Screaming Eagle on the Prowl...er

[GlenP]

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.

 

[GlenP]

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.

 

[GlenP]

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.

 

[GlenP]

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.

 

[GlenP]

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.

 

[GlenP]

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.

 

[crossfire]

Looks like you did a nice job.

 

[GlenP]

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...

 

[GlenP]

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!



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.

 

[GlenP]

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!

 

[GlenP]

A little more sanding, a little more rounding. Fine tuning the fin edges and corners. Sanded off most of the label stickers. Epoxied the centering rings (and thrust ring - I know, could have left that out) on the 29mm engine mount tube. I made little angled glue stick, so after I put the top-most epoxy ring in place for the forward centering ring, I can partially insert the engine mount tube in the body, and use this angled glue stick to spread epoxy at the right depth for the lower centering ring. Will be a tight fit, but should work.

 

[GlenP]

I got the engine mount epoxied in place in the body tube. The angled stick worked fine to get some epoxy in place for the lower centering ring. Will let this cure overnight before adding the fins and engine retainer.

For the stock kit plastic fins, the Estes instructions recommend epoxy. Since I am using ply fins, I was thinking about just using Titebond. I suppose I could put epoxy in the ends of the plastic centering ring fin slots, but since most of the fin joint is wood to cardboard, wouldn't Titebond be strong enough for this 29mm power bird?

 

[GlenP]

Mounted the fins with Titebond. I thought I was pretty careful about getting all of the fins uniform, but one of the four ends up being a little high, so it does not rest on all of them when standing upright, like about 1/16" off. I can even them up with a little more sanding of the rounded corners. Will slowly build up a fillet with the wood glue after this first round dries completely. I may try to find the No-Run No-Drip variety, I was just using the original Titebond, and it does like to run.

 

[GlenP]

 

[neil_w]

I may try to find the No-Run No-Drip variety, I was just using the original Titebond, and it does like to run.

Look for Quick and Thick, it's not too hard to find. Ace Hardware carries it if you have one of those near you. And see if my tutorial is helpful. The stuff behaves somewhat differently.

 

[GlenP]

I need to get some wood filler too, so I will see if that have that kind of Titebond at my local Ace. This kit bash is pretty standard, nothing really special about this build. I used epoxy for the plastic centering rings of the engine mount and wood glue for the ply fins. Have not installed the retainer yet, but will also use epoxy.

What makes this 4FNC rocket special are the metallic stickers/decals. I had some good results using metallic Trim Monokote with print at home ink-jet decals on top. May be a while before I can do the painting until the weather warms up. I have a good redraw of the Eagle. I will need to change the data & engines on the spec plate for the upscale though.

 

[GlenP]

So far, roughly 9 oz without the retainer, lugs, and recovery stuff, hoping that final weight after painting will come in less than 12 oz.

Quick and dirty check of the recommended Prowler engines on ThrustCurve,
so take this with a grain of salt:

 

[GlenP]

test print of my decal artwork, in black & white on copy paper. The body tube wraps are not quite the right size, need to enlarge them a little bit to get the seam right. Starting to make this cat look like a bird. Not sure if will use the stock plastic lugs in the kit, or make my own upscale lug, which would be overkill at roughly 4" long, but might look interesting...just not sure.

 

[GlenP]

I found some TBQ&T and also picked up some Elmer's CWF at Ace. The Q&T is really like the consistency of mayo, it really stays where you put it. I wonder if it will bond well to the initial layers of regular TB that I put down on the fins already. I don't want to build up a really large radius fillet, but I might use my thumb instead of my index finger to get a slightly larger radius than on an LPR sized rocket. The Q&T should work really well. Thanks for the tip!

 

[Nytrunner]

It plays with the TBII just fin!

There's a ply pair of wings on my L2 that that flew 550 mph with nothing but TBII and TBQ&T (after the initial TBII bead, I do one thin layer of Q&T for every inch of airframe diameter)

 

[GlenP]

I completed my fillets with the Titebond Quick & Thick, man that stuff works great. Dries clear, so I can't really take a good picture of it until I prime/paint. Where it really helps is with that one little spot right at the leading edge. Regular runny glue just does not stay put there, but this stuff lets you shape a nice fillet around the leading edge that connects the side fillets smoothly. Why have I not started using this stuff sooner?

I will have to do some wood filling along some of the fin edges to clean up the chipping from the jig saw that I couldn't quite sand out completely, then seal the grain with sanding sealer.

 

[GlenP]

Getting the fins smooth after two coats of sealer and sanding in between. Not sure if my filled fin slots, the unused slots, will need something thicker like CWF or spackle to fill the seams with my cardstock inserts.

Still considering some additional deviations from the kit for this bash: baffle, or partial baffle with Kevlar leader. Instead of the kit lugs, making a 2X scale lug 1/4" x 4" long, and finally, re-radiusing the nose cone tip. The stock kit looks a little too sharp to be a 2X Screaming Eagle nose cone, I might saw off the tip and epoxy a block of balsa and shape it to give it a larger radius. Kind of minor detail, but might look better. Then it would be ready for primer/paint.

 

[GlenP]

Lug: stock kit two-part plastic lug (epoxy), or 2X upscale 1/4" x 4" long retro-looking lug rolled from cardstock (titebond) ...

hmm... here's what they look like, temporarily taped in position. I kind of like the retro lug for this one.

 

[GlenP]

Scaled up cardstock lug it is, rolled about 3 layers of #110 around a 1/4" dowel with a thin film of glue stick to hold it together. To me this just looks more like a Screaming Eagle. Scuffed up the body tube a little and used Titebond for the initial fillet, may overlay a thicker fillet with Quick&Thick after this fully dries.

 

[GlenP]

Was a little windy today, but it died down a bit, and nearly hit 50-deg F. So, I was able to get a first base/primer coat on. I will end up sanding this down a lot, almost covers up all the pink color underneath already. I still have some grain on the ply fins showing, but not too much, I put down two coats of Deft sanding sealer sanding in between before I hit it with the Rusto2X white. The closed up fin slots are pretty well filled in, may need a couple more coats with sanding to completely mask the seams.

 

[GlenP]

sanding...

 

[GlenP]

a little more sanding, and a 2nd coat, glossy white Rusto 2X. Not sure why I keep getting that stuff to crinkle. Will have to do some more sanding of this coat to get it smooth again and will just let it cure for a long while before adding another coat. The nose and fins came out fine, and just one side of the body and in some spots it just crinkled up.

 

[GlenP]

I decided not to try to round off the leading edge of the nose cone to a larger radius. The shape is not quite a true upscale of the Screaming Eagle nose, and I would like to improve on it, but I am not confident that I could make it truly axisymmetric with out a proper lathe. Would be better to just have a new custom balsa cone reproduced in the right size and shape, since the length is a little off too. But, I will just use the stock Prowler cone as that seems to be almost just close enough.

 

[GDJ]

Excellent upscale of one of my favourite and first rocket. Looks great!

 

[GlenP]

Coincidentally this is my first 29mm power rocket. Using the Estes Prowler kit as a starting point made this clone really easy, nearly idiot proof. Many thanks! Just wait until I paint that nose cone red and the fin can blue. Then it will start to look like the real thing.