Fat Boy 4in 38mm

Been wanting to build this version and started by doing up an Openrocket file to see how it will work. Played with it all weekend and I think I have it down enough to get started building.

Building with LOC 3.9 tubing, through the wall ply fins and ply rings. 38mm motor mount. Looks like it will rock and roll pretty good.

Working to get the cone made, and will have fins and rings done soon also.

Should be fun!
See ya,
Rod

View attachment Fat boy 4in 38mm.ork

Sounds good!

Doing a build thread??? This looks cool!

3FNC

Pretty boring build thread really. But I may. Will be a month or so before I can build. Too much going on right now.

Feel free to build one, not my design anyway. I just wanted to build one in 4in size. The motor in the file is the one that hit closest to the delay. Sure will be a walk if it works this good!

See ya,
Rod

Let's spice this build thread up a bit!! Here's the fin and ring setup for the model.... No glue required!



Nat Kinsey
UpscaleCNC

Thanks for that pic!

Very nice fin ring set.

Got it glued together with the motor mount tube and a kevlar shock cord "wildman style" Used gorilla glue. This stuff is great.

Will take some pics this weekend. But not much to see really. Fins look just like above. I took one of the rings and used the fin slot to mark the tubing then used alum angle to transfer line up and slowly cut slots with a single edge blade. Body tube fits nice and tight. Won't glue fins into body until I can drill and install the retainer inserts.

Now to get a nose cone. Anyone know where a mosquito, bertha, fat boy style cone in 4 inch could be found?

Going to be a fun rocket!

See ya,
Rod

RodRocket said:

Now to get a nose cone. Anyone know where a mosquito, bertha, fat boy style cone in 4 inch could be found?
Rod

Click to expand...

Rod,
Try here: https://www.scotglas.com/components2.htm
Bob

Thanks guys.

Just what I was looking for!

Have fun with that new Cub Bob. Had a great time listening to your fly it home story at the Kloudbusters party.

See ya,
Rod

Looks like we are working on similar projects!! Except mine is only a 29mm mount.

https://www.rocketryforum.com/showthread.php?70798-Scratch-4-quot-Fat-Boy-Upscale

I got my cone from Rocketry Warehouse, the one in terryg's post.

What body tubing did you use FatBoy? Looks like the Rocketry Warehouse nose cone is just a wee bit oversized to the tubing. But if your are planning a vinyl wrap it will probably match up nice.

Even with 29mm this little guy should perform nice. I chose 38 because I had a long tube of the motor tubing and decided it would work and I can always adapt down if I want.

I used a 4" paper body tube that I picked up at a local hobby shop. Sorry - I don't have any clue what brand it is, but it matches perfectly with some of my LOC tubing, so it may be the same manufacturer.

Yes, the nose is slightly larger than the tubing, but for me it was close enough.

I like your idea about the 38 mm mount. I chose 29 mm because I also have a 5.5" Fatboy (Polecat Aerospace kit) that has a 54 mm mount that I adapt down to 38 and fly it on I's. Since this 4" version is so much smaller I didn't think I would need a 38 mm mount. But yours will scream!

The progress on the Fat Boy has been slow. I did get the Scot Glass nose cone. It too was a tiny bit oversize but close enough so it's gonna work. Got the seam filed down and filled with glazing putty. It's a nice cone. Tough and light. Now have to figure out how I want to do the inside of the cone. Need to get real and decide just how hard I want to push this rocket and figure out the motor, then build cone to suit. This Fat Boy will rock with just about any 38 mm motor I care to use.

Will use the aluminum rail guides to keep it clean and simple. They work really well for me so far on other paper tube rockets.

This is a big project I want to get done for our annual AIRFest this year. Along with my 4 in Kinda Swifty. It too needs finished. It too is about this far along. Hate it when work gets in the way, but gotta work to afford to play, so...

A few pics of the progress

Dang has it really been that long? Started working on this rocket again. The nose cone weight is curing. Had to go back into OR file to see how i wanted to do the cone. Ended up just over 4oz with shot and rocketpoxy. I know i will hit this rocket with larger motors so that was added to planning of how much to add. Once that cures, then install bulkhead with Merrick mount style shock absorber. Then start finishing. Classic red body with white fins and blue fin letters. Nice bright neon orange and white panel 36" chute.

This one is going to be fun to launch!

See ya,
Rod

RodRocket said:

Been wanting to build this version and started by doing up an Openrocket file to see how it will work. Played with it all weekend and I think I have it down enough to get started building.
Building with LOC 3.9 tubing, through the wall ply fins and ply rings. 38mm motor mount. Looks like it will rock and roll pretty good.
Working to get the cone made, and will have fins and rings done soon also.
Should be fun!See ya,Rod

Click to expand...

I don't have Open Rocket, although I did use my version of Rocksim at the time when I did an Upscale Fat Boy.
Answered my questions about unnecessary nose weight for stability.
RockSim allows you to account for base drag for short stubby rockets.

"Stability margin rule of thumb for short and fat rockets" - tips for modeling the base drag stability in RocSim in Apogee's Peak of Flight Newsletters #154 and #158. Links below:
https://www.apogeerockets.com/education/downloads/Newsletter154.pdf
https://www.apogeerockets.com/education/downloads/Newsletter158.pdf

Thanks for those. Will be good reading. I just play with figures in OR until it works and then build to suit. For the motor i simmed with rocket needed about 3 oz, I fudged it higher for more motor options. This won't be a very heavy rocket for the motors planned so...... I'm letting it rip! I gots trackers!

Should start paint over the weekend.

See ya,
Rod

Here is the only pic I managed to get of the fat boy. Launched on an Aerotech I single use. Jumped off the pad nice thrust but I had the delay a little long, made a note and will adjust. The Merrick mount did it's job, no damage. The rocket was just about out of site. Had a tracker just in case, but rocket landed in plowed field.

Next launch will include a jolly logic altimeter and maybe on of their chute release devices.

This thing is tough with the interlocking fins and rings. Going to be fun to see what I can launch it on.

Nice rocket. You may have gotten one of last nose cones from scotglass. The website appears to be no more.

Been awhile! Work got crazy, but now more time rockets. This one is an excellent flyer. Made a small av-bay inside shoulder of nose cone. Worked great until i got a little over charged on ejection charge. Snapped cord, but got everything back. No damage and cord is easy fix. Will get better finished pics at AIRFest.

Flights are awesome on I motors. Going to redo av-bay, want to put it down in body tube. Will work something out.

This one always goes with me to the launches!

See ya at AIRFest!

Rod