Understanding Washout

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Written by David Andersen
As featured on page 58 in the March 2012 issue.
Read an except from the magazine and share your experiences.


Washout is a design characteristic built into the wing, where the angle of attack is reduced span-wise from root to tip, typically 1° to 2°. The reduction creates a situation where the root of the wing stalls before the tip, softening the stall and allowing the ailerons to be functional deep in the stall. Review some of the author's highlights from the magazine and share your experiences in the comment section below.




Washout is a twist in a wing that causes the wingtip to meet the airflow at a lower angle than the root in normal upright flight. Some airplanes don’t need it; some airplanes can’t fly without it.




Washout can be added after construction by slightly raising both ailerons. This is recommended for the maiden flights of a new model.




Bob Patton’s Cessna Aerobat uses drooped wingtips for stall control, typical of STOL aircraft.




The author’s Howard Pete has washout in only the last rib bay—enough for a nearly constant chord wing.




The glider-like wing of the author’s 114-inch span Focke Wulf Ta 152H requires washout for stability. The aircraft would be uncontrollable without it.




In case of engine failure, washout provides good yaw control in Greg Hahn’s B-17.




The author’s 1/3-scale Grumman Lynx has a constant chord wing with no washout. It instead uses Hoerner wingtips and stall strips, which are effective.




There’s no washout and no incidence in Dave Deschenes’ Wildcat—typical of constant-chord dive bombers.




Despite its thin, pointed wingtips, Dave Szabo’s Spitfire has excellent handling in part because of 2.5° of washout—roughly the same as the full-scale Spitfire. A low pass before a chandelle is shown here.




A 90° sharp-edge stall strip is added to the LE of the Grumman Lynx to lower the stall angle in the root area of the wing. This alternative to washout also works when inverted.




Leo Spychalla’s Ziroli Stuka has a gentle stall despite its pointed wings. The wings have 4° of washout, starting outboard of the landing gear.



8 comments

Can you possibly explain how washout provides good yaw control in case of engine failure?

When one engine of a multi-engine aicraft fails, the wing with the live engine yaws forward. The angle-of-attack of this wing increases in proportion to the amount of dihedral, increasing the possibility of a wingtip stall. Washout reduces this effect, thus improving yaw control when one engine fails.

I also wondered about how washout helps improve yaw control in case an engine flames out.

You wrote:There’s no washout and no incidence in Dave Deschenes’ Wildcat—typical of constant-chord dive bombers.

The wildcat had neither a constant chord wing (it was double taper) and was NOT a dive bomber.

Seeing this article being presented stuns me. It just happens that In RCU Beginners I just introduced "Washout" concerning heavier - spelled War Bird - to a thread, Some knew my technique, many doubted it, and some find the theory unacceptal. HA!
The average modeler with an average regular wing with real ailerons simply has to roll each aileron up a few degrees, 2-5 will do it but I had a heavy Spitfir that needed 8. Washout is NOT a Patten thing but it can save a lot of models from the WB Snap Roll on take-offs, plus a lot more items. I could write a book on that part of applied aerodynamics for pilots.

Hi Dave,

In all your research on the Ta-152H what did you discover regarding the location of the wash out? I have read of a subtle kink which exists in the traling edge of the full scale airplane which, I assume, defines the point at which the wash out starts. Any idea where that point is? Is the wash out all contained within the section of wing that includes the aileron? Do you know how much was used in the full size airplane?

I have an ARF trainer kit from a reputable brand, a conventional high wing .46 size model with parallel chord and trike gear.
It has 20mm washout in each wing panel, just over 4 degrees. This seems quite extreme, do you think I should go ahead and build it and see how it flies, or look for something else?

Hi Andrew! We suggest that you try to research this model online at places such as RCGroups or RCUniverse and see what others have experienced with the model. Generally, we suggest that it be built as the manufacturer recommends. We wish you the best of luck!

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