Army helicopter school (III): Autorotation...
by John DeWalt
The big milestone in flight school is the first solo flight. The instructor finally thinks the student can survive a few minutes without the instructor at his side to prevent fatal blunders. This generally occurs soon after the student grasps the input-out principle and stops over-controlling the aircraft. The day of the student’s first solo, he goes through an initiation ceremony: he’s flung into a swimming pool (they let you remove your wallet and watch) by all the other students. Every student has pictures of that event: the wind-up, the flight, the splash, the proud, grinning, drenched student climbing out of the pool.
Half a day of classroom instruction began the first day and continued throughout flight school. But the army did a surprisingly innovative thing. It used “programmed texts.” The format of these texts was to provide a page or two of information followed by several pages of multiple-choice questions. Each question was followed by instructions. If you answered a, go back to page x of the text. If you answered b, go back to page y. If you answered c, go back to page z. If you answered d, you answered correctly: proceed to the next page.
The army didn’t have much confidence in the intelligence of its students. Each new page of information was a mere nugget, and you’d have to be a moron to give a wrong answer to the multiple-choice questions. I never had to return to a prior lesson and was able to whip through those books in no time.
Did I say that half a day of classroom instruction continued throughout flight school? It didn’t, really. After about a month, we’d still spend half a day on the flight line, but we were released to do our classroom work at home with “programmed texts,” and given credit for half a day’s work.
From that point on, I had it made. Half a day flying and fifteen minutes studying. We’d be tested every day on the previous day’s homework before being released to go home and do it again; I always got 100% on the daily quiz. Then I’d have the rest of the day to explore huge distances around Fort Wolters on my Beamer. I was having the time of my life...
After the uncertainty of the first two weeks, the remaining seven-and-a-half months of flight school were wonderful. The instructors parceled out new techniques parsimoniously so they were not difficult to master. Once we’d acquired a new skill, there was plenty of practice time to perfect it. There were exceptions, of course, so flying remained a challenge throughout the course. As every pilot knows, emergency procedures are a constant part of flight instruction, and they aren’t easy.
What do you do if you’re flying along and your engine quits? How do you land a helicopter without power? Believe it or not, it’s a lot safer than landing an airplane without power, but it’s not easy.
It’s safer because a helicopter needs a lot less space to land. Even without power, the aircraft can land with almost no forward airspeed—in other words, descend almost vertically, and stop immediately after landing. It is feasible to land in a tiny clearing. An airplane, on the other hand, must maintain a significant forward airspeed and needs a long strip to land on. Flying over forested or hilly land, an airplane might find no suitable landing strips, whereas a helicopter can always find a landing spot.
I’ll explain the principles as simply as I can. The main rotor blades of a chopper are big and heavy. Consequently they have a lot of inertia. It takes a lot of force to make them slow down from the rate of rotation they were in before loss of power. During normal flight, the engine drives the rotor blades, and the pilot adjusts the “pitch” of the blades to maintain altitude. To keep from losing altitude, the pilot uses the collective to maintain pitch in the blades, and the main rotor blades function as a big propeller pointing straight up. The more pitch in the blades, the more the propeller pulls the helicopter up. Of course, it takes more power to increase pitch and increase altitude.
When the engine quits, the helicopter starts to fall. (That’s a surprise, isn’t it?) But if the pitch in the blades is reduced to zero, the blades, with their great inertia, continue to rotate at the same rate though they provide no lift. When the engine quits, the emergency procedure is to slam the collective pitch control lever to the bottom instantly. The blades then provide no lift, the helicopter falls, and the blades continue to rotate at the same rate. This is called “autorotation.”
While autorotating, the pilot picks a landing spot and heads for it. When he is around 50 feet above the spot, he pulls the collective upward rather sharply. This increases the pitch in the main rotor blades which makes them provide lift, thus slowing the descent. It takes energy to stop the descent and because the engine is not driving the blades, they immediately begin to slow down. The big heavy blades with all their inertia can stop the descent entirely before they slow down enough to lose their lifting power. So if the procedure is done properly the helicopter can be landed quite gently in a very small space with no power.
