[1.9 Advanced Blade Controls]

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.

[1.9 Advanced Blade Controls]

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.

[1.9 Advanced Blade Controls]

2 hours ago, Slysix said:

It seems that the new controls always wants to "zero" the orientation of my quad copter to "hover".

Even with SAS engaged and forcing the nose of the craft to point down.  The C/C would over power SAS and orient into "hover" once the keyboard inputs are released.

What you're experiencing is normal.  In real helicopters this is called dis-symmetry of lift, and requires more forward cyclic to counter the pitch up tendency the faster you go.  As a result, you will need to trim the nose down to maintain attitude, in lieu of physically holding the controls forward.  As an alternative, try adding a horizontal stabilator to the tail, and map the trim to something like the Translate U/D action groups.  As you speed up, you can apply more and more stabilator incidence to keep the pitch stabilized.

To avoid large forward cyclic applications in the CH-47, the flight controls have what's called a Longitudinal Cyclic Trim (LCT), which you can read about in the hyperlink in Maxsimal's post at the top.  Also included is talk about main rotor flapping, which is not simulated in KSP.  As a result, KSP helicopters will experience much greater pitch down attitudes in forward flight compared to their real-life counterparts.  And unfortunately, this also prevents designing a tandem-style helicopter with authentic yaw control.

[1.9 Advanced Blade Controls]

Like Kamov and Mil had a baby...wait a sec, why is the Mk3 Cockpit white?

[1.9 Advanced Blade Controls]

There are a lot of real-world helicopter physics not simulated in the KSP rotor blade physics.  However, to be fair, there are a lot of real-world aerodynamic and rocket physics not simulated either.

In regards to stabilizing a KSP helicopter using trim vs SAS, I'll say this: Flying a helicopter requires a lot more control inputs and "cross-control" compensation to keep all the competing physical forces in a constant state of balance, when compared to controlling a fixed wing aircraft.  Any change in cyclic position, collective position, pedal input, airspeed, etc, requires the controls to be adjusted to maintain the balance of forces and the desired attitude and flight path.  The SAS in KSP is very rudimentary and comes nowhere close to the complex flight control systems in modern aircraft.  Depending on the sophistication of the flight controls and avionics, some real-world helicopter SAS systems have very limited authority to maintain the desired attitude, requiring the pilot to constantly adjust the controls to a position that the SAS can operate within it's authority envelope.

The most common "trimming" mechanism for helicopters is called "force trim", which can be augmented with SAS, or further augmented by active flight control systems where the computer has complete authority to control the helicopter in a similar manner to autopilot in fixed wing aircraft.  To read a brief run down of each, you can go here: https://www.danubewings.com/stability-augmentations-systems/.  However, the level of sophistication required for the KSP SAS to account for any number of rotary-winged craft that may be "lego-ed" together is (in my opinion) unrealistic.

What I'm getting at is that real-world helo pilots must constantly adjust controls to maintain level flight, so it is reasonable to assume any simulation of such physical mechanics (even a semi-realistic one), would require the same level of constant attention to the controls.  I would recommend using a more complex flight control setup, like a joystick with twist yaw control or rudder pedals, if you plan on doing long-duration helicopter flight.  This would also allow you to more easily "phase in" Alt-WASDQE trim input to decrease your workload.  But if you plan on using just a mouse and keyboard, don't expect rapid changes in flight condition, like airspeed, to come without it's associated workload tapping those keys.

I was able to make a compound helicopter very similar to the S-97 Raider using a coaxial twin-rotor with a rear-facing propulser using fan-blades.  The craft was very well balanced, but did require a horizontal stabilator to maintain pitch stability throughout all speed regimes, and the only real trim I had to apply was roll to account for the torque generated by the tail propulser blades when in use.  But to easily fly an "asymmetric" helo design like a single main rotor with anti-torque tail rotor throughout all possible flight conditions using just a keyboard is quite a tall order for what could be asked from KSP.

[1.7.3 Design Notes - Propellers, Rotors and EC usage]

5 hours ago, Nuke said:

i still haven't been able to get cyclic control to work. thats kind of stopping my single rotor designs from working. 

Unfortunately, it appears that the rotor blades do not have the capability to control attitude of rotor craft via cyclically-feathering blade pitch as helicopters do; despite the rotor blades' PAW having Pitch/Roll/Yaw toggles.  For the moment, conventional helicopter designs will require other means to control attitude, such as reaction wheels.

[Who needs a level runway anyway?]

I don't think the bumpy Level 1 runway would be getting as much grief if the KSC wasn't surrounded by a city-sized putter's green , but I don't expect a KSC redo.  I just find it humorous, and actually pretty appropriate for Kerbal engineering.

Kerbal hipsters...they build runways ironically...