Autorotation Explained

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.


…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.


Some thoughts from a writer (and reader).

Earlier this month, I wrote a post that briefly touched upon my experience as an author finding my copyrighted books freely distributable on a pirate Web site. (Refer to “Copyright for Writers and Bloggers – Part I: Why Copyright is Important.”) The post generated some comments that made me think more about the electronic versions of my books that my publishers sell: eBooks.

About eBooks

An eBook is an electronic book. While some eBooks are published in electronic format only, others are published in print and then are followed up with eBook versions of the same book.

Sometimes both print and eBook versions of a book are put out by the same publisher. This is common with modern-day titles. But there are also a number of eBook publishers out there who take older titles that are still in copyright and make arrangements with the publisher or author to create and sell eBook versions. And, of course, anyone can take an out-of-copyright book, like the works of Mark Twain, Charles Dickens, Edgar Allan Poe — the list goes on and on — and publish them anyway they like: in print, electronically, or even tattooed on someone’s leg. Project Gutenberg came into existence by making out-of-copyright works available to the world and that’s what you’ll find among its thousands of titles.

eBooks are available in a wide variety of formats, from plain text to PDF to Windows Help Viewer format. They can include or exclude illustrations. They can contain hyperlinks to make it easy to move from one topic to another. They can be printable as a single document or by pages or sections.

My first involvement with eBooks was way back in the 1990s when I used a program called DocMaker on the Mac to create my monthly, freely distributable newsletter, Macintosh Tips & Tricks. I later moved to PDF format. 10 Quick Steps, one of my publishers, publishes all of its books as PDFs optimized for onscreen reading. I later published some of my own eBooks in the same format.

eBooks and Copyright

eBooks are usually sold with the same licensing used for software. One copy, one user. This is pretty basic stuff. Although I admit that I’ve never read an EULA for an eBook, I assume that if an buyer is finished with it and wants to give his/her only copy to someone else, he can. After all, that’s how books work. And, as someone who has legally transferred ownership of software by selling it (after removing the original from my computer), I’m pretty sure eBooks have a legal second hand market.

Unfortunately, due to their portable nature — pop them on a CD or compress them and send them in email or leave them on an FTP server for others to download — they are often the victim of piracy and copyright infringement. People put eBooks — whether they obtained them from legal means or not — on pirate Web sites, FTP servers, or other file sharing systems for free or paid download to anyone who wants them.

As this problem becomes more and more widespread, readers begin to think that there’s nothing wrong with downloading and sharing illegally distributed eBooks. They begin looking to illegal sources of eBooks rather than legal sources, hoping to save $10 or $15 or $20. They justify their participation in this illegal activity by saying that “knowledge should be free” or that the publisher makes enough money or that eBooks cost nothing to produce. And soon this affects the sale of both printed and electronically published books.

Who Suffers?

Are you an author concerned about illegal distribution of your eBooks? You may be interested in the new Authors Against Piracy group I’ve started to discuss the issue and share solutions. It’s a private group, so you’ll need an invitation to join. Contact me to introduce yourself. Be sure to identify your most recent published work; the group is open to published authors only.

The real victim of this is the author, who often makes less than a dollar for every book sold.

Most authors these days can’t afford to just write for a living. Some of them have regular day jobs. Others are consultants or speakers or programmers or some combination of those things.

About 95% of my net income comes from writing books and articles. My helicopter charter business, which is still in its infancy, eats up all the cash it brings in. (Helicopters are extremely costly to own and operate.) And between writing and flying, I simply don’t have time to do anything else to earn money.

So when I find my books being illegally distributed on pirate Web sites, I get angry. Can you blame me?

Is It Worth It?

In the comments for my “Copyright is Important” post, reader Nathanael Holt asked this question: “Do your digital sales warrant the increased risk posed by piracy?”

This is a really good question — one I had to go to my royalty statements to answer. And, after a quick glance at that most recent 60-page document, I’d have to say no.

For example, one of my recent titles sold more than 2,600 printed copies in the quarter ending March 31, 2007. That same title sold only 2 electronic “subscriptions.” Another title, which is older and which I have found online on pirate sites, had 9 copies of the PDF sold during the same quarter, earning me less than $15.

