Yaw oscillation - a possible explanation?

[Reflected]

Guys,

 

As you are all aware, some planes in BoS have an especially low yaw stability. When you use the rudder, the plane doesn’t yaw smoothly like a ship in the water, but springs/ oscillates left and right, as if it was fixed on a rubber band. It causes heated debates between RL pilots. Some say it’s  very unrealistic, some others say it is plausible, it’s just that we’re not flying real planes with such huge control movements.

 

I don’t know what to believe (I fly gliders in real life), but I think I might have come up with an explanation why it MIGHT be realistic.

 

When you apply a big amount of rudder suddenly, the speed of the outer wing increases, and along with it the lift and drag it produces. The extra lift can be accounted for the rolling motion, and I think it’s the sudden extra drag on the outer wing that counteracts the yaw induced by the outward lift generated on the rudder & stabilizer.

 

Can this be it? Or am I talking total nonsense? (which is very well possible)

 

I’ve learned to fly the 109 with small and gentle movements, so I hardly ever notice this springing movement, or oscillation, but it’s certainly a feature that is way more pronunced in BoS than in other sims.

 

What do you think?

[Brano]

Sounds as reasonable explanation.I am not aeronautic engineer.But the guy doing FM is graduate of Moscow Aviation Institute.Thats an authority for me 

[LLv34_Flanker]

S!

 

 I think it depends on plane. I have been in the turboprop trainer FiAF had and there was no tendency of bopping sideways when rudder was used, not even in the piston engined trainer. Slight movement was exactly that, a slight movement. Not a sudden jerky movement seen in BoS even from slightest input and the insane tendency to roll the plane almost as fast as with ailerons?! Sometimes planes feel like they are attached to rubberbands from nose, tail and wingtips. Slightest movement and wobblety wobble it goes.

[Finkeren]

I think the effect might be somewhat overdone in BoS (particularly on the 109s) but as a whole it doesn't feel that "off" to me (mind you: my knowledge on aerodynamics is very basic) it gives you the feeling of being in a 3 ton machine traveling at 450km/h, which you just can't control with pinpoint precision.

 

Still, shouldn't the 109 have less lateral stability than average? There must be a reason why they introduced the enlarged wooden tailfin to the design in 1944.

[CaK_Rumcajs]

My bet is that this behaviour is a combination of

 

a) limitation of simulation

b) non realistick movement of control surfaces induced by our short spring loaded sticks and pedals

c) input lag that causes over reactions

d) lack of body response to moves we do, we use high g manouvres without consequences

 

This could be fixed by introduction of some sort of filtering but filtering would result in additional input lag.

[LLv34_Flanker]

S!

 

 Also what strikes is this phenomenal roll rate you get with rudder only. I understand pilots used rudder to assist in a roll, but now you can roll without ailerons nearly as fast just using the rudder  Well, a game is a game and has it's limitations.

[JG1_Pragr]

Of course the rudder input shall roll the plane. The problem I see in the BoS is that the plane (109 particularly) rolls like with full aileron even with the tiniest rudder input. I'm not a RL pilot so I can hardly argue with real personal experience. I can based my opinion on reading of RL pilots experience only. And when I compare it with real WWII pilots comments of how they literally "kicked the rudder" to slow down their planes and that they do it even during the landing approach, I can hardly say it is OK in the BoS.

 

Anyway I think the main problem is a combination software/hardware limits on program itself and end users (players) hardware/setting. If the developers should based the model with respect of these limitation is a different question.

[SR-F_Winger]

do th russian planes do the same thing?

Or only the german planes?

If the later - oh well.

[JG4_Widukind]

I think thaths my bigest problem with bos too.and the reason why i stopt bos in the moment.

When i push my yaw iam only rolling! I have absolute no yaw effekt on my planes.

The roll effekt from 250-300kmh is to much.

But i losing intresst to talk ever and ever for nothing.

[sturmkraehe]

Sounds as reasonable explanation.I am not aeronautic engineer.But the guy doing FM is graduate of Moscow Aviation Institute.Thats an authority for me 

 

MAI has excellent reputation, probably the best aeronautical institute of Russia afaik. So +1

 

@Winger: Sensitivity of roll wrt to rudder input is not a natural law in itself but a result of aircraft design. It is only natural that different planes react differently to rudder input.

Edited October 30, 2014 by sturmkraehe

[SR-F_Winger]

MAI has excellent reputation, probably the best aeronautical institute of Russia afaik. So +1

 

@Winger: Sensitivity of roll wrt to rudder input is not a natural law in itself but a result of aircraft design. It is only natural that different planes react differently to rudder input.

So only german planes oscillate?

