Posted: 1/10/2010 19:51:46
Is "wash in" or "wash out" necessary in a high wing tube and fabric airplane? What are the pros and cons if any? Any thoughts or insight would be appreciated.
Posted: 1/10/2010 22:19:34
Wash in - guarantees the wing will stall at the tip first assuring an exciting stall spin characteristic.
Posted: 1/11/2010 18:21:31
I can think of a couple of planes with zero wash out and none with wash in. By far the most common is to have some washout to make sure the wing tip is flying when the inboard section stalls. This allows the ailerons to retain effectiveness even in a stall. It also helps keep the stall from being abrupt. An abrupt stall can catch a pilot off guard. Most planes should give the pilot a warning before stalling even those without stall buzzers or horns. The most common warning I have felt is having the stick or yolk shake as the separated airflow stikes the tail. At the time the stick begins to shake the outboard portion of the wing with the ailerons is still flying with the air attached.
Posted: 1/12/2010 20:37:58
wash out is also best for STOL operation ,..on a 28 foot wing span I usually incorperate 1 inch of wash out on a semi semtrical airfoil,..1.5 inch on a flat bottom airfoil,....up to 3 inches of wash out on a airfoil with a less then full covered bottom surface depending on wing span
Posted: 1/12/2010 21:37:38
Thanks for the replys so far. I'm leaning towards no wash out in my wing. My airplane has a 36 foot wing span with the Ribblett airfoil, which has great stall characteristics already. Looking for any bit of cruise speed I can get. I'm building as light as I can and as clean as I can for my kit.
Thanks again for the replys,
Posted: 1/16/2010 16:11:29
In addition to the improvements in stall characteristics, wash-out can also reduce drag by shaping the lift pattern of the wing at cruise speed to be more elliptical in shape. This can also be used to help keep the airfoil operating in or near the drag bucket if the airfoil has one.
Always thinking about airplanes