My conclusion from this: eBook versions of my books aren’t selling very well. And apparently the ones that get out there are going to pirate Web sites.

I’ve e-mailed my publisher’s royalty department to get lifetime figures for all of my in-print titles. I’m hoping the numbers they deliver will paint a more rosy picture. But I doubt it.

I’m an eBook Reader, Too

This is disappointing for me. You see, I’m an eBook reader.

A while back, I was looking for a book about .htaccess. That’s a normally invisible configuration file found on servers. I wanted to modify the .htaccess file for my Web site so it would do certain things for me.

This is an extremely technical topic and one I didn’t expect to find a book about. But I did: The Definitive Guide to Apache mod_rewrite by Rich Bowen. And after a bit of research, I learned that I could either buy the book from for $40 and wait a week to get it or buy it as an eBook in PDF format from the publisher’s Web site for $20 and download it immediately. I admit that the deciding factor was the length of the book: 160 pages. Since I like to be able to look at a computer-related book (rather than switch back and forth between a book and an application onscreen), I could print it for reference.

And that’s what I did: I downloaded the book as a DRM-protected PDF and sent it to my printer. Within an hour, I had the whole thing in a binder and was editing my .htaccess file to my heart’s content, with all kinds of notes jotted in the margins of my new reference book. (That’s another thing: I’m far more likely to mark up a printed eBook than a printed and bound traditionally-published book.)

I also read eBooks on my Treo (when I’m trapped somewhere with nothing to do).

The only reason I don’t buy and read more eBooks to read onscreen is because I think I spend enough time in front of a computer without using one to read, too.

What Does All this Mean?

Well, first I need some solid information from my publisher regarding lifetime eBook sales. Then I need to sit down with my editor (figuratively, of course — we never see each other in person) and decide whether eBook editions of my work are something we want to continue to publish. If we decide to go forward, we need to come up with a solution that will protect eBooks from piracy.

What Do You Think?

Have you ever bought an eBook? Why did you buy that version instead of a traditional print version? Did you like it? What do you think about eBooks in general: pricing, formats, licensing, etc?

Don’t keep it all to yourself! Use the Comments link or form to share your thoughts with me and other readers.

I Don’t Like Being Seriously Dugg

The activity finally winds down — I think.

In yesterday’s post, “Getting Seriously Dugg,” I reported the history of a blog post that rose quickly to stardom in the world of Digg users. But that report was done early in the day, before the shit hit the fan (so to speak).

The Heat is On

The Digg count continued to rise throughout the day. And the hits kept coming. All morning long, there were at least 100 visitors online at my site at once. This is not normal here. And it was rather frightening. I kept expecting something to break.

But it wasn’t just the popular Digg post that was getting hits. It was the post about getting Dugg, too. Soon, it had more hits than the dugg post — even though it wasn’t dug by anyone at all. I’m still trying to figure that one out.

Things came to a head at 11:15 AM when I got an e-mail message from my ISP:

Our Hosting Operations Admins have alerted us to an issue with your hosting account. The account has overutilized resources within the shared environment. As a result, the account has been moved to an isolated server for Terms of Service violators. You have 30 days to research and resolve this issue. After this time, the account will be evaluated again. If the issue is resolved, the account will be migrated back to the shared environment. If it persists, you will need to move to a full Dedicated server.

I got on the phone immediately and called my ISP. To my knowledge, I hadn’t violated any terms of service by getting hits. My plan allows 2,000 GB of bandwidth per month. The billing month starts on the third — that day. So far, in all the years I’ve hosted there, I’ve never exceeded 6% of my monthly allowance. Just because I was getting 30 times the usual number of hits I get in a day, it was still not much more than I’d get in a total month. So there was no way I’d even come close to 10% of the monthly allowance — let alone exceed it.

The guy who answered the phone was extremely polite but equally clueless. He had to talk to Advanced Hosting. He couldn’t let me talk to them. They gave him a song and dance about too many domain names pointing to the same site. He attempted to hand the same thing to me. I told him that that shouldn’t matter since none of those domain names were advertised anywhere. Besides, there were only about a dozen of them pointing to one site and maybe 15 pointing to another. I wasn’t aware of any limitation.

