Tag Archives: novels

Autorotation Explained

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A primer for non-pilots.

One of my pet peeves is finding inaccurate information in works of fiction (or non-fiction, for that matter). You can argue all day long that fiction is fiction and the writer can write whatever he wants. After all, fiction, by definition, is a made up story. That gives the author license to make things up as he goes along.

I agree that it’s fine to make up the story, but unless it’s a work of science fiction or fantasy (where it might be acceptable to change the laws of physics), it’s not okay to make up the details of how existing things work. I explored this theme in my post “Facts in Fiction,” and picked apart the work of a bestselling author in “Dan Brown Doesn’t Know Much about Helicopters.” Both posts were triggered, in part, by basic errors about how helicopters work that appeared in works of fiction.

The Question

“Facts in Fiction” was also triggered by an email message I received from a writer looking for facts about how helicopters fly. Oddly, I just received another one of those messages not long ago:

I’ve recently been writing a novel in which I have to describe the sound a helicopter makes, how they fly and things along these lines.

But there is a section of my book where a helicopter runs out of fuel and begins to drop. However, below them is a forest and they crash into the canopy. But in order to minimize damage the pilot uses autorotation to make the helicopter somewhat stable. I don’t want to be an ignorant writer that makes stuff up at the expense of fact. I’ve looked up autorotation but it’s still not clear to me- would you be able to help me out with how a pilot would initiate autorotation (in simple terms!)

Again, I applaud this writer’s desire to get it right. The aviation community certainly doesn’t need yet another work of fiction that misrepresents basic aerodynamic facts.

Unfortunately, it’s pretty clear that this writer does not understand how helicopters fly. This is common among non-pilots. Some folks think that the rotor disc — when the blades are spinning — works like a giant fan that keeps the helicopter in the air. Other folks — well, I don’t know what they think. But very few seem to realize that like airplanes, helicopters have wings.

Yes, wings. What do you think the rotor blades are?

Helicopters are rotary wing aircraft. This means that they have wings that rotate.

The Real Question

Although this writer seems to want an explanation of “how a pilot would initiate autorotation,” he has a bigger misunderstanding to clear up first. It all stems around these two phrases:

…a helicopter runs out of fuel and begins to drop.

and

…in order to minimize damage the pilot uses autorotation to make the helicopter somewhat stable.

The problem is that if a helicopter ran out of fuel and the engine quit (assumed), the pilot has only about 2 seconds to enter an autorotation to prevent a catastrophic crash. You don’t enter an autorotation to “make the helicopter somewhat stable.” You enter an autorotation to maintain a controlled glide to the ground that, hopefully, concludes with a landing everyone can walk away from.

Or, put it another way, in the event of an engine failure, the pilot must perform an autorotation if he wants to survive.

So in order to answer the question this writer asked, I need to first address his misunderstanding of how helicopters fly and what autorotation does.

How Helicopters Fly

Let’s start with something most people do understand — at least partially: how an airplane flies.

An airplane has at least one pair of wings that are fixed to the sides of the fuselage. The wings have a specific shape called an airfoil that makes lift possible.

When the pilot wants to take off, he rolls down the runway, gathering speed. This causes wind to flow over and under the airfoil. After reaching a certain predetermined minimum speed, the pilot pulls back on the yoke or stick which lifts the airplane’s nose. This also changes the angle of attack of the relative wind on the wings. That change produces lift and the plane takes off.

Obviously, this is an extremely simplified explanation of how airfoils, relative wind, and angle of attack produce lift. But it’s really all you need to know (unless you’re a pilot).

A helicopter’s wings — remember, they’re rotary wings — work much the same way. But instead of moving the entire aircraft to increase the relative wind over the airfoil, the wings rotate faster and faster until they get to 100% (or thereabouts; long story) RPM. Then, when the pilot wants to take off, he pulls up on a control called the collective which increases the pitch or angle of attack of all the rotor blades. That change produces lift and the helicopter takes off.

It’s important to note here that when you increase angle of attack, you also increase drag. Whether you’re in an airplane or in a helicopter, you’ll need to increase the throttle or power setting to overcome the increased drag without decreasing forward speed (airplane) or rotor RPM (helicopter).

Rotorcraft Flying HandbookIf you’re interested in learning more about lift and how helicopters fly, I highly recommend a free FAA publication called Rotorcraft Flying Handbook. This is a great guide for anyone interested in learning more about flying helicopters. You don’t need to be an aeronautical engineer to understand it, either. If the text isn’t enough to explain something, the accompanying diagrams should clear up any confusion. I cannot recommend this book highly enough.

