Rotor Blade Visual Model works opposite of Rudder Input.

[ShuRugal]

I have just noticed that the rotor blades change pitch backwards with rudder movement. The upper (CW rotating) blades reduce pitch when left rudder is applied, and increase it when right rudder is applied (with the lowers doing the opposite). In reality, this should be the other direction: to turn CCW, the CW rotating blades need to increase pitch (and thus torque) while the CCW blades decrease.

 

Pictures attached so the effect can be seen relative to the direction of the rudder.

 

[outlawal2]

Nope read up on it... What you see is correct. (The term is gyroscopic progression and means that as the rotor turns and you put an input into it, it actually rotates ninety degrees before the input takes effect.. So you put the input into the rotr ninety degrees BEFORE the direction you wish to move.. Then when the rotor is turning it "catches up". What you see in the simulation is correct even though it doesn't look right..

 

From the Huey manual pg. 29:

 

"The result of applying force against a rotating body occurs at 90° in the direction of rotation from where the force is applied. This effect is called gyroscopic precession and it is illustrated in Figure 3.4. For example: if a downward force is applied at the 9 o'clock position in the diagram, then the result appears at the 6 o'clock position as shown. This will result in the 12 o'clock position tilting up an equal amount in the opposite direction.

Figure 3.5 illustrates the offset control linkage needed to tilt the main rotor disc in the direction the pilot inputs with the cyclic. If such a linkage were not used, the pilot would have to move the cyclic 90° to the right of the desired direction. The offset control linkage is attached to a lever extending 90° in the direction of rotation from the main rotor blade."

 

I tried to copy the diagram but the board refused to let me paste it in..

Edited June 8, 2015 by outlawal2

[sobek]

Nope read up on it... What you see is correct. (The term is gyroscopic progression and means that as the rotor turns and you put an input into it, it actually rotates ninety degrees before the input takes effect.. So you put the input into the rotr ninety degrees BEFORE the direction you wish to move.. Then when the rotor is turning it "catches up". What you see in the simulation is correct even though it doesn't look right..

 

Precession only applies to cyclic inputs, not to collective (rudder is quasi collective). If what he describes is true, then it is indeed a bug.

[HungaroJET]

Precession only applies to cyclic inputs, not to collective (rudder is quasi collective). If what he describes is true, then it is indeed a bug.

 

Sorry Outlawal but ShuRugal and Sobek is right.

Let me explain in a very simple way.

 

The upper, CW rotating rotor blades can rotate the helicopter (only) left.

To the left, when the upper blades get higher angles (AOA) than lower blades.

 

Then the upper CW blades have more drag therefore these will/want "slow down" in the air (while these create more lift) but the torque effect wants to rotate the airframe to the opposite direction: counter-clockwise as a left yaw-turn. (because the CW rotating blades "turn slower" now).

 

 

Fortunately the rotor flight model is correct. In a left yaw-turn all the upper blades are raised bacause of the higher AOA and drag.

In a right yaw-turn all the lower blades are raised.

 

So "only" the increased/decreased blade pitch programming (plus&minus AOA behaviour) is wrong what connected to blade animation rotation (each blade) when a pedal yaw input applied.

[AlphaOneSix]

While correct in powered flight, Kamov helicopters have some doohicky that reverses this without engine power, so that the pedals work as expected during an autorotative descent without power.

 

Try it again with the engines running and see if it still does it. Or maybe actually try it in powered flight if you can without it being too distracting.

 

Kamov designs its coaxial aircraft so that in an autorotation, left pedal input still turns the nose left. On a "normal" coaxial rotor system, in an autorotation, left pedal input would actually turn the nose to the right, because the torque is backwards. In other words, in powered flight, torque is transmitted from the main gearbox to the rotor system, but in an autorotation, torque is transmitted from the rotor system to the main gearbox, so that pedals input on a coaxial aircraft would be backwards (right pedal to go nose left). Kamov does something (not sure exactly what) so that when the rotors are not powered by the aircraft, the pedal input is reversed. I do not know if ED modeled this effect, but like I say, I'd try it again under power and see if you get the same result.

