Little Guy

This turned into a longer post than I anticipated but whatever.

Something I've been seeing quite often in the comments under helicopter posts that make it to the broader internet spaces is discussions on autorotation. These discussions are mostly incomplete information at best and outright wrong at worst. A lot of people seem to be able to recall it as a fact about how helicopters can glide to a safe landing, but aren't aware of the actual process. So here's a guide on what an autorotation is, how its performed, and some of the nuances to it.

For the uninitiated, an autorotation is a maneuver that every helicopter is capable of performing which allows it to land safely in the event of a power failure. Even more simply put - its how a helicopter glides.

I've already made previous posts about helicopter controls and some principles of flight which I recommend checking out first if you're unfamiliar with those.

Under normal flight the engine(s) drive the rotors at a constant flight rpm and all control is made by pitching (changing the angle) The blades to make more or less lift. Essentially the same process as sticking your hand out the window of a moving car and making rise or fall in the wind. However the rotors are experiencing a lot of drag (wind resistance) which requires the engine to produce a lot of power to overcome and maintain rpm.

When an engine failure occurs there is no more power driving the rotors and the high drag will cause the rotor rpm to start to decay rapidly. If nothing is done about that then the rpm will fall so low that the rotors will stall or worse and the helicopter will fall out of the air like a rock. Thankfully we have the option to autorotate instead of that outcome.

The first thing that happens to initiate an autorotation is to fully lower the collective. This will flatten out the blade pitch and minimize the drag on the main rotor, slowing the rpm decay. As the collective is lowered the cyclic will need to come aft slightly to prevent the nose from dropping. Also the right pedal will have been pushed in as the power failure initially occured to prevent yawing.

Now the helicopter is in a steep descent and the autorotation has begun. The airflow through the main rotor has reversed from normal flight. Instead of being drawn from above and expelled downward there is a diagonally upward flow of air through the main rotor.

Now the rotor rpm will begin to rise again thanks to the special design of the rotor blades. A rotor blade has an airfoil shape which is sort of like an elongated teardrop with the wider end on the leading edge. This shape minimizes drag and maximizes lift. But the blade is also slightly twisted. It has a positive pitch at the root where the blade attaches to the rotor hub which gradually transitions to a negative pitch at the tip.

Because of this twist and the difference in relative speed along the blade length (tip travels relatively faster than the root) the blades will develop three distinct regions. These are the driven, driving, and stall regions

The driven and stall regions at the blade tip and root are still producing drag but the middle driving region is actually producing lift, in an upward and slightly forward direction. This forward lift is the thrust that causes the rotor rpm to increase during an autorotation.

So now you are in a descent and recovering rpm back to the normal flight range. If you leave the collective fully lowered the rpm will now start to increase past the normal range and begin to overspeed. If the overspeed becomes too great the blades will be damaged and one could eject. Not ideal.

You have to manage the rpm manually to prevent it from becoming too low or too high. You also do this with the collective. Remember, to start the auto you should lower the collective fully to minimize rpm loss initially and then to start recovering it. As the rpm reaches the normal range the collective should be raised again just a bit to "catch" the rpm. Now you can manually adjust rpm with a tiny amount of collective movement. Rpms a little too fast? Raise it a bit. A little too slow? Lower it a bit. What this is doing is changing the size of the driven and driving regions of the blade, thanks to the twist. Lowering the collective grows the driving region and shrinks the driven region, and vice versa for raising it.

Now the helicopter is safely gliding and can be steered to a landing spot. There's not much to do until you're approaching the ground. The next maneuver will be the level and flare. The height at which you initiate the level and flare depends on the helicopter. Generally a larger helicopter will have more momentum and need to start the maneuver sooner.

Starting with the level off. You will be gliding with a high rate of descent and forward speed in an autorotation. The purpose of the level off is to drastically reduce the rate of descent. By using some aft cyclic input you will pull the nose up and put the helicopter in a level flight attitude. This causes the upwards lift of the rotor disc to act as a sort of parachute and arrest the descent.

Now with the descent rate minimal you apply more aft cyclic to pitch the nose up further and neutralize the forward speed. This is the flare and its the last opportunity to build rotor rpm in an autorotation.

Now you are just over the ground with little to no forward speed and the helicopter will start to settle and sink. Apply forward cyclic to level the helicopter parallel with the ground and use the pedals to keep the nose pointed straight ahead. Then you have whatever rpm is built up to cushion the landing. Smoothly raise the collective fully as the helicopter sinks to touchdown and the landing can be shockingly smooth.

