Express elevator, going down

The other day my instructor and I flew over the shoulder of the volcanic ridge that crowns the island of Hawaii. It was a spectacular flight that took us to the heavens at five thousand feet. The chilly air dimpled our skin, wisps of cloud fluttered at our feet, and stark sunshine streamed into the cockpit. Cows in the fields below looked like pepper spilled on moss.

On the other side of the ridge, I was happily filming some video when he hit me with the first of two surprises that day.

"Autorotation in three-two-one."

Without even giving each count a full second, he flattened the rotor blades and cut the throttle to enter an engineless descent. I was caught a bit by surprise, and you can see the lurch in my footage as gravity is momentarily lost.

"You asshole," I jabbed, jokingly. I tend to curse when I get suddenly spooked by heights, so much so that my first instructor instituted a three-expletives-per-flight rule.

Besides being used for emergency landings, autorotation is the express elevator down in a helicopter. He was using it to quickly lose altitude down the long slope to our next objective, the seaside cliffs of the northern shore. Halfway down, it became apparent that our descent was too steep to clear the cliff edge and glide out over the sea.

Rather than re-engage the throttle, he chose to demonstrate a peculiarity of the helicopter's design. By allowing rotor rotation to slow to 90% of normal RPM, a Robinson R22 pilot can maximize the glide angle in an autorotation, buying more horizontal distance per altitude lost.

It's a maneuver not to be taken lightly. At any value below 97%, the Low RPM Horn begins wailing, alerting the pilot of the vulnerable condition. At any value below 80%, the rotor stalls, and you fall out of the sky.

So there we were, falling almost 2000 feet per minute without any engine power, the rim of a cliff looming to cut short our approach to the sea, and the Low RPM Horn lamenting our imminent demise. I'm proud to say I wasn't really fazed; I just kept filming.

My instructor's tactic worked, and we cleared the cliff with room to spare. I've shared a short clip below. As you watch it, notice how our altitude changes relative to the clouds as we float down from a mile high to nearly sea level.



I'll share my instructor's second surprise that day in another post.

Somewhere beyond the sea...

The other day I mentioned "good news," but never finished the thought. That day, I had my flight evaluation with the chief instructor. It went well; by some miracle I demonstrated a respectable entry into autorotation.

The procedure calls for a rapid "Left hand down, right foot forward, right hand back," to settle into a controlled, engine-less descent. It's a precise sequence.

Going into the evaluation, I'd never done it without hands-on assistance, so my procedure that morning was "Left hand down, right foot forward, right hand back, pray." The helicopter cooperated, and I passed, clearing me for solo flight.

Which brings me to this morning: I flew for the first time by myself!

My instructor and I did a short flight to begin, then he got out and cut me loose to fly around the airport a few times. On the radio, I introduced myself as a first-timer, so the control tower was kind enough to slow their machine-gun chatter to a more intelligible pace.

See if you can spot the use of ETL in this video. There's nobody in the bird but me, and a beautiful day for it indeed.

[Edit: This video was originally set to music, Bobby Darin's "Somewhere Beyond the Sea." It was much better that way, but the copyright authorities objected. Oh well, just sing along in your head.]

Marauding manta caught on tape

By some stroke of fantastic luck (I guess?), the underwater videographer was still rolling when that manta ray did its dastardly deed. Be sure to read what happened before watching the video, so you know what to look for. (By the way, I do actually have two arms; I put one in my wetsuit because I was cold.)

A very personal wildlife experience

There are no helicopters in this post, but it's still worth making. Last night I got kicked in the nuts by a manta ray.

I was on a nighttime snorkel/dive adventure with a local outfit. The way it works is all the divers sit on the bottom, 80 feet deep, and all the snorkelers float on the surface, and everyone points their dive lights into the middle. The column of light attracts clouds of plankton, creating a Las Vegas-style all-you-can-eat buffet for the mantas.

There were over a dozen of them, averaging ten feet across and a thousand pounds each, swooping in great inverted loops with their alabaster bellies brushing just inches from us snorkelers. You can see where this is going.

