Lightweight Large Pershing 1A

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

burkefj

Well-Known Member
TRF Supporter
Joined
Jan 27, 2009
Messages
4,475
Reaction score
2,933
After flying my Jupiter C, Hellfire and TitanII/Dyanasoar, I think I have the lightweight foam structure concept undersood, and have confidence they will last more than a few flights. It was really fun flying these large rockets on small motors. I decided to apply it to another model that typically weighs a lot and needs lots of nose weight, lets see how it turns out. I'm thinking this will end up at 3.75-4.5 pounds, be 8" in diameter and about 80" long. Will have an altimeter bay and use the stuffer tube to route the deployment wires up into the parachute bay. Will only need a 48" chute. I'm basing this on my foam 5.25" version that weighs 20 oz rtf as I know the CG location and that it flies straight. Simulation shows an I-200 to 1000 feet.

I calculated the top tapered cone section of a pershing 1A would have a 4" base and 11" length if I used a body diameter of around 8 inches. So, that's the diameter of the parachute cup at the top that I'm using a 12" pml section for. I got a good deal on some sunward bt-56 tubes so I assembled those with couplers to make the stuffer tube/spine.

I found a craft cone at a store that had the right proportions, cut it to length, added a foam tip and and ran a carbon 3/16" rod down the middle to take landing loads and attach it to the base plate. I added a 1/8" base plate with a doubled 4" pml coupler to make the shoulder and added an eye bolt. the styrfoam is porous and rough so I covered it in a layer of 2mm depron, sanded and then covered it with monokote self adhesive trim in black for protection and the cone is ready to go. I'll add the red/orange afterward as an extra layer. This is the piece that will eject and pull the 48" chute out.

I made the fins from doubled 6mm depron with carbon strips on the leading and trailing edges for landing protection/stiffness and the lower fin has a carbon rod spar to the tip, again to help with landing loads.

I'm using a spreadsheet to track estimated(based on density of parts) total weight, and then putting in actual weights as I get them. So far tracking ok.

Also interesting to see what the costs wind up being to compared to highpower components...

Foam cost ~$35
Tubes and couplers $30
PML Tubing $10(got a $10 discount)
retainer $27
plywood $20
Hardware $7
Carbon fiber $22

I already have a chute, kevlar line, altimeter and nomex that can be swapped from another model.


Frank

View attachment Pershing8foam.ork

Capture.JPG

Capturexls.JPG

WP_20150624_007.jpg

WP_20150624_002.jpg

WP_20150624_001.jpg

WP_20150624_003.jpg

WP_20150624_005.jpg

WP_20150624_004.jpg

WP_20150624_008.jpg
 
Last edited:
here's the color scheme...and the 5.25" diameter version in a slightly different test scheme that weighs 20 ounces for flying on F-32's...it's a similar construction with just the small forward cone ejecting.

PershingAd_005_jpg.jpg

WP_20141130_009 (1).jpg
 
Last edited:
Cut the other two plywood centering rings out tonight, and one as a template for cutting the majority of the foam centering rings, took about 15 minutes to cut 13 rings. So far, weight is right on track, about .5 oz over plan. Also cut out the stringers. One problem is I like to have at least 8 stringers to suppor the skin or it won't look round, but with 3 fins spaced 120 degrees apart and given their thickness the root of the stringers and the fins start to collide...so I have use 9 stringers and remove part of the stringer where the fit fits in and the fin will take the place of the stringer, the fin will be slotted and fit into a centering ring in any case.
 
Last edited:
Had some time after dinner and cut the slots in the cr's and stringers and assembled the lower for fit, starting to look like something. for some reason I just like seeing/building a structure like this, makes me feel like i'm really building something. Weight for the structure here so far(which is most of the structure, is 32 ounces.

Frank

WP_20150625_002.jpg

WP_20150625_003.jpg
 
Added the little ply blocks on the ply cr's for the rail button attachment. Slotted the first two fins to go over the middle centering rings to help support/located them. You can see how the fin root bottoms out between two of the stringers at the tube to help align and support them, so I don't need true fin boxes.

I decided that since I'm not going to use motor ejection, I can use the stuffer tube to route my ejection charg through. The altimeter will be mounted at the forward end of the straight section so I have to go about three feet up into the bay. I figured I'll cut a hole in the stuffer tube to go from the altimeter bay up to the parachute bay, then use a rubber stopper into the top of the stuffer tube to block off the gas from blowing back down. That way I don't have to drill/install an aluminum tube for the same thing. Saves a bit of weight/hassle.

It's starting to look like a pershing at least...waiting for more foam to arrive to finish the upper section...three more centering rings and stringers up to the top of the parachute bay, then skinning.

Right now the CG is around the second centering ring from the top, the fins will move it back, the altimeter and forward eye bolt will move it back up. The parachute/kevlar/nomex weighs about 7-8 ounces which is about what an H-128 weighs. Depending on how the upper structure/skinning goes I might not have to add much to the model except for the longer/heavier I200-I205 motors..
CG limit should be around 1 diameter forward of the forward fins, about at the second centering ring.