What Happens when the Engine Quits

Things get a bit more interesting when an aircraft’s engine quits.

On an airplane, the engine is used for propulsion. If the engine stops running, there’s nothing pushing the airplane forward to maintain that relative wind. Because it’s the forward speed that keeps an airplane flying, its vital to maintain airspeed above what’s called stall speed — the speed at which the wings can no longer produce lift. To maintain airspeed, the pilot pushes the airplane’s nose forward and begins a descent, thus trading altitude for airspeed. The plane glides to the ground. With luck, there’s something near the ground resembling a runway and the airplane can land safely.

On a helicopter, the engine is used to turn the rotor blades. If the engine stops running, there’s nothing driving the blades. Because it’s the spinning of the rotor blades or rotor RPM that keeps a helicopter flying, its vital to keep the rotor RPM above stall speed. The pilot pushes the collective all the way down, thus reducing drag on the rotor blades — this is how he enters autorotation. (The helicopter’s freewheeling unit has already disengaged the engine from the drive system, so the blades can rotate on their own.) The reduction of the angle of attack of the blades starts a descent, trading altitude for airspeed and rotor RPM. The helicopter glides to the ground. With luck, there’s a clearing or parking lot and the helicopter can land safely.

It’s extremely important to note that as long as the pilot maintains sufficient rotor RPM, he has full control of the helicopter all the way down to the ground. He can steer in any direction, circle an appropriate landing zone, and even fly sideways or backwards if necessary (and he has the skill and nerve!) to make the landing spot. So to say “the pilot uses autorotation to make the helicopter somewhat stable” shows complete ignorance about how autorotation works.

About 30 feet above the ground, the pilot pulls back on the cyclic to slow his forward airspeed. The resulting flare trades airspeed for rotor RPM, thus giving the main rotor blades extra speed. That comes in handy when he levels the helicopter and pulls the collective full up — thus bleeding off RPM, which he won’t need on the ground — to cushion the landing before touching the ground.

The point that needs to be made here is that helicopter engine failures and autorotations don’t always end in a crash. In fact, with a skilled pilot and a suitable landing zone, there’s no reason why it should end in a crash. So in the example presented by this writer, the helicopter doesn’t have to crash at all. It could have an engine failure and safely land in a clearing.

And here’s another newsflash: every helicopter pilot not only knows how to perform an autorotation, but he’s tested on it before he can get his pilot certificate. He’s also required to prove he can do one every two years during a biennial flight review. And if he’s like me, he’s tested annually by an FAA inspector for a Part 135 check ride.

Writers: Do Your Homework!

It’s good to see this writer trying to get the information he needs. But in my opinion, he went about it all the wrong way.

It’s been over a month since I got his emailed request for information. I never replied by email; this is my reply. Has he written his passage without the answers to his question? I have no idea. He never followed up.

But wouldn’t it have been smarter to simply talk face-to-face with a helicopter pilot? Any helicopter pilot could answer these questions and set him straight. Helicopter pilots aren’t so hard to find. Flight schools, tour operators, medevac bases, police helicopter bases, etc. Not only could the writer get his questions answered by someone who knows the answers from experience, but he could gather a wealth of information about helicopters, including their sound, why they don’t usually take off straight up, and other operation aspects. And if he visited a flight school or tour operator and had some extra money to spend, he could even go on a flight to see what it’s like from the inside of the aircraft.

Emailing a blogger who happens to write a lot about helicopters and complain when novelists get it wrong [hand raised] is downright lazy.

And despite what you might think, writing is not a job for lazy people.

Dan Brown Doesn’t Know Much about Helicopters

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I guess a best-selling author doesn’t need to check his facts.

A few weeks ago, I forced myself to slog through Dan Brown’s The Lost Symbol. I’m trying really hard to understand why people like this guy’s work. He’s a gawdawful writer. Have we become a nation of illiterates?

As a helicopter pilot, I’m really sensitive to errors about helicopters that appear in fiction. The Lost Symbol was chock full of them. Apparently, it’s too much to ask Dan Brown to take a peek at Wikipedia or talk to a helicopter pilot when writing passages that concern helicopters. It makes me wonder what other “facts” he got wrong.

This bugged me so much at the time that I wrote a post title “Facts in Fiction,” where I discuss the failure of novelists to check the real-life components of their fictional worlds. I wanted to include a discussion of Brown’s failures in that post, but didn’t have time to complete it. Instead, I’ll cover them here.

