A weighty matter...
Many of todays flyers may not be aware that, at one time, the use of metal in rotor blades was forbidden, Actually, it was forbidden by the FAI for FAI contests. At that time, there was quite an active FAI contest scene in this country (UK) and it was generally taken as a universal law.
Ah yes, you may ask, but how did anyone know whether there was metal in the blades or not? Very simple, by using a metal detector. Small hand-held devices were easily obtainable at that time.
This led to several interesting developments in rotor blade design. The Kalt company produced rotor blades which used a very heavy wood in the leading edges. This was laminated from layers about 1 mm thick and resembled the material called hydulignum which was used at one time (Er - like back in the forties and fifties) to make propellers. The point here was that the amount of glue involved made the material very heavy. It was also very dense and quite difficult to cut.
Apart from the leading edge, there was an extra piece let in at the tip at mid-chord to help with autos. The length of the blade could be adjusted to suit by cutting it down at the root end and then gluing on the root reinforcements. A young lad called Dave Whitney took things a stage further and reworked the blade tips into a scimitar shape before covering the whole blade with glass cloth. No metal, but very heavy and with a forward CG. I wonder what became of him?
Another development was to cut a slot in the leading edge and fill it with heavy glue - a sort of epoxy putty used in fishing floats by the environmentally responsible. Almost immediately someone discovered that a mix of finely powdered non-ferrous metal and epoxy was even heavier and didn't activate the metal detector. the words 'rule' and 'bending' spring easily to mind.
At this point, sanity made a welcome return and someone in authority(?) realised that being hit by a piece of lead was probably indistinguishable (you saw it first in W3MH) from being clobbered by a lump of solidified bronze powder. It seems quite likely that the former had more chance of staying in the blade too. We have been using lead ever since.
You might have thought that things stopped there, but have you ever considered the number of methods that are available for sticking the lead into a wooden blade (let's leave the other blade materials to the specialists)? Perhaps we should stress here that 'sticking' does NOT mean covering it with a piece of sellotape (titter ye not - it's not unknown).
The great ZAP company have now produced a special gap-filling cyano which is specifically intended for gluing lead rod into wooden blades. With great originality, they have called it 'Blade-Zap'. I have not the slightest doubt that it works, but I won't be trying it, thank you.
One respected manufacturer advocates using baking powder and cyano. Once again, although they have a great reputation and lots of satisfied customers, it doesn't appeal to me.
This brings us back to the good old stand-by, epoxy. Ah yes, but WHICH epoxy? It can be done with the 5 minute variety but it's quite a rush. Back in the days of bronze powder, I started using SP113 which worked very well but it takes quite a while to go off and it has an incredible ability to 'creep' while doing so. Covering it with tape while it set could be quite messy if you didn't keep an eye on it.
For me, the best solution is the often forgotten Stabilit Express. This has just the right amount of working time and it goes through a putty-like stage just before it sets which makes it easy to trim with a sharp blade. It is also very useful for a whole host of jobs on helicopters because it will stick almost anything to anything - including polyester to epoxy - and it is thixotropic. That's an interesting word which is Greek for 'it stays where it's put'.
A friend of mine recently used this adhesive to produce three sets of 'X-Cell' blades, all of which came out rather heavier than expected - like 220g instead of 185g. A well-known X-Cell pilot was puzzled by this until he learned that it was done by using Stabilit. "Ah, that's it", he said, "Stabilit is heavy." Come off it, if a slot full of Stabilit weighs 35g, why the hell did we ever bother with bronze powder? Come to think of it, why did we ever need lead?
It has always intrigued me that one of the direct results of allowing lead to be used in rotor blades was that the autorotation manoeuvre was considered to be too easy and it became necessary to introduce the 180 degree auto. This led to the use of continuously driven tail rotors. And what did that lead to, you may ask? Yes, heavier blades! Wouldn't it have been simpler and easier to have a maximum blade weight - say 100g?
Er, and isn't this where we came in?