Friday, October 14, 2005

spinning class

For the better part of the last five years, a good portion of my flight training has been devoted to practicing stalls and avoiding spins. The idea that spins should be feared is drilled into every student from day one, and consequently, I am terrified of them.

I had never even come close to entering a spin until last Friday, when I deliberately entered one with my grizzled flight instructor on board. Spin training is one of the final requirements for my own flight instructor certification, and also the coolest thing I have ever done in an airplane.

Which is why I'm subjecting you to a rudimentary spin-training lesson.

Before we begin, I need to do some explaining and improve your aviation savvy. A spin -- what some of you might consider a death spiral toward the ground -- results from a stalled condition of the plane.

What the hell is a stall, you ask? You'd probably be surprised that you already know the basics.

Contrary to what it might sound like, this is not akin to your car keeling over on the side of the road. An aviation stall has nothing to do with the engine dying; it's a consequence of airflow separating from the wing.

You know when you're driving down the road, stick your hand out the window and follow the grooves of the wind by moving your hand?

This is similar to how a wing generates lift. Smooth airflow around the wings produces lift. As you probably noticed with your hand out the window, if you tilt your hand upward, it rises. If you tilt it too far, your hand flops down.

The same thing happens in the airplane. If we pitch up too high, past what we call the critical angle of attack, that smooth airstream across the wings gets broken and we lose lift. Still, our wing is better-equipped to handle the recovery than your hand.

Generally speaking, when the plane can no longer sustain flight past the critical angle, the nose falls forward. But once we are back under that critical angle, our wings start producing lift again and with some help from a pilot, we recover from the stall.



This is going to get a little complicated next, so feel free to take a break now if I've put you to sleep so far.


OK, welcome back.

The above recovery is predicated on the airplane being in coordinated flight while we go through the stall. Much like a car, an airplane can skid and slip through the air.Much like in a car, these things are bad.

Allowing slipping and skidding conditions to persist results in uncoordinated flight. And flying uncoordinated in a stall is what can turn our ordinary stall practice into the much dreaded and feared spin.

Why does uncoordination causes a spin? I'm thrilled you asked.

Go back to our example of the hand out the window. Now imagine you have one hand out the left window of your car and one out the right window. Yes, you have really long arms. Because of the slip/skid, the lift-and-drag forces acting on each wing are different.

Although both wings are stalled, they are stalled to different extents. The plane rolls and yaws in the direction of the more-stalled wing.

For the sake of example, let's say we've created uncoordinated conditions so our left wing is more stalled than our right wing.

The right wing, less stalled, is producing more lift than its counterpart. So it rises. This rolls us toward the left while the other wing falls. At the same time, the more-stalled left wing produces more drag than the right side, and this yaws us to the left -- think of sitting in your office chair and turning.

Simultaneously, we are sharply rolling and pitching to the left. We seemingly roll onto our back, start screaming like lunatics at a full moon, shit our pants and then spin toward the earth with a windshield filled with nothing but terra firma.

If you go down to No. 4, this video shows an aggravated stall followed by a one-turn spin. Seeing this picture will hopefully make what I've written more sensible and also give a good visual picture.

For the record, the dude in the video only does a one-turn spin. My instructor and I did three four-turn spins, which is a bit more lengthy and exhilarating.

And my pants are still in the washing machine.



At 9:36 AM, Blogger Erik said...

You can be my wingman anytime, Maverick.


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