visual demonstration of spiraling slipstream

[N355DW]

http://www.youtube.com/watch?v=JxreiysDpwo

[tkatc]

I think you posted the wrong video, Damon. But its a cool Extra 300 video anyway.

[mike newall]

The European says....

Why only 2 blades

[N355DW]

Originally Posted by tkatc

I think you posted the wrong video, Damon. But its a cool Extra 300 video anyway.

You didn't notice the spiral slipstream from the prop tips at the top of the hammer? I used to see that all the time in humid weather!

[hevansrv7a]

The tip vortexes (vortices?), assuming the airplane is moving in those shots, suggest something other than a spiral airstream hitting the rudder and empennage.

I am not saying that the spiral of accelerated air is not there, only that the tip trails don't actually show it.

In a way this reminds me of the argument about "slowdown" of air as it approaches the plane of the prop because of the fuselage or cowl behind it. Most agree there is higher pressure. So how can there be both slowdown and higher pressure? All the videos of smoke in wind tunnels, mostly of motorcycle fairings, suggest that there is deflection, but no slowdown.

I know that the P factor is evidence, but that gets mixed up with gyroscopic forces. Do we have direct evidence of air moving somewhat sideways?

[N282S]

Originally Posted by hevansrv7a

The tip vortexes (vortices?), assuming the airplane is moving in those shots, suggest something other than a spiral airstream hitting the rudder and empennage.

I am not saying that the spiral of accelerated air is not there, only that the tip trails don't actually show it.

In a way this reminds me of the argument about "slowdown" of air as it approaches the plane of the prop because of the fuselage or cowl behind it. Most agree there is higher pressure. So how can there be both slowdown and higher pressure? All the videos of smoke in wind tunnels, mostly of motorcycle fairings, suggest that there is deflection, but no slowdown.

I know that the P factor is evidence, but that gets mixed up with gyroscopic forces. Do we have direct evidence of air moving somewhat sideways?

"corn's lookin' good....."

[Alan Carroll]

Originally Posted by hevansrv7a

I know that the P factor is evidence, but that gets mixed up with gyroscopic forces. Do we have direct evidence of air moving somewhat sideways?

I experimented with putting dirty oil on the sides of the fuselage a couple of years ago to test this. No spiral that I could see. I did see evidence for downward air deflection on the aft fuselage though - a nice illustration that the horizontal tail has a negative angle of attack (as expected). The pattern looked the pretty much symmetrical on both sides.

[johnny stick]

OK I wasn't going to comment, but you talked me into it. To me the photo shows the propeller tip vortices, not the spiral slipstream. As the prop screws through the air, it makes like a screw in wood, and that is what I am seeing. Whether or not the air is actually twisting as it moves back, I can't tell from the photo. What is neat is that the prop does not drag all the air with it; there is actually a large gap between suggestive revolutions of the prop (every other contrail). kind of cool.

[John Clark]

Originally Posted by mike newall

The European says....

Why only 2 blades

OK, how about 16 blades?



John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

[hevansrv7a]

Originally Posted by Alan Carroll

I experimented with putting dirty oil on the sides of the fuselage a couple of years ago to test this. No spiral that I could see. I did see evidence for downward air deflection on the aft fuselage though - a nice illustration that the horizontal tail has a negative angle of attack (as expected). The pattern looked the pretty much symmetrical on both sides.

The bold-red is mine.

If the air is being deflected downward then normal lift would be produced. Negative lift would require air deflected upward. Right?