Wingtips - a couple of questions...

[DBeaulieu]

Q/B wing...fitted my first wingtip after putting in nutplates on the previously rivets parts of the wing skin. Hung aileron and swung thru range of motion. Questions...

(1) Do I trim the ends of the fiberglass wingtip inline with the trailing edge of the aileron in neutral position?
(2) How best to finish trimmed end?
(3) Countersunk screws with beveled washers for the nutplate - I assume you do not countersink the fiberglass but enlarge the fiberglass hole for the screw to accept the beveled dimple in the washer?
(4) Good epoxy for adding a wingtip position light base (either aluminum or wood)?

Open to all thoughts ideas or suggestions --- Thanks so much

Dave

[Utah-Jay]

Following this as I am nearing wing time

[Bcone1381]

1) Yes, trim it to match the trailing edge of the aileron for a pleasing visual appearance.
2) Cut it with your favorite cutting tool, I might have cut mine with a Dremel Tool Cuttting wheel. Then tune it up with a file. If you leave it slightly long for now, 1/4" thats ok. Then after it is closed up file it to match.
3) I defer this to others....I countersunk mine, but maybe a larger hole with CS washer is better....What is does is the Industry Best Standard?
4)Rough up the inside surface mating traiing edges with a course abrasive. Use Epoxy + Flocked Cotton. (AKA Flox is available from A/C SPruce) Mix up some to peanut butter consistancy apply it to the trailing edge.

I like AeroPoxy (A/Cspruce) because its structurally stronger, I measure by weight, not Pumps and can make a small amount without waste. But I also have West Here at the house, and it's quicker to pump than weigh. So for surface finish with a MicroBalloon mix I lean towards West. I dont think the brand of Epoxy is critical. Thats just what I use. I've never not had a problem with Aeropoxy curing and I've let it sit in cold temps a week. It eventually hardened up.

I am curious what others use and can add to this discussion.

[alaskabearhawk]

I used West Systems epoxy for pretty much everything. I'm not a fan of polyester resin, especially the way it sands. It seems to gum things up much quicker than epoxy.

[jaredyates]

I like the Superfill filler sold by Polyfiber. It sands easily, is a nice light weight, and doesn't shrink. I suspect the flocking stuff yields a similar result.

[alaskabearhawk]

FWIW, how I did mine.

Position lights:

http://www.mykitlog.com/users/display_log.php?user=yeeeha&project=527&category=3973&log=279560&row=43

http://www.mykitlog.com/users/display_log.php?user=yeeeha&project=527&category=3973&log=279561&row=42

http://www.mykitlog.com/users/display_log.php?user=yeeeha&project=527&category=3973&log=279562&row=41

Wing tips:

http://www.mykitlog.com/users/display_log.php?user=yeeeha&project=527&category=3973&log=286908&row=11

http://www.mykitlog.com/users/display_log.php?user=yeeeha&project=527&category=3973&log=286909&row=9

http://www.mykitlog.com/users/display_log.php?user=yeeeha&project=527&category=3973&log=286910&row=7

[Dpearson]

I'm in the midst of modifying my factory wingtips to accommodate the FlyLEDS landing/taxi/position light system "built into" the front of the wingtip using inspiration from Eric Newton's build site and Erbman's design. My wingtips (4-Place A model, probably made between 2005 and 2010) were originally made with polyester resin and chopped strand mat. I wanted to use similar materials for the modifications so I'm using polyester resin (Tap Plastics) and counting drops of MEKP. It's stinky stuff - use a good respirator if you go that route! I will definitely switch over to Aeropoxy for the other fiberglass parts I'll need to finish up the build.
I did take the EAA "Van's RV Aircraft Fiberglass Techniques" SportAir workshop last spring - everything I learned there is very applicable to the fiberglass parts of a Bearhawk build.

The advice from Bcone1381 regarding when/where to use flox and microballoons matches what I'm doing, and what I learned in the EAA workshop.

[Paul Johnston]

For the #6 screw and countersunk stainless washer I drilled the fiberglass wingtip with a 5/16” drill bit- this does well to “capture”the wingtip.

[Bcone1381]

I like the Superfill filler sold by Polyfiber. It sands easily, is a nice light weight, and doesn't shrink. I suspect the flocking stuff yields a similar result.

Edit: Adding Definitions of three things commonly added to Epoxy.

