Control -Question for pilots..
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Control - Question for pilots..
A fair while ago I noticed an archived thread of a Newsgroup that caught my attention (the tread, in fact the whole archive, is well worth a read-through).
Within the thread was a statement by Dave Lednicer as follows:
To this I have a few questions for you pilots out there, the questions relate to all controls; pedals, collective and cyclic:
Is linearity in the controls a notable issue, such that you would think about it?
Is it something you personally reflect on when you think “-do I like this ship or not?”
Would you say any A/C is so marked that you would like to have it ‘fixed’?
For those of you who on a day to day basis fly different ships, e.g. AS350 and EC130, would it be easier if they behaved more alike?
Thanks a lot in advance for your answers!
Within the thread was a statement by Dave Lednicer as follows:
Getting good, linear pedal response involves trade-offs. The S-67 fan used high twist to get good disk loading and low power consumption. This was found to produce a non-linear pedal response, due to the fan going through a largish region of collective where the thrust was near zero. The answer that Aerospatiale found on the SA342, after having a similar problem on the SA341, was to use low, non-optimal blade twist.
They bragged about this in an AHS paper and I included it in the design guidelines. This led to low twist being used on the H-76 and Comanche, giving you the nice, linear pedal response you have.
They bragged about this in an AHS paper and I included it in the design guidelines. This led to low twist being used on the H-76 and Comanche, giving you the nice, linear pedal response you have.
Is linearity in the controls a notable issue, such that you would think about it?
Is it something you personally reflect on when you think “-do I like this ship or not?”
Would you say any A/C is so marked that you would like to have it ‘fixed’?
For those of you who on a day to day basis fly different ships, e.g. AS350 and EC130, would it be easier if they behaved more alike?
Thanks a lot in advance for your answers!
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"For those of you who on a day to day basis fly different ships, e.g. AS350 and EC130, would it be easier if they behaved more alike?"
Yes.
Would it be worth the expense and effort? Probably not.
For me it takes about three take off and landings to get back into the feel of the EC130. Less to go back the other way for some reason.
Yes.
Would it be worth the expense and effort? Probably not.
For me it takes about three take off and landings to get back into the feel of the EC130. Less to go back the other way for some reason.
I find Dave's comments intriguing. I agree that linear response is important, I'm surprised that a tail rotor blade compromise was required to achieve it. Surely in a simple type this could be achieved by mechanical biase within the controls, and within the comanche by the FBW system?
I never understand the issue regarding rotor turning direction - you look out the window and move the pedals to keep the nose straight.
I never understand the issue regarding rotor turning direction - you look out the window and move the pedals to keep the nose straight.
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thats what i'm doing wrong. always used that excuise swapping between the 204 and 206, then someone told me the blades are going the same way. don't know what to blame now. 
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I find Dave's comments intriguing. I agree that linear response is important, I'm surprised that a tail rotor blade compromise was required to achieve it. Surely in a simple type this could be achieved by mechanical biase within the controls, and within the comanche by the FBW system?
Then I opted for just asking your opinion..
Still might just ask him, if I do and he answers I will get back..
"mechanical biase within the controls" might just be a bit more complex. There is normally more of a problem due to unwanted mechanical bias. A mechanical fix would be sweet though..
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One of the problems with any kind of control mixing, whether it's electrical or mechanical is that it has to be optimized for one weight and CG.
For the UH-60, that optimization was done for the original design weight and CG - the inter-relationships between cyclic, collective and pedals were such that a pedal turn at that design point resulted in only a yaw rate. If you were not at the design point in terms of weight or CG, you got some strange effects- moving the pedals resulted in pitch and roll movement of the nose- lighter than the design weight, and the aircraft moved one way - heavier than the design weight, and the aircraft moved the other way. Not a lot, but enough to be noticeable.
So if you're going to do electronic mixing, it would be wise to add a weight/cg bias capability.
For the UH-60, that optimization was done for the original design weight and CG - the inter-relationships between cyclic, collective and pedals were such that a pedal turn at that design point resulted in only a yaw rate. If you were not at the design point in terms of weight or CG, you got some strange effects- moving the pedals resulted in pitch and roll movement of the nose- lighter than the design weight, and the aircraft moved one way - heavier than the design weight, and the aircraft moved the other way. Not a lot, but enough to be noticeable.
So if you're going to do electronic mixing, it would be wise to add a weight/cg bias capability.
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too many variables
Engineers, in the confines of the lab, can come up with many ways to affect the controllability of helicopters. Unfortunately the variables in the field more that counteract their plans. Start with environmental conditions. The real weight of the aircraft. Rigging by mechanics 1 thru infinity. General differences in the materials used to create the machine and the subtle differences created over time on each component. If you have SAS etc. the differences electrons make over time on each component. In the U.S. army i could fly one of fifteen to eighteen different UH-60's in several months time. Different years, different total AC times and yes, different components installed in the same series of aircraft. The system on the A model 60 was designed to hover with no pedal input at 16,825 lbs. No one will ever convince me that it worked that precisely so what I did was I did what I had to do to keep the nose pointed where I wanted it. This year I have been signed off to fly the R44, AS350B2, EC-145 and BK117 A and B model. They are all different and initally I didn't like any of them, generally based on the difficulty to hover comfortably because of the differences in tail rotor control. After a few short hours I have that figured out and can then move on to the other things I don't like about each one. ie BK cyclic trim system. ( I took my checkride on the BK today and I am sure I will warm up to the system soon) The bottom line is they are all flyable in their own way. All the science and engineering is nice but eventually its in the hands of the pilot and we make the best of it. Does the EC145 really fly any better that a UH1H? Cheers
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Hello,
Thanks for the answers thus far.
I think I need to point out however that I am not wanting to address the general ‘trim’ of the A/C, but rather how you arrive at this ‘trim’.
That is, a linear coupling / gain between for example pedals and TR-thrust. So that the achieved thrust delta if moving the pedals, for instance 1”, is equal at both ‘pedal stops’, ‘centre position’ and all the way in-between (if this is wanted).
This would then be to make it easier to anticipate the needed input for any given manoeuvre.
Clearly the A/C will trim differently at different weights (the amount of needed input will differ), but the amount of pedal needed should for any given state be equal through the entire control range (e.g. I have 4000N thrust on the TR and need 500N more requires the same amount of pedal input as if I had ‘negative’ 2000N thrust and need 500N less..).
If that was in any way clear, or made sense
, it was in this perspective I was asking the question..
Thanks again!
Thanks for the answers thus far.
I think I need to point out however that I am not wanting to address the general ‘trim’ of the A/C, but rather how you arrive at this ‘trim’.
That is, a linear coupling / gain between for example pedals and TR-thrust. So that the achieved thrust delta if moving the pedals, for instance 1”, is equal at both ‘pedal stops’, ‘centre position’ and all the way in-between (if this is wanted).
This would then be to make it easier to anticipate the needed input for any given manoeuvre.
Clearly the A/C will trim differently at different weights (the amount of needed input will differ), but the amount of pedal needed should for any given state be equal through the entire control range (e.g. I have 4000N thrust on the TR and need 500N more requires the same amount of pedal input as if I had ‘negative’ 2000N thrust and need 500N less..).
If that was in any way clear, or made sense
, it was in this perspective I was asking the question..Thanks again!
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Collective to pedal mixing has been around for a long time on a lot of Sikorsky products. In fact, on several models you won't get maximum tail rotor pitch until the collective is well up in position.
Not many other manufacturers seem to have picked up on the concept.
Not many other manufacturers seem to have picked up on the concept.
