Ultra low RRPM
Boy I really struck a nerve with all of you.
let me offer a couple of precisions to maybe calm dowm the opnion
let me offer a couple of precisions to maybe calm dowm the opnion
John,
Heard a variation on that story involving another person on the receiving end and in another situation. I wonder if Jimmy used it more than once. He did have a way with words. Jim Chudars could also.
Heard a variation on that story involving another person on the receiving end and in another situation. I wonder if Jimmy used it more than once. He did have a way with words. Jim Chudars could also.
Agile,
First, I don’t understand your statement reference that ground effect hover is not flight. From every point of view, hovering is flight. Furthermore, as an aero engineer you should know a few things about a test point. For example, it’s purpose and the amount of study, calculation, simulation, and risk analysis prior to execution. The stunt seems more akin to that of an amateur daredevil. I also feel that an explanation of how and why the aircraft was never to be flown again would be most entertaining.
First, I don’t understand your statement reference that ground effect hover is not flight. From every point of view, hovering is flight. Furthermore, as an aero engineer you should know a few things about a test point. For example, it’s purpose and the amount of study, calculation, simulation, and risk analysis prior to execution. The stunt seems more akin to that of an amateur daredevil. I also feel that an explanation of how and why the aircraft was never to be flown again would be most entertaining.
Originally Posted by Ascend Charlie
Thinking out loud here:
The rotor is at idle or below.
The engine starts out at idle.
Agile pulls up on lever, the correlator will try to add throttle
Must hold throttle closed against the spring to keep correlator out of it, and engine stays at idle.
Agile then pulls pitch to get off ground. Supposedly gets to the hover.
How the fork can an idling engine, with 40% rotor RPM, lift the machine off the ground? It has enough trouble doing it at 100% engine and rotor RPM.
If engine is at idle, how can he get max MAP?
If he has max MAP, then he sure isn't at idle, which is around 13" by memory.
If the engine isn't at idle, then the RRPM aren't either.
I think this whole story smells of bovine excreta.
The rotor is at idle or below.
The engine starts out at idle.
Agile pulls up on lever, the correlator will try to add throttle
Must hold throttle closed against the spring to keep correlator out of it, and engine stays at idle.
Agile then pulls pitch to get off ground. Supposedly gets to the hover.
How the fork can an idling engine, with 40% rotor RPM, lift the machine off the ground? It has enough trouble doing it at 100% engine and rotor RPM.
If engine is at idle, how can he get max MAP?
If he has max MAP, then he sure isn't at idle, which is around 13" by memory.
If the engine isn't at idle, then the RRPM aren't either.
I think this whole story smells of bovine excreta.
Conclusion: your verdict of the excretus bovus strikes me as spot on.
Last edited by Lonewolf_50; 15th Mar 2020 at 15:18.
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OK you are coming back with your student, governor-off training, all goes well, correlator is making things easy. good approach, student start to taxi carefully, RRPM gets a bit low but ok, now student start to taxi down wind (only way to the pad), wind engages the tail, student puts full power pedal, lose more RRPM, buzzer is on, student get nervous, rotor lose more efficiency, AC harder to control, student crank a lot of throttle, MAP is now the red, rotor dangerously decayed and you are still flying. this situation could have happened. not necessarily a stunt.
Engine-off autorotation, same thing, in the last few seconds as you adjust your touch point, you will find yourself flying with the rotor decayed to its absolute limit of lift vs RRPM
For the technical reasoning, the factor that would deserve primary attention is the impact on the blades due to the reduced centrifugal forces if you assume that at nominal RPM the rotor can endure a maximum load factor of 2 to 3 at MTOW (ie a turn of 60 deg bank+) then the rotor should be able to assume a reduction of centrifugal force of 2 to 3 at MTOW or almost 4 at MTOW-30% (a lightly loaded AC) this translate into a reduction of RPM of 50% (square root of 4) not too far fetched.
I retain the disclaimer:
The normal and only practice is the flight manual that has been defined by much more qualified people this side thinking is a distraction that is keep very well separated.
Another point:
I think students are not exposed enough to low RRPM, yes they teach you to lower collective until it becomes a motor reflex but you will still find individuals doing the wrong thing or freezing or suffering brain fart when the buzzer is blaring and the rotor noise is lowering its pitch I could dare to assume that more exposure to this low RRPM condition can tech the brain that there is no reason to freeze.
Engine-off autorotation, same thing, in the last few seconds as you adjust your touch point, you will find yourself flying with the rotor decayed to its absolute limit of lift vs RRPM
For the technical reasoning, the factor that would deserve primary attention is the impact on the blades due to the reduced centrifugal forces if you assume that at nominal RPM the rotor can endure a maximum load factor of 2 to 3 at MTOW (ie a turn of 60 deg bank+) then the rotor should be able to assume a reduction of centrifugal force of 2 to 3 at MTOW or almost 4 at MTOW-30% (a lightly loaded AC) this translate into a reduction of RPM of 50% (square root of 4) not too far fetched.
I retain the disclaimer:
The normal and only practice is the flight manual that has been defined by much more qualified people this side thinking is a distraction that is keep very well separated.
Another point:
I think students are not exposed enough to low RRPM, yes they teach you to lower collective until it becomes a motor reflex but you will still find individuals doing the wrong thing or freezing or suffering brain fart when the buzzer is blaring and the rotor noise is lowering its pitch I could dare to assume that more exposure to this low RRPM condition can tech the brain that there is no reason to freeze.
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this situation could have happened.
if you assume that at nominal RPM the rotor can endure a maximum load factor of 2 to 3 at MTOW (ie a turn of 60 deg bank+)
then the rotor should be able to assume a reduction of centrifugal force of 2 to 3 at MTOW or almost 4 at MTOW-30% (a lightly loaded AC)
this translate into a reduction of RPM of 50% (square root of 4) not too far fetched.
then the rotor should be able to assume a reduction of centrifugal force of 2 to 3 at MTOW or almost 4 at MTOW-30% (a lightly loaded AC)
this translate into a reduction of RPM of 50% (square root of 4) not too far fetched.
But let those revs decay to 40%, and you will find that you are not flying any more. The rigidity of the blades is vastly reduced, the blades will cone excessively, and Frank Robinson will be really annoyed. Yes, it is too far fetched.
Engine-off autorotation, same thing, in the last few seconds as you adjust your touch point, you will find yourself flying with the rotor decayed to its absolute limit of lift vs RRPM
If you let a student decay the Nr to 40% - or anywhere near that - you should give back your instructor ticket.
