Please remind me of the upcoming Flight Dynamics tunning...

January 18, 2017

I'm not trying to be that guy but the issue is with the general flight model - all aircraft suffer from varying degrees of exaggerated pitch oscillation and it goes deeper than tweaking sensitivities/noise filters.

Edit: I think we hear this more regarding the LW aircraft due to the relation of the vert-stab and stick force modeling versus trim tabs and generally less responsive controls for VVS birds.

On this I am in total agreement with you sir, it is indeed a global issue that plagues all aircraft in the sim.

January 18, 2017

I-16 and MiG-3 have such large Ailerons, and the Yak also has quite large ones.

Large Surfaces tend to stiffen up quite a lot faster with Speed than Smaller ones I think.

The Mitsubishi A6M series had nearly full length ailerons which imparted great agility at lower speeds, but really hampered the aircraft at the speeds necessary to compete with late war Allied aircraft, as they would stiffen up dramatically at high speed.

January 19, 2017

The Extra 300 has very special wings with near 100% semitrical air foils allowing this fast roll rates and moves and also the large ailerons.

Size and type of ailerons determined by wing design.

A Non Symetrical wing with negetive camber cannot use full length ailerons and must use only tip ones.

January 19, 2017

Well even if as you say this is not the same P/W ratio and inertia as a WW2 fighter it seems to be quite representative. Granted, the Yak and Me-109 we see below do not carry the same payload as they did in WW2 but I seriously doubt that that would make what we see in the clips below unrepresentative:

Yak-3:

And of course Red 7:

If you look at these its like the planes were "on rails" compared to the wobbliness in many sims today. I think it probably has to do with how the planes need to be modeled due to the limitations of our hardware but I for one would be very happy if we could get something closer to the "on rails" characteristics many seem to equate with the older generations sims which in fact actually looks closer to IRL. Sure, if you look at the ball in the Yak you can see it move from the center when aileron is applied but also note how it jumps right back and stays put as soon as the pilot return aileron to neutral. Not much wobbliness there as far as I can see.......

So if it is possible to tweak this within the constraints of how this is modeled in IL-2 and the next tuning decreases wobbliness I will for sure see that as a step in the right direction.

EDIT: I'm of course talking about the "real" wobbliness, not the wobbliness in the camera mount in those clips.......

+1000 but I am afraid that this lightness/instability/tail heavy flight dynamics is the feeling of flight illusion that many people praising in this game. It's been here since the beginning of the game when it was in pre-alpha and like it was suggest, perhaps a legacy from rise of flight. I've also wish they fixed it since 2014

January 19, 2017

Yak-3 in the video flys a lot like the Yak-1b we have ingame now. In a dynamic flight model you will have some problems modelling some specifics which can not easily be reproduced, given how stable the Yak-1b is however, the team seems to have been able to tweak it quite nicely.

Edited January 19, 2017 by 216th_Jordan

January 19, 2017

+1000 but I am afraid that this lightness/instability/tail heavy flight dynamics is the feeling of flight illusion that many people praising in this game. It's been here since the beginning of the game when it was in pre-alpha and like it was suggest, perhaps a legacy from rise of flight. I've also wish they fixed it since 2014

I feel that this is not quite correct, the "feeling" of flight and wobbling/instability are two different things

The 'feeling of flight' comes about from a much more sophisticated flight model which was also present in RoF

Very very early example, not exactly showing 'FM' but interesting nonetheless

The issues jcomm is talking about are different

The whole suggestion that because DN engine was used for WW1 aircraft and that there is 'somehow' a problem translating to more modern WWII FM is one of those silly perpetuated myths that just won't go away

There are many ways that the FM can be improved, and issues that need to be resolved, but the whole frequently trotted out, "because WWI" mantra is just tosh (IMHO)

Cheers Dakpilot

January 19, 2017

Yes, and X-Plane, which also uses a similiar approach, and more recently Aerofly FS 2, can also have "good" and "bad" or "nor so good" pitch behaviour.

I believe one of the youtubes I linked above can show how realistic the Extra 300 can feel in AEFS2, but in X-Plane we can also have aircraft with that "pitch wobbling" and others that behave plausibly.

I am tempted to guess that is can also be due to the way the Cm is being calculated for the airfoils, and tied to this, the static margin calculations based on the model geometry, but this is just a rough guess because I do not make the slightest idea about how it is implemented in IL.2...

