Auto-rotated I meant, obviously.
Fascinating discussion on this.
It’s particularly interesting to see the mix of opinion among pilots and engineering/aerodynamics thinkers. The information about rotor “flap” is unexpected. I wondered about how dynamic forces would affect fuel flow to the engine. The fact that Army instructors couldn’t get a restart from 5k feet is quite interesting, too. I must reread the technical note about low rpm stalls.
One of the later posts may be right that the blades were in the stowed position at some point in the process of Bond and Jinx getting aboard and ejecting the helicopter from the cargo bay door, which would seem to render moot the entire question, but I also seem to remember that “somehow” they were in proper position in the first shot of the freefalling scene, so we can keep our assumptions intact for the purposes of the larger problem under consideration.
I was interested in the technical problem presented in the movie party because as a young teen in the early 1960’s I witnessed a helicopter crash into Gastineau Channel in Juneau, Alaska, and autorotation WAS used quite effectively by the pilot to prevent injury to himself and his sole passenger.
The helicopter was an Alaska Coastal Airlines “Hiller,” I think the model was a UH-12A, B, or C. It took off from a dock, reached an altitude of a few hundred feet, and the engine failed. It “stopped” in midair, nosed down sharply and dove, just before hitting the water the nose pulled up sharply as the pilot arrested the descent, it hovered 10 feet above the water for a few seconds, then fell backward and to the left into the water with a great splash. As it slowly sank two dots bobbed up alongside, and a fishing boat raced out to pick them up, perhaps a quarter mile off the dock. No harm to either occupant.
I don’t know why the instructors would actually shut down the engine, unless it was to teach the student how to do an in-flight restart. This is not done in the civilian world. As TriPolar notes, helicopters have a freewheeling unit (aka Sprag clutch) that disconnects the rotor system from the engine. Rolling the throttle down, as rsat3acr said they did, is the same as shutting the engine down in that in either case the rotor system is freewheeling. I’ve never flown a turbine-powered helicopter, but I understand that they’re a bit more involved to start than piston-powered ones. As I said, we never actually turned the engine off. We did our autorotations from 1,000 ft. AGL. The Robbo R22 and the Schweizer 300 (TH-55 to you Army guys) come down at about 1,500 feet per minute. Not really a lot of time to attempt a restart.
I’m not entirely sure how ‘flap’ is being used in this thread. If I understand flight’s post, he’s talking about ‘blade flapping’, which is how I use it. Here is an article on blade flapping.
When entering an autorotation, inertia keeps the blades turning while the pilot lowers the collective to reduce the pitch and drag so that aerodynamic forces can take over. Hovering autorotations have been mentioned. Here, you need to pay attention to inertia. I’ve never flown a UH-1; but I’ve been told that one could be in a hover, chop the throttle, turn 180º, and set it down gently. A Robbo or Schweizer doesn’t have that much inertia in the rotor system. Still, the drill is to wait a full second before pulling collective, for the reason posted by rsat3acr.
I linked to blade flapping. That link is from this page. If you want to read more about helicopter aerodynamics, that’s a good set of articles. The source is Army Field Manual FM 1-203, Fundamentals Of Flight, 9 September 1983. I think my copy is the same one. (In my training, I used the FAA publication. I haven’t had time to study FM 1-203.) I have a newer copy, but I don’t recall where I got it. For the older one, I contacted the Army and they sent one. For the newer version, it was only available as a download. I took the file to a printer and had a bound hardcopy made.
Yeah, flapping is the up/down motion of the blade as measured by the angle at the root of the blade. When most people use the term they mean the 1/rev component: basically the thing that defines disk plane. Here I am just using it the general sense of the blade moving up and down while it goes around. Without a good rpm to hold the blade point out from the hub, it can flap however it feels like and will very likely damage itself and anything else nearby.
Yep. The NZ Air Force used to demonstrate this at air shows by having a UH-1 sitting on the ground then cutting the power and, on rotor inertia alone, lifting up to a hover, turning through 360°, and landing gently.
