Scratch built USS Pensacola

As a kid, my dad always supported my model rocketry, taking me to the hobby shop and paying for my kits, supplies, and motors. At first, I launched them at the school across the street, but as my rockets got bigger, he'd drive drive me miles away to a huge vacant field. He'd get out his lawn chair, open the hood of his truck so I could hook up to the battery, and then he'd settle down and watch the show. He got as much of a thrill from them as I did. Even as an adult, I'd go to the school and launch rockets for him on the Fourth of July. He never got tired of watching them.

In his memory, I've decided to make a rocket specifically honoring him. He was in the Navy in WW2, stationed aboard the USS Pensacola (a heavy cruiser). So I'm scratch building the USS Pensacola rocket. The body tube will be 3" x 34", and will have a 29mm motor mount. She will have six plywood fins, and four main "gun turrets".

I started by cutting out the centering rings and ejection baffles from 1/8" plywood. I epoxied a 1/4" plywood block to each centering ring for the rail buttons to screw into. I also epoxied two 1/8" plywood blocks to the aft centering ring for the tee nuts. I filled the pilot holes in the baffles with epoxy. I cut the 34" long 29mm motor tube in half with my miter saw. I just put a finer blade on it, and even though it doesn't look like it, it did make a cleaner cut.

I trimmed the rail button blocks, and drilled and pressed the tee nuts in. I epoxied the tee nuts in place to keep them from pushing out, and cut about a third off each baffle disk.

I epoxied the forward centering ring to the motor tube, using a piece of plastic pipe as a spacer to keep it level. I also installed the eyebolt.

I epoxied the three ejection baffle disks into the top of the motor tube, with the spaces in opposing directions.

I started a thread about the turrets earlier in the Techniques forum. I'll make the final turrets from balsa blacks, but for experimentation, I used some pine blocks. I needed a 3" sanding drum to sand the body tube profile in the bottoms of the turrets, but couldn't find one. So I made one. I cut three pine disks with a hole saw, and mounted them in my lathe to cut them to the correct diameter. I cut a slit in the side of the disks to put the end of the sandpaper into. I stuck the sandpaper to the drum with carpet tape, and mounted it in my drill press.

My homemade sanding drum worked better than I had hoped, sanding a perfect concave surface in the bottom of the turrets.

I played with straight and angled sides on the test turrets, and have decided on straight sides since the real Pensacola had straight sided turrets. The barrels here are 3/16" brass tubing, but I may use acrylic tubing instead. There will eventually be two 3-gun turrets facing forward, and two 2-gun turrets facing aft. They will be on the top and bottom of the rocket to keep it balanced.

That looks great! Much better than my suggestion of tubes in tubes.

*subscribed*

Another incredible build,can't wait to see the finished rocket.

I think you've answered your own question about what to use for turrets.

Balsa will be much lighter but bass wood may be more resistant to damage at only a small weight penalty.

What about snagging the recovery train on the gun tubes? Might want to simulate the gun tubes with slats that stand on the body tube to prevent the harness or shrouds from getting caught under the gun barrels. Basically just fill in the void under the barrels.

This is going to be an interesting build.

o1d_dude said:

I think you've answered your own question about what to use for turrets.

Balsa will be much lighter but bass wood may be more resistant to damage at only a small weight penalty.

What about snagging the recovery train on the gun tubes? Might want to simulate the gun tubes with slats that stand on the body tube to prevent the harness or shrouds from getting caught under the gun barrels. Basically just fill in the void under the barrels.

This is going to be an interesting build.

Click to expand...

I never thought about basswood, that's a really good idea. I've been thinking about working with the balsa, and I'm getting a little afraid of it. It's so soft, it will be a lot easier to make mistakes, especially when using power tools. But the pine turrets, even with brass barrels, aren't exactly heavy. The three gun turret weighs 14 grams, and the two gun turret weighs 8 grams. But it adds up, all four turrets would weigh 44 grams, or about 1-1/2 oz. I'm guessing that the balsa could be half the weight, so it is a consideration.

As for snagging the recovery harness, I hadn't even considered that. I don't think it'll be a consideration though. I would only have to worry about the aft facing turrets, but they'll be far aft, almost between the fins. Plus the barrels are so short and so close to the body tube, I doubt if there's much chance the webbing or rope will catch.

I did some more playing around with pine blocks, and made a 3-gun turret, and a 2-gun. I like how they turned out. They're big enough to be noticeable, but not overwhelming. I clamped a piece of aluminum angle to my drill press table to use as a fence for drilling the barrel holes. Worked well, and made sure all the holes are even.

More photos of the latest turrets. I'm really happy with how these are turning out.

bradycros said:

I hate to nit pic, but after stare'n at enlarged photos of the ship a'while, it seems to me your turret bodys should be longer in relationship to the width and the navel rifles should also have a bit more length.

Just say'n...

Click to expand...

You're right, the barrels need to be longer. But I ran out of the brass tubing, so had to cut them short for the practice versions. I think the 2-gun turret length is fine, but the 3-gun needs to be longer.

bradycros said:

I may need to do some more stare'n. The length of the two & three gun turrets look the same to me.

Click to expand...

I think you're right. But the 2-gun turrets were a little narrower. The Pensacola is in the center in this photo.

bradycros said:

Your absolutly right, your photo clearly shows the difference between the two turrets widths.

Are the navel rifle barrels going to be step'd like in the first set of photos?

Click to expand...

If you mean the 3-gun turrets above the 2-gun turrets, then no. I need to keep it balanced for stability, so I'll be putting one 3-gun and one 2-gun on the top and bottom of the rocket. The 3-gun turrets will be forward, and the 2-gun turrets aft. I'm concentrating on the number of guns, rather than their positions.

bradycros said:

Nope, that's not what I'm trying to get across. Looking at your photo, the navel rifle barrel has a reinforceing band around the base that 'steps' up and then there is a 'step' down to the barrel. The end of the barrel flairs out a bit also.

Enlarge the picture to see this step more clearly.

Click to expand...

I think it's beyond the scope of this project and my abilities to consider such details. Like I said, I'm just trying to get the "gist" of the turrets.

I decided to take a break and get the fins and wings cut out. There will be six fins total, but I'm calling the two larger ones "wings". I pinned the four fin blanks with 1/4" dowels so I could cut them out and match sand them simultaneously. I match sanded them on my 6" stationary belt sander, and sanded around the tabs with my 1" belt sander.

Since there are only two wings, I decided not to bother pinning them. I cut them out separately with my bandsaw, and match sanded them on the belt sander. As usual on my MPR/HPR builds, I used 1/8" birch plywood. They turned out nice.

Nice work so far. I'm subscribed to this thread. Good work on the turrets.

I'm confused, who's build is this?

I got the forward centering ring and motor tube epoxied in. Yes, it's probably my messiest epoxy job to date. But strength is more important here, than beauty. Using a piece of aluminum angle, I got all six slots cut out. Using my homemade fin alignment jig, I started epoxying the wings and fins on. And yes, I actually use my stove to cook on. Sometimes. :tongue:

Got the rest of the fins and wings epoxied on. Next will be internal and external fillets.

I'm really liking the design of the wings with fins. It has a lot of visual interest.