These are the passages that bugged me most:

Without warning, Omar felt a deafening vibration all around him, as if a tractor trailer were about to collide with his cab. He looked up, but the street was deserted. The noise increased, and suddenly a sleek black helicopter dropped down out of the night and landed hard in the middle of the plaza map.

Deafening vibration? We get it: helicopters are loud. But do they deafen with their vibrations?

Black Hawk Helicopter

Public domain image of UH-60L by SSGT Suzanne M. Jenkins, USAF from Wikipedia.

The “sleek black helicopter” he’s describing is a “Modified Sikorsky UH-60,” which is basically a Black Hawk. I’m not sure what kind of modifications Brown is talking about — there are many versions of this helicopter. I’m also not sure I’d use the adjective “sleek.”

But what bothers me more is how it “dropped down out of the night and landed hard” — if it “dropped out of the night,” it would indeed “land hard.” This poor helicopter “landed hard” three times in the book. I think the CIA should consider getting a new pilot.

CIA field agent Turner Simkins was perched on the strut of the Sikorsky helicopter as it touched down on the frosty grass. He leaped off, joined by his men, and immediately waved the chopper back up into the air to keep an eye on all the exits.

“Perched on the strut,” huh? Not perched on a skid? Oh, yeah, that’s right: A Black Hawk doesn’t have skids. It has wheels. If someone can tell me where a Black Hawk’s perchable strut is, please do.

High above the National Cathedral, the CIA pilot locked the helicopter in auto-hover mode and surveyed the perimeter of the building and the grounds. No movement. His thermal imaging couldn’t penetrate the cathedral stone, and so he couldn’t tell what the team was doing inside, but if anyone tried to slip out, the thermal would pick it up.

I honestly don’t know if there’s an auto pilot in a Black Hawk or whether it has an “auto-hover mode.” I suppose I could research this and find out. But I do know that there’s no way in hell that a CIA Black Hawk pilot (if there is such a thing) would be responsible for flying a helicopter and doing overhead surveillance using thermal imaging at the same time. Pilots fly, on-board observers observe.

As they rounded the corner at the top of the stairs, Katherine stopped short and pointed into a sitting room across the hall. Through the bay window, Langdon could see a sleek black helicopter sitting silent on the lawn. A lone pilot stood beside it, facing away from them and talking on his radio. There was also a black Escalade with tinted windows parked nearby.

Hello? Mr. Brown? A Black Hawk has a crew of two pilots. The original Black Hawk had a crew of four pilots. Yet the book consistently uses the word pilot — a singular noun — when referring to the person flying the helicopter. I guess it’s easier to write one character than two.

The modified UH-60 skimmed in low over the expansive rooftops of Kalorama Heights, thundering toward the coordinates given to them by the support team. Agent Simkins was the first to spot the black Escalade parked haphazardly on a lawn in front of one of the mansions. The driveway gate was closed, and the house was dark and quiet.

Sato gave the signal to touch down.

The aircraft landed hard on the front lawn amid several other vehicles . . . one of them a security sedan with a bubble light on top.

Google Maps shows Kalorama Heights to be a densely populated area of Washington, D.C. filled primarily with embassies. This is an especially poor location for the bad guy’s lair:

Black Hawk Dimensions

Sikorsky UH-60 Black Hawk dimensions public domain line drawing from Wikipedia.

  • An area filled with embassies is likely to have very, very tight security. It’s unlikely that the events Brown reports could happen at a “mansion” there without anyone noticing and calling the police.
  • Properties are not large — not in relation to the buildings on them. The fronts of buildings are generally right up on the street. It would be a stretch to park multiple vehicles on a lawn.
  • The area is heavily vegetated with lots of tall trees. This makes me wonder how a helicopter that’s almost 65 feet long and has a rotor diameter of nearly 54 feet can land on a lawn full of parked cars in this area.

So we’ve got a big helicopter and some loud activity happening in a densely populated, heavily treed embassy area of Washington, D.C.

Sato moved the group toward the dining room. Outside, the helicopter was warming up, its blades thundering louder and louder.

Warming up is a function of the engine. The blade sound would not be different. Spinning up is a function of the blades. In either case, the sound of the blades would not get louder. If the helicopter were spinning up, the sound of the blades — the rhythm of the blades — would get faster.

Sato could hear the whine of the helicopter blades at full pitch.

Pitch is a poor choice of words here. “Helicopter blades at full pitch” literally means the collective is full up. The helicopter should be flying, not on the ground (as it is in this passage). Full speed — meaning that they’re spinning at 100% RPM — is probably what Brown meant here.