Even in good old MSFS we can have aircraft correctly and incorrectly modeled regarding this particular "feature" :-)

Edited January 19, 2017 by jcomm

January 19, 2017

I feel that this is not quite correct, the "feeling" of flight and wobbling/instability are two different things

The 'feeling of flight' comes about from a much more sophisticated flight model which was also present in RoF

Very very early example, not exactly showing 'FM' but interesting nonetheless

The issues jcomm is talking about are different

The whole suggestion that because DN engine was used for WW1 aircraft and that there is 'somehow' a problem translating to more modern WWII FM is one of those silly perpetuated myths that just won't go away

There are many ways that the FM can be improved, and issues that need to be resolved, but the whole frequently trotted out, "because WWI" mantra is just tosh (IMHO)

Cheers Dakpilot

I understand your point Dakpilot, but for me, since I don't have or sense that feeling of flight, I've ask my friend or people that I fly with to describe to me want they mean by in BoS they have the feeling of flying most if not all they say it's because they feel that the aircraft is not on rail. Put aside the atmospheric effect, turbulence, wind, temperature inversion etc, most aircraft will fly like it's on rail and wont be wobbling around and sliding all the time like that. Wind or not, summer or winter, cold or warm.

January 19, 2017

Not quite because you still have:

- engine torque

- prop wash

- pilot induced oscillation

- adverse yaw

These effects are also well modeled in BoS (saying well because I cant say if correct).

January 19, 2017

The pitch instability in the sim that we call the "wobble" is why many of us, myself included, concluded that some artifact from modeling the WW1 kites in the RoF engine has transferred to this sim.

Is this a correct analysis? Hard to say, but it is one way to explain the problem without having access to the actual internal workings, and ability to understand, the game engine. It also may explain why in the early days one of the criticisms of the sim was that the aircraft felt as if they had no weight.

Does this mean that too much RoF is in BoX? I don't really know, but it is one way that the phenomenon can be explained, right or wrong.

What is wrong, without question, is the pitch instability that is present to one degree or another on all the aircraft in the sim.

The "on rails" argument, I feel and it's just my observation of being a PC flight sim enthusiast for over 15 years now, is in a way an extension of the "harder is more real" mantra that most desk flyers have come to believe. I believed it too for a while, then I had the good fortune to be able to fly in, and also to fly, an aircraft from this era, which changed forever how I looked at flight sims. The actual act of flying in sims is harder than it is in reality. I'm not talking systems management stuff here, just the stick and rudder work, and ground handling. You have to go way out of your way to get a real aircraft to be as squirrely on the ground as the planes in our sim are, for example.

There are things that current sims, and BoS/BoM in particular, do very very well. Their ability to induce a palpable suspension of disbelief and put you in a time, place, and. situation that is utterly removed from our daily reality is just amazing. The basics of aircraft control in the air, and many times the techniques of stopping bad things (spins etc.) from happening work pretty well.

It's just some of the finer points that toss the proverbial shoe into the works. Roll coupling, which is known to be off and will be (hopefully) fixed soon, and the wobble thing that still is so elusive.

I am confident that the dev team can fix these issues, given time. But I also feel for them as they are walking a tightrope of player expectations, and often those expectations go counter to reality. Many simmers want the game to be more difficult than reality, either because they think that uber difficulty is the reality of it, or because they simply want a greater challenge.

The real challenge is accepting that reality is often not as difficult as it is portrayed on a computer screen.

January 19, 2017

Interesting interpretation, and, maybe you're hitting the right spots!

Edited January 19, 2017 by jcomm

January 19, 2017

The following is my personal understanding and from all that I have read it has not been contested:

The engine is called digital nature and not digital WWI or digital WWII.

The planes are modelled with bladed element theory and all calculations ingame are based on scientific formulas. However there are many real life physics problems, firstly the lack of efficient formulas for some phenomenos, take wake turbulence and wing vortexes for example. Secondly there are real life effects that science did not even find formulas or understanding for.

So there are dynamics that are just not very well computable without supercomputers and dynamics that are not yet understood by science and thus hardly programmable. Theoretically (from todays knowledge) a plane should pitch back rather fast to its previous position, in real life this effect however seems less pronounced than in theory, but why is that so? It will probably be an effect of above problems 1 and 2. Many questions are still unanswered and you cannot just apply some values hoping it will fix something, you need to understand the problem first: see yaw-roll coupling.

To get back to my point: WWI planes were built using this engine and this engine is designed to simulate real life physics. It was not that WWI planes were built and then some physics around them to make them fly. That is why the argument of an outdated WWI engine just fails to hit the nail.

