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Jun 26, 2015, 10:34 AM
KC4JAJ - ex N0DVJ
Jim Johns's Avatar
Thread OP
Question

Wing Center Section Fiberglass Tape


Does anyone know of a good source for 4" to 6" wide fiberglass tape to reinforce the center section of the wing? I haven't had much luck finding anything I like.

I'm including me and my latest SPA competition plane last weekend at the Andersonville, GA, contest. It's a Daddy Rabbit powered by an OS FS-95V 4-stroke. it's a slightly modified version of the plane Jim Whitley used to win the 1961 Nats. I was able to take 3rd in Advanced with only 9 1/2 flights on the airframe. That says a lot about the airplane - it flies extremely well, and the design was way ahead of it's time.

Thanks,
Jim
Last edited by Jim Johns; Jun 26, 2015 at 10:41 AM.
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Jun 26, 2015, 12:18 PM
DavidsPlanes
doxilia's Avatar
Jim,

use any FG cloth that you like. I have never used "tape" per se but cutting a piece to the width you roughly need is pretty straight forward.

Use masking tape at the width you want, glass the center section with FG of the weight you desire (I usually use two layers of different widths and cloth weight) and laminating epoxy and when the epoxy is 50% set, you can inscribe the edge of the glass along the masking tape line and peel off the outboard portion with the painters tape for a nice clean line.

Hope this helps, David
Jun 26, 2015, 04:57 PM
KC4JAJ - ex N0DVJ
Jim Johns's Avatar
Thread OP
Quote:
Originally Posted by doxilia
Jim,

use any FG cloth that you like. I have never used "tape" per se but cutting a piece to the width you roughly need is pretty straight forward.

Use masking tape at the width you want, glass the center section with FG of the weight you desire (I usually use two layers of different widths and cloth weight) and laminating epoxy and when the epoxy is 50% set, you can inscribe the edge of the glass along the masking tape line and peel off the outboard portion with the painters tape for a nice clean line.

Hope this helps, David
David,

Thanks, but I need a translation on "inscribe" and a little more detail please. Sorry.

Jim
Jun 26, 2015, 05:10 PM
Registered User
Roguedog's Avatar
Jim,

Aircraft Spruce has it in 50 yd rolls. Here's the link

http://www.aircraftspruce.com/pages/cm/tape/etapes.php
Jun 26, 2015, 05:22 PM
Registered User
Quote:
Originally Posted by doxilia
Hope this helps, David
As mentioned in the other thread, I sand the fiberglass off over the edge of the tape instead but both methods give a nice, clean edge. Something not mentioned yet is fiber orientation in the glass cloth. I put the cloth on a 45 degree bias, what do others do? This lowers the bending strength but maximizes the torsional strength.


Quote:
Originally Posted by ReelDoc
David,

Thanks, but I need a translation on "inscribe" and a little more detail please. Sorry.

Jim
David waits until the epoxy has partially cured, past gummy but not full hard, and then takes a sharp blade and cuts the edge of the cloth along the tape, then peels the loose edge of epoxy/glass off.


Mark
Jun 26, 2015, 06:38 PM
f5b-uk
Mike Seale's Avatar
Mark, you don't need much torsional rigidity at the centre section. 90/90 is probably better than 45/45, but we probably over-engineer the joint and it's too strong anyway...IOW, if there are 'in flight wing failures', I bet they happen outside the glass-fibre joint?
Jun 26, 2015, 07:21 PM
Registered User
Roguedog's Avatar
Quote:
Originally Posted by Mike Seale
Mark, you don't need much torsional rigidity at the centre section. 90/90 is probably better than 45/45, but we probably over-engineer the joint and it's too strong anyway...IOW, if there are 'in flight wing failures', I bet they happen outside the glass-fibre joint?
I agree 100% with you Mark.

I get my epoxy from a local manufacturer and in conversation with him about structural strength and whether I should use carbon fiber or regular fiberglass cloth, as an engineer who designs his own epoxy formulas and which cloth to use, his opinion is that because of the relative weight of RC Planes as compared to the weight of a stealth fighter in comparison, that he doesn't see a need for carbon fiber in RC planes.

I have said this before and had others argue the point but he agrees with you as well that we over engineer our planes and in doing so add unnecessary weight in the process.

It's way more work then needed to place cloth at a 45 degree angle and doing so also wastes the cloth as the cloth is in rolls that are not on a 45.

I specifically asked him about adding Carbonfiber to strengthen some fuses I'm making and was told that carbon fiber was no good for torsional strength and would actually be a waste of money as regular cloth and epoxy are more than enough for as far as what are planes would need structurally FWIW. Same goes lacing cloth layers at 45, 90,-45,-90 as far as layups or wing center sections.
Jun 26, 2015, 08:43 PM
Registered User
Quote:
Originally Posted by Mike Seale
Mark, you don't need much torsional rigidity at the centre section. 90/90 is probably better than 45/45, but we probably over-engineer the joint and it's too strong anyway...IOW, if there are 'in flight wing failures', I bet they happen outside the glass-fibre joint?
I didn't state myself very well in my last post and I did a bit of checking after I asked the question about 0-90 or 45 degree bias.

With bi-directional cloth at 45 degree bias all the fibers work and you maximize torsional strength with decent bending strength. With unidirectional cloth running spanwise (not what we typically use for center sections) you maximize bending strength with poor torsional strength. With bi-directional cloth at 0-90 you only get half the fibers working because the ones running chordwise do nothing for bending strength and it ends up weaker in bending and torsion than bi-directional cloth on a bias.

I do agree that we over-build for the most part, especially a lot of the classic pattern planes which appear to be built to survive a nuclear strike.

