I’m not really a complainer, I’m British after all, but someone at Rotorway deserves a good spanking for this. My secondary pulley came embedded in Polyurethane packing foam in it’s box. That stuff sticks like ****!!

Four hours of picking and scraping with a plastic business card taking sooo much care not to damage the anodised finish.

SETTING UP THE SECONDARY SHAFT

Way back when I first started my apprenticeship as a very green sixteen year-old with no formal metal working experience, my first training task was to hand-file a lump of sawn steel to a perfect rectangular block of 1 inch x 1/2 inch x 1/2 inch and within one thousandth of an inch flat and square. This piece would eventually form the body of a miniature tap wrench which is still in my tool box today. I know from bitter experience how difficult it is to achieve a perfectly flat surface on a small piece of metal,.so my jaw dropped a little when I saw that I could be required to file an angle across the mounting face of the upper secondary bearing carrier to correct any misalignment with the main shaft.

Now, the latest upper secondary bearing supplied by Rotorway is, in fact, a self-aligning, spherical bearing that, in theory, has a misalignment tolerance of at least one degree. However, Rotorway still insist that the mounting face of the bearing carrier be filed at an angle to correct for an out-of square frame. There are differences of opinion on the validity of this requirement and I’m yet to be convinced that 0.2 degrees misalignment is not easily within the safe operating range of this particular bearing. Anyhow, Rotorway says it has to be done and our CAA will expect all builders to comply. So, ours is not to reason why.

 When shaping small items it is sometimes easier to perfect the surface flatness by rubbing the material on the file rather than filing the material. But the bearing carrier is part of an assembly that cannot be dismantled and is difficult to support firmly for accurate filing. Besides, filing seems a very crude method of perfecting the alignment of what is probably the most controversial and safety-critical component on the ship.so the search was on to find a way to engineer the job properly.

First off, I needed to accurately measure the angle required. Rotorway instruct the builder to install shims of flatstock between the underside of the bearing and the top pulley to keep it all perfectly parallel. Whether by coincidence or design, I discovered that some 3/8in x 1 1/2 in rectangular aluminium bar I had on the shelf did the job perfectly. The square mounting tubes on the frame are actually anything but flat and square - that’s what happens when steel tubes are welded together - they distort. With a lot of careful measurement and comparison of several measuring methods I calculated a correction 0.2 degrees on the bearing carrier was required. I recommend that you double check everything and don’t assume that the Rotorway digital level is spot on accurate - mine wanders by 0.1 sometimes.

This is one of the bearing mounting bushes welded through the square frame tube. They hadn’t been dressed off properly and were all at least 0.2mm proud of the tube face. Not a good start.

I used a new, sharp fine file, cutting across both welded bushes on each stroke to take them down to the tube surface.

It ain’t easy but here’s the flush bush.

I held the large secondary pulley in a big vice on my universal milling machine and supported the bearing carrier on a contraption of V blocks and jacks made from M8 studding and a few nuts and washers.

All was set level and square.

With the bearing clamped at each end and the head of the machine tilted at 0.2 degrees it took only a single light cut to machine a perfectly flat, corrected angle on the carrier mating face. I used a dovetail cutter because it’s the largest diameter cutter I have and I could make the cut in one hit

Here it is - 0.2 degrees. I hand-filed the ends of the face where the clamps had prevented the cutter from completing its job

For anyone not fortunate enough to have access to a milling machine, I recommend that you purchase a top quality, large, fine, flat file. Take off the handle and use it like a sanding block, similar to the filing picture above. File along the length of the carrier face making sure that the file always covers the whole surface but keep a slight pressure bias on the side where you want to remove more material. Clear the file of swarf every few strokes and keep checking for flatness along the carrier with a steel rule. Check the angle with an engineers square and feeler gauges. The construction video shows this method of checking squareness. If you feel the need you can calculate the required feeler gauge thickness by trig. As a guide, a 005in feeler gauge represents and angle of 0.3 degrees across the mounting face of the carrier.

This is gonna take a lot of time and care to get perfectly right with a file. I feel there is great potential to make things worse, ending up with a mounting face that is not even flat, let alone at the correct angle. But hey, there are a lot of Execs out there, flying safely so maybe I’m being a little pedantic. And don’t forget, this stuff is all only my opinion - not a set of instructions.

CLUTCH

A couple of points i came across when installing the clutch. The manual is not much help but the video shows the builder aligning the idle pulley to the secondary pulley using two steel plates and a clamp. Fine, if both pulleys are the same height. But my idle pulley is 0.011” (11 thousandths) of an inch shorter in height than the secondary pulley. Not much at the pulleys but it can translate to quite a large positional error at the arm pivot. I used a 5 thou shim either side of the idle pulley when clamping will keep it all perfect whilst I marked the length of the clutch arm weldment pivot bush.

The manual tells you to grind excess material from the welded bushes but it’s worth investing in a few spot face drills like the one above. Here the clutch pivot arm is clamped directly to the bed of a small pillar drill. This method works just as well using a hand drill when shortening other welded bushes in the frame. You’ll always have a neat, square end to your tube

Interestingly, when the video builder gets to the job of drilling the frame bracket for the clutch arm pivot, the main chain sprocket has magically disappeared leaving him clear access. It is possible (at least on my ship) to drill this bracket without the pain of removing the sprocket.

I made up a long series 5/16in drill by turning down the end of a drill and silver soldering a 3 inch long drilled extension sleeve to it. This enabled me to reach the bottom bracket by drilling between the sprocket spokes.

It’s close but it can be done.

There’s an issue on the idler/ belt tensioner installation that gets only a small mention on the drawing and none in the manual or video but I reckon it’s worth a mention here.

Because the main tensioning force (the sprung piston) is on the top of the pulley, the design and geometry of the sprung idle pulley fork is such that, under tension, the belts will tend to push away the bottom of the pulley giving slightly less tension on the lower belts. Rather like trying to use a garden fork that has the handle at one end of the spikes instead of in the centre. Check it out by putting your digital level acoss the idle pulley. With top and bottom pulley rod ends equally set in the threads and the larger rod end in the piston sitting gently on the actuator arm I had almost a degree difference in pulley alignment between the in and out clutch positions. Not much maybe, but RW are asking for perfection. (‘Close enough is not good enough!!’

To compensate for this the drawing tells us to pre-load the lower rod end by winding it out a few threads more than the top one. Unfortunately this action has other consequences.

With the pulley clear of the belts, the larger rod end on the sprung piston will tend to rise clear of the actuator arm. To achieve the desired pre-load it must be pulled down into position with its fixing bolt. This, in turn, exerts a sideways loading on the sprung piston inside the tube. Not necessarily a big problem if the sliding contact surfaces are smooth and well greased. And here’s the final rub (pun intended) The weld around the joint of the lower arm to the spring tube will have penetrated through to the inside of the tube. You’ll be lucky if you can get the piston to slide past the weld at all, let alone freely.

I used a flap wheel in a drill to remove the excess penetrated weld and polish the  inside the tube.

Not the perfect geometric solution but fine if set up correctly.

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