Mega Alpha Build Thread

[CPA - not an Engineer]

My daughter says I'm unimaginative because I frequently upscale other rockets I've built (6 various sizes of Goblin, 3 Der Red Max, 2 Big Daddy, etc...) so she wasn't at all impressed when I announced plans for my 4th Alpha, a 4" model. Given that the venerated original is a 12" BT-50 variety, it needs to grow 410%. That puts it at 50" per Rocksim - assuming that will be the nose to ground length, not the length of the nosecone and body tube. Either way, it will be a good deal taller than my 4" LOC Goblin and Mega Der Red Max clone, both of which come to about 40-41". Like those other two birds, this one will be a 54mm motor mount.

So off we go. I'm in the middle of helping my parents move so who knows how long this build will take...

 

[CPA - not an Engineer]

Here are all the goods to start with - including the smaller members of the family. Have to remember to find some 1010 rail screws - sure I've got some in a bag - otherwise that will be a disappointing maiden launch attempt!

Most of the supplies are from LOC Precision, save the decals from the incomparable Stickershock23.

And no, I wasn’t able to get all three fins from that piece of wood.

 

[CPA - not an Engineer]

It’s always startling to see a 54mm motor tube, especially when it alone is bigger than the model inspiring the build.

Convenient that the centering rings are already slotted for TTW fins. I’m horrible at making my own marking templates. Won’t use all the hardware that came with the rings - I want to use an Aeropack 38mm retainer so the Z clips can be saved for another project.

Printed out a handy fin template from RockSim and cut out the fins from 1/4” hobby plywood. Notched the fin tabs so as to easily fit the centering rings.

 

[CPA - not an Engineer]

As stated, it’s always startling to see a motor mount that is bigger than another model.

Did I mention I’m horrible at making marking templates? Since I’m a CPA, not an engineer, I have to try other methods like just dry fitting the fins onto the motor mount and tracing the body tube to mark where I’ll need to cut the fin slots. Also, cutting fin slots with a hobby knife is a pain. More on that later.

 

[CPA - not an Engineer]

Seems like instructions I’ve read for other rockets say to attach the eye bolt to the forward centering ring early in the process. But then you can’t easily flip the fin can on its head - so I’ll put in the eye bolt last.

Epoxied the top and bottom of the forward and mid centering rings, taking care to not get any in the eye bolt hole, or on the outer edge of the mid ring. Not epoxying the aft centering ring yet, because I will be taking it off when I insert the fin can into the body tube. I’m not good at injecting internal fin fillets.

Will let this round cure overnight. Hopefully tomorrow I'll epoxy the fin roots to the motor mount tube. Now off to order a 54mm Aeropack retainer body from Chris' Rocket Supplies.

 

[CPA - not an Engineer]

Got the fin roots epoxied to the motor mount tube, then marked out the fine spots on the body tube. Cut them out while the epoxy dried enough to slide the fin can in place. Looks beautiful and with the aft centering ring pulled out, will have easy access to apply internal fillets.

BUT WAIT I see that I was a little eager with the fin slot length, and a little too wide as well.

Crap, didn’t measure right. The fin slot should have been only as long as the tab on the fin. That was a mistake because now the fin can’t at all rest on the body tube. Securing the fin in place with Fix-It epoxy clay won’t give enough stability.

Gonna have to buy a new tube and start over. Well, I can always use this tube for another project later.

 

[MidOH]

30min Z-poxy should hold that together fine, with fillets.

 

[86mustang408w]

So did you start over? I'm really interested in a Alpha 3 upscale.

 

[Hobie1dog]

So did you start over? I'm really interested in a Alpha 3 upscale.

He most likely forgot he even started this thread 2 years ago.