Mike James

Hi everybody,

I've made plenty of (hand laid up) fiberglass wing tube sockets in the past, using a typical method of barber-pole wrapping some resin-saturated glass around the wing tube, but have had typical results... Often they're hard to get off the wing tube, the edges are ragged and need to be sanded, and they've been relatively heavy.

Yesterday, I made my first ones via vacuum bag, and was surprised at the good results. Here's what I did...

First, I waxed the wing tube, just in case I got any resin on it. Then I wrapped a single piece of vacuum bag material around the tube, and taped it in place with a couple of pieces of Scotch tape. Wearing gloves, i wrapped a piece of 3" wide, resin-saturated (6 oz.) cloth around the tube, overlapping each wrap by approximately 1 inch. Next, I wrapped a piece of peel-ply around the tube, and finally, a piece of breather felt. The epoxy on the outside held all of this together well enough to be put into the bag. (It's helpful to leave several inches of the wing tube uncoated, so you have a gripping surface later, to twist the finished tube off.)

Releasing it from the tube wasn't "easy", but it only took a few minutes of twisting before I could slide it off... Not too bad.

Here's the surprise..A 7-inch long 3/4" diameter socket only weighed .2 ounces. That's the same weight as the typical phenolic tubes you get with Pattern-style tubes and sockets, and quite a bit stronger. I expected it to be almost double that weight. And, due to the vacuum bagging process, there are no ragged edges, and no sanding required. Nice.

Anybody else making these? Same method?

SCALECRAFT

My Feedback: (13)

Mike

I must say that you always post "good" info on composite fabrication as it becomes available to you.



I'm always looking to learn and share good info also.


Thanks

Steve

Mike James

Thanks, Steve.

RCU has been a great source for me, so I try and return the favors when possible. I think we're all learning a lot from each other, by making specific examples, posting photos, etc.. Many of these things you just don't find in typical "composites" books or videos.

What are you up to? I remember seeing photos of your nice molded Corsair. What's next for you?

macro-RCU

My Feedback: (1)

Mike, due to your great information, at this moment I weighted the wing carbon socket I made for Extra showed at Extra thread....

It is hand layup, carbon cloth 5oz, lenght is 6 7/8", Inlet diameter is 1"...

Weight is 0.6 oz... that is 3 times your result.... OK, this is 1" ID but If I vacuum I can expect the half weight...

I must learn more about composites to reduce weight in laminates...

Great info as always....

Countryboy

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Mike,

Does this not create for a loose fit of the wing tube within the socket ? How thick is the vacuum bagging material used too wrap the tube?

jetflyer

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Mike,

I just started vacuum bagging things and I am quite impress with the results I get. I recently helped a buddy vacuum bag some wings in which we did live hinges too. Compared to my normal glassing method I use to use for glassing wings, vacuum bagging wings elimates all the sanding time involved.

Currently I am getting ready to make a vacuum bagged composite fuel tank for my Super Reaper. I'm almost done with the female mold and should be read to go sometime next week.

I'll have to try your method for wing tube sockets after I'm done with my fuel tank. Thanks for the tip!

JR Gautreaux

PS. The video that Phil Barnes produced for working with composites is a great source of information.

SCALECRAFT

My Feedback: (13)

Hi Mike

Right now I'm working on an 80" Bf 109G in all composite. So far I have the composite spinner, scale composite flying 3 blades adjustable pitch, back plate for 3 blade, rubber scale tires, fuse plug (almost), vac form canopy, resin engine headers, can't remember what else.

As a family man, I have no time of my own. Only when I sneak away can I work on this model. But they always seam to find me right when I begin to "get going on a part.

couldn't find pics of my blades on the engine. I guess my wifes right, when she says "You can't find anything in here". I guess that extends to the computer also.

Steve

SCALECRAFT

My Feedback: (13)

That was the first blade with unidirectional. The pthers are weave, they look like a regular carbon blade, shiny and pretty.

Mike James

Hi everybody,

Countryboy,

I used the #1400 nylon vacuum bagging material (transparent green) from Aircraft Spruce, at http://www.aircraftspruce.com/catalo...es/vacbag1.php I don't know the thickness, but it's thin enough that with just one wrap of it, the socket still fits snugly around the tube. If there was a problem, I'd switch to a thinner plastic, or wax and PVA only.

The amount of weight you save by vacuum bagging is remarkable. On small parts, we're saving 20% to 30%, over a hand layup. I can't wait to make our wings and fuselage for the sport jet ( http://www.nextcraft.com/j47_sportjet01.html ) and see how those turn out. If the ratio is anywhere near what we've gotten on the small parts, we'll be well below target weigh... Cool.

