A question about the cyclic delay
leviterande - it says R44 helicopter simulator at the top
Don't confuse rotor/fuselage response times with the time taken to overcome the inertia of the helicopter and accelerate it. The graph doesn't show fuselage attitude, only cyclic input.
The simulation also doesn't show inflow roll (or transverse flow for US trained pilots) so don't put too much faith in it.
If rotor/fuselage response times were in the order of 2 seconds, no-one would need ASE/SAS/AFCS to reduce pilot workload since they tend to provide rate damping to slow down the rotor response to cyclic inputs
Don't confuse rotor/fuselage response times with the time taken to overcome the inertia of the helicopter and accelerate it. The graph doesn't show fuselage attitude, only cyclic input.
The simulation also doesn't show inflow roll (or transverse flow for US trained pilots) so don't put too much faith in it.
If rotor/fuselage response times were in the order of 2 seconds, no-one would need ASE/SAS/AFCS to reduce pilot workload since they tend to provide rate damping to slow down the rotor response to cyclic inputs
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Ahaha o yeah didnt see that ops! hehe simulator it is!
"Don't confuse rotor/fuselage response times with the time taken to overcome the inertia of the helicopter and accelerate it. The graph doesn't show fuselage attitude, only cyclic input."
Your absolutely correct, inertia effects can be pretty significant in a 60 ton russian Mil Mi-26 where the tilted rotordisc&fuselage do not impart movement until 40 years later
!"Don't confuse rotor/fuselage response times with the time taken to overcome the inertia of the helicopter and accelerate it. The graph doesn't show fuselage attitude, only cyclic input."
Your absolutely correct, inertia effects can be pretty significant in a 60 ton russian Mil Mi-26 where the tilted rotordisc&fuselage do not impart movement until 40 years later
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Well, bear in mind that on a 60 ton Mi-26, for a given tilt angle of the disc, the horizontal thrust component is somewhat bigger than in an R-22 
- hence the movement of the fuselage shouldn't take too long either 
- hence the movement of the fuselage shouldn't take too long either
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To try to put a final slant on this topic. On all types that I've flown (and that is quite a few), it is very difficult to demonstrate convincingly a perceptible lag between cyclic input and fuselage attitude change, although the rate of attitude change obviously does vary due to inertia differences. The possible exceptions were the Hiller 12b/c where moving the cyclic operated the paddles which then changed the disc attitude and the Bell 47's where the cyclic input goes through the stabiliser bar and induces a tiny delay (the .47 sec). If you can see half a second delay, good luck!
Inertia then affects the rate at which the change of speed occurs viz R22 at one end and MIL 26 at the other.
Inertia then affects the rate at which the change of speed occurs viz R22 at one end and MIL 26 at the other.
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Crab
You are jumping a little fast to conclusions.
It pretend this is an advanced integrated simulator developped 6 years ago. (not really a humble statement, because I made it). It does very detailed aero dynamic calculations about 500 times per second based on pretty advanced aerodynamic models (not just your plain to earth second order model, but full viscous flow, including stall, but that has been explained 5 years ago). It models most aerodynamic parts including rotor blades, hull, fins and implements inertial calculations in full detail of most (ridgid) parts. So it can correctly predict extreme flight paths and explain detailed air flow in the rotor. It cannot predict vibrations. In all experiments I checked to date with real flight data it showed to be more precise then measurable (typically better then 5%)
I have the complete film the simulator generates from different view points (pilot, outside observer) but from where I am, I cannot extract and post it. Perhaps I will post some snap shots if I can find the time.