I always scratch my head when I read that by the way (no offense):

It also may explain why in the early days one of the criticisms of the sim was that the aircraft felt as if they had no weight.

Most of the planes never felt like they had no weight to me, quite the opposite, I really wonder where this feeling of "no weight" comes from..

Stall a P-40 or a Lagg or even a Yak and tell me it has no weight

Edited January 19, 2017 by 216th_Jordan

January 19, 2017

The old Sims simply didn't simulate a number of things, like Adverse Yaw and Side Slipping doesn't really have a lot of Effect Either. And in some ways the old Flight Model rminded me much more of flying Kites or Canards than conventional Aircraft.

The wobble might just be that inertia around the lateral axis is quite high ingame, maybe too high, but another thing is that on a real Aircraft the Elevator doesn't return into neutral position unless it's spring loaded or an all moving tail.

The Normal Layout of a stabilizer and a control surface is called "Gedämpftes Höhenleitwerk" engl.: dampened Elevator because it dampens the oscillations that naturally occur around the lateral Axis when there is no longer a Force on the Stick.

Edited January 19, 2017 by 6./ZG26_Klaus_Mann

January 19, 2017

I agree that much is not understood about airflow modeling, and that none of our home computers could possibly be up to the task of doing it.

That fact then should force simulation developers to make some kind of artificial work around to make the aircraft in the sim behave more realistically, yes? Or am i wrong here?

If no computer that civilians have in their homes will be capable of doing something that science still doesn't fully have a grasp of, why try to simulate that in the first place?

Pilots know how an aircraft feels/behaves in flight, even if they don't understand all the math of it. I don't think that is all that wrong a way to look at it.

Edited January 19, 2017 by BlitzPig_EL

January 19, 2017

If no computer that civilians have in their homes will be capable of doing something that science still doesn't fully have a grasp of, why try to simulate that in the first place?

Well, you can make approximations and they can work quite well, just in some situations they will produce results that differ from real life. That does not mean that the rest is bad though. I think BoX delivers quite a good performance, and it can surely be tweaked more in the future. Some things however will never be modelled absolutely correct. Look at where we have come since old 1946 where the only stall a plane could experience was a tipstall that would spin you around. I would say that is pretty awesome.

There are pros and cons of dynamic and static flight models, if you like the static ones more that is not a problem, DCS produces very good static FMs for example, they just have other quirks then.

Edited January 19, 2017 by 216th_Jordan

January 19, 2017

A lot of good points made above and it’s nice when people can share ideas in a constructive manner like is going on in this thread right now.

Anyway, that being said I agree about no model being perfect but what we have here in BoX is certainly very nice and IMHO it’s amazing that such a complex simulation can run on a home PC.

When it comes to the wobbling, I don’t think it’s limited to pitch but that it’s there in yaw as well. Maybe there is some element in roll but I can’t say it’s something I’ve been bothered by to the same extent as the pitch and yaw wobble (which of course generates a roll component as a well). As to why we have this issue I believe this could in theory be coupled to how the viscous effects are modelled but before that it would be good to discuss how the lifting forces are generated in the model:

A theory I have is that everything from the wings, stabilisers, rudders and propeller blades etc. are built up of superimposed horseshoe vortices with the vorticity (or lift if you will) proportional to the local angle of attack. So for example, a wing is built up of one vortex as wide as the span and then you add as many vortices as you can from a processing perspective to build up the lift distribution. You can then add ailerons in the same way etc. The beauty if this is that all vortices work together, inducing aoa on each other to build up a decent representation of the actual flow field around the plane. As an example, the vortices shed from the wing will if you deflect a flap increase their vortex strength proportional to the angle of flap deflection. This will increase the downwash on the tail just as IRL. Rudders, stabilizers etc. are built up in the same way and propellers are “just” spinning mini wings and if you do it like this you will capture slipstream and P-effects as well.

However, no home computer will be able to in real time calculate the viscous effects on top of this as well. So I believe at the bottom in the model is some kind of constant zero lift drag for each panel and then a rule for how much the drag increases as the vorticity of the panel goes up. So from this we get the forces and to calculate the movement of the plane we need the inertia and I’m assuming here of course that you have this modelled as well but that should be far easier to do IMHO: It’s making a good model of the aerodynamic forces that is the challenge I think.

