Scratch-Built Scimitar

I opted to make my second effort at a mid to level one high power rocket a scratch build. I do woodworking as one of my other hobbies, so I felt like this would be an approach that let me apply those skills better than a kit build. I took inspiration from The Launch Pad with their Scimitar model. My version retains a similar style, but incorporates a lot of different construction methods that make it far more robust. The basic specs are a 2.2" diameter thick wall airframe with slots for laminated fins made from 1/64" plywood and 3/32" basswood. Motor mount is 29mm with enough length for I motor flights. Recovery is by a 30" x-form chute and an Aerotech baffle doubles as the mount for the recovery system.

The build starts with the fins. I did the general layout in Open Rocket although that didn't give me the option for making a compound bevel for the leading and trailing edges. Thanks to John Corker for posting video on that method. I deviated a little in my construction so I could avoid fiberglass, but the method was pretty much the same. Eight fins, 64 total pieces, 24 total lamination steps in vacuum bags with a lot of sanding in between. Fins finished to less than half a gram of deviation between any two fore and aft.

Moving on to the motor mount, centering rings and aft tailcone. I made the mount a good bit longer than I needed for mid power flying so I could support the full range of 29mm options. Centering rings for the forward fins and aft were all 1/4" thick plywood. This allowed for me to make a 1/8" deep groove along their faces to accept the fin roots. No jig needed to keep the fins straight when they are inserted. There's also more surface area in the joint for bonding and in the connection is on both the lateral and vertical axis. It was a little tricky to get the jig set up just right, but it worked beautifully once it was. The tailcone took a few extra steps as it was a solid, balsa transition. I cut off extra material from each end to shorten the piece so it could fit in my drill press. A 1 1/4" forstner bit made a hole for the motor mount to fit through. The hole was a touch oversized, but nothing that epoxy couldn't fill once I got to assembly. It got grooves added for the aft fin roots to lock in to and everything fit up nicely. The biggest challenge on this build was to get the centering rings to line up perfectly with each other. I made a guide out of some scrap and notched tabs at the same dimensions as the fore and aft fin roots and set that in the rings to tack them in place. The rings all got a dose of thin epoxy to bond the joints and a thicker application to fillet sides away from the fins. I took some leftover motor mount tube and added pieces in between the fin slots to make shallow beds for the base of the fin root to sit in. This would allow for a place for some extra epoxy come assembly time since I cant add internal fillets using this method.

Nice work. I really like the radial dadoes in the centering rings.

Assembly went really quickly compared to the prior build steps. I took a similar approach to mounting the recovery system as North Coast Rocketry does. A metal cable makes the first connection to the eye bolt in the baffle. This stops short of the length of the body tube. A softer, and wider, paracord connects to the end loop of the cable to complete the shock cord system. Fins all inserted into their respective wells and had no issues with being dead straight with each other and their flight planes. I did have a touch of a gap on some of the root overlays. The notches were made on my table saw and I didn't switch the blade for a dado set. The gaps were addressed in the fillet stage. I was really able to appreciate the solid feel of the construction once everything got assembled. My local fields don't offer the most gentle landing surfaces and this build should be able to handle whatever ends up underneath it.

Finished the build and was pretty happy with the results. My son's a huge Marvel fan so this was built to add on that theme. I figure those quin jets needed more than a Vulcan cannon for armament and this seemed to fit the style. The first launch day was a dodgy one for flying with unpredictable, gusty winds. The F27-7 I had on hand was a good motor for a relatively low altitude shakedown flight under good conditions but it was definitely the wrong choice in retrospect. It took a few minutes on the pad to get a moment where the wind calmed and the moment didn't last. As soon as the launch command was sent, wind picked back up again. The mid body fins caught at lot of resistance. The result was a weathercock during thrust phase, and then an arc with the wind on the coast. I probably lost a hundred feet or more of altitude but it kept a stable orientation with no spinning. The delay was far too long given the altitude shortfall. The recovery was nearly a ballistic lawn dart. Deployment went at 50 feet above the ground and the chute inflated right before ground contact. Thankfully, everything held together. It was built tough and certainly showed that it could take a rough landing. I'm expecting a better flight experience on G power the next time out. There's enough room in the motor mount for every 29mm out there, so this rocket has a lot of growth potential for the future.

Finished the build and was pretty happy with the results. My son's a huge Marvel fan so this was built to add on that theme. I figure those quin jets needed more than a Vulcan cannon for armament and this seemed to fit the style. The first launch day was a dodgy one for flying with unpredictable, gusty winds. The F27-7 I had on hand was a good motor for a relatively low altitude shakedown flight under good conditions but it was definitely the wrong choice in retrospect. It took a few minutes on the pad to get a moment where the wind calmed and the moment didn't last. As soon as the launch command was sent, wind picked back up again. The mid body fins caught a lot of resistance. The result was a weathercock during thrust phase, and then an arc with the wind on the coast. I probably lost a hundred feet or more of altitude but it kept a stable orientation with no spinning. The delay was far too long given the altitude shortfall. The recovery was nearly a ballistic lawn dart. Deployment went at 50 feet above the ground and the chute inflated right before ground contact. Thankfully, everything held together. It was built tough and certainly showed that it could take a rough landing. I'm expecting a better flight experience on G power the next time out. There's enough room in the motor mount for every 29mm out there, so this rocket has a lot of growth potential for the future.

Finally got another flight day and a chance to put a little more kick in the exhaust nozzle for this one. G64-10 took the Scimitar to 1328 AGL and 230mph. I'd have gotten a couple hundred feet higher if I hadn't gotten another weathercock trajectory. It was a long walk over the hills and through the woods to recover, but she didn't have a scratch. I looked over the open rocket file for it when I got home and decided to explore an audible recovery beacon in a nose bay. I've got farm fields and woodland scrub in my launching field and I walked the same area quite a few times before I saw the chute. The design modification also adds some more to the stability margin. Certainly a feature it needs to have if the motors get any more powerful. It's been a great experience learning from this build. Plenty more TLP designs out there that can fly as HPR.

A higher stability margin means more weathercocking, not less. That's why the term "overstable" exists.

More thrust means less weathercocking. Better than that, instead of trying to avoid it, try to compensate for it; launch into the wind.

And by the way, really nice rocket. Great launch pic.