question about flight model - sideway G force

[Guest mlracing]

I am trying out WOI, and find this sim quite interesting, especially the flight modeling.

but here is a problem, yaw angle itself does not induce sideway G force?

try doing this: apply full rudder while keeping bank angle at zero with aileron. after some time, you will find the heading of flight path is not changed, which means the yaw angle of the whole aircraft didn't create sideway G force. I tried that at speed of around 300 knots, on F15 and F16.

anyone noticed that problem?

[Fubar512 1,350]

Aircraft are stressed in the pitch axis. One cannot generate enough lateral acceleration in yaw to generate more than 1-2 Gs (using the rudder), that is, short of entering a spin. Modern aircraft also sport rudders which lockout at speed to prevent issues with stability in the yaw-axis.

[Guest mlracing]

but it seems to me that the lateral acceleration is zero. its being small is understandable, but being zero is not.

[Fubar512 1,350]

And how do you quantify it being zero?

[Guest mlracing]

by doing this:

at speed around 300 knots, apply full rudder, and keep bank angle at zero.

the aircraft yaws to a certain angle, say 5 degree or whatever, and wait till the aircraft is stable.

now read the heading on HUD, say 12 or whatever.

and keep this state for 10 seconds or 20 seconds etc. the longer the better.

read the heading on HUD again. if it says 12, that means the nose didn't turn any angle. and because the yaw angle is stable, that means the flight path didn't turn any angle. which means the air didn't generate sideway G force.

 

if bank angle is not zero, the flight path will turn. that's the effect of lift vector, not the effect of yaw angle.

[Fubar512 1,350]

First off, most swept wing aircraft ROLL to some degree when rudder is applied. In fact, that's SOP for rolling the F-4 Phantom above 12-14 units of AoA, as it would hardly repond to the ailerons at that point.

 

Secondly, aircraft generate resistance to yaw due to the airflow over the fuselage and vertical stbilizer(s)...this tendency obviously increases with velocity of the airflow. That is one reason that rudder deflections at speed do little other than impart roll and a slight yaw effect, or, what's referred to as "dutch roll". This is why those surfaces are effectively limited or locked out on FBW aircraft over a set airspeed (in fact, the F-15 Eagle uses a control augmentation system that limits rudder deflection to less than 15 degrees to prevent roll-due-to-yaw, unless the aircraft is in a high alpha-state maneuver).

[Guest mlracing]

i know aircraft rolls when rudder is applied, that's why i said "try doing this: apply full rudder while keeping bank angle at zero with aileron" in the 1st post.

that's also why i said "the aircraft yaws to a certain angle, say 5 degree or whatever, and wait till the aircraft is stable" in the 3rd post. "wait till the aircraft is stable" means that, at first the aircraft is not stable, with pitch or roll or whatever other movements, but after sometime (1 or 2 seconds or whatever), the aircraft will reach a stable state.

 

and, i am not talking about real aircrafts, i am talking about WOI. in WOI, the rudders deflect, and the whole aircraft yaws to an apparent angle in the circumstance that i mentioned in the above posts.

 

i just started to learn this sim, i hope i had wrong perception of the phenomena. and if i am not wrong, i hope TK will fix that by patch or in the next product.

 

 

[Fubar512 1,350]

 

and, i am not talking about real aircrafts, i am talking about WOI. in WOI, the rudders deflect, and the whole aircraft yaws to an apparent angle in the circumstance that i mentioned in the above posts.

 

i just started to learn this sim, i hope i had wrong perception of the phenomena. and if i am not wrong, i hope TK will fix that by patch or in the next product.

 

Since you've termed it a sim, tell, me, what is the definition of a sim, I mean, what's its purpose? Isn't it to SIMULTE real life, as in real aircraft? Doesn't that mean that your own statements are somewhat at odds with your conclusions?

[Romflyer 25]

I have never actually tried to do an intentional side-slip (which is similar to what you are describing) in this game, I will say that I like to have a little more rudder authority at higher speeds than what most models allow, so what I do is go into the aircraft data.ini and adjust the MaxControlSpeed=XX

this is taken from the MF F-14 and it is set at 180......I would change this to 380.....it may not be exactly correct, but I find it to feel much better, especially in a knife fight or trying to line up ground targets.

It might very well change the results of your slipping experiment too.....especially if your doing more than 180kts....which you probably were.

