Spars for foam wings 428 ?
12-10-2006, 01:37 PM
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Spars for foam wings 428 ?
I have seen loads of pictures showing foam wings being put together, but non show any spars. What do you use for a spar in foam wing 428 models?
12-10-2006, 09:38 PM
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RE: Spars for foam wings 428 ?
I have generally used hard balsa or basswood - especially when using lightweight contest wood for skins sometimes with CF caps sometimes not. I get the same or better strength at similar weight (1 pound wing with servo) by using a 1" strip or .005 CF top and bottom with 6-8 LB balsa skins with no spar and I glass the center with 2 layers of 2 OZ Top and bottom internally staggered. Finish by glassing/paint or monycote.
If you insist on a spar.... I cut the core as normal.... use a fine saw that is same thickness as spar to cut a slot at the high point of cord the length of desired spar. Coat the spar with lightweight alphetic resin (good white glue) insert into core and align, tape together and place back into foam shucks and weight down with weight or bag it and let dry. when dry lightly sand/plane down the spar even with airfoil... be carful not to change airfoil. Skin them as normal. With the prebuilt composite wings being the rage... foam cored wings are quickly becoming a lost art. Have fun.
If you insist on a spar.... I cut the core as normal.... use a fine saw that is same thickness as spar to cut a slot at the high point of cord the length of desired spar. Coat the spar with lightweight alphetic resin (good white glue) insert into core and align, tape together and place back into foam shucks and weight down with weight or bag it and let dry. when dry lightly sand/plane down the spar even with airfoil... be carful not to change airfoil. Skin them as normal. With the prebuilt composite wings being the rage... foam cored wings are quickly becoming a lost art. Have fun.
12-10-2006, 11:36 PM
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RE: Spars for foam wings 428 ?
I put two strips of 1" by .014 cf on top or 1 on bottom and 1 on top and sheet with 1/16 contest balsa. I also use .040 cf in the leading edge and .014cf in the trailing edge. Center section is 2 layers of 2 oz glass top and bottom and then wing is covered with 1/2 oz glass top and bottom.
