FS9 Real Weather Take Offs

[uniform7]

When I use Real Weather (REX, default, ect.) my aircraft want to drift off the runway even in calm winds and I have to correct with the rudder or nose gear. All planes, all airports. Is this normal? Doesn't do this in my FSX program just FS9. Tried auto rudder. This happen to anyone else? Doesn't happen with user defined weather just live weather.

[stuartcox]

This is a programming issue within FS9.
The aircraft will shear extremely with the slightest crosswind.
Landing is even trickier. 'Crabbing' to touchdown is quite easy, but as soon as the nosewheel hits the runway you're all over the place - even with the rudder back on neutral.
I have also noticed that certain AC drift to the opposite wind direction as indicated...

[phantomx1]

In the FS9 > settings > Realism > Flight model > P-factor, could it be that you have P-factor set all the way to the right which would cause all your planes to lose directional control on take-off?

Mine were doing the same thing and I had that P-factor set all the way to the right maxed out. All the way to the right setting is not fully realistic imo and often makes most planes too sensitive for reality.

[uniform7]

Thanks guys, thought it might be just me. I do a lot of addons and tweaking so sometimes I can't tell if its a bug or me. Nobody would answer me in the other forums which I thought odd because I usually get a response on everything. I guess nobody gave it anymore thought then I cause I have been flying FS9 since it came out. Didn't think about it until I started flying FSX and started addressing it's bugs Jeepers creepers!

[Naismith]

I wonder if it is possible as per FSX to increase the ground friction through FSUIPC as described here http://fs-mp.com/sim1/

[SSI01]

That sudden crosswind shear previously mentioned - is that related to the sudden shear one gets when changing altitudes and running into a different wind layer? Even with the weather change set to "mild" or mid-range the aircraft, no matter how heavy, is frequently tossed markedly to one side when in the air in flight - not during takeoff/landing - but changing altitude. During my 23-year gov career I traveled very frequently by air but never experienced anything in a commercial airliner like what the sim does. This occurs whether the aircraft is jet or recip.

[stuartcox]

In my case the problem only occurs on ground handling.
One example: Take off at Shoreham - Runway 02- Wind 275, 3 knts - default Cessna 172.
After only a few Yards, the AC shears off the runway (without rudder), but into the wind, to the left. Not as in real life to the right.
To say it simple, facing North the AC is blown into a westerly direction, despite having a westerly wind.
Settings are on easy for this experiment, no P-factor active.
On a landing approach under the same conditions I can crab down with left rudder input, but need right rudder when taxiing on the ground heading North. The opposite as it should be!

[Naismith]

P-Factor, I have been doing some tests this Sunday pm with various a/c (sizes, engines, free, pay) and there does seem to be some validity in toning down the P-Factor. Less skating about on the runway, and more control. I don't know if there is more in depth scientific testing by anyone in the know, but until I know differently my slider stays at about 75%.

[srgalahad]

In my case the problem only occurs on ground handling.
One example: Take off at Shoreham - Runway 02- Wind 275, 3 knts - default Cessna 172.
After only a few Yards, the AC shears off the runway (without rudder), but into the wind, to the left. Not as in real life to the right.
To say it simple, facing North the AC is blown into a westerly direction, despite having a westerly wind.
Settings are on easy for this experiment, no P-factor active.
On a landing approach under the same conditions I can crab down with left rudder input, but need right rudder when taxiing on the ground heading North. The opposite as it should be!

Actually it is JUST as it should be - the forces acting on an aircraft on the ground and in the air are not the same. (OK, the "forces" are the same but have different results.) The aircraft on ground is 'anchored' by the friction of it's wheels on the surface so it tends not to drift sideways but 'weathervane'.

