Blown away

Damn. It’s windy again. I mean really windy. I can hear it crashing against the west wall of my house, tearing across the roof, and rattling the screen doors. Our weather station says the wind is 38 miles per hour. With gusts to 45.

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Artwork: ClipartFox

Not a great day for flying.

Not that I couldn’t fly, but I’ve decided to stay home and curl up with a good book rather than take on the wind gods. But before I do—curl up with the book that is—this is a great opportunity to discuss wind and airplanes. In the past, we’ve talked about how wind blowing in the opposite direction of the airplane’s course (a headwind) can slow down your progress in getting to your destination, while wind blowing the same direction as the airplane’s course (a tailwind) can get you there faster. And if you are down low in the atmosphere, strong winds can make for a bumpy ride, as the wind creates turbulence as it flows over, around, and through ground features.

But other than these issues with ground speed and smoothness of ride, wind doesn’t have much of an effect on airplanes in the air. Just like a fish is largely immune to the actions of the water it’s swimming in, airplanes don’t care much about the wind.

Except when they are taking off or landing.

Then wind matters. A lot. Especially if the wind is from one side or the other, what’s called a crosswind. By definition, a crosswind is any wind that’s blowing across a runway. Most airplanes really don’t care for crosswinds. The crosswind will try to blow them off the runway that you’re trying to take off from, or land on, and the trick to operating in a crosswind is to use the controls of the plane to counteract the effects of the wind.

Unless the wind is so strong that you run out of control travel.

Simply put, at some amount of wind there just isn’t enough aileron or rudder authority to overcome the wind. Taking off or landing in these conditions pushes you off the runway and you can end up in a sad little pile of twisted aluminum in the weeds downwind of the taxiway.

So how do we pilots know how much wind is too much for our airplanes so that we don’t end up in a sad little pile of twisted aluminum?

I’m glad you asked.

First, know that the wind practically never blows directly across a runway. It generally blows at some sort of an angle to it instead. This brings us to our aviation term of the day: Crosswind component. It’s the percentage of the wind speed that’s acting in a crosswise manner adjusted for the difference between the direction of the runway and the direction of the wind.

We can use a table, graph, or an app to determine the crosswind component.

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I grant you that at first this all seems a little obtuse, but it’s actually one of the most important aspects of aviation weather because all general aviation airplanes (at least modern ones) have what’s called a “demonstrated crosswind component” as part of their certification, and this number is printed in the aircraft’s operating handbook.

This number tells you how much of a crosswind your plane can handle, at least when it’s flown by a professional test pilot. So there are two things to consider: First, it’s not a maximum. The plane can probably handle more. And second, it doesn’t matter that it can probably handle more because most pilots probably don’t have the skill to fly the damn thing up to the demonstrated crosswind component in the first place.

Still, it’s a nice way to compare apples to apples when operating in different airplanes.

Most general aviation aircraft have a demonstrated crosswind component of somewhere in the 15-20 mph range (of course in most aviation circles, winds is reported in knots, so our range would be 13-17 knots).

But Tessie isn’t most airplanes.

Her design makes her the Crosswind Queen. But to understand why she is, I need to quickly introduce you to how crosswinds are handled in lesser planes. To keep it simple, let’s just focus on landings. When landing most planes in crosswinds, there are two basic techniques.

The most common technique is called a sideslip. The upwind wing is lowered to keep the plane from being blown off course, and opposite rudder is used to keep the plane from turning into the wind. This has you landing at a crazy bank angle, usually touching down on one main landing gear before the other, but it works.

The other way is to use the “crab” method: The plane is held level with its nose pointed into the wind. The ground track follows the runway heading, but the plane is flying somewhat sideways, hence the name “crab.” Right as you flare for landing, you need to kick the rudder to straighten out the plane for touchdown. Why? Because touching down sideways in most planes will rip the landing gear right off. One FAA course on crosswind landings states that crab landings require “timely and accurate action” in the final phase of touchdown.

OK. So sharp readers might have noticed that both techniques require using the rudder peddles. But the Plane Tales Plane doesn’t have rudder pedals, as her rudders are physically attached to her ailerons, so you might be thinking, how on earth can she handle crosswinds at all, much less be Queen of them?

Right. No side slips for me. If I lower the upwind wing, the plane will turn, as I have no way to apply opposite rudder. I would end up circling the runway numbers, never landing. However, I can fly in a crab, no problem. Still, with no rudder peddles, how can I take that last-minute “timely and accurate” rudder kick to straighten the plane?

I can’t. But I don’t need to. And the secret is in the Ercoupe’s main landing gear design, not in her rudder operation. Ercoupes have a robust trailing link main gear that makes them pretty much immune from side load damage. In a ‘Coupe you hold the crab all the way trough touchdown, when the forward motion of travel will pivot the plane nicely parallel to the runway seconds after landing on it at a crazy angle. This unique way of returning to earth has created the legend that Ercoupes have castering landing gear. They don’t. It’s just simple physics.

It takes time for pilots trained in less robust planes (including me when we first had Tessie) to overcome their training-instilled fear and simply land the damn plane sideways, but it works. And because there’s no need to cross-control to handle the winds, it means Coupes can land in winds that leave the rest of the fleet grounded.

The “book” crosswind component of the later Ercoupes is 25 mph, already 5 mph higher than almost any other general aviation airplane; and many experienced Ercoupe pilots don’t even pay attention to crosswind components until it exceeds 30 miles per hour (roughly double what the typical plane can handle).

So why aren’t I flying the Crosswind Queen today? Is the wind beyond my personal skill?

Actually, no. I’m one of those who have landed with crosswinds somewhere in the 30 mph range. So I can do it if I need to.

But there’s a difference between what’s possible, and what’s fun. So if it fell to me to deliver the serum that would stop a plague today, I would be out there right now, not even worrying about the wind. But while Tess is Queen in the crosswind, such strong winds bring a lot of turbulence. And she’s no Queen in turbulence. Her lightweight and wing loading make her like a bucking bronc in weather like this.

What’s wing loading, you ask? That’s a subject for another day…

 

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