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Old 07-05-2013, 02:56 PM   #1
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1978 Bud Barkley Tiger Moth

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The plans call for using "polyester resin" (see image) to join bottom half fibreglass gas tank to ply framing inside it. Can I get away with using 15min. epoxy? what is the reasoning behind the use of resin vs epoxy, Is resilience the issue?
Please help !!
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Old 07-06-2013, 11:07 AM   #2
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Re: 1978 Bud Barkley Tiger Moth

I don't see why you couldn't use epoxy, I would use the 30min though. The back of that fibreglass is plenty rough for adhesion.

''engine hoarder''
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Old 07-06-2013, 07:43 PM   #3
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Re: 1978 Bud Barkley Tiger Moth

Hi tronic5,

I do not understand why they would call for polyester rather than epoxy.

Epoxy will bond to polyester.
Polyester will NOT bond to epoxy.

Rough up the (I assume polyester) tank with 40grit. Wipe clean with acetone and rag.

Use a longer curing epoxy. I like the 3hr stuff, or West brand.

5min/15min is like cheese, compared to the longer setting stuff. (try doing samples)

I would mix up an epoxy putty using microballoons/milled glass fibres to fill any gaps/voids and put a fillet between the ribs and tank.

Hope this helps.

Looks like a great project !

Take care,
Have fun,
Maac 6437
Unabashed Combat Team
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Old 07-26-2013, 08:25 AM   #4
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Re: 1978 Bud Barkley Tiger Moth

Looking at the info below I almost think they don't want a strong bond. Is the fit of the tank in the space where it goes almost an interference fit? Maybe they are afraid the epoxy will set up before you can squeeze the tank in place.

Epoxy materials tend to harden somewhat more gradually, while polyester materials tend to harden quickly, particularly if a lot of catalyst is used. The chemical reactions in both cases are exothermic. Large quantities of mix will generate their own heat and greatly speed the reaction, so it is usual to mix small amounts which can be used quickly.

While it is common to associate polyester resins and epoxy resins, their properties are sufficiently different that they are properly treated as distinct materials. Polyester resins are typically low strength unless used with a reinforcing material like glass fibre, are relatively brittle unless reinforced, and have low adhesion. Epoxies, by contrast, are inherently strong, somewhat flexible and have excellent adhesion. However, polyester resins are much cheaper.

Epoxy resins typically require a precise mix of two components which form a third chemical. Depending on the properties required, the ratio may be anything from 1:1 or over 10:1, but in every case they must be mixed in exactly the right proportions, and thoroughly to avoid unmixed portions. The final product is then a precise thermo-setting plastic. Until they are mixed the two elements are relatively inert, although the 'hardeners' tend to be more chemically active and should be protected from the atmosphere and moisture. The rate of the reaction can be changed by using different hardeners, which may change the nature of the final product, or by controlling the temperature.

By contrast, polyester resins are usually made available in a 'promoted' form, such that the progress of previously-mixed resins from liquid to solid is already underway, albeit very slowly. The only variable available to the user is to change the rate of this process using a catalyst, often Methyl-Ethyl-Ketone-Peroxide (MEKP), which is very toxic. The presence of the catalyst in the final product actually detracts from the desirable properties; just enough catalyst to harden fast enough is preferable. The rate of cure of polyesters is controlled by the amount and type of catalyst, and the temperature.

As adhesives, epoxies bond in three ways: a) mechanically, because the bonding surfaces are roughened; b) by proximity, because the cured resins are physically so close to the bonding surfaces that they are hard to separate; c) ionically, because the epoxy resins form ionic bonds at an atomic level with the bonding surfaces. This last is substantially the strongest of the three. By contrast, polyester resins can only bond using the first two of these, which greatly reduces their utility as adhesives and in marine repair.
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Old 09-01-2013, 03:38 PM   #5
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Re: 1978 Bud Barkley Tiger Moth

I have acquired a wonderful old Bud Barkley Tiger Moth. It looks like it might be 1/4 scale. According to the faded message on the instrument panel, it was built or owned by W. Jones in 1979. There's a phone number but no area code. I have no plans for this model and no idea what the CG is. If you have the plans showing the CG could you please let me know what it is.

I am close to flying readiness. I have just mounted a Zenoah 38CC on it and am in the process of replacing the pull/pull cables that have worn thin or were damaged over years of flying and storage.

Many thanks for your help on this.

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Old 09-03-2013, 02:42 PM   #6
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Re: 1978 Bud Barkley Tiger Moth


A reply from someone who has flown the model would be more useful...... but I happen to still have Barkley kit and on the plans the center of gravity symbol is located on the side view of the plan on the rear aluminum strut that connects the fuselage to upper wing fuel tank, 1" down from the bolt point of the top of that strut to the metal tab that are screwed into the tank assembly at two points. The ' 1 inch down' is measured along the centerline of the strut, not 1 inch horizontally forward of that bolt point.

When I drop a vertical line from that center of gravity symbol, the line intersects with the center of the forward aluminum jointer tube in the bottom wing.

Curiously the several pages of plan directions don't mention center of gravity.

Again, get some feedback from people who have flown the model (It would not be the first time that a plan was wrong - smiley) There should be flight, if not build logs on some of the model forums..... and I believe a quarter scale Tiger Moth in almost ready to fly format came out several years ago so there should be lots of forum postings about that model.

good luck and post some pictures

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Old 09-03-2013, 03:07 PM   #7
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Re: 1978 Bud Barkley Tiger Moth

Hi Michael:

The information you have provided is just what I needed!

With this data, I am sure that the CG won't be far out when I fly this old bird.

You mentioned you still have a Barkley Kit of the Tiger Moth. If you are not going to build it and would be willing to part with it, I would be most interested.

Thanks for the information.

I will post some pictures of the Moth.


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