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This was another of those jobs that I’d been thinking about long before I began tackling it. For non owners, the Main Rotor Blades consist of a sheet aluminium skin wrapped around an extruded aluminium core in the leading edge. At the inboard end, the aluminium assembly is sandwiched between a pair of sculptured glassfibre doublers which, in turn have wooden blocks bonded to them. Four steel straps secure the whole assembly to the Rotor Head through (ultimately) a single 9/16 inch bolt at the very end. The whole thing is immensely strong and confidence inspiring. R22 blades seem, by comparison, quite delicate and weedy.
The first job is to trim off the inboard corner of the blades and install a wooden end plug.
I blacked the area with a magic marker, scribed an accurate line and sawed through from both sides.
I have Xavier de Tracy to thank for this idea. I used a spare piece of the aluminium tape used for the fuel tank insulation to make a template for the end plug.
I cut the plug approximately 1/16 inch larger all-round the template.
Because this plug is inserted at approximately 45 degrees it can’t be sanded to size in the same way as all the other plugs. An even thickness of wood must be maintained on a line parallel to the blade - otherwise it’ll be a poor fit.
I used my Digital Calipers as a ‘parallel’ gauge.
I tilted the bed of my disc sander a few degrees by trial and error until I had it about right ....
.....then finished them off by hand
Glued and screwed in place. You can also see here that I’ve cleaned off all the gungy black paint from the end of the blade.
Same method on the outer end plugs
I’m not sure if I’ve mentioned this elsewhere on this site but my first job as a green 16 year old apprentice without any metal-working experience was to make a mini tap wrench. This involved, by sawing and filing only, shaping a rectangle 1 inch by 1/2 inch by 1/2 inch from a lump of steel cut from a 2 inch round bar. OK, not too much of a challenge, until we were told that the tolerance on all dimensions would be .001” (one thousandth of an inch). And we would have to keep making them until we got it right.
I eventually achieved the task and here it is 35 years on - battered but still occasionally in use. That first exercise was carefully formulated to drive home, from day one, the importance of accuracy and how it is possible to achieve it with the most basic tools.
The next challenge would bring back those memories. The wooden filler blocks on either side of the blade are supplied slightly oversize and have to be sanded down to exactly 2.250” total thickness with exactly 1/125” each side of the scribed ‘chord line’ on the end of the blade. What’s more, the specifications called for both surfaces to be parallel with each other and with the blade. The recommended method was to rub them down with a piece of abrasive paper wrapped around a wooden block. I’m not entirely convinced that this level of accuracy is really necessary over the whole surface area of the filler blocks. At the end, adjacent to the aligner blocks , OK it needs to be about right but I don’t think a thou or two run off would have much effect on the big picture. Anyway, how many wooden sanding blocks can boast a surface flatness of better than one thou?
Once I had removed the black paint I discovered that Rotorway had already made a pretty good job of machining the blocks flat and parallel. One side needed just a few thou removed and the other side twelve. My challenge - how to reduce them down in size whilst maintaining the surface level and flatness.
One thing was for sure - I’m not skilled enough to achieve it with a wooden sanding block wrapped with a piece of sandpaper so I rifled through my scrap bins until I found a piece of steel from an old milling fixture.
It turned out to be just about perfect - 8” x 3” X 1” thick and weighing in at 7 lb.. Both sides had been ground and apart from a few holes it was as perfect a sanding block as I was likely to find.
I carefully covered one side with double sided tape and stuck on a sheet of good quality 3M 120 grit production paper. By simply pushing the steel billet around, allowing its own weight to press evenly on the wooden block surface I was able to reduce the thickness quickly, evenly and accurately.
I deburred the blade straps and removed the mill scale and welding splatter with a wire brush and file.
These are the ‘all-thread’ bolts that push the alignment block in the blade straps. I machined the uneven ends flat.
With the blade straps correctly aligned I used a 5/16” reamer to clean up the bolt holes right through the blade.
I gave the straps a light dusting of Engine Enamel (except for the glue surfaces) and cooked them off in a makeshift oven.
Here I’m checking the blade strap alignment before final gluing and tightening of the bolts. The rule you see here was liberated from a 2 foot aluminium square. I chose it because one edge is 3/16” thick making it easy to hold against the blades leading edge. I notched the edge for clearance around the aligner bolt and calculated the overall dimension to edge of the the 9/16” bolt. I measured it with the depth facility on my Caliper.
This pic shows the Pitch Horn riding up on the weld on the Blade strap. I filed a small clearance fillet in the underside of the Horn.
I machined a couple of 3/8” long aluminium spacers to save the nyloc insert in the Blade retaining nuts.
A chance conversation with Jonathan Bull of Southern Helicopters highlighted a tip that I don’t think is mentioned anywhere in the manual or videos. He suggested filing some clearance scallops on the thrust blocks to maximise the potential pitch change when they’re installed on the pitch pins.
I dug this old stage lighting stand out of our store shed and modified the top into a blade support covered with pipe insulation foam. It has a wind-up handle on the side - perfect for supporting the blades during installation or removal. The last time this thing saw any action I was on a stage in front of a thousand screaming kids surrounded by smoke and pyrotechnics dressed in a Ghostbusters outfit !! - The things we do to earn a crust!
The blades were painted Gloss Black (see Painting Section). Black is the worst colour to show up undulations and surface defects on Auto panels which, in my mind, makes it the best colour for Rotor Blades. Every pre-flight check on my Robinson trainer features a careful inspection of the reflected light along the blades to check for ripples or delamination.
The blades were left for almost a week to cure at ambient temperature (‘fraid we don’t have an oven) then flatted with a rubber block and 2000 grit wet and dry paper.
A foam mop in a mini Air Polisher and G3 compound takes out all the rubbing down marks. Repeating the process with G10 compound and a softer mop brings the surface up like glass. The jury’s still out however, on whether a shiny or matt finish is best for aerodynamics. UPDATE Sept 05. I’ve asked around and carried out some research and it seems that most opinions favour polishing. Guru and author of ‘Principles of Helicopter Flight’, W J Wagtendonk says: ‘Surface Roughness. The rougher the surface of an aerofoil, the thicker the (boundary) layer and the greater the skin friction drag.’ and ‘ Blade surfaces should be smooth and clean to reduce skin friction drag as much as possible.’
A recent page addition to the build manual instructs the builder to file away two angled sides of the Pitch Horn Clevises to ensure that the maximum blade pitch can be achieved without the control rod-end fouling the clevis.
It calls for a steady hand, a magnifying glass and a carbide burr in my Dremel to grind away aluminium material to extend the angular limits of the rod-end body whilst leaving the seat untouched for the rod-end’s spherical bearing.
Like this.
The angle we’re after is 16 degrees.
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