So, I am wondering who puts the glass on a bias (besides me)?


Quote:
Originally Posted by Roguedog
his opinion is that because of the relative weight of RC Planes as compared to the weight of a stealth fighter in comparison, that he doesn't see a need for carbon fiber in RC planes.
That depends on the R/C model in question. For the typical R/C wood & foam powered model that is pretty reasonable, though carbon does work nicely in a few critical spots even on our models.

There are other areas of R/C where carbon is essential, such as hotliners, pylon racers and many gliders. The handlaunch glider guys could not build the models they do without carbon fiber and serious effort in the fabrication process. The typical competition DLG these days spans 59" (1.5m span limit in the rules), weighs 8.5oz, has ~300sq.in. of wing and survives a 50g pull during the launch. That simply isn't possible without the extensive use of carbon fiber in the airframe.


Mark
Jun 26, 2015, 10:42 PM
DavidsPlanes
doxilia's Avatar
Quote:
Originally Posted by mmattock
David waits until the epoxy has partially cured, past gummy but not full hard, and then takes a sharp blade and cuts the edge of the cloth along the tape, then peels the loose edge of epoxy/glass off.

Mark
Exactly. I don't have an exact time for how long I wait for the laminating epoxy to cure (it varies by cloth used, model size, etc.) but you definitely don't want it to be crystalline as it has cured too long for a peel back. I think something on the order of 4-5 hours is what I might wait with Z-poxy laminating resin.

I lay my painters tape chord wise at the width I want the cloth to span, lay the cloth over top extending beyond the tape, glass down with the room temp thin resin insuring wrinkle free and then, when the epoxy has setup so that it will actually cut yet also peel back, I pass a #11 blade along the inside tape line using a flexible ruler along the tape and cut into the resin. It's cutting the resin more than the cloth as the latter really cuts very easily once glassed and has melded with the resin for the 5 hours or so. You mainly just want to watch your blade making sure you don't cut into the sheeting whether a built up or foam core wing. Personally I have never given it much thought and never cut into the wood because the resin is hard enough yet sort of rubbery that it prevents this but I can see how one could accidentally do so if careless.

In any case, I like to glass in 2 or sometimes 3 layers starting narrow with heavier cloth first and progressively thinner cloth to encompass areas such as retract bays on the underside if needed or other "open frame" areas to give some structure to the wood (e.g., around a retract or flap center servo). On a 40-60 size model, I usually do something like 2" wide on 5-6 oz cloth (I don't get too hung up on weight and bias) first followed by a 6-8" width of 2 oz cloth or sometime two layers of 3/4 oz cloth atop the 2" initial strip. I don't do it systematically (unlike some other things) but rather stick my thumb out to see how the wind is, and then say, alright lets do this given the kind of wing it is...

I tend to agree with the comments that we worry too much about "sufficient wing strength" in 40-60 size model as indeed most failures on a properly built wing typically happen outside of the glassed center section. I am a believer in CF tow in a span wise direction used as spars in foam core wings with thin skins (i.e., 1/32"). It is easy to do and when the CF is captured by resin between the core and skin, the chances of such a wing failing in flight are IMO close to nil. A crack might occur in a crash situation but unlike a built up wing which can indeed shatter in a crash, a foam/CF/resin/balsa composite wing will typically just suffer one or two major breaks or substantial bites in areas where there may only be foam, resin and balsa skins.

I might add that large 40-50% 3D aerobats with plug-in wings are a different story and undergo considerably more stress than most of our classics so if those models can hold up under most situations with how they build them, we probably do tend to over engineer our smaller models. On the other hand, an example of a poorly conceived wing would be a 2m aerobat which uses no glass for the center section and simply a 1/8" ply spar or two to join the panels under some MK. Some ARF's are designed this way and in a model that size with the power that is often put into them, well, I think its poorly engineered.

'nough of that!

David
Jun 27, 2015, 07:06 AM
PhoenixFlyer
PhoenixFlyer's Avatar

Glass the Center Section


Easy Fix. We all have our own methods. For center section, I use 2 oz. cloth. For the weight watchers, this is not going to add that much weight. This medium cloth has a wider weave. L&R secured, just rough the balsa up a little, to help with adhesion of the cloth. Marine resin is good, as it will sand easier then epoxy, but either is fine. Cut to cloth so on the top of the wing center, it will also cover the saddle of the fuselage. This will give that area a good hard surface for the saddle.
Bottom first, lay it on for measure. I also dust the cloth with hair spray, which will give it resilency for cutting, and no angel hair. I do the bottom first, after cure, you can sand and feather the edges. Mix up some micro-balloons, it will cover the edges, fill in where needed. I usually do this after the wing is glassed.
You an add the pan and feather in the micro B mix, let all cure, sand, then on to primer. These pictures are from a wing re-build.
I have threads on RCU under name Crankpin, showing wing and stab foam prep and wrapping the balsa, all way to finish paint. I don't know it all, but this is just my method. Glass on a bias ? Good idea, never thought of that.
Vince
Last edited by PhoenixFlyer; Jun 27, 2015 at 07:13 AM.
Jun 27, 2015, 10:11 PM
Registered User
View 12 is the way to go, put the epoxy on and get out the heat gun. With brush in one hand, heat gun in the other chase the epoxy over the cloth. The epoxy will run like water, no build up, that needs to be sanded. Not too much heat or the epoxy will start to harden. Heat gun and brush, easiest way to spread epoxy on cloth, in a tank or engine bay
Jun 28, 2015, 03:47 AM
PhoenixFlyer
PhoenixFlyer's Avatar

Epoxy App


Good thing about epoxy, you can add some alcohol to thin it to the consistency you need. Check out Tom Scotts P-5.

V


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