But I sincerely think the graph answers precisely Levi's question, without having to go in such detail. I'll try to post the pilot view every second, pretty scarry indeed because after 10 second you crash). You will see the first two seconds consist mostly of a forward pitching and that the blow back if very impressive.
d3
It pretend this is an advanced integrated simulator developped 6 years ago. (not really a humble statement, because I made it). It does very detailed aero dynamic calculations about 500 times per second based on pretty advanced aerodynamic models (not just your plain to earth second order model, but full viscous flow, including stall, but that has been explained 5 years ago). It models most aerodynamic parts including rotor blades, hull, fins and implements inertial calculations in full detail of most (ridgid) parts. So it can correctly predict extreme flight paths and explain detailed air flow in the rotor. It cannot predict vibrations. In all experiments I checked to date with real flight data it showed to be more precise then measurable (typically better then 5%)
I have the complete film the simulator generates from different view points (pilot, outside observer) but from where I am, I cannot extract and post it. Perhaps I will post some snap shots if I can find the time.
But I sincerely think the graph answers precisely Levi's question, without having to go in such detail. I'll try to post the pilot view every second, pretty scarry indeed because after 10 second you crash). You will see the first two seconds consist mostly of a forward pitching and that the blow back if very impressive.
d3
that during these 2 seconds in your diagram, the fuselage is tilting but not yet acquired forward movement
Delta3 - I am sure it is a very clever simulator but does it show roll towards the advancing side during a transition? If not then your sums (advanced as they may be) are wrong.
In my humble experience, the problem with simulators is that they are just computers and, like any computer, if you put garbage in you get garbage out.
Many full-size sims costing millions still can't replicate the actual handling qualities of a specific helicopter because all the data has to come from an instrumented aircraft of the same sort to be accurate, instead of the data being modelled with clever mathematics.
In my humble experience, the problem with simulators is that they are just computers and, like any computer, if you put garbage in you get garbage out.
Many full-size sims costing millions still can't replicate the actual handling qualities of a specific helicopter because all the data has to come from an instrumented aircraft of the same sort to be accurate, instead of the data being modelled with clever mathematics.
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Crab
Crab
Crab, yes it does.
It starts from basic physics, not from modelled behaviour, which makes it quite unique, but a formidably complex mathematical project (even including ground effect, tail fin down-wash interference etc...) This setup was specifically deveopped to have a precise view on full rotor dynamics during all parts of flight.
In the scenario shown here, model was operating in what I call 2-D mode, auto-pilot feature was doing lateral cyclic and tail rotor. That is an approriate set-up to answer Levi's question, not for your question of lateral transients.
The problem is -as discussed years ago with Nick Lappos- in order to have reproducible data, autopilots capable of flying predetermined paths need to be developped, which is again a project, and as it was supposed to run of a PC, not a super-mini, there is a CPU limitation. We found -as Nick predicted- that it is not possible to get reproducible data by hand flying the sim, you cannot fly it that precisely. So a number of path controllers were added to te sim.
Further more the amount of data produced is enormous, rendering, graphing up to generating full 3D sim like films etc, is again a project.
Development stopped 5 years ago, because the goals of simulating advanced auto rotations at many different configurations (W&B, RPM, density etc...), all sorts of low G situations, the said Frank's Wiwa and all sorts of coning/delta3 related rotor dynamics. Where do you think my alias comes from, I assume you should know that delta3's are related to lateral rolling....
It was for instanced used on this forum while discussing good old Lu's big problem = he strongly believed the R22/R44 was fundamentally not well designed, dynamically speaking. The model showed that it is not the rotor but the rotor/body interaction that is the limiting factor (combination of theetering rotor and R22/R44 inertial body behaviour)
You quote a "role to the advancing side" and put it as a absolute given for sim-consistency, where does that come from?
Years ago there was also the 90° precession dogma...
From all the tests I have seen, these coning related transitional rotor dynamics are very specific to a given rotor and riging, which can be very different, the only common factor is coning.
As I stated many years ago, personally I was surprised by the balance in the simple design of Frank's rotor that minimizes that lateral behaviour. Frank called it WiWa, because a simple way of reproducing it, is tracking the betas when just putting cyclic forward/backward and monitoring the rotor at different coning angles, the reason behind is that the tilting motion also creates transvers flows, even skids on the ground. I am sure that by 'over riging' the rotor I could get a different lateral behaviour, perhaps even a role to the other side. I cannot speak in great detail of other rotor systems, but I know that for instance a stiff four blade rotor has quite different dynamic behaviour than a theetering 2 blade.
