days later. In zero wind, it did the same exact thing but in a different direction. Relative to the rocket, it could've been the same direction, as I didn't pay much attention to what the orientation of it was when I put it in the tower. But when plotted out, their flight paths to apogee look almost identical, with the second flight not being as good as the first. The second flight ended up reaching an apogee of around 14,870 or so. Also worth noting that the second flight's landing seemed to be a bit harder, as some of the fillets' adhesion broke from the fins. This is probably partly due to me having rushed the fillets. Glad they worked out fine on the first launch, but definitely worth having some better fillets (amongst other fixes) next time.
Potential Improvements
Some hopeful fixes for next time:- Longer tower
- Better designed tower braces (may have interfered with the rocket's exit)
- More stiff tower tiedowns (was paracord)
- 3D printed Von Karman NoseCone (heavier, but shoulder should fit into the BT better, eliminating possible NC tilt)
- Trapezoidal fin shape to reduce the chance of impact damage
- Fins will have tabs that go into the tailcone for a "through the wall" type support and (hopefully) better fin alignment when used in conjunction with a fin jig.
- And of course, the next one will be properly painted and polished for better aero.
Thanks for reading!
Last edited: