Flying wings, washout and funny elevons.

[omega blood]

First a question about wash out on a flying wing with out vert stabs. Is the wash out that is required only at the wing tip or is it required thruough out the whole wing? This leads me to my next question do elevons that cut across the wing such as the ones on the paoli flying wing http://perso.wanadoo.fr/scherrer/matthieu/english/paolie.html
provide wash out at the tip when reflexed ? Or other elevons are longer but have a similar shape where it starts out narrow near the root of the wing and taimpers out tword the tip of the wing. I made a small hand chuck wing and I cut a similar elevon and noticed that the reflex on this shape of elevon looks like crude wash out. so I'm wondering if it has the effect of washout.

[Sparky Paul]

The last image at the site shows how the washout works, due to the triangular shape of the elevon.
As for washout (or verticals) being required, no it's not.
Just watch your speed.

[cwatters]

You need this site...

http://www.mh-aerotools.de/airfoils/flywing1.htm
http://www.mh-aerotools.de/airfoils/index.htm

and the home page..

http://www.mh-aerotools.de/airfoils/index.htm

[airboss]

you need washout in a flying wing
if you rely on elevon to correct for natural tendancy of wing to dive aerodynamic efficiency is lost and drag is increased
the wing would fly level with about 15 degrees of up elevon

all wings dive(except symmetrical) due to curve of top surface
washout counteracts this diving

washout could be in any part of the wing but having it in wing tips is easier to produce with hot wire production

washout also helps lateral stability since the center section stalls before the wingtips... preventing tip snap

enjoy
allen

[omega blood]

I guess I should have worded my question differntly. What I meant to ask was if the shape of the triangular elevon in a reflex position added wash out because of it's unusual shape and mounting. Never theless your answers were quite informative and helpfull. Thank you.

Airboss, Although that was not the answer I was looking for that info realy clears up a lot. It was like reading a section of wing design for dummies book. Thanks!

[Ollie]

The heart of an airfoil is its mean line (half way between its upper and lower surfaces). In a symmetrical airfoil the mean line is a straight line. A mean line that is concave down has a nose down pitching moment. A mean line that is concave up has a nose up pitching moment. A mean line that is S-shaped has a pitching moment resulting from the nose up and nose down tendencies. The net pitching moment of an airfoil with an S-shaped mean line can be zero, nose up or nose down depending on the net effect of the conflicting tendencies. When the trailing edge is reflexed, the incidence is reduced and the pitching moment tends to be less nose down.

Typically non-swept or plank planforms tend to use reflexed airfoils all along their span.

Flying wings with sweep back tend to use more reflex and washout near the wing tips.

In a swept back wing the washout is necessary to counteract the sweep's tendency to tip stall and to achieve a more efficient lift distribution, even on planes with horizontal tails. Next time you are at the airport, sight down the length of a jet transport wing to see the generous washout associated with sweep back.

In any tailless configuration, reflex is used to achieve pitch trim.