Karmy Flying Adventures

Next up is a quick maintenance task to do a dynamic balance on the prop. There is this neat little device called the DynaVibe which allows you to do a very good dynamic balance on your prop / engine combo. You mount an accelerometer on the engine, a photo-cell and tape on a prop blade, then run the engine at cruise RPM to determine how much out of balance it is. Then you add some weight to the spot it tells you to, and run again. This will tell you how much you moved the numbers and in what direction so you can adjust the weights to correct the balance condition. You lather / rinse / repeat this cycle until you get the prop balanced.

I started out at .35 IPS (Inches per second) that means that the engine was moving 1/3 of an inch every second, glad I have rubber engine mounts. When all was said and done, it was at 0.01 IPS! That’s basically none. It’s amazing that it really makes a difference. The plane is so smooth now. I had to add 0.24 oz to one side of the spinner back plate to balance it.

It’s time to find out the damage. Have I made it lighter, or heavier? All those good ideas add up and the day of recogining comes when you roll onto the scales. No matter “WHY” you added those items, they will all show up in the final weight. Now keep in mind that I got this plane as a tri-gear, with wheel pants, dual alternators, dual batteries, etc etc etc…

The grand total = 837lbs! I was really hoping for closer to 800, but hey wach-u-gonna-do? The original W&B I have from the builder lists 833. That was without wheel pants as a tri-gear. Makes me wonder if the scales were calibrated. Oh well, at least it didn’t gain too much!

Well, Since it’s one of the key “features” of the Kitfox, I figured I best try and fold the wings and make sure everything was rigged properly. Also, I had to replace some fuel lines so I needed access to the end of the fuel tanks. Final results, yep, they fold. It’s amazing how easy it is to do it.

So one of the recent additions by Rotax is the recommendation to have a return fuel line from the engine to the tank to ensure cool fresh fuel gets to the carbs. There are a couple of ways that you can plumb that line, but they all share a common requirement. You must put a restrictor somewhere in the line to ensure there is more fuel pressure going to the carbs than going down the return line. This takes the form of a “Pilot Jet” that is installed in either the Banjo bolt, or in the actual fuel T. In my case I was removing the 2 port fitting to go to the 1 port fitting. All I had to do was remove the pilot jet from the 2 port fitting and install it into the banjo bolt. Look at the attached pictures for details of how the jet fits into the system.

Then the actual return line is simply a section of 1/4″ fuel line that runs back to the top of the header tank behind the seat. This gives a slow trickle of fuel back to the tank when the engine is running.