The single kit shroud was scanned, copied and printed on some 110 lb. card stock.
Why so many?
I always make up three or four and use the one that fits the best. The slightest difference in the glue tab positioning can make a better fit over a body tube.
This one is different. It only has to fit well over the BT-20 engine mount tube. The wide end slips inside the BT-55 main body. The wide end of the shroud butts up against the lower centering ring on the engine mount.
Use the rotary punch to make the hole first. then cut the sides with a sharp knife and strait edge. Enlarge the inset picture to see the cuts.
Notice the punch is made deeper than the original box end. I didn't think the slot depth would allow enough movement of the hook when inserting and engine. After making the first two shrouds I had to make two more with an even deeper slot punch.
You mention "The pattern shows a rectangular engine hook relief slot. The sharp corners of a slot like this can tear. Punching a rounded slot will be stronger."
ReplyDeleteYep [nodding in agreement]... Square corners in openings tend to concentrate stresses at the corner.
Not uncommon to see diagonal cracks leading away from inside corners on windows and doorways in buildings after an earthquake.
Square corners on a hatches and windows in the DeHavilland Comet airliner was implicated as one of the important factor in many of the early crashes -- and later versions of the airliner featured round windows and hatches and doors with rounded corners.
Ever notice how there is either a slit or "vee" notch where you're supposed to tear those condiment packets you find for take-out food. The ones with circular notches tend to be a bit harder unless the packet was designed to be weaker to shear forces at that point.
Hi Naoto,
DeleteAs you can guess, I've had square corners tear before. A lot of rocket builds has lead me to do this.
Interesting history on the Comet Airliner, thanks for taking the time to share that.