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A nobody; a nitwit; a pilot; a motorcyclist; a raconteur; a lover...of life - who loves to laugh, who tries to not take myself (or anything) too seriously...just a normal guy who knows his place in the universe by being in touch with my spiritual side. What more is there?

24 July 2011

Flying The Sikorsky S-55, Part 1

Here I am, just landed after a one-hour cherry-drying flight. They stopped us short because it started raining again. Which means Travis and I will have to go out and dry the whole place again when the sun comes out. Oh-friggin'-joy.

Understand, the S-55 was designed in 1949 and produced through the 1950's. Helicopters have come a long way since then.

It took me a little while to get used to flying this strange machine. The control system is old and crude by modern standards. The three-blade main rotor has a diameter of 53 feet. But it only turns at about 220 rpm - very slowly in comparison to modern helicopter rotors which typically turn close to 400 rpm. The low rpm of the Sikorsky means that the long, limber blades can “whip” if you make sudden, jerky or aggressive cyclic stick control inputs (the “cyclic” is the main stick between your legs). The S-55 teaches…demands…you to be smoooooth on the controls.

The collective lever is located alongside the pilot’s seat on the left, and is hinged at the rear. It controls overall thrust of the main rotor. Pull up and all three blades change pitch at the same time. Here is an image taken from the FAA's "Basic Helicopter Handbook." It shows the controls of a small Enstrom helicopter, but all helicopters have similar control setups.

On the end of the collective is the twist-grip throttle, which as you would assume controls the rpm of the engine. In flight, the engine and transmission (i.e. main rotor blades) are "married." That is, if you increase engine rpm, you'll increase main rotor rpm. And vice-versa.

As you lift the collective lever higher, the main rotor blades increase their “bite” of the air. The more bite (we call it “pitch angle”) the more wind resistance (we call it “drag”). So they will slow down unless you increase the throttle to compensate. Thus, as you move the collective up and down in response to varying demands for power, you must also increase and decrease the throttle to keep the engine running at a very specific rpm.

Most modern piston engine helicopters have correlators that mechanically match the engine speed to main rotor pitch angle. Turbine-powered helicopters have speed governors that automatically control rpm. These devices make the pilot’s job a whole lot easier. Does the S-55 have one? Nope! Well, let me rephrase that: The manufacturer claims that there is a throttle correlator. However, if there is one installed, it doesn’t work very well. And by not very well I mean “at all.” This makes for a high workload - difficult at first for a guy who's spent the last, oh, thirty years flying turbine helicopters where you just set the throttle to "FULL OPEN" and leave it there.

Other Sikorsky helicopters I’ve flown have what we call a “heavy” collective. What this means is that even though the collective is hydraulically boosted, it will drop like a rock if you don’t deliberately hold it up. The S-55 does this as well. There is a crude friction lock, but they do not all work well on these sixty year-old helicopters. Most of these S-55’s have very heavy collectives. It feels like you’re lifting the whole helicopter up by your left arm. It quickly gets tiring. What we shorter pilots do is wedge our left knee under the collective to hold it up. Not the greatest solution, but it works.

The fourth control we have is for the tail rotor, controlled by two pedals. The tail rotor is that sideways-facing prop on the back of the helicopter that counteracts the torque of the main rotor and allows us to point the nose of the helicopter in any direction we want while hovering. Without it, the fuselage of the helicopter would spin uncontrollably under the main rotor. I think there’s some Newton’s Law that explains this. Anyway, that tail rotor is simply a big, controllable pitch fan. In the case of the S-55, the tail rotor measures 8’6” in diameter. The pedals my feet rest on control the pitch of the tail rotor through a linkage consisting of a series of stretchy cables and sloppy chains. Hey Sikorsky, were you perhaps related to that Rube Goldberg guy?

Modern helicopters have tail rotor controls that are hydraulically boosted; you control tail rotor pitch with the balls of your feet, like pressing the accelerator in your car. Not the S-55. This is a he-man helicopter! You stick your whole foot on the pedal and mash it like you’re trying to kickstart a Harley – or panic-stop your stuck-accelerator Toyota. Weird.

Did I mention the noise? The unmuffled 700 horsepower radial engine underneath my feet roars like a funny-car dragster at full throttle. The main rotor transmission located right behind my head also screams like a heavy metal rock band singer with his amp turned up to 11. Modern transmissions have gears that are cut on an angle so they run more quietly. Sadly, that particular bit of technology had yet to be developed when the engineers were laboring over the S-55 design. And soundproofing hadn’t been invented yet either. At least we have better noise-canceling headsets now. It's a wonder my father wasn't stone deaf. Oh yeah, and the seats suck (that was one of the first things I had to rectify – my poor, aching lower back!).

All in all, as crude as it is, the S-55 is a strong, dependable helicopter. Nothing fancy, no gizmos or newfangled electronic crap. Just a simple, basic helicopter that is well-suited for its role as a cherry-dryer. And in its own kooky way, it’s got a lot of, um, character and is actually a lot of fun to fly. But Lord almighty, do I miss my nice, modern, easy-to-fly, quiet, smooth, comfortable, turbine-powered Bell 206. My father must have been a real man to fly these things for as long as he did. Me? I am a wuss by comparison.


Anonymous said...

Your description reminds me of a comment by my DC-8 ground school instructor to the effect that someone had gone out some 50-odd yrs ago to measure exactly how much cable was used for the various engine and flight controls in the -8.....he had yet to report back on his findings.
Mechanical controls may be heavy, but they are rarely susceptible to indescribable, unpredictable, irrational behavior.
By the bye, I do NOT miss it.
Barbara & I are visiting Adrienne (and her newborn Sarah) in Jackson MS.....regards, Mike

Greybeard said...

Neat old bird.
You didn't mention the other thing that makes it a little difficult for us old motorcyclists...
The learning interference we faced with the throttle turning the opposite direction we're accustomed to!
We ARE spoiled with good governors, fuel controls, and correlators today, aren't we?
Hughes 269
Bell 47
Enstrom 280C
Hiller 12's...
Perfectly comfortable in 'em years ago, they'd WEAR ME OUT today.

Helicopter License said...

Woah, cool-looking chopper! 1949 to 1950? Was it restored? Maybe that's a dumb question. I've always been curious about the average life span of different helicopters and if it's changed over time. Love this post!

Bob Barbanes: said...

Helicopter License, since the S-55 was only built up until 1962, all that are currently in use have been restored (we call it "overhauled") numerous times. Life-limited components get replaced, and rebuildable components get overhauled. "New" engines are always available. As long as the external sheet metal and internal structure are solid (not corroded or cracked), a new coat of paint gets slapped on and the aircraft goes back to work.

Believe it or not, these old girls don't have a tremendous amount of flight time. The military kicked them out with not a whole lot of flight time, and let's face it, most of them have only been getting seasonal or limited use ever since.

There are operators of Bell 206's that have close to (if not more than) 20,000 hours. The one I flew in my last job has 12,000 hours - and you can't really tell it from a new one (well, you can if you're a 206 expert). With helicopters, you just keep replacing and replacing components on the same old airframe.

GB, since I've been riding motorcycles for at least as long as I've been flying, for some reason the throttle confusion never really bothered me. If the helicopter throttle were mounted on the right side then yeah, it would probably be an issue. Fortunately for us, the collective/throttle is on our left.

By the time I had 5 hours or so in the S-55, the throttle-twisting was second nature.

And Anonymous Mike, funny you mention that! The DC-8 and 707 must have had MILES of control cables! I always wondered how they kept all of them in proper tension?