Frank

WP_20150626_001.jpg

WP_20150626_002.jpg

WP_20150626_003.jpg

WP_20150626_004.jpg

WP_20150626_005.jpg

WP_20150626_006.jpg

WP_20150626_007.jpg

WP_20150626_008.jpg
 
Last edited:
Back from a great vacation. Got the top stringers cut, removed the assembly and glued it together, then mounted the parachute bay and centering rings to the stuffer tube. I then slid on the top structure and glued it to the stuffer/parachute bay. Once it was set I sanded the stringers flush, and layed it on a sheet of 2mm depron. I made a line on the depron, then rolled one full roll over the depron to mark the cut for my shroud. I then used 3m-77 spray contact cement on the structure and skin and then rolled the skin on. A little trim at the seam and some reinforcing tape and it was good. Trimmed the ends and mounted the top centering ring with rail button block. Ready for the bottom section. The upper turned out pretty nicely. Right now weight is looking like 61.5 oz dry, so on target.

Frank

WP_20150703_001.jpg

WP_20150703_002.jpg

WP_20150703_003.jpg

WP_20150703_004.jpg

WP_20150703_005.jpg
 

Attachments

  • WP_20150626_008.jpg
    WP_20150626_008.jpg
    45.8 KB · Views: 47
Finished the skinning and test slotted/fit the first set of fins, starting to look like something. the CG right now is about an inch and a half behind the the front end of the non-tapered fuse, with the rear fins it should be slightly rearward of this. Too early to know for sure, but it looks like this might be the first large pershing 1A that does not require any added nose weight.

Frank

WP_20150703_007.jpg
 
Thank you!

I got back from the vintage rifle/pistol match I run and got a bit more done.

Glued the fins in, made and installed the pivot plates around the fins, and added some foam conduit and the warhead straps made from styrene. Also installed the rail buttons. I also made the access door with magnets for the altimeter pod, altimeter pod will velcro in, the wires go up through the stuffer tube through a cap that fits into the top of the stuffer tube, the wires pass through the cap and connect to the deployment charge which will sit on top of the cap.

Frank

WP_20150704_008.jpg

WP_20150704_010.jpg

WP_20150704_011.jpg

WP_20150704_012.jpg

WP_20150704_013.jpg
 
Ok, here she is, with loaded H-180 motor it is balancing about 2" ahead of where I wanted the CG which gives me some margin for larger motors and is weighing in at 72 oz rtf, about 63 ounces dry. I don't think the minor paint/trim is going to add any significant weight.
I think it's looking like a pershing 1A should look.

WP_20150705_001.jpg
 
Last edited:
Maybe.....you do have to have a softer landing spot, and you have to watch speed/g's, but my hellfire had 12 g's and 350 fps and was fine..

Its fun to have some big stuff that doesn't take a large field and $65 motors.
 
Wow! That's some impressive work!
Looking forward to the flight pics and video.
 
Got the center and bottom bands painted, just waiting for the black trim to arrive tomorrow to finish it up. I also took a family portrait.

8" foamy on the left, 72 oz rtf with H-180, 5.25" version next, 20 oz with F-32 rtf, 4" scratch built using loc tubing, but with proline fiberglass nose that just barely makes far 101 and needs a G-80 or G-75 to fly..., and my scratch built 7.5" version using a fiberglass conical nose I ran accross at a good price, and loc tubing that weighs 20# and flies on J-570 and J-510, and K-550/K535 motors.

WP_20150707_002.jpg

WP_20150707_001.jpg
 
Last edited:
Here she is all finished with the trim, hopefully in August I'll get to fly it in washington with my dynasoar and jupiter C and Hellfire.

WP_20150708_003.jpg
 
I loved the Hellfire flight at FITS and would be thrilled to see this one fly as well :)
 
You all are too kind. Hopefully I fly it next month at the tri-cities launch.

Dick, it's funny how similarly we approached the lightweight rocket design thing, even though I didn't see your redstone build till after I had started my foamies...

Frank
 
You all are too kind. Hopefully I fly it next month at the tri-cities launch.

Dick, it's funny how similarly we approached the lightweight rocket design thing, even though I didn't see your redstone build till after I had started my foamies...

Frank

Hehe...great minds :) If I ever build something similar again, I'll have to check back with you on the types of foam you use. Looks much better than paper! My Redstone was damaged in a basement flood. I am considering cutting it down to look more like a little Joe. Or I can rebuild it as a Redstone. Neither is on my near term radar.
 
That's the nice thing about depron compared to foam-board/cardboard, water won't damage it, and you don't need a clear coat.

I think a 12" or 15" little joe in depron would be pretty neat, not very big/heavy.. Could maybe even do side ejection to bring the entire thing down horizontal.....

Frank
 
Last edited:
Might as well ask now and store the info for future reference. What thickness/grade do you use for skins, CRs, fins? What's a good supplier for someone who may not buy gobs of it?
 
Back
Top