[ShuRugal]

Kamov designs its coaxial aircraft so that in an autorotation, left pedal input still turns the nose left. On a "normal" coaxial rotor system, in an autorotation, left pedal input would actually turn the nose to the right, because the torque is backwards.

 

That's pretty clever, and if it is indeed the cause of what i'm seeing, then kudos to ED for modelling it.

 

Just checked with the blades turning, and I can't tell if the pitch is changing correctly, but everything seems to be: the coning angles change correctly and the linkages all seem to move the correct direction, I just can't tell if the actual twist animation is the right way. Which i suppose means it doesn't matter: It works correctly with power off according to your description, and does not appear to work incorrectly with power on.

[HungaroJET]

While correct in powered flight, Kamov helicopters have some doohicky that reverses this without engine power, so that the pedals work as expected during an autorotative descent without power.

.

 

Sorry Darrell but blades work same under power. (and not reversed without power)

 

Both screenshots show left yaw-turn. First one is focusing on the angles of upper blades, other focusing on the lower blades.

 

You can see the raised upper blades/rotor disc/increased coning, but all upper blades show low collective pitch.

 

By contrast on the second pic the lower blades show lowered rotor disc/decreased coning but all blades are on high collective pitch/angle. Blade tip lights show it also.

 

Edited June 8, 2015 by HungaroJET

[sobek]

You can see the raised upper blades/rotor disc/increased coning, but all upper blades show low collective pitch.

 

I think you don't understand how coning/flapping and blade angle relate. Coning/Flapping reduces blade AoA.

[HungaroJET]

I think you don't understand how coning/flapping and blade angle relate. Coning/Flapping reduces blade AoA.

 

Believe me, I understand it, and i know how flapping reduces blade AOA :smilewink:

 

What you can see on the screenshots that's modded flight model, ... for showing more visible how the blade AOA changes on lower rotor and on the upper rotor. The helicopter is in stable hovering but in rapid left yaw-turn. Zero speed, no altitude changes.

 

I changed/increased the GeneralPitch and the DifferentPitch values. The flight model is able to follow the changes but the blade AOA rotation animations are not. (i did not changed the animations, that's the stock model)

 

With those increased GeneralPitch and the DifferentPitch values clearly visible when player make yaw-turns then all 6 blades AOA animation rotates into the wrong directions.

[sobek]

I don't think that your method is qualified to judge AoA nor to see how it works when autorotating. After all, the lower disk operates in the downwash of the upper disk.

[HungaroJET]

The animation effect is still wrong when autorotating, but you know what?: i want neither hurt you nor convince you but "it is indeed a bug", as you draw up on the first try.

 

Regards

[EagleEye]

Interesting discussion. I wonder if Airtito is still around and could give some input?

I´ve read that the Kamov helicopters have that aileron on the tail fin to control the yaw axies in non powered flight (i.e. autorotations), because there is no coordinated lift without engine power.

Edited June 9, 2015 by EagleEye

[AlphaOneSix]

Differential collective inputs still work without engine power (although it's backwards). But the torque, as you might guess, it quite a bit lower. The fins in the back are there just to assist and are not the sole yaw control in an autorotation.

[P3CFE]

Hello,

 

Just to see if i got my facts straight.

 

The Fuselage will turn into the opposite direction of the torque delivered to the rotors.

So it will not turn if both rotors are driven with the same torque.

 

If the Top rotor (driven to turn CW) gets more torque from the engine drive train than the lower (Higher pitch takes more torque to keep rpm from decaying), the fuselage wil turn CCW (yaw left).

 

If the lower gets more torque from the engine drive train then the upper the fusalage wil turn right.

 

If there is no torque to both rotors (like in autorotation) there can be no difference in torque, and so , no yaw effect from torque difference.

The only way to control Yaw then, is the Rudder on the Ka50 , and so you must have forward speed.

 

Prove me wrong if you think i'm

 

Greetz

[AlphaOneSix]

If there is no torque to both rotors (like in autorotation) there can be no difference in torque, and so , no yaw effect from torque difference.

The only way to control Yaw then, is the Rudder on the Ka50 , and so you must have forward speed.

