This blog will help you understand what the new functionality does and how you can use it.

When you enable Pitch/Yaw/Roll control on a rotating blade now, the blades themselves will make a decision on whether the blade needs to be in cyclic or collective mode - on a per axis basis.

For this craft above, the blades are aligned with the center of mass in the forward direction - so they’ll use cyclic mode for pitch.  They’re far apart horizontally, so they’ll use collective mode for roll.  And because their axis of rotation is flat, they won’t attempt to provide any control input in yaw.

Cyclic mode:  Cyclic mode is what a normal helicopter’s main rotor does to control the pitch and roll of the helicopter.  They will change their pitch - by the limits you set in the authority limiter control of the blade - as they spin around.   This creates more or less lift to one side or the other of the blade’s disc of rotation.

Image 2: Cyclic Mode Pitch

Collective mode: Collective mode is what a normal helicopter does when it wants to change how much overall lift is created.  But as you can see in the picture below, adjusting the relative lift on the two different sets of rotors will cause the craft to roll.

Image 3: Collective Mode Roll

Summary and Videos:
So that’s what our blades now do in a nutshell.  However, understanding these topics can be pretty complicated.  I really recommend checking out some of these excellent Youtube videos for further study.

Smarter Everyday’s series on Helicopters - Dustin’s videos are fantastic, and these are no different:

Craft Building Tips:

1. Make sure to set your authority limiter pretty low.  One of the potential trouble spots you can have is if the blade pitches too much trying to generate control - if it goes OVER the stall limit and starts generating less lift, you’ll get the opposite of what you wanted.  2 or 3 degrees will often be enough.
2. Helicopters can be finicky to control.  Even if you’ve got everything right, any change in a helicopters forward or vertical motion affects the lift on the blades, which generate input coupling.  If flying a plane is like driving a car, then flying a helicopter is like riding a unicycle - don’t be surprised if you have to constantly adjust inputs.
3. Chinook-style craft will generate interesting and unpredictable effects due to axis coupling effects.  If you want to build a really stable Chinook style craft, consider looking into how those are actually built - they adjust their whole rotor assembly plane of rotation, rather than just using cyclic/collective.  http://www.chinook-helicopter.com/standards/Army_D_Model_AQC_Classes/Flight_Controls.pdf
4. The blade controls will work well for using a tail rotor, blades rotating in any axis will respond appropriately.  That said - it’s still easier to manage a helicopter with two counter rotating blades.

Finally - if you decide none of this is for you and you just want a helicopter without worrying about the physics so much, feel free to just turn off the Pitch/Yaw/Roll blade controls, and use a reaction wheel to generate the torque you want - no one on the dev team will accuse you of cheating, we promise!

## User Feedback

Posted (edited)

On 2/26/2020 at 11:58 PM, AHHans said:

Also the cyclic control has essentially the same effect as physically moving the plane of rotation of the rotor: the direction of thrust the the rotor generates changes.

I believe that in the cited document (and others) the control is shown as tilting the rotor because that is easier to display and understand and not because the rotor really physically changes.

Helicopters do in fact adjust their main rotor plane of rotation to generate rotational attitude changes.  It just isn't very obvious unless you observe them on the ground with a crew that is deliberately moving the tip path plane without collective applied, which they won't do because there is no need for it and in some helicopters can cause damage to main rotor components.  However, you can see the effect demonstrated at 5:23 in this video: https://www.youtube.com/watch?v=XNd5cF2DIgI.  What is happening is in flight the main rotor thrust is being offset to one side, instead of remaining in line with the aircraft center-of-mass, which is lower in the fuselage.  This "thrust" vector, called Total Aerodynamic Force in helicopter speak, is creating a rotation movement since the the vector is being generated from a location that is above the center-of-mass.  It's like if you mounted an engine high above a plane's center-of-mass in the SPH, the plane will want to nose down because the thrust is not in line with the center-of-mass.  When a helicopter rotor disk is tilted in a direction due to movement of the cyclic, the lift vector being generated by the main rotor is tilted away from straight vertical, and offset away from the center-of-mass below it, causing a rotational movement in roll or pitch, or both.

In KSP, this is not simulated with the stock rotor mechanics, but instead relies on differential lift vectors.  So it simulates the effect of the cyclic application, but does not recreate the real physics behind it.  This creates a problem when creating a tandem helicopter like the CH-47 Chinook, since yaw control in that aircraft relies on differential cyclic tilting, as shown in the cited document.

EDIT: I should clarify that cyclic blade feathering in rotor systems do create differential lift on one side of the rotor disc, but the differential lift is what tilts the rotor disk as a whole, which generates the offset lift vector, which in turn creates the rotational motion around the CoM. In KSP, the differential lift itself is what causes the rotational motion around the CoM.  The lack of rotor disk tilting is what differentiates KSP rotor mechanics from real life.

On 2/26/2020 at 11:58 PM, AHHans said:

I'm pretty sure that the CH-47 Chinook and other tandem rotor helicopters use regular swashplates and don't actually "bend" the central axis of the rotors. In the descriptions I found they show that the CH-47 does have swashplates fore and aft, but I haven't seen any mention of a coupling that allows it to tilt the central axis.

In the Chinook, the Roll and Collective are controlled similarly to conventional single-rotor helicopters, and because of this, Roll and Collective are easily simulated by the KSP rotor mechanics.  Pitch, relying on differential collective, is also easily simulated by the KSP rotor mechanics.  However, without an actual rotor disk tilting, Yaw cannot be accomplished through the standard KSP rotor control input method.

So in effect, there is no direct swashplate movement to control the Chinook in the Pitch axis, since it relies on differential collective for Pitch control.  However, through the Longitudinal Cyclic Trim (LCT), both rotor systems can be tilted forward (as described in the document) to increase overall speed without having to pitch the aircraft itself down as much as would be required to attain the same effect without it.  So in effect you have both rotor systems tilting forward in unison, much like they tilt left or right in unison to generate roll.  However in this case, this increases speed rather than pitch due to the layout of the tandem rotor systems.

Edited by Raptor9
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Rotors are creating Yaw issues for me even when using counter rotating props / rotors.

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Posted (edited)

So far, I'm not really a fan of this update...

I commend the effort, but It seems to have introduced something squirrely in the aerodynamics that causes unwanted yaw in multi-engine (non-helicopter) craft resulting in a performance loss.  ...while trying to appease a crowd that wants to build some sort of pristine helo simulation in an aerodynamic/flight/control-system model that is just NOT up for that challenge.

I'm not sure we really gained anything here, but we do seem to have lost something.

Edited by XLjedi
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On 2/19/2020 at 9:25 AM, Maxsimal said:

(snip)

Helicopters are complicated, and I'm impressed with how much of the community has figured out how to work with them.  In many ways I'd say they're more complicated, at least physics-wise- than rockets - more force interactions and coupling.

The other Rocket Equation explained:

Helicopters complexity > Rocket Complexity

Rockets:  Pointy end to space.  Flamey end to ground.  Not is space yet ? = MOAR Boosters

Helicopters:  Pointy end anywhere(s).  Rotors anywhere(s).  Physics?  MOAR Rotors != Flight

M'eh.  Make it go.  Anywhere(s), but probably not to space.

@Raptor9  Are you an aircraft engineer or pilot?  Those were some impressive dissertations.

@Maxsimal  Great work.  Love the blog and the work you and the team have put in.

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On 4/12/2020 at 12:56 PM, smotheredrun said:

@Raptor9  Are you an aircraft engineer or pilot?

Helo pilot.  The closest I'll ever be to an engineer is the KSP VAB/SPH.

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Hi guys big step forward today https://www.youtube.com/watch?v=egcZfOJDC2o&feature=youtu.be as 30 days guarantee period was due to finish i check launch controller and made video fortunately work stronger than i thought . Waiting for praise as for me it was great experience and audience from behind same was happy. Now only do more steps to grow bigger in this field as i have specified plan but will write later due to multitasking. Anyway I wait for praise, likes and good words.

Much love:>

Keeps the things together.

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Posted (edited)

On 4/1/2020 at 10:50 AM, Redacted said:

Rotors are creating Yaw issues for me even when using counter rotating props / rotors.

I've noticed this a lot.  It happens in real planes as well.

Counter-rotation reduces roll shifting dramatically, though.

It's why I say they need to add an acceleration limiter so that the yaw force shifts are slow instead of sudden.

Edited by Ruedii
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Posted (edited)

I'd much prefer that the motors rotational torque not also include a forward vector. (This is what propellers are for) Not the absolute spaghetti mess that passes for a propeller system under KSP.

In a nutshell, what the current game mechanics mean is that any rear-ward facing motor would induce negative thrust with / without a propeller attached. Which if you think about it is bloody bonkers. Yeah granted, the motors should still induce rotational forces but those can easily be countered by adding a 2nd counter-rotating motor.

Side Note: In a perfect system with the aircraft flying straight , the torque / thrust should be equal across both motors. (see preceding image) However this is not currently possible within KSP mechanics. Even on a test stand the entire system goes nuts as the angle of attack changes while the stand rotates from the induced Yaw. Its why a prop driven aircraft in KSP flies like poopy, no matter how well built they are.

Edited by Redacted
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Posted (edited)

After much discussion, debate, and testing the rotational vectors...  I have accepted the conclusion that there is no forward or reverse thrust associated with the green vectors that indicate motor rotation.

