Fiberglass adds strength to the rocket, but it also adds the need for some finishing work. Fibrglass resin leaves pits in the surface wich need to be filled in. I use a profesional glazing putty made by Bondo and available at any local auto parts store. This putty can also be used to clean up the transition between sections of fiberglass and fixing the transition between the fins and airframe. After sanding the rocket it is time for primer. I use 2 coats of a sandable filler primer and finish the preperation for paint by sanding the entire rocket with 400 grit sand paper.

Altimeter Bay - Electronics Selection

Designing the altimeter bay on any 38mm minimum diameter rocket is never a simple task. Trying to fit the altimeter, battery, switch, and wiring into such a confined space is both challenging and limiting. Choosing the right altimeter is always the best place to start. I wanted to have an altimeter that could keep up with the performance demands of a supersonic project. I compiled a list of the following needs/wants.

1. Needs a mach delay setting.

2. Has audible reporting.

3. Small enough to fit in the 38mm coupler.

4. Data recording capabilities.

5. Able to opperate at altitdes above 15K.

A brief internet research session yeilded the Perfectflite MAWD altimeter as the best choice. A battery designed for a minimum diameter rocket also removed the bulky 9V battery from the equation.

Altimeter Bay - Switch Design

The only other problem with the altimeter bay(AB) is caused by the one piece airframe design. For the altimeter to work on a switch system the switch itself needed to be internal. I decided to solve this problem with a slap switch that implemented a pull pin system. This setup will be easier to understand from the photos. This is a cool way to arm your electronics on the pad that doesn't take alot of time.

Altimeter Bay - Construction

The actual construction of the AB is pretty basic and strait forward. I used a sled design and incorporated anchor points on both sides of the AB(one for shock chord attachment and the other for a radio transmitter). The last major component in the AB is the ejection canister. A spent 357 magnum casing or shell is a great fit for a 38mm rocket. Shell casings are durable and can take the abuse of multiple charges before replacemnent is required. Attaching the AB to the airframe in a way it can still be removed for reloading charges and altimeter data retrieval is accomplished using 4 small plastic rivots.

Parts Are In !

I ordered all the basic rocket parts from Public Missiles. The rocket is a simple design made up of a 38mm motor tube 36 inches long. I had this dato cut for the 3 Cirrus Dart fins. The only other major structure component is the solid nose cone wich is 7.5 inches long.

The total build length will come in at just under 42 inches and the estimated finished weight should be around 30-35 oz (including all electronics).

Construction Begins

Anyone who knows me will tell you the same- patience may be a virtue, but Jimmy was born without it. I built my level 1/2 rocket in just under a week. It took about an hour after bringing the box in from the front porch to get this one tacked together with instabond. Who can resist getting a glimpse at the final product!!

Attaching The Fins

I wanted to use the same 3 step method of fin attachment on this rocket as I used on Bad Idea 1.

1. Tack the fins in place and secure alighnment using instabond epoxy.

2. Install fillets with 30 min slow cure epoxy for strength.

3. Overlay the fin section with 10oz fiberglass cloth for added strength and distribution of force inacted on the rocket.

Since the airframe is one solid piece, I went ahead and fiberglassed the air frame in the same 10 oz cloth. Public Missiles boasts that their 38mm motor mount tube can withstand the force of mach 2. When I read something like that, the phrase "better safe than sorry" comes to mind. Not to mention if I am going to get anywhere near optimal mass for a CTI J530 motor, I need to look to add wieght anywhere I can.