Ash is really strong, but it's heavy.So, not really needed for an ultra light (IMO). Could you use it? Sure, but then you would want to go through another exercise in optimization because without that it would be heavier, and stronger than it needs to be. Less dense wood is generally more stable for a given E*A at -- especially at lower loads where the stronger material goes unstable before the material allowable is reached. This is when, for instance we use aluminum on the outer skins of airplanes instead of steel, which is a stronger material. Where loads are high, like landing gear you'll see steel.
