On Hiller & Bells with wood blades the root butts and tips are not finished.
A tip cap and a coat of black paint
A Blade gots to breathe

Hello Murray,

thank you for your efforts to make me understand, I again had trouble understanding English ... rather then understanding what Cam's meant

I had thought that "undercoat" meant the paint Cameron was adding on the side of the blade facing the ground .. I thought he meant that it was necessary to leave this part naked ..

I understand now what undercoat means ...

in France we call it "couche primaire" which means "primer layer" ... i think that undersoat and primer are the same in English right ? ..

in French we also use undercoat in fact which is "sous couche" ..

tonite I will go to bed being less ignorant they I was yesterday

as for the shimming process to modify the pitch of the blade, I would prefer to glue a part of metal to the blade root and then screw it to the hub bar using what we call a "cale biaise" which I would translate to English using the term "bias wedge" btw the metal glued to the blade root and the hub bar

then I would tune the track by adding shims in btw the teeter block and the hub bar as I was saying Cameron in one of my previous messages

But when I say I would I don't mean this is what must be done of course I am just trying to understand why he is doing thing like this .. I a not a rotor maker , I know very little about rotor construction .. so don't get me wrong my "I woulds" actually mean "I thought is was ok to" ... I am certainly wrong in my "I woulds'' in fact

I agree 100 %

"the fiberglass rotors are also limited in terms of ability to fly in rain, even with my aluminium rotor I have rarely been caught under the rain
first of all I don't fly when it is raining ... I have the choice .. I am not forced to fly ... even when a collective flight has been planned by the hangar fellows I always give up when the conditions are not perfect.

when I have the slightest issue with the gyro, when I don't feel good, or when I estimate that the weather conditions are beyond my personal skills.. I give up.. go to the bar and have a couple of coffees and start maintaining my bird ... I have often been bullied for this but I don't mind .."

Absolutely agree with all of that. In the gyroglider while training we'd often cut things close given we only trained once a month, people had often driven 5 or 6 hours to get there and we could land instantly if needed. So we'd fly between rain showers on a patchy weekend and occasionally catch the edge and fly through a bit of rain then land and pull in. Not good for wooden rotors so best avoided. I know guys with the N8H12 section rotors (some of which were glass) seemed to loose their laminar flow if caught in rain. They certainly lost a noticeable amount of performance. I don't know how the gel coat would withstand water spray itself.

There is some undercoat but not much you can't undercoat the notch where the steel strap is glued and screwed to the underside and the last foot or so of the root end is left unglued as it needs to be free to be trimmed for angle of attack with shims. When I was repainting them I noticed they had some (I think) etch primer. It been 30 years or so since I originally painted them but I suspect what was going on was I etch primed the then unpainted root end of the steel strap to provide some protection from corrosion (not sure if this does or not just what I did at the time). that part is then clamped with the cluster plate bolts. The blades and the spar were then painted but I made no effort to paint that part of the blade as you really can't do a proper job as you can only bend the root section strap so far and its mostly clamped up and on the underside. Not sure how much moisture can get in or out but not completely sealed as it would be if painted properly with several coats. All I can say is after a long gap of flying when I was testing them for the jump take off head we discussed (it had been 15 years at that point approximately) they were balanced (but out of track - trim tabs bend a bit probably).

Terry who'd build many more sets over many more years explained after the first 5-10 hours the balance settled, so he'd do an initial balance but would notice occasionally he'd have to do another balance after that time which he suspected was due to moisture moving out to the tips through the capillaries in the wood being subjected to centrifugal forces, but that after a final re-balance it stopped being an issue. Neither Ivan or I had to do this on ours but it might be down to many things. One of the things we tried (which may or may not have made any difference) was we made two blade benches so each step were built with both rotors together. So the skins were glued on the same moment, the bottom skins to wood spar same time etc. We reasoned this would not only save time but that given that the wood would absorb moisture or dry out as conditions changed from day to day this would at least ensure that whatever moisture was trapped would be trapped at the same level in each rotor and hopefully avoid one blade being sealed off on one day and another being sealed on a more humid day. This may have made zero difference but where ever we could we tried to think and build like this being aware that any differences we added would be additional issues we'd latter need to deal with when tracking and balancing.

