Upscale Big Bertha

[Missileman]

Well I now have everything gathered to make a 2.5X upscaled Estes Big Bertha.
So now it is time to make this thing.
The first part was planning.
I used Rocsim for all the size conversions.
Below is the Rocsim file

 

[Missileman]

The next step was to gather all the materials.
I already had most of what I needed with the exception of a nosecone.
The nosecone was supplied by our very own Sandman.
(wonderful job)
Here is a pic of that
https://rocketryforum.com/attachment.php?postid=68843

I then printed a fin template on posterboard cut to fit my printer and upscaled the decal sheet (found at JimZs website) using Adobe Photo Delux
Here is a pic of the template and decal sheet

 

[Missileman]

Fins are cut out on a band saw and leading edges slightly rounded with a palm sander

 

[Missileman]

Through the wall fin slots are cut on a router table with a strait flute 1/4" bit and using a fence to guide the cut.
Body tube is 3.9" PML phenolic.
2 pieces are used to make the 44.5" length.
1 at 36" and a payload section at 8.5"
After cutting slots I pre-assembled the fins to test fit , see attachment below (my daughter is next to rocket to show scale)

 

[Rocketmaniac]

Looking really good!!!!........ I noticed you had a 38mm motor mount........... What motor are you planning to use?

 

[Missileman]

I would like to start with an I211 but made the motor mount long enough to accomodate perhaps a J350 in the future.
That brings up a question I have.
I am using PML construction methods with fin and motor mounting ie...
Do not epoxy aft CR in place until after applying fillets to internal fin roots.
The question is should I add PML expanding foam to the fincan?
On the one hand, yes things are stronger, on the other, that adds more aft weight.
Anyone have an opinion on that?

 

[raw9jr]

This IS a REALLY Big Bertha!

Looks great!

 

[Missileman]

Here is a view of the coupler and motor mount.
Notice the piston strap epoxied to the side of the motor tube.

 

[Missileman]

Here is a view of the piston assembly.

 

[Missileman]

Here is a look at the business end.
The pic is to show the inside fillets but they are kind of hard to see.

 

[Missileman]

A layer of 3.5 oz. glass on the fincan area.
Fins are 1/4" birch ply purchased at the local hardware store.

 

[Orbital]

Wow very nice.. Good job...

 

[Ryan S.]

looks awesome, I am gonna have to stop by my local harware store and ssee if I can get my hands on some of that fin material

 

[Missileman]

upscale Big Bertha is finished and ready to fly.
Here she is

 

[sandman]

Great job!

Love the classsic paint job.

But really should you be building rockets bigger than your kids?

sandman

 

[Martin Vrstal]

Awesome upscale build. Your Bertha should really scoot.

 

[Missileman]

I finally got to fly Bertha today.
It went up on an I195J for a perfect flight to 2,500 ft.
Here is a launch pic.

 

[Fore Check]

Great launch pic of a very cool build!!!