Can any of you cite any vids to anything helpful here ( and I don’t mean Bond…).
Johnny L.A.
To clarify, we were told that a pair of instructors actually cut the engine of to attempt a restart. No students involved. With students the throttle was rolled off, never cut the engine off. We did our autorotations to touchdown, now so I am told, they do a power recovery. The throttle is rolled on a helicopter brought to a hover. Too much wear and tear on the skids I assume.
Could a helicopter be designed or modified to do this? Have the blades be able to tilt 90 degrees, and gradually rotate towards level as they spin up, with a modified clutch to allow restarting the engine from the rotor rotation? Could the blades be modified to reduce the amount of flapping?
Restarting the engine from rotation is extremely dangerous. It will rob the rotor of energy, and if the engine does not start the helicopter will be dropping like a rock. If the engine can be started, it’s own starter motor should be able to do the job.
Also, I think getting the blades to spin up while tilted up at 90 degrees won’t work. The foils won’t be angled in the direction of airflow. In theory a properly designed rotor should be able to spin up from the airflow in normal configuration because that’s how small gyros work. But it takes a long take off run to get a gyro rotor spinning fast enough to produce positive lift, that’s why many of them have small motors to spin the rotor up to a decent initial speed before attempting the take off run.
I don’t think the maneuver in the OP can be done, so I doubt there are any videos.
I don’t know if these are helpful to you, but here are some videos of autorotations:
0-Speed Autorotation from 100-200 feet, R22 helicopter
Autorotation - Landing a Helicopter without Engine Power. This one’s a little dull, but it does show ‘splitting the needles’ and has some explanatory notes.
This one has the an instructor talking a student through an autorotation. In this video, you can hear the low rotor RPM warning horn (and see the annunciator light). The page says the student has about 15 hours at this point.
One thing you may notice in these videos is how uneventful they are. Everything is safe and under control. You really have to get up and do it to feel how much fun they are. It’s like your own, personal roller coaster. 
[quote=“Johnny_L.A, post:30, topic:655850”]
I don’t think the maneuver in the OP can be done, so I doubt there are any videos.
Yes, that’s pretty much what I’m getting from the responses here, though I don’t quite get the 90 degree blade angle problem “Tri-Polar” cites.
Does he mean that in straight freefall (no forward airspeed), from zero rpm, the blades cannot be set in a position to harness the air-flow needed to spin them up to an rpm allowing the pilot to apply lift, as opposed to the already turning blades and forward airspeed assumed to be present in a “normal” autorotation emergency? Guess I need to read the Army manual link.
From Tri-Polar’s last post it also doesn’t seem you would be much better off trying to start the engine and power up the blades. Probably you’d still risk losing a blade and your tail boom to blade strike.
I’m uncertain about any interplay between blade instability from lack of centrifugal force at low rpm’s, as someone mentioned, vs. the unbalanced-lift “flap” of advancing and retreating blades within the rotor disk due to low rpm stall on the retreating blades.
In any event, it begins to appear that Bond and Jinx will not, in fact, “Die Another Day.”
Not sure what your asking about here. In my last post I interpretted ZenBeam as asking if the blades could be parallel to the main rotor shaft initially, I assume to avoid flapping issues. In that position while in a straight down free fall the air flow is running along the length of the blades and not doing anything to make them turn.
The collective pitch of the rotor blades can be lowered (i.e each rotor blade is tilted down), but based on what it takes to get autogyro blades spinning I doubt there’s time to spin them up fast enough to generate lift if they are not moving initially. Autogyros are essentially always autorotating from airflow moving through the rotor, but they don’t start up easily. A simple gyro has to be pushed (or pulled) by a propellor through a long take off run with the whole rotor tilted back to get the rotor up to sufficient speed to generate lift. Many include a seperare pre-rotator motor to get the blades spinning fairly fast to reduce that take off roll, although there are some that can use a pre-rotator to achieve full rotational speed and even ‘jump start’ similar as to what’s described in post #25 by Richard Pearse. It is basically lift that causes the blades to spin. They are pitched downward, so as air flows around the foils creating lift the force is directed forward relative to the rotor blade, causing it to rotate. In order to land while dropping straight down you need to be able to increase the pitch of the rotor blades as helicopters almost all do, and generate positive lift. Some gyros can do that, but many have fixed pitch blades and can only tilt the rotor and require converting the air speed from totally downward into a forward direction.