It was also beneficial I think that we built them together as we would constantly check each others work. I think these things paid off in general as Ivan's blades for example were the most perfect blades I ever flew on first up. Two up in the glider we'd be off at 19mph flying nicely at 30mph smooth as I've ever flown. So nice.

Hi mate,

for what its worth I find rotor blades absolutely fascinating so I will happy answer questions all day. I will try to answer as briefly as a I can though but as you know this stuff is complicated.

The steel spar is 3mm mild steel plate tapered towards the tip (getting thinner at the tip). It is glued and screwed over most of the length except at the root end where the cluster plate clamps with a number of 1/4 inch bolts which then in turn are bolted to the hub bar. You don't glue this part because let's say one blade is slightly warped down and you need to pitch it up again. You have a number of choices here.

1. Use trim tabs. these are easy and quick and can be adjusted with minimal effort on the side of the stip even with the motor still running on the gyro. But I don't like this because the trailing edge is very thin and delicate and they only work at certain speeds so they may be tracked in straight and level but with more airspeed more force and out of track etc. Also its more drag.

2. You can use bronze shim material (or even aluminum can material) and simply put a strip between the leading edge or trailing edge between the steel strap and blade and the opposite side at the top cluster plate changing the angle of incidence of the rotor of the offending blade. I suppose you could do it with washers but we didn't. I don't like this method much either.

my preferred method was as follows

3. Once through testing you have established which blade is flying higher. You make a jig and slightly bend the top cluster plate where it meets the wood rotor and the bottom strap ever so slightly. This is quicker than two, permanent and offers no chance of being bumped about of in any way changing the mass of one rotor.

I have flown on blades using all the above methods they all work. And even the ones requiring you to take the rotors off and re-adjust still don't take more than a couple of hours to get the blades in track. I've only flown on one set of rotors we couldn't really make work which had one wood rotor warped out to at least 5 degrees we did get them tracked using trim tabs and bending the straps (step 3) but both were limited and without a pre-rotator which wasn't practical on Graftons glider they were a bitch to hand wind because they still had more than 2.5 degrees which came out when they got fast enough so we retired that set. But I was involved in a many sets of wood rotors (10-12 something like that) over the years and they were the only set we couldn't save for our purposes hand winding.

Hi Mate,

we painted them sealed them including at the tips at the start but the root end under the steel strap wasn't painted a bit of etch primer from hitting the steel strap after we'd glued them (the last foot or so isn't glued). Terry suggested that the moisture inside the blade tended to migrate to the tips so an otherwise sealed rotor might have slightly different levels of moisture in the wood lets say one has 5% and another 8% evenly distributed inside the blade (a guess). Once sealed and balanced with paint the blades will fly with no stick shake. But Terry found after 5-10 hours they can develop stick shake and required re-balancing span wise but never needed it again. He speculated the differences in moisture were coming into play as the centrifugal forces would concentrate the additional moisture of the both blades deferentially if there were different amounts to begin with. So to clarify both would draw moisture towards the tip but the 8% blade would be drawing more changing the span mass at the tips slightly overcoming the span wise balance achieved from painting. After this process had happened a second span wise balance would solve it permanently.

I never experienced this with any Ivan and I made but we built ours together but also never build anywhere near as many as Terry did. When I met Terry he'd already build 12-14 gyros for himself at least 12 of those with wood rotors (he build his first powered gyro in the kitchen of their house with his first two children at their feet ;) all I can say is Judy his wife is a saint - the perfect pilots wife to put up with dodging around a VW gyro in her kitchen while making dinner for months), he'd also build several other sets of wood rotors for others and for club gyro gliders. He'd been involved with tracking and balancing those and many, many more. Ivan and I build I think 5 sets together for ourselves and for a few other people I was heavily involved with 3 of those and less so with 2 others, I had test flown and helped track and balance at least 10 sets though over the years with the gyroglider. So I can't imagine how many Terry must have set up over the years, a lot though.

cheers