Tuesday, June 26, 2012

Reworked a couple of rockets

I haven't decided on a new build but have done some tweaking of a couple of rockets.

First up is my oft-reworked BNC-R1 from the mid '80's.  It started with a custom turned balsa nose cone. This was my first hand turned cone after I became a BAR.  A couple of years ago, the cone separated and drifted over the horizon.  To replace it, I turned a bi-conical cone from pink foamboard.  I generally like that shape cone but for some reason it didn't look right on this old bird.  Finally, this model is a tad heavy for its size and the un-reinforced foam cone didn't seem optimal. So, I re-purposed an acrylic cone made from a wine glass.   I have no ninght launch aspirations so I painted it with plastic primer and Krylon H2O paint.  I hate that paint but it seemed like a good way to use some of it up.  I'm happier with the results.

Next up was the MRBR-1.  Despite what Rocksim said, this rocket flew to about 20' on an D24.  I reviewed the Rocksim file and decided to add some clear fin extensions and try an F24. Rocksim says the rocket is stable without the extensions but I though a little more margin would be prudent given the first flight.  To that end, I replaced the nose cone tip that was lost after the first flight and added three fins.  I made these from quarter section pieces of the clear spacer discs that come with CDs.  This seemed like a good middle ground between heavy(ish) Lexan and the other flimsy plastic stock that I scrounged.  The fins on this rocket, despite being a quarter of an inch thick, are not very sturdy.  Whoever built the birdhouse didn't place the grain on the leading edge. I decided to attach the fins with Styrene rods that I have used for shear pins. One bit made a hole that was too tight and the next size up was too loose.  So, I melted the end of the rod sections to make them bigger.  The best outcome as these will act like shear pins on landing and the worst is they work like shear pins when the fins flutter.  Time will tell!