Spiraling Slipstream OR Coriolis Force? You decide. . .
 

https://youtu.be/6-XBSLtG8Mk

https://youtu.be/nTMEMn6rge8

https://youtu.be/059N-fsW53I

https://youtu.be/IE2aiPCQ40s

Great job. Quite evident that something is happening.

Surely you've seen Alex Voicu's thread: http://www.rcuniverse.com/forum/rc-p...alisation.html

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Nope.
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I have and for this case, I think this is better.

The OP video, I only watched the first one, part way at that, illustrates why the old time tufting visualization used short pieces of string as a more effective way to examine airflow. The tufts were cut short enough so that they didn't flutter. The long threads in the OP videos are in turbulence and so it is difficult to see exactly what is going on.

Keith,

Thanks for posting links to your videos.

I'm favorably impressed with their quality, would you please post a description of the equipment used, camera make & model, resolution and how its mounted.


J e r

Yes, these tufts seem a bit long. But in any case, you can average their angle to the centerline and in doing so, one can indeed see the flow on top of the fuselage from left to right - a clear indication of the Coriolis Effect on the airflow, which is also probably why the US voted for the right-wing candidate in the recent election.

:)
Religion and politics are both no-no's on a forum and or in a pub :D

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I used a RunCam2 mounted on top of the vertical stab with a small piece of sheet metal between the top and the rudder. I'll post a picture later of the actual installation.
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What surprised me, and now that I've had a few days to think about it - it shouldn't have, is the massive amount of turbulence caused by the canopy.
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The worst effect of all that turbulence is simply wasted energy. Energy that comes from your batteries or glow fuel. That's why modern airliners don't have canopies sticking up into the airstream . . . perhaps Boeing and Airbus possibly know something that our pattern plane designers don't?
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The second negative effect of all that turbulence is what it does to the control surfaces. All that turbulent (and thus randomized) air is hitting the vertical and horizontal stab, and is also affecting the rudder and elevator. Kinda like trying to steer a canoe down a whitewater rapids. However, you can see that the nose of the airplane doesn't hunt around at all, so I imagine that the top part of the vertical stab / rudder are still in smooth air and able to steer the airplane.
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So . . . . like wheel pants, what purpose does the canopy on a pattern airplane serve other than "It will look weird and you won't get good scores without it"?

I assume it assists knife edge performance, especially with it being up front where it will have the most effect.

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Still, it doesn't make sense to basically have a drag chute attached to your plane 100% of the time just for knife edge.
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You could do the same thing more effectively with a vertical canard located over the CG.
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You mean something like this? http://www.insightrc.com/insightrc-VoodooOrder2.html

Ken

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Yup . . . LOL.
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Makes you wonder why more folks don't fly planes shaped like that.
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Keith,

I remember seeing pictures of a guy I think from Finland or Norway that flew a plane like that 2 or 3 years ago. If I find it I'll post a link.

Thanks for the RunCam2 info. Xavier Mouraux from Canada does something similar, https://www.youtube.com/watch?v=MUce24921kI


J e r

Because they aren't "pretty".

Ken

There's no massive turbulence caused by the canopy, unless the canopy is very poorly designed which is not the case for the Allure. I've seen jets designed to fly at Mach 2 with less streamlined canopies than those used on our pattern planes. If there's any turbulent flow, it's mostly caused by the spinning propeller and not by the canopy.
I think the tufts in the videos are way too long and may give you the wrong impression about the amount of turbulent airflow around the plane.

You can try moving the tufts elsewhere on the airframe and if you keep the same length i'm pretty sure you will get the same results. It doesn't mean the canopy or other parts are causing turbulence.

If the tufts are short, they will align themselves with the local airflow without shaking too much:
http://www.rcuniverse.com/forum/atta...mentid=2189987

If there's any turbulent airflow, the tufts will show it even if they are cut short :
http://www.rcuniverse.com/forum/atta...mentid=2189989

Even if the airflow is perfect, the canopy still presents unneeded frontal area that does nothing but increase induced drag.
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I've never seen anything functional installed in anyone's canopy . . . . ever.
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In a fighter jet, the pilot's head is installed inside the canopy, but our pattern planes . . . .
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I'm thinking we ADD drag in an attempt to slow them down. We have gone from thin ballistic Curares to slow flying Contra Allures with huge frontal area.

Also, note that the strings are frayed as well. That will amplify some of the disturbance. Another factor is the diameter of the yarn. You wind up measuring airflow too far away from the fuselage. That said, very impressed with the work. For the next round, I would suggest using flourescent fishing filament taped to the fuselage every 3-4 inches. That will give you a better indication of airflow. Though I have to say, I didn't see anything wrong with the airflow.... taking into account the fray and large length and diameter of the yearn. Very nice. Thanks for posting. I love the videos.. Nice flying too!!
Ken

You under rotated the snap on the triangle loop

Don't let any of these comments bug you, Keith. Good science involves criticism.
Keep up the good work.

I trust we assume jetmech43 just forgot the smiley;)

Go Team Airflow Analysis!

Good point. One thing I can think of as someone who has been attracted to models and miniatures of all kinds since a young age, is that the canopy adds that satisfying (and illusional) hint that if one were really small, one could crawl in that little airplane and ride around in it. It's for this reason (the wish for realism) that I find myself wishing for a pattern plane I could buy that has wing & stabilizer root fairings.

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Not bothered at all.
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I didn't really invest a lot of time or effort into this endeavor - some blue painter's tape and yarn. I was looking for what happens in general to the airflow around the fuse of my pattern plane. But mainly I was checking if I had the rudder trim set properly. Anyone who has flown a Cessna will recognize where I got the yarn idea from.
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After watching the videos, I noticed at low to medium airspeeds that the left string always curled up towards the top of the plane. However, it doesn't seem to have any effect on the tracking of the nose of the airplane. My guess is that the "spiraling slipstream" is there, but it only has a negligible effect on the airplane.
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As for jetmech . . . I know where to find him . . .
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