PS: What a great site.
Entrance: rotorheadsrus.us
That’s the first time I’ve seen that domain, and it’s on the money.
Describing lead-lag acceleration as “Coriolis effect” is weird, although I’ve heard it before. It’s conservation of angular momentum.
First of all, flapping:
“Dissymmetry of lift” occurs in forward flight, because the aircraft’s forward motion is added to the airspeed of the advancing blade, but subtracted from the airspeed of the retreating blade. Flapping is vertical movement of a blade perpendicular to the axis of rotation that effectively varies the angle of attack (decreased on the advancing blade that flaps up, increased on the retreating blade that flaps down) to help eliminate dissymmetry of lift.
When a blade flaps (vertically), the center of mass of the blade inevitably moves (horizontally) very slightly closer to / further from the axis of rotation. Conservation of angular momentum then makes the blade want to accelerate / decelerate slightly (the same principle as ice skaters pulling their arms in tight). The lead/lag hinges allow this acceleration/deceleration to occur to each blade independently as it advances/retreats during each rotation, alleviating stress at the rotor hub.
The classic example is an ice skater performing a spin. With her arms and leg extended, her rotation is slower, and when she pulls her arms and leg in, her rate of rotation increases. Short video, A longer video explaining the Coriolis Effect.
As a rotor blade flaps up or down, the distance from the tip of the blade to the axis of rotation becomes shorter (cosθ * hypotenuse = length of adjacent side). Since the tip of the blade is closer to the axis of rotation, it needs to speed up. In a semi-rigid (‘teetering’, two-blade) rotor system, the blades flap up and down as a unit. Since the distance from the axis of rotation remains equal on each side, they speed up and slow down at the same time and there is no need for a lead-lag hinge. In a fully-articulated rotor system (three or more blades), the up-flapping blade reaches its highest point before the down-flapping blade reaches its lowest point (and vice-versa). Since the blade tips are different distances from the axis of rotation, they want to travel at different speeds. The lead-lag hinge allows them to do that. The highest/lowest blade can move forward a little, and the other blades can move backward a little.
ETA: Beaten by Riemann.
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There’s a picture of the hinges and axes of movement in a fully-articulated system here:
In the 1960’s the USN studied a concept where a radar picket helicopter would hover continuously at its operational altitude, with a several thousand foot long very thin and light refueling hose, as opposed to the HIFR concept in actual practice where the helicopter hovers while refueling from a ~150 foot hose at lower altitude than that, but then goes back about its mission untethered. The central problem of course was to make the hose light enough not to subtract more payload than it was worth to avoid interruption of the surveillance. And it must not have worked out practically.
But as Shagnasty suggested, it’s a lot more practical to think of changing crews in a hovering helicopter than a plane (the quoted record of a flight on Wikipedia is an unmanned helicopter, Boeing A-160, without aerial refueling). In fact this was done on what was held as the longest ‘operational’ mission of a helicopter at the time, where a Royal Navy Sea King embarked on HMS Hermes in the Falklands War operated for 10 hours 20 minutes including not only refueling but crew exchange via the rescue winch from the frigates Brilliant and Yarmouth without landing on them. Of course a big plane or even helicopter could carry spare crews instead.
It seems very feasible with hover refueling/crew changes to make engine lubricating oil consumption the limiting factor in helicopter endurance, continuously hovering or not, as with fixed wing planes intended for very long aerial refueled missions (VC-25, etc). Then you could work on that also.
Yeah, I didn’t say that too gud. 
What I meant was that as of a few years ago or earlier, hovering was always 100% pilot skill on all helos always everywhere. Nowadays it’s possible that Leo was watching a computer doing or helping the work. But it might still have only been a human good at his job.
His opening idea that there’s some specification for hovering position-keeping quality implies (at least to me) that he assumed it was a machine doing the work.
Yes it is. It taint Coriolis effect and I was too intimidated to do av:dubious: because basically I’ve been schooled.
Sure, it is. (At least, as used by helicopter pilots. 
)
Yeah, I took lessons that said that too. It’s obviously not the Coriolis Effect, any more than it’s the Coriolis Effect that creates the fluid vortex in your loo. I don’t know where the mistaken notion originated, but it has been copied and disseminated in various instruction manuals. And the Wikipedia, “helicopter rotor” article, I see.
Interestingly, in the example you cite, the guy gives a perfectly accurate description of what the phenomenon really is - conservation of angular momentum - but just calls it the Coriolis Effect. So in this case, at least, it appears to be a misunderstanding of what the Coriolis Effect is, rather than a misunderstanding of what’s actually happening in a heli rotor.
Agree it’s not properly Coriolis. Also FTR IANA helo expert.
In thinking about it, I suspect somebody decided that because the blades are “transported” into a higher plane as they flap (or cone) up, and because they are rotating, that the lead/lag effect represented a consequence of transport in a rotating reference frame.
It doesn’t, but it sounded plausible to somebody writing a manual for 1950s-60s Army helo pilots. And such are the way legends are born.
I attended a race and events at the Milwaukee Mile once. There was a chopper hovering above pretty high. Probably a media/camera crew. At the time there were no LEO agencies with a hilicopter around here. The one the Sheriff had crashed a while previously.
That thing was absolutely stationary up there. I mean it didn’t move an inch.
And I had been there for over 7 hours so it had been it that position for at least that long, and it was there when I got there!
Explains why all the radar operators are always talking about the aether.
[quote=“Riemann, post:8, topic:760613”]
It’s CJ from The Fall And Rise Of Reginald Perrin. That brings back some memories.
[/QUOTE]Lol, God I love that show.
