This boost glider comes complete with a clear payload section, which can be used to carry small pieces of cargo. The Semroc kit does not include instructions, those are to be downloaded online. This rocket kit provides all parts (other than a pin) required to build your own out-of-production Centuri X-21.

This having instructions online, you can preview instructions to help you decide if you want to buy this rocket glider kit.

Parts List

The X-21 glider kit comes in a clear plastic bag with a booklet with colorful front cover.

- body tube and balsa tube coupler
- clear payload tube
- nose block (engine block)
- 20 laser cut wing and fin pieces
- elevon stop wires
- hinge sheet
- elastic thread and shroud line
- 7 balsa pieces for wing mounting jig
- 2 balsa pieces for stabilizer angle template
- empty casing (rocket motor sized)
- screw eye and 3 washer weights
- launch lug
- informational booklet and specifications card

Hobby supplies such as sand paper, CA, wood glue, scissors and a hobby knife are required to build this model.

Construction

While this kit is listed as a level 1 kit on the Semroc web sit, this may not be the best kit for beginners. If you follow the instructions and pay attention, you should have no trouble. However, elevons needs to be rigged, CA is used and the glider needs to be trimmed which may challenging for an inexperienced modeler.

That said, the glider really really isn't that difficult to build and the wing mounting jig and stabilizer angle template make things quite a bit easier. The mounting jig in shown on the left. These tools are used to easily attach the wings and stabilizers correctly. Accuracy is important, especially with gliders.

A few steps of the original instructions are replaced by Semroc-provided instructions. One of these involves substituting the elevon release clip with a straight pin. The instructions don't seem to mention how this pin would be attached to the release line. Surely, one would not want a straight pin falling down at ejection with one of more spectators staring straight up at the glider.

An eyepin was used instead, these are used for jewelry making and beading and can be found in craft stores. You may need to use small pliers to ensure the eye loop is 100% closed.

The nose cone had a lose fit. Some balsa sealer was put around the shoulder to give it a tighter fit, without modifying its appearance.

Please don't understand the above comments. This model rocket kit is fun and very enjoyable to build. When done, you end up with a very nice looking glider.

Finishing

While the X-21 can be painted, doing so with enamel paint would add too much weight. The instructions mention using spray laquer or laquerized enamel. At this time, the glider built for the review will be left bare, at least until after some flight data has been gathered.

Measurements

This boost glider has a diameter of 0.759" (2.6 cm) and is 16.2" (41.1 cm) long, with a fin span of 10.7" (27.2 cm).

Flight Data

Suggested model rocket engines for the X-21 are : A8-3, B4-4 and B6-4.

Launched with a B4-4, the rocket went up nicely. Very straight for a glider. The motor ejected and the glider started its way down. It made several broad spirals on the way down. Two washer weights were used, it looks like 1 may have been enough. Then again, it may be better to have the glider come down a little fast than to remove a washer and have it catch a gust of wind and get carried away into bushes or trees.

Made the mistake of launching this glider on a C6-3. For some reason I remembered it as being on the list of recommended engines. Don't try this yourself. It started straight up, followed by a more erratic flight pattern. Ejection occurred a split second after apogee and it appeared to glide down in spirals, be it faster than before. Upon recovery, it became obvious this rocket couldn't handle a C model rocket motor, it shredded one of the wings.