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BS Auto Pilot description and operation


IvanK

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That is a very good question!

 

I think the difference might be the following:

 

Route without task - holds heading via yaw and bank authority, pitches for captured speed

AP Holds active without route - holds heading strictly with yaw authority, holds bank with bank authority, holds pitch at captured value

 

So the Route logic will bank the aircraft to maintain the heading without it bank is merely held by the K-hold-damper channel to captured value. With Route logic the aircraft will pitch to maintain the captured airspeed but without it it will simply hold absolute INU pitch and the speed will run wild.

 

I think that is the difference. Also you don't need to set the DH/DT switch to neutral to get route without task, you just have to extinguish all PVI task lights.

 

As for making changes to the captured values simply by moving the stick... sounds like it could be nice but the Ka-50 doesn't work that way in any mode. I think pilots like having the control over what and when values are captured and having to religiously press and hold trim during their maneuvers is a small price to pay.

 

Also unrelated is the question of whether the FCS gives up its 20% authority when it detects pilot input... this source says no (Page 2/3 this thread)

It does not magically switch off, as some have suggested, when you apply input. My newest GlovePIE solution for Blackshark is evidence of this.

 

A16 says yes

However, if the pilot moves the cyclic or the pedals, the autopilot is aware of that and makes no move to interfere

 

What I don't understand is that I can turn on Turn to Target and the nose almost points at the target. I can then add some pedal and hold it until I'm stable pointing directly at the target say with a Vikhr symbol right over the Shkval symbol and then I blip the trimmer so it should hold that exact heading. Then I release the pedals and wait for the aircraft to settle on my exact heading hold heading... and it doesn't. It's off to the side.


Edited by Frederf
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That is a very good question!

 

I think the difference might be the following:

 

Route without task - holds heading via yaw and bank authority, pitches for captured speed

AP Holds active without route - holds heading strictly with yaw authority, holds bank with bank authority, holds pitch at captured value

 

So the Route logic will bank the aircraft to maintain the heading without it bank is merely held by the K-hold-damper channel to captured value. With Route logic the aircraft will pitch to maintain the captured airspeed but without it it will simply hold absolute INU pitch and the speed will run wild.

 

 

That sounds like a fairly reasonable explanation, and fits with some recent observations I've made.

 

As for making changes to the captured values simply by moving the stick... sounds like it could be nice but the Ka-50 doesn't work that way in any mode. I think pilots like having the control over what and when values are captured and having to religiously press and hold trim during their maneuvers is a small price to pay.

 

Fine, this actually sounds reasonable to me, I think perhaps my main issue is with the following:

 

Also unrelated is the question of whether the FCS gives up its 20% authority when it detects pilot input... this source says no (Page 2/3 this thread)

 

 

A16 says yes

 

A16 says yes, and I believe it would make far more sense if it was yes. However:

 

What I don't understand is that I can turn on Turn to Target and the nose almost points at the target. I can then add some pedal and hold it until I'm stable pointing directly at the target say with a Vikhr symbol right over the Shkval symbol and then I blip the trimmer so it should hold that exact heading. Then I release the pedals and wait for the aircraft to settle on my exact heading hold heading... and it doesn't. It's off to the side.

 

I get the same. Trimming with turn-to-target is just one example of the issue; it seems that each time you trim at a new attitude, the aircraft over-corrects. This seems to indicate that the FCS does not give up it's 20% authority when it detects pilot input, and so each time you trim, your controls are deflected 20% more than they should be for the new attitude, and hence the overcorrection. This, of course, is remedied by holding down the trimmer while making large attitude adjustments, but apparently this is not the real life procedure. Therefore I still wonder if this particular aspect of trimming is implemented correctly.

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The FCS does not give up its input when you make a correction. However the FCS doesn't fight you. This means if you have the AP commanding 16% right cyclic and the pilot adds 4% left cyclic the results are additive. This way you end up at 12% right cyclic from the real zero point.

