WING-TIP WASH-OUT -
Submitted by RAY DiNOBLE

Here's a method of checking and correcting a wing for excessive wash-in (bad) or wash-out (good). Wash-in and wash-out describes the relationship of the wing's trailing edge to the wing's leading edge. Wash-out (good) refers to the trailing edge being HIGHER than the leading edge. Without going into the aerodynamic reasoning for using wash-out, let's just say that wash-out is 99% preferred versus wash-in (trailing edge lower).

Greg Clemensen and his dad Bob recently finished a new Spirit 100 ARF. Greg asked me to make the initial flights to help get the ship sorted-out and trimmed. The first flight showed considerable tip-stalling when making both right turns and left turns. Several 'tricks' were made to the aileron and rudder adjustments but tip stalling was still there. A quick visual check at the field seemed to show some wash-in (bad) on both wing tips.

I told Greg that I would take the wing home and make the necessary corrections. The photos show how I accomplished the job.

I first taped on a piece of a yard stick (any 12 to 18 inch piece of straight wood will work nicely) to the flat bottom of the wing-tip (photo 1) The angle of the long piece of wood shows the excessive wash-in quiet easily (photo 2). Next I weighted the wing down on the flat working surface using the local telephone book. Using my heat gun, I applied heat to the top and bottom Monokote surface while twisting the wing tip into a wash-out shape (photo 3). The heat relaxes the original Monokote and wing shape while the twisting forces the wing structure into the desired wash-out shape. This might take a minute or two to get enough heat on the wing structure. HOLD the twist in place while the Monokote cools ( several minutes). The wing will 'relax' slightly after cooling so I like to check the wash-out several hours later or even the next day just to make sure the relaxation didn't make the wing go back to a wash-in condition (photo 4).

When satisfied that the wing now has wash-out, I measure the amount and make sure both wing tips have the same amount. Generally I like the trailing edge to be about 1/8 inch to 3/16 inch higher than the leading edge. This amount will be very forgiving and stable in slow tight turns.

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