Steve,

I'd love to see some photos of your BF 109 parts. The adjustable pitch prop sounds like a challenge. It that adjustable on the ground, or adjustable in the air? (Either way is great, just curious.) How did you do the tires? Resin casting of some kind?

ptxman

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Pretty much what I have done Mike with a few slight mods. Iwrapped the mandrel with drafting mylar sized to overlap by about 1/8" kind of tacked down on the ends with scotch tape. I used 3m type spray adhesive to maintain the overlap joint. The mylar is very thin which results in a good socket to spar fit. Also you can slide the finished layup + mylar right off the mandrel. It has inherant releasing properties so it comes off from inside the layup very easy, but a release agent just helps a but more.

I eventually used braided glass or carbon socks (CST or ACP) vrs straight cloth. They are pretty comparable in the end, socks cost a bot more butjust easier to conform & aesthetically nicer. On certain loose weaves of carbon I think I used a thin cloth on the mylar first but that was just because sometimes I had pinholes on the socket & didnt want to lock the spar in when gluing.

I use a very fine peel ply weave (cant recall off hand, equivalent to 0.75 or so) & that leaves a nice surface texture & bleeds the right amount of resin. I dont bother with felt, just a wrap of paper towel. For a bag I use construction grade poly & toss it out vs bagging nylon.

Mike James

Peter,

I'll have to try the mylar. You got my attention with the "slide it right off" remark. That seems to be the toughest part of this job, no matter how you do it.

Thanks!

SCALECRAFT

My Feedback: (13)

Mike

On the tires, they are made just lke a fuse but its a tire. I'll post some pics of the molds as soon as I take some.

The props are ground adjustable. Don't make me do in flight adjustable, I'll won't stop till I get it.

The tires are made from 60 shore rubber. the headers are urethane resin (alumalite), and the scale spoked hubs are also urethane resin.

All the stuff you may need is available from Smoothon.com. Or search Smooth On. It is a candy store of molding, casting materials.

If you need the products part numbers I use, let me know and I'll get them.

Steve

TT2

My Feedback: (13)

I have gone about it the same way ptxman does, with and without bagging. I use 0.003" acetate film with a mist coat of 3M77 to adhere it to the wing tube. Unlike mylar, acetate needs no release agent...it HATES epoxy! Wax paper works in a pinch but some of it will stay inside the socket when it's removed from the wing tube...not tough to remove if you grab one end and keep rotating the tube. This twists the paper up very tightly and peels it from the inside of the socket.

The braided sleeve is very, very cool and makes a quicker task of this but it can be cost prohibitive. Instead, I have been using 4 oz satin cloth. I roll out about a foot, smooth it out on the table, true up the 'free' edge with a straightedge, use a cardboard 'mask' and apply a mist coat of 3M77 along the edge about 1/4" wide. Then I roll my acetate-covered wingtube over the glass until it contacts the sticky edge then keep rolling the glass on the tube slowly. You can wet out the glass with epoxy on a paper towel (you don't need much if you're bagging) as you continue to roll the tube. Keep the glass tight on the tube as you roll. Cut the glass from the roll, roll on the peel ply and paper towels. Very easy, very quick...less mess and handling than spiral wrapping. Cheap too!

-Tom

Mike James

Always good to hear input from others... Thanks!

I'm making another test tonight, with a single wrap of full-length glass, rather than the spiral wrap. Should be lighter. I'll pull it and weigh it tomorrow.

Mike James

Not good...

Although I cut the glass on the bias, the single wrap version of the wing tube socket is rather obviously weaker than the spiral wrap version. Oh well... Worth a try. Weight difference was negligible.

TT2

My Feedback: (13)

Hmmm...sounds like the extra glass in the overlap of the spiral wrapping is adding lots of strength...which makes sense since it's doubling the amount of glass there.

I don't put the glass on a bias so there is a slight gain in stiffness but a decrease in strength. To me the sleeve simply serves as a guide for the wingtube to go through the holes in sub-ribs, fuselage sides, etc. The wingtube itself distributes the load through these parts. The highest concentration of stress on the wingtube is right where the socket is cut...at the root end of the wing. Regardless of how strong the socket is, the stress on the tube at this point remains the same. The phenolic tubes seem to be overkill, but maybe I'm missing something??? I've had ARFs with very thin glass wingtube sockets and never had a problem with them.

I suppose that the 'ultimate' would be to use an oversized braided sleeve (carbon or glass) about 2 x the diameter of the tube. For example if you were to use a 3" braided sleeve and pull the ends until the resulting diameter of the braided sleeve was 1.5" the angle of the tows would be 20.7-ish degrees. No seams, extremely consistent strength and stiffness. I thought about going the braided sleeve route on a plane I plan on kitting but it proved to be more expensive than phenolic tubes.

