Are you saying that reaching CT/sigma max due to high speed disc loading where there is no RRPM reduction ie pullup or steep turn as high G manoeuver - is the same as overpitching with collective where there is obvious RRPM reduction (not enough engine power) where the might only be a very small increase in G.

Surely the 2 don't correlate - you have achieved the same aim eg producing as much TRT as possible but by 2 different means and with 2 clearly different coning angles.

AnFI, can you point me to an official accident report that has rotor stall as being causative in an accident. Many thanks.

And you know there won't be one.......

I suspect that ANFI would pontificate that the investigators haven't "Had a moment or clarity" that would allow them to discover this oversight.

Apologize in advance for the diversion, but am a bit surprised that with all the " commotion " regarding coning, it hasn't been mentioned that the S-70 rotor head, since initial design, has " pre-coning " built into the head, which of course would go to support the premise advanced in this thread, right?

Wrong: the pre-coning was incorporated for a single non-related reason: to reduce the steady state amount of flapping required of the elastomeric bearings, thereby allowing for the goals set for their component replacement time. Same goes for the pre-lag.

B212 has pre-coning too....

Hmm, could it be that this whole thread was just about AnFi thinking out loud to see what people thought of his idea?

That probably would have been OK if he hadn't insulted and rejected anyone who tried to give him advice or disagreed with his point of view.

Punto
thank you
"allowing pilots to enter the pull more get less zone without warnings"
you have been warned and the vibration and the rapid increase in energy consumption are thought to be sufficient

Lala
The first happens when you do have sufficient energy available from somewhere and the second occurs when there is not, just pulling more that the engine has doesnt get you to the limit of the blades untill the RRPM has been reduced whereupon the CA will be approximately the same for both cases

Brian Abraham
No official accident reports mention limit of Rotor Thrust being the cause. You are right, Strange when there are so many accidents like that, you'd have thought 'they'd' notice.
I think they just say if you hit the ground then you were too low (as Crab said) indisputably true and reasonably obvious.

JD
and the many of the Bell family because they don't have independant flapping hinges or coning hinges and the difference needs to be taken up by sheer loads on the blades (or elastomerics where present), so chosing an average coning value minimises the stresses. As you know well. (and some tail rotors that don't have coning hinges have pre-cone)

Crab
Still pricking away, eh? "AnFi thinking out loud to see what people thought of his idea?" yes that is partially true, and I am a little surprised at either how few got it or were willing to support it out aloud who did get it.

thank you for your time, especially those that gave it genuinely

I think you meant to write "shear loads" but in any case, shouldn't that be "bending loads"?

But you have said that the amount of coning is related to the amount of G loading - eg 10 degrees for 2 G and higher for more G.

In the power limited example there will be a high angle of coning for minimal G.

You have asserted that you can assess G loading from the coning angle but that can't be true.

The amount of coning in the high G manoeuver will be far less since the RRPM hasn't decayed and you haven't reached the engine limits.

yet you have tried to present this idea as absolute truth with mathematical proof which is clearly disingenuous - it is your take on what MIGHT happen based on nothing but speculation.

Trouble is, people are starting to see through you.

Can you not see that people might not get it because there is nothing to get?

Surely, G loading on helicopters is mainly a result of flapping rather than coning, in any case?

And you haven't really addressed the issue of the stall characteristics of the rotor - your soft or dirty stalls don't correlate with the experience of retreating blade stall which will be the limiting factor of what the rotor system can produce.

If you try and pull through RBS, you will just aggravate the condition which will manifest itself as a pitching nose up and a roll towards the retreating side. Niether of the conditions you talk about (pulling hard to avoid the ground or overpitching without enough power) show any indications of RBS so the conclusion is that the rotor hasn't stalled and that coning angle is irrelevant.

In the case of the apache video, it is likely that more TRT was available because he still had speed (which you calculated to be circa 90 kts) to convert to additional load factor. There is no indication of RBS (no pitching or rolling) so no evidence that the rotor had stalled.

The bit I struggle with logically is if there is an ultimate coning angle then the disc is self limiting. It can't pull any more lift. The pilot can pull as much collective as they want. So all that needs to be monitored is Nr as the most lift is at the ultimate cone and the highest Nr. So why worry about the proximity of the ultimate coning angle?

AnFI, sorry to disappoint, but that isn't what I wrote and you took it to be something it isn't:

The pre-cone was put in so that the 1P flapping number ( that's the max during one revolution ) remained under the endurance limit for the bearings. After the stabilator was added during the development period, we used that as a tool to fine tune the stabilator schedule to walk the fine line between the flapping endurance limit and the everpresent need to pay attention to the level flight performance numbers ( and both of those factors as they applied at the extremes of Center of Gravity ).

So, nix on der average coning nonsense.

Perhaps AnFi is confusing aerodynamic damping with his UCA.

He's confusing everything with everything....

Lala you are Crab, no! hitting the Max Thrust the rotor can make is described well by NL, go and read that. Just because a rotor doesn't actually do what you think it does, doesn't change the point and its all been written now I think, there is no further clarification to make I think. Ctmax gives the max thrust the rotor can make. partially stalled blades just cause vibration and the loss is spread around the disk, the power required goes up. If you get catestrophic then I gues you will see blowback etc


dc/da
"The bit I struggle with logically is if there is an ultimate coning angle then the disc is self limiting." Yes effectively

"It can't pull any more lift." Correct

"The pilot can pull as much collective as they want." er NO how does that follow? 'Pulling' can be by pitch up as in pulling out of a dive. You probably can pull as hard as you want (stressful vibration) in terms of pitch rate but it won't do you any good in terms of extra g because you are already at Ctmax, just more energy washed off. You'll be at UCA

"So all that needs to be monitored is Nr as the most lift is at the ultimate cone and the highest Nr." Nr tells you wether you are using more energy from the rotor that you are supplying to it. Coning angle tells you how much of what the rotor can do it is doing.

"So why worry about the proximity of the ultimate coning angle?" dont worry about it just note that regardless of the RRPM when you hit the Ctmax that will happen at approximately the same CA regardless of RRPM, if your RRPM is drooping you are not supplying the rotor with the energy it needs so you have bigger problems (but you'll get to UCA)

Shytalk
"Surely, G loading on helicopters is mainly a result of flapping rather than coning, in any case? "
Not sure you mean that?
G loading is the ratio of Thrust Force to weight(at 1g). So it is about how much Thrust you make compared to your '1g-weight'. You make more thrust with either the Collective Lever OR the Cyclic Stick (by pitching nose up whilst at speed), or both, this increases Angles of Attack.
If you use only the lever you will probably reach the engine limits NOT the Thrust limit of the disk, so the RRPM will droop, before Ultimate Thrust is reached. ONCE the RRPM has drooped then the Max Thrust the rotor can make will be less, if you continue to that Max Thrust (whether high at high RRPM or low at low RRPM) the UCA will be reached, and it'll be about the same regardless of RRPM.
Coning is just a symptom of Thrust (TRT). It indicates how much thrust you are making as a proportion of your Cf (Nr), because CA=TRT/Cf
Maybe you are thinking about feathering rather than flapping?


let's try this , open question
if a Rotor can only make enough thrust to pull 3g when light, and it's 1g coning angle is 3degress, then what coning angle would it have at 3g ??
Everyone's answer
please

Been away for a couple of weeks, can't believe this is still rumbling along. Did nobody get the memo about not feeding the troll?

Who really gives a stuff?

If it takes a yard and a half of calico to weave an elephant's underpants, how long will it take a double-breasted cockroach to tap-dance through a barrel of treacle??