Friday, March 29, 2024

Washout

 


Washout in a built up wing has always been a challenge. I use a ceiling tile so I can pin down the parts on top of the plan. Depending on the construction of the wing determines the technique in building in the washout. The wing panels of the Yellow Jacket are built upon a carbon fiber spar. Therefore the wing is strong and resistant to twisting. In a conventional wood spar wing, washout can be induced with covering. Many of my Gentle Lady and Bird of Time wings were twisted with the application of the Monocoat. I would heat up the covering while twisting the wing then let it cool till I achieved the amount of washout was obtained. 

Washout is important for high AOA (angle of attack) or the angle that the wing is carving/flying through the air relative to the inertia of the flight path. The twist or washout in the tips of the wing allow the tips to stall or laminar airflow to separate last. 

Important for slow speed thermaling.

The technique I used for the Yellow Jacket regular wig is to take a one inch wide strip of 1/64th plywood 12 inches long. Then tack on the same thickness and width nine inches, same application for six and three inches. I ended up with a semi wedge shaped strip that goes from zero to one sixteenth of an inch that is called for in the plans. I flipped it upside down on the plan and pined down under the wing panel trailing edge and pushed down all ribs to get a uniform twist. I then glued in the ends of the leading edge, used clamps to set the twist and then locked in all ribs to set the wing twist.

This type of wing structure is strong! I do not think a good uniform washout could be induced with covering on this type of wing, it must be built in and this is how I did it.

I’m happy with the results and am ready to move on to the next panel.



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