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I propose an experiment.

A technical discussion about wingsuiting, AOA, ground clearance, etc. is well underway in another thread here, stemming from Mr. Corliss' unfortunate incident. I am not a wingsuiter, so I can't contribute anything from my own experience. However I have a question to ask, and was wondering if a wingsuiter out there (BASE or skydiving, doesn't matter) would be kind enough to take a shot at this?

I propose a method for making a reasonably approximate measurement of Angle Of Attack. It is very simple... just take a piece of yarn and affix it to your left hand before exiting. In flight, the yarn will theoretically extend parallel the slipstream. Now the hard part: a photograph taken from a directly horizontal perspective would allow one to measure the angle between the yarn and the chord of the wing. This is a direct measurement of your AOA. The yarn would have to be big & bright enough to render on a hi-res photograph. Maybe a foot or two long? The cameraman should probably be a fellow flocker since a ground-based camerman could doubtful get the right angle or a fast enough exposure for the detail required.

I did a cursory search through various forums, but it did not turn up anything like this being done yet.

But before anyone gets too excited, what matters for not hitting your feet on the rocks, is not one's AOA, but one's pitch angle relative to the earth's surface (i.e., "relative pitch" if you will). AOA is not pitch, but they might be very similar in strictly unaccelerated wingsuit flying. In a dynamic proxy flying regime, this is certainly an unwarranted assumption.

One might measure pitch angle best by getting a horizontal image of the wingsuiter with a distant, flat horizon in the background. So, the second part of this experiment would be to get some shots horizontal to the wingsuiter, in different body positions (i.e. mimicking proxy flying positions) with reference to a flat horizon.

If you could get a photo with a piece of yarn, a horizon, and a good view of the wing chord, all in the same frame, you'd be my hero.

Any pilots game for trying this?

[Edit: clarifying a point]

The prob with the yarn is that it needs to be very long to clear the burble to provide useful info. Otherwise, it'll do "Dirty Dancing" and that's all you'll see.

AoA can be measured by smoke trail. There's lots of photos and videos out there. For example, in Robi's videos you'll see low, efficient AoA (in 10-15 degree range) and tightly spinning smoke trail. On the contrary, in f10cking videos (AoA ~ 45 degrees, L/D ~ 1.0) you'll see that smoke oftentimes engulfs the whole f10cker's back and even stains their rig.

would it be affected by the burble if you have the yarn in your hand? I know there are some eddie winds but "measuring" close to the hand won't be affected so much I think. My guess is that the yarn needs to be short for the best indication, but why don't you try a long one in one hand and a short one on the other, to compare?

There will be some flutter of the yarn, but I do not think this is a show-stopper. The flutter will probably be length-dependent and a little experimentation should determine the optimal length. A shorter length would probably flutter less, but the downsides include difficulty visualizing it photographically and a less accurate measurement. A longer string may flutter a bit more, hurting precision, but would be easier to measure, and presumably more accurate.

You might even be surprised how stable a piece of yarn can be. Yarn is commonly used on gliders as a cheap but highly effective "slip indicator". It works because it is within a laminar flow domain. By attaching the piece of yarn at the left hand, it is projected some distance from the worst of the wake turbulence / burble. It would not work if attached at the feet. It might work on the side of a helmet if the spot is chosen with care.

A smoke trail might be informative, but it shows a general trend, not an instantaneous measurement. I strongly suspect that the trail becomes unreliable as a reference line as you get close to the body. I'm not dismissing its use, but there are a lot more confounders.

If you had any particularly good smoke-trail examples to post, I'd be interested to see what you thought were the best examples!

The most expensive piece of yarn can be found on a helicopter, they use it as a slip indicator as well( might not be the name for it). But it gives you an idea of how well this idea may work. In exited to see pictures and hear about results of this!!!

Yaw string ?
.

"yaw string" is another name for it, but that's a technical misnomer

Very easy... 100 ft (30 M) ribbon attached WS. Real world AOA

Or
Two hot air balloons and a highspeed camera, seems safer that 100m of yarn :)

Jarno, venom, Idt camera

http://www.youtube.com/...youtube_gdata_player

hey nice vid!

now this is getting at what I am talking about here... note the little thing flapping in the breeze (arrow)... see it doesn't have to be very long at all.

too bad the angle isn't just a little more perpendicular. but i'm certainly not criticizing, that's a cool flyby.

thanks for posting