I was on the periphery of the group, and fairly consumed by the experience, so I didn't notice when all the divers and snorkelers started leaving, taking their lights with them. Before long, I was the only light left, which is the equivalent of being that last lonely triangle of double-fudge cake when a busload of ranchers from the Arkansas Cattlemen's Convention is just finishing their buffet.

Suddenly, every manta within five miles wanted their mouth right in front of me. I was a fragile slice of humanity trapped in eight inches of water above a horde of ancient giants swirling up out of the gloom to assault my tiny candle.

Right about that time, I heard the dive guide call my name to tell me to get moving. I popped my head out of the water to listen, which thrust my hips slightly down into the water.

They may look graceful when they swim, but getting hit by a thousand pounds of anything, even if its a glancing blow, is pretty rough. It's like getting racked by a Volkswagen. Luckily, my thigh took most of the shot, or I might have become the tragic dead end to an otherwise long line of vibrant male virility.

Next time, I'm wearing a cup.

Why don't helicopters go straight up?

If you watch helicopters in action, you may notice that they usually take off and land using a gradual slope through the air, similar to airplanes.

Given that helicopters can rise and descend vertically, why would a pilot opt for a more modest angle?

Three words: Effective translational lift.

Helicopter rotor blades are basically airplane wings that spin in a circle (the rotor disc). Like wings, they create lift when air moves smoothly across their upper surface.

When a helicopter is hovering without any forward movement, it's dragging the air above it straight down through the rotor disc. The blades still create lift, because they are moving horizontally through the air like wings, but the effect is partially corrupted by the air that is descending vertically.

Due to this confused or "dirty" air, the engine has to work pretty hard to generate enough lift to maintain a hover.

As a helicopter adds forward speed, the dirty air is pushed farther and farther to the rear of the rotor disc by undisturbed "clean" air ahead. The faster the helicopter moves forward, the cleaner and more horizontal the air flow, and the greater the lift generated by the blades.

This dynamic is called effective translational lift, or ETL. Effective translational lift increases as the helicopter accelerates forward during take off, eventually reaching a strength that enables the pilot to pull the helicopter into the sky, similar to an airplane.

Weirdly, with ETL the helicopter can actually climb using less engine power than what is required to hover.

Although helicopters do typically have enough muscle to climb vertically through dirty air, it's safer to take advantage of ETL. A vertically climbing helicopter is more vulnerable to an irreversible -- and likely fatal -- rotor stall, for reasons I'll explain in another post.

If a helicopter is heavily loaded, or under certain conditions of air temperature, air pressure, humidity, and wind, the pilot may have no choice but to climb using forward movement and ETL.

In Chickenhawk, a riveting first-hand account of the helicopter war in Vietnam, pilot Robert Mason is forced to rely on ETL to lift his overloaded Huey -- filled with infantry -- out of battlefields being overrun by Viet Cong.

The same dynamic applies to landings. Rather than descending vertically, helicopter pilots will typically maintain forward speed (and ETL) all the way to the final hover over the landing spot.

A little make-believe

I have some good news from school today, but not much time, so I'll have to get to that later. For now, a quick anecdote...

Yesterday in the local coffee shop there was a kid with a helicopter on his t-shirt.

I told him I was a helicopter pilot (ok, that's a stretch, but easier than explaining the larger truth).

Although I couldn't actually take him for a helicopter ride, he did end up wearing my headset and sunglasses, and I taught him how to ask air traffic control for clearance to land.

Here's a picture, I think his name was Laith (Leyth?). He seemed to enjoy pretending to be a helicopter pilot. And for the record, I did too.

I can fly a helicopter

I had a great flight today, and I figure I should make a note of it here to counterbalance all my bellyaching about fear and crisis.

Today, for the first time, I managed every segment of the flight, from pick up to set down, without needing help from my instructor. It was sloppy in places, but even if Grant hadn't been there, I still could have taken off, flown around, and come back in one piece.

Not surprisingly, I had another first: As soon as the lesson was over, I wanted to go again.