MajorTomski wrote:
I came to the conclusion that spiraling slipstream is a myth because it is the only aircraft stability function that is not quantified. Designing the aerodynamics of an airplane is a cookbook plug and crank set of mathematical operations. Take a set of interactive equations. Plug in a bunch of numbers, and it cranks out the answers of area and angle of attack for all of the flight controls. The one thing missing in all those equations is the mathematical definition of the slipstream and how much the fin should be offset to fix it.
The spiraling slipstream is not a myth although when graphically represented in pictures, the twist angle is often very exaggerated.
NACA has investigated the magnitude of the twist in the propeller slipstream experimentally. If you look up p. 9 and 10 in the [link=http://naca.larc.nasa.gov/digidoc/report/tr/12/NACA-TR-712.PDF]NACA-TR-712[/link] technical report you will find the result of an experimental measurement of the twist of the propeller slipstream. Twist does exist!
In this [link=http://pdf.aiaa.org/jaPreview/JA/1987/PVJAPRE45440.pdf]article[/link] from NASA Ames the effect of the spiraling slip stream on the stalling behaviour of light aircraft is experimentally investigated.
/Red B.