Of course, possible or not, the OP is talking about an exceptionally unusual operating environment. From this discussion, though, I am amazed that helicopters fly at all. Is it particularly difficult to learn to operate a helicopter, at least relative to fixed-wing aircraft?
IANA pilot, but I’ve never heard an argument that helicopters are easier to fly than a fixed wing craft. Helicopters are unstable and require constant input to keep from becoming expensive bricks. As a comparison, the first auto-pilot for an airplane dates to 1912. I don’t think there was an auto-pilot for helicopters until the late 1980s.
I’ve never flown a fixed wing, but I don’t think straight and level flight would differ too much between the two as far as difficulty. Hovering is a different matter, there is no equivilant in fixed wing and it was the hardest part of learning to fly a helicopter. Flew straight and level first time in a helicopter with no problem. Hovering took a coule of weeks of practice to be able to do.
oops, meant to quote TriPolar on if helicopters are easier to fly than fixed wing.
I wouldn’t say that either a helicopter or fixed-wing is more difficult to fly than the other; they’re ‘different to fly’. As has been said, an airplane with basically fly itself; and a helicopter needs constant inputs. In cruise, flying a helicopter is similar to flying a fixed-wing (remembering that some things done in airplanes are the Wrong Thing to do in helicopters). The most difficult part of learning to fly a helicopter is hovering. It’s also the first thing you need to learn. Once you have hovering, the rest is easy. All of those ‘constant, minute control inputs’ become automatic.
The light, 2-place helicopters I’ve flown are much lighter on the controls than a Cessna Skyhawk – which I found out on my intro flight. [Aside: I met a USMC Super Sea Stallion pilot who said, 'You fly an R22? Those things scare the shit out of me! They’re too squirrelly. A friend of his, a Sea Cobra pilot walked up and said, ‘You fly an R22? I love those! They’re so nimble!’] The view is superior to airplanes, and the rules are more to my liking. I find that landing a helicopter is easier than landing an airplane.
So: Hovering is a steep learning curve, but you can learn how to do it in a couple of hours. (It takes several more hours until you’re smooth and proficient at it.) The required control inputs are quickly committed to ‘muscle memory’, so that’s not difficult at all (once you let your body fly the aircraft instead of your head). You need to ‘stay ahead of the aircraft’ no matter what you fly; but it’s easier to ‘get behind the aircraft’ in a helicopter. Each type has advantages and disadvantages, but as far as the ‘which is more difficult to fly’ question, they are equally difficult or equally easy. They’re just different.
The difficulty with flying a fixed wing is that it can’t stop. If you’re flying into deteriorating weather you need to make decisions and they need to be the right ones made before it is too late. That opportunity to turn back that you just let slip away might have been the last one. When you’re doing 450 knots things can go bad awfully fast. Even in a light fixed wing at 120 knots, things can still turn bad very quickly. In a helicopter, unless over rugged terrain, you typically have the option of just landing somewhere. On the other hand I don’t think there is any doubt that helicopter flying requires more coordination. Like most skills though, once learned it becomes somewhat automatic, that goes for mentally keeping up with a fast fixed wing as well.
I spent an hour on Shelter Island (San Diego) yesterday watching SH-60’s practicing autorotation at North Island Naval Air Station. Depending upon how its done, it can be pretty scary to watch if recovery is delayed until petty close to the ground.
Maybe 90 degrees is too far. I meant that the blades could be angled to use the air speed to bring them from stopped up to speed, to be able to start the engine using the torque from the spinning blades.
Minimizing flapping is a separate problem, possibly just requiring different material or design.