|Aug 19, 2013, 12:33 PM|
United States, MO, Wentzville
Joined Oct 2009
Hangar 9 Katana 50 failure analysis
I'll post some pics later, but for now, I wanted to warn any Katana 50 owners...
I finished my Katana 50 earlier this summer and flew it for the first time last week. The first few flights went beautifully. My first landing was dead stick and a little long on our short hilltop field and I had to walk out to retrieve it, but no damage... Leaned out the barely-broken in OS Max 55AX and put her right back in the sky. Flew a few circuits and made some full-stop landings. The Katana flew perfectly straight with only one click of aileron trim and every landing was perfect! Not to toot my own horn - as I told the friend who was with me, today Danny has been replaced by aliens who know how to fly! That was Friday - I had my new favorite airplane!
Saturday was our end of the summer airshow and after a couple of delicious burgers in the company of my friends at the field, I decided it was time to put the Katana in the wind again. After takeoff I attempted to perform an aileron roll. My spotter immediately asked if I had intended to perform a barrel roll. Enough said? After that, I managed a correct aileron roll followed by a nearly perfect loop - again more a tribute to the airplane than to my piloting skills.
So after a few easy circuits, I decided it was time to buzz the strip. I lined her up on a long final about 200' above the runway and pointed the nose straight at the (imaginary) numbers - about a 10-15 degree downward pitch - and pushed throttle to full. A second later the scream of the 55AX was drowned out by a sickening and heart rending fluttering sound and the perfect front cross-section of the airplane marred with wings presenting 3-4x their normal size. I immediately cut the throttle, but in the 10 milliseconds that it took to chop power, the Katana had entered a spin. The flutter subsided 20-30 feet above the ground and I made a desparate but futile attempt to level her off and then began the long walk out to what I was certain would be a pile of splinters. To close this already too-long story, let me just say, I think it's repairable and I'm going to try just that since I can't buy a new one!
Building the Katana has been an exercise in patience for me. There were a few qc issues with my aircraft and I had just expected better from a Hangar 9 aircraft. She was fully assembled back in April and I had wanted to fly her then, but I kept finding one more thing that wasn't just perfect and I would decide better to make everything right. Right up to the flutter, every flight experience reinforced that my patience had been rewarded and I was very happy with the results - the airplane really was a dream to fly! I replaced a lot of hardware - like those junky clevises and cheap ball links. I upgraded the pull-pull system to the better one made by GP.
But there were two building mistakes that I will never make again:
1 - The "recommended" aileron control rod geometry in the manual is BAD. The manual directs you to place the servo side on the farthest hole from the output shaft and to place the aileron side on the 2nd closest hole to the aileron hinge line. I sure wish I had read this post before flying - I'd have exercised my patience again...
2 - The recommended aileron servos were Spektrum A6060. It's an ok standard servo, but the stock arms (which the manual directs the builder to cut down and use) are frankly just too thin. They are about 2/3 the thickness of the stock hitec arms. I wish I had put some metal-geared servos and beefier control arms on this plane.
So, if you have a Katana 50 flying and have not already addressed the aileron control geometry, I would highly recommend taking a look at the post I linked above.
|Apr 11, 2014, 07:41 AM|
United States, MO, Wentzville
Joined Oct 2009
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