Wingtip Confusion

[Eric Page]

While I was waiting for stain to dry this afternoon, I grabbed the wingtips and tried to figure out what the first builder had done to them. Anyone familiar with my build will not be surprised to see that they're a bit of a mess.

There are aluminum strips messily bonded into the inner face of the wing tips, where they would attach to the aluminum attachment strips that are bonded/riveted to the #10 cap strip (Series 5, long wings) after covering. At the forward end of one of them, the Scotch-Weld has failed and the aluminum has come loose.

27163 27164

QUESTION 1: It appears to me that these strips were installed in order to make the outer surface of the wing tips flush with the cap strips. Does that sound right? Has anyone else had to do this to install their wing tips?

I found a pile of aluminum pieces that appear to be the attachment strips. However, there are too many pieces and I can't make any of the holes in them align with the holes in the #10 rib cap strips. Strangely, there are also holes drilled through the fiberglass of the wing tip edges (now filled with plugs of Scotch-Weld and covered by the bonded-in aluminum), but the holes in these strips don't match any of those holes either. Some of these strips appear to have glue residue on them, as if they'd been installed somewhere at one time. It's all very strange.

27165

QUESTION 2: Clearly, I need to fabricate my own wing tip attachment strips. Can someone please confirm that they're made from 1" wide x 0.050" thick aluminum?

Finally, this is the state of the trailing edges of both wing tips. As you can see, they've already been trimmed to length (accurately, thank goodness), but one appears to have either split or been cut (the one that's completely out of focus; sorry...), and the other has so much resin between the upper and lower surfaces that you'd never be able to glue the trailing edge closed.

27166 27167

QUESTION 3: Is this situation with the excess resin a common problem? Do you just cut the tip open, grind out the excess resin, bond it back together and do some bodywork magic before painting?

Thanks!

[taff]

When I was building my IV, I riveted aluminum strips to the outboard rib and installed nutplates to these strips.
I used screws to fasten the wing tips.
These are the only photos I have during the wing tip attach.
I don't think it matters much as the the width of the strip, 1.5"? As to the gauge, as long as it can securely hold the nutplates and your able to countersink the nutplate rivets.

[n85ae]

I riveted aluminum strips into my end ribs and put in nutplates. My wingtips are drilled and attached with
screws to the strips. The sloppy mess with the glass in the wingtip is typical of all the parts I got from
Skystar when I built mine. I would never try to bond to the polyester resin with 3M 2216 or Hysol, because
I don't think it would hold.

Jeff

[Eric Page]

When I was building my IV, I riveted aluminum strips to the outboard rib and installed nutplates to these strips.
I used screws to fasten the wing tips.


I riveted aluminum strips into my end ribs and put in nutplates. My wingtips are drilled and attached with
screws to the strips.

Yes, both the S5 and S7 manuals mention this as an option, and I think the S7 manual pitches a kit of parts to do it. I can't imagine what the kit contains other than nutplates, flush rivets, screws and maybe countersunk washers.

I'm planning to make mine removable. I don't expect to remove them, but I'll definitely need to if I glue and rivet them!


I don't think it matters much as the the width of the strip, 1.5"? As to the gauge, as long as it can securely hold the nutplates and your able to countersink the nutplate rivets.
Good point. I'm assuming the strips I found are them (and they're 1" x 0.050"), but I just don't understand how the holes don't line up unless they were drilled separately from the cap strips!


The sloppy mess with the glass in the wingtip is typical of all the parts I got from Skystar when I built mine. I would never try to bond to the polyester resin with 3M 2216 or Hysol, because I don't think it would hold.
Hmm, that's interesting. Oddly, the bond failure in my wing tips is at the aluminum, not the fiberglass/resin. I suppose it's not critical that I achieve a structural bond on those strips, as they're really only there as spacers anyway.

If the structural adhesives we use aren't reliable on polyester resin, then I presume we have to use more resin to close the tail of the tips.

[taff]

"Yes, both the S5 and S7 manuals mention this as an option, and I think the S7 manual pitches a kit of parts to do it. I can't imagine what the kit contains other than nutplates, flush rivets, screws and maybe countersunk washers.

I'm planning to make mine removable. I don't expect to remove them, but I'll definitely need to if I glue and rivet them!"

Hi Eric,
If your thinking of attaching wing tip strobes, maybe having removable wing tips will be a good idea. It's easy to connect the wires before attaching the wing tips.

Ah' the kit. I remember the kit, bags and bags. little bags of say 20 rivets and maybe a bag or two of small quantities of screws that match the building method. All good.
But I still found that going on line to Aircraft Spruce and ordering small quantities of hardware beneficial.

