BRS Hobbies
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- Mar 30, 2009
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The U.S. Interroc is a versatile mid power rocket that comes with two interchangable motor mounts - 29mm and 3 x 24mm. I chose to build this rocket so I could use it with my Aerotech RMS reloads and also launch it as a Estes "D" or "E" cluster. Initial inspection of the kit was very good. The tubes are heavy walled and very smooth, fins and centering rings are nicely cut out of 1/8" plywood and the balsa nose cone is of good quality. The kit is kind of old school but I like that. It takes you back to a lot of the true builder kits of the past like the early Estes kits. I did a quick check of the parts and couldn't find the parachute. I e-mailed Jerry Irvine of U.S. rockets and he offered to send out a parachute free of charge. I received the parachute via Priority Mail 3 or 4 days later.
The first few steps are sanding the fins, marking the body tube and attaching the fins. Everything is very straight forward. I chose to tack on the fins with CA and then use epoxy for the fin/body fillets. For some reason the CA didn't stick to the body tube very good. Looking back, I think the recommended wood glue would be the way to go to tack on the fins and then either wood glue or epoxy for the fin/body fillets.
Next is the coupler assembly. I decided to make the separation point at the nose cone rather than at the two body tubes. I don't really need a payload bay for this rocket. I made a small baffle ring by drilling three holes in the included plywood bulkhead to help keep the recovery system up in the tube. I glued the baffle ring in the upper tube first and then the tube coupler with wood glue. After this dried, I glued the other end of the coupler to the lower body tube.
Next is making the engine mounts. I prepped each tube by slightly sanding the inside diameter of each tube to clean the edges and then coated each inside diameter with CA to make the tubes more durable. This really helps keep the edges of the motor tubes from rolling over inside the tubes when inserting the motor. The centering rings fit kind of loose on the 29mm motor mount tube so I coated the inner diameter with wood glue. This did the job and provided a good fit with the tube. Both engine mounts went together very smoothly. The instructions suggest wrapping masking tape around the outside of each motor mount to act as a thrust ring. I decided to cut 2 - 1/2" sections from one end of the body tube. Using the nose cone shoulder as a mandrel, I cut each 1/2" section. I then glued one of the 1/2" section ring to the 29mm motor mount. On the 3 x 24mm motor mount, I wrapped a 1" wide strip of brown paper bag around the aft end to provide a better fit of the motor mount tubes inside the main body tube. I then glued the other 1/2" section over the brown paper bag wrap a 1/2" from the end of the motor tubes. The fit of each motor mount is very good inside the motor tube.
Next is gluing the on the launch lugs. I cut the front end of the launch lug at an angle as shown in the directions. This gives the lugs a more streamlined appearance. After the glue dried, I added some glue fillets to each side of each launch lug.
Next is the shock cord mount. The kit came with a tri-fold paper shock cord mount. I have had a lot of success with this style mount. I chose to use a brown paper bag instead of the included cardstock. I have read that the the brown paper absorbs the wood glue better. I also used a small length of Kevlar thread instead of the elastic. I put a small loop on the end of the kevlar and glued the mount inside the body tube so the Kevlar is just short of the end of the body tube. I then tied the elastic shock cord to to the loop of Kevlar. This will allow me to change the elastic shock cord easily. I applied a nice layer of wood glue over the shock cord mount to help give it some extra strength.
Finishing up and getting ready to paint. I used some finishing resin to coat the balsa nose cone. I have never tried this before but am really happy with the results. The finishing resin is a really slow curing epoxy (2 hours). I hung the nose cone with the tip pointing done and then brushed on the epoxy and let it drip down the entire nose cone. I put some wax paper under the tip to catch the drips. The result is a hardened sandable surface that should help protect it from dings. I then brushed some Delta sealer on the fins to seal the fins and keep them from warping. After the sealer dried, I sanded the entire rocket to get it ready to paint.
The first few steps are sanding the fins, marking the body tube and attaching the fins. Everything is very straight forward. I chose to tack on the fins with CA and then use epoxy for the fin/body fillets. For some reason the CA didn't stick to the body tube very good. Looking back, I think the recommended wood glue would be the way to go to tack on the fins and then either wood glue or epoxy for the fin/body fillets.
Next is the coupler assembly. I decided to make the separation point at the nose cone rather than at the two body tubes. I don't really need a payload bay for this rocket. I made a small baffle ring by drilling three holes in the included plywood bulkhead to help keep the recovery system up in the tube. I glued the baffle ring in the upper tube first and then the tube coupler with wood glue. After this dried, I glued the other end of the coupler to the lower body tube.
Next is making the engine mounts. I prepped each tube by slightly sanding the inside diameter of each tube to clean the edges and then coated each inside diameter with CA to make the tubes more durable. This really helps keep the edges of the motor tubes from rolling over inside the tubes when inserting the motor. The centering rings fit kind of loose on the 29mm motor mount tube so I coated the inner diameter with wood glue. This did the job and provided a good fit with the tube. Both engine mounts went together very smoothly. The instructions suggest wrapping masking tape around the outside of each motor mount to act as a thrust ring. I decided to cut 2 - 1/2" sections from one end of the body tube. Using the nose cone shoulder as a mandrel, I cut each 1/2" section. I then glued one of the 1/2" section ring to the 29mm motor mount. On the 3 x 24mm motor mount, I wrapped a 1" wide strip of brown paper bag around the aft end to provide a better fit of the motor mount tubes inside the main body tube. I then glued the other 1/2" section over the brown paper bag wrap a 1/2" from the end of the motor tubes. The fit of each motor mount is very good inside the motor tube.
Next is gluing the on the launch lugs. I cut the front end of the launch lug at an angle as shown in the directions. This gives the lugs a more streamlined appearance. After the glue dried, I added some glue fillets to each side of each launch lug.
Next is the shock cord mount. The kit came with a tri-fold paper shock cord mount. I have had a lot of success with this style mount. I chose to use a brown paper bag instead of the included cardstock. I have read that the the brown paper absorbs the wood glue better. I also used a small length of Kevlar thread instead of the elastic. I put a small loop on the end of the kevlar and glued the mount inside the body tube so the Kevlar is just short of the end of the body tube. I then tied the elastic shock cord to to the loop of Kevlar. This will allow me to change the elastic shock cord easily. I applied a nice layer of wood glue over the shock cord mount to help give it some extra strength.
Finishing up and getting ready to paint. I used some finishing resin to coat the balsa nose cone. I have never tried this before but am really happy with the results. The finishing resin is a really slow curing epoxy (2 hours). I hung the nose cone with the tip pointing done and then brushed on the epoxy and let it drip down the entire nose cone. I put some wax paper under the tip to catch the drips. The result is a hardened sandable surface that should help protect it from dings. I then brushed some Delta sealer on the fins to seal the fins and keep them from warping. After the sealer dried, I sanded the entire rocket to get it ready to paint.
