I've started working on building a clone of the Centuri X-21, whose plans are available here at Ye Olde Rocket Shoppe at http://www.oldrocketplans.com/centu...1/cenKBG-21.pdf

One of the things I've noticed is that the wing section can be cut out as one piece instead of as three (Main Wing, Insert, and Runner pieces) by using 4"-wide balsa. This simplifies assembly and, I think, strengthens the rear edge of the wing with a better grain orientation.

A full-size single-piece Main Wing pattern is attached as a .tif file. The pattern includes a 1" square as a dimension reference.

From the original wing pattern, there is a reference mark showing where to mount the under-wing runner. The mark is about 1/16" wide, so I'm assuming that the original kit's balsa sheets were 1/16" thick by 3" wide.

The root edge of the Main Wing, is 5" long. From the assembly diagram, the main body tube appears to be a BT-20 that is 5-1/4" to 5-3/16" long. However, the instructions specify that the motor block is mounted one full engine length in the main body tube. I prefer being able to grip the back end of the motor in case I have to pull it out of there, so I cut the main body to 5" long, mounted the motor block with 3/16" of the motor sticking out, and mounted the wings 3/16" back from the front of the main body.

The wing mounting jig appears to have originally been die-cut from cardboard, apparently about 1/16" thick. I put it together with 1/16" balsa.

I plan to cut the elevon hinges out of a mailing envelope made out of Tyvek. I've had great success with this stuff so far with other glider projects.

The clip for the elevon tension cord is a mystery. The exposed end of it appears in the Bottom View of the assembly drawing, but its shape is not clearly visible. The length of the inserted part of the clip is not mentioned or drawing anywhere. Any suggestions?

The launch lug looks to be about 1-3/4" long from the assembly drawing.

The control stop wires and aluminum tubes are a bit of a mystery as well. I'm thinking that some suitably pliable wire will do the job.

From the length of the root edge of the Forward Wing, the payload section is 2" of BT-20-diameter payload section. I thought the local hobby shop had a few (recent) Estes X-Ray kits around, which include a BT-20-diameter payload section, though I don't know if the tube is 2". I can't find plans for these kits anywhere on the Internet, so I can't find out. If I can't find an X-Ray kit to bash, the payload section will be a standard, boring BT-20 tube.

Attached Files

x21_wing.tif (44.4 KB, 165 views)