Thank goodness for Murle
Hi all!
I haven't posted for a while. I've been working like gang-busters on my KF5 due to the isolationism we are under. While the cause has not been a good thing, the resulting "get up and do something" has. I've accomplished a great deal in a short time; But, I digress. My reason for writing today is because of a squawk on my air frame. This may not apply to later models but for those flying/building KF5s you may be interested in what I learned.
A little history first. As I've mentioned before, this is my 2nd KF5 build. After finishing my first KF5 and flying the time off I made a cross country to my old home town of Amarillo from Phoenix. I had the trim set to neutral. I did not change the trim on the plane much on the flight as I was used to flying an aerobatic plane mostly before the Kitfox thus, I was used to hands on flying however; when I got to Amarillo, the next day I took my brother for a ride in the KF and this is when things got ugly. It was a very windy day (25mph quartering crosswind with gusts) but growing up in and learning to fly in Amarillo, if you couldn't handle the wind you just did not fly.
After reaching altitude of 2K ft I saw evidence of a thermal and decided to get some help to go on up to my planed altitude. Once I got into the thermal I started using the trim to help but, adding trim began to decrease elevator authority. I added more trim and soon I had little if any down elevator. I took the trim back to neutral and things were fine but, I headed back to the airport to investigate. I couldn't figure out the problem but so long as I didn't use much trim everything was fine. I didn't have a problem again after this initial one, that is until now on the current KF5.
In my current build I was testing the trim motor and the stabilizer and elevator control and as I added nose down trim the elevator began to become more inhibited. The more trim I added the worse it got. I messed with it until I was frustrated not finding the issue so, I asked Murle Williams to help me figure this out. He was quick to find the problem. On the KF5 you have the speed option or to go without. Because of this option, the former manufacturer, SkyStar, welded two tabs on the fuselage for the side covers for when you don't add the speed fairings. These tabs are irrelevant if you have the speed fairings but, these tabs can be a problem. These tabs actually inhibit the spar of the elevator to be able to deflect down when the trim raises the front of the stabilizer. Murle found the issue quickly and grinding these off made a quick solution. Murle suggested that this may not be a common issue because, he says, you likely will never need to trim your airplane to the degree that it would take to move the stabilizer up that much that it would cause a problem. My former problem was while flying in extreme conditions but, as Murle said, if it happened once it could happen again so let's grind those un-used tabs off and not have the possibility of the issue again.
I can't thank Murle enough for his help. He's looked my plane over several times and offered many recommendations that have turned out to be greatly beneficial. He's going to help me do the final rig on the wings next week, weigh the plane, and do the fuel flow check. I hope to be on the Glendale airport by Sept. 1st. and be ready to fly by October 1st. Again, I can't thank Murle enough for his help as well as the invaluable knowledge that many of you have also provided via TeamKitfox or direct connect.
Fred
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