There’s a fly in the ointment. You guessed it: the timing is tricky. If the pilot stops the descent too early, the blades will run out of steam too far above the ground and the chopper will fall the rest of the way. If the pilot waits too long, there isn’t enough altitude to slow the descent and the chopper will make a controlled crash. But these are mere details. In principle, it’s quite safe to land a helicopter without power.
But it’s not easy. I hate to think of how many hours I practiced autorotation. And of course, the army figures that if your engine quits probably something else is going wrong as well. So engine failure techniques were practiced, as often as not, in conjunction with a separate emergency.
What happens if your engine quits at night and you can’t see where you’re going to land?
That’s easy. The aircraft has a searchlight on the bottom. Use it.
That’s too easy. What if your engine quits at night and the aircraft suffers a complete electrical failure at the same time so you can’t use the searchlight? I don’t remember the precise answer to that one. It begins to get ticklish.
Solo sessions were without question the most most fun part of flight school. They were a chance to improve one’s skills without an instructor at one’s side, constantly criticizing every move. They were a chance to goof off.
Fort Wolters, Texas is surrounded by many, many miles of empty land. Each student, during a solo session, would leave the airfield, fly a good distance off, then spend the hour practicing a prescribed list of techniques assigned for the session. During the following session, the instructor would evaluate his performance of those techniques then teach another one or two which would be practiced during the next solo session.
Lest I give the wrong impression, I graduated second in my class of one hundred, so I didn’t spend all my time goofing off. Nevertheless, solo sessions afforded an opportunity to go beyond the assigned lesson and practice skills that weren’t in the curriculum.
Texas began to get hot as summer arrived, so our OH-23 training choppers had the doors removed. The downdraft from the main rotor made the cockpit a veritable wind tunnel. It was a challenge to take my hands off the controls long enough to light a cigarette in all that wind.
The cyclic, collective, and throttle were equipped with friction rings which controlled their rigidity or resistance to movement. The more you tighten down on the friction rings, the harder it is to move the controls; they tend to stay where you put them. This was necessary to light a cigarette.
Match after match would go out. I found, as I struggled with a cigarette, that if the aircraft started to leave the straight and level path I intended, I could control its path simply by leaning to the right or left or forward or backward, never touching the controls.
This phenomenon interested me. I began trying to fly longer and longer periods with my hands off the controls. I got good at it.
I believed I had perfected the skill on the first day I spent the entire solo session flying hands-off. As soon as I left the airfield, I flew straight out, establishing the aircraft in straight and level flight at its normal cruising speed of forty or fifty knots, tightened the friction rings, then controlled the flight by leaning to shift the center of gravity. I flew straight out for half an hour, then made a huge 180° turn by leaning to the side with a little superfluous help from the tail rotor―I had my feet on the pedals; where else would I put them?―then flew home in the second half hour, all without touching the controls.
Oh, I thought I was clever! In this way I amused myself, honed some extracurricular skills, and smoked an awful lot of cigarettes. Not to worry, dear reader. Your tax dollar was at work paying for my education. Flight school didn’t cost me a thing.
One high point late in flight school was the movie M*A*S*H. Because Fort Rucker was isolated, not near any towns with movie theaters, the special services officer bent over backwards to provide good entertainment on post. As a result, the post theater screened M*A*S*H before it was released to commercial theaters. The flight students were thrilled because the movie, set in Korea, featured OH-23 helicopters, the same helicopters we used in flight training twenty years later.
It was uproariously funny to see the doctors and nurses and Radar getting away with irreverent if not actually insubordinant shenanigans. The flight students, my schoolmates, filling the theater just couldn’t stop laughing. Even though flight school was relaxed compared to IOBC and jump school, we were used to the demands of “military courtesy” and the need to recognize and acknowledge the privileges of rank and seniority. To watch the M*A*S*H characters making a mockery of those standards was hilarious. And of course, the OH-23 choppers, our same helicopters, flying in and out with injured troops added to the attraction.