Ok, so something has been rattling in my brain for some time. Listening to one of the podcasts with Kane just set me off again.
Manufacturer’s foil measurements and specs drive me nuts.
Why does Axis advertise wingspan, then projected area, then actual area in cm2… Unifoil is in in2 so on a so forth.
Then we get to aspect ratios. Are we looking at ratio of wingspan vs chord at center of wing, an average of chord?
So what if we just decide, as consumers what the standards units are?
Once we have that figured out, can we come up with a basic lift power standard?
Say a foil is placed in a current tunnel(water version of wind tunnel) and a lift test is performed with the fuse at 0°, 10° and -10°. The lift produced for each os measured at the top of the mast and is then recorded in an overall weight at a constant water speed to give us an idea of the actual lift power in comparison to another foil.
Maybe even add a stall speed to that testing based on a constant weight.
With all of the “reviews” online these days, I thought something along these lines would aid in determining what wings to try and what wing not to.
To make it worse, the new foils mean the old numbers mean nothing. A 700cm foil is no longer small. Unless you’re on one of the brands where it is small. Then it’s tiny.
Span and stall speed would probably be the most accurate, except stall speed will change with weight, tail wing etc. and 2 wings with the same stall speed can also feel completely different sizes due to severity of stall onset, aspect ratio, front wing angle, placement in the track and a million other factors.
I think wing design will eventually reach more of an equilibrium, where there aren’t as many variations in section, and area measurements become more meaningful again.
Stall speed makes a lot of sense. The variables on a front wing have to be cut down to get a comparison we could use, if only as a point of reference.
So using factory mast to fuse to wing angle, a constant weight, either the same tail wing, or no tail wing and same mounting position in tracks.
I agree that the foil sections will eventually get to that point. Will the subtle differences between designs not still keep us guessing?
Here is what started these thoughts around measuring the lift power. I was over foiled and being blown out of a wave vertically or in line with mast on one wing(old Axis 900). Then riding the same wave on another wing, similar surface area and a bit more span(Progression 200). The power generated vertically seems to drop a fair bit on the Progression 200, to the point it was controllable, but I would argue the stall speed was lower.
The above is an example of how different foil sections can change the ride characteristic. Comparing the generated lift and stall at a given angle of attack and speed is a good reference for me, as the numbers are easier to look at than trying to dissect a diagram of a foil section.
This video is a very crude representation of a test. This isn’t meant to debate Bernoulli’s Principle one way or another.
In climbing grades(difficulty ratings of climbs) are consensus based. Concurrently, the sizes of cams, which front wings remind me of in their size range nature, are sized, in some cases, from 000-10 or so. I was thinking recently that all foils could be rated by consensus. 0 being some tiny race foil, 10 being a beta. 00 and 000 and 11 being for outliers.
Edit: any time we talk about wings being equivalent to those of a different size, like the new ha wings, I think about this.
And if I ever start a foil company, I’d take along the way of color coding cams. Each wing would be a different color. So you can grab the right one out of your bin quickly.
I put a uni progression 200 straight on top of a lift 180X last week, they looked excatly the same. I couldn’t spot the 20" of area by eye.
I know surface area isn’t a good measurement. A stall speed/lift rating under generic load would be great, but it would need to be independent as companies can’t get the basic measurements right.
