Thursday, December 30, 2010

Review: Shrox Industria - SHX-15

Any 'rocket scientist' will immediately recognize the similarity between the SHX-15 and the actual X-15 rocket plane. I assume the new name just absolved Shrox from keeping to scale. This cool rocket flies on 24mm motors, and is made from top-notch materials. (This kit is long OOP. However, Shrox is working with Apogee Components so the SHX-15 may yet return.  Meanwhile, you can but other futuristic Shrox designs from Apogee.)

The kit came bagged in clear plastic, with all the small components in their own zip-lock bag. The instructions are brief, with clear illustrations. However, the instructions for the shock cord were unclear and deviated from the parts list. More about this later. One thing did concern me - the decals were missing. There was a note enclosed that said they were backordered and would be provided later. It also gave a URL where the decal sheet could be downloaded.

As I said, the components are of above average quality. The 13" BT-55 tube is thicker than the Estes tubing. The motor mount consists of a section of BT50, an engine block and two nice thick centering rings. The chute is 12" Nylon, and the recovery system includes 13" of Kevlar® twine and a 13" section of ¼" elastic. This is quickly becoming my favorite combination for small modrocs. The fin stock is good quality 3/32" basswood. The remaining components include the plastic nose cone, a standard launch lug, clay nose weight, an Estes-style shock cord mount, and a card stock cockpit cutout.

Following the instructions, I first built the motor mount. In case I wanted to use the new Estes E9, I replaced the 24mm tube with a slightly larger piece. I went ahead and used the motor block, and will need a spacer for a D12. I also drilled a hole in the front centering ring for attachment of the Kevlar® tether.

The fins have to be cut from the basswood stock. I was pleasantly surprised how easily the basswood cut. It was nicer than the stock I have bought from hobby stores. The instructions included two copies of the fin patterns, and there was more than enough wood provided. I hate it when every bit is used up - I'm sure to screw something up in that case. There was no fin marking guide, but it is easy to make one and do your own marking. The large wings consist of 3 pieces and are first glued together on a flat surface. A sheet of wax paper insured they did not gunk up the kitchen counter. The side fins are attached at a -20 degree angle from the wings, so I made a small paper triangle to make sure I got this angle right.

As I said, the instructions for the shock cord assembly were unclear and did not match the parts list. Oh well, I did things differently anyway. First, I added a piece of 500 lb Kevlar® the length of the body tube. One end is fed through the hole I drilled in the centering ring, tied off, and glued. The other end is tied to the provided Kevlar® tether, which was in turn tied to the elastic cord. Thus, the elastic will be well removed from the hot ejection gasses. The nose cone came with the plastic hook removed. Evidently, Shrox felt that this would be too weak given the nose weight required for stability. Since it would be tough to feed the elastic through the small hole provided in the nose, I also added a few inches of Kevlar® twine as a leader. I installed one snap swivel where the lower Kevlar® tether is connected to the elastic cord, and the other is attached to the chute. Well, this was probably more than you ever wanted to know about a simple recovery harness.

I had problems with the last two steps. The card stock cockpit caved in' slightly at the ends as it dried - a minor issue, as it still looks fine. Next, the instructions say to glue the launch lug to the underside of the side wing at its root edge. However, the rear, angled fins will block the launch rod if the lug is in the prescribed location. I double-checked the fin installation and it is correct, so the options were to move the lug away from the body tube, or put it on the top side of the wing. I did the latter.

I went all-out on the paint, using purple/green Duplicolor Mirage. This stuff goes on in three steps: a black undercoat, the color coat, and a clear topcoat. The results look fantastic if I do say so myself! I will add the decals if they ever show up.

The instructions did not indicate a recommended motor, but the web site said to use a D12-7.  I decided to use an adapter and try a C6-5 for the first flight. The model boosted well and weathercocked a bit (the wind was 5+ mph). I have since logged 15 flight, mostly on C11-3s.  The C11-3 uniformly gives a fast flight with the characteristic roll and glide after burnout. This is fairly typical for 'winged' rockets and really looks cool.  The -3 delay is a little short but the -5 is a little long.