My good friend David Brick posed a question in a comment about an illusion of discontinuity in the geometric plane presented by the bottoms of the flaperon, fairing box, and main wing section. In one photo, it looked like perhaps the front of the fairing box was hanging down below that horizontal line. In response to his comment, I posted this next photo, showing that the bottom lines of flaperons, fairing box, and wing are all pretty much in the same horizontal plane.

However, if you look closely, this photo raises another issue. When the trailing edge of the flaperon is in this "neutral" position, it is even with the trailing edge of the fairing box (and the wing tip when installed.) But look at the forward section of the flaperon in the photo above. It actually curves up a bit, leaving a "cavity" in the transition from flaperon to wing. Why is this? Looks like it would create some turbulence and drag there -- and it does, particularly at cruise speeds, because drag increases by the square of speed increase.

The answer is that this rounded shape to the front of the flaperon is intentional in this wing, which is designed to have its least amount of drag not in the "neutral" position, but in a "reflex" position, where the trailing edge of the flaperon is actually about 5-8 deg. up from neutral and the plane is flying in level cruise with the wing flying at a relatively low angle of attack. The next photo shows the bottom of the wing with the flaperon in an approx. 5 deg. up, or "reflex" position.

Notice that in the photo above, the forward section of the flaperon curves smoothly into the bottom of the wing, leaving no "cavity" at the front of the flaperon as it does in the "neutral" position. The next photo is a rear view of the same 5 deg. reflex flaperon position.

The next shot gives yet another view of the wing shape when the flaperon is in the same 5 deg. reflex position.

The benefits of the reflex shape with this particular wing design are substantial. For example, when the plane is flying with flaperons in "neutral" position, trimmed for straight and level flight (low angle of attack) at max. continuous cruise power, and the flaperon is suddenly raised to a 5-8 deg. up "reflex" position, the change in speed is dramatic and felt as a distinct and immediate acceleration. How much speed does it add? In the Murphy Rebel, somewhere between 5-8 knots! (Other airplanes also use a reflex position in cruise -- the 4-place RV-10 being just one example.)

Because the flaperons act on the wing shape along the entire length of the wing, the effects are enhanced -- even though the fairing box and the wing tips are still in neutral position! You'd think that those two discontinuities, causing drag from turbulence, would cancel out any advantage of the reflex positioning, but that's not the case. A thoughtful reader may wonder, "If reflex is so beneficial to this shape of wing, why not just mount the fairing boxes and the wing tips up in the reflex position to start with, so they would assist the increased efficiency of the reflexed flaperons at cruise speed?" A good question, because indeed, if the boxes and tips (or at least the latter) were also aligned upward in reflex position, cruise speed would be a bit faster.

Fortunately, however, the question has a good answer, which is that all wing designs are compromises, based on the intended primary mission of the aircraft. Because the primary mission of the Rebel is to be a sturdy, short takeoff and landing (STOL) airplane, the wing is optimized not for top speed (and least drag) but for high lift at takeoff and relatively slow climb speeds. With the fairing boxes and wing tips built fixed in the "neutral" position, the wing is able to produce maximum lift, at takeoff and slower speeds, throughout a wider range of flaperon positions, giving the airplane its greatest overall asset for its intended mission, namely, the ability to takeoff and land in short spaces, at relatively slow speeds, on rough strips (or floats), while carrying substantial loads.

There are numerous tradeoffs inherent in design decisons to maximize lift or minimize drag at various speeds and other performances requirements of the aircraft. In short, cruise speed is a nice thing when you can get it, but not the only thing.