Taking yaw as an example is the directional stability only due to the fin and rudder being modelled like this? If so then as you get a sideslip angle you will primarily get a rightening moment due to the horizontally oriented vortex “lift” in rudder and the fin. However, you would also get a contribution from the drag which will also push you back in line. But IRL you also have the fuselage. Now is and if so to what extent is this (and likewise a destabilizing moment from the nose) modelled in Il-2? This should also generate horizontal “lift” in the same way and drag as well. Also, IRL as soon as you start to sideslip you will get flow separations here and there on the fuselage that will increase drag and contribute to reducing sideslip angle and dampening the yaw oscillations. In addition, the above only covers a force proportional to the sideslip angle but I believe that to mimic IRL effects you would not only get a component proportional to this but also one due to the sideslip speed and sideslip acceleration. So if you take away or simplify any of the above too much due to processing limitations, it stands to reason that it would take longer to dampen out a disturbance so one would expect things to oscillate more I think.

Anyway, all the above comes with the caveat that this is just a theory and I have very diffuse ideas about how all this is actually modelled in IL-2 (and DCS for that matter). So I would really like to understand more about how state of the art flight sims actually does this but at the same time I appreciate that no developer will ever share the details since you need to keep your company secrets in flight sim development just like in any other business but maybe someone in the forum has some ideas on this or links to info from open sources about how they actually do it? I think this would be very helpful in understanding what is going on here and why we are seeing what we are seeing......

January 20, 2017

From ED forum. What is AFM (advanced flight model) and what it brings comparing to SFM (simple/ified) of previous simulations (like Il2 1946 or ClOD)

Aircraft dynamics are calculated on the basis of the same physics equations describing translational and rotational motion of a solid body under the influence of external forces and moments, disregarding the nature of their origin.

Trajectory and angle movements look more natural due to correct modeling of the aircraft’s inertial properties.

Transitions between the flight modes in a smooth manner without abrupt changes of angle rotational speeds and attitude (for example: after a tail-slide or when landing with an angle of roll on one landing wheel).

Gyroscopic effect with the aircraft’s rotation taken into account.

The asymmetric effect of external forces is taken into account, along with the effect of external forces not going through the center-of-gravity (for example: engine thrust, drag chute forces). These forces are correctly modeled at any flight mode and cause an adequate rotary moment.

The center-of-gravity can change its location within the speed axis system.

The modeling of lateral and longitudinal center of mass has been introduced. This can change depending on fuel load and weapon loads.

The asymmetrical loading of weapon and fuel pylons, which influence the characteristics of lateral control (depending on flight speed, regular overload, etc), is also modeled.

When calculating aerodynamic characteristics, the aircraft is represented as a combination of airframe components (fuselage, outer wing panel, stabilizer, etc). Separate calculations for the aerodynamic performance of each of these components are performed. This is done over the entire range of local angles of attack and slip (including supercritical), local dynamic pressure and Mach number. This takes into consideration the change and level of destruction of control surfaces and various airframe components.

Aerodynamics are accurately modeled in the entire range of angles of attack and glide.

The efficiency of lateral control, and degree of lateral and static lateral stability, now depend on the angle of attack, longitudinal and lateral center-of-gravity.

The wing autorotation effect when performing a rolling rotation at high angles of attack is modeled.

Kinematic, aerodynamic and inertial interaction of longitudinal, dihedral and lateral channels (yaw movement when performing a rolling turn, rolling motion at rudder pedal forward, etc).

Angle of glide availability is determined by the pilot’s efforts and the plane’s position.

Possibly the most important distinction between SFM and AFM is this......"When calculating aerodynamic characteristics, the aircraft is represented as a combination of airframe components (fuselage, outer wing panel, stabilizer, etc). Separate calculations for the aerodynamic performance of each of these components are performed."

AFAIK it was the work of Andrey Petrowich, starting at ED with Su-25T AFM and transferring to BoX. Danil also worked at ED.

January 20, 2017

How this is realted to DN which was avaliable before this ?

January 20, 2017

Thx Brano,

I once read that description but had forgoten about it.

So, X-Plane, DCS, IL.2 BoX ( and probably CloD too ), Aerofly FS2 and 1, and other sims share this BeT approach.

January 20, 2017

look at origin of DN engine, amazing how it evolved...

http://www.d-strict.com/index.php?lang=eng&page=faq

January 20, 2017

Amazing indeed Tomcat! Thx for sharing - couldn't rate you up because I've reached today's limit ... sry :-/

January 20, 2017

Disclaimer THIS IS ONLY A DID OF KNOWLEDGE AND BRAIN STORMING! I DO NOT CLAIM ANY OF MY SPECULATION TO BE EVEN REMOTELY TRUE

Just have to add this first because a lot of people have the definitions such as stability incorrect/misunderstood and really without knowing these a lot of the discussions are impossible to have.. For example there are no aircraft in BOS that are unstable in pitch!!!!!!!