 

While there is no torque TO the rotors, there is still a torque effect FROM the rotors. So differential torque can still be used to control yaw, although, as noted, the effect is backwards from a pilot control perspective, and the torque effect is less pronounced than it is when in powered flight. Due to the lower torque, the rudders are used to assist in yaw control at low power settings and in autorotations, but they are not the sole source for yaw control.

[P3CFE]

Oké "AlphaOneSix", thanks.

 

I thought the torque from the rotors was very very little because they are free rotating in autorotation, and the torque transfered from the rotor to the airframe is only caused by gearcase and bearings.

 

But i forgot that there are also accessories driven by the gearcase, like generator, Oilpumps and Hydraulic pumps.

 

Makes me wonder howmuch negative torque is generated by the rotor (s) during autorotation, and howmuch is noted by the pilot in real live.

 

Is this effect really simulated in DCS ?? that would really supprise me !! :)

 

 

Thanks again

[sobek]

While there is no torque TO the rotors, there is still a torque effect FROM the rotors.

 

To expand on that, there is a torque from one rotor to the other, and the fuselage acts as "fulcrum" for the directional change.

[Suchacz]

Everything is about a simple physics, see 1st Newtons law - action and reaction.

 

This article should help you much with understanding this - http://www.simhq.com/_air13/air_427a.html

[sobek]

I just tested powered flight and it works as intended. Left pedal increases the upper disk coning and vice versa.

[sobek]

The animation effect is still wrong when autorotating, but you know what?: i want neither hurt you nor convince you but "it is indeed a bug", as you draw up on the first try.

 

How did you test it? The two pictures you posted are clearly from powered flight.

[P3CFE]

Hey Guys,

 

Regarding the blade angle change of the upper and lower rotor with rudder deflection...

 

If you are on the ground, engines off and kick the rudder to the left.

What do you expect to see, and what do you see in DCS.

 

I think HungaroJET has a point here.

[sobek]

If you are on the ground, engines off and kick the rudder to the left.

What do you expect to see, and what do you see in DCS.

 

The exact opposite of powered flight, the upper disk lowering AoA and the lower disk increasing it, which is exactly what happens.

 

I think HungaroJET has a point here.

 

What is that point?

Edited June 11, 2015 by sobek

[P3CFE]

Oké, could you explain why it should be differend on the ground (no rotation of rotors), an during powered flight.

Its a mechanical linckage from pedals to rotor system.

 

I checked during powered (hover...no wind) flight again, and though the coning effect is correct, if you pause the sim and look at the AOA of the blades, they show the same reaction as on the ground....so opposite from wat it should.

 

If you look at the dynamic coning effect when pushing rudder left and right it looks Oke.

 

But if you look at the AOA just after you kick the rudder and paused you wil see that a lowered AOA wil give a coning up reaction....that cant be right.'

 

The point here is .. (as HungaroJET said).. the animation of the blada angle change is reversed, on ground engines out and also during powered flight.

[EagleEye]

Oké, could you explain why it should be differend on the ground (no rotation of rotors), an during powered flight.

Its a mechanical linckage from pedals to rotor system.

This is how I would understand it: On non-powered flight the greater torque produced (because of higher AoA) from the left turning lower blades will turn the heli cell to the left (if left rudder is applied) , while the torque produced from the upper blades (turning to the right) is lower (because of lower AoA) and therefore have lesser effect on the cell.

Though, how this reversed behavior of the rudders (in non-powered flight) can be done (if it is what on a real Ka-50 happens?), via the mechanical linkage as you said, is out of my mind.

 

Would like to hear more about from AlphaOneSix, because he works with helicopters (although with conventional russian helo types, I think).

Edited June 11, 2015 by EagleEye

[AlphaOneSix]

This is as close as I could get to an explanation from a quick Google search:

 

Coaxial and most Intermeshing helicopters use differential collective to effect yaw. When the craft is in autorotation, the pedals must be reversed to maintain the same rotational direction of yaw. Kamov and Kaman have a linkage changeover so that the pilot still uses right pedal to effect right yaw. It appears that the linkage changeover is dictated by the position of the collective lever.

 

I have found very detailed descriptions of how this mechanical changeover works on a Kaman, but not for Kamov. I could assume that it's roughly similar, but I don't know that for sure. Just search for "kaman yaw reverser" and you should be able to find a good description of it.