Thursday, April 26, 2007

My Brain on Drugs

Just returned from a long week on the other coast, fortunate to have escaped most of the heavy rains and high wings that had plagued the area for several days. We had a delay in New York, waiting for the aircraft for our connecting flight. When the aircraft finally arrived, was unloaded and serviced, we were over a hour late pushing back from the gate. We then joined what I can only describe as a long rumba line of aircraft that snaked its way through the dark around practically every square foot of taxiway space while we made our way to one of the active runways. At one point we were perpendicular to a taxiway and I saw a very long line of aircraft in front of us. The captain announced a few minutes later that we were number 22 for takeoff.

On approach to our destination, bumping and grinding through heavy precipitation, I had a ring side seat to the icing conditions. From my window seat by the leading edge of the wing root and with the landing lights turned on, the layer of mixed ice on the leading edge was easy to make out. This would have been a concern in the smaller, slower aircraft I fly, but the crud just slid off as we descended out of the clouds. Having a heated wing and 220 knots of airspeed is a good thing.

During part of our stay, a long-time friend who is a rural doctor and commercial helicopter pilot gave me my first taste of ... drum roll please ... actually flying a helicopter. While I'd ridden in helicopters in the past, I'd never occupied a pilot seat or touched the controls. The aircraft was a Schweizer 330Ci training helicopter and I found it to be solid, well-made, and very well maintained.



Prior to the flight, I perused various books on helicopters lent to me by my friend. The first one I picked up was more about aerodynamics and involved quite a lot of physics and math. I quickly switched to a book written in a more pragmatic style. My first goal was simply to understand the functions of the various controls in a helicopter and most of the books I read gave a pretty good explanation.

As an experienced flight instructor, I was struck by the assumptions made about the reader in each of these books. It was almost as if they expected that you already knew quite a bit about flying a helicopter and that you just wanted a review. My sense early on was that my understanding would be limited without some concrete examples of the topics being discussed, but I pressed on. I was both excited and a bit frustrated by being a beginner again, but I managed get a very basic handle on the flight controls in a helicopter. Here's my beginner's understanding.

The helicopter's main rotor is just a rotating wing. Unlike the fixed wing of an airplane, the pilot of a helicopter can change the pitch of the rotating wing using a flight control called the collective. Resistance is futile - you will be assimilated ... Since there are a few ways to change the rotor's angle of attack, the term "pitch" is preferred for describing the rotor's blade angle. The collective is a lever that resembles a parking brake in a car and one is situated next to the seat, under each pilot's left hand. Pulling the collective up will uniformly increase the rotor's pitch, thereby increasing the amount of downward thrust generated by the rotor. Given enough power and the correct inputs on the other controls, this means you probably will be going up straight up vertically. Lowering the collective will generally make the aircraft descend vertically.

Like a propeller, the rotor has a desirable RPM range and without sufficient RPM, you're not going to get much, if any, lift. Low rotor RPM is dangerous while you're airborne so many helicopters, like the Schweizer, have a low rotor RPM warning light and a governor that works to keep the RPM in the desired range. Even with an RPM governor, the pilot has to be careful to increase engine power during certain phases of flight, such as before you raise the collective to climb or while hovering, to keep the rotor RPM from decaying. If the RPM gets too low in flight, the rotor may stall and I'm told that is dangerous and the results are unpleasant.

In the Schweizer, the throttle is a twist grip on the end of the collective. One negative transfer of learning is that you twist the throttle grip opposite the way you would twist a motorcycle's throttle. After a bit of reflection I realized that this arrangement made sense - when you extend your arm to lower the collective, you generally need to decrease the throttle and releasing the curl in your wrist is a natural movement while extending your arm. Curling your wrist to increase the throttle goes well with bending your arm when you raise the collective.

For every action, there is an equal and opposite reaction so many helicopters have a tail rotor that generates lateral thrust to offset the main rotor's torque. This keeps the aircraft body from rotating opposite the direction of the main rotor. The tail rotor turns at a much higher RPM and has two anti-torque pedals that increase or decrease the lateral thrust by increasing or decreasing the pitch of the tail rotor blades. For the purposes of my flight, I conceptualized the anti-torque pedals as acting in a similar fashion to rudder pedals in a fixed wing aircraft. Another negative transfer of learning from fixed wing flying is that when you increase power and/or raise the collective to takeoff, you need to add a significant amount of left anti-torque pedal pressure to offset the main rotor's increased torque.

The cyclic is the last control I needed to ... er ... get a handle on. The cyclic is a stick that resembles the control stick in a tailwheel airplane. The cyclic allows the pilot to increase or decrease the pitch of the rotor at a certain point in the plane of rotation, thereby causing the aircraft to move forward, backward, left, right, or anywhere in between. In the Schweizer the cyclic is ultra-sensitive, especially while hovering.

During my flight, I mostly experimented with the cyclic while flying at altitude. At first I was a bit flummoxed by how sensitive the cyclic was. While flying through some turbulence and trying to make cyclic inputs, I mostly succeeded in creating pilot-induced oscillations. This is where my friend made just the right observation - the body of the helicopter is like a pendulum suspended beneath the main rotor. With just those few words, I suddenly was able to visualize how to dampen out the oscillations with the cyclic. Everything fell into place and all at once I was flying smoothly and reacting to the turbulence in a productive way. I'm still amazed when I think about how quickly I stabilized the aircraft and this led to my first epiphany: Flying a helicopter is a lot like trying to walk briskly while holding a full cup of coffee without spilling any.



