When an airplane loses power, it becomes a glider. When a helicopter loses power, I’d expect it to fall like a rock. So why have I never heard of this happening? Do helicopters have incredibly reliable engines that aren’t in airplanes and cars? Do they have two engines for redundancy? I’m sure the mechanics check everything very frequently, but they do that for airplanes too and people still occasionally have to glide into fields when the engine fails. What’s the explanation for this?
Why? The spinning rotor is still providing lift, albeit less as it slows down. It won’t fall like a rock since lift doesn’t disappear as soon as you lose power.
Heli pilot checking in.
Helicopters have the same engines as airplanes. Some are piston, and some are turbine. Some helicopters have one engine, some have two, and some have three. Sometimes they fail.
Helicopters have a sprag clutch or ‘freewheeling unit’ that disengages the rotor system from the engine in case the engine loses power. This allows the rotors to keep spinning, and the helicopter enters autorotation. That is, you glide to a landing.
When the engine fails, the pilot lowers the collective immediately. This is especially important in helicopters with low-inertia rotor systems, which are commonly flown by civilian pilots. At the same time, the anti-torque rotor is adjusted with the pedals since there is no longer any torque to counteract, and the nose is put forward to maintain airspeed. The collective is used to maintain proper rotor RPM. (e.g., if you’re light, then you want a little up-collective so that you don’t overspeed.) Once you’re in a glide you proceed to your landing site. Flare at about 40 feet, level the skids at about eight feet, use the stored energy of your rotor system (trade RPM for lift) to cushion the landing. Often the landing will be indistinguishable from a normal landing.
Autorotations (practice ones, anyway) are one of the most fun things you can do in a helicopter. 
Maybe they do? (note: I know absolutely nothing about helicopters.) Our big local news story is this helicopter crash.
Quotation from article: “Also, a witness driving on a nearby road saw the helicopter flying normally before it dropped rapidly, then exploded in a fireball when it hit the ground, the Federal Aviation Administration reported.”
Sometimes they do fall out of the sky. I buried a friend of mine that was on a chopper that did. There was some catastrophic failure at alititude, and then rotor ended up slicing through the cabin…where my buddy happened to be.
There’s not enough information in the article to determine a cause. Since the pilot called a mayday, I’d guess there was some sort of mechanical failure. Engine? Transmission? Tail rotor failure? Who can say? The article does not state the height of the aircraft, nor its speed. There are areas of flight you want to avoid, as shown in this height-velocity diagram. The article has a photo of a small hill. Terrain may also have been a factor.
So what’s a collective? I take it it has a lot of angular momentum. I figured the blades would slow down a lot within seconds of losing power.
Sorry. The collective is the collective lever, which lives to the pilot’s left. The cyclic is the cyclic control or the ‘joystick’. Both controls alter the pitch of the main rotor blades. The collective changes the pitch collectively; that is, the blades are both (or all) changed the same amount at the same time. This is basically the ‘up or down’ stick. The cyclic changes pitch cyclically; that is, as the rotor turns, the pitch of each blade is changed a different amount depending upon where it is in the rotation. The cyclic controls direction.
Yes, the blades will slow down quickly in case of an engine or transmission failure. You don’t have seconds to react. You have part of a second (in a low-inertia system). Pilots are trained to lower the collective immediately in case of a failure to conserve rotor RPM. Lowering the collective reduces pitch, which reduces drag, which allows the blades to keep turning until you’re autorotating.
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The collective pitch control simultaneously changes the angle of attack on all the rotor blades; it normally controls altitude. By lowering the collective, the pilot reduces both lift and drag, immediately starting a descent. The descent causes air to turn the blades, and with the right balance of lift and drag, the rotor keeps turning, and keeps providing lift, and permits a controlled glide. I know it sounds like pushing a sailboat with a fan, but it works.
So what do airplanes do when they lose power? Glide down…really fast? Isn’t that pretty much the same as falling?
Are there any helicopters with ejection seats? Obviously it would have to eject out to the side and not upwards or else the pilot would be killed by the rotors.
Not to burst anybody’s bubble or anything, but a google search shows that helicopter crashes aren’t rare at all.
In my state, for a time in the 90’s, we were getting around 2-3 helicopter crashes per year, mostly from 1 company. The state finally shut them down.
Wow, this site lists over 20:
http://helicopter.stevestedman.com/
They’re relatively rare. Aviation accidents are rare enough that they tend to be Big News, unlike car crashes.
A controlled fall is called a ‘descent’. 
(And pilots do it all the time, else the skies would be very, very crowded.)
I think the Russians experimented with a system that blew the rotor blades off before ejecting the crew.
Falling is to gliding what jumping off a cliff is to skiing down a hill.
Falling is an uncontrolled descent. Gliding is a controlled descent. You’re using the air and the aircraft controls to go down in a controlled manner that allows for a gentle touchdown. When I fly airplanes, on my final descent the engine is commonly at idle, burning just enough fuel to keep moving at all, and what I’m really doing is gliding. In fact, if the engine quit during that descent in theory a passenger may notice very little difference from a normal landing. In a sense, most normal landings are a rehearsal of a no-power landing. This optimizes safety in many respects.
In fact, because an airplane pilot suddenly without a working engine will be very careful to conserve altitude as long as possible and unpowered descent that starts mid-flight may, in fact, approach the ground more slowly than one with power. The best glide speed on many airplanes I fly is slower than normal cruise, and I’m going to wait to apply things such as flaps.
So no, gliding is NOT the same thing as falling, not at all.
I have a friend who was in a helicopter when the engine really did fail, so yes, it can happen. He did his best to autorotate and both he and his student survived, although he suffered some broken ribs. Still, an uncontrolled fall from that height - several hundred feet - would without a doubt have been fatal. The fact they landed on rocky, broken ground didn’t help, either, but he didn’t have many choices for landing spots.
I was always under impression there was a hand rule or something: if you can count the dead bodies on one hand, it’s not “big” news, therefore a full bus accident gets reported, but an empty bus accident doesn’t, same with cargo plane vs passenger plane.
In the army we had a couple of hours instructions on a helicopter before we had our first flight in one - and I seem to recall the pilot holding the talk saying something about a “death altitude” that was an altitude in which a engine failure would most likely be catastrophic - apparently this was between 10m - 100m (or something like that) altitude. Under 10m and the helicopter could resist the impact, over 100m and you had enough height to allow autorotation to bring you down safely. Any helo pilot care to confirm or deny such a term/theory?
See the height-velocity diagram in post #3.
The difference between falling & gliding can be the difference between life & death. As an example, consider Air Transat 236, which ran out of fuel over the Atlantic but was able to glide almost 100 miles to the nearest airport in the Azores. If it had just fallen into the ocean when the fuel ran out, the ending of the story would have been very different indeed.
They certainly happen. A helicopter pilot friend of mine was killed a few months ago when trying to come in for an emergency landing after having engine problems. He almost had made it to an airfield when the helicopter more or less exploded at 900 feet.