You can read all about it, and review the "unwanted yaw" test craft and associated explanations:

I have single and multi-engine craft that seem to do fine...

Your prop planes may fly like poopy, but it's not related to those rotational vectors.  More likely, it has to do with counter-rotating engines that are "torquey" and the actual engine part the blades are attached to being "rubbery".  The rotor blades on coaxial helos can actually bend and touch now when flown at high forward speeds (I don't care to argue the RL validity of KSP helo designs).  And at top speeds, a multi-engine can get on marbles a bit if the SAS is disengaged.

The lack of rigidity in the robotics parts in general is a real problem.  Combine that with the lift vector position changing from centered to off-center in a 1.8 or 1.9 update and you get a dual engine platform that goes squirrely at high speeds if SAS is not engaged to tame it.  I believe the problem was introduced when @Squad included cycle control options for rotors.  Which really provided no ultimate improvement in craft stability with helos, but did seem to make things a bit more unstable overall.  ...and propeller craft (single or multi-engine) lost some of their top-end speed in the process.

It was not really a good update.

Edited by XLjedi
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Posted (edited)

This is akin to saying that there isn't a problem with propeller based aircraft, when its clear via direct observation that this is indeed the case. Hell, it's not like we can build an aircraft "around" the problem to take advantage of the mechanics to make something that sorta flies as expected. With the game as it is currently there is no reliable in-game application for the Prop / Rotor system period! In the best of situations is a novelty and a poorly scripted one at that.

Side note: Yes, I realize that the propeller angle / flutter is also part of the problem. That being said, on a test-stand with it's rotational axis locked, the props will still flutter about without the motors Yaw-Torque compounding things. From that I'm of the opinion that the problem has more to do with the games handling of physic's not being able to keep up with the rotational speed of the propellers. (Game tick rate limitations)

Edited by Redacted
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XLjedi, redacted .I just did test launch as received remote controller, launch [recoil] was much stronger than expect. Currently having 5 rockets waiting for launch [there are no propellers in estes model as engine rotor consist of rotor, igniters and lid. Recoil[ launch is strong] using remote launch controller.

Next launch i will try on of the smaller rockets with launch controller pad and metal stick which will avoid rotational torque.

Also i did not fit recovery wadding into payload and hell knows if parachute will appear . Currently postponing launch due to coronavirus, same postponing kerbal space program but every day read rocket and spacecraft propulsion and I try to make own ebook or articles basing on rocket and spaceraft propulsion also mixed with fluid mechanics.

Much LovE:>

Keeps things together.

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Posted (edited)

On 5/12/2020 at 7:38 AM, Redacted said:

I'd much prefer that the motors rotational torque not also include a forward vector. (This is what propellers are for) Not the absolute spaghetti mess that passes for a propeller system under KSP.

In a nutshell, what the current game mechanics mean is that any rear-ward facing motor would induce negative thrust with / without a propeller attached. Which if you think about it is bloody bonkers. Yeah granted, the motors should still induce rotational forces but those can easily be countered by adding a 2nd counter-rotating motor.

Side Note: In a perfect system with the aircraft flying straight , the torque / thrust should be equal across both motors. (see preceding image) However this is not currently possible within KSP mechanics. Even on a test stand the entire system goes nuts as the angle of attack changes while the stand rotates from the induced Yaw. Its why a prop driven aircraft in KSP flies like poopy, no matter how well built they are.

So divide the actual vector into the two virtual subcomponents on the aerodynamic diagram?  This would be nice.  It would be no difference in the physics to do this breakdown there, so I wouldn't bother, but for visualization this would be very helpful.

That would be very useful when designing aircraft as it would make it easier to visualize what is going on (or more acruately wrong.)

I'd like the visualized vectors to be combined of all blades connected to the motor and blended instead of instantaneous of each blade too.  I would visualize the torquing as the 4 directions (up-down-left-right) at the center of aeordynamics of the blades as they pass.

As  of actual physics, the current system is right.  However, blending the physics over the path of the propeller considering the propeller's position response (if this is possible on the current physics engine) would give MUCH better physics response.

Edited by Ruedii
Moar detail, differentiating visual representation if bevior from actual behavior.
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On 5/14/2020 at 3:23 AM, Redacted said:

With the game as it is currently there is no reliable in-game application for the Prop / Rotor system period! In the best of situations is a novelty and a poorly scripted one at that.

It isn't perfect, but that is just NOT a true statement.

I have well documented and flight tested propeller/rotor craft that fly very reliably in the world of Kerbal.  They are very mission capable and very reliable.  I have links to them in my signature, well over a thousand downloads...  I send them on missions, they work wonderfully!  My rescue missions are often more fun than the missions that resulted in the need for a rescue.