For an aircraft's pitch axis there are two types of stability 1) Static stability 2) dynamic stability.

Static stability is a measure of if the aircraft is disturbed by an input(from pilot, gust of wind...) will the aerodynamics tend to create a force the will return the aircraft towards the undisurbed state.

For example if I provide an nose up input to the elevator and then return the elevator to its original state will the tail and wing act together to create a restoring force that will push the aircraft back to wards the undisturbed state. If it does it is deemed statically stable. If the aircraft's aerodynamics create forces after the disturbance that cause it to move away from the original undisturbed state then the aircraft is said to be statically unstable.

If an aircraft is statically unstable it cannot be dynamically stable i.e it is completely unstable in pitch and would just keep pulling up after and nose up disturbance by the pilot.

Note that for an aircraft to be deemed statically stable there is absolutely no need to know how the aircraft will try and return to its original state. All we need to know to determine if it is stable in pitch is that it will initially move back towards that original state after being disturbed.

Static stability is associated with something called the short term pitching frequency/mode. Within this mode there is said to be no change in velocity only a change of angle of attack of the wing.

Dynamics stability describes how the aircraft after the initial disturbance (if it is statically stable) will behave. Often referred to as the phugoid or long term frequency/mode. This mode contains oscillations about the initial undisturbed point and often last in the order of minutes. In this mode it is generally accepted that angle of attack stays constant and velocity is changing

There are three types of dynamic stability 1) stable 2) neutral 3) unstable

Dynamically stable is where after being disturbed the aircraft will oscillate about the undisturbed initial position with the oscillation overshoot getting smaller each time, finally arriving back at the original undisturbed position.

Dynamically neutral is where after being disturbed the aircraft will oscillate about the undisturbed initial position with the oscillation overshoot staying the same each time, never arriving back at the original undisturbed position but never getting worse.

Dynamically unstable is where after being disturbed the aircraft will oscillate about the undisturbed initial position with the oscillation overshoot getting bigger each time, never arriving back at the original undisturbed position and finally ending with aircraft stalling.

Finally for both the short term and long terms modes there are associated damming factors that determine how quickly the oscillation settle down. If a system is over damped, after a disturbance the plane will return quickly to its original position with out oscillation but not very efficiently.

If a system is critically damped, after a disturbance the plane will return quickly to its original position with out oscillation the most efficiently.

If a system is under damped, after a disturbance the plane will return to original position with oscillations depending on the level of damping.

This wobbling that some are experiencing will be related to the short term mode and the wobbling behaviour is indicative of a under damped system or a short time pitching dampening coefficient that is smaller than it should be.

If this is a general problem for all aircraft it would seem like the method of creating these FMs are underestimating this parameter. This is quite a hard figure to get correct even for real aircraft designers and often is only found during flight testing and then has to be compensated for. The reason it is hard to estimate and get correct is because almost every bit of physics of flight goes towards this figure. If i an remembering correctly from class most simulation methods(akin to flight sims) tend to over/under estimate these things.

So the solution is(if Im correct)???? I have no idea!!!! But I will say that even if the devs are using all of the correct figures that they can get, unless they can do some serious simulation or actual flight testing they will most likely have a mismatch with the numbers. To what confidence I have no idea and Im sure they will know how to adjust for it so......... Basically if I am correct which I dont claim to be them getting this wrong may just be inevitable unless they have access to NASA.

Ow almost forgot!!! Referring back to my original para, as all planes is box tend to return back to there original position after being disturbed. They are all statically stable and im pretty sure they are all dynamically stable as well. So technically all planes in BOX are stable (well defo in the context of the wobble) and what people should be talking about is how well damped there are!

Send the AAA

PS just thought I would add for those that might be interested that the error in the dampening coefficients that I talked about above I believe are due to the method of simulation, more precisely the linearisation of the equations of motion for aircraft. If you want to know more search "Princeton Flight Dynamics".

Edited January 20, 2017 by AeroAce

January 21, 2017

Thx AeroAce.

I mentioned that in this post on this very same thread.

Regarding yesterday's DD, I wonder if the update announced for the A3 flight dynamics will also be the one bringing those promised changes to the yaw-roll coupling ? Maybe not yet, but I really look fwd for it.