 

The FCS doesn't give up it's 16 right and just drop back down to 0 and then apply the -4 from the pilot. Instead the AP is a baseline for pilot input. That would be giving up all of the FCS input when the springs were tensioned by the pilot's hands.

 

What it doesn't do is fight you and add change its 16 to a full 20 to try to counter your -4 to get back to the 16 the FCS thinks it needs.

 

As for trimming a turn-to-target thing... it doesn't seem right. I should be able to trim an exact INU heading and have it held there... not 0.5 degrees to the left... RIGHT THERE.

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What I don't understand is that I can turn on Turn to Target and the nose almost points at the target. I can then add some pedal and hold it until I'm stable pointing directly at the target say with a Vikhr symbol right over the Shkval symbol and then I blip the trimmer so it should hold that exact heading. Then I release the pedals and wait for the aircraft to settle on my exact heading hold heading... and it doesn't. It's off to the side.

 

This happens because your rudder is "out of trim" and AP has no more authority to turn all the way to the target. You will find this will happen alot if you always leave heading hold on.. It may seem like your in a well trimmed hover but what u don't realize is heading hold is using a certain amount of its authority to keep you pointing in that direction. If you leave heading hold on and come to a hover you can never really trim the rudder 100% right because you don't know how much yaw authority AP is applying. You need to take heading hold off, come to hover .trim trim etc. Now turn on heading hold and turn to tgt. You should find turn to tgt much more effective.

IMO heading hold should really only be on when you've trimmed out in forward flight to keep tracking in that direction (turn on after trimmed for stable flight) or when used in conjunction with turn to tgt etc.

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  • 2 years later...
One of the most valuable threads that is not easily accessible via sticky nor FAQ I might add :P

 

Still... ;) (I couldn't find the original)

 

Well, I can't do anything about a sticky but since I was going to make a PDF from IvanK's original post I might as well leave a copy here.

 

This is just the first post of the thread in a PDF.

BS Auto Pilot description and operation.pdf

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  • 1 month later...
  • 4 weeks later...

Question:

 

Cyclic brake act as the trim in pressure/release behaviour?

 

example: the ALT-HOLD set the new altitude every time I release the cyclic brake... so, if I keep the cyclic brake depressed, the ALT-HOLD "damping" does not work, or simply try keep the previous altitude set?

 

I'm asking cause I have the same "damped" feeling when I try to climb or descent disregarding of the cyclic brake depressed/released state. I have a more natural feeling in changing altitude when I disable the ALT-HOLD damping.

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The thing is, helicopters are different from planes. An airplane by it's nature wants to fly, and if not interfered with too strongly by unusual events or by a deliberately incompetent pilot, it will fly. A helicopter does not want to fly. It is maintained in the air by a variety of forces in opposition to each other, and if there is any disturbance in this delicate balance the helicopter stops flying; immediately and disastrously.

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Question:

 

I'm asking cause I have the same "damped" feeling when I try to climb or descent disregarding of the cyclic brake depressed/released state. I have a more natural feeling in changing altitude when I disable the ALT-HOLD damping.

 

I usually leave alt-hold off when moving to/from areas*. If i need to enter hover hold it automatically comes on. Then say I'm trying to look over an obstruction, trees, building, etc. You can press and hold (f) the collective brake until you reach the desired altitude you want. At that point the alt-hold channel will set it self to that altitude datum, rather than your original height (auto hover engaged moment). Had you not reset the altitude datum, you of course would have sunk back down. You could also apply the tap methodology

 

*Exception being if i'm going heads down and the general area is relatively flat. I won't stay in it long though...sneaky power lines....


Edited by Daniel M
though i do agree it does feel less smooth with alt-hold left on
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  • 4 years later...

I use Flight Director switch on quite often, actually most of the time. Only downfall for me is rudder is manual feet input.

 

in Multiplayer, on a combat server, most likely the enemy guys, the smart ones, they already know the pre-planned canned mission. I try not to fly predictable if I want to last very long!

 

Thanks for this thread, just bookmarked it.


Edited by DieHard

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