Reply to Hoerner Wing Tips by Bill438

[Tom H]

Bill 438, seems you posted your question in the "Builders" folder, which allows only the original author to post to the subject. Does not allow replies from others.

Your question was what foam will allow dissolving with acetone?

I have used the styrofoams, specifically the house insulation foam sheets to carve a shape, cover it with fiberglass using EPOXY resin (the styrenes and vinyl-esters will melt the styrofoams), then dissolved with acetone. I have heard of folks using gasoline for the solvent.

There are probably others with more experience that can chime in.

 

[n3480h1]

Tom H is correct in the above post. Some thoughts: Be aware that after the foam is dissolved away, the remaining surface is quite rough. I'm certainly no expert, but if one is inclined to manually produce and commercially offer multiple wingtip sets for sale, there are two common ways of dealing with this roughness:
1. Make female forms. This seems simple at first glance, but it is not - especially with a form such as a wingtip.
2. Make male forms, finish the exteriors to a very fine surface, spray on a very smooth finish coat, like a gelcoat, cover that with wax/PVA, then use them to produce female "tooling". The female form may also require additional fine finishing.

If you are only making one set of tips (right and left), you can use a simple set of male molds and finish the parts by hand. If you want production - and a tool that will withstand repeated use - you will need to make a very rigid surround for the tooling. You can google fiberglass production tooling and get an idea of what is involved. This is why good quality short run fiberglass or carbon fiber parts are expensive. If you have a CNC mill, a high end CAD system, and the funds for serious tooling, you're in like a porch climber. You might even look into resin infusion systems for production.

If you can manage all that, there is one more consideration: Every builder's wings will be a little different in size and in its precise airfoil. . . . just enough to get angry when trying to fit the wingtips. How does one make a "universal" product that will fit ALL of them?

I don't mean to discourage anyone from going ahead with wingtip production, just wanted to raise the awareness of what may be required. Bill438, you may be just the guy to solve these challenges.

Tom

 

[Bil4381]

Tom,
Thanks for your reply. I asked a year ago if anyone wanted the 3 gallon Hoerner Wingtips I'm going to make. There were no nibbles, so a male plug it is. I might use packing tape on the plug to get a better internal finish but I like the idea of glassing in the tank, with bulkheads all at once. Once the foam is dissolved through the hole for the fill cap, the foam residue and tape can be cleaned out.

The owner of Puma LSA suggested I use strips of .025 aluminum between the rib and wing skin to provide a better surface for installing the tips. Apparently f'glas will tolerate a little stretching say for a few days after layup, but will buckle if compressed. Using these strips will enlarge the wingtip attachment by .025 all around. Bill E

 

[n3480h1]

It always makes me stutter when people say "fiberglass". ;D

Which resin will you use? Polyester resin layups will shrink as they cure, and are very prone to tiny pinholes. Epoxy not as much. For a surface in contact with fuel I've read that vinylester is the right choice. I considered wingtip tanks for about 30 seconds, then decided that - for my own use on my aircraft, I would prefer aux fuel inside the first two inboard bays on the wing. Easy for me to say as I have not yet built the wings. I also wonder if it wouldn't be necessary to reinforce the spar because of the weight of 3 gallons out on the wingtip? In turbulence, that weight would be something that would make me sweat. A friend has converted the root bays forward of the spars into tanks, and has been successful so far. The one thing that raises the caution flag for me is which sealant to use. Will it eventually flake and peel? I don't know. I also have the option for a real live aux fuel tank in the passenger's position, removable as needed. Finally, I have to ask myself: If I have enough fuel in the primary tank to fly for two hours . . . won't I feel like landing to stretch my legs, take a whiz, and have a soda? I think I would.

Tom

 

[Bil4381]

Good questions Tom,
I already have Epoxy Resin for that job so that's what it will be.
I use avgas 100LL in my Sonerai because the Jabiru engines exhaust valves do better with it. Sometimes I add Marvel mystery oil to the fuel but never the oil.
Proseal make it now but the sealant is more or less the same as PRC 1422, which is a Thiokol Rubber. It works so well I've no reason to switch.
WHy? I'm going to a bigger engine which burns say 21 litres per hour. I want the tip tanks for more reserve fuel, because sometimes you do need to go to an alternate. The tip-tanks will give me 22 gals. Perhaps 20 gals are usable.
Stress- I have the B wings but even so am always prepared to cancel a flight. Engines burn the most fuel during takeoff and climb. My plan is to transfer most or all of the fuel from the tip tanks say 30 to 60 minutes into a flight.
Bill E

 

[bhcishere]

I was thinking along the lines of borrowing a highly proven design for wing fuel tanks. I intend to build leading leading edge fuel tanks the same way they are done on RV aircraft. Puts the fuel right on the CG, adds very little weight and keeps the fuel inboard where it can't cause major balance problems if a pump fails.

Bryan

 

[eschrom]

I already have Epoxy Resin

As Tom suggested, check the compatibility with fuel. I tested vinylester and know it's good but I'm not sure about epoxy.

Bill, it sounds like your plan to avoid excessive spar loading is to not fly in turbulent weather and/or to transfer fuel as early as possible in the flight? Sometimes it takes you by surprise though, or there's always the possibility of pranging a landing. Be careful, brother.

Ed

 

[n3480h1]

Relevant to this thread and to composite construction in general, IF one wanted a better understanding of composites there is a pretty good tutorial here:
https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/ama_Ch07.pdf

While (believe it or not) this does not cover everything, its a good start to understanding. Further information, such as chemical compatibility/suitability, can be obtained from resin manufacturers. From what I have learned, the commonly available epoxies are fine for boat and go kart fuel tanks, but vinylester is the correct and safe resin . . . at altitudes above 24 inches. ;D

Tom

 

[Bil4381]

Tom
Thanks for the link.

I was able to make a start hotwiring the wingtip plugs from Foam today. I'll need to sand them and provide some sort of a resin barrier before the layup. I hope to have the layups done this week.

So far it has gone pretty well.

At this point it appears the finished wing tips might cost $250-$300. Fuel components will be extra.

Bill E

 

[brunopitts]

Bill, here in Rimouski there's 2 Sonerai with Hoerner wing tips. The first , my friend Michel he did the mold and the 4 fiberglass wing tip and the second mine. I think he still has the mold. I'll try to think to take pictures and put them on my site and I'll ask for the mold.

 

[Bil4381]

Thanks Bruno,
I have one male mould at the point where I can make one wingtip.

I will look at the links for your photos.
Bill E