State any mission goal/objective you have in mind for a prop or rotorcraft in KSP and I will post a video of my craft completing it.  It would be fun to have some more rescue mission challenges!  So what do you have in mind?

However, I did not view the update that added cyclic control for rotorcraft to be an improvement.  It was more a novelty (if anything) and seemed to take away from performance while adding a bit of instability under certain situations.

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Any design discussion of a Prop based craft is pointless so long as the motors induce Yaw when spinning in twin configuration. (CW and CCW)

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On 5/18/2020 at 10:10 AM, Redacted said:

Any design discussion of a Prop based craft is pointless so long as the motors induce Yaw when spinning in twin configuration. (CW and CCW)

Your building it wrong. You have two motors spinning in the same direction, which is NOT how they work even IRL. Have one spin CW, and one spin CCW.

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7 hours ago, Lilithvia said:

Your building it wrong. You have two motors spinning in the same direction, which is NOT how they work even IRL. Have one spin CW, and one spin CCW.

He still seems to think a CW and CCW motor spinning in opposite directions induces yaw.  The motors themselves have nothing to do with it.  Mount two of them without blades and spin them to your hearts content, they don't influence yaw.  Those vectors are not thrust indicators.  Why they even chose to display them along with aerodynamic forces boggles the mind, but that's a different story.  I do understand his confusion though; I thought the same thing when I first saw them and was trying to diagnose some instability in a multiengine design.

It's the blades/rotors that go unstable when deployed at a decent angle for thrust.  ...but you can still build perfectly functional twin engine craft.  The instability only becomes noticeable on the outside edge of their top-end performance envelope.

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Please excuse me if this is a dumb question but are these rotor and prop engines stock to 1.9.1 or are they mods.

I just upgraded to 1.9.1 and have one game that is advanced enough for serious aviation but I don't see any prop or rotor engines.

The examples look awesome, and I've always wanted to send out helicopters to recover my Kerbals (and their krafts) from their landing sites. Help anyone?

Regards

Ork

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Just now, Orc said:

Please excuse me if this is a dumb question but are these rotor and prop engines stock to 1.9.1 or are they mods.

I just upgraded to 1.9.1 and have one game that is advanced enough for serious aviation but I don't see any prop or rotor engines.

The examples look awesome, and I've always wanted to send out helicopters to recover my Kerbals (and their krafts) from their landing sites. Help anyone?

Regards

Ork

They are stock if you have the Breaking Ground DLC.

Some refer to them as "Stock+"

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Posted (edited)

Does "Yaw" do anything at all on rotor blade controls?

I have yet to find it do anything; just built a Chinook-style and did read the manual as suggested, should be for yaw that the rear rotor cyclic roll to one side, front rotor cyclic roll to the other to create yaw effect.

Would be good if we had an option there for yaw to set it to be cyclic one way or the other on a per-rotor basis and let designer figure out what it should be; so yaw can function identically to roll or opposite of it(but bound to yaw axis).  This is how the actual chinook works as the controls are mixed together and rotation can be around front or back axis by using the pedals(for yaw) as well as the cyclic for roll together.

So would be great that for "Yaw" rather than it just do nothing full stop, it can work either same as roll or opposite of it, and for there just to be a switch there for the designer to choose what it does.  Then proper chinooks(and I guess a bunch of other stuff too) can built and yaw is just not doing nothing.  All that is needed is another binary option that if yaw is on, whether it acts same as roll or roll inverted(bound to yaw axis of course).  And helicopter blades can start with "Yaw" disabled completely as a default state so as not to confuse beginners.

Am I missing something here, does yaw actually work in some contexts ?

To answer my own question: Yaw works for vertical blades only, in which they have collective control to counteract main blade torq and provide yaw.

It would be great if for each input { pitch, roll, yaw }, that one could MANUALLY choose which action it did.  Rather than there being just on/off.

Option 0: Off

Option 1 : Automatic -> KSP chooses as it does now,
Option 2 : Cyclic Pitch +
Option 3 : Cyclic Pitch -
Option 4 : Cyclic Roll +
Option 5 : Cyclic Roll -
Option 6 : Collective +
Option 7 : Collective -

Then we can have true Chinooks with true yaw(as per manual).  We can have drones that can rotate in yaw without having to use Kals to change RPM to create torq differential.  Chinooks have a "mixer" that mixes the hydraulics so that both roll and yaw can be added together, same simple solution can be done when 2 axis control same cyclic, just add together.  These are the only helicopter swash plate controls and any blade/rotor configuration can be made if they can be manually chosen like this.

So I would humbly request SQUAD implements this in next update so we can finally have helicoptering perfected, and have real chinooks and drone-style yaw control with swash plates and not rpm altering.

Edited by Gavin786