By comparison, a Cessna 172 Skyhawk has a glide ratio of about 7.5:1.
ETA: A Robinson R22 has a glide ratio of about 2:1. Hey, this is a helicopter thread!
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Back on topic then, I’ve seen student helicopter pilots practicing tail-rotor failures, it’s not pretty but they seem to get on the ground ok.
I’ve always thought of autorotation as being like those trees where the seed pods fall off and then spin as they’re falling. By spinning, they drop a lot slower than a plain old seed would.
And, with a person at the controls, he can pull up at just the right time and the spinning rotor will cushion the landing before it slows down.
Isn’t it the same principle as those paper helicopters made by kids?
So is this autorotation thing basically that the rotors act kind of like a parachute, spinning from the fall through the air and providing enough lift to slow the descent to a survivable speed?
Correct.
I’m sure someone with advanced knowledge of the subject might find reason to quibble about that statement, but for layman’s purposes it does well enough.
Indeed. One of the videos I looked at when looking for examples of autorotations used the sycamore leaf analogy. Close enough for this thread.
According to this page, testing has shown that the V-22 cannot safely autorotate. While it was originally intended to be able to autorotate, the rotor inertia is too low and the rotor loading to high for it to work in practice.
That’ll teach me to trust Wikipedia pages — it said 85 nautical miles. As soon as I’ve posted here, I’ll edit the page.
I’m surprised no one has yet mentioned the autogyro, an aircraft that is based on the idea of autorotation. The aircraft is pushed forward by a powered propeller, but instead of a wing, lift is provided by an unpowered main rotor; this thing performs sustained flights in a way similar to how an ordinary helicopter flies without power to its main rotor.
I have friends who fly gyrocopters - there are some things you can’t do, such as hover, but prior to the invention of the actual helicopter there were much more common and very useful as they have very short take-off and landing distances. Gyros can also autorotate in the event of a power failure.
I imagine their experiments showed it wasn’t worth the effort.
- ejection seats are rather dangerous. Spinal injuries are fairly common on them. And that’s from ones that blow straight up, and then to compress the neck & spinal column. If they blew sideways I’d think they would snap the pilots neck like a twig. Or the pilot would have to be in a very tightly confined seat. Which fighter pilots already are, but normally helicopter pilots need to be more mobile and able to look around. I wouldn’t be surprised if statistics showed that helicopter pilots would be safer using autorotation to try to land the helicopter rather than be blown out of it by ejection seats.
- A system to blow the rotor blades off would add complexity to the already complicated gearbox of a helicopter. It would have to be very powerful, to blow the rotors off quickly enough and have them fly far enough away that the ejection seat could then blow the pilot away. A real risk that the rotors (or many pieces of them) would still be spinning around in the air where the pilot would be ejected.
- the system to blow the rotors away, and under the seats to blow them away, would add expense & weight to the helicopter, reducing efficiency on every flight.
- You would also need a component to blow open a hole in to canopy, for the pilot & ejection seat to go thru. In fighter planes this is fairly easy; the cockpit roof already opens, since that is how the pilot enters. You just need a mechanism to blow the cockpit roof off automatically. In a helicopter, there is no such roof exit, the roof is a solidly-built part of the helicopter body. It’d be much harder to open an appropriate hole.
- all of this is useful only if the pilot is wearing a parachute. Do they normally do so? I haven’t seen that in pictures. And there has to be time for the parachute to open and slow down their descent. Easy, for planes flying thousands of feet in the air. But helicopters are often operating fairly close to the ground. I’d think that much of the time, even if a pilot could eject, they would be too close to the ground for a parachute to save them.
The whole idea seems to have many obstacles in the way of a working solution. I’m not surprised that it isn’t used.
They are used. For example the Kamov Ka-50 and Ka-52 (single/double seater) have ejection seats. The canopy and rotor blades are blown off before ejection.
Missed edit window.
The low flight altitude that helicopters often operate at is not an issue as they have zero-zero ejection seats, meaning that they work even at zero altitude and zero velocity. A rocket pulls the pilot out of the helicopter (while the seat actually stays behind), high enough to land safely by parachute.
military pilot, countour flying is rather encouraged [or at least maintaining proficiency in it =)]
though thisincludes stuff going boom, so it would be lots of fun also …
Not really. They’d only have to be powerful enough to sever the connection between the blade and the hub. Once they’re free, they’ll fly away by themselves without any additional thrust from explosives. There’s a whole lot of force keeping the rotating blades straight, instead of flexing and breaking under (well, above) the weight of the airframe.
Henrichek: Thanks for the links. I knew the Russians experimented with ejection seats, but I couldn’t remember if they ever put them into production.
This last one may be an error. There are ejection/parachute systems designed to work at low speeds and altitudes. In todays fighter jets, a pilot can eject from a jet sitting still on the ground, and his chute opens and slows his landing.
Sorry. I see that this has been addressed already. :smack:
Just to add my favorite story of a “glider”:
I guess most any plane can glide but some you really want to avoid doing it in. Clearly though there are instances where a landing was achieved even with a commercial jet (pray you have some solid pilots at the controls).
The biggest problem is actually getting rid of the blades. The US government experimented with explosive bolts, but they couldn’t get the timing right. Fractions of a second in delay between the bolts exploding leaves you with a helicopter missing a few blades for a tiny amount of time. The resulting loads are so large that the helicopter will flip and and destroy itself, preventing anyone from getting out with an ejection seat. So, we gave up. The Russians were able to make it work, but it is not widely used. It is only practical for attack helicopters (that do not carry passengers).
Sikorsky actually had a prototype with a downward ejection seat, they never took the idea forward.
Robert Mason, in his excellent Vietnam helicopter-pilot memoir Chickenhawk, tells of training in Hueys which had an off-switch for the instructor, who loved to turn off the helicopter’s engine at the most inconvenient moments. It made for instinctive autorotations, though, and after awhile Mason actually enjoyed them.
Gary Powers, best known as the pilot of the U-2 spyplane shot down by the Soviets in 1960, was a helicopter pilot in later life and died in 1977 when his news chopper ran out of fuel (through no fault of his own). He did an autorotation but swerved to avoid kids on the ground, crashing and killing himself and his cameraman: Francis Gary Powers - Wikipedia