What an autorotation really comes down to is energy. You often start at a high-ish altitude with some forward speed and this becomes the potential and kinetic energy you trade to power the rotors instead of the engine. The energy is an absolute requirement though. If you dont have enough of a combination of speed and/or altitude then an autorotation can be impossible. There are phases of flight and certain missions where you have to accept the risk of a power failure and rely on the crash-worthiness of the airframe.

Despite that, I've done a lot of engine failure procedures in small planes and helicopters and 9 times out of 10 I would rather experience a real one in a helicopter.

that's true love

Madagascar Sucker-Footed Bat, photographed by Manuel Ruedi, (source)

Eastern Red Bats, unknown photographer, (source)

Here is my small piece of advice/plea for for the future for y'all for today, and I may be lightly skirting an NDA to say it, so please listen:

If you can, buy physical books.

I work in publishing and I'm scared about what the election results are going to mean for the future of books by and about marginalized people, especially books for children. There are a lot of things you can do by trying to get involved locally, especially to mobilize against book bans and laws targeting libraries and schools. Voting with your wallet is still an extremely important tactic, because we're going to be hit with economic issues re: diverse books before we get hit with legal ones. But my immediate concern is what might happen with e-books.

It's already a known problem that if you "buy" a book on Kindle or another e-reader, that you're essentially renting it from that retailer, and if that retailer decides to remove that book, they can wipe it from your device. We also know that servers can be shut down. Content policies can change. It could get very difficult to find a copy of the files to pirate, much less to purchase.

But you can't delete a physical book from the world.

Physical books are about to become very important repositories. Collect them, if you can. Go to library sales. Go to thrift stores. Go to your local bookstore -- and bonus point here: independent bookstores are and will be great hubs for organizing in the coming days. Hell, I'd even encourage you to go through Amazon to send a message that these books are still financially viable. Lord knows the latter doesn't want to advertise them to you.

I know (I know) that physical books are expensive and getting more so. I know space is at a premium in a world where we're being pushed to live in smaller and smaller apartments with more and more roommates. But if there's a book that was important to you, and if it's a book you think a bigot wouldn't want to exist in the world, I urge you to get your hands on a physical copy of that book. If nothing else, to preserve it for the next generation.

ALL of us can be librarians. ALL of us can be archivists. ALL of us can work together to preserve marginalized voices, and to ensure that they are heard.

I love you. Keep fighting. We're in this together.

I love everything about this concept. Although my mind goes in the direction of then informing Mr. Heuristic about some of those absolutely wonky esolangs.

...tmw dude just starts coding exclusively in malbolge and it's just... how?

I feel like nibblers would absolutely LOVE computers if they ever got the chance to try one out

So I drew a nibbler trying to learn how to code on a Macintosh plus. His name is Heuristic

murderfloof rolled a 1 on that check, lol bat's definitely caught red-han-... red-chested? red-faced? red all over, really.

exceptionally creepy. terrifying. (great work!) ... TUC had zero flier antagonists. closest to such could be Ajax, I guess? but, like, that dude got zero characterization other than 'nobody likes him' and being Solovet's bond.

so,, why not have a floof-flier be a malevolent bitch? albeit not to the same scale as the other malevolent bitch that affected damn near everyone in the North American Eastern Seaboard region of the Underland with their machinations, and 'just' limited to those that she might encounter by roaming around.

Hoary bat but underland. Maybe hiding a body beneath her. hoaries sometimes kill and eat smaller bats irl. jus surreptiously extretching her wing to conceal a bloody hand, foot, or limb. expression of who, me?~

dunno name. Who was the Greek bloke with the carnivorous horses? Sisyphus? Typhon? Could be selffulfilling prophecy, girl got a rotten name, shunned for rotten name, succumbed to inner demons or malign thoughts because everybody expected the worst from her so why not?

Possibly unrepentant manipulator. Exploits lack of knowledge or innocent assumptions. Missing people? Oh drat the gnawers got them.

You always ask me to draw such depressing bats 😢

Disturbing image under the cut, you were warned

Krita always de-saturates stuff when I export it (yes I've seen that srgb post going around, no the fix suggested didn't work), so I have to manually re-add the saturation after export. I hope I got the caught in the act feigned innocence expression right. To make the bats as expressive as they are in the books I have to give them binocular vision, larger eyes, and usually brows and eyelashes. It kinda makes them look 30% dog 70% bat. I hope the fur patterns and colors still make the species recognizable.

Friend Stack

WUH-OH!

If you're reading this, that means you just got sniffed by a bat! Share and tag your friends to totally sniff them!