January 21, 2017

Jcomm, have you tried the bf109e7? Compared to other planes it supposedly feels less wobbly. IIRC bringing planes FM in line with the e7 is on the list of things devs would like to do, but no time plan known to us as of now.

January 21, 2017

@Brano: Thanks for posting the ED forum info on the AFM: Some good stuff there:

“When calculating aerodynamic characteristics, the aircraft is represented as a combination of airframe components (fuselage, outer wing panel, stabilizer, etc). Separate calculations for the aerodynamic performance of each of these components are performed. This is done over the entire range of local angles of attack and slip (including supercritical), local dynamic pressure and Mach number. This takes into consideration the change and level of destruction of control surfaces and various airframe components. Aerodynamics are accurately modeled in the entire range of angles of attack and glide.”

However, there is no info there on how they actually derive the aerodynamic forces and if they use some kind of lifting line, horseshoe vortex or panel method and how tight the grid is and how they connect the lifting forces to the drag etc. Again, I don’t suppose any flight sim developer will give us the exact details of how they do it but it would be good to understand a bit more about the general principles.

Also since the subject of instability was brought up, that is actually not what I was talking about earlier: The wobbliness problem is not an instability problem (at least that’s my view) but that it seems like the ratio of aerodynamic to inertial forces in the latest generation flight sims is lower than IRL: I have two examples: One is the Yak-3 and Me-109G videos I posted earlier, the other example is aerial refuelling. I recently got the Mirage 2000C in DCS and have been testing drogue refuelling and when I compare that to what you see in videos like this (Pretty cool video as such but notice how crisply the aircraft move at refuelling ca 4:50 into the clip and during the subsequent manouvering after that). Of course these are higher speeds but really you see pretty much the same in the Yak-3 and Me-109 videos: There is basically no wobbliness and the response to control input is crisp and the plane return basically at once to an equilibrium once the controls cease moving.

So I’m starting to suspect that getting this right with state of the art PC and flight sim software (like IL-2 and DCS) is either not possible or at least very difficult. Either it’s that or that we are getting what we are asking for since it seems to be that a lot of people equate more realistic with wobbliness rather than the derogatory on rails behaviour which actually seems to be closer to the truth if you compare to the IRL flying we see in videos.

If you have the time, watching the VFA-83 tour clip from the beginning is time well spent IMHO and don’t miss the supersonic fly-by’s around 6:40 min into the video…..

January 21, 2017

But comparing DCS and BOS, DCS WW2 planes are much less wobble in pitch movement then BOS ones - which is more like should be IRL. I tried yesterday and found great difference between them. In DCS plane keep new pitch altitutude without too much oscilation where in BOS they want to back to original path (spring effect - expecially German 109s).

Other hand i found some things in DCS "too mechanical" or not quite natural where BOS simulate some things more natural - e.x. taking off or some stall behaviour.

I think if BOS improve rudder effects ( less roll side effect to allow make more side slip angle), and change late 109 for close to 109E in pitch behaviour it could reach good compromise between game and reality.

Edited January 21, 2017 by 303_Kwiatek

January 21, 2017

Now that you say it: I agree that DCS does not have the same wobbliness as IL-2. But even so, now that we started talking about it in this thread and I re-watched both the Yak-3 and Me-109 it is striking that flying those planes IRL seems to be much more solid and crisp compared to both DCS and especially the IL-2 Me-109 G2 for example. I wonder why that is? I'm still thinking it may have something to do with how the aerodynamic forces need to be modeled in a sim. Getting the moments of inertia and even modifying those based on fuel level, adding or removing guns should be pretty simple to model and will take minuscule processing power to keep track of.

January 21, 2017

This goes back to the very origins of the engine. It would be interesting to know if the decisions outlined below are still in effect 8 years later.

Posted 24 August 2009 - 14:43

On a regular basis in different sections of the forum the topic of "incorrect positioning of the elevators when control column is in neutral" or comments that the aircraft have "excessive control sensitivity in the pitch axis" are being brought up. I think it's time to discuss these issues in detail.

Let's consider some facts.
Starting first with the characteristics of a PC joystick:

Fact 1.1. For all PC joysticks the forward and rearward travel are the same.

Fact 1.2. The absolute amount of PC joystick handle travel in millimeters or inches is significantly less than that found in a real aircraft, since the PC joystick is much shorter than real control column - (with the exception of a few home brews, or when compared to certain aircraft that use joystick-like control sticks, the F-16 for example).

