Chopper flight models

[Piipu]

The chopper flight models in PR seem to be quite unrealistic and, as a result, unintuitive. I'm having a lot more problems doing small scale maneuvers in PR than I do with the study simulation-grade flight models in DCS: World. I've flown helicopters quite a bit in them, and I can tell that flying in PR feels very weird compared to that. I've heard others mention the low cruise speeds of all choppers, and I think that also comes from the same issue.

I'm not entirely 100% on this but it seems to me that choppers have too little upwards thrust on the main rotor. The climb rates achievable with most choppers seem really low compared to those I've seen in DCS. It also seems that there's some sort of weird horizontal force boost system that makes the horizontal movement feel really slippery compared to the better models. This line (found in gb_ahe_apache.tweak) seems to point that way as well:

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ObjectTemplate.horizontalSpeedMagnifier 5.2

With the 'real' models, you have to tilt the chopper quite a lot to achieve maximum cruise speed, whereas in PR you're only talking about a few degrees of tilt. In PR, tilting the chopper even a little makes you lose altitude even at full thrust, which seems really odd to me. Let me show a simplified force model of the situation:



Hopefully you can tell from the image that in order to stay in level flight, a chopper must provide enough vertical thrust (labeled t_y in the image) to cancel out the gravitational force affecting the chopper. Any additional thrust (labeled t) that isn't needed for level flight, can then be converted into horizontal acceleration by tilting the chopper forward.

Now, if you don't have enough overall thrust in the first place, you have to compensate for the lack of forward thrust by adding in a horizontal velocity multiplier. This approach however has the negative qualities mentioned earlier: even tiny changes in the angle of the chopper cause huge accelerations, and the climb rate of the chopper will suffer greatly.

I think getting rid of the horizontal velocity multiplier and readjusting rotor thrust rates would fix both the handling issues, as well as making it possible to have higher cruise speeds for choppers without breaking anything in the flight physics. I don't know enough about the BF2 editor to give you any solid examples yet, but I'll try fiddling around with the variables and see if I can make any sense out of it. I'd also appreciate any advice you can give to me with regards to chopper flight models in PR.

[rPoXoTauJIo]

Forget about real world and DCS, this is bf2 shit
Instead of theory make minimal valuable product(le ingame\in bfeditor)by playing with values that will make choppers great again.

Problem with bf2 engine is that you have no air, only thing that make you fall is gravity. Rest of helicoter behavior is rotor rotate(that's how it control chopper, instead of swashplate its simply turning rotor itself) and engine torque.

PR helicopters has additional "wings" through. In bf2 world wings are nothing but to prevent moving against air, that's why jets flying(cuz "wings" prevent plane to change direction a lot). On a PR helicopters they're used to disallow turning on high speed, and to "try" fix diving tactic(althogh caswhores still good in it despite all the efforts made by noob devs )

Parameters in .tweak file you should be interested in:
That's "air resistance" against helicopter mesh in air

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ObjectTemplate.drag float

Modifiers of inertia for diffirent directions, x for yaw, y for height, z for roll

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ObjectTemplate.dragModifier float/float/float

Speaks for itself but doesn't represent actual mass ingame

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ObjectTemplate.mass 16000

That's what you have to consider for adding "weight" to physics model

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ObjectTemplate.gravityModifier 2.0

And modifiers for inertia

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ObjectTemplate.inertiaModifier 0.4/0.4/0.2

For next examples i'll take us_the_uh1n huey.
That's your rotors(RotorHead), you have to look at its params

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ObjectTemplate.create RotationalBundle us_the_uh1n_RotorHead1

Your max rotations for pitch and roll of parent rotor.

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ObjectTemplate.setMinRotation 0/-5/-2 
ObjectTemplate.setMaxRotation 0/5/2

Rotor will turn to it's max&min rotations with this speed.

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ObjectTemplate.setMaxSpeed 0/50/50

And it's acceleration to max speed.

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ObjectTemplate.setAcceleration 0/-1000/1000

Inputs that will affect parent rotor rotation.

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ObjectTemplate.setInputToPitch PIPitch
ObjectTemplate.setInputToRoll PIRoll

Reset rotation if no input.

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ObjectTemplate.setAutomaticReset 1

Additionally, our parent rotor has child rotor.
It's 20 bf meters high than our parent rotor through

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ObjectTemplate.addTemplate us_the_uh1n_RotorHead2
ObjectTemplate.setPosition 0/20/0

And it's 2nd rotor has our engine
Whish is 86m under child rotor, which give us true engine position of -66m under heli

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ObjectTemplate.addTemplate us_the_uh1n_Rotor
ObjectTemplate.setRotation 0/-86/0

Note those values. They're displaying not rotation, but rather "power" values from 0% to 100%.

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ObjectTemplate.setMinRotation 0/0/-20
ObjectTemplate.setMaxRotation 0/0/900

Speed with which "power" will increase.

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ObjectTemplate.setMaxSpeed 0/0/1

Acceleration to "max speed".

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ObjectTemplate.setAcceleration 0/0/13

Which input affect engine, PItrolle is W and S by default f.e.

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ObjectTemplate.setInputToRoll PIThrottle

That's your "power" of engine.

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ObjectTemplate.setTorque 240

Have low idea what those means for heli, when played barely got any effect.

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ObjectTemplate.setDifferential 180
ObjectTemplate.setGearUp 0.99
ObjectTemplate.setGearDown 0.01
ObjectTemplate.setGearChangeTime 0.1
ObjectTemplate.setGearRatios 3.5 2.2 1.5 1.1 0.94 

That's indeed gives some boost for horizontal speed, but it's barely relevant to altitude drop when flying fast.

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ObjectTemplate.horizontalSpeedMagnifier 3.1

Some values for hover stabilization.

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ObjectTemplate.horizontalDampAngle 0.1
ObjectTemplate.horizontalDampAngleFactor 0.001
ObjectTemplate.defaultAngleOfAttack 2
ObjectTemplate.decreaseAngleToZeroVerticalVel 0.5
ObjectTemplate.dampHorizontalVel 5
ObjectTemplate.dampHorizontalVelFactor -0.5

That's values you're looking for probably.

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ObjectTemplate.maxAngleOfAttack 12
ObjectTemplate.attackSpeed 10

When max angle of attack exceeded, helicopter will not increase speed anymore.
Attack speed is something you have to play with, i have not understood effect of this fully.

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ObjectTemplate.create Wing us_the_uh1n_Rudder
ObjectTemplate.modifiedByUser K4on
ObjectTemplate.createdInEditor 1
ObjectTemplate.floaterMod 0
ObjectTemplate.hasMobilePhysics 0
rem -------------------------------------
ObjectTemplate.addTemplate S_us_the_uh1n_Rudder_RotationRpm
rem -------------------------------------
ObjectTemplate.setPositionOffset 0/0/0
ObjectTemplate.setWingLift 4
ObjectTemplate.setFlapLift 0

Additionally huey use wings for some stabs effects of whatsoever, but they give less impact on helicopter on low speed, for understanding what they're affect you have to take a look on wings postion, rotation, and lift values.

[solidfire93]

rPoXo PRO MLG CODER..

Trans Choppers are great, attack chopper's need a bump in their speed a bit....

[Piipu]

Thanks, those should be helpful. One thing though, I did some testing in the editor and the horizontalSpeedMagnifier certainly has something to do with how the helicopter moves vertically. It looks like the factor just forces a certain amount of vertical thrust into horizontal. If you set it to 0, you can stay level with an angle of attack of about 85 degrees (and you won't move horizontally at all of course) while at 5 you'll start sinking at around 5 degrees. I'll try playing around with the wings and the angle of attack values as well and see what they do.

On another note, do you know of some easy way to quickly reload changes you've made to the .tweaks file? It seems that reloading the object in the editor doesn't reload the changes you've made. Also, it'd be nice to be able to quickly test these changes while having an actual map loaded, the grid floating in empty space is not that great when you want to fly around for longer distances.

Edit: nevermind, I figured it out. I just had terrain rendering disabled :/

[Mats391]

Tools -> Options -> ReloadFileSettings, Check everything. Should reload files when you edit them

[Piipu]

Here's what I've found so far based on some quick testing.

Min and Max rotation speed don't seem to have much effect on rotor lift, aka thrust. Maybe they're scaled away and it only affects startup time? I don't know.

Torque (ObjectTemplate.setTorque) controls the lift directly. Increasing it increases climb rate and max speed, but also increases the amount of chopper tilt you can have before you start losing altitude.

Angle of attack has nothing to do with chopper tilt, it's the angle of attack of the rotor blades. Your thrust (aka pressing W) increases the angle of attack of rotor blades, increasing lift as well. Basically it seems to be a multiplier to torque.

attackSpeed tells how fast the angle of attack of rotor blades can change, so basically how quickly you can change the amount of lift generated by the rotor. Doesn't have much to do with max speed of the chopper, and seems to be at reasonable levels for most choppers.

horizontalSpeedMagnifier is some magic value that governs how much of your upwards thrust is converted to horizontal acceleration. Setting it to 1 seems to produce the most realistic behaviour for choppers. After setting it to 1 for the British Apache, it behaves otherwise pretty nicely but the max level flight speed is capped at around 360 km/h. I tried removing drag from the chopper and lift from all wings and it still doesn't change, which seems very odd to me. There must be some other drag variable somewhere that I haven't found yet.

[rPoXoTauJIo]

Min and Max rotation speed don't seem to have much effect on rotor lift, aka thrust. Maybe they're scaled away and it only affects startup time? I don't know.

Note those values. They're displaying not rotation, but rather "power" values from 0% to 100%.

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ObjectTemplate.setMinRotation 0/0/-20
ObjectTemplate.setMaxRotation 0/0/900

Speed with which "power" will increase.

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ObjectTemplate.setMaxSpeed 0/0/1

Acceleration to "max speed".

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ObjectTemplate.setAcceleration 0/0/13

Someone did not read
900 is 100%, 0 is 0%, -20 is negative thrust, that's allows me to do barrel rolls on carrier deck.
Those values indeed have effect on startup speed.

horizontalSpeedMagnifier is some magic value that governs how much of your upwards thrust is converted to horizontal acceleration. Setting it to 1 seems to produce the most realistic behaviour for choppers. After setting it to 1 for the British Apache, it behaves otherwise pretty nicely but the max level flight speed is capped at around 360 km/h. I tried removing drag from the chopper and lift from all wings and it still doesn't change, which seems very odd to me. There must be some other drag variable somewhere that I haven't found yet.

You probably should try to remove wings(as they're responsible for dragging you on high speed), increase maxAngleOfAttack, increase horizontalSpeedMagnifier or either torque.

[Mats391]

Check this setting:
objectTemplate.noEffectAtPerpSpeed float -> float
This is somehow caps the max speed

[Piipu]

Someone did not read
900 is 100%, 0 is 0%, -20 is negative thrust, that's allows me to do barrel rolls on carrier deck.
Those values indeed have effect on startup speed.

You probably should try to remove wings(as they're responsible for dragging you on high speed), increase maxAngleOfAttack, increase horizontalSpeedMagnifier or either torque.

I believe you're mistaken about the RPM values. Unless you have some reliable source saying otherwise, I'm more inclined to believe my own tests. I just tried to see what happens when you set min RPM to -2000 and max RPM to 7000. The only thing that changed was that the warmup sequence where you have to wait for your rotor to start spinning fast enough to lift off takes 5 minutes instead of 30 seconds. After the warmup is done, it flies just the same as with -20 and 700.

Based on my tests, the negative thrust is governed by the relation of max and default angle of attack. The default angle of attack is the 'rest' position for the rotor blades, while the maximum is the highest angle they can turn into. It seems that their movement range is governed by the difference of max and default AoA: the blades can turn the same angle in the negative direction that they can in the positive one.

This means that with default AoA of 2 and max AoA of 15, like on the British Apache, the blades can turn +-13 degrees from the default, which translates to a minimum angle of -11 degrees. You can verify this by setting default AoA to 13 degrees and max AoA to 15. Now you won't be able to stop your chopper from lifting off, as the minimum AoA will be at +11 degrees, which gives you a lot of vertical thrust.

There also seems to be some sort of autohover system in place which adjusts the default thrust level to be at level flight, if that's possible. Even if you double the gravity affecting the chopper or increase rotor torque by a lot, the chopper will stay hovering without thrust input. This makes the engines a lot easier to balance, as you don't have to worry about keeping the idle thrust at neutral lift.

[Piipu]

Check this setting:
objectTemplate.noEffectAtPerpSpeed float -> float
This is somehow caps the max speed

I tried that already, it just gradually removes lift from the rotor, and lift will be zero once your chopper reaches that value. You need to set AirFlowAffect to 1 as well I think for it to work. I believe that's the system that decreases the tail rotor effectiveness at higher speeds, but I don't see how that would be useful with limiting your max speed. It just makes the chopper drop like a rock once you reach that speed, which is not really desirable.

Edit: It looks like that doesn't work as simply as that. If you set it to 10, your chopper will drop with any horizontal velocity at all, but at 150 it has no effect anymore. It also looks like AirFlowAffect does something different, it didn't have any effect on that.

I also found the variables that control the autohover behaviour. RegulateVerticalPos and the next few variables control it. It looks like MaxVertRegAngle and NoVertRegAngle have something to do with it, it feels like they actually tilt the main rotor to keep your chopper level.

Here's a demonstration with the angles changed from around 40 to around 10 degrees (loud music warning, can't be bothered to edit it out). I don't touch the thrust at any point, this is all on neutral. I only change the angle of the chopper.
https://dl.dropbox.com/s/9tvy5dr7juhrst ... .44.01.mp4

Here's the same with with regulation angles set at 60 degrees. Note how the chopper doesn't start losing altitude until angle of attack is at 60 degrees.
https://dl.dropbox.com/s/6kz2wm4fca1uvg ... 2.mp4?dl=0

[rPoXoTauJIo]

I believe you're mistaken about the RPM values. Unless you have some reliable source saying otherwise, I'm more inclined to believe my own tests. I just tried to see what happens when you set min RPM to -2000 and max RPM to 7000. The only thing that changed was that the warmup sequence where you have to wait for your rotor to start spinning fast enough to lift off takes 5 minutes instead of 30 seconds. After the warmup is done, it flies just the same as with -20 and 700.

That's indeed something new to me, guess other things were mixed when i have tested that.

Based on my tests, the negative thrust is governed by the relation of max and default angle of attack. The default angle of attack is the 'rest' position for the rotor blades, while the maximum is the highest angle they can turn into. It seems that their movement range is governed by the difference of max and default AoA: the blades can turn the same angle in the negative direction that they can in the positive one.

This means that with default AoA of 2 and max AoA of 15, like on the British Apache, the blades can turn +-13 degrees from the default, which translates to a minimum angle of -11 degrees. You can verify this by setting default AoA to 13 degrees and max AoA to 15. Now you won't be able to stop your chopper from lifting off, as the minimum AoA will be at +11 degrees, which gives you a lot of vertical thrust.

That's interesting stuff, never through that aoa values works this way aswell, keep it up, good work

[Piipu]

Here's my findings so far, I wrote them down in a document so it doesn't get lost.

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=========================================================================
================== helicopter body properties: ==========================
=========================================================================
eg. the root object of the chopper

========
physics:
========
gravityMultiplier: how strongly gravity affects the chopper. Should be 1.0 for realistic
behaviour.

Drag: air resistance multiplier

DragModifier: per-axis multipliers for drag. For rotation only or what though??

Mass: slows down acceleration, doesn't affect speeds or whether or not the chopper can lift off.

InertialModifier: moment of inertia of object. Basically adds mass to rotation only. 
Should be bigger for large choppers.

=======================
PlayerControllerObject:
=======================
controls camera and seat positions etc. as well as some input stuff

RegulateVerticalPos: These seem to be multipliers for some autopilot PID controller that 
maintains level altitude. The two values control how strong the autopilot behaviour is I 
guess. Setting these to 0 will disable the behaviour.

MaxVertRegAngle: ????? doesn't seem to affect much?

NoVertRegAngle: the chopper tilt angle at which the altitude hold autopilot stops working. 
If neutral thrust is not close to hovering, will drop off sharply. Keep this angle small 
(10 degrees or so) and make sure neutral thrust is slightly below a hover. This way chopper 
can hover, and won't lift off the airfield or flip around on its own if pilot goes AFK.

=========================================================================
================== rotor engine properties: =============================
=========================================================================
the main rotor engine at least for british apache is kind of hidden in the editor. It's 
hierarchy path is gb_ahe_apahce->gb_ahe_apache_Rotorhead1->gb_ahe_apache_Rotorhead2->
gb_ahe_apache_rotor. Note the misleading name. Tail rotor engine is gb_ahe_apache->
gb_ahe_apahce-tailEngine, which is a lot less obscure.

========
physics:
========
torque: how much overall thrust can be had from rotor. Affects chopper tilt rates as 
well as far as I can tell.

max angle of attack: upper limit of rotor blade angle

default angle of attack: 'neutral' angle of rotor blades. range of movement is default 
+- difference to max from default, so minimum = default - (max - default) large negative 
minimum AoA should be avoided, otherwise barrel rolls and other weird behaviour becomes easier.

torque and angle of attack of blades determine total lift from rotor.

HorizontalSpeedMagnifier: magic value that converts upwards thrust into horizontal acceleration. 
Values other than 1 are nonphysical and should be avoided, otherwise behaviour (ratio of climb 
rate versus horizontal movement) will feel wrong.

NoEffectAtPerpSpeed: percentage value that determines the percentage of maximum lift when 
moving at horizontal max speed. Used to decrease tail rotor effectiveness at higher speeds.

=========
rotation:
=========
max speed of rotation determines how long it will take for the rotor blades to reach maximum 
spin velocity. Rotor lift scales as a percentage value of max RPM - with lower RPM values, 
produced lift will be lower as well. Increasing max RPM won't increase lift directly however - 
only the speed relative to the maximum matters for lift generation.

I still haven't been able to increase the max speed of the chopper though. Even after setting drag to 0 for all components, there's still something that causes drag. I did manage to make it go faster by increasing the gravityMultiplier as well as the torque, but it's not really that great either. It makes the chopper fall down too fast, and works a bit similiarly to the horizontalSpeedMultiplier.

Here's some shitty keyboard and mouse aerobatics to show you how the apache works currently:
https://dl.dropbox.com/s/57hw3k0fjkoztm ... 38.09.webm

[Mats391]

Did you try out the modifying the differential already? On land vehicles torque+differential define speed.

Edit: And mass also has other physics influences e.g. what happens when you ram another vehicle.

[Piipu]

Did you try out the modifying the differential already? On land vehicles torque+differential define speed.

Edit: And mass also has other physics influences e.g. what happens when you ram another vehicle.

Differential seems to have something to do with the relation of the engine torque and the rotor RPM. It doesn't seem to increase lift as long as the value is large enough, but with huge values you can see that the rotor spins only very slowly. (it doesn't get blurred at all, you can see the individual blades spinning)

And yes I could guess that about the mass already. I have no idea what range it should be in though so I didn't include it there.

[Mats391]

Then the other things that might influence speed are the rotorHeads. The rotation of the rotor heads controls how far the engine is in front of the chopper. Like this:


Maybe if engine is further away it increases speed?

[Piipu]

Mats391;2127710']Then the other things that might influence speed are the rotorHeads. The rotation of the rotor heads controls how far the engine is in front of the chopper. Like this:
http://i.imgur.com/wxXOdbj.png

Maybe if engine is further away it increases speed?

I don't know who would code up a system like that in their right mind. But I guess it's a good idea to see what they do. I'll do more testing later, I've had my fill for now.

[Mats391]

Thats how bf2 does it and we took over this system. Maybe there is a better one. No idea what is going to happen if you actually rotate the engine, right now it stays at same angle all the time. E.g. on apache it is at -86deg angle.

[Piipu]

It looks like the position of the engine relative to rotorhead1 controls how big is the torque imparted by steering movements of the rotor. So moving rotorhead1 away from chopper body while keeping the engine at the chopper center of mass makes the chopper quicker to turn. I guess that makes some sense at least.

Other than that, it seems the position of the engine doesn't have much to do with speed. Obviously it has to stay at (or very close to) the center of mass, otherwise the chopper will just fly out of control since the thrust is going to be imbalanced. The angle of the engine determines the angle of thrust imparted by the rotor, and that can't be adjusted too much either without causing issues (to make chopper hover you have to cancel out the angle of the rotor.)

I'm not sure why the rotorhead2 even exists though, maybe it has some function as well.

[Rabbit]

-snip-

Out of the blue question but does it have to do with why you need to tip the nose forward and by how much to go forward rather than up?

[Mats391]

I'm not sure why the rotorhead2 even exists though, maybe it has some function as well.

RotorHead2 is solely to cancle out the RotorHead1. It makes sure the engine stays at same angle all the time and around the center of mass.