Originally Posted by
stressmerchant
The flow behind the propeller is anything but orderly. Many years ago I had to do some work with the stability of a twin turboprop. The simplistic view of the propeller slipstream may envisage a cylinder of high speed air trailing back from the prop disk. From the research that I did at the time, it appears that the air is split above and below the wing, which each half of the flow forming its own smaller "cylinder", although now a bit squashed. Due to a bit of sideflow, the two cylinders don't meet again in the same vertical plane - the lower one is usually displaced towards the wingtip, so the cross-section now looks like a figure 8 with a diagonal slant. The prop rotation can push them a bit as well, so if both your props are turning in the same direction, the left and right cross sections are not symmetric about the centreline. Add to that the fact that the"cylinders" are being subject to fluid shear at the boundary with the relative wind, and you can imagine that, even before reaching the tail, the shapes have started to break up. Now add to the the effect of nacelles, fuselage interference, etc....
So yes, I'm sure that the wing position and fuselage shape do affect the nature of the airflow. However, the stability impact of wing height alone is probably one of the smaller variables. It may be instructive to look at the Cessna Caravan and then some of the military trainers, all with similar engines. Are their varied handling characteristics solely a function of their wing height, or do planform and inertia play a bigger role?
By the way, why don't you have a look through the old NACA data and see what they have on the Grumman Wildcat stability.
Very interesting stuff! I cannot thank you enough for providing all these additional details, as they are very valuable in visualizing what I am theorizing about...
The thing I was concerned about is the splitting action of the main wings, so this is definitely before the "shapes have broken up".
As to the Wildcat, you are absolutely right that it is a mid-wing I had forgotten about... It had superb handling in turns, so that doesn't appear to have hurt it...
Gaston