Fact 1.3. PC joysticks without Force Feedback use a spring, so with no force applied to them by the user they will always return to the neutral/centered stick position. Only FFB sticks allow the developers to control the zero-force stick position in the software, as well as the absolute amounts of stick forces. The FFB joysticks without a spring (like MS FFB2) are more precise than the ones that, along with FFB, use a spring or rubber neck (Saitek Cyborg Evo Force or Logitech Force 3D Pro).

Fact 1.4. Joystick spring (or FFB motors) are capable of creating only a small fraction of the amount of force that a pilot would have to contend with in a real flight.

Now on to the facts related to airplanes:

Fact 2.1. For the majority of airplanes, the upward deflection of the elevator control surface is greater than the downward deflection. As a result, the control column/stick in the cockpit has more travel aft than it has forward travel (from aerodynamic center).

Fact 2.2. For the most part, the airflow around horizontal stabilizers is complex, resulting in asymmetrical pressures on the upper surface of the elevators compared with the lower surface of the elevators. That's why, if the control column is let free or control lines are severed, the elevators will practically never end up with zero deflection, albeit close to it. The resulting elevator deflection depends on a large number of factors, related to the aerodynamics of the flow around tail surfaces of an airplane (which itself is related to many factors).

Fact 2.3. It follows from the fact 2.2 that for airplanes with a simple mechanical control linkage that the zero-force control column position rarely coincides with the geometrically neutral column position, albeit close to it. Given fact 2.1 it follows that the zero-force control column. Position is rarely going to be half-way between full-aft and full-forward control column positions, and on top of that the zero-force control column position constantly changes in flight depending on the airflow around the airplane tail surfaces (which changes with airspeed, propeller RPM, Angle of Attack, side sleep, etc).

Fact 2.4. For each value of elevator deflection (and corresponding control column position) in flight, there is a particular value of Angle of Attack (AoA) that the airplane will settle to. This correspondence changes very little for a wide range of speeds, so we can consider it constant for any practical purpose (we are not considering supersonic flight

). Engine RPM is also a factor here - due to prop wash effect on the airplane surfaces - but this effect does not change anything in principle - the airplane AoA is defined by elevators deflection (and control column position).

Fact 2.5. The greater the airspeed the greater the force of lift (and G load) given the same value of AoA of the airplane.

Fact 2.6. It follows from fact 2.5, that in order to maintain level flight at constant altitude, with an increase in airspeed the AoA will have to be reduced to prevent climbing. Conversely, AoA must increase when airspeed is reduced to avoid descending. So in order to maintain constant altitude, level flight, for low airspeeds the airplane must have a high AoA, and for high speeds a low AoA.

Fact 2.7. It follows from 2.4 and 2.6 that in level flight for different airspeeds that the elevator deflection will be different in order to provide the required AoA. While some modern aircraft might do this automatically, for airplanes with only basic flight controls (like those of WWI vintage), the pilot will be required to move the control column forward as airspeed increases, and conversely, to move the control column aft as airspeed decreases. So unless the aircraft is equipped with a cockpit adjustable trim system to relieve these forces the pilot will be holding constant pressure on the controls.

Now let's analyze the above facts.

If you consider fact 1.1 and fact 2.1, it is evident that we can not make each position of the PC joystick handle correspond with the position of the control column in the real cockpit exactly, without any geometrical distortions. There are 3 simple and obvious solutions to this problem:

Solution A:

- Max aft deflection of the real aircraft control column corresponds to max aft PC joystick position.
- Max forward deflection of the real aircraft control column corresponds to the maximum forward PC joystick position.
- Between these two extremes there is direct linear dependency between the real aircraft control column and the position of the PC joystick.

This means that the neutral control column position does not coincide with the neutral PC joystick handle position, and the elevator control surfaces may be deflected somewhat when the PC joystick is centered.

Solution B:

- Max aft deflection of the control column corresponds to max aft PC joystick deflection.
- Max forward deflection of the control column corresponds to the maximum forward PC joystick position.
- Neutral control column position corresponds to neutral PC joystick handle position.

This means that dependency between the control column position in the cockpit and PC joystick handle position is no longer linear, with a discontinuity (bend) at the neutral point.

Solution C:

- Max aft deflection of the control column corresponds to max aft PC joystick deflection.
- Neutral control column position corresponds to the neutral PC joystick position.
- There is direct linear dependency between the control column position in the cockpit and the PC joystick position.

This means that Max forward control column position corresponds to a fraction of the full forward deflection of the PC joystick handle, and there is an unused sector of the PC joystick travel when commanding large forward deflections (deadzone at near the travel limits).