[Y-29.Silky]

This is what I think.. and it's the same with the pitch and roll...  Every aircraft I've flown in real life, and more experienced pilots will agree with this.. when you roll/yaw/pitch, you barely have to move your yoke, and you let the plane move itself, and it moves gradually. In this game, after I release my rudder, the aircraft will bounce back and forth violently, little mini twitches. And my experience comes with a little Cessna, I can only imagine a much more powerful engine such as the ones that were in WWII, shouldn't be so twitchy, as the more powerful engines were heavier. The only games I don't have to create deadzones for, is DCS :/

But at the same time, I can see where the developers are coming from... Soo many people will have different configurations, different preferences, different joysticks, some will have pedals, and some won't... So the best thing to do, is to make it overly sensitive and let the players find their comfort zone..

It's better to be too hot, than too cold...

Edited October 30, 2014 by Silky

[SKG51_robtek]

I think the effect might be somewhat overdone in BoS (particularly on the 109s) but as a whole it doesn't feel that "off" to me (mind you: my knowledge on aerodynamics is very basic) it gives you the feeling of being in a 3 ton machine traveling at 450km/h, which you just can't control with pinpoint precision.

 

Still, shouldn't the 109 have less lateral stability than average? There must be a reason why they introduced the enlarged wooden tailfin to the design in 1944.

The bigger Tailfin was needed because of the heavier and more powerful engines.

[Phant0m]

So only german planes oscillate?

He was referring to roll not oscillation.

[71st_AH_Mastiff]

no its a problem, in BOS. you certainly don't see this in DCS.

[Finkeren]

The bigger Tailfin was needed because of the heavier and more powerful engines.

Correct me if I'm wrong, but the new tailfin was introduced on the late production G6s and made standard on the G14. IIRC both versions used exactly the same engine as the G2 we have in BoS except for the MW50 boost, right?

[LLv34_Flanker]

S!

 

 Wooden tailfin, to save precious metal and also better control of yaw. Attachment of the wooden tailfin required a 35kg ballast in the engine compartment of the Bf109G-6 and FiAF changed back to metal tails if possible. Saved in weight. Bf109G-2, 4, 6, 8 used DB605A-1 rated 1475hp at take off 1.42ata. More info here..http://en.wikipedia.org/wiki/Daimler-Benz_DB_605

Edited October 30, 2014 by LLv34_Flanker

[6./ZG26_5tuka]

Agree on rudder reaction issue. It should reflect a great jaw and small roll momentum when using rudder, not vise versa.

 

This issue is most noticeably when trying to slip with the 109s, it's close to impossible to do so. The rudder roll momentum is simply supreme to roll input, which makes the whole manouvre redundant.

 

Funny eniught i checked this issue in RoF lately with biplanes. Same story,same FM habbits as the 109.

 

Quite funny if you consider sliping was an essentiell manoure for pilots to ensure safe landings due to bad forward visibilty,which also accounts for the 109.

 

Lets hope they fix this in time. At least VVS planes tend to behave correctly.

Edited October 30, 2014 by [Jg26]5tuka

[DD_bongodriver]

But the Katana in that video is doing a spin not a roll......completely different situation, it would not roll as good on pure rudder as it would aileron.

 

edit, the videos have changed:

 

but still what Jcomm is demonstrating are snap/flick rolls which are effectively just spins and not pure roll on rudder alone.

Edited October 30, 2014 by DD_bongodriver

[=LD=Hethwill]

IMO it is a limitation of representation. We are not in the plane so the way we perceive it is different. Also the tail fin profile is to be accounted for and a Lagg rudder certainly is not a 109 rudder. Lagg will dampen the speed for a more controlled skid while 109 will slap the air into the yaw making it really fast changes.

 

I am no aerodynamics professional though.

Even a modern airframe with assisted flight systems will suffer the same. And it is proper, no way to make the BoS planes skid if you didn't have these oscillations and tendency to roll the opposite wing.

 

 

 

For gameplay sake do adjust the sensitivities of your rudders, low angle up to 60 - 70% of the entire length and then sudden rise up steep angle. You will have a fantastic fine tuned control of your vertical sail.

[Y-29.Silky]

no its a problem, in BOS. you certainly don't see this in DCS.

Agreed. I don't remeber this problem in 1946 either. I wish we knew what the devs think about this. It'd be nice recieve some feedback from them.

[6./ZG26_5tuka]

But regarding the use of rudder only for a roll, there's nothing wrong with it...

 

http://www.aerobatics.org.uk/judging/judging-flickrolls.htm

 

You dont really intend to compare lightweight stuntplanes with relative large rudder area with 3t Bf109s, do you?

 

Of course the basic effect is apllying to every plane but to a variing extent based on certain factors. The 109 had bad rudder effetiency due to high prop wash interferrences along the fin and obviously shouldn't behave like a stunt plane.

