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#4388575 - 11/07/17 07:55 AM Flight model discussion  
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Staniol Offline
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Staniol  Offline
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Thanks for the welcome guys.
It is a complex question.
For me the flight model in EECH doesn't feel right, hard to explain, but I am missing some inertia, I don't feel the weight (and the difference between small nimble helos and huge ones). For this, some tweaking can help.
I also feel that the choppers are not really hanging on their rotor if you know what I mean.
Additionally, there is the ground effect, vortex ring state, plus those counter rotating helos, etc. Can be hell of a ride, but will try to tackle them one by one.
Most probably I will try to tweak what we have there for the first round and develop additional things later on.
Building a new model from scratch can be a pain, good that you mentioned the opensource ones, I'll check them out.
I have done some similar calculations and physics earlier in another project, but obviously, cannot promise anything till I check what is in the code. Maybe its soooo complex that I will just admire it for a couple of weeks and give up. smile

Last edited by messyhead; 11/07/17 07:47 PM. Reason: my arch enemy, grammar.

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#4388598 - 11/07/17 11:43 AM Re: EECH source code [Re: tulyopt]  
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Viper1970 Offline
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Good helicopter physics are a real challenge. Not many games I played had a believeable helicopter flight model. EECH Allmods isn't so bad in my opinion. The power of some helos is a bit low, I think. They tend to overtorque a bit to quick, especially the OH-58D Kiowa.

And yes, the inertia could really be better to represent the differences between the helos. I never had much time to fly with DCS, because of my home cockpit building, but I was not so impressed of the flight model of the KA-50, although many guys mentioned it the best helicopter flight model. It's hard to evaluate because the KA-50 is a exception with it's koax system. For the Huey I can't say anything, although I have this DLC, but I thought that it doesn't make a sense to fly it before my cockpit is finished. I hardly believe you need a fully working HOTAS with cyclic, collective and rudders for it to fly it in full realism.

In newer helicopter like the Apache, the Viper, the Comanche or the Blackhawk I suppose that the moment of torque from the main rotor is eliminated by the fly by wire system, so no more need to hold the nose in direction with the pedals while a hover. I don't know it for sure, but I spoke with an rescue chopper pilot of the ADAC here in Germany some time ago, who was flying the EC-145 and he told me that there is no more need to use the pedals while hovering. You only use them to rotate in the direction you want, but you don't have to compensate the torque of the main rotor anymore. Most of the adjustments you had to make in older helos while a hover or in flight are not needed anymore in this modern rescue chopper and that's why I think that it is the case in modern military choppers also, because their avionics and flight systems are much more advanced.

He said that this bird compared to the older BK-117 is flying on it's own. You can even take the hands off the cyclic, something you never should do in an older helicopter. I also asked him if he is flying some flight simulators and what is the best flight model he ever experienced in a hobby simulation. To my surprise he told me that the flight model of SAR-4 (representing older helicopters with the use of pedals) isn't bad as long as you stay in normal flight conditions (no rolls or something else). The flight model of the MSFS out of the box for example is a real joke he said and has nothing to do with real life helicopter flying. Even with the often mentioned tweaks it's no more near a helo flight model.

I think that in consideration of the modern fly by wire systems the flight model of EECH Allmods is relatively realistic for the newer helicopters. For older helicopter like the MI-24 or the OH-58D (don't know if the OH-58D even had something comparable like a flight control computer for correcting the inputs to stay better in position while using the optics or weapons) some tweaks had to be made to make it feel a bit more realistic.

Last edited by Viper1970; 11/07/17 11:48 AM.

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#4388609 - 11/07/17 12:40 PM Re: EECH source code [Re: tulyopt]  
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Staniol Offline
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I have DCS, both Huey and KA50. Let's just skip the KA-50 part, as the counter rotating rotors are quite game-changing, not to mention the multiple autopilot systems.
Huey is a beast to be tamed and yes, you are right, it has no sophisticated fly by wire, so you need to counter pedal and such.
Good that you mentioned, I really enjoyed SAR4 and it felt somewhat realistic, I will revisit it.
Also tried the new FM in Arma3 and have the same issue with it what I have with eech, I just don't feel the weight.
Yes, EECH is still good enough, hope I can find some places to tweak.

On a side-note, dear Admin, shall we move this conversation into a separate FM thread, before we mess up this topic completely? smile


Freedom of speech is our birth right, but the privilege of being heard needs to be gained.
#4388707 - 11/07/17 08:58 PM Re: Flight model discussion [Re: Staniol]  
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Yes SAR-4 was really fun to fly. I have Vietnam Medevac also, but the Huey wasn't made very realistic, even for the possibilities back those days.

