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Thread: Couple o' questions..

  1. #11
    cub builder's Avatar
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    Resourcenal is good stuff and works well, but does require a good fit and proper clamping pressures. When working on certificated aircraft with wood parts, it is often times the only acceptable wood bonding agent.

    Epoxy resins are more tolerant of less than perfect workmanship and do not require (or even desire) so much clamping pressure. The bashing of epoxy resins here is a bit overblown and there are hundreds of thousands of epoxy resins, most with their own designed purpose. Not all Epoxy resins are equal. Several, including T-88, work very well for aircraft construction. It is highly unlikely that you are going to approach transition temperatures to where your aircraft may be heat damaged unless it is painted black and lives outside in southern AZ. I have a wood airframe aircraft that is now approaching 20 years old with well over 1000 hours of flight time on it. To date, I have seen -0- failures in the epoxy resins used in construction. This would include all of the fuselage, and the built up box spars.

    I have observed a poorly built, aged and weathered example of the same aircraft that was not airworthy tortured to failure using a jacking frame and chains. The distortion of the box spars and airframe before failure was incredible, but the ultimate failures were in the shear webbing of the spars as the webbing plywood finally ripped right down the middle. No failures of the epoxy bonds were observed in the failure testing.

    While I do agree that Resourcenal probably has a better bond than T-88 or other epoxy resins, many of the epoxy resins available and recommended for aircraft construction are more than adequate and will exceed the strength of the woods they are bonding.

    Cub Builder

  2. #12

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    I have no doubt that epoxy can be stronger than wood, but:

    I want some Weldwood, so 20 min to hdwe store and $10 and I have it. For epoxy, mail off a chunk of bucks to ACS and wait for it to arrive.
    To use the Weldwood, pour a tablespoon or so into a dixie cup, mix with water and an icecream stick and use.. Clean up afterward with a damp paper towel. For epoxy, isolate building area from the rest of the house to block fumes. Don gloves mask and other protective gear as required, mix ingredients as required, glue parts, clean up with acetone..

    In the end, each way gets the same result, a well glued joint. Why bother with epoxy?

    "Works with less than perfect workmanship", = you can get away with sloppy workmanship. Not a message I want to hear in aircraft construction..
    Last edited by briankk; 01-15-2015 at 12:48 PM.

  3. #13
    Aaron Novak's Avatar
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    Quote Originally Posted by cub builder View Post
    Resourcenal is good stuff and works well, but does require a good fit and proper clamping pressures. When working on certificated aircraft with wood parts, it is often times the only acceptable wood bonding agent.Epoxy resins are more tolerant of less than perfect workmanship and do not require (or even desire) so much clamping pressure. The bashing of epoxy resins here is a bit overblown and there are hundreds of thousands of epoxy resins, most with their own designed purpose. Not all Epoxy resins are equal. Several, including T-88, work very well for aircraft construction. It is highly unlikely that you are going to approach transition temperatures to where your aircraft may be heat damaged unless it is painted black and lives outside in southern AZ. I have a wood airframe aircraft that is now approaching 20 years old with well over 1000 hours of flight time on it. To date, I have seen -0- failures in the epoxy resins used in construction. This would include all of the fuselage, and the built up box spars. I have observed a poorly built, aged and weathered example of the same aircraft that was not airworthy tortured to failure using a jacking frame and chains. The distortion of the box spars and airframe before failure was incredible, but the ultimate failures were in the shear webbing of the spars as the webbing plywood finally ripped right down the middle. No failures of the epoxy bonds were observed in the failure testing.While I do agree that Resourcenal probably has a better bond than T-88 or other epoxy resins, many of the epoxy resins available and recommended for aircraft construction are more than adequate and will exceed the strength of the woods they are bonding. Cub Builder
    I think most epoxy's heat deflection temperature is around 120f, so if you have something under load at those temperatures or above, thats where epoxys fall out of favor from an engineering standpoint. At around 200F most have strengths af less than half of what they have at room temperature. Things that dont see elevated temperatures or constant load are probably the best applications for epoxys when good joinery or clamp pressure are impossible to obtain. Things that see constant load and higher temps, probably a better location for resorcinol or UF adhesives with good joinery and clamping. Designs engineered for casein adhesive are probably a lot safer to replicate with epoxy. If it was originally a high performance design engineered around resorcinol or UF's I would have a harder time substituting a lower performance adhesive like epoxys or caseins. It would be like substituting 6061 for 2024 in a design, and maybe allowances would have to be made for the lower performance.
    Last edited by Aaron Novak; 01-15-2015 at 01:14 PM.

  4. #14
    Sam Buchanan's Avatar
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    Quote Originally Posted by briankk View Post
    I have no doubt that epoxy can be stronger than wood, but:

    I want some Weldwood, so 20 min to hdwe store and $10 and I have it. For epoxy, mail off a chunk of bucks to ACS and wait for it to arrive.
    To use the Weldwood, pour a tablespoon or so into a dixie cup, mix with water and an icecream stick and use.. Clean up afterward with a damp paper towel. For epoxy, isolate building area from the rest of the house to block fumes. Don gloves mask and other protective gear as required, mix ingredients as required, glue parts, clean up with acetone..

