In article said:Ryan Cousineau <[email hidden]> wrote
Quoted message said:As has been pointed out before, aerodynamics depends first on frontal area, which is actually
more important than coefficient of drag (it's just that Cd can vary widely for two objects with
the same frontal area, and Cd changes are relatively free; it's usually hard to make a person's
frontal area smaller).
I disagree. You can make a person's frontal area smaller by getting their back and shoulders
lower. Have a look at
damonrinard.com01may06.htmOpen ↗
for some contrasting positions, and how close some people get to horizontal. Not surprisingly, the
ones who look most aero in the pictures could not use these positions in a UCI race (seat and bars
too far forward).
I was aware of Damon's study. And yeah, some frontal areas are smaller than others. But in a bit of
semantic dodging, I would describe this as optimising frontal area, not reducing it 🙂.
Quoted message said:These guys are very low on a tandem: damonrinard.commvc363s.jpgOpen ↗.
The other way to decrease your frontal area is to get narrower. The forearms should be close
together to pull the upper arms inward and the shoulders narrowed by rolling them forward.
I don't know what you mean about "Cd changes are relatively free." Aero tubes, disk wheels,
skinsuits, shoe covers, and aero helmets all are attempts to lower Cd, but aren't free by
any means.
I meant that Cd changes don't rely on changing frontal area, just making existing parts more
aerodynamic, and that there is a lot of leeway to make parts more aero within UCI rules. You can't
go recumbent or faired, but you can make "helmets" that happen to work better as fairings than
protection, wheels can be as aero as possible within some safety rules and the desire to avoid
wind-steering, and similarly the frame can be made more aero within certain limits.
Quoted message said:What you might consider "free" is that getting more horizontal will actually lower your Cd at the
same time it lowers your frontal area: less turbulence behind your shoulders, and MUCH less
turbulence in your concave "lap" area, which gets increasingly protected from the wind by your
trunk as you get lower in front.
As you point out, it's often hard to separate Cd and frontal area. It's possible to create
structures with lower Cd and higher frontal area than non-aero structures for the same purpose. The
classic example is an teardrop shape versus a round shape (say, spokes). The teardrop can have a
much larger frontal area than the "ball" before their total drag becomes equal.
--
Ryan Cousineau, [email hidden] sfu.ca~rcousineOpen ↗ President, Fabrizio Mazzoleni Fan Club