Each of the above solutions has its own pros and cons. Since we have to pick "the least evil" solution out of those available, I will only go over the disadvantages of each.

https://riseofflight.com/forum/topic/2564-about-wrong-elevator-position-and-pitch-sensitive/page-1?hl=+stick%20+compromise

I couldn't get the whole post in so here is a link instead.

January 21, 2017

Best way to make things clear would be if one of the Devs could hop into this thread and say something about the current FM status and their plans to solve the issues!

January 21, 2017

Jcomm, have you tried the bf109e7? Compared to other planes it supposedly feels less wobbly. IIRC bringing planes FM in line with the e7 is on the list of things devs would like to do, but no time plan known to us as of now.

Yes, indeed the E-7 looks better tuned in this respect.

But comparing DCS and BOS, DCS WW2 planes are much less wobble in pitch movement then BOS ones - which is more like should be IRL. I tried yesterday and found great difference between them. In DCS plane keep new pitch altitutude without too much oscilation where in BOS they want to back to original path (spring effect - expecially German 109s).

Other hand i found some things in DCS "too mechanical" or not quite natural where BOS simulate some things more natural - e.x. taking off or some stall behaviour.

I think if BOS improve rudder effects ( less roll side effect to allow make more side slip angle), and change late 109 for close to 109E in pitch behaviour it could reach good compromise between game and reality.

Excellent points!

And yes Semor76, that would be great to have... Excellent post to SYN! Reading through it.

Edited January 21, 2017 by jcomm

January 22, 2017

Idont even know why I bothered posting lol

January 22, 2017

Idont even know why I bothered posting lol

Why ? It was very useful! I liked to read it AeroAce - good points in it for sure.

BTW: at a thread at the Aerofly FS 2 forum, Murmur asked some important things about the modelling of downwash on aircraft surfaces, and the thread is worth reading.

http://www.ipacs.de/forum/showthread.php/7789-Technical-question-on-flight-model-Alpha-dot-derivatives

I don't know how these effects are being modelled in IL.2 BoX, but I think the Alpha-Dot approach is not the one used ( it's the one used in MSFS and JSBSim because these are used in the "stability-derivative-based flight models" as Murmur so well classifies it.

This might be yet another reason for that abnormal very short period reaction to pitch inputs ?

Edited January 22, 2017 by jcomm

January 22, 2017

There are some interesting posts worth studying in this thread. Let's hope it continues that way.

Personally I'm not entirely sure this 'issue' is totally down to aerodynamics. More likely, as Holzauge mentioned above, I think it's a combination of aerodynamic forces and inertia momentums interacting in a certain way that produces the observeable behaviour. If you compare different aircraft ingame with different CoGs you'll notice their behaviour differs. Generally speaking my observation has been the heavier the aircraft and the further forward the CoG the less noticeable it becomes. My primary examples for that are the Bf 110, He 111 and the recent Ju-52.

My speculation is that on smaller aircraft like the Bf 109s the reason for the sudden return to the horizontal attitude when releasing the stick comes from the fact that although you're pulling the stick increasing the AoA the interia forces are strong enought to keep the plane on the same flight path. I've made a vidoes some time ago shoing how I managed to fly straight and level in the F4 while rocking the stick forth and back causing the aircraft to oscillate along the Y axis. Nothing I've expirienced in reality came close to this behaviour.

Edited January 22, 2017 by 6./ZG26_5tuka

January 22, 2017

There are some interesting posts worth studying in this thread. Let's hope it continues that way.

Personally I'm not entirely sure this 'issue' is totally down to aerodynamics. More likely, as Holzauge mentioned above, I think it's a combination of aerodynamic forces and inertia momentums interacting in a certain way that produces the observeable behaviour. If you compare different aircraft ingame with different CoGs you'll notice their behaviour differs. Generally speaking my observation has been the heavier the aircraft and the further forward the CoG the less noticeable it becomes. My primary examples for that are the Bf 110, He 111 and the recent Ju-52.

My speculation is that on smaller aircraft like the Bf 109s the reason for the sudden return to the horizontal attitude when releasing the stick comes from the fact that although you're pulling the stick increasing the AoA the interia forces are strong enought to keep the plane on the same flight path. I've made a vidoes some time ago shoing how I managed to fly straight and level in the F4 while rocking the stick forth and back causing the aircraft to oscillate along the Y axis. Nothing I've expirienced in reality came close to this behaviour.

Indeed, just tried with the empty Ju52, and it reacts differently, without the wobbling!

Please remind me of the upcoming Flight Dynamics tunning...

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