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Flight Controls

 

The Mi-8 flight control system includes:

  • Cyclic, Collective, and Directional controls for both pilot and co-pilot.
  • Separate engine condition levers (ECLs) for the pilot.
  • Engine shutdown levers for the pilot.
  • Main rotor brake control for the pilot.
  • Rotor RPM re-adjustment switch for both pilots.
  • Electromagnetic brake and feel-spring assemblies for the cyclic and directional controls.
  • Hydraulic actuators for lateral, longitudinal, collective pitch, and tail rotor controls.
  • Tail rotor pitch limiting system.

 

Mi-8%20Flight%20Controls.png


Edited by AlphaOneSix
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Hydraulic Actuators

 

There are four hydraulic actuators mounted on the Mi-8.

  • Longitudinal and Lateral actuators, controlled by the cyclic.
  • Collective pitch actuator, controlled by the collective.
  • Directional actuator, controlled by the foot pedals.

 

Each actuator has a control rod input from the pilot's controls, an electrical connector for receiving input signals from the AP-34B autopilot, and hydraulic connections for both the main and auxiliary hydraulic systems.

 

The Longitudinal, Lateral, and Collective actuators are of type KAU-30B. For safety reasons, the servo rod travel is limited to 20% from the autopilot.

 

The Directional actuator is of type RA-60B. The autopilot is allowed to move the servo rod through 100% of its travel range for this actuator.

 

Mi-8%20Hydraulic%20Actuators.png


Edited by AlphaOneSix
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I assume the bell crank (where the control rod is connected) is connected to a (spring loaded?) valve that controls how fast and which direction the actuator is moving so that the actuator basically follows the movement of the pull rod. How much movement the valve has and how much force you need to apply to fully open it? How fast the actuator moves when the valve is fully open?

 

I don't really need to know all this but I'm curious and I'm interested about stuff that affects the feel of the controls. Maybe some day when I have money and time I will build myself a set of proper helicopter cyclic, collective and pedals with force feel trim mechanism and I want them to have realistic feel.

 

KAU-30B and PA-60B seem like they have the same body but PA-60B just has some extra stuff attached outside, is this correct?

 

You don't get this detailed look under the bonnet of a helicopter everyday. Thanks a lot for your trouble.

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KAU-30B and PA-60B seem like they have the same body but PA-60B just has some extra stuff attached outside, is this correct?

 

Yes, some additional autopilot-related stuff. Otherwise they are the same.

 

You don't get this detailed look under the bonnet of a helicopter everyday. Thanks a lot for your trouble.

 

I do get a detailed look at them every day! :P

 

No trouble for me...well, a tiny bit, but it helps keep me sharp. I am actually one of my company's maintenance trainers, and I'm in charge of Mi-17 systems classes for the whole company, and I do flight training for crew chiefs as well, although that's not my primary job.

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I assume the bell crank (where the control rod is connected) is connected to a (spring loaded?) valve that controls how fast and which direction the actuator is moving so that the actuator basically follows the movement of the pull rod. How much movement the valve has and how much force you need to apply to fully open it? How fast the actuator moves when the valve is fully open?

 

The bolded statement is exactly correct.

 

I'll have to dig into a book I have out on the flight line to answer some of this specifically, so this will be from memory and I'll edit later if I goof something up.

 

There is no spring, and therefore almost no force required at all to get the actuator to move (beyond the friction in the system between the controls in the cockpit and the actuator itself). The item labelled "bell crank" in the picture connects to a shuttle valve. If the shuttle valve is neutral (controls not moving) then the actuator doesn't move. If you "push" in on the bell crank, the shuttle valve allows hydraulic pressure to flow in one direction, forcing the actuator to move away from the bell crank. If you "pull" out on the bell crank the opposite happens, and the actuator moves toward the bell crank. Basically, whichever direction the input control rod moves, the actuator will try to move away from it or toward it in order to maintain that "middle" state where the shuttle valve is neutral.

 

Here are some stats, which are actually from a KAU-115 actuator (mounted in newer Mi-17 models, such as the Mi-17V-5 which I work on mostly)...if any of these numbers are incorrect for the KAU-30B, I'll edit this post with updated numbers:

 

  • Maximum developed force....not less that 1700kgf (~3750lbf)
  • Speed of movement (unloaded, i.e. not connected to the rotor system)...not less than 90mm/s (~3.5in/s)
  • "Dead" zone...no more than 0.25mm (0.01in)
  • Effort to move shuttle valve...not more than 1kgf (2.2lbf)
  • Mass of the actuator...11kg

 

Once I dig into the manual I have at the flight line, I'll see if I can get a scan of the internal schematics of the actuator.