“I’ve been dugg,” I told him. When I got no answer, I asked, “Do you know what that means?”

“No,” he said.

I explained that it meant that one of my blog’s posts had become very popular and that people were flocking to my site to read it. I told him this was a temporary thing and that it should be back to normal by the end of the day. I hoped.

He told me that if I continued to get so many hits to my site, I’d have to get a dedicated server. I told him I’d evaluate after I’d seen my stats for the day. (My account is updated daily in the middle of the night.)

We hung up.

A Brief Intermission

I went flying. I took a couple from Virginia on an hour-long helicopter tour in the Wickenburg area. I showed them mine sites and canyons from the air. We saw a lot of cows, too. Afterward, I goofed off at the airport, chatting with two jet pilots who’d come in and were waiting for passengers. Then I went shopping for dinner. I got home and had a snack. Then I looked at Digg. It was 4 PM.

What Happened in Five Hours

The post that had started it all now had more than 1,200 diggs. It had been viewed almost 30,000 times. The post about that post, which hadn’t been dugg at all, had been viewed more than 40,000 times.

But thankfully, there were only 33 people online. So the flood had begun to subside.

On the Digg Technology page, my dugg post was listed near the bottom, under newly popular. (Ironically, on the same page, near the top, was a post about how Digg was losing popularity. That had more than 1,200 diggs, too.)

The Morning After

It’s the next day. I can now look back objectively on my blog’s day with a Digg Top 10 Tech post by studying some of the stats for the day and how the differ from other days.

My ISP reports that for the first day of my billing period — yesterday — I used up .55% (that’s just over half a percent, folks) of my monthly bandwidth. That means that if every day was like yesterday, I’d still come in at less than 20% allowable bandwidth. So I don’t know what “terms of service violation” they were whining about.

W3Counter, which I use to track page hits and visits, says I got just over 27,000 page hits yesterday. Look at the chart below; it makes my site look flat-line dead before yesterday. Honestly — it wasn’t that dead.


Today’s hits are about 3 times a normal day. Nice, but I’m willing to bet it drops down to normal within the next few days.

W3Counter also sent me an e-mail message warning me that their free service doesn’t cover sites that get more than 5,000 hits a day.They say I need to upgrade to a pro account for $4.95/month. We’ll see how long before they disable my current account — I’m not paying them to tell me how many hits I get when I can easily set up some stat software with a free WordPress plugin. (ShortStats, which we wrote about in our WordPress book, comes to mind.)

(I have not been able to reconcile page hits as reported by W3Counter with article reads as reported by a WordPress plugin. I have a sneaking suspicion that the WordPress plugin counts bots.)

Digg, as a source of hits, kicked Google out of the top spot on my site. Google used to account for 54% of my visitors. Now, for the 14-day period tracked by W3Counter, Digg is the big source. Google doesn’t even make the list any more, with all the different Digg URLs people used to find my site. So my sources stat is completely skewed and pretty much useless for the next 13 days. And 93% of the hits in the past 14 days have been to the 18-year-old mouse story.

Meanwhile, WP-UserOnline reports that yesterday saw the most users online at once on this site: 375. I don’t think this site will ever see that many concurrent users again.

My RSS feed subscriptions have more than doubled. That’s great. (If you’re a new subscriber, thanks for tuning in. And don’t worry — I don’t write about Digg every day.) It’ll be interesting to see if that number continues to climb or if I manage to scare all the new folks off by failing to provide more Diggable content on a daily basis.

My Google AdSense revenue for yesterday was right in line with an average high day. When you consider that I got about 20 times my normal number of page hits yesterday, you might think that I’d get 20 times the revenue. I didn’t. Obviously, Digg users don’t click Google ads.

The last I checked, the 18-year-old mouse story got just over 1,357 Diggs. I think that I actually encouraged the extra Diggs by placing the Digg icon at the top of the post. I’ve since taken it away from all posts.

I’ve realized that I don’t want to be seriously Dugg. Other than the surge in new RSS subscribers, there really isn’t any benefit to it.

What do you think?

Have you been slammed by being dugg? How did it affect your hosting account or other services? Use the Comments link or form to let the rest of us know.