    In the end, each way gets the same result, a well glued joint. Why bother with epoxy?

    "Works with less than perfect workmanship", = you can get away with sloppy workmanship. Not a message I want to hear in aircraft construction..
    Some additional data (counter?) points:

    I have built three light aircraft with T-88 epoxy adhesive. I have never tolerated 'sloppy' workmanship but don't consider my craftsmanship to be 'perfect'. I have seen a couple of examples of what I consider 'perfect' and realize I will never have the skill or patience to achieve that level of artisanship. I want my planes to fly within my lifetime.....

    T-88 is relatively inexpensive and I can get it shipped via USPS from ACS in two days. A couple of quart kits will build a lot of structure.

    Mixing involves squirting out equal length beads of parts A and B on a mixing board (scrap piece of cardboard) and mixing with an ice cream stick.

    I have never used gloves, mask, and other protective gear and haven't experienced any unpleasant fumes...fumes...fumes...But vinyl gloves are not a bad idea just to keep it off skin...easier than chewing off a wad of epoxy......

    Cleanup of the joint involves a quick wipe-off with a paper towel while the epoxy is fresh.

    But hey....I used TiteBond II on the last set of ribs I built, worked great and the Pietenpol guys love the stuff.
    Last edited by Sam Buchanan; 01-15-2015 at 02:51 PM.
    Sam Buchanan
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  5. #15
    amv8vol's Avatar
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    This talk of the lack of suitability of T-88 for aircraft construction has me very concerned as my project is almost completely fabricated with T-88. I must say though, I have through out the course of construction made samples for destructive testing and have yet to have an epoxy joint fail at the glue line.
    I did do a birch plywood lamination with CASCOPHEN (resorcinol) that failed testing. The test piece split at the glue line and when I tested the actual piece and it also split at the glue line rather easily. To be fair this glue was nearly 2 years old and I suspect that was the problem. I had used the Cascophen on a previous spruce bent lamination about a year before and that test piece was good.
    If the strength of the glue line/joint is greater than the material (wood) being glued is there an advantage to a higher strength adhesive? It was said that Oak joints do not glue well but I have some Ash pieces that I tested last night (Glued up months ago) the results are attached.
    I have sent System Three an email for their data on cold creep with T-88.
    So, at this point, I am not sure if I should accept the information that T-88 is an inadequate product and scrape my project before I go any further or accept that the epoxy appears to be working for me and continue?

    Attached Images Attached Images   
    David North
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    Rudder complete
    Tailplane complete
    Bulkheads complete
    Wing ribs complete
    Flaps complete
    Ailerons complete
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    Fuselage Partial
    Spar complete
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  6. #16
    Aaron Novak's Avatar
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    Quote Originally Posted by amv8vol View Post
    This talk of the lack of suitability of T-88 for aircraft construction has me very concerned as my project is almost completely fabricated with T-88. I must say though, I have through out the course of construction made samples for destructive testing and have yet to have an epoxy joint fail at the glue line.
    I did do a birch plywood lamination with CASCOPHEN (resorcinol) that failed testing. The test piece split at the glue line and when I tested the actual piece and it also split at the glue line rather easily. To be fair this glue was nearly 2 years old and I suspect that was the problem. I had used the Cascophen on a previous spruce bent lamination about a year before and that test piece was good.
    If the strength of the glue line/joint is greater than the material (wood) being glued is there an advantage to a higher strength adhesive? It was said that Oak joints do not glue well but I have some Ash pieces that I tested last night (Glued up months ago) the results are attached.
    I have sent System Three an email for their data on cold creep with T-88.
    So, at this point, I am not sure if I should accept the information that T-88 is an inadequate product and scrape my project before I go any further or accept that the epoxy appears to be working for me and continue?

    I wouldn't go running to the scrap bin, luckily most designs are overbuilt by a large margin. Odd you had a glue failure, but considering the shelf life of the resorcinol part B is 9 months, and yours was almost 2 years old......well that's a pretty easy one. In the end its a homebuilt, and you can use what you like. There are production aircraft using epoxy in their wood structure, so its not unheard of by any stretch. Good Luck!

  7. #17

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    Gday from Aussie chaps,I have read this thread with interest as I am procrastinating heavily about building an aeroplane and just Wanted to make a quick comment .The RAF brought the Mosquito to Australia at the end of ww2(VE) and had to withdraw it as the aeroplane had problems with the spars delaminating. It was only up north in the tropics that the problem became apparent so the Japanese were lucky not to have to face a awesome aeroplane such as the Mossie. The glues used did not seem to like the hot humid weather. I don't know what it was but I know the CAA were against wooden homebuilt aeroplanes for a long time. Cheers Ross

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