 

[Rudder1]

SystemType=CONTROL_SURFACE

InputName=YAW_CONTROL

ReverseInput=TRUE

MaxDeflection=10.0

MinDeflection=-10.0

CDdc=0.0144

Cydc=0.2777

Cldc=-0.0055

Cndc=-0.1367

CldcAlphaTableNumData=15

CldcAlphaTableDeltaX=4.00

CldcAlphaTableStartX=-28.00

CldcAlphaTableData=-12.433,-10.883,-9.281,-7.632,-5.947,-4.233,-2.498,-0.751,1.000,2.746,4.478,6.189,7.870,9.512,11.108

CndcAlphaTableNumData=15

CndcAlphaTableDeltaX=4.00

CndcAlphaTableStartX=-28.00

CndcAlphaTableData=0.869,0.902,0.930,0.953,0.972,0.986,0.996,1.000,1.000,0.995,0.985,0.970,0.950,0.926,0.897

ControlRate=5.0

MaxControlSpeed=180

ModelNodeName=rudder1

RotationAxis=Z-Axis

ReverseModelOrientation=TRUE

[Guest mlracing]

what i want is to clarify whether that behaviour in WOI is wrong, or that i missed something in observation. i certainly hope WOI is as realistic as possible, since i haven't found a flight sim that can satisfy me - in the department of physics engine.

i started studying WOI a few days ago, and found the physics engine of WOI is on the right path - calculating forces on seperated surfaces and transfering forces to the fuselage, unlike some other "sims" which calculate forces on only 1 object.

some aspects are still not modeled in WOI, such as weight shift on ground. but nothing can be perfect , and this is a flight sim, not a ground vehicle sim, so i focus on the flight physics. so far i found just 1 problem in flight, which was mentioned above. i hope that can be improved so WOI is still the best physics simulation that can run on my PC.

 

BTW i am not just any casual game player, here is some work i did with physics simulation, although it's not satisfying me. (if i was satisfied, i wouldn't seek out WOI in the first place)

http://player.youku.com/player.php/sid/XMjE3MDAxNDY4/v.swf

http://player.youku.com/player.php/sid/XMjAyMTM2NTQ4/v.swf

http://player.youku.com/player.php/sid/XMTk3Mjc1MjQw/v.swf

[Guest mlracing]

I have never actually tried to do an intentional side-slip (which is similar to what you are describing) in this game, I will say that I like to have a little more rudder authority at higher speeds than what most models allow, so what I do is go into the aircraft data.ini and adjust the MaxControlSpeed=XX

this is taken from the MF F-14 and it is set at 180......I would change this to 380.....it may not be exactly correct, but I find it to feel much better, especially in a knife fight or trying to line up ground targets.

It might very well change the results of your slipping experiment too.....especially if your doing more than 180kts....which you probably were.

 

Romflyer, i just tried doing the manuveur at below 180knots, on the stock F-16 in WOI, still no joy.

the rudder only affects the yaw angle - better rudder effeciency generates bigger yaw angle.

but the problem is , yaw angle itself doesn't generate sideway acceleration in WOI.

 

did someone get different result on other circumstance or other aircrafts?

[Romflyer 25]

Romflyer, i just tried doing the manuveur at below 180knots, on the stock F-16 in WOI, still no joy.

the rudder only affects the yaw angle - better rudder effeciency generates bigger yaw angle.

but the problem is , yaw angle itself doesn't generate sideway acceleration in WOI.

 

did someone get different result on other circumstance or other aircrafts?

 

Well I'm not completely clear on what "sideways excelleration" means.......But the next time I sit down with the game I will defineately explore the effects of yaw, adverse yaw, slipping, spinning, etc. etc.......I have to say that the Strike fighter series is the best sim that I have found that really does a great job of feeling like you are strapped into a fast aircraft.

 

I might suggest you ask these questions over at the Thirdwire forums, I am sure TK will be pleased straighten you out on any concerns you might have.

 

I'm curious to know what sim was used in the three videos you posted?

[Guest mlracing]

i can't logon to TW website without proxy, and i can't post a thread through the proxy - technical problem, so i can't post in TW forums.

 

imagine the whole aircraft as a vertial wing, ( although the shape is not good to be a wing ) when the wing yaws to the right, the air generates pressure on the left suface, pushing the wing to the right, that induces acceleration to the right, so called sideway acceleration / lateral acceleration.