They only made a new 3D model added a Vietnam like terrain and the rest was original like SAR-4. The single engined Huey had a second engine rpm display which was left from SAR an they had forgotten to remove it biggrin There are two other games too, based on that engine.

One is Apache Air Assault (not to mix up with Apache Air Assault from Gaijin Entertainment) and the other is Apache Longbow Assault. Sadly those two titles were only low budget productions cause if they had added more realism to them they really could have been good attack helicopter simulations. In Europe they were sold as Operation Air Assault and Operation Air Assault 2 with a fictive attack helo model.

I'm trying to get a flyable AH-1F Cobra to Allmods too, if I'm able to do so, but there is a lot to add in the code for a new helo with a cockpit and the code is exactly what I'm not really able to understand. Maybe if the model and the cockpit is sexy enough someone will be gracious and do the code work for me hahaha This one really needs a kick in the pedals for keeping the nose straight.


Main Cockpit System: AMD Ryzen 7 2700X / ASRock Taichi X470 / 32GB Ram GSkill F4-2800C15Q-32GVR / Asus ROG Strix GeForce RTX 2080 OC

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#4388720 - 11/07/17 10:27 PM Re: Flight model discussion [Re: Staniol]  
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thealx Offline
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Hey! Nice to see someone being interested in physics, it's very poor at this moment.

Since the original release not much changes was applied to the dynamics. Shorty - there is no such thing as "physics" in the game. All forces, that affecting helicopter object, are just poor emulation - like, "hey, this guy loosing altitude too fast, let's cast vortex ring on him!", instead of precise calculation for each rotor blade all the time and simulating real processes (as example - vortex process happen continuously, but it affect dynamics dramatically only in special conditions). And it's everywhere - ground effect, overspeed, lift power and so on - it just bunch of simple calculations like z += a * b + c;
Another problem - there is no real mass in the game, and as result - no inertia. It replaced with artificial modifiers of the DYN files, and that is only thing to separate large helicopters from small one.

I made some experiments lately, it wasn't attempt to make real dynamics but improve the code - default flight model functions are duplicated for each helicopter what makes really hard to apply even simple changes to it. I have combined all of them in single function, and added some new data in DYN files (for FM=2 files stored in \common\data\dynamics folder). I succeed, I suppose, at least helicopters are still flying (some people doesn't like new FM and that's ok - I made it little more challenging). It was one step forward, from 2 miles walk.

To introduce yourself with code, I recommend to start with FM parameters and basic functions tweaking, you can make game little better in the learning process. It is possible to replace FM with some existing scripts, it may take a lot of time for adjustments but still anyone with some programming skills and physics knowledge can do that. Several years passed since I have worked with dynamics last time, but I can try to explain some basic things if it will be necessary. Previously Arneh applied dramatic changes to the FM, but not sure that he is available right now.

If you wish to follow my advice - I have first task for you! =) currently, when you exceed maximum speed, helicopter starting to jump around like a crazy horse, and at the end you will loose all your rotor blades at once. that's not really what happen in real - first vibrations appear, then controls effectiveness decreased, and last - helicopter starting to roll (to the right for clockwise rotating rotor, and to the left - for counterclockwise). It's much more complicated of course, it just a list of obvious differences, but still good thing to start. Just look around and think about it, maybe you will be interested.

#4388776 - 11/08/17 09:43 AM Re: Flight model discussion [Re: Staniol]  
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Staniol Offline
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Hi Thealx, thank you for all the valuable information.
Some comments/questions.
- Combining FM for all helos means that you managed to use one function for all helos (obviously with different input parameters)? That's already a huge achievement!
- Inertia: Yes, that is the most standout problem for me currently.
- Yes, I am planning to start with small tweaks.
- I also noticed the absence of retreating blade stall, which should occur at high speeds after some vibration, but definitely before the whole thing falls apart.:) I promise to check it out with highest priority! smile


Freedom of speech is our birth right, but the privilege of being heard needs to be gained.
#4388780 - 11/08/17 10:25 AM Re: Flight model discussion [Re: Staniol]  
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Viper1970 Offline
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How does retreating blade stall effect in koax helos?

In normal helos the helicopter rolls to the blade which runs against flight direction, but how does this happen in koax helos, where both sides get this effect?