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:doh::book:

Almost feel sry for the crew chief/mechanics responsible for doing service on this beast.

Why? Russian machines are known for easy maintenance, am I right?

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:doh::book:

Almost feel sry for the crew chief/mechanics responsible for doing service on this beast.

 

Why's that?

 

In some ways it is easier than many other helicopters...and a little harder in other ways. I guess if you're afraid of getting oily and/or greasy...then yeah, this is not the helicopter for you.

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Why? Russian machines are known for easy maintenance, am I right?

 

Well...no. But let me explain. The Mi-8, for example, is a very old design, and does not incorporate a lot of "ease of maintenance" advancements seen on more recent Western aircraft. The Russian do, however, have an answer to that...

 

Don't break in the first place.

 

A good example: I used to work on AH-64's. I could change an engine with the help of two other people in about an hour. On an Mi-8, it takes all day (8-12 hours).

 

Mi-8's are extremely reliable, and rarely need maintenance beyond their normal inspection and lubrication intervals. When they do need "extra" maintenance...sometimes it's really easy...sometimes it's a huge pain in the rear end. I would not want even my worst enemy to have to change a main gearbox on an Mi-8, for example.

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I would not want even my worst enemy to have to change a main gearbox on an Mi-8, for example.

Sounds like a challenge. Can i come help once one needs changing?

 

Also, the more pics you show of this helicopters, the more similarities i see whit the S61.

 

Quite interesting to see that the push/pull rods actually run trough some kind of bearing keeping them in place.

(and preventing metal fatigue due to vibrations?)

 

About easy maintenance on Western helicopters. Forget it.

It's just what they promise, reality is quite different though.

(referencing AW139)

For example, Agusta says you can do an Daily Inspection in just 4 minutes.

Whit 3 experienced engineers it actually takes about 10 to 20 minutes.

[sIGPIC][/sIGPIC]

The keeper of all mathematical knowledge and the oracle of flight modeling.:)
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One thing you learn quickly about fixing helicopters is that NOTHING ever goes smoothly. There's always something wrong in the most awkward and difficult to get at spot. The manufacture may boast about how easy it is to fix. No. Never believe them.

 

Ever.

 

You may be able to take it apart and reassemble it with 5 tools, but there is always a safety somewhere you can only reach with the tips of your fingers or the angle is 1 degree too awkward for a tool to work. :doh:

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Cyclic (Longitudinal/Lateral) Flight Controls

 

Mi-8%20Flight%20Controls%20Cyclic.png

 

The trigger for the Intercom/Radio is a two-position trigger. The first detent transmits on the intercom, continue pressing to the second detent and it transmits over the radio. (Most civil helicopters operate this way.)

 

Mi-8%20Cyclic%20Grip.png


Edited by AlphaOneSix
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Longitudinal Stop

 

The longitudinal control shaft (for pitch, or fore-and-aft, movement) incorporates a longitudinal stop to prevent the pilot from applying to much aft cyclic while the helicopter is on the ground.

 

While operating on the ground (parked or taxiing), the hydraulic-powered stop is in an extended position, so that aft movement of the cyclic corresponding to 2° of swashplate tilt will cause the roller (attached to the flight control rods) comes into contact with the longitudinal stop.

 

Hitting the stop causes an increase in control forces required to move the cyclic to 12kg (26.2lb). In this way, the stop can be overridden by the pilot in an emergency, but the increase in required control force warns the pilot to stop puling aft on the cyclic.

 

Once the helicopter leaves the ground, the longitudinal stop retracts, and the swashplate can move through its entire range (5° aft) without difficulty.

 

Mi-8%20Flight%20Controls%20Longitudinal%


Edited by AlphaOneSix
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That longitudinal stop better not malfunction's during flight restricting it to 2°.

 

Any kind of safety mechanism?

 

And how is it controlled? manually by the pilots or automatically by something like an weight on wheel switch or maybe its linked to position of the collective?

[sIGPIC][/sIGPIC]

The keeper of all mathematical knowledge and the oracle of flight modeling.:)
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Any kind of safety mechanism?

