It's been a while since I posted anything as the weather here in Chicago hasn't really been great for priming or painting. I finally got the itch to do something and decided to build something that didn't need paint.
Looking at the build pile I grabbed a Sky Writer I picked up on clearance a while back. After a quick thumb through the instructions I knew there was a few things I was going to change.
The first thing I did was to modify the fin can. I have never been a fan of the shape of this fin can. I much prefer the tapered almost diamond shape of the old Challenger Fin can. With a little tape for a guide and a fresh blade in the hobby knife, I cut an angle into the lower portion of the fins that matches the angle on the top. The plastic is super soft and this only took about 5 mins to complete.
Next it was on to the motor mount. It was here that I was shocked at how the motor attaches, or rather doesn't attach to the fin can. If you build per the instructions, there is NOTHING connecting the fin can to the motor mount except for a the motor clip retainer which really doesn't touch anything inside the fin can. To correct this I added a pair of BT20/50 centering rings to the outside of the motor tube as shown below. You can see that the upper ring will sit on the lip inside the fin can. The lower ring will sit even with the bottom of the fin can.
Also note that I left the motor spring out as I prefer my rocket to stand on their own. The motor will be friction fit for flight. The spring retainer was used to add a bit of additional strength to the motor tube since I will be friction fitting the motor.
Next I sanded the inside of the fin can with some 240 grit and glued the motor mount in place using a generous amount of thick CA. I then applied TBII to the inside of the adapter ring as well as the outside of the motor tube and slide the adapter ring in place. Note the green outer layer of the adapter ring was removed so the glue would soak into the cardboard for the next step.
This was left to dry overnight.
The next day I attached the fin can to the lower body tube. The inside of the lower body tube was lightly sanded with 240 grit for better adhesion. I wasn't trying to remove material here, just scuff it up so the glue would soak in.
A generous amount of TBII was added to the outside of the adapter ring as well as the inside of the lower body tube. The pieces were then slide together. Any glue that pushed out was wiped up with a damp towel and the rocket was stood upright to allow the glue to dry.
I recently bought a few baffle kits from Qualman Rocketry. I initially bought them for my square New Way rockets but I was so impressed with them that I went back and bought a bunch in various sizes.
Below you can see a completely assembled Qualman baffle. After assembly, I coated the entire baffle in thinned wood glue to give it some heat protection. Also note that I doubled up on the thickness of the upper plate as I will be adding a screw eye as an attachment point for the Kevlar leader. The fit was perfect but I still hit the outside edges with some 100grit to give me a surface for the glue to soak into.
This was slid about two inches up into the upper body tube. It was glued in place using a generous amount of TBII.
Next I decided to replace the stock coupler which is very short with a piece of 4 inch coupler stock that I sourced from Balsa Machine. I feel the longer coupler gives the joint more strength and stability so I have a better chance of getting and keeping the tubes straight during assembly and flight.
Not shown. I coated the inside top two or so inches of the upper body tube with thin CA to help prevent zippering and dents.
In this pic you can see the lower half of the rocket completed. The Baffle has already been inserted into the upper half and the Kevlar leader is visible hanging out the top of the upper tube. The new center coupler is shown between the rocket halves.
The entire coupler was covered in TBII glue and a generous amount was also spread around the inside of the upper tube. The coupler was slid into place and butted against the bottom of the baffle. Next I added a generous amount of TBII glue to the inside of the lower tube and the two halves of the rocket were slid together. NOTE. I was able to do this at one time as the coupler was being held in place by the baffle in the upper tube so it could not move.
Excess glue was wiped away with a damp towel.
Next added approx. 4ft of 1/8 elastic to the Kevlar leader. This was then attached to the nosecone. The stock attachment point on this nose cone is very thin. I removed it an drilled a hole for the Elastic to fit through and tied it off.
Last step in the build process is to add the decal. While the kit does come with self stick, I know the quality isn't the greatest so I cut my own on vinyl and applied them. I'm happy with the way they turned out. Overall, not a bad build for about 2 hours of actual work time.
I often get asked what all my changes add as far as weight goes or how it effects the rockets flight. With this rocket I'm not concerned with stability due to its length. But I was careful to add weight with things like the baffle and longer coupler to offset some of the weight of the additional parts in the rear of the rocket.
Final weight with the stock chute but no motor is 1.8oz as shown. A quick sim with the adjusted fin design and added weight still show good performance. A normal C6-7 will still get you just shy of 1000ft while an A8-3 would make this a great small park flier. You can get silly with a composite and put it up 1700+ft on a D21-7.