MicroBalloons, aka Micro Bubbles or Glass Bubble, or Glass Balloons are ver tiny glass bubbles. Its is pourable white dust. Do not breath them in. Wear a mask when measuring pouring or mixing them into epoxy.

Flocking, aka Flox, Flocked Cotton. It is cotton chopped up very fine. It is also white, but does not pour. It is not like dust.

Cabosil: An epoxy thickening agent that I understand is used to prevent Epoxy and Micro mix from drips, runs and drapes.

Although I've not tried Superfill. I believe Superfill is Epoxy resin premixed with the right amount of Micro Balloons . Then the hardener is mixed at the workbench in to get the chemical hardening process of Epoxy started. I have mixed Micro Balloons in myself and the result is what Jared describes. We call this consitancy "Dry Micro" because we stop adding the glasss bubble micro ballons when the appearance is dry, and like smooth peanut butter.

However, a number of times I wished I had Superfill just because it would save time. After developing skills in mixing up dry micro I know what too dry results are and too wet, and I can now get it consistant and adapt to what a need might be. What I'm saying is....I bet Superfill is nice...use it. If your pinching pennies, then a pound of Micro Glass Bubble Balloons is cheap, and goes a long way.

Micro is smooth, and non structural. Don't use it for structural stuff like attaching a Nav Light mount to your wing tip.

Cotton Flocking (aka Flox, or Flocked Cotton) is also inexpensive but very different. When mixed up with Epoxy it becomes structural. Mix a golf ball size up of both micro and flox then try to destroy them with a hammer. You'll see what I mean...divots and crators every where. Try to sand flox and you'll give up, get your file out. Its surface is not smooth like Superfill/Micro. Its not even close to a finished surface. Get the flox to shape, let it cure then smooth out the finish with a bit of micro. And I mean a few grams of resin mixed up then add micro and you don't have a bunch left to throw out in the trash when your done.

[dramsey]

Good descriptions. You can mix and match all of the above to get the best of both worlds. For instance if you want to build a pad for the landing light you can combine flox and micro in the epoxy slurry and get something tough but more sandable. But I suck at getting it right the first time and sometimes have to follow in behind with a thin micro touch up. I used that mix also at the intersection of my horizontal stab and vertical stab on the lancair as well as tapering the horizontal to the fuselage. No cracks in 1300hrs of flight. Micro by itself is prone to crack. Any thick buildup needs flox mixed in. Flox by itself is a great epoxy sponge and makes a heavy mix. The combined mix will have adequate strength and lighter weight.

Cabosil is interesting stuff. Did not use it on the Lancair but its used on the Velocity I am building some on. Velocity recommends a structural adhesive that is very runny. It would just run off the spar when bonding on the skins but mix in a little cabosil and it stays where you put it. It makes the epoxy sticky to the point its difficult to get off the trowels. it helps it hold a shape as well.

Superfil is convenient …great for touch ups where you would use micro. I used it prefabric on a Just Highlander and grew to like it. A Friend also used it for body work on a wooden Emeraude. I used it on touchups on friends rv10 as well. A big plus is you dont have to deal with the dangers of microglass in your lungs

[alaskabearhawk]

I've had great results using products from these folks: https://www.fiberlay.com/catalognonshopable

[Frank]

I'm wondering if fabric covered wing tips would be feasible. Would be simpler construction and easier repair. I really doubt this is a new idea.

[SpruceForest]

And another question: is there a good reason why one would not to trim the tip rib at the aft spar and closeout the fiberglass tip with that offset? Awfully delicate piece of aluminum hanging out there in the shop for a bit until the wings get hung. I can see a bracket to tie into the closeout, but don't see an apparent issue with avoiding the in-progress hanger rash.

[alaskabearhawk]

The rib will add some structure and help to align the aft portion of the wing tip. FWIW, I had my wings all over the shop for years, up and down the shop wall, down on a bench, on the airplane, in the rotisserie for prep and paint, etc, and I never had an issue. You can always back it up with a wooden stick if you are concerned about bending it. If it gets destroyed, go with Plan B. My .02 cents.

[svyolo]

I used "wood" epoxy stick for the base for my wingtip LED lights. Balsa wood is slightly lighter. The epoxy stick was just too easy. The total time was measured in minutes. Maybe an hour.