 

No, but you can pull past it if you really need to...with an extra 12kg of force.

 

And how is it controlled? manually by the pilots or automatically by something like an weight on wheel switch or maybe its linked to position of the collective?

 

Weight on wheels switch. Or a failure of the main hydraulic system.

 

EDIT: The electromagnetic valve that controls the longitudinal stop is the same type of electromagnetic valve used to turn the autopilot on and off, and also used for the hydraulic friction clutch for the collective. When it receives power, it opens, allowing fluid to pass. So if it fails, or loses power, it is spring-loaded shut. I have never heard of a longitudinal stop getting stuck in the extended position, but I have seen them fail where they would not extend (requires the pilot to be very careful when taxiing). Same goes for the weight on wheels switches...if the electricity to them fails, it's the same as if you are off the ground. So in just about every failure mode that's likely to occur, the stop will fail in the retracted position, not extended.


Edited by AlphaOneSix
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This just made me realize...

 

All of the stuff I'm posting is actual aircraft info, and is not based (at least not directly) on what exists in the simulator. Once the module enters public beta, I will probably go through these posts and mention which things are implemented and which are not.

 

I will likely cover things in these posts that will not get implemented in-game.

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I was being sarcastic 8)- after seeing that first photo 8)- As first pic I've seen of the inards of one. As far as easiness I dunno, I only worked briefly on tanks in my time (M1) but I would imagine they'd be on the same pg an make the vitals easy to swap out/repair I just know I saw that 1st pic an seemed a lil complicated.


Edited by Call911
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This just made me realize...

 

All of the stuff I'm posting is actual aircraft info, and is not based (at least not directly) on what exists in the simulator. Once the module enters public beta, I will probably go through these posts and mention which things are implemented and which are not.

 

I will likely cover things in these posts that will not get implemented in-game.

 

 

Hehe, keep it coming. Find it quite interesting to find out about the workings of the MI-8

 

Guess you will have to take the bug reports caused by these threads for granted though.:D

[sIGPIC][/sIGPIC]

The keeper of all mathematical knowledge and the oracle of flight modeling.:)
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Directional (Tail Rotor/Yaw) Flight Controls

 

Mi-8%20Flight%20Controls%20Tail%20Rotor.

 

The pedals have microswitches in them. This basically tells the yaw channel of the autopilot when the pilot's feet are on the pedals. In this way, when the pilot's feet are OFF the pedals (not depressing microswitches), the autopilot will hold the helicopter's heading. When the pilot's feet are ON the pedals, the autopilot will not attempt to hold the aircraft's heading. If the yaw servo (RA-60B) reaches the limit of its 20% authority, it will begin to move the control rod itself, and through the control rod, the foot pedals will move. So within the 20% authority built into the actuator, the pedals will not move due to autopilot input. Beyond this 20% authority, the auto-travel mechanism on the actuator will begin to move the foot pedals. This allows the autopilot to have 100% control authority of the tail rotor when the pilot's feet are NOT on the pedals. Remember that when the pilot's feet are ON the pedals, the autopilot goes into "matching" or "synchronization" mode, where it actually has no input and the pilot provides all inputs (actually, the autopilot simply mirrors the pilot's inputs, resulting in the autopilot having no effect on the actuator position).

 

Mi-8%20Flight%20Controls%20Foot%20Pedals


Edited by AlphaOneSix
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Hey thats clever with those microswitches. So the yaw axis is independent to the cyclic trim? And is the cyclic trimmer conected to the autopilot (SAS)?


Edited by Suchacz
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So the yaw axis is independent to the cyclic trim? And is the cyclic trimmer conected to the autopilot (SAS)?

 

Nope, the pedals and the cyclic both have electromagnetic brakes and feel springs that are released with the trimmer button on the cyclic. The microswitches are purely to tell the autopilot to either maintain aircraft heading (feet off pedals) or just follow along with input from the pilot (feet on pedals).

 

And no, the trimmer switch on the cyclic does not connect to the autopilot. It only releases the mag brakes for the force trim (cyclic and pedals).

 

I'll be getting to the autopilot eventually...although I'm not looking forward to it too much...I'm expecting too many comparisons to the in-game Ka-50. But I'm a glutton for punishment.

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Sounds almost identical to the Blackhawk. :p

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