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I've been wanting to try this for a while, the work I did on my Dyna-soar/Titan II got me motiviated. I do a lot of depron RC airplane construction, my thought was to do a model that typically needs lots of nose weight or is very heavy, and see if using stringers/centering rings and 1mm depron skin I could make a large light model to fly on E-15's......
The only wood in this model are two centering rings in the upper portion that are lite ply, and the balsa coupler I used for my BT-70 upper tube since it was handy at the hobby shop, the rest is depron sheet, cardboard motor tubes and some .04 styrene sheet.
For drawing centering rings I've been simply using a strip of cardboard, put a thumbtack in one end, and measure to the needed radius, poke a hole and insert my fine sharpe and draw it directly on whatever I need to cut, no need for a compass. This can be used for drawing cones or transition shrouds as well where you need a very long radius.
I cut a 7" by 2" triangle out of 6mm depron, grooved and glued in a 1/8" carbon rod which will take the brunt of the nose cone landing force....I then added perpendicular triangles, and took turns gluing in triangle filler pieces and carving those to match the original triangle pieces a quarter at a time...eventually I had nose cone shape. I left one quadrant unfinished so I could add weight if needed, then finish it. I added a few gradually increasing centering rings to get the needed outer diameter.
I cut off a section of balsa bt-70 coupler and glued it to the carbon rod at the end to make the cone shoulder.
I decided on 5" diameter centering rings, so cut the rear .04 styrene plate which takes the thrust. I then used that as a template to cut the upper three centering rings.
I cut some interlocking stringers and notches in the centering rings, and added some fin boxes also in 6mm depron.
I joined all the 24mm tubes and added the upper bt70 cup which will hold the parachute. It doesn't need to be very long as at 16 ounces, I only need a 24-30" chute.
Once the upper cup and recovery attachment was epoxied in, I inserted all of the centering rings, tapering as needed for the upper section and the lower section. I added the interlocking stringers and make sure everything was straight. I glued it all together with foam safe CA, added stringers for the upper conical section to support the skin and did a bit of minor sanding to make sure there weren't any areas higher than the rest.
Now came the interesting part. I haven't used 1mm depron before, it's very thin and has a nice hard surface. It does have a grain and bends easier one way than the other. I did some testing and even though thin it still wanted to kink if you roll it too tightly. I made a cone template using this https://craig-russell.co.uk/demos/cone_calculator/ and cut it out. I used 3m-77 spray on both pieces to add the sheeting to the fuse and nose areas. Once done, I taped the seam, and applied a second sheet with the joint at 180 degrees to the first one. I knew from my dynasoar that the 2mm sheet was good for about 7-8" diameter but was too thick to curve more. I had a real pain trying to get the seams aligned at the top and bottom. Once you make contact, you can't pull the foam off without destroying it.
Unfortunately, much wailing and gnashing of teeth later, I decided the first go was not good and so fortunately it turns out, CA accellerator debonds the contact cement...so I spent an hour peeling off the sheeting and doing a touch up sanding. So much for a quick build.....I started over and did a much better job the second time. It worked pretty well and the 1mm sheet has a nice surface on both sides, but even though I had six stringers on the cone, it still flattened out somewhat between the stringers, so it's a bit hexagon shaped. The fuse was much better. The laminated 1mm sheets are pretty strong and tough. I might need to experiment with heating or adding more stringers/centering rings to get a smoother outer surface.
I made some vane pads to slip over the fins using 2mm depron. Those were glued in place after the fin slots were re-cut into the fin boxes after sheeting.
I made the fins using a core of .04 styrene sheet and one 2mm and one 3mm depron laminate (2mm on one side and 3mm on the other) This allowed me to round the edges and keep the 6mm width I used to build the fin boxes. If it flies ok and isn't too draggy, I may do a built up surface to match the wedge upper and double diamond lower profiles on the real thing. I may use .015 styrene sheet to skin over the foam...
For rail button attachment, I made some doubled .04 styrene strips to mimick the pershing cable cover, contact cemented them to the tube, and then used machine screws to hold the buttons in place in the middle of the conduits...the pulling on the button will pull on the entire styrene strip and seems to be plenty strong.
I made some charge covers(straps) out of styrene and added those with contact cement as well.
Once done I balanced and needed 3/4 ounce of nose weight in the cone and finished adding the fillers and sanding it to shape. After the cone was done I sheeted it with 1mm depron, two layers to match the forward profile.
For the markings, I wanted to minimize paint weight, so chose a primarily white round. I masked and painted the middle and lower black bands only, and used monokote self adhesive trim for the upper bands, stripes, squares. I used tapered sheets of red to cover the nose since it wasn't perfectly round I couldn't just use my cone template, there would have been wrinkles. The trim monokote adds a lot to the surface durability.
All completed, weighs 17 oz and should fly nice on any 24mm F30's. 5.25" outer diameter and 52.25" long. It was an interesting build, I wished the skinning worked better. It did come out light, about the same as a BT-101 4" maxi pershing but much larger, and the 3.75" tlp kit is around 12 or 13 oz. There aren't any real sources of light 5.5" tubing I found, loc is 18 ounces just for the 27" lower tube. It did allow me to pick whatever diameter I felt like and just build it. I used 1/2 sheet of 6mm depron and 4 sheets of 1mm, and 1/2 sheet of 2mm, for a cost of about $20, and the tubing and other pieces were about $15(my local hobby shop carries sunward parts)....sheet styrene and trim monokote I had already on hand.
I think in the 5" and up size it has huge advantages in weight and cost if you are looking to fly smaller, far 101 motors. As a comparison, my 4" pershing build using loc parts and a fiberglass conical nose and 1/16" fiberglass fins weighs 3# with proper balast and has to fly on at least G80 or G75's.......my 7.5" version weighs 20 pounds, again using loc cardboard.