Edited October 30, 2014 by [Jg26]5tuka

[DD_bongodriver]

 

 

Even a modern airframe with assisted flight systems will suffer the same

 

Dutch roll is really something that only affects swept wing aircraft.

It depends on the aircraft. Even on gliders, a K21 will have unsufficient aileron authority when you side / fwd slip, while for instance a Pw6 will have way too much roll authority... etc...

 

Yes bongo, I noticed that after actually looking at the video... and it's updated with snap rolls in various aircraft ... hundreds in the Tube available :-)

 

Done it to in gliders, where you do have a LOT of roll inertia!!!

 

A snap roll is not a roll in the proper sense, it is an autorotation caused by stalling one wing....the same as a spin.

[6./ZG26_5tuka]

It depends on the aircraft. Even on gliders, a K21 will have unsufficient aileron authority when you side / fwd slip to overcome the yaw-induced roll by the deflected rudder, while for instance a Pw6 will have way too much roll authority requiring far from full aileron to counter it,... etc...

Can't comment on your examples so I'll pick my own, namely ASK-21 (two seated trainer), LS-4 and DG-300.

 

None of which does show any behaviour alike the 109 when slipping. Both single seaters have very stable yaw response and you end up using ailerouns primarily to hold your course rather than stabilizing the roll momentum inflicted by the rudder.

 

On the ASK-21 the rudder shows worse response so slipping works with ~ 60% ailerouns only. Still nothing alike the 109 ingame.

 

Tested slipping with the Mustang and 190 in a certain other sim and the difference is impressive. They certainly got it right.

Edited October 30, 2014 by [Jg26]5tuka

[DD_bongodriver]

 

 

A snap roll can be performed using ** only ** elevator ** and ** rudder.

 

That's correct, and the end result is a spin not a roll.

 

 

Not necessarily.... You can even have it in a B1900d IRL :-)

 

Like I said, mainly an issue for swept wing aircraft, never said there were no straight wing exceptions, many aircraft have unique qualities that need their own explanations.

[Dakpilot]

Purely relating to the FW190, in real life the rudder had a bell crank linkage in the controls that had exactly the same effect as putting a curve on the yaw axis as standard, in that the initial inputs had a lesser effect, It did not have a linear input

 

IF you do this through controls setting and add a little noise filter in Devices  you will get a more accurate representation of the real Aircraft rudder controls.

 

You still have the full rudder movement with big input heavy manoeuvres but retain sensitivity in co-ordinated flight which is where you need it, from what I understand that is how Kurt Tank designed it

 

One very lacking feature is the ability to adjust control settings for individual aircraft

 

Until control forces are simulated correctly we are able to put instant forces at a speed that is mostly not representative of the real aircraft, hence the pilot induced oscillations we are experiencing are exaggerated, the natural input force needed would damp these out...which does not happen in a sim, we apply stick and rudder with superhuman force

 

Cheers Dakpilot  

[Lusekofte]

I personally only got experience from cessna and I always believed it was the high wing mount making the rudder behave that nice, and the rudder would be more BOS like in more unstable fighter types. However I think the rudder is wrong on the Heinkel, because you got the same strength and sensitive reaction in it.

I basically think the fm got a ww1 feel to it, they are just to light. 

Edited October 30, 2014 by LuseKofte

[DD_bongodriver]

 

 

Until control forces are simulated correctly we are able to put instant forces at a speed that is mostly not representative of the real aircraft, hence the pilot induced oscillations we are experiencing are exaggerated, the natural input force needed would damp these out...which does not happen in a sim, we apply stick and rudder with superhuman force

 

While this is true it does not explain why those of us that are aware of the fact and can make inputs on our devices that are correctly proportional still suffer excessive reactions.

And... what exactly does the Bf109 perform in IL2 BOS when you kick the rudder? A roll?  I'll have to test it myself, and will report back, latter today ( if life permits... ) :-)

 

Yes, precisely, because you use just rudder and no elevator as per your example to give the snap roll, the result is a roll of greater magnitude than possible on aileron alone.

[=LD=Hethwill]

Thanks for the Dutch Roll point jcomm.

 

But the effect I see on the lateral displacement is similar to what we have.

 

But then I've said a while ago in two threads that the air resistance could and should be increased in BoS. It is good so far, great sense of being there but the authority on all surfaces is fickle and results in these "snappy" situations. IF you had way more density and strength affecting your tail fin when you push the pedal maybe we would have a less pronounced effect when releasing it ? No idea.

 

What I do know is most flight games that have this effect less felt have a much more "fly on a monorail" feeling and do not have such a "in the air" feeling as BoS does.