Langdon felt his stomach drop as the CIA helicopter leaped off the lawn, banked hard, and accelerated faster than he ever imagined a helicopter could move.

This is a classic ignorant writer passage. If the helicopter could leap off the lawn — which it might, depending on load — Langdon’s stomach wouldn’t drop. He might feel pushed back in his seat. The only time you’re likely to feel a helicopter motion in your stomach is if the helicopter entered autorotation, which feels — especially the first time — as if you’ve crested the top hill of a kiddie roller coaster and are suddenly zipping downward.

As for accelerating fast, I don’t know much about Robert Langdon’s imagination, but helicopters generally don’t accelerate quickly. It’s not like slamming down the gas pedal in a Ferrari in first gear. (In fact, one of the challenges I face when photographing car and boat races is catching up to a high-speed car or boat that has passed us while we’re hovering.) Can’t say I’ve flown a Black Hawk lately, though.

Langdon held his breath as the helicopter dropped from the sky toward Dupont Circle. A handful of pedestrians scattered as the aircraft descended through an opening in the trees and landed hard on the lawn just south of the famous two-tiered fountain designed by the same two men who created the Lincoln Memorial.

There’s that hard-landing helicopter again. Maybe the problem is that Brown — and most of the rest of the population — doesn’t understand that helicopters don’t just “drop out of the sky” to land. There’s a thing called “settling with power” that will basically ensure a very hard landing if you descend too quickly straight down.

And don’t even get me started on the encyclopedic fact that has nothing to do with the plot, fouling up the end of that sentence.

Once everyone had jumped out, the pilot immediately lifted off, banking to the east, where he would climb to “silent altitude” and provide invisible support from above.

Silent altitude? What’s that? About 50,000 feet? I don’t know of any altitude above a point where a helicopter would be silent — especially if it still had to provide “invisible support” — whatever that is. I look forward to the day when the words silent and helicopter can be used in the same sentence as adjective describing noun.

The UH-60 pilot threw his rotors into overdrive, trying to keep his skids from touching any part of the large glass skylight. He knew the six thousand pounds of lift force that surged downward from his rotors was already straining the glass to its breaking point. Unfortunately, the incline of the pyramid beneath the helicopter was efficiently shedding the thrust sideways, robbing him of lift.

He threw his rotors into what? What the hell is that supposed to mean? And what’s with the “six thousand pounds of lift force” surging down from this rotors? Is he trying to say that rotor wash is exerting 6,000 pounds of force?

Hello? Helicopters do not work just like big fans blowing air down to fly. They have wings, just like airplanes do. Airfoils create the lift that makes a helicopter fly. Downwash just helps a bit when the helicopter is near the ground. That’s called ground effect.

And let’s look at this in real life — the helicopter had only 2 or 3 people on board. It had already discharged its passengers. Is Brown trying to say that the pilot was depending on ground effect to fly? On a winter night (cold; it landed on “frosty grass” once) in Washington DC (sea level)? How did it get off the ground with passengers on board — let alone leap into the sky — if it couldn’t even hover out of ground effect when it was nearly empty?

And what’s all this about skids? Didn’t we already establish that the Black Hawk has wheels? If you can’t read the words, Mr. Brown, at least look at the pictures.

Errors like this just prove that the writer has no understanding of how helicopters fly. Yet this and many of the other helicopter-related errors in this book could have been prevented if the passages were handed off to an experienced helicopter pilot as part of the editing process.

But I guess a bestselling author is beyond all that.

Facts in Fiction

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Why fiction authors should get the facts straight in their writing.

The vast majority of people who want to be writers want to write fiction. While I don’t have the statistical sources to back up that claim, I don’t think anyone can deny it. There’s something about writing fiction that really appeals to people who want to write — including me. The only reason I don’t write fiction for publication is that I found that I could make a good living writing non-fiction. Making a living as a writer is more important to me than writing fiction.

With all that said, what many fiction writers don’t understand is the importance of getting their facts straight in what they write.

How Deep is Your Fictional World?

When you write fiction, you build a fictional world. The depth of your world — how similar it is to the real world — can vary.

Suppose, for example, that you’re writing a science fiction adventure that takes place on a distant planet that isn’t even very Earth-like. You’re making up the setting and all that goes with it. Is the sky on your planet pink? Are there four suns? Do the people have eyes where our mouths are and four arms instead of two? You’re making everything up. Your world may have nothing in common with the real world. You have license to make everything up as you go along.