Building a plans built biplane was different, apart from 14 pages (the plans) you have nothing. I spent a fortune at aircraft spruce.

"Hmm, that's interesting. Oddly, the bond failure in my wing tips is at the aluminum, not the fiberglass/resin. I suppose it's not critical that I achieve a structural bond on those strips, as they're really only there as spacers anyway".

It is a structural bond? Well not so much a bond but the aluminum strips are riveted to the wing rib cap strips and the fiberglass wing tip is securely attached to the aluminum These aluminum strips hold the wing tip to the aircraft.

As to closing up the open trailing end. I used fiberglass and resin to laminate the two together. I thoroughly sanded, as best I could with P 40 grit sandpaper and cleaned the area with MEK.
First wrap where the squeeze out will be with kitchen wax paper. Get two wooden paint stirring sticks from Home Depot and then clamp the halves together before brushing in the resin and fiberglass.

[Jerrytex]

I ran into the same thing with the aluminum strips. What threw me off is I had a stack of 3/4" and a stack of 1" wide aluminum strips. I discovered that the 3/4" ones are for the wingtips and the 1 " are for the door panels. My kit, and probably yours, came with the fiberglass lower panels and these strips are used there. On the new kits, they use 1" wide strips on the wingtips. Since I bought the bubbles doors, I used the 1" strips from the doors, on the wingtips and I am glad I did. I can see what kitfox changed since it would be close to mount a nut plate on the 3/4" strip.

I am also contemplating the idea of how the wingtips attach strips mount and the order of it. The manual calls for wrapping the fabric around the #10 rib and then gluing the aluminum strip to it and riveting. Essentially you are only gluing the strip to the fabric which makes no sense. Would make more sense to glue the strips to the rib first, and then cover?

Also, I posted about the wingtip leading edge awhile back. Since you'll be in the same boat as me since you have new spars, I ended up cutting 1/2" off the front spar to allow the lead edge of the fiberglass tip to the lead edge of the wing.

[Jerrytex]

Just saw the question bout the trailing edge. I used hysol as I think most do. The very tip is a little thicker but you can sand it all uniform. If you screw it up, it's fiberglass and easy to fix. Personally, I am going to leave mine alone and just have it be a little thicker on the tip. I'll fill in and shape with polyfill to make it smooth.

Also, I think the wingtips should be removable. Every condition inspection, I would pull them off on my KF4 to inspect. You can see a lot of the wing and it's condition through the wingtip end.


27174

[Eric Page]

If your thinking of attaching wing tip strobes, maybe having removable wing tips will be a good idea. It's easy to connect the wires before attaching the wing tips.
Good point. I am.


Ah' the kit. I remember the kit, bags and bags. little bags of say 20 rivets and maybe a bag or two of small quantities of screws that match the building method.
About what I figured. I'll roll my own from the Spruce catalog.


It is a structural bond? Well not so much a bond but the aluminum strips are riveted to the wing rib cap strips and the fiberglass wing tip is securely attached to the aluminum These aluminum strips hold the wing tip to the aircraft.
The non-structural bond I was referring to is the aluminum strip that's glued into the inner surface of my wingtips. It's just a spacer to make the wing tip outer surface flush with the cap strip. I would of course need a structural bond to hold the tips onto the wing.


As to closing up the open trailing end. I used fiberglass and resin to laminate the two together. I thoroughly sanded, as best I could with P 40 grit sandpaper and cleaned the area with MEK. First wrap where the squeeze out will be with kitchen wax paper. Get two wooden paint stirring sticks from Home Depot and then clamp the halves together before brushing in the resin and fiberglass.
Sounds reasonable. Messy, but doable.

Thanks for the info.

[Eric Page]

I ran into the same thing with the aluminum strips. What threw me off is I had a stack of 3/4" and a stack of 1" wide aluminum strips. I discovered that the 3/4" ones are for the wingtips and the 1 " are for the door panels. My kit, and probably yours, came with the fiberglass lower panels and these strips are used there. On the new kits, they use 1" wide strips on the wingtips. Since I bought the bubbles doors, I used the 1" strips from the doors, on the wingtips and I am glad I did. I can see what kitfox changed since it would be close to mount a nut plate on the 3/4" strip.
Yes, mine had the fiberglass lower door panels as well, also removed in favor of bubbles.

AAAAH!! That's where my pile of aluminum strips with non-matching hole layout came from -- the doors! Boy do I feel dumb; I only removed those a month ago. I guess the wing tip attach strips are just missing.