 

 

But a question to the aerodynamics buffs out there, given I pull the pedal, the sail closes the air flow and makes the section turn and roll with proportional angle as to the affected through the rudder sail, right ?

 

What if i release it and the air flow returns, shouldn't I have a opposite reaction with the longitudinal section ( and wing traverse angle ) adjust as the flow rushes through ?

Edited October 30, 2014 by =LD=Hethwill_Khan

[SCG_Neun]

Of course the rudder input shall roll the plane. The problem I see in the BoS is that the plane (109 particularly) rolls like with full aileron even with the tiniest rudder input. I'm not a RL pilot so I can hardly argue with real personal experience. I can based my opinion on reading of RL pilots experience only. And when I compare it with real WWII pilots comments of how they literally "kicked the rudder" to slow down their planes and that they do it even during the landing approach, I can hardly say it is OK in the BoS.

 

Anyway I think the main problem is a combination software/hardware limits on program itself and end users (players) hardware/setting. If the developers should based the model with respect of these limitation is a different question.

I too, base a lot of the incorrect feel of the rudder on real life pilots who stated how they "kicked" the rudder for a snap shot or correction in combat, something that is a no no within BOS. It's not a game breaker for me but I really feel that it is not modeled properly.

[=LD=Hethwill]

I too, base a lot of the incorrect feel of the rudder on real life pilots who stated how they "kicked" the rudder for a snap shot or correction in combat, something that is a no no within BOS. It's not a game breaker for me but I really feel that it is not modeled properly.

 

Yep, we can and we risk our own "safety" doing things they wouldn't do IRL. Such is the nature of a sim  

[HagarTheHorrible]

Maybe it's all to do with "feel"

 

The physical and mathematical calculations are correct and the aircraft are responding correctly, maybe what is missing is the human element. The natural allowances and corrections or "feel" of a pilots muscles and reactions, possibly almost imperceptible or even registering on the pilots subconscious.

[=LD=Hethwill]

Tests were

made of the model with and without the flaps and with and

without the vertical tail for all wing positions. 

 

https://archive.org/stream/nasa_techdoc_19930081537/19930081537#page/n5/mode/2up

 

Hope some buff can read through it and come up with a "gamer" appraisal.

Edited October 30, 2014 by =LD=Hethwill_Khan

[JG4_Widukind]

Try clod...there is a good ruder yaw effekt...need a bit mor sensitive but its good

Simmulat.

In bos i have nothing abaut it...only a roll effekt. Special in landings thefe is no slipping.

[Reflected]

1) don't hijack my thread, it's not about rolling with rudder, but the oscillating rubber-band movement.

 

2) Ifound this post by Zak, quoted on the RoF forums:

 

 

 

“And before we begin, let me make the rudder issue clear.
As I said, we acknowledge that current implementation of rudder control is questionable. You as experienced virtual pilots feel that rudder doesn't work correctly - and we agree with you on that.
We know where this peculiar sensation of Bf 109 is located and it doesn't fit the expectations (same thing as you experience, isn't it?). But IL2BOS is a simulator modeled painstakingly and with greatest attention to the most trustworthy tool that we have - maths. Current version of Bf 109 (as well as any other plane in the project) is a purely mathematical model based on all avalilable data on the original aircraft. And after the entire FM development procedure (2 months or smth, can't remember for sure now) we came to what we have now. And we CAN and we WANT to revise the FM for BF 109 because of the questionable rudder performance.
But being a flight sim (not an WT, WOWP grade arcade game) IL2BOS does not allow us to switch smth off, or to grab a "rudder hypersensitivity" slider and move it to minimum. The only way to fix it is to go thru the entire Fm production process. We plan to do that. Obviously, it has to wait until Fw 190 and He 111 are finished and released to early access, and lacking game modes added too. After that we will have resources to revise Bf 109 FM. You know, it is like developing a real plane back then in 1940s - we roll out a prototype, it fails our expectations and we have to put it apart all over again to find what the problem is.
That's official. Pretty much everything I can tell about the topic. And honestly, I think it gives you all a certain answer.”

[=LD=Hethwill]

Thanks Reflected.

[DD_bongodriver]

it is an interesting quote, a bit weird that one of the best answers to an issue plaguing the BOS FM is found on the forum for another product.

[Lusekofte]

This is what you learn on PPL

 

Here is some reactions on a unstable plane

 

 

I cannot find anything proof of what is right, in COD and IL2 I think it is too gentle. In Corsairs they applied Hard rudder for countering torque at low speed

[Dakpilot]

it is an interesting quote, a bit weird that one of the best answers to an issue plaguing the BOS FM is found on the forum for another product.

 

It was simply quoted from here (BoS forums) and posted on RoF forums

 

Cheers Dakpilot

[DD_bongodriver]

Roger