[+Monty CZ 209]

Interesting question...

As I understand it, If I change exhaust emmiter to something similar to smoke (which will

stay in the air for long time) and then apply rudder and eliminate roll with ailerons to

have plane in horizon the emmiter (visible path) would be straight (which is probably not right)

Did I understand what do you want to say?

Monty CZ

[Fubar512 1,350]

Someone seriously lacks a grasp of basic physics.

[Guest mlracing]

Interesting question...

As I understand it, If I change exhaust emmiter to something similar to smoke (which will

stay in the air for long time) and then apply rudder and eliminate roll with ailerons to

have plane in horizon the emmiter (visible path) would be straight (which is probably not right)

Did I understand what do you want to say?

Monty CZ

 

exactly what i meant.

did you test that out? what result do you get in WOI?

in your opinion, in reality, should it be straight or should it be curved?

[Fubar512 1,350]

A body of mass m subject to a force, undergoes an acceleration a that has the same direction as the force and a magnitude that is directly proportional to the force and inversely proportional to the mass, i.e., F = ma. Alternatively, the total force applied on a body is equal to the time derivative of linear momentum of the body.

[ArturR 17]

Well I noticed that in aircrafts with two vertical stabs(rudders) ie: stock A-10, F-15, mods F/a-18 etc. yawing is incorrect, sometimes even we have reverse movement so it could be bug.

BUT... mlracing have you tried yawing F-4 Phantom in SF2 series?? I don't know if it's realistic but it's nice effect.

[+Monty CZ 209]

I am no physicist but by my experience with RC models the ruder cause

Roll moment and Yaw moment. The Roll moment I can eliminate with ailerons

so there could be still the missing Yaw moment so by my opinion the path

of plane flying under those condition should be curved not straight.

Monty CZ

I can check it only in SF2

[Fubar512 1,350]

Monty, you are absolutely right. A swept wing aircraft will generally ROLL more than it yaws with rudder displacement at speed. My comment regarding physics was not directed at you.

[Romflyer 25]

I think that maybe we are all stumbling over a difference in terminology, as I said earlier you are essentially describing a slip....here is a quick clip of a 172 doing a slipe on final

 

 

So I would suggest you try the same maneuver in the F-16 or F-15.... on short final lower your left wing(or right ) when the plane starts to turn in whichever direction you chose then kick your opposite rudder.....adjust those two cross-controls until you are stabilized in a crabbing motion toward the threshold.......the velocity vector in your hud should point to the center of the runway but the nose of your plane will point to the weeds on the side of the runway........Voila!! you have acheived......lateral/sideways exceleration....or whatever you called it

[Guest mlracing]

in a sideslip landing maneuver, (when there is no cross wind), the bank angle is not zero. that is using the lift vector to counteract the lateral force created by yaw angle.

if there is crosswind, pilots use yaw angle to counteract the wind. many videos of passenger aircraft (747 737...) on youtube show crosswind landing, just check it out.

again, if there is no wind and when bank angle is zero, the yaw angle creates lateral force which bends the flight path.

 

has anyone tried to do a so-called KNIFE-EDGE maneuver in WOI ? i bet no one has successfully done it in WOI.

and does anyone believe in the possibility of the knife-edge maneuver on a real F15/F16 ?

if someone believes in the possibility of knife-edge manuever and when he can't do it in WOI, how would he explain that?

 

and, does someone understand the relationship between an knift-edge manuever and the effects of yaw angle?

[Romflyer 25]

Actually in a crosswind landing you use bank angle to correct for the wind and you use rudder to keep parallel to the runway.

I have no idea about whether or not you can do a knife-edge in an f-16, but it is definately not the aircraft one would usually associate with that manuever

[MigBuster 2,879]

in a sideslip landing maneuver, (when there is no cross wind), the bank angle is not zero. that is using the lift vector to counteract the lateral force created by yaw angle.

if there is crosswind, pilots use yaw angle to counteract the wind. many videos of passenger aircraft (747 737...) on youtube show crosswind landing, just check it out.

again, if there is no wind and when bank angle is zero, the yaw angle creates lateral force which bends the flight path.

