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Any thoughts from members about designing an all metal wing for the Kitfox?
RANS is building one all metal poly fuel tanks, discreet flap and aileron.
Downside no folding wing. I do like all metal durability, stronger wing, faster cruise due to better air penetration.
Other downsides would be less useful load due to increased weight, repairability from damaged caused by rocks when operating in unimproved conditions. Any feedback would be appreciated.
Depends on what thickness aluminium you use, but the one thing to keep in mind is that the fabric is shrunk when attached to the wing structure, which introduces pre-tension in the covering. This helps in keeping the wing profile reasonably stable under load. I would think changing to aluminium skins will introduce new and untried issues, aside from the additional weight. I guess what I'm saying is why change a tried and proven structural arrangement for something unknown. As for speed, this type of aircraft is designed more for low and slow. Who's to say that using aluminium skins will necessarily get you, say, an extra 10kts. FWIW.
There are lots of planes on this forum that can hit Vne in level flight so I don’t think faster is neccesarily required. I believe the Vne in the kitfox is due to the flapperons. It is experimental but the kitfox is one of the best kitplanes out there. Why change something that works so well already?
I don't think it would be very hard to modify the current wing and put aluminum skins on instead of fabric. The strength of the KF wing is already there, so this is not an issue. Therefore you could use 0.016" aluminum and the skins would only make the wings stronger. Doing this would retain the ability to fold the wings.
I think this could be done with very little modification to the existing wing:
-Use the Laker leading edge, and make it so you can slide the aluminum skin underneath 1/2 to 3/4". If you are more adventurous you could form your own aluminum LE and eliminate the Laker LE.
-Add some aluminum caps to the top and bottom of the ribs with countersunk screws & Hysol. Make the caps with 1/2" overhang on one side to provide and area to rivet the skins too.
-Fit the aluminum skins into place. Drill and cleco them as you go.
-Install the bottom and top skins going front to back. Rivet them under the leading edge. Then rivet them to the ribs.
-I would use 3/32" solid rivets. They could be round head or countersunk, but you would have to dimple the skins as it would be too thin to use the countersink tool.
-Have the top skin bend around the trailing edge and use blind rivets to close it up.
FYI I had a C-120 that had and STC for metalized wings and I believe it only added 12 pounds. So the weight increase on a KF would be minimal and readily calculated.
As far as repairability I think aluminum is so much easier than fabric.
Would I do it? Maybe, but probably not.
Part of the purchase agreement (if you bought from Kitfox) is not modifying the kit.
I spoke with John about this because I know people sometimes vary the way they assemble the kit. If one was serious about this, it might be a good idea to check with Kitfox about their thoughts about how it might affect airworthiness.
Ercoupe wings were initially fabric also. Some were later metalized using .019. Climb performance suffered tremendously.
Ralph
There are other examples of older original fabric covered wings on factory-built aircraft that have been metalized like Ralph mentioned, and if I remember correctly they are sometimes less desirable upon resale - usually performance issues. From an engineering standpoint with the Kitfox wing design, you must keep in mind that it is a relatively flexible wing, and that is the reason that metal fuel tanks haven't been found to be a good option. You'd be creating different load paths with aluminum skins, and I think a thorough engineering analysis would be very prudent before even considering something like that. That's just my considered opinion.
The flexibility of the wing that John mentioned is also the reason that aluminum leading edges have been unsuccessful, because of oil-canning.
Why add so much weight to the aircraft for no benefit? Nothing lighter than fabric! I have stripped a kitfox 3 of all fabric, wings fuselage and tail (all) and weighed it. Very surprised it only weighed 6.5 kg including paint! I love fabric.