O.k. found something about this at Bladeslapper.com but don't know if it's right:

Quote
With a twin rotor (coaxial) machine, there is a blade on each side that is in some stage of advancing. This means that the retreating blades don't have to work so hard to support their side, because the other blade's advancing section is helping it out. Thus, the retreating blade doesn't need such a big angle of attack, and it doesn't stall the way a single rotor system does.

In a twin rotor (tandem) such as the Chinook, the advancing bits are separated by the length of the fuselage, but the rear blade's advancing bit is on the left side and the front blade's is on the right side, so there is still a balance. Retreating blade stall will happen at a much higher speed than for a single blade.

Last edited by Viper1970; 11/08/17 10:46 AM.

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#4388781 - 11/08/17 10:47 AM Re: Flight model discussion [Re: Viper1970]  
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Staniol Offline
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Originally Posted by Viper1970
How does retreating blade stall effect in koax helos?

In normal helos the helicopter rolls to the blade which runs against flight direction, but how does this happen in koax helos, where both sides get this effect?

For single rotor helos, , lift loss is increasing with speed, it's compensated with blade pitch adjustments on the opposite sides, which causing more and more lift loss obviously. At one point it cannot be compensated more as the speed difference is huge, that is when it stalls and start to roll the plane.
This is causing the speed limit of helos and its hard to get around that.
For coaxial rotors, lift loss and retreating blade stall still occurs although due to air movement its not that bad is it is with singles. It starts with lift loss and vibration, no clear roll effect to either side. Later on you'll have increasing vibration and finally loosing blades, they either break apart from huge forces pushing them or hitting each other (which is really a bad thing with coaxials).
Sorry if something is not clear, I am not a native speaker, especially writer, not to mention, that I am not a helicopter expert, just interested in the topic....:D

Edit: Just saw what you copied. Yes, its sounds correct, but I think we need to do a couple of things, before we can argue on the exact speed limit and simulation of forces for coaxial helicopter blades smile

Last edited by Staniol; 11/08/17 10:51 AM.

Freedom of speech is our birth right, but the privilege of being heard needs to be gained.
#4388783 - 11/08/17 11:09 AM Re: Flight model discussion [Re: Staniol]  
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Viper1970 Offline
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Thank's for your description Staniol!

Sorry for the overlapping! I just had found this after I posted and don't wanted to make a new post. I' m also no native speaker or writer, only my bad school english and sometimes the LEO online dictionary biggrin

It's an interesting subject and I have asked my self a few times what happens here in koax or tandem systems.

I also have in mind that there was something with the advancing blade which reaches mach speed at higher forward speeds. I had a video tape which descriped all the phenomenons of helicopter flight years ago, but it gets lost during my numberless moves to other locations and besides that I don't own a video recorder anymore which is able to run tapes hahaha


Main Cockpit System: AMD Ryzen 7 2700X / ASRock Taichi X470 / 32GB Ram GSkill F4-2800C15Q-32GVR / Asus ROG Strix GeForce RTX 2080 OC

WSO Cockpit System: AMD Ryzen 5 2600X / Asus Prime B450 Plus / 16GB Ram GSkill F4-2666C15Q-16GRR / KFA2 GeForce RTX 2060

Retro System: AMD Athlon X2 3000Mhz / ASRock AM2NF3-VSTA / 2GB Ram / Gigabyte GV-N68T256DH GeForce AGP 6800 GT 256MB DDR3 / Diamond Monster 3D II 12MB SLI
#4388791 - 11/08/17 12:01 PM Re: Flight model discussion [Re: Staniol]  
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thealx Offline
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Originally Posted by Staniol
- Combining FM for all helos means that you managed to use one function for all helos (obviously with different input parameters)? That's already a huge achievement!


Yes, that was the idea - make further improvements simpler, applying new FM shouldn't be so painful as before. Old FM functions still exists (and player able to use them with FM=1), but they shouldn't cause any compatible issues.

I remember DCS Ka-50's manual explain such process clearly - even if helicopter is co-axial, upper rotor provide different lift power than lower. they compensating each other in normal conditions, but at blade stall state forces became unbalanced.

#4388796 - 11/08/17 02:34 PM Re: Flight model discussion [Re: Staniol]  
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Viper1970 Offline
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Viper1970  Offline
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Ah yes, the DCS manuals. Have totally forgotten about them, cause I haven't used DCS that much. I love EECH Allmods and Falcon BMS wink


Main Cockpit System: AMD Ryzen 7 2700X / ASRock Taichi X470 / 32GB Ram GSkill F4-2800C15Q-32GVR / Asus ROG Strix GeForce RTX 2080 OC

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