 

has anyone tried to do a so-called KNIFE-EDGE maneuver in WOI ? i bet no one has successfully done it in WOI.

and does anyone believe in the possibility of the knife-edge maneuver on a real F15/F16 ?

if someone believes in the possibility of knife-edge manuever and when he can't do it in WOI, how would he explain that?

 

and, does someone understand the relationship between an knift-edge manuever and the effects of yaw angle?

 

 

 

Well if you want to know ask at f-16.net - a few ex 16 pilots on there.

 

The nearest we have is Falcon 4 which has about 20 years of hardcore input.

 

You get no rudder authority over 300kts in that - and at low level, low speed even with rudder and a clean F-16D the nose drops too much despite full rudder.

 

in SF2I (Dont have WOI anymore) - clean F-16A - here you get to use rudder way over 300kts - but regardless of <200kts or >300kts speeds the nose still drops too much despite full rudder like the Falcon FM. Unlike the Falcon FM - The SF2 FM requires no elevon movement to keep the jet on the same heading.

 

Unfortunatley the only application for such a pointless sustained manouver would be at an airshow - or if you had to fly down a very narrow star wars trench

[FastCargo 412]

Actually in a crosswind landing you use bank angle to correct for the wind and you use rudder to keep parallel to the runway.

 

This is exactly correct. Landings are done in cross control at touchdown...most heavy aircraft cannot handle large sideways loads unless they have steerable landing gear. It is easier to simply do a wing low landing and let one main gear touch first. Aircraft may fly on final in a crab (ie sideways, wings level) to maintain ground track, but then transition to the wing low method in the flare, or accept a small sideways load for light crosswinds.

 

Now, lets talk about the 'knife edge pass'. What makes you assume that a stock aircraft, even a fighter type aircraft can maintain altitude on a knife edge pass? You'll note in some aircraft, that pass is actually started in a climb, then rolls to 90 degrees bank, and even with full rudder deflection, the nose slowly tracks downward. What the crowd sees is an illusion caused by looking slightly upward as the aircraft traverses the showline.

 

For, other aircraft, they are slightly modified to exceed their normal rudder authority at high speed. High yaw angles, especially in aircraft with long, snaking intakes, are not something jet engines enjoy, and so at higher speeds rudder authority is actually reduced. This even occurs in jetliners for the same reason (and to avoid high sideloads). For instance, in the T-38A, which when it used to be in the Thunderbirds, would do knife edge passes. However, the stock T-38A could not hold altitude long enough to complete such a pass at the rudder authority of 6 degrees. The rudder actually had the ability to go a full 30 degrees, but that was only with the landing gear down. However, for the Thunderbirds, that limiter was removed in order to be able to do things such as a knife edge pass...while still being able to say the T-birds used a 'stock' aircraft. There isn't anything that says they haven't done the same thing for other aircraft.

 

Now, finally, lets talk about rudders in high speed, swept wing aircraft.

 

When any aircraft goes into a standard turn, more lift is created on the upper wing than the lower wing. This in turn creates more induced drag, which pulls the upper wing away from the turn (called adverse yaw). This can be countered by pro turn rudder, either manually, or automatically using flight control augmentation. Another way (which a lot of aircraft have done since the 1930s) is by deflecting the ailerons asymmetrically (sometimes called frise ailerons), increasing the deflection of the downward wing's aileron to increase the drag to match the upward wing's induced drag to coordinate the turn.

 

Next, when swept wing aircraft are put into a yaw, the forward moving wing presents more leading edge toward the relative wind, increasing lift, which increases induced drag, and increases frontal drag, both of which contribute to the lateral stability of the aircraft by tending to take out the yaw.

 

So, after that explanation, lets talk about the situation where you use full rudder to try to turn a swept wing fighter, while using cross aileron to keep the wings level.

 

First, rudder authority may have already been limited by the hardware or software at higher speeds. Secondly, the inherent drag properties of the forward wing in a yaw situation contribute to additional drag that wing is exerting against the turning force of the rudder. Third, the differential aileron you are using to keep the forward wing from rising is also adding more drag on that wing then the rearward wing. Fourth, the form drag of the air over the fuselage sideways will try to force the nose against the direction of yaw. All of these forces could easily add up and counter the rudder deflection and reduce the ground track change to trival levels, if any.

 

So, the answer is that there may not be enough rudder authority to change the ground track in the situation you stated in real life. It depends on the aircraft and specific situation.

 

FC