The Big Bertha is a classic rocket built and flown by thousands of people around the world since 1965. Its was designed to have a rather impressive size and to develop the skills of people who are advancing themselves further in the hobby of model rocketry. Because of its size and performance, it is a great rocket to fly on a football field on C motors, and it is perfect for beginners of model rocketry and demonstration flights.
The rocket overall is rather simple to build although it requires proper fin alignment, finishing, and proper building techniques. As said before, building this rocket will give the beginning rocketeer a good introduction into using these skills. There are things to watch for when building this rocket. First of all, like many rockets, the motor mount centering rings can angle when you glue them onto the motor tube. Not only should you make sure that they are straight when you first glue them on, but keep any eye on them. They can angle by themselves as the glue dries. Second, the motor hook is held with masking tape that is wrapped around the motor tube. Tape will work just fine. Just make sure that the hook runs straight down the motor tube and use plenty of tape. Third, its very common for plastic nose cones to have flash leftover from the manufacturing process. Be sure to trip any flash off of the nose cone with a hobby knife. Finally, its very important to make sure that the launch lug is glued in between two fins. The rocket is only good for pitching into the trash can when it is in line with a fin, because of course, you can't load the rocket onto the launch pad.
There is a method of gluing the motor mount into the rocket that I used on this rocket. Its a method that I learned building high impulse rockets. I put the motor mount into the body tube without yet getting out the glue. Then I used a ruler to line the back end of the motor tube with the back end of the body tube. I then put a glue fillet around inside where the back centering ring meets the body tube. I then stood the body tube on its front end and let the glue dry completely before doing anything else. Then I took a long balsa stick and through the front end of the tube, I reached the stick down and spread glue inside around where the front centering ring meets the body tube. This method works very well in gluing the motor mount in strongly.
When gluing on the fins, make sure that you have good marks drawn on the tube. Preglue the fins before gluing them onto the body tube. Pregluing creates a stronger joint between the fins and the body tube and also helps to have a nice flat root edge for gluing. These are the steps to the pregluing process:
1.Put a thin coat of glue on the root edge (edge that glues onto the body
tube) of the fin.
2.Wipe off any excess glue off from the coat you just put on the root edge of the fin. You don't need much glue for this. All you need is a thin, flat film of glue.
3.Let it dry before gluing onto the body tube.
And last, be sure that you glue the fins around the rear end of the body tube. I nearly made the mistake of gluing a fin to the front end of the tube. Not good.
Finishing this rocket isn't anything too complex. Its all black, so you won't need to worry about being an artist. I am using Krylon black paint, and before I paint the rocket, I spray Krylon sandable primer on it, and sand it smooth. This really improves the finish. Krylon clear coat really adds to the finish too after the decals are added on.
One reason this rocket is a classic is because of its unique look and performance. It flies best on C motors. It likes all of the power you can give it. Its design allows it to fly perfectly straight up. Many people also like the way it floats back down on its 45 centimeter parachute. It doesn't wobble or fall too fast. It comes down slow and majestically.