Brief:
Took a Fat Boy kit and added Big Bertha like fins to make a Super Baby Bertha.

Modifications:
NARHAMS held a Fat Boy theme sport launch this month, and I was looking for something different to do with my last Fat Boy kit. I had just finished repairing my Super Big Bertha when inspiration struck. I have a Big Bertha, Super Big Bertha and a Baby Bertha, why not a Super Baby Bertha?

Build the motor mount per kit directions, making sure that the centering rings close off the fin slots. For the fins, the standard Bertha fins were too small in proportion to the diameter of the BT-80, and the Super Bertha fins were too big for the length of the Fat Boy tube. I scaled the fins to be exactly halfway between the two, a size that was pleasing to the eye. I cut 4 new fins from 1/8" balsa and glue them on so that one of the fin slots is halfway between 2 of the fins. I used the launch lug to cover one of the slots, and monokote trim to cover the others. RockSim says you'll need to add a little more than 1/2oz. of nose weight for stable flight.

Construction:
Uses all of the Fat Boy kit materiales with the exception of the fins. Here's a parts list if you don't have a Fat Boy kit:

• 1 PNC-80BB
• 8" BT-80
• 2.75" BT-20
• 2 CR-2080
• 24" of your favorite shock cord
• 2.375" of 1/8" launch lug
• 1 EB-20 engine block
• 1 standard engine hook
• 1 12-18" parachute your choice
• 1/8" balsa fin stock

Finishing:
I finished my Super Baby Bertha using self-adhesive Monokote trim. In addition to covering the TTW fin slots, it makes a glass smoth finish on the body and the fins... with no filling needed! I painted the nose cone red, then covered the tube and 3 fins with white monolote trim. I covered the remaining fin with red trim and added some red stripes to the upper part of the tube. Looks kind of like a reverse of the Super Big Bertha paint scheme.

Flight:
Because I was using a Fat boy as the basis for this model, I decided to keep the 18mm motor mount. For the 1st flight I used an Estes C6-3 slipped into the mount and secured by the standard Estes motor hook. Wadding was added to protect the chute, and the model was prepped. Pretty standard mod roc prepping. The rocket had a good flight, nice and straight. I did cut a spill hole in the 18 inch plastic chute, our launch site is prone to be breezy.

Second flight was on a B4-2 and the chute got a little melted, the model landed fast on the snow and broke the glue joint on the red fin. Easy to fix.

Summary:
This was a fun conversion and adds a compliment to my collection of Big Bertha models.