Mike James

You're right.

The added strength of the glass is just a bonus... It wasn't my goal. The phenolic tubes have a nice finish, but can break, via hangar rash. In fact, you can squeeze them in your hand, and they'll shatter. So, the glass was just a means of adding a little durability. Since they weigh the same, and are stronger, I'd say "Mission Accomplished".

Having done quite a few test parts (not just wing tube sockets) over the last few months, I'm having to readjust my thinking somewhat. Parts that I used to make by hand with only 1 or 2 layers of light cloth have been strong enough, but I'm finding that I need to use more, or heavier glass now, since the excess resin isn't fooling me any more. Some of the single-layer parts I've made lately are almost like paper, they're so light. I especially like the interior finish that the peel-ply gives on large parts, like fuselages. It's so clean looking, and is a great gluing surface. Wish I'd been vacuum bagging all along.

The other thing that's really impressed me is the tests we've done with sandwich construction. We're using light glass on both sides of a piece of 1/32" balsa. What it adds to the strength and stiffness of parts, for very little weight gain, is great. We're not using this glass/balsa/glass on all parts, but for specific areas like landing gear doors, hatches, etc.. I believe the balsa resists delamination better than foam, too.

TT2

My Feedback: (13)

If we ever cross paths I'll have to remember to NOT shake your hand! Most of the phenolic tubes I've had are 1 1/4" or 1 1/2" diameter, 1/16" wall thickness and seem strong enough to stand on. I've seen them available in 1/32" wall thicknesses which is what I suppose you're referring to...unless all those years of drumming have resulted in a hurculean grip! I'd like to get some of the thinner sockets...should weigh about half what the thicker ones do...could knock off 2 oz or so on the 50cc Edge I'm working on. If I can't source them then I might try spiral wrapping them with FG based on your reports. Maybe a super-light misting of 3M77, spiral wrap it 'dry' then wet it out with a foam roller? If you're only using one layer that should work fine.

I'm with you on the peel-ply surface inside a fuselage. I hate having to sand a fuse interior for secondary bonding of bulkheads, etc. Usually if you sand all the gloss off an open-layup fuse you are cutting into the glass resulting in a thin spot...yuk.

Sandwich composites are the ultimate. 4 times the strength and 37 times the stiffness for the added 'expense' of a core material. I typically replace 1/8" lite ply with carbon / divinycel / carbon wherever practical. The stiffness is MUCH greater than the lite ply (it's 'WOW!' good) and it weighs less than half. I wish someone made endgrain balsa in 'modeling' thicknesses ( 1/32" to 1/8" )...I haven't been able to locate any and have been searching for years. Rohacell is the only core material I'm aware of that can be obtained in very thin sheets... < 1/8" ...but it's terribly expensive. Awesome stuff though. Divinycel is similar but slightly lagging behind in terms of compressive strength : weight.

-Tom

Mike James

Hi Tom,

I'm not that scary...
The phenolic tube sockets I've been referring to are the thin-walled ones. (supplied for Pattern guys by Gator RC) Ive never had one break as a result of flight loads, but I've fractured the ends of a few around the shop.

Years ago, I tried hand layups of various end grain balsa items... carbon/balsa/carbon, glass/balsa/glass, etc., and saw that they were strong, but they were also heavy. I'm excited to now retry these things with vacuum.

Next up for me (after making the molds in the next few days) is molded wings. I've planned to make the wing skin centers (not the whole surface) a glass/balsa/glass sandwich, based on tests we did of tail parts. Can't wait. My "Eliminator 2" article is becoming a little bloated, so I'm in the process of creating a separte, dedicated "Vacuum Bagging" section on my site, showing all these tests, and some tips, based on what I'm learning. It's at http://homepage.mac.com/mikejames/rc...agging_01.html, for those interested. Not a lot there now, but I'll add to it as I learn more.

I'm really having a ball, discovering all these "new" techniques for myself. Reading about them is one thing, but holding them in your hand is something quite different.

Magne

Mike:
I have found that it makes quite a big difference how the epoxy is applied to the cloth. If you add the epoxy to the cloth ON THE BALSA, then a lot of the epoxy will soak into the wood. I have found that it is best to wet out the cloth on a piece of polythene sheet, release film or similar first, and then transfer it to the balsa. I generally use a foam roller to wet out, and when you lift the polythene off the glass, a lot of the epoxy comes off with the plastic. Leaves only just enough epoxy in the glass. I suppose this also applies if the core is foam.

Magne

bestrcpilot

Here is a trick I found. Use shrink tubing in place of Vac. bagging that way you can go right to the curing in the oven. You will get a lot better finish on the out side of the wing tube (no need to sand) .
Hope someone find this helpfull
Scott