FYI for the list Thanks again Jeff, yes I have abandoned the idea and will use a tab.
Craig ________________________________ From: Jeff Scott <jscott.pla...@gmx.com> To: Craig Williams <kr2seaf...@yahoo.com> Sent: Monday, December 12, 2011 2:34 PM Subject: Re: KR> Spring trim system Sorry, but anything I would write about how to improve the Sonex system would be purely speculation. Having invested a lot of time playing with spring type trim systems, my recommendation is to keep life simple and use a tried and true positive trim system. A Ray Allen servo actuated trim tab is about as positive of a trim as you are going to get. I had the Mac (now Ray Allen) trim servo on my plane and removed it in favor of a spring system when I built the larger tail. I consider the change in trim to be a failed experiment. I plan to cut a trim tab into my tail and mount the Mac servo into the tail to operate the tab next time I get a notion to do major surgery on the plane. My spring trim system is going to come off the plane and go in the trash. The problem with using springs to trim the plane is that the control forces change significantly with speed. The KR has a huge speed range, which you can also interpret to read, the KR had a huge range of stick forces, from very light to moderately heavy depending on the speed. The force exerted by a spring is constant. So, with any change in speed, the air loads on the tail change, and the amount of force being exerted by the spring is suddenly incorrect, so the plane is out of trim. I discovered this very quickly with the system I currently have in my KR. The Sonex displays the same issue, but has stronger springs, so can actually be trimmed for a given speed in smooth air, but is also easily upset causign it to diverge either nose up or nose down, so you spend a whole lot of time cranking on the trim handle without ever really getting it right. The Tomahawk I used to own had the most effective of the spring trim systems, but the springs were HUGE (and heavy). There were 4 springs in the aft fuselage that stretched darned near the length of the empinage, with two springs pulling nose up and two springs pulling nose down. Trim was accomplished by the trim wheel pulling more or less tension on the nose up spring pair. Some Tomahawk owners complained about running out of nose up trim as the springs got old. Breaking a trim spring in flight made for a real strong armed struggle to get the plane on the ground. Even at that, the trim was nowhere near as stabile or effective as the simple trim tab that was mounted on the nearly identical Beech Skipper I was also flying. -Jeff ----- Original Message ----- >From: Craig Williams >Sent: 12/11/11 03:27 PM >To: Jeff Scott >Subject: Re: KR> Spring trim system > >Great analysis Jeff. Do you think there is anything that can be done to >improve the effectiveness. Maybe progressive springs? > >Craig > >________________________________ > From: Jeff Scott <jscott.pla...@gmx.com> >To: Craig Williams <kr2seaf...@yahoo.com>; KRnet <kr...@mylist.net> >Sent: Sunday, December 11, 2011 1:26 PM >Subject: Re: KR> Spring trim system > > >I flew a Sonex with that exact trim system in it for about an hour this >morning. Very nice flying plane. Flies very much like the KR except the >elevator is significantly heavier and the ailerons quite a bit lighter. The >only thing about the plane that I didn't like was the trim system. As the >aerodynamic loads would go up at speed, the loads would stretch the trim >spring, so it just didn't want to trim up. But as soon as you would start >slowing down, with a lesser load on the elevator, the spring would contract >and the plane wanted to keep pitching up. The more I slowed down, the more it >pitched up, which cause it to slow down and pitch up even more. In effect, >when you wanted to go fast, it didn't have enough nose up trim, and when you >wanted to climb, it didn't have enough nose down trim. The owner says the >trim system is one of the few things they plan to change on the plane. I >should mention that the trim works much better with a more forward CG. When the owner flies the plane, he's flying with the CG at the forward limit. The trim works much better in that scenario. With me on board, we were flying right in the middle of the CG range. The trim was more of an annoying distraction than it was effective. > >This is the fourth plane I have flown with a spring type trim system, all 4 >different designs. Probably the most effective one I've flown was in the >Piper Tomahawk, the second most effective was the spring trim system on some >of the GlasAirs. The one on my KR is the least effective and will be replaced >with a trim tab next time I do major surgery on the plane. The one on the >Sonex is easily the most annoying. Of the four different spring trim systems >I have flown, none are as effective as the simple trim tab you find on most >aircraft. > >Jeff Scott >Los Alamos, NM > > > >----- Original Message ----- >>From: Craig Williams >>Sent: 12/09/11 10:44 AM >>To: KRNet >>Subject: KR> Spring trim system >> >>http://www.sonexaircraft.com/orders/trimfaq.html Has anyone used the Sonex >>trim system in their KR? I have convinced myself that the this is a good >>system and want to try it. Craig www.kr2seafury.com >
