Wash in or washout!

[martin collins 1]

My latest foamboard build is from a plan a friend drew up for me, it has never been built from before and he was in the process of re doing it when he passed away as he said it would not build correctly. I have no idea which parts he thought needed re doing but to me the wing ribs look to be wrong and i would like others opinions before i start gluing the wing together. 

This picture shows the inner and outer ribs as they would be i.e. glued against the back of the main spar and sitting on their `tabs` which are cut off once the main wing structure is glued together before fitting the lower skin. To me this looks like it is putting `wash in` to the wing tip in that it sits quite a bit lower than the inner rib trailing edge. Am i correct in my thinking or am i missing something? 🤔 The picture angle is slightly deceiving, the front of both ribs are in line.

[Martin Harris - Moderator]

Difficult to tell from the picture but allowing for parallax the chord lines could be parallel. If so then there’s no wash-in or out. 
 

It will give a measure of anhedral though - is this a high wing and/or swept wing design?

[martin collins 1]

Douglas DC4 wing, a little bit of angle back but the trailing edge comes forward more than the l/e goes back. It is a low wing a/c.

[Martin Harris - Moderator]

Seems a bit odd in that case - unless the wing is built inverted?

[martin collins 1]

No, wing is intended to be built the right way up as the tabs are on the bottom of the ribs.

 

[flight1]

if those datum lines are true to the section then it looks like you have wash in which is not a good solution. wash out  is good and can be achieved by either angle of attack of wing section or increased camber for the out sections of the wing. you need to check  sections  used.

your friend had obviously worked this out as he had mentioned it being wrong.  ?

[Robin Colbourne]

23 minutes ago, Martin Harris - Moderator said:

Seems a bit odd in that case - unless the wing is built inverted?

Martin, That was my first thought too!

 

[kc]

How do you know the ribs have the tabs on the bottom?   It looks to me that the wing is built inverted ( tabs onto building board ) and will end up with a little dihedral but no wash out or wash in.   Put a few ribs onto the building board and have a dry run to check.

Edited November 2, 2022 by kc

[flight1]

need full wing section lined up?

 

[martin collins 1]

The bottom of the ribs is definitely the side with the tabs on, the curve on the opposite side is much greater particularly towards the leading edge with would generate more lift meaning the tab side is the underside of the wing. Hopefully this photo shows the difference in the curves between the two sides.

[flight1]

yes that looks the right way up  ., but do you know the wing sections used/? to determine required angle of attack?

[martin collins 1]

Afraid not, the line i have put through the rib is parallel to the datum line through from the nose to the tail of the aircraft.

 

[Trevor]

Looking at the size of the tabs, maybe the two wing panels are meant to be built separately and joined later, after the tabs have been cut off?

[Simon Chaddock]

martin you are looking at only the rear part of the wing. The part ahead of the spar could effect the full wing section.

When in doubt look at the full size!

There is no noticeable wash out but remember the wing section is much thicker at the root which could give an 'aerodynamic' washout.

Note also the significant dihedral.

Hope this helps.