Looking at the build pile I grabbed a Sky Writer I picked up on clearance a while back. After a quick thumb through the instructions I knew there was a few things I was going to change.
The first thing I did was to modify the fin can. I have never been a fan of the shape of this fin can. I much prefer the tapered almost diamond shape of the old Challenger Fin can. With a little tape for a guide and a fresh blade in the hobby knife, I cut an angle into the lower portion of the fins that matches the angle on the top. The plastic is super soft and this only took about 5 mins to complete.
Next it was on to the motor mount. It was here that I was shocked at how the motor attaches, or rather doesn't attach to the fin can. If you build per the instructions, there is NOTHING connecting the fin can to the motor mount except for a the motor clip retainer which really doesn't touch anything inside the fin can. To correct this I added a pair of BT20/50 centering rings to the outside of the motor tube as shown below. You can see that the upper ring will sit on the lip inside the fin can. The lower ring will sit even with the bottom of the fin can.
Also note that I left the motor spring out as I prefer my rocket to stand on their own. The motor will be friction fit for flight. The spring retainer was used to add a bit of additional strength to the motor tube since I will be friction fitting the motor.
Next I sanded the inside of the fin can with some 240 grit and glued the motor mount in place using a generous amount of thick CA. I then applied TBII to the inside of the adapter ring as well as the outside of the motor tube and slide the adapter ring in place. Note the green outer layer of the adapter ring was removed so the glue would soak into the cardboard for the next step.
This was left to dry overnight.
The next day I attached the fin can to the lower body tube. The inside of the lower body tube was lightly sanded with 240 grit for better adhesion. I wasn't trying to remove material here, just scuff it up so the glue would soak in.
A generous amount of TBII was added to the outside of the adapter ring as well as the inside of the lower body tube. The pieces were then slide together. Any glue that pushed out was wiped up with a damp towel and the rocket was stood upright to allow the glue to dry.
I recently bought a few baffle kits from Qualman Rocketry. I initially bought them for my square New Way rockets but I was so impressed with them that I went back and bought a bunch in various sizes.
Below you can see a completely assembled Qualman baffle. After assembly, I coated the entire baffle in thinned wood glue to give it some heat protection. Also note that I doubled up on the thickness of the upper plate as I will be adding a screw eye as an attachment point for the Kevlar leader. The fit was perfect but I still hit the outside edges with some 100grit to give me a surface for the glue to soak into.
This was slid about two inches up into the upper body tube. It was glued in place using a generous amount of TBII.
Next I decided to replace the stock coupler which is very short with a piece of 4 inch coupler stock that I sourced from Balsa Machine. I feel the longer coupler gives the joint more strength and stability so I have a better chance of getting and keeping the tubes straight during assembly and flight.
Not shown. I coated the inside top two or so inches of the upper body tube with thin CA to help prevent zippering and dents.
In this pic you can see the lower half of the rocket completed. The Baffle has already been inserted into the upper half and the Kevlar leader is visible hanging out the top of the upper tube. The new center coupler is shown between the rocket halves.
The entire coupler was covered in TBII glue and a generous amount was also spread around the inside of the upper tube. The coupler was slid into place and butted against the bottom of the baffle. Next I added a generous amount of TBII glue to the inside of the lower tube and the two halves of the rocket were slid together. NOTE. I was able to do this at one time as the coupler was being held in place by the baffle in the upper tube so it could not move.
Excess glue was wiped away with a damp towel.
Next added approx. 4ft of 1/8 elastic to the Kevlar leader. This was then attached to the nosecone. The stock attachment point on this nose cone is very thin. I removed it an drilled a hole for the Elastic to fit through and tied it off.
Last step in the build process is to add the decal. While the kit does come with self stick, I know the quality isn't the greatest so I cut my own on vinyl and applied them. I'm happy with the way they turned out. Overall, not a bad build for about 2 hours of actual work time.
I often get asked what all my changes add as far as weight goes or how it effects the rockets flight. With this rocket I'm not concerned with stability due to its length. But I was careful to add weight with things like the baffle and longer coupler to offset some of the weight of the additional parts in the rear of the rocket.
Final weight with the stock chute but no motor is 1.8oz as shown. A quick sim with the adjusted fin design and added weight still show good performance. A normal C6-7 will still get you just shy of 1000ft while an A8-3 would make this a great small park flier. You can get silly with a composite and put it up 1700+ft on a D21-7.
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