does balsa harden with age?

[Robert Parker]

Hi Phil,

Just read this through and can only say that I recently built a Global kits Cessna Skylane dating back to the 80's I believe. The balsa in it was like oak and extremely heavy, I lost count of how many pins I snapped during the build I was totally shocked at the weight of the tail assembly, I've built models lighter.

With such a heavy tail I had my concerns about adding a lot of weight to the nose but as the rest of the kit was also heavy the Skylane actually came out pretty good with almost no weight being added.

I was informed by one forum member that back in those days the American kit manufacturers used very heavy grades of balsa. I also had a very old Topflite Texan almost built and again the balsa in that was extremely heavy.

So I would agree with the above comments regarding how the balsa was sourced back then and that today we are lucky to have such light grades available to us, great for electric flight.

Regards

Robert

[Cuban8]

Posted by Percy Verance on 03/02/2018 13:02:27:

I think Sig even sold some specially formulated adhesive to stick the sheeting on the foam cores if I recall correctly. The trend was for US builders to cover their own foam core wings, whereas here in the UK we expected ours to be already covered when we lifted the box lid.

The SIG instructions called for you to make up the veneer from single 3" balsa sheets,apply contact glue and then roll the core onto the wood. Given how thin and flexible the foam cores were, it sounded like a certain recipe for disaster.

As the cores were cut from a single rectangular block of white foam  I used a large carpenter's saw down the centre of the block to separate the cores into individuals, each now with a single flat bottom that could be jigged on the bench, thereby allowing the veneer to be easily (but carefully) applied and weighted down, thus avoiding warps and maintaining the tip washout and slight under-camber.

Very easy to do, and when I checked with my incidence meter at final assembly, all was bang on the money.

Edited By Cuban8 on 04/02/2018 10:44:54

[Bob Cotsford]

Not that long ago I built a Frog Mustfire kit dating from the mid to late '60s, I don't remember having to replace any of the wood in that. I also have a part built TF P40 where the fuselage, which must have been stored exposed, shows a little ageing and drying of the wood while the wood in the box is pristine. I built a Marvik Models Joker some years ago and had to reject several of the supplied pieces as they were rock hard and weighed a ton - just very poor wood selection by the kit manufacturer.

I guess it all depends on how and where the wood has been kept, certainly all my 20-30 year old balsa stored indoors in an unheated room has survived in good condition. Also the wood supplied in the kits was a bit of a lottery when it comes to suitability for it's purpose.

[Djay]

I have lived in Dubai for over 10 years and find that due to high heat (50c in summer) and the high humidity it affects the balsa greatly.

Some goes hard and very brittle so it snaps very easy, other balsa turns to dust. My Boomerang Sprint fuselage started to get a layer of balsa dust which when cleaned off would return, turned out the wood itself was breaking down and crumbling with age, so a new fuse was constructed using the old as templates. I use UK sourced balsa where possible as this is so different to the USA sourced stuff. Lighter more flexible, softer and just appears so much better.

All the USA kits I by I normally scrap a lot of the wood as it is beyond belief how hard and heavy it is.

Talking of wood crumbling, I recently rebuilt a full size truck automatic gearbox in my workshop and some of the ATF fluid spilled onto a belly fairing for one of my sport models. A couple of weeks later I found the fairing under the bench and the wood had turned grey and mummified and turned to dust when touched. The fluid had broken down the cellulose in the grain and it just crumbled and was gone. Most strange to see and feel.

Darryl

Edited By Djay on 04/02/2018 11:46:10

[Martin_H]

Balsa, like any aircraft timber, should not be allowed to dry out. Most aircraft timbers have a moisture content of between 8 and 15% and this moisture content gives the timber its resilience when in use. Above 15% and you risk rotting, and below 8% the timber becomes too dry to function beyond decorative purposes. In full-size use, timber is varnished or otherwise sealed to prevent moisture loss, something we don't tend to do with our balsa models because of the weight. When building full-size wooden aircraft, a moisture content meter is essential and part of the recording and certifying process.

So, apart from sealing all exposed timber surfaces, the ideal solution would be to keep your kits and models in an environment, not too dry and not too humid, that prevents the timber from drying out or from going mouldy and rotten.

I would suggest trying Deluxe Materials Ezy-Dope or (my choice) Ezy-Cote when building models, and good storage practices including bagging for unbuilt kits or timber supplies.