Will this rain ever stop?
I flew for a couple hours this morning. It sure was nice. I should have taken pictures, but I kept the doors closed and just enjoyed the flight. I have a flight review due soon, so I went through a bunch of stalls, S turns, slow flight, and other maneuvers, maintaining steady altitude. The flight was followed with the hard slip and soft three point that my short field requires. The field has some bumps, so the landing isn’t always as soft as it was today. It’s always really satisfying to grease it in there like that. Last winter, I made some adjustment to my flaps. I had found that the plane would fly level, without stick pressure, with the flap lever pulled up about an inch. Typical thing that many Kitfox owners do to trim the plane’s pitch. I figured that was just wasting a few degrees of flap, and adjusted it to fly level with the flaps up all the way. That is, with the lever down as far as it will go, the plane is trimmed in flight. As a side note, I had first needed to adjust the angle of the horizontal stabilizer in order to be able to trim it and not need forward stick pressure. With the flap adjustment, I got it close, but need just a hair of back pressure now.
I’ve been debating whether to make that last bit of adjustment by moving the flaps back up slightly, decreasing the total down angle with full flaps, or by moving the front of the horizontal stabilizer back down. I did see a slightly lower stall speed after the flap adjustment.
After my morning flight, I decided to check the flap angle, along with the angles of the wings and horizontal stabilizer. With the plane sitting on 25” mains, on the relatively flat ground, I used the handy level feature of my iPhone to check the angles. I used a straightedge from leading edge to trailing edge of the wings, checking the angle at root and tip, as well as measuring the angle of the flat-bottomed flaperons while “flaps” were down, then up, and also checked the angle of the horizontal stabilizer, and the floor, which is used to determine level for weight and balance.
With the flaps down, and both flaperons at the same angle, flaps were at 26°. Note that 26° is not the flap angle, in regard to wings or angle of incidence, as the plane had all three wheels on the ground.
With flaps up, both sides showed 9°. This is a difference of 17°. Full flaps = 17°. I wonder how much less flap angle there was before my last adjustment. Maybe 2°-3°? 20% less?
Full flaperon deflection netted a range of 8° to 50°, with the flaps down. That’s 42° total up to down on flaperons. That 8° is only 1° more than the wingtips, or 6° up at the root. I hadn’t considered previously, that the flaperons move up relatively less at the wingtip, due to wing twist. It has 18° up, and 24° down. It should be the other way around. Everything about it is in favor of adverse yaw.
The wingtips showed the same 9° as the flaperons, flapped up. Both wings had the same angles for root and tip. The angle at the last rib was the same as the droop tip.
Wing roots showed 14°. That’s 5° of twist, root to tip. The floor was the same angle, 14°.
The horizontal stabilizer was at 11°.
While I concluded several things from this, I’d love to hear any input you might have.
First, let’s put in perspective. Obviously, it won’t fly a steady altitude with the floor level. The root would have zero AOA, and wingtips would be minus 5°. Flaperons would likewise be reflexed to -5°, while the horizontal stabilizer would be at -3°. I’ve often thought it could use a bit more angle of incidence. But, the floor is just a reference, anyway. A flat plane, if you will, that’s easy to level.
Ignoring all that, I think I ought to give it another 1° to 3° of flap, and put the horizontal back to its original position. Doing that would put the flaps, while retracted, at approximately the same angle as the bottom of the wing, while also increasing the total angle of the flaps, extended. That would be the same angle as the middle of the wing, rather than the tip.
I believe that this would make it more efficient inflight, as the flaperons, wings, horizontal, and elevator would not be fighting each other as much.
My wife shoots video of most of my takeoffs and landings, here at the house. Today’s video of the landing showed that the tailwheel stayed off the ground while I had the stick back a good bit. I don’t believe that I was hard on the brakes, if at all. My usual routine is to keep the tail up, after I touch down, so the tailwheel isn’t eating the bumps, and let it roll out. Balance would have been neutral or slightly aft, with just a few gallons in the panel tank, and wing tanks empty.
On the negative side, it would have about zero up aileron, at least at the wingtip, with flaps deflected. I’m not sure if it could have much more adverse yaw than it currently does, but the rudder works just fine. One more thing, that might become an issue, if it’s not already, is that the flaps might not fold up flat enough when the wings are folded back. I had considered that that was the reason for that geometry, in the first place. If I ever need another project, I could convert to differential control, but I’m not planning to do that, at this point in time. I like the ease of folding the wings back, without disconnecting anything, even if I hardly do it anymore
I wouldn’t think there’s any benefit to taking the flaps back up. The ailerons don’t go up any further, at least, not if it’s trimmed to fly without stick pressure. I don’t have a stopper for the flap lever. It stops against the torque tube for the sticks. I’ve read the old concerns about control reversal and the need to limit flap travel, but never experienced anything like it, with about 275 hours and lots of full flap landings. Maybe that was first flight nervousness by those unfamiliar with the amount of adverse yaw, and they mistook the effect.
Here are the stats, simplified, as with the floor leveled:
Angle of incidence, wings, average: -2.5°
Range of motion, flaps: 17°
Range of motion, ailerons: -18°/+24°; 42° total
Angle of incidence, stabilizer: -3°
Is it ever going to stop raining? Look what it’s done to me. I hope you’re all enjoying your Kitfox, whether working on it, flying it, or just considering its different angles.