While everyone else is building their lander, I decided to start my semroc X-21 today (after reading the instructions through a few times). I have some questions for folks that have built a clone or original. First, for the engine bulkhead, the instructions say to push the spacer tube all the way in. Gee, this doesn't seem right, I'm used to leaving 1/4" out the back. I realize the engine is supposed to kick, so I suppose I don't need the engine to stick out the back, but still... Was the original spacer tube shorter than an engine? Second question is how to sand the root stress supports. The instructions say to "taper sand the supports as indicated on the balsa". No indication. I think this means sand the taper so the thick edge is on the BT, then tapered away from the BT down to the wing. The original instruction pic seems to indicate this. Lastly, the release clip thingy is unclear. The original instructions don't say much about it, and the semroc instructions say to substitute a straight pin. Huh? I read the post here (and EMRR) about using a piece of soda can, though it sounds like something less sharp would be better. I'm guessing the original was simply a thin piece of metal.

Other tips are of course welcome. And I'll post my tips as I go along. No pics yet, as I've just started, stay tuned, and thanks for your help!

-Paul

Paul, the X-21 is my next project.

I haven't read the plans too closely yet but so far the Centuri plans are a bit vague in spots.

I guess I'm spoiled with all of the step by steps with pictures that everyone else uses.

I haven't even opened mine yet to see what SEMROC has to say.

__________________
"I'm a sandman. I've never killed anyone. I terminate runners when their time is up." Logan from "Logan's Run"

http://sandmandecals.com/

Many old Estes plans showed motors mounted so they didn't extend from the rear of the body tube. You used a dowel to shove the extended casing out the rear.

I built my Cloud Buster and Mark this way.

It is possible that the X-21 shared this "feature."

Gordon,

You have to download the plans so you are actually using the old Centuri plans. The Semroc plans have some construction notes for the downloaded plans and a nice exploded view. The balsa is all laser cut, as you'd expect in a Semroc kit. The first downloaded plans I got are kinda hard to follow though. Mainly because the print is small.....gonna do it again but increase the size so I don't need the magnifier along with the reading glasses. My first read thru did leave me kinda baffled about the release mechanism. After I finish the Mars Lander, I'm going to go through the plans again but slower......First reading had me wondering about the same things Paul has mentioned.

Don
NAR 53455

I haven't been able to figure out the strategy that Semroc uses to determine when plans are included with their kits. It seems that all the CC: kits have no instructions, but all the Retro-Repro ones do. Maybe it has to do with whether or not they are an exact clone; for example the SST Shuttle and Space Plane are, but the Mars Lander is not.
No matter for me anyway, as I cannot build a Mars Lander (I have #7) or an X-21 (I have #15) until I order builder (higher production #) kits.

__________________
When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, TURMOIL, FIASCOS, and HAVOC !

Don, I meant the downloaded plans. There is only the blowup pic (top and bottom) to go by.

The cc and Retro Repro thing I think has to to with copyrights.

__________________
"I'm a sandman. I've never killed anyone. I terminate runners when their time is up." Logan from "Logan's Run"

http://sandmandecals.com/

StephanJ,

The X-21 has a motor bulkhead, so there would be no way to push the engine out from the front. The idea is that the motor kicks itself out. The only problem would be if I for some reason need to get the motor out without launching. ("Oh dang, did I accidentally put a C6-5 in there?")

-Paul

Heres my first tip. When gluing on the root stress supports, glue on both sides to one wing at the same time. I glued on only the bottom stress supports, left overnight to dry in the cradle, and this severely warped the wings. I suppose the shrinkage of the wood glue caused this. I'm trying to unwarp them now with moisture & weights. Stay tuned...

-Paul

The X-21 is ready for priming. The warping issue was solved by moistening the wings and weighting down overnight. I also noticed that one of the 1/16" wings had some defective balsa, it was very thin in the middle (around 1/32) which it made it warp much more than the other. So I built it up with some scrap 1/16 and sanded it down. Wish I would have noticed that before I glued it together .

-Paul

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I had the same thing happen to me, only while it was drying. It curled just a little on the edges.

I slid some glue in on my xacto and then tape the edges down with the elevon scraps. Seems to have worked fine, but I also did the "thin sanding" after they were glued down.

Question: Is the payload rear connector glued to either the body tube or clear tube? Mine slides around very easily though the nose cone is tight.

Not a lot of room in there for payload either.