Tri-fold shock cord mounts can block the ejection of a parachute.
On BT-5, BT-20 and BT-50 sized models, drop the tri-fold mounts and go with Kevlar tied to the engine mount.
BT-5 models with this type of mount are especially problematic. This was more common years back when mini-motor kits were introduced.
As for myself, the main problem I've got with tri-fold shock cord mount on smaller diameter body tubes like BT-20 and BT-5 are that my fingers either barely fit (BT-20) or not fit at all (BT-5) to be able to insert and then press into place the shock cord mount (granted, tweezers could be used, albeit possibly getting fiddly)...
ReplyDeleteBefore Kevlar became common, the usual methods for anchoring shock cord would include threading the elastic band through slit(s) cut in body tube (e.g. K-18 Astron X-ray, TK-2 Screamer) or anchoring it to a coupler positioned somewhere in the middle (e.g. Javelin from the Javelin/Super Flea mini-brute combo kit).
One of my first Estes kits was the Wac Corporal. I remember slitting the body tube for the shock cord and thinking: "How unsightly!"
DeleteOn later builds I attempted to fill the slits with wood putty before painting but that left a raised bulge.
Though I did have some worry about the shock cord mount through the slits cut in body tube on the Astron X-ray, -- other issues occurred before I saw any visible damage in that area (e.g. fins breaking off, kink in body tube). Ultimately that kink in body tube (just ahead of the engine block) was resulted in the X-ray being retired from flight.
ReplyDeleteHi Naoto,
DeleteI've had too many models kink above the fins and engine mount. On questionable thin wall tubes, I add a few inches of coupler above the engine mount.