Monday, November 19, 2012

And now we wait...

I've been plodding along on my acceptance testing with no great sense of urgency because, well.... it's out of my hands. Yes, another open-ended, unforeseen delay. 'Tis the nature of the game. This time it has to do with the landing gear. One Service Bulletin has already been released by Van's that has grounded the fleet until such time as some inspections and adjustments are made to the way the landing gear legs are bolted to the center section of the fuselage. Those of us still building are furthermore even more firmly enmeshed in the problem in that there is a special directive aimed at us, the Reader's Digest version of which can be encompassed in a single word: "STOP!"

 The latest update from the factory is that they have developed a small parts kit comprised of some skin doublers that will have to be riveted to the sides of the airplane. Unfortunately, the couple of hundred rivet holes that the doublers will be riveted into already contain a couple of hundred rivets on my particular plane. Those will all have to be drilled out in order to install the new doublers. I haven't talked to the FAA guys about this - I suppose that it's possible that they would go ahead and do the airworthiness inspection even with outstanding Service Bulletins, but I kind of doubt it. In any event, I'm waiting. Which isn't to say that there is nothing to be done while I wait. It's more the case that what there is left to be done is not sufficient to fill the available time, so I've just been dabbling at it. Which means more time to play with Cabot!

And his friend Buster:

The acceptance inspection has things coming on and off of the airplane at a prodigious rate. The lower spark plugs needed to come out for one part of the inspection and I was a little concerned about the difference in the look of the plugs between the front cylinders and those in the back two cylinders.

This is apparently common to the Rotax, so it was an unwarranted period of angst. I'm having a lot of those, lately.

Van's wants us to test the sanctity of the pitot-static system which is, of course, a laudable directive. Thet said, their chosen methodology was not very confidence inspiring. Slipping a syringe over the pitot tube and holding it while testing the leakage rate was nearly impossible without tainting the results with uncontrollably small changes in the pressure from the thumb holding the plunger. 

It was accurate enough to detect a massive leak in the pitot system, though, which I (not very) quickly tracked back to a problem that I had encountered when putting the pitot fitting into the ADAHRS box.  See the threads showing on the fitting on the left? Yeah, that ain't quite right. The thing is, it was as tight as I could get it without risking breaking something. I ended up taking it back out and putting a very, very small dab of Boelube on the threads. That made it screw back in without the discordant resistance. It sounds easy now, but a lot of hours were spent on this operation. 

Testing the static system was better, but not by much. The way that is done is to tape over one of the ports, then use clay to form a seal around the syringe and the other static port. This too was a completely imprecise method and it took quite awhile to get comfortable with the results. Which isn't even to mention the concern over getting modeling clay into one of the static ports.  

Then it was time to remove the gascolator to check the internal filter for obstructions that may have flowed down from the fuel tank. The location and design of the gascolator makes this a burdensome job. Getting it off of the plane was bad enough, but replacing the safety wire when re-installing it was an exercise in frustration. The first effort was sub-par and despite the strong temptation to just leave it in place I ended up re-doing it. Knowing that I'm going to have to do this every year for the rest of my life, well, that's not the happiest thought right now. Especially when you consider that the filter screen was impeccably clean.

Having exhausted all of the little things, I moved onto the weighing. The first step is getting the airplane level before it even goes on the scales. The idea is to place a line on the hangar floor that gives a consistent measuring point from which to determine how far aft each axle is. You would think they would be identical, but one of mine ended up being a half inch further aft than the other. 


Van's has us put the main wheels on 2" thick blocks, then add or remove air from the nosewheel to get the plane level.

Two amazing things happened when it came time to plumb the spot on the floor. 1) I had a plumb bob. 2) I was able to find it.  Amazing!!

Once the requisite measurements are recorded, the plane goes up on the scales. I accomplished this via an inadvisable method: I got under the wing and lifted it with my back while Pete slid the scales and block under the wheels. It ended up requiring that nearly all of the air be let out of the mains (not the nose, as expected by Van's) to get the plane level. 

The final result was 701 pounds. Which considering that a more typical weight is 726 pounds sounded wrong to me. Very wrong.  

I stewed about it over night and decided that the only recourse would be a re-weighing. Having had a night for my back to register quite strident complaints about my lifting method, I decided to use a slower yet decidedly more back-friendly approach.

Thinking that maybe the extremes that we had to go through to level the plane with the 2" blocks had adversely affected the precision of the weighing, we didn't use them the second time. By releasing equal pressure from the left and right mains, we were able to get a nice level. The results were much more realistic at 719 pounds (the picture shows 718, but the two little side panels that close the fuselage sides at the top of the landing gear legs aren't installed and the number on the scale was bouncing between 718 and 719 indicating something between 718.9 and 719.0). The 719 value stands favorably against a 726 pound airplane that has the lighting and/or interior kit(s) installed.

There are a few more inspection things to be done, the paperwork needs to be gathered and sorted into a presentable package, and I have to find someone to engrave the data plate. After that, it's just a matter of waiting.

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