It was another classic Hurl, as always, it was the best Hurl ever.
In the support event, Jim Aron had a pretty rough day after he apparently got food poisoning at The Burger Saloon, while the rest of us (Ted, Kestes, Howard, Mary Lou, and I) avoided it somehow. So the lovely and talented Christiana Tran did most of the work today.
Scott Dinger and his very patient wife Christine had quite a day yesterday. He was having all sorts of issues with trim, including severe hinging at times. After some diagnosis, we ended up adding some rudder and moving the leadouts back *about an inch*, putting in some down elevator, and removing a lot weight from the tail. On the first attempt at the down elevator, Ted and I suggested about a "turn", expecting maybe 3/32-1/8" of elevator drop. But somehow, using the turnbuckle system in the airplane, it wound up with a HUGE adjustment, and on takeoff he nosed over and broke the prop. So he had to go repitch a prop overnight. Saturday was a *miserable* day for him, we were there from sunup to 5:30 pm, and he left the field with nothing but problems. Ted checked the elevator adjustment and have him remove most of it to get the original desired bias, and adjust the handle to compensate. He also put on his new prop. Almost from takeoff, it looked better, and after a few maneuvers, it was clearly a completely different and much more controllable machine.
Scott had a few issues not related to trim or power that resulting it less-than-ideal final results (in a very tough crowd - David, Howard, and I, and glittering array of local experts) but the airplane was really working when he left.
One takeaway - basic trim adjustments *are very important* and absent some misalignment, there isn't a lot of chance for a big surprise, like having you leadouts right on the CG. You can use that sort of fact to diagnose other problems, if you think it needs the leadouts in the wrong place, either you are wrong, or you are seeing the result of some other problem.
In Scott's case, the airplane was flying with the outboard wing up a bit upright, and up a fair amount in inverted flight. This would normally indicate that it needed more tip weight, but it also was hinging out very severely in hard corners. Adding tipweight to get it level in 1G flight would have greatly exacerbated this issue. He also saw the outboard wheel ahead of the inboard in level flight, suggesting that the airplane was yawed in at him. It was also clearly yawing in abruptly even more on both inside and outside maneuvers.
The diagnosis was that the leadouts were WAY too far forward, fighting the small outboard rudder offset. This was causing the inboard wing to be dragged behind the outboard, leaving a static yaw angle, limited by the aerodynamic yaw stabilty that was trying to make it fly tangent to the circle, or even yawed out, if otherwise left to its devices. Putting in control increased the tension, the severe outboard roll also increased the tension, both forcing the nose to yaw in even further (not to mention increaseing the control deflection). On inspection, the leadouts were right on the CG - I think the front leadout was actually in front of the CG - which should NEVER be the case unless you have done something very strange. Leadouts should always be behind the CG, and for typical 40-60 airplanes it's about an inch or so.
The solution was to move the leadouts back about an inch and add a tiny bit of rudder offset. This yawed the airplane to approximately tangent or slightly nose-out, and that lowered the outboard wing in level flight. Tipweight was removed, and then the airplane flew much more consistently, without as much tendency to tighten up in the corners, or wildly yaw around.
A second issue was that the airplane was very nearly, or actually, unstable in pitch, because the CG was too far aft. You can fly an airplane that is unstable (defined as wanting to tighten the corner radius without any further input, once started) but you have to have a very tight control feedback, basically, you kick the elevator in the direction you want to go, then immediately have to counter-control it to keep it from tightening up the corner on its own. But it's extremely difficult, and in Scott's case, the control system ratios are so slow, that it was essentially impossible for him to prevent it from wrapping up into the corner, particularly on insides. We tried the elevator droop to remove it on insides, with success- except now it did the same thing on OUTSIDEs. This suggested that the problem was probably insoluble without running the CG forward. This was duly accomplished by removing about 1/2 ounce of taped-on weight from the tail. That was accomplished over night, and hey, this morning everything started working great.
I give Scott and Christine a lot of credit. Yesterday had to be a very frustrating day for them both, it just went on and on through the evening, and ended with an uncertain result and leaving the field with an non-working airplane. We have all been in that boat at one time or another, and it's really easy to just say "screw it, I can find less annoying ways of spending my afternoons". They they kept plugging and the next morning was like a different world.
Brett
Topic: Fox 15 Hurl 2018 " The most important event in the year’s calendar" (Read 4022 times)