Semroc Start

Semroc - Start {Kit} (KA-25) [?-?]

Contributed by Chan Stevens

Construction Rating: starstarstarstarstar_border
Flight Rating: starstarstarstarstar_border
Overall Rating: starstarstarstarstar_border
Published: 2010-12-13
Diameter: 1.04 inches
Length: 13.00 inches
Manufacturer: Semroc
Skill Level: 1
Style: Sport

Brief:
This is #1 of 10 "ready to build" models released by Semroc at NARAM-52. The design is a Semroc original, though inspired by a Bill Simon/Estes design intended to introduce new modelers to rocketry with a relatively easy to build kit.

Construction:
Parts were excellent quality, and the sealed bag contained:

  • Balsa nose cone
  • Series 10 slotted body tube (1" ID)
  • Series 9 stuffer tube (1" OD)
  • 18mm motor mount (tube, metal hook, centering rings)
  • Laser-cut balsa fins (3)
  • Elastic shock cord
  • 12" plastic chute
  • Waterslide decals

The "ready to build" series is Semroc's answer to numerous requests for "ready to fly" rockets. In the RTB series, the modeler still has to actually do work to build and fly the model, but the design includes a number of features that simplify the build process, including slotted body tubes for thru-wall fin mounting, an alignment jig, and a stuffer tube to serve as shock cord anchor and reinforce the body tube.

The RTB series are all fairly easy to build, with almost all of the construction process using the same standardized steps. This is definitely a skill level 1 model, and aside from paint and surface prep, the total build is well under an hour.

The motor mount is a standard BT-20 tube, metal hook, and a pair of centering rings. Unlike the typical mount, though, there are two different centering rings involved with slightly different diameters. Pay careful attention to the instructions, as the white ring goes forward and the brown ring goes aft. This is critical later in the process. Surprisingly, the mount does not include an inner motor block, so the metal hook will have to hold for the life of the model. I found the centering rings a bit too snug, and had to peel off a layer of paper from the inside of each, plus one layer of paper from the outside of the white ring.

The stuffer tube contains a couple slits, which are used to slip the elastic shock cord through, serving as an anchor. After knotting the cord and reinforcing with a drop of glue, it's ready for the motor mount. The motor mount slides just a tiny bit into the stuffer tube, enough that the forward (white) centering ring is flush with the aft end of the stuffer tube. Do not slide the motor tube any further--the aft/brown ring is too large for the stuffer tube and instead is used to align inside the large series 10 body tube. Sliding the assembly into the body tube to dry fit is a good idea at this point, to make sure the forward centering ring is aligned properly inside the stuffer tube. Once the motor mount/stuffer tube assembly has completely dried, it can then be glued inside the body tube (though be careful to make sure the metal engine hook does not line up under a fin slot).

As noted, fins are thru-wall, and the fit against the motor tube was very good. Included in the kit is a nifty little cardboard fin alignment jig, which fits smoothly on the series 10 body tube and has notches to accept 3 and 4 fin patterns. The fixture fits well for most fins in the RTB series, though for fins that have a significant span and are not swept back very far, the slots in the jig are not long enough to be of much use. That was not the case with this model, though.

Tack on a launch lug, make the chute and construction's done, though be careful about the lug placement (see finishing notes).

Finishing:
I went with the stock paint scheme on this, starting with two coats of primer, following up with a couple thin coats of gloss white, then masking off to paint the fins gloss red and the nose cone royal blue.

The waterslide decals add the name and vertical blue stripes. The stripes wound up being a bit too long and needed to be cut down. Also, with 3 stripes/names, the default alignment would be centered between each fin, though this will likely run over the top of the launch lug unless you think ahead and place the lug in the fin/root joint.

Construction Rating: 4 out of 5

Flight:
For the first flight, I was working on the short end of a field overrun by soccer games, so wimped out with an A8-3. It boosted very well on that low impulse motor, though, and the -3 delay was just about right. No sign of roll, dead straight boost in winds around 5 mph.

Recovery:
The 12" chute is plenty for this model, and you could certainly go with a spill hole or even reefing it a bit. I recovered mine on dry/hard grass with no signs of damage.

Flight Rating: 4 out of 5

Summary:
As with all the RTB series, this one's a good flyer, quick and easy build, and a solid beginner-type kit. Sure, it's a basic 3FNC, but for the price and under an hour's construction time, it serves its purpose, and the simplification tools/techniques incorporated in these RTB models are effective.

Overall Rating: 4 out of 5

Flights

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