I am also contemplating the idea of how the wingtips attach strips mount and the order of it. The manual calls for wrapping the fabric around the #10 rib and then gluing the aluminum strip to it and riveting. Essentially you are only gluing the strip to the fabric which makes no sense. Would make more sense to glue the strips to the rib first, and then cover?
I've also been trying to picture how that would work. As you say, gluing the tip attach strips to fabric doesn't sound like a good idea. However, I don't think having the fabric overlap the attach strips is a good idea either, as it would tend to form a wedge under the inside edge of the wing tip and the fabric would wear along that line.

I would be tempted to end the fabric with a clean cut at the outboard edge of the #10 cap strip. That would leave the underside of the cap strip clean for bonding and the fabric wouldn't foul the wingtip installation. If I do that, I see no reason not to install the strips before covering, and the fabric can hide the rivet line.


Also, I posted about the wingtip leading edge awhile back. Since you'll be in the same boat as me since you have new spars, I ended up cutting 1/2" off the front spar to allow the lead edge of the fiberglass tip to the lead edge of the wing.
One of my wings is in the rotisserie, so I can't check that one, but the other seems to fit fine as-is. The wing tip has already been trimmed, so I'm more or less stuck with what I've got. Maybe my spars were already trimmed, but there's no evidence of it. I would expect to see chainsaw marks.

Thanks for the wing tip trailing edge info also. It doesn't sound too hard to close them up and make them look decent.

[jrevens]

... I would never try to bond to the polyester resin with 3M 2216 or Hysol, because
I don't think it would hold. Jeff

If the surfaces are cleaned & prepared properly epoxy will make a stronger, some would say better joint than polyester resin. The issue that can be encountered is that wax is sometimes added to resin, which rises to the surface and helps facilitate the cure with polyester resins. It is also sometimes applied afterwards for the same reason. If that is the case it has to be removed before epoxy or additional polyester resin will bond properly. A good acetone wipe, followed by sanding and another wipe is effective. Epoxy is the best, strength wise, for repairing fiberglass structures whether they are made with polyester resin or epoxy resin.

[PapuaPilot]

Also, I think the wingtips should be removable. Every condition inspection, I would pull them off on my KF4 to inspect. You can see a lot of the wing and it's condition through the wingtip end.

I agree. I pull my wingtips every inspection. I adds just a few minutes and allows you to see the inside. It gives me access to my landing lights, nav lights and magnetometer.

[Maverick]

I've also been trying to picture how that would work. As you say, gluing the tip attach strips to fabric doesn't sound like a good idea. However, I don't think having the fabric overlap the attach strips is a good idea either, as it would tend to form a wedge under the inside edge of the wing tip and the fabric would wear along that line.

I would be tempted to end the fabric with a clean cut at the outboard edge of the #10 cap strip. That would leave the underside of the cap strip clean for bonding and the fabric wouldn't foul the wingtip installation. If I do that, I see no reason not to install the strips before covering, and the fabric can hide the rivet line.

I looked at my pics and I wrapped the fabric around the side of the cap-strip of #10. I remember wondering about that but I recall that I sanded the epoxy varnish to roughen it up a little before applying the fabric and taking extra care to make a good glue bond of the fabric and then shrinking it so that it was good and flat against the underside of the cap-strip. I then bonded the aluminum with 3-M and rivets. I used nut plates for holding the wing tips on for reasons stated by Papua.

I don't know about cutting the fabric off. There's only 1" of surface on the cap-strip for bonding too. That idea crossed my mind but with the ironing of the fabric to shrink it, the idea of the strength of wrapping around the cap-strip was more appealing to me. With all the bonding and rivets holding the aluminum strips on, I don't feel concerned that the wing tips will go anywhere.

[taff]

This is how I done mine.
First dry fit the aluminum strip to the cap strip before fabric covering and drill the rivet holes, Countersink the cap strip for the rivet that will be installed later.
Apply the fabric and tuck it /glue it under the cap strip. Heat iron and shrink as normal.

Install the aluminum strips. No need for "bonding" you will be bonding to the fabric = no structural strength.
Rivet the strips in place with countersunk rivets. Use soft rivets or you may be damaging the rib cap strip.
When everything is secure fit the wing tip and drill pilot holes for where the Rivnut is going to be riveted. You need a tool for aligning the holes for the Rivnut.

Use countersink washers if you want to use countersink screws, or pan head screws.

Use a little beeswax on the threads of the screws. Makes easier removal from rivnut.

[Eric Page]

Yeah, I suppose wrapping the fabric makes sense to prevent it from lifting at the end of the wing, and given the number of rivets holding the attachment strip in place, the adhesive is probably superfluous anyway.

Thanks, everyone.