Rubberbanded Wing Connectors for F-86 Combat Foamie
12-11-2003, 03:02 AM
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Rubberbanded Wing Connectors for F-86 Combat Foamie
I'm preparing to build a 48" EPP [link=http://www.mmglidertech.com/f86.html]F-86 combat foamie from MM GliderTech[/link]. The plans call for attaching the wings permanently to the saddle with Household GOOP, but I've decided to go with a modified rubberbanded connector instead so I can remove the wings during transport.
I need some advice on the best way to do this. Specifically:
[ul][*] How should I reinforce the sides of the fuselage in the area of the wing saddle? At the very least, I figure I'll need 1" square blocks fore and aft of the saddle ends to accept the dowels. But I'm also considering using a coping saw and plywood to cut out two templates that match the contour of the wing saddle, with flares at the ends to accomodate drill holes for the dowels. This should significantly strengthen the middle third of the fuselage for a slight tradeoff in weight.
[*] If I use plywood, how thick should it be? Alternatively, I can use some of the scrap coroplast that came with the kit for the tail surfaces. The coroplast looks like it will be strong enough, but it doesn't look like it will be very easy to cut out the contoured shapes I need.
[*] What size diameter dowels should I use, and how far out from the side of the fuselage should each peg extend? And should I consider using a material other than wood (or hardwood) for the dowels (like a graphite rod from a stunt kite)?
[*] The F-86 is a swept-wing aircraft, so the leading and trailing edges of the wings do not sit flush in the wing saddle. At the leading edge, there is an inverted "V" shape with wedge-shaped gaps to either side of the wing's center point -- the apex of the "V" is the only point of contact between the leading edge and saddle. And at the trailing edge there is a triangular gap behind the center line and two points of contact with the saddle's edges (one for each wing). It seems like this configuration might be prone to movement or sliding in big lift unless I try to fill in these gaps. I this something I need to consider, or will rubberbands alone hold the wing securely in place?
[*] I'm also planning to reinforce the leading and trailing edge of the wing near the root with hardwood to keep the rubberbands from crushing the EPP foam. But should I also consider strengthening the top and/or bottom surfaces of the wing near the center line (perhaps with some semi-flexible plastic sheeting or even fiberglass)?
[/ul]
I need some advice on the best way to do this. Specifically:
[ul][*] How should I reinforce the sides of the fuselage in the area of the wing saddle? At the very least, I figure I'll need 1" square blocks fore and aft of the saddle ends to accept the dowels. But I'm also considering using a coping saw and plywood to cut out two templates that match the contour of the wing saddle, with flares at the ends to accomodate drill holes for the dowels. This should significantly strengthen the middle third of the fuselage for a slight tradeoff in weight.
[*] If I use plywood, how thick should it be? Alternatively, I can use some of the scrap coroplast that came with the kit for the tail surfaces. The coroplast looks like it will be strong enough, but it doesn't look like it will be very easy to cut out the contoured shapes I need.
[*] What size diameter dowels should I use, and how far out from the side of the fuselage should each peg extend? And should I consider using a material other than wood (or hardwood) for the dowels (like a graphite rod from a stunt kite)?
[*] The F-86 is a swept-wing aircraft, so the leading and trailing edges of the wings do not sit flush in the wing saddle. At the leading edge, there is an inverted "V" shape with wedge-shaped gaps to either side of the wing's center point -- the apex of the "V" is the only point of contact between the leading edge and saddle. And at the trailing edge there is a triangular gap behind the center line and two points of contact with the saddle's edges (one for each wing). It seems like this configuration might be prone to movement or sliding in big lift unless I try to fill in these gaps. I this something I need to consider, or will rubberbands alone hold the wing securely in place?
[*] I'm also planning to reinforce the leading and trailing edge of the wing near the root with hardwood to keep the rubberbands from crushing the EPP foam. But should I also consider strengthening the top and/or bottom surfaces of the wing near the center line (perhaps with some semi-flexible plastic sheeting or even fiberglass)?