Currently I do no longer have the time nor the environment to do elaborate experiments, I am lucky that a basic working setup still is available to do some simple check's (see for instance a fairly recent thread on low rpm blow back during autorotion, or delta3 positive versus negative in the 407 TR).
Given a full working system I could extract precise beta graphs of the blades that precisely show you the blade dynamics during the current experiment, which would answer your question in detail.
d3
Crab, yes it does.
It starts from basic physics, not from modelled behaviour, which makes it quite unique, but a formidably complex mathematical project (even including ground effect, tail fin down-wash interference etc...) This setup was specifically deveopped to have a precise view on full rotor dynamics during all parts of flight.
In the scenario shown here, model was operating in what I call 2-D mode, auto-pilot feature was doing lateral cyclic and tail rotor. That is an approriate set-up to answer Levi's question, not for your question of lateral transients.
The problem is -as discussed years ago with Nick Lappos- in order to have reproducible data, autopilots capable of flying predetermined paths need to be developped, which is again a project, and as it was supposed to run of a PC, not a super-mini, there is a CPU limitation. We found -as Nick predicted- that it is not possible to get reproducible data by hand flying the sim, you cannot fly it that precisely. So a number of path controllers were added to te sim.
Further more the amount of data produced is enormous, rendering, graphing up to generating full 3D sim like films etc, is again a project.
Development stopped 5 years ago, because the goals of simulating advanced auto rotations at many different configurations (W&B, RPM, density etc...), all sorts of low G situations, the said Frank's Wiwa and all sorts of coning/delta3 related rotor dynamics. Where do you think my alias comes from, I assume you should know that delta3's are related to lateral rolling....
It was for instanced used on this forum while discussing good old Lu's big problem = he strongly believed the R22/R44 was fundamentally not well designed, dynamically speaking. The model showed that it is not the rotor but the rotor/body interaction that is the limiting factor (combination of theetering rotor and R22/R44 inertial body behaviour)
You quote a "role to the advancing side" and put it as a absolute given for sim-consistency, where does that come from?
Years ago there was also the 90° precession dogma...
From all the tests I have seen, these coning related transitional rotor dynamics are very specific to a given rotor and riging, which can be very different, the only common factor is coning.
As I stated many years ago, personally I was surprised by the balance in the simple design of Frank's rotor that minimizes that lateral behaviour. Frank called it WiWa, because a simple way of reproducing it, is tracking the betas when just putting cyclic forward/backward and monitoring the rotor at different coning angles, the reason behind is that the tilting motion also creates transvers flows, even skids on the ground. I am sure that by 'over riging' the rotor I could get a different lateral behaviour, perhaps even a role to the other side. I cannot speak in great detail of other rotor systems, but I know that for instance a stiff four blade rotor has quite different dynamic behaviour than a theetering 2 blade.
Currently I do no longer have the time nor the environment to do elaborate experiments, I am lucky that a basic working setup still is available to do some simple check's (see for instance a fairly recent thread on low rpm blow back during autorotion, or delta3 positive versus negative in the 407 TR).
Given a full working system I could extract precise beta graphs of the blades that precisely show you the blade dynamics during the current experiment, which would answer your question in detail.
d3
Delta3 - you are clearly a clever chap but not, in fact, a helicopter pilot - if you were you would know that inflow roll (or transverse flow) is a fact of life in a helicopter, even in an R22. And it's nothing to do with precession
Just because your basic physics and advanced maths doesn't reveal its existence in your modelling, doesn't mean it doesn't happen - ask why there is a lateral trim facility on the Robinson!
You'll be telling me your simulator doesn't experience inherent sideslip next
Just because your basic physics and advanced maths doesn't reveal its existence in your modelling, doesn't mean it doesn't happen - ask why there is a lateral trim facility on the Robinson!
You'll be telling me your simulator doesn't experience inherent sideslip next
What??? you mean you are not a clever chap
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Crab
AHHH the inflight roll.................used to be an "Oggie" down in Cornwall...........
