Monday, June 15, 2015

Riding Faster than the Wind

In my last post I described riding through the winds of the Outer Banks of North Carolina. I also, awkwardly, and completely not naturally--Paps was raised on a goat farm, after all--had the chance to steer--navigate, I guess, is what they call it--a sailboat.

The boat's owner designs and builds very fast sailboats. I asked if they are carbon fiber, and, of course, they are. Crabon? Go on. I asked more questions, like about how fast they go.  He said they go fast. Is it dependent on the winds? Yes, but...and here's what blew my mind...some of these boats, he said, can travel faster than the wind that pushes them forward.

That seems impossible. Imagine wind as an invisible hand, pushing a boat along--how can the boat move faster than the hand?

What's especially impossible about this is that the boat actually travels fastest into the wind, not with it.

Something is clearly different about how a sailboat addresses the wind and how a bike and a rider address it.

Square Rigged Ships
The ship below--the kind of ship that made the voyage from England to the New World in the 16th and 17th Centuries--is harbored in Manteo, NC, the very harbor from which we sailed. It uses square sails that act in the same way Performance brand cycling tops do: they catch the wind like a bag. A ship rigged like this can only move with a tailwind. It can also never move faster than the wind, unless you hide a motor inside it.
Queen Elizabeth II
Aerodynamics in cycling are, for now, solely concerned with minimized drag. That is, becoming the opposite of the Queen Elizabeth II. We want to catch as little of the wind as possible, whereas square-rigged sailboats of this type were designed to catch as much wind as possible.

Sails as Airfoils
Romans, Arabs, and others used triangular sails to sail into the wind. These sailors used the same effect, of different air pressures over a large surface, as the Wright brothers would later use to fly.

Sails are vertical and force travels laterally.

Wings are horizontal so the force pushes the plan vertically, as lift. 

Just imagine how an airplane wing produces lift. Then look at the sails of this America's cup boat--and it's clear how that translates to forward motion in sailboats with sails shaped like wings. 

As these boats head into winds, the apparent wind increases (e.g., in the same way the force of impact of two bicycles traveling at 20 mph is 40mph), the sail generates even greater "lift", the boat goes faster, apparent speed increases, and so on.

And that's how a boat can travel at 15 knots into the 10-knot wind. 

Not that we care, except as it might play into going faster on the bike.

If you're looking for a reason why you suck at time trials, blame Bernouli's principle, which states "in a perfect fluid, an increase in speed and a decrease in pressure occur simultaneously."  You have a bunch of high pressure air all balled around your front, and behind you have a vacuum where you've just pushed the air out of the way with your huge head and fat ass. All the dense molecules of air are trying to get back to that vacuum behind your ass. 

That's all fine, except you're trying to go forward. You've got to fight all of them as they work their way backwards...and that accounts for why you suck--you get hosed by Bernouli.

Bikes as Airfoils
Except what if your bike or you was shaped less like a square-rigged sail, and more like the triangular sail? What if you, like them, could use at least generate forward motion from a headwind?

Sailing requires--as I discovered in my brief time on a sailboat--constant adjustment. You get "luffing" and inefficiencies. You have to tack, moving the sail dramatically to opposite sides of the boat. And you never really head directly into the wind. 

This presents a number of challenges: (1) Unless we ride on roads as wide as the open sea, bikes can't tack (although I have paperboyed my way up a few nasty climbs); (2) our bikes and our bodies are not as modifiable as are sails. We can't wear clothing or build traditional bike frames in a way that allows us to shift them to take advantage of every different wind angle.

A bike or skinsuit that cheats Bernouli is the best we can hope for, without some serious foam foils--and those are, of course not UCI kosher. We'll never be glad to see a headwind.

And that's a bit sad. Every time I ride into a wind, now, and especially a cross/headwind, I'll think about how I'm missing out on all that energy.

What about a helmet sail? I'm thinking maybe a jib, main, spinnaker. Some hardware. Hook it up to a CPU. Get an anemometer. Write some software. Pop that baby up during Church Creek. Get a "Suck it, Bernouli" tat.


Anonymous said...

What about Zipp's "negative drag"? Oh wait, that has been debunked, along with the dimples:

Kevin Cross said...

I was wondering if a company had tried to sell this! Thanks, anon.