We flew from the airport to the small town where he lives with his family, then out over a lake covered with a layer of thawing ice. What looks to be a landing strip on the ice was actually a drag racing area created for the local snowmobile enthusiasts. Most helicopter flying is done in the 600' to 1000' AGL range, which seems a bit odd for a fixed-wing pilot, but the view is simply amazing.



The light helicopter I was flying in is not very practical for long-distance flying due to the 70 to 80 knot cruise speed. I have newfound respect for Greybeard's numerous flights ferrying R44 helicopters across the country. But during my flight, we were able to see some sights that would have been difficult, uncomfortable, or just plain impossible without the Schweizer.



When we returned to the airport, my friend did some hovering practice and demonstrated a confined area landing and takeoff. He then hovered over to an area where some orange traffic cones had been lined up and began carefully maneuvering such that he knocked over one of the cones. Then he really began showing off by hovering and using one of the landing skids to carefully nudge the cone back into an upright position. While he was flying the pattern, I managed to take a photo of two Lockheed Constellations in various stages of restoration.



With my friend handing the anti-torque pedals, the collective, and the throttle, I tried my hand at using the cyclic while hovering. Again, visualizing the helicopter as a pendulum helped me to do a credible job, though I discovered another negative transfer of learning for fixed-wing pilots. It is very counter-intuitive to pull back on the collective during hovering. I found I had a constant inner conversation with myself that this was okay to do. There's something about being close to the ground and not moving that makes a fixed-wing pilot want to push forward on the stick. Hey Greybeard, I might just be a fixed wing pilot who could learn to hover in a couple of hours!

It was great visiting with friends and family. And the cities all have a different atmosphere, given the older buildings made of bricks, of all things. Oh, and I had a job interview and an offer of employment and all too soon we crawled through traffic on our way to the airport for the flight back to the Left Coast.

9 comments:

eric said...

Sounds like a really great time. I've got .5 in a R22, and had a ton of fun doing the same basics you got to try your hand at in the Schweizer. I'd love to move over to the helicopter world (rather than up to the airline one), but cost is pretty prohibitive.

Still, down the road it's something I definitely hope to do. My old roommate is on his way through the Army's helicopter qualification course at Ft. Rucker now, and he's promised to trade me a couple of rides (somehow) in exchange for a few in the Yankee... I guess that will have to fit the vertical bill for now.

Colin Summers said...

"Oh, and I had a job interview and an offer of employment..."

Tease tease tease...

"Chickenhawk" is an awesome book about how to fly a helicopter. It happens to be set during the Vietnam war, but the interesting stuff is all about flying a helicopter.

Anonymous said...

You said that in fixed-wing planes, you can't change the pitch of the wing. I'm not a pilot, but don't the aeilerons and flaps change the "pitch" of a fixed wing? Thanks.

eric said...

East coast, offer of employment... JetBlue? ;)

flyaway said...

While doing my preflight today I saw a helicopter doing the equivalent of touch and go's (I think). He was coming in fast down the runway and losing altitude pretty quickly. Then he would suddenly level (at maybe 10 feet) and the continue down the runway and suddenly climb back into the pattern. I was pretty impressed. The first time I saw it I thought he was going to hit the runway for sure.

Doug
http://flysomewhere.blogspot.com/

John said...

Eric,

No, it wasn't Jet Blue, though we did fly that airline to and from the East Coast. I'm hesitant to give details about the job offer because I'm not in a position to know yet whether or not I can accept the offer.

Anonymous,

In a fixed-wing aircraft, a line from the center of the leading edge of the wing to the trailing edge is called the chord line. The angle of incidence is the angle between the chord line and the longitudinal axis of the aircraft. That angle is fixed.

The angle of attack is the angle between the chord line and the relative wind.

In a helicopter, the angle between the chord line of the rotor blade and the longitudinal axis of the helicopter is not fixed - it can be changed by moving the collective. The angle of attack in a helicopter is more complicated as it depends on the motion of the helicopter (and consequently the rotor).

Flaps and ailerons in a fixed-wing aircraft alter the wing's chamber, but not the angle of attack or angle of incidence.

Christian said...

I did 1.1 in a helicopter, and I decided that unless I somehow find a gold mine, I won't be pursuing it. There are too many "negative transfers" from airplane flying - the push-over reflex just being one of them, and the only way to overcome them is by lots of practice...

Greybeard said...

So, I take off on vacation and don't check any blogs during my 10 day stay, and you go and get into a fling-winger! Good for you.
Are ya bitten?

Yeah John, you just might be that one in a thousand that takes to it naturally. Then again, remember that your Bud was controlling the pedals during the time you were using the cyclic. There is some stimulation interference between the yaw caused by the pedals, and the horizontal movement of the helicopter in the hover caused by the cyclic. Most students will allow the machine to yaw with the pedals, but try to stop it with cyclic control, resulting in some interesting attitudes. Helicopter instructors, more than anything, ride along just to keep the student from making scrap of the machine until they learn what each of the controls do and that movement of the collective requires a corresponding movement of the anti-torque pedals. Normally that happens at about the five hour mark. I'd like to see if that also applies to you!

Go sign up, then blog about it!

John said...

Greybeard,

Thanks for your observations. Of course I was just joking about being a heli-creature whiz.

I would love to do a helicopter add-on, but my lottery tickets have yet to pay out the requisite dough. Now if I could find a good helicopter simulator that was reasonably priced, it might make the training more cost-effective.

Some day ...