Frank
The only wood in this model are two centering rings in the upper portion that are lite ply, and the balsa coupler I used for my BT-70 upper tube since it was handy at the hobby shop, the rest is depron sheet, cardboard motor tubes and some .04 styrene sheet.
For drawing centering rings I've been simply using a strip of cardboard, put a thumbtack in one end, and measure to the needed radius, poke a hole and insert my fine sharpe and draw it directly on whatever I need to cut, no need for a compass. This can be used for drawing cones or transition shrouds as well where you need a very long radius.
I cut a 7" by 2" triangle out of 6mm depron, grooved and glued in a 1/8" carbon rod which will take the brunt of the nose cone landing force....I then added perpendicular triangles, and took turns gluing in triangle filler pieces and carving those to match the original triangle pieces a quarter at a time...eventually I had nose cone shape. I left one quadrant unfinished so I could add weight if needed, then finish it. I added a few gradually increasing centering rings to get the needed outer diameter.
I cut off a section of balsa bt-70 coupler and glued it to the carbon rod at the end to make the cone shoulder.
I decided on 5" diameter centering rings, so cut the rear .04 styrene plate which takes the thrust. I then used that as a template to cut the upper three centering rings.
I cut some interlocking stringers and notches in the centering rings, and added some fin boxes also in 6mm depron.
I joined all the 24mm tubes and added the upper bt70 cup which will hold the parachute. It doesn't need to be very long as at 16 ounces, I only need a 24-30" chute.
Once the upper cup and recovery attachment was epoxied in, I inserted all of the centering rings, tapering as needed for the upper section and the lower section. I added the interlocking stringers and make sure everything was straight. I glued it all together with foam safe CA, added stringers for the upper conical section to support the skin and did a bit of minor sanding to make sure there weren't any areas higher than the rest.
Now came the interesting part. I haven't used 1mm depron before, it's very thin and has a nice hard surface. It does have a grain and bends easier one way than the other. I did some testing and even though thin it still wanted to kink if you roll it too tightly. I made a cone template using this https://craig-russell.co.uk/demos/cone_calculator/ and cut it out. I used 3m-77 spray on both pieces to add the sheeting to the fuse and nose areas. Once done, I taped the seam, and applied a second sheet with the joint at 180 degrees to the first one. I knew from my dynasoar that the 2mm sheet was good for about 7-8" diameter but was too thick to curve more. I had a real pain trying to get the seams aligned at the top and bottom. Once you make contact, you can't pull the foam off without destroying it.
Unfortunately, much wailing and gnashing of teeth later, I decided the first go was not good and so fortunately it turns out, CA accellerator debonds the contact cement...so I spent an hour peeling off the sheeting and doing a touch up sanding. So much for a quick build.....I started over and did a much better job the second time. It worked pretty well and the 1mm sheet has a nice surface on both sides, but even though I had six stringers on the cone, it still flattened out somewhat between the stringers, so it's a bit hexagon shaped. The fuse was much better. The laminated 1mm sheets are pretty strong and tough. I might need to experiment with heating or adding more stringers/centering rings to get a smoother outer surface.
I made some vane pads to slip over the fins using 2mm depron. Those were glued in place after the fin slots were re-cut into the fin boxes after sheeting.
I made the fins using a core of .04 styrene sheet and one 2mm and one 3mm depron laminate (2mm on one side and 3mm on the other) This allowed me to round the edges and keep the 6mm width I used to build the fin boxes. If it flies ok and isn't too draggy, I may do a built up surface to match the wedge upper and double diamond lower profiles on the real thing. I may use .015 styrene sheet to skin over the foam...
For rail button attachment, I made some doubled .04 styrene strips to mimick the pershing cable cover, contact cemented them to the tube, and then used machine screws to hold the buttons in place in the middle of the conduits...the pulling on the button will pull on the entire styrene strip and seems to be plenty strong.
I made some charge covers(straps) out of styrene and added those with contact cement as well.
Once done I balanced and needed 3/4 ounce of nose weight in the cone and finished adding the fillers and sanding it to shape. After the cone was done I sheeted it with 1mm depron, two layers to match the forward profile.
For the markings, I wanted to minimize paint weight, so chose a primarily white round. I masked and painted the middle and lower black bands only, and used monokote self adhesive trim for the upper bands, stripes, squares. I used tapered sheets of red to cover the nose since it wasn't perfectly round I couldn't just use my cone template, there would have been wrinkles. The trim monokote adds a lot to the surface durability.
All completed, weighs 17 oz and should fly nice on any 24mm F30's. 5.25" outer diameter and 52.25" long. It was an interesting build, I wished the skinning worked better. It did come out light, about the same as a BT-101 4" maxi pershing but much larger, and the 3.75" tlp kit is around 12 or 13 oz. There aren't any real sources of light 5.5" tubing I found, loc is 18 ounces just for the 27" lower tube. It did allow me to pick whatever diameter I felt like and just build it. I used 1/2 sheet of 6mm depron and 4 sheets of 1mm, and 1/2 sheet of 2mm, for a cost of about $20, and the tubing and other pieces were about $15(my local hobby shop carries sunward parts)....sheet styrene and trim monokote I had already on hand.
I think in the 5" and up size it has huge advantages in weight and cost if you are looking to fly smaller, far 101 motors. As a comparison, my 4" pershing build using loc parts and a fiberglass conical nose and 1/16" fiberglass fins weighs 3# with proper balast and has to fly on at least G80 or G75's.......my 7.5" version weighs 20 pounds, again using loc cardboard.
Frank
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