The Boosted Bertha is Estes’ latest addition to their popular Bertha family of rockets. These low-power rockets fly on 18mm engines, and sport fat BT-60 body tubes, retro-futuristic fin shape, and a blunt nose cone. These rockets are a lot of fun to launch, as they have nice, slow liftoffs and are easy to watch in flight and track during descent. Their lower apogees allow you to fly a “big” rocket in smaller fields. Always a crowd pleaser.
The Boosted Bertha takes the Bertha line to a new level both in terms of the design and kitting of this model. The sustainer is essentially a Big Bertha, but has a couple of nice upgrades. Most notably, they’ve included screw-in motor retention instead of the traditional motor hook. They’ve also provided water slide decals; a very nice upgrade from prior Bertha iterations, which include self-adhesive decals instead.
The booster design is probably the most interesting part of this kit. At first glance, you might think they pretty much truncated a Baby Bertha and scaled up the fins. However, there’s quite a lot of engineering that’s gone into this part of the kit. Like the sustainer, they provide screw-in motor retention. However, that’s where the similarities to previous iterations of the Bertha line end.
The first thing you’ll notice is that the booster’s body tube has laser-cut slots for through-the-wall fins. A design feature that will certainly improve the longevity of this rather large tumble-recovery part of the rocket. I’ve certainly expended a few bottles of CA re-attaching fins on other Bertha’s I’ve owned after a few hard landings.
The next thing you’ll notice is the longer motor mount tube for the booster as well as the vented centering rings. That’s right – the Boosted Bertha is gap staged. The motor tube for the booster is 4″ long, and the instructions indicate that you should install the motor block so that it allows the motor to project 1/4″ from the end of the tube. This leaves the forward end of the motor 1 1/2″ from the end of the motor tube.
The forward end of the booster’s motor tube is not vented as is typical in gap staging. My guess is that the motor tube stops just short of the engine retainer on the sustainer, and the vented centering rings do the job of venting the pressure wave, allowing the hot gasses from the expended motor to travel up the tube and ignite the sustainer’s motor. I wonder how this will affect the plastic motor retainer in the sustainer … time will tell. I do plan to coat the end of the booster’s motor tube with epoxy to prevent (forestall?) it burning away over time.
I’ll update this post with more thoughts and impressions as I go through the build process and first few flights.