Saturday, July 23, 2011

Rebuilding Rama

Continuing with repairing about half my fleet this summer, I'm doing a major overhaul on the Rama. It started out as an attempt to make a finless scale model, then it was just a scale model, and then it was just ugly. I have more about it here.

Any other rocket with its record would just get retired. It's survived six launches, which is an eternity for a scratchbuilt rocket. In the first went unstable, in the second it got its fins broken off, in the third it crashed, in the fourth it crashed again, in the fifth it actually did well on a D motor (after previous failures on Cs and a B), and in the sixth it wasn't quite stable.

But, I don't want to retire it just yet. It's a fun and hardy rocket; that 3" mailing tube can take a lot of damage. It also makes a good testbed for high-thrust 18mm motors; I plan to use it to test my own someday once I'm Level 2 certified.

So instead of scrapping it, it gets a complete rebuild.

The nose 'cone' - which is actually flat - is a mailing tube end cap filled with solidified wood glue for weight. I trashed the foam board than formerly covered it; my replacement covering will be a better-fitting piece of poster board. I trimmed down the screw eye so it won't poke through any more.

The forward edge of the body tube is squished and the layers are coming apart from the multiple crashes. I'm squeezing white glue between the layers, then clamping them shut till they dry, which should render it pretty solid. The inside of the tube has gotten pretty chewed up, so I'll give it a coat of wood glue to make it smooth. Easy exit for the parachute, and easy to clean after the flight.

I realize now that part of the reason it's so survivable is the filling - I filled the space between the motor mount and body tube with cotton batting, stuffed tight. Which is not as stupid as it sounds - the stuff comes chemically treated to be flameproof.

The shock cord mount is pretty solid, but I needed to add some filets to the forward centering ring. Next I'll trim the motor mount tube to be flushed with the centering ring, which will give me more parachute space.

I ripped out the rear centering ring entirely; it'll be replaced by a higher-quality, better-centered ring made from several layers of cardboard. I'm leaving out the motor hook and moving the motor mount slightly forward to correct the stability problems with the 18mm reloadables.

The launch lug needed reglued. The fins, ugly as they are, are solidly set so they'll stay for now. Once all the internal work is complete, I will prime everything (except of course the fins) and then paint it a nice flat white - no more red mailing tube label showing through.

No comments: