Chopper flight models

[[R-DEV]​rPoXoTauJIo]

Originally Posted by Piipu

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.

Originally Posted by Piipu

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.

=========================================================================
================== 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/57hw3k0fjko....28.38.09.webm

[[R-DEV]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]

Originally Posted by [R-DEV]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.

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.

[[R-DEV]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]

Originally Posted by [R-DEV]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:
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.

[[R-DEV]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]

Originally Posted by Piipu

-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?

[[R-DEV]Mats391]

Originally Posted by Piipu

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.