The radiator cooling fan supplied by RW is made from moulded GRP and is very light and strong, but its rather ‘home-made’ appearance made me wonder about its state of balance. From everything I’ve read about helicopters it seems that vibration is the number one enemy and the elimination of it makes a safer, more comfortable and less tiring flying experience, not to mention reducing unnecessary wear and tear on components and bearings. I thought I’d check the fan blade for balance.

I first clamped the blade to the bearing pulley and drilled the four fixing holes through both components on a 3.3125 in PCD on my milling machine. It’s worth getting the spacing exactly right because off-axis holes will have a detrimental effect on the balance.

With the fan securely bolted to the pulley I used a piece of 1 inch silver steel as a dummy shaft and sat the assembly on a pair of levelled tubes supported across one of our (under construction) car chassis. It was immediately evident that the fan had a heavy spot which always rotated to the bottom. Turning the assembly 180 degrees on the support tubes produced the same result demonstrating that the tubes were pretty level. I added small pieces of Gaffer tape to the highest blade tip until the fan no longer rotated under it’s own imbalance in any direction. It just stayed where it was put.

I weighed the tape purely as a matter of interest - it was 2.2 grammes. I could see that Rotorway had already made an attempt at balancing the fan. The rough woven mat texture of the three blades opposite my tape had been rubbed smooth.

I continued to rub down the same three blades, continually checking the balance and removing pieces of tape until all the tape had been removed and the fan assembly was perfectly in balance. I’m not sure if correcting a 2.2 gram imbalance would make any perceptible difference but I reckon it was worth doing.

FAN PULLEYS AND SHAFT

I wrecked a shaft and top pulley before I worked out a method of measuring and transferring the pulley spacing accurately.

I made a simple aluminium jig made from a piece of 1 in x 1 in Aluminium angle and two strips of 3/4 x 1/8 flat Aluminium. I  twisted the ends of the flat strips at 90 degrees and, holding the angle vertically against the secondary belts on the pulley, I located the ends of the strips in the bottom of the ‘V’ grooves of the two fan drive pulleys on the secondary shaft. I then clamped, drilled and bolted the three components together

The pulley ‘V’ groove centres turned out to be exactly 7 1/2 inches.

With the large, bottom pulley already drilled and bolted to the shaft, (which needed shortening by approximately 3/8 inch) I drilled and tapped a small thread (M5) in the top pulley for a temporary grub screw location. I set the pulley spacing with the jig and tightened the grub screw.

I set my drilling positions using the digital readout on my milling machine but I found this handy little centering gadget at a recent show that would do the job accurately enough on a bench pillar drill.

The mounting plate for the lower pulley shaft bearing was welded onto the frame at an angle of a couple of degrees. I’ve seen the lower bearings mounted on the top side of the mounting plate on other ships but it would have meant trimming the carrier to clear the frame tube. Besides, I wanted the bearing to be as close as possible to the pulley. In theory, no problem because the bearing race can align itself in its carrier but the bottom pulley was touching the bearing and still needed to move upwards a couple of millimeters to be in line with the fan blade pulley.

I started to solve the problem by removing a little material from the mount to give extra clearance to the bearing carrier plate allowing it to be raised. This will not weaken the mount - there’s just too much material there anyway.

I then machined the aluminium spacers supplied to wedge shapes, one thinner than the other, to correct the bearings horizontal misalignment. You can see how far out the mount is where it is close the the bearing carrier.

RADIATOR AND SHROUD

Not too much bother with the radiator mounting and fan shroud.

I found that the two aluminium spacers supplied for bolting the radiator to the frame brackets were 0.080in too thin. Using them would have meant bending the tail boom bracing tubes slightly as the bolts are tightened. What’s the point of trying to keep the frame and everything bolted to it square and level only to distort it when you mount incorrectly sized parts to it?

I made two new spacers the correct width.

And found a use for the old ones as clearance spacers on the rear radiator hanger plates.

I didn’t much like the idea of riveting the fan shroud ring from above. It’s impossible to achieve a straight pull on the rivets. So I riveted the ring to the shroud from below with a reinforcing washer on the rivet. Much nicer.

HEADER TANK

A few other builders have made various mounting pads for the header tank. I reckon it needs to be completely isolated from the frame so I made these rubber mounts from a 1/2 inch long piece of 5 mm (3/16 in) fuel hose and two 1/8 in rubber washers. I drilled the tank mounting ears a little larger than the fuel hose which was a little longer than the rubber washer/tank sandwich.

A penny washer under the bolt head squeezes it all together.

[Home] [Specifications] [Frame] [Tub Split] [Body Assembly] [Roof Panel Modifications] [More Body Mods] [Interior Finishing] [Painting] [Screen] [Doors] [Skid Pants] [Controls] [Tail Boom & Fins] [Tail Rotor & Drive] [Chain Oil Bath] [Drive Train] [Rigging] [Cooling] [Instruments & Wiring] [Cabin Comfort] [Exhaust] [Silencer] [Heat Shield] [Fuel Tanks] [IT LIVES!! &Teething Troubles] [Testing] [Main Rotor Blades] [Miscellaneous] [Tools] [Parts Supply] [Build Diary] [Events] [Flight Training] [Links] [Toys and Dogs]