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I was able to pick up a new polecat pershing 2 from Tim Z at our last launch. I made a few modifications to the kit and it turned out pretty well.
The cone was very nicely made, just required filling a bit of the seam with auto-body filler. I'm never happy trying to sand cone shoulder bands to fit body tubes, I've tried to do this with other fiberglass cones and am never happy with the fit. So in this case I simply cut 10" of body tube and attached it to the very tight nose cone shoulder with screws. I then made a coupler that is permanently mounted to the lower tube and the coupler and body tube act as the shoulder and they fit very nicely. The coupler I got was also very tight, so I had to slice and remove a bit of material, I then sliced and adjusted a second coupler to fit inside this first one as a doubler. I used 3m-77 spray contact cement to attach the couplers together with the seams offset and used some CA wicked into the ends as well. The kit design intends for the builder to put a bulkhead ahead of the root of the forward fins. The bulkhead has a large opening to allow for adding ballast but leaves the model with a large amount of volume to pressurize.
I made a 5.5" bulkhead from 1/4" ply that butts against the nose cone shoulder instead. I also drilled out the tip of the nose cone and installed a 3/8" piece of allthread from the bulkhead to the nose cone tip. I added a nut and washer at the end of the allthread to fit inside the tip and then added my ballast. The idea is the shot/epoxy is attached to the cone and allthread and washer/nut so all the recovery force is on the allthread and so the cone is just a shroud with no load bearing really. I reprofiled the tip of the allthread to match the cone and now any landing force is also directed on the allthread instead of the fiberglass. I put some 1/4" ply tabs and hold the forward plate to the body tube portion with screws so I can remove the screws and the nut on the allthread and pull it out if I need to add more nose weight later.
I have an altimiter bay that I made out of 38mm motor tube with a ply end plate, lipo battery and misileworks altimiter with switch and port, and a ply cap with deployment leads that I used in all of my other 7.5" rockets. It simply mounts to the inside of the rocket against the top centering ring and is held with two screws from the outside. All of my rockets are drilled with the same screw pattern, vent hole, and switch hole so I can swap them. I've made an epoxy flange on the altimiter bay to fit the insde of the body tube to give a nice 1" wide seal/fit to the inside of the tube. Since this is a 5.5" tube there wasn't enough room between the 38mm motor tube and the side wall so I built a 1/2" platform to allow the altimiter bay to sit on top of that. The flange still fit fine to the 5.5" tube. I don't run dual deployment, just main and redundant main+1s and those charges sit on the forward centering ring.
The fin slots are rounded because they are cut with a round cutter, and required me to just square up the ends to fit the fin tabs, took a few minutes with a mill file. The fins don't come beveled now but it was short work by hand on my belt sander to add them.
The kit comes with rail lugs and screws, but no nuts for them, I added 1/4" ply plates and T nuts on the inside of the body tube ahead of the rear and forward centering rings to secure them in place.
I'm not a fan of tubular nylon recovery attachment nor of permanently attached recovery tethers. I also didn't like the short 12" motor tube. For a rocket that will require nose weight for CG I didn't want a pound of parachute/recovery weight down that far into the tube, and I wanted to be able to reach in and swap out the quick/link/recovery kevlar so I ordered a 20" motor tube to push the forward centering ring up higher. The kit does come with nice u bolts with backing plates. I added top plates to them as well since that's just me.
The fit of the fins was quite nice and they went in place with no problems. This was my first time finishing pre-glassed cardboard tubes, it took a good amount of sanding with 180 to get through the gelcoat and even out the glass fiber. They are wrapped twice so don't feel shy about sanding to even out any wrinkles and the overlap as there is material and gel coat there. I used three coats of plasticote gray filler primer with sanding inbetween and then used krylon camo olive spray and some titanium on the nose. I didn't have silver or white so will have to finish the white of the nose at a later date. Mark at stickershock provided the vinyl and it looks very nice. The army markings are done in a way to make them look like slightly rough stenciled paint application which is neat. There were two minor issues with the upper two red wraps and Mark has adjusted them and they now fit great.
recommended CG is 35" from the nose which is about in the middle of the lower orange band. If you use small 38mm or 29mm motors only and use motor ejection and a light chute/recovery hardware you might be able to get away with little or no nose weight and come in around 6-7 pounds rtf but I built mine to fly on j's primarily so that's how I built it.
Chute is left up to the builder, a single 60" seems like 22fps and 78 is 17fps decent rate so I'll have to see how gently it comes down on the first flight and make a call on whether to use the smaller chute.
I sized my body tube area to just fit some dog barf, the nomex blankets, kevlar recovery and chute and there is no room left for much air, so I didn't add any vent holes for pressure build up as this wont' go that high or fast, and there isn't any empty space filled with air.
There are a lot of little details you can add if you want to, Sodmeister has done a great job in his thread and for some reason I just didn't feel like doing them on this rocket. AUW dry rtf is 8 pounds with ballast and 10# with j350 or 10#11oz with J570 or J575. With the stretched motor tube the J510 will fit, It should fly between 2500-3500 on the 350-570 motors and higher on the 510.
Here she is ready to go. And along with my two other intermediate range ballistic missile brothers.
