Saturday, January 08, 2011

Review: SpaceShipSqrt(-1)

When one of my rocketry buddies decided to hold a building session, I was scrambling to decide what to work on. I decided to use a 50% off Michael's coupon to grab an Estes SS1 kit for bashing. I turned it into a retro-styled spaceship with more conventional fins and wing-tip pods. I also converted it for 24mm motors.

(This was built at a Warthog build session and was cross posted in honor of today's session. Hopefully, it isn't scrubbed due to snow!)

Parts list:
* One Estes SS1 (the original, smaller version)
* Fin set from an Estes Fat Boy kit
* 24mm motor tube
* Kevlar® twine
* Three and a half plastic Christmas ornaments
* Lead shot
* 3/16” launch lug

The two obvious kit mods are the conversion to 24mm and the replacement of the stock wing with fins/pods. I used 5-minute epoxy throughout.

The SS1 comes with a plastic tail cone. One of the first steps on the stock kit is to cut the end of this off, leaving the scale engine bell. I wasn't sure how much of the stock bell would remain after I added the larger motor tube, so I initially left this on. I started by cutting the aft end of the tail cone at its thinnest part and then expanding the cuts until the motor tube fit. When I was done, I left the back most part of the tail cone, which is a ~1/8” tubular section. After re-reading this description I found it a tad more cryptic than when I first wrote it. But since it's been a while since the build, I won't try to clarify the process. I think it should be clearer if you are holding the tail cone from the kit when you read the review.

Once I expanded the provided centering "rings" for the larger motor tube, I mounted the motor mount pretty much as in the stock kit.

I came upon a set of unused Fat Boy fins in my junk box and decided these would work just fine. I slotted the tail cone in between the centering rings and modified the through-the-wall tabs on the fins by trial and error. The positions are such that there are two side "wings" and a "stabilizer fin". Since the tail cone is not ovate, these sit at different heights.  The pods at the end of each fin are silver colored plastic Christmas ornaments.

A fourth ornament was cut in half to form the cockpit section. I filled the gaps between the cockpit and the body tube with modeling putty.

I also implemented a tip that I picked up at the build session. I'd done this before, but it wasn't integrated into my normal repertoire. That is, to cover the lower end of the Kevlar shock cord with a piece of flame proof cloth that is glued to the inside wall. In this case, I used a small square of car air bag material. This is the best 'chute protector I've used, being better than Kevlar or Nomex pads. I don't have enough unused material to make additional protectors, but I do have some scraggly remnants to use for such cord protection. I should have grabbed a bunch more of the spent airbags when I had the chance!

The last thing to do was add nose weight.  RockSim-9 says the CP is 7.5" from the nose tip, just at the leading edge of the dorsal fin.  I added lead shot and epoxy so that the unloaded CG is at 4.5" from the nose tip.  This provides a margin of 0.8 with a D12-5 loaded.

The finish is mostly white primer. I hand painted the nozzle area silver and quickly slapped on some of the decals supplied with the SS1 kit.

I first flew the Sqrt(-1) on a D12-5 at MDRA's Red Glare IV. It flew great and the delay appeared right. Prep consisted of packing dog barf in the tail cone and clipping on a 12" nylon chute. The motor was friction fit.

Flight number two was on another D12-5. It too was a nice flight with apogee ejection. It did angle over so it landed in a field beyond the close stand of trees. Not a bad walk but I had to transverse a field of chest high grass.

The third flight was at NARAM-50 on, yep, another D12-5. The flight was good but the ejection charge melted the plastic tail cone. I don't know why this happened, maybe it was the amount of wadding, or lack thereof? I have filled the warps and repainted it. Hopefully, it will fly again some time in 2011.

The SS1 provided the basis of a nice retro-styled spaceship. It flies so much better than the stock kit, for fairly obvious reasons (hint: it's basically a 3FNC rocket). Yeah, the some of the big dawgs of MDRA liked it...but thought it need to be upscaled.