Forums: Skydiving Disciplines: Wing Suit Flying:
Phat vs. Skinny, or Perceived performance

 


yuri_base

Nov 3, 2006, 8:51 PM
Post #1 of 6 (3480 views)
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Phat vs. Skinny, or Perceived performance Can't Post

Yo!

While playing with some calculations (don't ask Wink), I scaled the polar curve to different weights and found answers to some old questions.

Take a look. The blue curve is a polar curve -- vertical speed vs. horizontal speed -- for a 230lbs (exit weight) jumper in some imaginary wingsuit. (the small numbers by the curve represent the angle of attack.) The orange curve is a 170lbs jumper of the same physical dimensions in the same suit. The jumpers have the same body positions for every flight mode, the only difference is weight. They both have the same maximum glide ratio (2.2), achieved at the same angle of attack (14 degrees), but their minimum fall rates are noticeably different: 44 and 38mph, respectively. Basically, the lighter jumper's curve is simply the heavier's one scaled by the factor of sqrt(170/230).

The semitransparent areas inside the curves represent the range. You can fly inside your range by partially collapsing wings, arching, etc. You cannot steadily fly outside the range, you can only "peek" outside by, for example, diving and planing out.

They can flock inside the intersection of their ranges. Star shows one possible - if not typical - flocking point: 80mph forward, 65mph down.

Now suppose at breakoff flyers "pop": while maintaining the same forward speed, they try to decrease their fallrate as much as they can. Mr.Phatty can only slow down his phat ass by 9mph to 56mph, while Mr.Skinny floats like a helium balloon straight up to his minimum rate of 37mph, a whopping 28mph change.

Different scenario: at breakoff flyers remain on the same level (65mph down), but increase the forward speed to the max. Skinny is much closer to the right boundary of his envelope and reaches almost 100mph in an instant. Phatty, since he was flying almost in a stall (his AoA was almost 20 degrees), needs first to break the stall (spilling a lot of air), then accelerate every one and each of his 230 pounds and by the time he reaches 100mph, Skinny already disapeared on the horizon. While Phatty is able to achieve speeds up to 115mph horizontally, it's time to pull before he can reach them. Wink

Short version: the performance of different wingsuits and flyers cannot be judged by observing the range when flocking and "smoking ass" on breakoff. High-performance machines specifically designed with BASE in mind can only be objectively evaluated in BASE.

Yuri
Attachments: PhatVsSkinny.png (19.4 KB)


BlindBrick  (C 35382)

Nov 3, 2006, 9:05 PM
Post #2 of 6 (3370 views)
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Re: [yuri_base] Phat vs. Skinny, or Perceived performance [In reply to] Can't Post

Yuri, could you scale that to 330 lbs and assume a Prodigy? I have this feeling I won't so much glide as plummet with style! Wink

-Blind


yuri_base

Nov 3, 2006, 9:16 PM
Post #3 of 6 (3364 views)
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Re: [BlindBrick] Phat vs. Skinny, or Perceived performance [In reply to] Can't Post

If you order an all-pink XXXXXL Prodigy, you'll definitely plummet with style!


BlindBrick  (C 35382)

Nov 3, 2006, 9:52 PM
Post #4 of 6 (3351 views)
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Re: [yuri_base] Phat vs. Skinny, or Perceived performance [In reply to] Can't Post

In reply to:
If you order an all-pink XXXXXL Prodigy, you'll definitely plummet with style!

Arrrgh, too late, I've already ordered it. Maybe when I'm ready to move up to a Phantom, I can go all pink!

-MaxGrav


KrisFlyZ  (C 34590)

Nov 3, 2006, 11:41 PM
Post #5 of 6 (3330 views)
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Re: [yuri_base] Phat vs. Skinny, or Perceived performance [In reply to] Can't Post

In real life 230 lb jumper has a very different wing thickness(vs imagining jumpers of same dimensions but different weights) and that IMO also has an effect on the form drag characteristics of the resultant wing.

Thinner wing can sustain a higher maximum speed so ideal calculations don't really play out like that in real life.

Want to argue that? Take it up with deadmanwalking Wink.

As for break off after a flock....I agree. It is not possible to judge who 'outflew' who. Too many visual issues and if you are watching someone, you are not maxing out.

Kris.


lurch  (D 27583)

Nov 6, 2006, 12:09 PM
Post #6 of 6 (3092 views)
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Re: [yuri_base] Phat vs. Skinny, or Perceived performance [In reply to] Can't Post

Interesting work. Surprisingly close to the real-world results I've seen with a couple new stars in the sky around here. Both started out with fallrates in the 80-90+ range. Both somewhere around 200 lbs, one just managed a phenomenal pop down to 51 mph in a Phantom. I just did a fallrate exercise with the other guy who, with less than 30 WS flights under his belt translated his weight into so much speed and lift I had to bust out most of the ninja tricks all at once to climb back up to him. Caught me by surprise... I was expecting the maneuver, just wasn't expecting him to do it THAT effectively. He outweighs me by 60 lbs easy, and was cruising at 64 mph at 9 grand flying a raggedy old GTI against my new S6. I gave the usual effort to go get him, and was like "Huh?" when the distance didn't change. I did catch him, but only after using techniques I normally only use for solo flights. Ruined my video, cause I couldn't fly like that and keep him in frame at the same time.
-B



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