Building with Foam Cure - more lessons learned

Hi everyone -

I have just completed another build of a prototype plane that Stephan and I have been working on, this time using Foam Cure in all the places I used to use Foam Tac.  I had written another article previously here about some lessons learned with a build where I used both Foam Cure and Foam Tac http://migsrus.blogspot.ca/2015/02/building-with-foam-cure-lessons-learned.html  In this link, you can also find a link to purchase Foam Cure from Hobby King and I also found it available in North America from Heads Up RC in the event that Hobby King is sold out http://www.headsuphobby.com/Flexible-Foam-Glue_c276.htm  At this link, you can compare the vast difference in cost between Foam Cure and Foam Tac as well, pretty significant.

Call me superstitious, I still used 5 minute epoxy on the control horns and motor mount, it has never let me down in those critical areas, and I didn't want to tempt fate.  I used Foam Cure to make the drywall tape hinges, reinforce the back of score lines (with the drywall tape as the hinge material), install the carbon fiber reinforcements and all other areas of the plane.  The difference in finished weight of the airframe (before installation of electronics and paint) is again 3 gr/0.1 oz heavier than a Foam Tac only build, but the construction overall is much stronger and cleaner, so I am OK with an extra 3 grams.

I pick my planes up by the nose quite a bit when moving them around and the first thing I noticed with this plane after the Foam Cure had fully set over night was that there was no flex in any of the joints/score lines.  With Foam Tac, I always found the nose joints to be flexible, almost like the nose was going to flex apart or break in my hand.

All the glue joints just feel stronger and more solid, leading me to believe there will be much less overall flex in the air frame when flying.  Too much flex in an air frame is energy for speed and maneuvers being wasted in the plane and not in the maneuver in my experience.  If you think of it in the extreme, a lot of EPP planes flex so much that in a tight roll for example, the tail can flex greatly in rolls, looking like it is playing "catch up" with the rest of the plane.  For this plane I just built which is a high performance, aerobatic park jet, I want the energy going into the maneuver, not the flexing of the plane.

Another nice thing I noticed this time and with the last build I did where I used Foam Cure for hinging is that once the glue spread over large areas is cured, it is not sticky.  Foam Tac remains somewhat sticky even after it is cured, meaning often on hinge areas it will pick up bits of dust and other work bench debris and as I mentioned in a comment to the link above, Foam Tac does not take paint as well as Foam Cure.

More on the point I made in the link above about hinging for areas other than control surface hinges.  As you can see in this picture looking from the back of the nacelle, I used a 1" wide strip of the fiberglass drywall tape attached with Foam Cure to strengthen the back of the score line on this 90 degree joint.

After spreading the glue evenly on the drywall tape, I let it set up for about a half hour, then cracked the score lines and it worked like a charm, there was no resistance or problems with the drywall tape lifting off as I mentioned in the link above.

Again, I am very impressed with how strong this glue sets up, it doesn't melt the foam, dries essentially the same weight as the same amount of Foam Tac, does not remain sticky after curing, can be cut, shaved, sanded to remove excess and allow me to finish my plane the way I like.  Of course it is also much, much cheaper and more readily available around the world than Foam Tac, so Foam Cure is definitely my main glue of choice from this point forward.

Cheers,

Scott