Screaming Eagle on the Prowl...er

Discussion in 'Mid Power Rocketry (MPR)' started by GlenP, Feb 3, 2019.

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  1. Feb 3, 2019 #1

    GlenP

    GlenP

    GlenP

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    Not sure what compelled me to take on a kit-bash the Estes Prowler PSII E2X for my next build, but the body tube and nose cone seem to be close enough for a 2X upscale clone of the Centuri Screaming Eagle. I just finished a 1X clone with SEMROC/eRockets parts and a 3D printed fin can, and it seems like it needs a big brother. I was thinking about a 1.33x (24/18 ratio) upscale for a 24mm power, but with the Prowler kit I just got on sale, to me it just looks like Screaming Eagle kit-bash material.

    First obvious modification is converting the 3-slotted body tube into a 4-slotted body tube. I laminated some cardstock strips to fill in the slots on two of the existing slots, and glued that to a strip of regular copy paper. Will fill and primer over these to hide the seams later. With these two slots filled, the centering rings still have enough tolerance to slide in over the copy paper strips on the inside of the tube. I plan to extend the length of the slots since I will have a longer fin root than the stock fins also.

    The Prowler kit is really a cool design in itself, I might have to buy another one to build it stock.

    DSC_8312.jpg
     
  2. Feb 3, 2019 #2

    GlenP

    GlenP

    GlenP

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    Initial balsa mockup of a new fin against the stock fin. Keeping the lower centering ring position, but moving the top centering ring to the end of the engine mount tube. Will make actual fins from 1/8" birch ply. I could move the lower centering ring all the way down to the retainer, but then it would not accommodate the PSII booster, if I ever wanted to try that. I may try to cut some new slots in the centering rings also for the 4 fins, since those are pre-slotted for 3 fins.

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  3. Feb 3, 2019 #3

    GlenP

    GlenP

    GlenP

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    If you squint hard enough, you can sort of see the similarity... will be adding lots of fin area to the Prowler, may be turning that into a weathervane, but no more than the Screaming Eagle itself, depending on c.g. location for the various engines. I will probably stick to D (with 24-29 adapter), E & F power with this one.

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  4. Feb 6, 2019 #4

    GlenP

    GlenP

    GlenP

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    With the recent cold snap, this is not the best season to start a MPR build where I would need to work in the cold garage. I may not make much progress on this one until we warm up a little bit here.
     
  5. Feb 10, 2019 #5

    GlenP

    GlenP

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    Very rough cut of the first two fins from 1/8" birch ply sheet, just using a scroller saw, I don't have a band saw or platform jig saw. Not a very clean cut, so I will have to do some sanding to clean these up and to fit more precisely. Also, I hand cut the slots in the centering rings opposite one of the existing slots with a hacksaw, will have to mark and cut the set of slots at 90-deg to these. These fins are 90% of 2X size, seems like they will be plenty big enough, will have to see how it looks with a dry-fit when I get all four fins cut. I was sizing them so I could get two fins from each ply sheet, they only had two of these smaller sheets left in stock on the shelf at the store, but then I found some larger size sheets, so if these just don't look right, I may go ahead and make full-size 2X fins.

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  6. Feb 10, 2019 #6

    GlenP

    GlenP

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    DSC_8318.jpg

    Finished slotting body tube for 4 fins, and centering rings. Very rough cut fins will need some sanding, but here is an initial dry fit. The Prowler body tube is slightly longer and the nose is slightly shorter, than 2X size would dictate, so I may paint a portion of the top of the body tube red to match the nose, to make it look more proportional to appear that the nose cone is longer.
     
  7. Feb 11, 2019 at 12:45 AM #7

    crossfire

    crossfire

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    Looks like you did a nice job.
     
  8. Feb 11, 2019 at 6:22 PM #8

    GlenP

    GlenP

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    Thanks, I think the kit bash shows some promise. Would be a good kit for other upscale ideas too, like a Viking or Wizard, maybe?
    Nothing glued up yet, this is just an initial friction fit of the engine mount and fins.

    I wasn’t sure if scaling the fins down a little would look okay, but if anything these fins already look huge. Here is how it stacks up next to another 2” dia rocket...
     

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  9. Feb 15, 2019 at 3:11 AM #9

    GlenP

    GlenP

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    did some initial sanding of the fin stack, medium grit, to remove the saw blade marks and splinters from the edges. Now I need to defrost my fingers, still pretty cold in the garage. Almost there, some pencil marks remain from my initial fin layouts that did not MAKE THE CUT! :)

    IMG_0100.jpg

    will do a little more shaping of the stack to final shape, then will softly round the edges with finer grit paper, except for the root and tab.
     
  10. Feb 16, 2019 at 8:16 PM #10

    GlenP

    GlenP

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    This is the jig saw that I used to cut this 1/8" ply, the fins were large enough that I could hand hold them over the edge of the workbench. I did get some chip out on the cross-grain cuts and after some light rounding of the edges with the medium grit, I still will have to add some wood filler to clean those edges up. I maybe could have done some test cuts with different speeds to avoid the splintering. Another idea I had, was maybe to draw a line of CA glue along the cut lines before cutting, that might help seal the surface sheet so that it won't splinter when you cut it. But these spots won't be too hard to fill and continue with the shaping on the finer grit.

    I did not want to add the weight of papering these fins. The problem I was having was UN-papering the fins. The paper label stickers they put on these are nearly impossible to remove. I will have to do some sanding to get the last bits of those off before I can apply some Deft sanding sealer. Next time I will just get the larger sheets, and discard the portion that has the label sticker on it as scrap.

    Finally thawing out here, might actually hit 40-deg today!

    DSC_8320.jpg
     
    Last edited: Feb 16, 2019 at 8:22 PM

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