Is This Spring?

It’s bright and sunny with a bit of a breeze today and yesterday it was definitely starting to feel like spring. I’ve managed to fly two weeks running now, which hasn’t happened in a while. The skylarks are back too.

It started out this morning with the heli guy doing his inverted thing and tail sliding with a big aerobatic helicopter. Then I was joined by the e-Flite Advance and then by an extremely polite drone pilot with a camera and a DJI Phantom in his backpack. A little later another two drone pilots arrived, having been told they were in the wrong field by some passers-by. They had what looked like a racing quad, but it took a while for them to set it up. We saw the DJI Phantom make a few flights, with its very distinctive shape in the air. Both sets of quad groups went to the opposite extreme ends of the field and left us to our proper aircraft in the middle.

This was the first flight of the RS352 after fixing the motor shaft which broke last week, so I had also brought my Acrostik along as a backup plane. I needn’t have worried as the RS352 worked fine and the thrust line was at least vaguely correct. It was hard to do a proper trim in the gale that was now blowing, but I got 3 flights with the RS352 and 1 with the Acrostik, taking off from the ground and proving that it still goes like a bat out of hell. For a plane that must be at least 15 years old it’s not doing bad and the speed is just what you want in windy conditions.

The RS352 took me all week to fix, as you have to cut off the fibreglass motor mount which is epoxied to the foam fuselage front and pinned with cocktail sticks. I had to drill out the cocktail sticks and then cut the fibreglass mount free just to get at the motor.

Once the Hyperion ZS22-13 18 motor was removed, then I could have a look at what caused the shaft to break.

IMG_20160313_142349.jpg

The broken ZS22 shaft. The front is the left end, so you can see how it broke cleanly at the groove to hold the circlip on the front of the motor bearings. The flat on the shaft goes at the back of the motor to hold it in the rear bearings with two grub screws.

Looking at how clean the break is, right through the circlip groove, this must be put down as a component failure as a motor shaft isn’t supposed to break as easily as this one did. Usually they get bent rather than snap in two. It’s also interesting to note that the replacement shaft is of a different type.

When I tried to order a replacement last Sunday, I found that the direct replacement was unavailable, so, looking at the specifications of the other two variants of the ZS22, I figured that the ZS2209 would probably work. You can see that it’s about 4mm shorter, but these motors are designed to have the prop attached to either the front or back and so have an extended shaft protruding from the rear bearings.

In the event, I needed to extend the flat milled into the shaft by 2mm to make sure that the grub screw locked onto it. Also, these motors require a huge amount of force to remove the shaft, which is a very tight interference fit in the rear bearing. I managed this with a bench vice and wooden spacers to exert pressure on the shaft from the back without damaging the motor can. Once it got to flush with the rear can I then had to use a 3mm bolt in a quickly bodged jig to push it all the way out the front. After that the new shaft went in fairly easily, using identification marks which I put on the rear of the motor to enable me to push the shaft in the right amount and also line up the flat on the shaft with the grub screw positions.

After a quick run on the bench to see that it worked, I then rebuilt the front of the RS352. The motor is placed into a plastic bag and the fibreglass motor mount is glued in place using epoxy and wooden pins to hold it in place. Due to the original pins being drilled out of the foam, this had left a bit of a mess, so the mount is now in a slightly skewed position. It’s actually rotated anti-clockwise a few degrees because of the fact that you can’t completely drill out all of the old pins, so the new ones are about 1mm out.

Once the motor was in, the glue had dried and I had cut the motor out of its protective bag, I gave it a first test. I put the prop back on, checked it was all running true and blipped the motor (very little). It was running backwards, so I swapped two of the ESC wires over and gave it another go. Everything seemed fine, so the only thing left was to go and fly it.

Like I said earlier, it all worked fine, although it does sound different in the air. I took it easy on the first flights and checked the grub screws were still in place and nothing else had come loose, but it all appears to be working perfectly. Only further flights will prove this though.

Well, that’s one aircraft fixed, so I’m now going to spend the rest of the day building an autogyro.

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