Stiffening Foam Board

[Hai-Lee]

How many times have you had issues with FB losing its rigidity and had to resort to adding skewers or CF rods to a design to allow it to fly without it flapping it wings? I have had a few such planes.

Recently I wanted to investigate Autogyros and as part of that investigation I wanted to see what I could do to make the rotor blades out of FB only without complex and difficult reinforcements.

Through a fair bit of T&E, (Trial and Error), I ended up with a blade that would support the 'Gyro in the air without such reinforcements. The technique was and is so very simple I just paint the FB in glue. Whilst a number of different glues work well the best cost/stiffness results have been achieved using white glue.

The rigidity of the FB is increased so much that I have built a FB version of the "Otto Vs Eddie" biplane design using slab wing construction and even though I have crashed it many times for many reasons the wings have never torn or broken. The struts have been torn out and the fuselage split but the wings are still as I first built them, (with a few LE dents of course).

Just a tip for those who see their FB starting to warp and sag on their favourite plane!:black_eyed:

 

[fixnfly]

Sounds like you basically made a foam core wood pulp composite structure with a polyvinyl acetate resin. White glue, or polyvinyl acetate adhesives are actually used as a binder to help the paper fibers stick together. Thinned white glue is used to make fireworks shells and other paper products. It will soak in to the paper best and end up weighing less if you reduce it 50% with water before applying it to the paper. I used printer paper and thinned elmers glue to reinforce the tail of my radian glider, although for that particular application I should have used a lighter weight paper product.

 

[Hai-Lee]

From my own experiments with AU FB if you dilute the glue it takes a lot longer to dry. The extra time allows the paper to actually soften and even separate from the foam before it dries. If it works with the FB you use great. Additionally the water weight is irrelevant as it all evaporates as the glue dries. Other glues dry quickly and weigh a little bit more.

Anyway what ever works I suppose!

 

[fixnfly]

I haven't tried it on foam board yet, but dollar tree foam board would probably delaminate also. I have mainly done this on foam that didn't already have paper on it.

 

[AkimboGlueGuns]

I wonder if you could use WBPU and talc as a paint on similar to what you're doing with glue. I would think that it would fill imperfections better and still increase rigidity.

 

[fixnfly]

If you have read the content on waterproofing foam board, apparently any water based coating can delaminate the paper if used in excess.

http://www.flitetest.com/articles/painting-foamboard

The catch, is that the chemicals in the oil based coatings is that they will eat the foam core material so you have to make sure to not let it soak in either. I have successfully used scotch guard to waterproof paper on a foam board without delamination, but it doesn't add much strength. It is a florinated polyurethane in alcohol solvent which also could eat the foam core.