New scratch build: Penumbra

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
I had a coupler, a 19" long piece of body tube, and a 19" long 38mm motor tube. I will repurpose a nose cone from a rocket I built several years ago, that broke a fin on landing. I just need to order a length of body tube. I decided to start on the coupler, to make sure it wouldn't be too tight. I've had that happen before. I flooded half of it with CA, and sanded it smooth on the lathe. It fits perfectly.

001.JPG

002.JPG

003.JPG

004.JPG
 
I bought a bunch of small u-bolts in bulk a while back. They didn't come with backing plates, so I made some from 1/8" x 1" aluminum bar.

005.JPG

006.JPG

007.JPG

008.JPG

009.jpg
 
Right now I'm leaning towards black and gray, but I'm open to suggestions.
 
Looking neat!

I personally think the design would be really set off by some small fins right at the front of the gray section, just to break up that right angle- just a thought.

Sent from my LGL44VL using Tapatalk
 
I like the design,how about a tail cone?As far as color red and grey?
 
I thought about a tail cone, but decided not to use one for a couple of reasons. One is cost. It would cost $30 with shipping to get a transition from LOC.
I could turn one, but it would cost about the same to get a basswood or balsa block big enough. The second reason is the weight. Even with a relatively light plastic tail cone, it would affect the stability. Right now I can get away with 4oz of nose weight. With a tail cone, that would increase to 8oz or more. The extra weight would seriously affect the altitude. So no tail cone.

As for color, I have to paint the forward body tube black because the eclipse decal will have a black background. Right now, I like black and a dark red. Since I prefer satin finish paint, I'll have to see what colors are available. There aren't as many satin colors as there are gloss.


black-red.jpg
 
Looks good.

When LithosphereRocketry mentioned some small fins ahead of the mains, I was actually thinking to put them in the black part, to give a bit more space and contrast between them....

Aren't we helpful? :)
 
Putting them closer together gives a better chance that they'll whistle. LOL
 
Really cool design! Your designs seem pretty closely aligned with my style, your build threads are always a good read.
 
I like the black and dark red,makes good sense not adding a tail cone.
 
Love the name.
Rather than extra fins I was visualizing a slight concavity to the leading edges of the fins, sort of like the inside edge of a crescent moon.
 
Dang, Jim. You've really come back to building rokcets with a passion.

FWIW I like the slotted fins. I cannot scientifically base my opinion on anything firm but I believe that anything spacing of one inch or less on a 3" or larger diameter rocket will whistle.

Oddly, tube fin rockets whistle all the way down to 2.6" diameter tubes.

No tailcone needed on your design.
 
I think I get back into building when A. I feel physically up to it. And B. when there are more chances that we'll have launches. I will say, I enjoy building them as much as I enjoy launching them.
 
I decided to start on the fins tonight. This is plywood that I got from Joann's. It was advertised as 1/4", but it's actually 6mm (0.236"). After printing the templates on cardstock, I traced them onto the plywood, and cut out rough "blanks". As usual, I pinned the blanks together to cut and sand them together.

012.JPG

013.JPG

014.JPG

016.JPG

018.JPG

019.JPG

020.JPG

021.JPG

022.JPG

023.JPG
 
Even though the small fins will be surface mounted, I put "sacrificial" tabs on them so I could pin them together. After I cut and sanded the leading and trailing edges, I cut the tabs off. Then just held them tight to sand the root edges. Finally, I rounded all the leading edges.

024.JPG

025.JPG

026.JPG

027.JPG

028.JPG
 
For what it's worth, I liked the Gray backend more than red.

Has more of an umbral aesthetic in my eyes.
 
I agree, black and gray match the name. But the black and red is more appealing to my eyes.
 
One of my issues with hole saws has always been ejecting the piece of wood from the saw. I found this Spyder mandrel that seems to work pretty well.

001.JPG

004.JPG

005.JPG

006.JPG

008.JPG

010.JPG

011.JPG

012.JPG

013.JPG
 
With my 4-1/4" hole saw, I cut out the centering rings and bulkhead. I cut the center holes of the centering rings with a 1-9/16" hole saw, and sized them with the Dremel.

030.JPG

031.JPG

032.JPG

033.JPG

035.JPG

039.JPG

040.JPG
 
Luv your builds QQ.

Just saying'. Always enjoy your builds.
Especially in the kitchen. :)
 
Last edited:
Thank you Jeff! Good to see you're still around, hope you're doing well.

It always annoys me when my son cooks on my workbench in the kitchen. :tongue:
 
Back
Top