[/ul]
12-11-2003, 07:10 AM
#2
RE: Rubberbanded Wing Connectors for F-86 Combat Foamie
Good questions, let me see if I can do them some justice:
1 I like your idea of matching the wing saddle, it will be much stronger, and won't add too much weight.
2 I would use 3/32" light ply
3 I would use 3/16" dowel for a small plane like that, and let it protrude 1/2 - 5/8"
4 This is ok as is, but if you want to close it up, you could lay waxed paper over the fuse bottom, then mount the wing, and fill both areas with some of that Super Light Spackle. let dry, and sand to shape.
5 definitely strengthen the rubber band area. I would suggest wrapping the TE with some aluminum cut from a soda can.
1 I like your idea of matching the wing saddle, it will be much stronger, and won't add too much weight.
2 I would use 3/32" light ply
3 I would use 3/16" dowel for a small plane like that, and let it protrude 1/2 - 5/8"
4 This is ok as is, but if you want to close it up, you could lay waxed paper over the fuse bottom, then mount the wing, and fill both areas with some of that Super Light Spackle. let dry, and sand to shape.
5 definitely strengthen the rubber band area. I would suggest wrapping the TE with some aluminum cut from a soda can.
12-11-2003, 01:53 PM
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RE: Rubberbanded Wing Connectors for F-86 Combat Foamie
Thanks for the feedback. These are excellent suggestions.
The spackle idea for #4 is really quite clever, and it should make the bottom of the fuselage look much cleaner and more to scale. I also like your suggestion to use cutouts from an aluminum can to strengthen the trailing edge for #5.
(Now all I have to do is find some silver or gray rubberbands to match my color scheme and I'll be in business!)
Unfortunately, I'm not a very good pilot. But after years of building slow and stable Gentle Lady-like polyhedral slopers, I've decided that if I'm going to crash and burn I ought to at least look cool doing it, preferably at a high rate of speed! Switching from a glued-on wing to a rubberbanded wing should give me a bit of insurance when I catch a wingtip and send my F-86 cartwheeling.
Speaking of cartwheeling, I have one last question. I'm modifying the aileron setup to have a dedicated aileron in each wing instead of a single server mounted in the center of the wing. Among other things, this will let me have a small ballast area in the bottom of the fuselage where the cutout for the aileron servo would normally go. My concern is that if the wings get ripped off during a cartwheel, I risk breaking the aileron servo leads. To address this, I was thinking of having a small internal teather tying the wing to the fuselage. Provided I make the aileron servo leads longer than the teather, this should keep the detached wing from ripping out or breaking the servo leads. Does this seem like a reasonable approach?
The spackle idea for #4 is really quite clever, and it should make the bottom of the fuselage look much cleaner and more to scale. I also like your suggestion to use cutouts from an aluminum can to strengthen the trailing edge for #5.
(Now all I have to do is find some silver or gray rubberbands to match my color scheme and I'll be in business!)
Unfortunately, I'm not a very good pilot. But after years of building slow and stable Gentle Lady-like polyhedral slopers, I've decided that if I'm going to crash and burn I ought to at least look cool doing it, preferably at a high rate of speed! Switching from a glued-on wing to a rubberbanded wing should give me a bit of insurance when I catch a wingtip and send my F-86 cartwheeling.
Speaking of cartwheeling, I have one last question. I'm modifying the aileron setup to have a dedicated aileron in each wing instead of a single server mounted in the center of the wing. Among other things, this will let me have a small ballast area in the bottom of the fuselage where the cutout for the aileron servo would normally go. My concern is that if the wings get ripped off during a cartwheel, I risk breaking the aileron servo leads. To address this, I was thinking of having a small internal teather tying the wing to the fuselage. Provided I make the aileron servo leads longer than the teather, this should keep the detached wing from ripping out or breaking the servo leads. Does this seem like a reasonable approach?
