Thanks for the lead to the Airmaster. It was a good looking airplane, and the only design I've heard of with a conventional wing/tail layout with a wing made via the hot-wired foam method.
Your previous writeup on the Airmaster was very revealing--glad I didn't go down that road. Ref your other comments on hot-wired foam wings and your decision to vary from that in your own design--why? Is it just too heavy to leave that foam there rather than go with built-up spar/ribs (seems it would be close to a wash after considering the need to glass both sides of the skins, etc). Or, is the sacrifice of the wing fuel storage the factor? I'm just surprised that only Burt and other designers of canards have gone with the hot-wired foam method, I'm sure there's a good reason for this. It's attractive to me as it would appear to cut construction time considerably.
Thanks to all for the input.
Any reason either the KR2S or the Vision couldn't be built with hot-wired wings, if properly engineered? And by "properly engineered" I suspect one would have to find a way to build in either an aluminum or PVC-based fuel cell.The KR2 (and derivatives) and the Vision (and deriviatives) do not have hotwired core wings, but are built up wings...
The Airmaster used hotwired cores, and stored fuel in the wings, but failed in that fuel diffused into the styrene foam and melted it, ultimately causing Jerry Stallings to attempt to replace the foam with two part PU foam. From doing post-crash analysis, his attempts were also bad news, and may have led to the double fatality crash of that airplane. Polystyrene foam does not belong anywhere near fuel. The known foams that are fuel-safe are either not readily hot-wired or emit poisonous gases when cut with a hot wire. Unless new plastics are invented that are both fuel safe and readily hotwired, massive foam core wings that are also fuel tanks are not really in the cards...
Yes, maybe a Vision with the first 24" of wing on either side made of PVC foam sandwich containing fuel, with hot wired removeable/foldable wings outboard of this (the overall width of fuselage (44") and wing stubs would be under 8 feet, allowing the acft to be put on a trailer and towed without special permits). How much fuel? A WAG (without looking for my copy of the plans): 48" wing chord, figure (after flaps and spars) 32"w available for fuel. Maybe 3" (??) high internally (average from LE to flaps)= 1152 cu in for fuel per foot of wing. That's 5 gallons per foot of wing, so 20 gallons in both stubs, without a header tank, fuel-proof fuel cells the hot-wired section of the wings, fuel under the seat, etc. That's a rough guess, but if it's close, that might be sufficient for an airplane designed for 100-125 HP (burning approx 6 GPH). For cross-country use an aux tank would be needed. (10 gallons in a portable polyethylene tank close behind the seat, periodic gravity feed to the wing stub tanks to top 'em off?)Any reason either the KR2S or the Vision couldn't be built with hot-wired wings, if properly engineered? And by "properly engineered" I suspect one would have to find a way to build in either an aluminum or PVC-based fuel cell.