But you are right and D3 ain't!
AHHH the inflight roll.................used to be an "Oggie" down in Cornwall...........
But you are right and D3 ain't!
Last edited by bast0n; 29th Apr 2011 at 07:47. Reason: missing words!
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Crab, bastOn
Gentlemen,
Perhaps you should take the time and the elementary politeness of reading what people say, before starting to jump on statements that were not there.
See previous post :
"Crab
Crab, yes it does.
It starts from...."
Perhaps you should take the time and the elementary politeness of reading what people say, before starting to jump on statements that were not there.
See previous post :
"Crab
Crab, yes it does.
It starts from...."
Now now Delta 3 - don't take offence, it was unfair of me to give you banter since English is not your first language
Inflow roll is most definitely a fact of life ... the aerody texts I learnt about it from (probably not dissimilar to what Crab would use) talked about a progressively increasing inflow into the disc from front to back in the early stages of forward flight, with associated lift reduction leading to flapping down on the advancing side.
This, along with flapback, is easily demonstrated (in the real thing) by initiating a transition from the hover and then holding the cyclic steady while watching what happens to the attitude - a pitch-up and a roll towards the advancing blade side.
Obviously any realistic simulator should replicate that.
Regarding the cyclic lag, it's easy to demo (in a teetering head like a Huey at least) by sitting in the hover and fairly rapidly moving the cyclic back and forth a couple of centimetres whilst watching the attitude and the tip of the disc. The disc will wobble back and forth quite a bit without significant fuselage movement, as by the time it would be thinking about moving you've already made the opposite input.
Which reminds me - hands up if you experienced something like this when you learnt to hover: working bloody hard to stay in one place, waving the cyclic around madly with arm muscles tensing up, instructor takes over, puts one finger on top of cyclic and says "See how much I'm moving the stick? Why don't you just do the same...?"
This, along with flapback, is easily demonstrated (in the real thing) by initiating a transition from the hover and then holding the cyclic steady while watching what happens to the attitude - a pitch-up and a roll towards the advancing blade side.
Obviously any realistic simulator should replicate that.
Regarding the cyclic lag, it's easy to demo (in a teetering head like a Huey at least) by sitting in the hover and fairly rapidly moving the cyclic back and forth a couple of centimetres whilst watching the attitude and the tip of the disc. The disc will wobble back and forth quite a bit without significant fuselage movement, as by the time it would be thinking about moving you've already made the opposite input.
Which reminds me - hands up if you experienced something like this when you learnt to hover: working bloody hard to stay in one place, waving the cyclic around madly with arm muscles tensing up, instructor takes over, puts one finger on top of cyclic and says "See how much I'm moving the stick? Why don't you just do the same...?"
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Perhaps the best examples of a "cyclic delay" were expressed very often by old time US Army H-1 drivers after their first flight in a Blackhawk.
Most said: "When you point the cyclic in the H60, you're there NOW whereas in the H1; She'll eventually get there".
In helos with more than two blades, Tech Reps call cyclic delays: hysteresis. Such "Cyclic delays" (as in the H53) can usually be eliminated by changing out marginal control rod bearings from top to bottom.
Most said: "When you point the cyclic in the H60, you're there NOW whereas in the H1; She'll eventually get there".
In helos with more than two blades, Tech Reps call cyclic delays: hysteresis. Such "Cyclic delays" (as in the H53) can usually be eliminated by changing out marginal control rod bearings from top to bottom.
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In a Bell with 2 blades, you have to know where to put the cyclic, put it there, and wait. You will eventually get the result you want, you just have to be patient and wait for it. In a 412 it happens a lot quicker, but with a lot more inertia, it still takes some time to start moving. In cruise flight it's a lot quicker. A more accurate comparison is the 206 vs the AS350, since the weights are more comparable. In a 206 you move the cyclic to where it should be and eventually you get a result. In the AS350 you think about moving the cyclic and you have a result, hopefully not too much. Probably about the same in an MD500.