Now suppose you’re writing a thriller that takes place in a Wall Street banking firm (if any are left). Wall Street is a real place in a real city. You’re not making any of that up. You might make up the firm and its customers. You’ll probably make up the characters and plot. But you’re still constrained by what’s real in your world. In New York, taxis are yellow and police cars are blue and white. (At least they were the last time I was there.) Wall Street is in Lower Manhattan and it’s crossed by Broadway. If you change any of these facts — or don’t get them straight — you’re making an error. (Of course, you could cheat by setting the plot in the distant future, thus adding a SciFi element to it. But do you really want to do that if it’s not part of the story?)

In many cases, you can ensure the accuracy of the facts in a piece of fiction by a lot of Googling or perhaps even a visit to Wikipedia. Other times, you need better resources — possibly even an “expert.”

I bring this up for two reasons:

  • I was recently asked a question by a writer about how a helicopter works. He wanted to get his facts straight.
  • I am repeatedly distracted by errors in facts in novels by authors who really should have the resources to get their facts straight.

Let’s take a look at some examples.

Question from a Writer

The other day, someone posted the following comment on my post titled “How Helicopters Fly“:

I am writing a novel in which a helicopter goes out of control and starts spinning. How would a pilot pull out of a spin? Gyrating.

This is a good question — kind of. It’s good because the person who asks does not understand the technical aspects of what he wants to include as a plot point. He realizes that he lacks this knowledge and he’s actively trying to get it. Great!

Unfortunately, it’s not a question that can be easily answered — even by someone who knows what the answer might be. (And I’m really not sure why he included the single word “Gyrating” at the end of his comment. What does he mean by that?) My response to him tries to get this point across:

It really depends on how the helicopter got into that spin. Normally, the rotor pedals will stop a spin, but if the tail rotor’s gone bad (or chopped off), the pedals probably won’t help. Sometimes flying straight at a high speed can keep you from spinning with a non-functioning tail rotor.

It’s not at all like an airplane. You don’t “pull out of a spin.” You prevent yourself from getting into one; if you start to spin, you use your pedals to stop it before it gets out of control.

A better way for him to approach this problem would be to sit down with a helicopter pilot or instructor and ask him/her what might cause a helicopter to start spinning and how a pilot might recover from each cause. He can then fit one of those causes into his plot and have the pilot stop the spin.

But he shouldn’t stop there. After writing the passage concerning the spin and recovery, he should pass over those manuscript pages to a pilot and let him read them. Does it ring true? Is it feasible? Are the correct terms used? Doing this will ensure that the passage is error-free.

Errors in Best-Selling Fiction

As a writer and a helicopter pilot, I’m especially sensitive to helicopter-related errors in popular fiction. A while back, I read a Lee Child book that included scenes with a helicopter. It was full of errors. Here are two that come to mind:

  • The helicopter was in a fuel-critical situation. The author stated that it was better to be lower than higher if the helicopter ran out of fuel. (The exact opposite is true; you want to be higher if your engine quits so you have more options for autorotative landing.)
  • The helicopter pilot is killed by a character breaking his neck. The author has the helicopter pilot land on dirt before he kills him so it looks like he broke his neck when the helicopter crashed-landed when it ran out of fuel. (But the helicopter didn’t crash. It landed upright on its skids. If it had been a “crash landing” — even on its skids — the skids would have been spread and the helicopter would have had other signs of a hard landing.)

These are absolutely glaring errors to a helicopter pilot. They ruined the book for me. How could I slip into the author’s world when its connections to the real world are so screwed up? If he got this stuff so wrong, what else did he get wrong?

I found more errors like this — although admittedly not as bad — in the latest Dan Brown book, The Lost Symbol. I’ll go through them in some detail in another post.

These Are Just Examples from My Real World

These are examples from my world, which includes helicopters. Maybe your world includes flying an airliner or managing an office building or designing computer security systems. Or anything that’s a lot more complex than it seems on the surface. When you read a piece of fiction and the author includes “facts” from your world as plot points — and gets them wrong — how do you feel? Doesn’t it bug you? Perhaps ruin the book for you?

The most commonly repeated advice to writers is to “Write what you know.” Although I agree with this and believe writers should start with what they know, there are often times when they have to stretch the boundaries and write a bit about what they don’t know. I believe they should make an extra effort to get the facts straight whenever they do this. And then go the final extra step in having an “expert” review the final written passages as a fact check before the book is published.

What do you think?