Control linkages and hydraulics question - Page 6 - ED Forums
 


Notices

Reply
 
Thread Tools Display Modes
Old 03-06-2019, 07:58 PM   #51
Gunnars Driver
Member
 
Gunnars Driver's Avatar
 
Join Date: Dec 2016
Location: Sweden
Posts: 235
Default

Quote:
Originally Posted by AlphaOneSix View Post
...and you stop moving the cyclic when you achieve that angle of bank, the autopilot will attempt to, within its 20% authority, hold that 10 degree angle of bank, with the cyclic still being deflected to the left. With the autopilot off, you're now dealing with just the standard aerodynamics. I believe on the Mi-8 it will tend to roll out of shallow banks by itself. That is, for shallow banks, you may need to keep the cyclic deflected or else it will just naturally roll back to level. Then at some intermediate angles of bank, it will naturally hold that bank angle and the cyclic would be returned to center (or very nearly center) and the bank angle will just sort of hold itself. And then beyond some intermediate bank angle you will get the overbanking tendency, where the aircraft will tend to bank even more and you will have to apply slight opposite cyclic (opposite side of being centered) to keep the bank from continuing to exaggerate. I do not know what the angles involved are, but if memory serves (and it probably doesn't), an shallow bank angle is 15 degrees or less, intermediate is from maybe 15-40 degrees, and beyond 40 degrees you'll get overbanking tendency. I could be very wrong on those so as soon as someone argues with me I'll just edit this post and delete it.

I could be thinking of the over and underbanking tendencies in my Cessna.

We had another thread going about cyclic position during a sustained turn.
( https://forums.eagle.ru/showthread.php?t=231698

It wasn't about the mi-8, but basic principles of flight and somehow the mi-8 entered the discussion. To sum it up, this discussion was basic helicopter without AP, and the conclusion is that all helos will have the cyclic close to center latterally in a turn and this have to be the same for the mi-8, at least with AP of. I found support for this in the flight manual, and also in some flight tests, where the lateral stick position was logged.

Basically, we know that the mi-8 need stick input around center, often opposite lateral during turn(as with lot of helos and aircrafts) and the question from the OP i think was related to the fact that in DCS mi-8 with AP of, stick is around center in a turn but when AP on, you need to keep it deflected. The OP question was about hydraulics and mechanical link from stick to swash, trying to find a reason why the module changes behavior with AP on/off.

The other thread had a long way to come to the conclusion that stick around center for a continuous banked turn is valid for virtually all helicopters( and aircrafts), I suggest reading this if the stick@center in turns isn't clear.
__________________
[T.M HOTAS Warthog Stick & Throttle + T.Flight pedals, Oculus Rift]
[DCS Mirage 2K; Huey; Spitfire Mk IX, AJS 37, F-18, FC3 ]
Gunnars Driver is offline   Reply With Quote
Old 03-07-2019, 03:28 AM   #52
msalama
Veteran
 
msalama's Avatar
 
Join Date: Apr 2008
Posts: 3,874
Default

Quote:
verifying the behavior of the DCS Mi-8 to be correct
From the explanation it does seem so. I've got to do some flight tests when I get off work today and really pay attention to how the stab system works and what are the control differences with it on and off.
__________________
Huey probs & gripes? Do read the following please: https://forums.eagle.ru/attachment.p...1&d=1555258147
msalama is offline   Reply With Quote
Old 03-09-2019, 09:39 AM   #53
DeMonteur
Junior Member
 
Join Date: Feb 2019
Posts: 18
Default

Quote:
Originally Posted by msalama View Post
Bonjour gents and gentettes. The Mi-17 Dash-10 manual states that:



But what does this mean exactly? Are there two separate systems for redundancy, one mechanical and the other hydraulic? Or does it mean that the control rods are connected to the servos/actuators and never interact with the swashplate directly?

It means that there is mechanical system from cabin controls through force feedback spring mechanism and trim to hydraulic actuators. Hydraulic actuators are connected to swashplate and ropes for controlling tail rotor. So there is no redundant systems. Only mechanical conected to hydro actuators conected to swashplate and tail rotor control.
DeMonteur is offline   Reply With Quote
Old 03-09-2019, 01:37 PM   #54
msalama
Veteran
 
msalama's Avatar
 
Join Date: Apr 2008
Posts: 3,874
Default

Yeah, that much is clear already, but thanks anyway.
__________________
Huey probs & gripes? Do read the following please: https://forums.eagle.ru/attachment.p...1&d=1555258147
msalama is offline   Reply With Quote
Old 03-09-2019, 06:52 PM   #55
Gunnars Driver
Member
 
Gunnars Driver's Avatar
 
Join Date: Dec 2016
Location: Sweden
Posts: 235
Default

Quote:
Originally Posted by msalama View Post
Yeah, that much is clear already, but thanks anyway.
Just found a very nice writeup and description with pictures from A16:
https://forums.eagle.ru/showthread.php?t=110313

