By Wayne Walker, SEFSD
It all started when I was given an old Multiplex AcroMaster pattern plane. I won it because I bought the late John Forester’s two model sailboats. They say never look a gift horse in the mouth, yeah right.
After I got the sailboats sorted out and ready to go sailing, I turned my attention to the AcroMaster as I wanted a rough & ready plane to practice my maneuvers & landings.
I went through it and everything seemed all right, so I found a 3S – 3000 battery for it, and put it in place, it didn’t balance at all, nose too heavy. Then I noticed it had a pretty big motor for that size plane, all the better I thought but it was obviously too heavy & why the plane didn’t balance with the battery in the location designed for it. Moved things around & added 4 ounces of lead to the battery and it now balanced.
Took it out to the field to test fly it. Roll out was good, but as soon as it was airborne it didn’t seem to have good control. I was able to make a 180 from the takeoff, but then it was all over the place! It ended up crashing over by the RotorPlex area. When I was gathering up the pieces, I noticed the right aileron was pulled out of the wing, hmmm probably what caused it to go out of control.
Later back at my shop I glued everything back together with my trusty 30 minute epoxy and paid extra attention to getting the aileron flex hinges glued in with plenty of epoxy to make sure they held in the future. I also had fun gluing the nose pieces back together and wrapping a fiberglass bandage around it all to keep it in place and hopefully straight and sound.
Back to the field to try again. Takeoff was normal & turnaround normal then as I got it about even with me where I was standing all heck broke loose and it was uncontrollable again! And it crashed.
When I was gluing things back together again, I noticed that most of the glue joints had turned brown, I just figured the builder used low grade epoxy or rubber cement. I was also mystified as to why the recently epoxied aileron joins had pulled out again. I asked around and everyone I asked said they thought the epoxy was the best way to glue Multiplex’s Elapor foam together.
Well, it turns out that epoxy & carpenters glue only proved a half-baked bond to Elapor & similar shiny skinned plastics! After getting what I term “Old Wives” tales of which glue to use I found the following on several Multiplex model airplane construction manuals:
From: MULTIPLEX Modellsport GmbH & Co. KG
“This model is not made of Styrofoam™, and it is not possible to glue the material using white glue, polyurethane glues or epoxy; these adhesives only produce a superficial bond which gives way when stressed. Use medium-viscosity cyano-acrylate glue for all joints, preferably our Zacki-ELAPOR®, # 59 2727 – the cyano glue optimized specifically for ELAPOR® particle foam. If you use Zacki-ELAPOR® you will find that you do not need cyano ‘kicker’ or activator for most joints.
However, if you wish to use a different adhesive, and are therefore obliged to use kicker / activator spray, we recommend that you apply the material in the open air as it can be injurious to health. Please be careful when working with any cyano-acrylate adhesive: these glues can harden in seconds, so do not allow them to contact your fingers or other body parts. Wear goggles to protect your eyes!”
In another Adhesives note I found the following advice on technique.
“On one surface spray on Kicker and let dry for several minutes.
On the other surface apply Medium CA as needed.
As the join will set in a very short time align the pieces carefully before letting them touch as there will only be several seconds before the CA hardens making a permanent bond.”
I found that using this procedure results in a 2-3 second flexible time, not really enough to align large pieces of work like an AcroMaster wing panel.
So with all this new information, what did I do? Of course I ran my own tests to see how well these adhesives bond Elapor. I also did a test of Formula 560 Canopy Glue.
Here’s the picture of the test samples I glued together and then 24 hours later tested for strength. All samples were on virgin Elapor foam.
I tested both “Plain”, no preparation, and Prepped with alcohol and then sanding to remove the gloss on the surface of the foam.
The Canopy Glue 560 was the weakest with only a small pressure to part the two pieces.
Using Odorless CA was almost as weak as the Canopy glue.
The high quality Epoxy joined pieces were next in strength, 1-3 pounds of pressure to break the bond.
I didn’t test White, Carpenter’s or Ambroid glues as these are seldom used in modern model construction.
The Medium CA plain & prepped samples I was not able to break apart, but my arthritic hands were only able to apply about 5-10 pounds of force to the joins, this is probably equivalent to a hard crash to the joined pieces.
When gluing Multiplex Elapor and similar shinny skinned foam use Med CA with or without Kicker, it will be the strongest join available, and no prep is needed to make a strong joint.
When gluing Styrofoam pieces use Odorless or Foam Safe CA glue, or epoxy.
As far as Hot Gun Glue goes, I’ve bought several Chinese models that have them, but don’t recommend the technique.
As an aside, I found that Du-Bro & other hardware suppliers have discontinued the line of hard plastic hinges and instead recommend the Fiberglass mat type of hinge material. I’ve now substituted this for all my flex hinges.