Originally Posted by
aerolearner
The (very interesting) NASA video lists the increase of AoA on the horizontal stabiliser due to the increased wing downwash with flap deflection as an aggravating factor. While I can understand this for a low tail configuration as on the Twin Otter, would wing downwash be a factor for T-tailed aircraft such as the DHC-8?
Yes, definitely.
The downwash flow field extends considerably above and below the plane of the wing. Think of the downwash as being the necessary opposite reaction by the air to the wing generating lift - the air pushes the plane "up", so the plane must push air "down". Now, if the air passing close to the wing is diverted "down", then the air below the wing has to "get out of the way" a bit and the air above the wing gets dragged downwards into the "gap". Eventually you get far enough above/below the wing flow that the downwash effect has decayed enough that it has "gone away" - but at the height of a typical "high tail", the downwash is still having an effect.