Frank
The cone was very nicely made, just required filling a bit of the seam with auto-body filler. I'm never happy trying to sand cone shoulder bands to fit body tubes, I've tried to do this with other fiberglass cones and am never happy with the fit. So in this case I simply cut 10" of body tube and attached it to the very tight nose cone shoulder with screws. I then made a coupler that is permanently mounted to the lower tube and the coupler and body tube act as the shoulder and they fit very nicely. The coupler I got was also very tight, so I had to slice and remove a bit of material, I then sliced and adjusted a second coupler to fit inside this first one as a doubler. I used 3m-77 spray contact cement to attach the couplers together with the seams offset and used some CA wicked into the ends as well. The kit design intends for the builder to put a bulkhead ahead of the root of the forward fins. The bulkhead has a large opening to allow for adding ballast but leaves the model with a large amount of volume to pressurize.
I made a 5.5" bulkhead from 1/4" ply that butts against the nose cone shoulder instead. I also drilled out the tip of the nose cone and installed a 3/8" piece of allthread from the bulkhead to the nose cone tip. I added a nut and washer at the end of the allthread to fit inside the tip and then added my ballast. The idea is the shot/epoxy is attached to the cone and allthread and washer/nut so all the recovery force is on the allthread and so the cone is just a shroud with no load bearing really. I reprofiled the tip of the allthread to match the cone and now any landing force is also directed on the allthread instead of the fiberglass. I put some 1/4" ply tabs and hold the forward plate to the body tube portion with screws so I can remove the screws and the nut on the allthread and pull it out if I need to add more nose weight later.
I have an altimiter bay that I made out of 38mm motor tube with a ply end plate, lipo battery and misileworks altimiter with switch and port, and a ply cap with deployment leads that I used in all of my other 7.5" rockets. It simply mounts to the inside of the rocket against the top centering ring and is held with two screws from the outside. All of my rockets are drilled with the same screw pattern, vent hole, and switch hole so I can swap them. I've made an epoxy flange on the altimiter bay to fit the insde of the body tube to give a nice 1" wide seal/fit to the inside of the tube. Since this is a 5.5" tube there wasn't enough room between the 38mm motor tube and the side wall so I built a 1/2" platform to allow the altimiter bay to sit on top of that. The flange still fit fine to the 5.5" tube. I don't run dual deployment, just main and redundant main+1s and those charges sit on the forward centering ring.
The fin slots are rounded because they are cut with a round cutter, and required me to just square up the ends to fit the fin tabs, took a few minutes with a mill file. The fins don't come beveled now but it was short work by hand on my belt sander to add them.
The kit comes with rail lugs and screws, but no nuts for them, I added 1/4" ply plates and T nuts on the inside of the body tube ahead of the rear and forward centering rings to secure them in place.
I'm not a fan of tubular nylon recovery attachment nor of permanently attached recovery tethers. I also didn't like the short 12" motor tube. For a rocket that will require nose weight for CG I didn't want a pound of parachute/recovery weight down that far into the tube, and I wanted to be able to reach in and swap out the quick/link/recovery kevlar so I ordered a 20" motor tube to push the forward centering ring up higher. The kit does come with nice u bolts with backing plates. I added top plates to them as well since that's just me.
The fit of the fins was quite nice and they went in place with no problems. This was my first time finishing pre-glassed cardboard tubes, it took a good amount of sanding with 180 to get through the gelcoat and even out the glass fiber. They are wrapped twice so don't feel shy about sanding to even out any wrinkles and the overlap as there is material and gel coat there. I used three coats of plasticote gray filler primer with sanding inbetween and then used krylon camo olive spray and some titanium on the nose. I didn't have silver or white so will have to finish the white of the nose at a later date. Mark at stickershock provided the vinyl and it looks very nice. The army markings are done in a way to make them look like slightly rough stenciled paint application which is neat. There were two minor issues with the upper two red wraps and Mark has adjusted them and they now fit great.
recommended CG is 35" from the nose which is about in the middle of the lower orange band. If you use small 38mm or 29mm motors only and use motor ejection and a light chute/recovery hardware you might be able to get away with little or no nose weight and come in around 6-7 pounds rtf but I built mine to fly on j's primarily so that's how I built it.
Chute is left up to the builder, a single 60" seems like 22fps and 78 is 17fps decent rate so I'll have to see how gently it comes down on the first flight and make a call on whether to use the smaller chute.
I sized my body tube area to just fit some dog barf, the nomex blankets, kevlar recovery and chute and there is no room left for much air, so I didn't add any vent holes for pressure build up as this wont' go that high or fast, and there isn't any empty space filled with air.
There are a lot of little details you can add if you want to, Sodmeister has done a great job in his thread and for some reason I just didn't feel like doing them on this rocket. AUW dry rtf is 8 pounds with ballast and 10# with j350 or 10#11oz with J570 or J575. With the stretched motor tube the J510 will fit, It should fly between 2500-3500 on the 350-570 motors and higher on the 510.
Here she is ready to go. And along with my two other intermediate range ballistic missile brothers.
Frank
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Can you do the same thing with a Barbie doll?
