Sunday, April 22, 2018

Building the Shrox Sniple - Part 1, Getting started...

Anyone who has been into hobby rocketry for a length of time has heard of Douglas Shrox - "The Master of the Dark Art of Rocketry". Shrox is legendary for his exotic designs, many of which have been turned into kits offered by Apogee, e.g., the Orion, the LexJet, the Sea Sting, the Stonebreaker, etc, etc. There is also some of his work published in the Apogee Peak of Flight newsletter, free for download; however, you need RockSim or Open Rocket (which can import RockSim files) in order to open the designs, extract the parts lists, and print out the fin patterns. I particularly liked the Bolaero, an Earth defense missile, and built it several years ago - it flies great! The downside to all this is that some of the plans (like the Tarmon) are missing, having fallen into Internet voids over the years. Hopefully they can be recovered by some enterprising sleuth.

The orange Rustoleum paint I applied to the Marauder yesterday did not turn out so well - I have some bubbles and a "cottage cheese" problem on the lower body and a couple of fins, which means sanding and more paint later on in the week when the current paint is fully dry. Feeling a bit frustrated, I sat down at the computer and started looking for something else to build. Nothing on my kit list appealed to me (though I should have considered the Trident or Starlight, which are on the 2018 build list). However, I did run across a Shrox design - the Sniple - stashed away on my hard drive, which caught my imagination with its Asian missile looks.

The Shrox Sniple (Click to enlarge).
I noticed that the Sniple had rather small fins, with one set being located fairly far from the rear of the rocket - not very stable. Sure enough, the RockSim file showed almost 30 grams of nose weight to insure stability, which means it's gonna fly like a pig - only about 180 feet on an A8-3. I also noticed that all that weight gave about 5 calibers of stability, so I kept reducing it until Open Rocket showed about 2 calibers with a C6-5 loaded - which occurred with 10 grams added to the nose. Much more reasonable, and a nice improvement in altitude. Still, I didn't quite trust the results - the rear fins look very tiny - so I loaded the modified file into RockSim, which produced a near match to the Open Rocket results. I feel better with both programs saying the model is stable, but the proof will be in the flying.

The Sniple in Open Rocket (Click to enlarge).
It's raining all day today, so I am gathering the parts to start building this little beauty. It appears to be the perfect project to occupy my time over the next couple of rainy evenings. If anyone else out there is looking to build something from scratch, I heartily recommend one of the Shrox designs (see post 65 in this thread) - they are very cool fliers!

Open Rocket visualization of the Sniple (Click to enlarge).


  1. That looks really good! You going to paint the star and bar or will that be a decal?

    1. Decals - they came with the design file. All I have to do is print them on decal paper.

  2. I missed this one somehow. I've got a disk of Shrox stuff that Chan Stevens made for me a while back, but I've never been able to figure out the whole RocSim thing. Flintstone rocketry is more my speed.