Quite easy to the that the control rods are mechanichally connected to the swash.
What we dont see is the 20% internal adjustment the autopilot can do. Either use the link below togheter with google.translate, or just believe it anyway

http://cnit.ssau.ru/vertolet/mi8/
__________________
[T.M HOTAS Warthog Stick & Throttle + T.Flight pedals, Oculus Rift]
[DCS Mirage 2K; Huey; Spitfire Mk IX, AJS 37, F-18, FC3 ]
Gunnars Driver is offline   Reply With Quote
Old 04-26-2019, 02:23 PM   #56
FragBum+
Posting Rights Revoked
 
Join Date: Jun 2016
Location: QLD, AUS.
Posts: 2,295
Default

Just wondering if there has been a resolve for this, without the autopilot the Mi-8 has the same feel as Huey and gazelle in response to cyclic input.

If not I guess we should raise a bug report given the two different cyclic actions with and without autopilot.
FragBum is offline   Reply With Quote
Old 05-16-2019, 04:07 PM   #57
msalama
Veteran
 
msalama's Avatar
 
Join Date: Apr 2008
Posts: 3,874
Default

Quote:
Just wondering if there has been a resolve for this
The consensus was that it is modelled correctly.

https://forums.eagle.ru/showpost.php...1&postcount=49
__________________
Huey probs & gripes? Do read the following please: https://forums.eagle.ru/attachment.p...1&d=1555258147
msalama is offline   Reply With Quote
Old 05-18-2019, 09:39 AM   #58
FragBum+
Posting Rights Revoked
 
Join Date: Jun 2016
Location: QLD, AUS.
Posts: 2,295
Default

Quote:
Originally Posted by AlphaOneSix View Post
The autopilot will attempt to hold the pitch and bank angles if the cyclic is not moving. That is, if the cyclic is stationary, the pitch and roll channels of the autopilot will attempt to hold the pitch and bank attitudes within its 20% authority.

If the cyclic is moving the autopilot still tries to hold the attitude, but essentially it's holding the attitude around a moving target, since the movement of the cyclic is being removed from the equation.

This is why it's more similar to a SAS-type system than what most people would consider a traditional "autopilot".

And so it follows that if you, for example, move the cyclic to the left to enter a 10 degree angle of bank, and you stop moving the cyclic when you achieve that angle of bank, the autopilot will attempt to, within its 20% authority, hold that 10 degree angle of bank, with the cyclic still being deflected to the left. With the autopilot off, you're now dealing with just the standard aerodynamics. I believe on the Mi-8 it will tend to roll out of shallow banks by itself. That is, for shallow banks, you may need to keep the cyclic deflected or else it will just naturally roll back to level. Then at some intermediate angles of bank, it will naturally hold that bank angle and the cyclic would be returned to center (or very nearly center) and the bank angle will just sort of hold itself. And then beyond some intermediate bank angle you will get the overbanking tendency, where the aircraft will tend to bank even more and you will have to apply slight opposite cyclic (opposite side of being centered) to keep the bank from continuing to exaggerate. I do not know what the angles involved are, but if memory serves (and it probably doesn't), an shallow bank angle is 15 degrees or less, intermediate is from maybe 15-40 degrees, and beyond 40 degrees you'll get overbanking tendency. I could be very wrong on those so as soon as someone argues with me I'll just edit this post and delete it.

I could be thinking of the over and underbanking tendencies in my Cessna.

EDIT: I asked one of our pilots about it and he said, basically, "Heck I don't know, I just do whatever makes it point where I want it to point." SO in other words he doesn't think about it enough to answer offhand.
Thanks however, respectfully there is no actual definitive answer for the cyclic behaviour with AP on.

FWIW With AP off the Mi-8 handles much like the Huey and Gazelle does in regard to cyclic deflection verse rate of roll. Interesting.
FragBum is offline   Reply With Quote
Old 05-18-2019, 11:19 PM   #59
AlphaOneSix
Veteran
 
AlphaOneSix's Avatar
 
Join Date: Sep 2006
Posts: 2,991
Default

The current behavior is correct.
AlphaOneSix is offline   Reply With Quote
Old 05-19-2019, 02:28 PM   #60
FragBum+
Posting Rights Revoked
 
Join Date: Jun 2016
Location: QLD, AUS.
Posts: 2,295
Default

Quote:
Originally Posted by AlphaOneSix View Post
The current behavior is correct.
Okay thanks I'll stick to turning AP off in that case, it actually "feels" better to fly it that way.
FragBum is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT. The time now is 07:12 PM. vBulletin Skin by ForumMonkeys. Powered by vBulletin®.
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.