It's all in the technique...
Beginning with an into-wind takeoff:

TAKEOFF ROLL

After taxiing onto the runway, the airplane should be carefully aligned with the intended takeoff direction, and the nosewheel positioned straight, or centered. After releasing the brakes, the throttle should be advanced smoothly and continuously to takeoff power. An abrupt application of power may cause the airplane to yaw sharply to the left because of the torque effects of the engine and propeller. This will be most apparent in high horsepower engines. As the airplane starts to roll forward, the pilot should assure both feet are on the rudder pedals so that the toes or balls of the feet are on the rudder portions, not on the brake portions. Engine instruments should be monitored during the takeoff roll for any malfunctions. In nosewheel-type airplanes, pressures on the elevator control are not necessary beyond those needed to steady it. Applying unnecessary pressure will only aggravate the takeoff and prevent the pilot from recognizing when elevator control pressure is actually needed to establish the takeoff attitude. As speed is gained, the elevator control will tend to assume a neutral position if the airplane is correctly trimmed. At the same time, directional control should be maintained with smooth, prompt, positive rudder corrections throughout the takeoff roll. The effects of engine torque and P-factor at the initial speeds tend to pull the nose to the left. The pilot must use whatever rudder pressure and aileron needed to correct for these effects or for existing wind conditions to keep the nose of the airplane headed straight down the runway. The use of brakes for steering purposes should be avoided, since this will cause slower acceleration of the airplane’s speed, lengthen the takeoff distance, and possibly result in severe swerving.

--FAA Airplane Handbook, Page 18

The technique used during the initial takeoff roll in a crosswind is generally the same as used in a normal takeoff, except that aileron control must be held INTO the crosswind. This raises the aileron on the upwind wing to impose a downward force on the wing to counteract the lifting force of the crosswind and prevents the wing from rising. As the airplane is taxied into takeoff position, it is essential that the windsock and other wind direction indicators be checked so that the presence of a crosswind may be recognized and anticipated. If a crosswind is indicated, FULL aileron should be held into the wind as the takeoff roll is started. This control position should be maintained while the airplane is accelerating and until the ailerons start becoming sufficiently effective for maneuvering the airplane about its longitudinal axis.

With the aileron held into the wind, the takeoff path must be held straight with the rudder. [Figure 5-3] Normally, this will require applying downwind rudder pressure, since on the ground the airplane will tend to weathervane into the wind. When takeoff power is applied, torque or P-factor that yaws the airplane to the left may be sufficient to counteract the weathervaning tendency caused by a crosswind from the right. On the other hand, it may also aggravate the tendency to swerve left when the wind is from the left. In any case, whatever rudder pressure is required to keep the airplane rolling straight down the runway should be applied.

--FAA Airplane Handbook, Page 21

As both main wheels leave the runway and ground friction no longer resists drifting, the airplane will be slowly carried sideways with the wind unless adequate drift correction is maintained by the pilot. Therefore, it is important to establish and maintain the proper amount of crosswind correction prior to lift-off by applying aileron pressure toward the wind to keep the upwind wing from rising and applying rudder pressure as needed to prevent weathervaning.


--FAA Airplane Handbook, Page 22


http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/airplane_handbook/media/faa-h-8083-3a-3of7.pdf

That's the basics. Obviously the lighter the aircraft, the more susceptible it will be to external pressures. Also some aircraft have different techniques or limitations due to things like low-hanging engines, etc. That's why a 747 looks "odd" in severe crosswinds as it must be flown relatively wings-level.

[srgalahad]

In FlightSim some of the components aren't perfect. Surface friction, for example is not ideally modeled. Also, the flight dynamics of a given aircraft may have had more effort put into getting speeds correct, as opposed to the effects of lateral forces, etc. There are some excellent, diligently-made models out there and some that are lacking the finer points. The environmental factors also are different due to the nature of the programming. Wind is an example - the sim says "275* @ 3 knots" or "30 knots"), but in the real world it's a fluid that is constantly changing (speed and direction) and applying varying forces on the aircraft. In Flight Sim those variances come more in "chunks" based on the program's 'cycles'.

In addition, many (most?) sim pilots never have the benefit of hours spent with an instructor exploring situations like this, nor do we have the benefit of 'feeling' the forces act upon us and the plane which plays a part in real-life.

It wouldn't surprise me to find that a majority of sim pilots also start with large aircraft (they are more 'impressive' or desireable) so the subtleties of basic flight in light aircraft aren't the first things to be ingrained in the process. Certainly, some simmers start with, and stay with light aircraft, but it's still not the same set of conditions and factors.

There's a bit of human nature at play too... it's a $50 computer program so it is easy to think like the carpenter who blames his tools... (that should get lots of hate mail :running: )

Actually, the reference I quoted in the above post is for Chapters 4-6. The entire Airplane Flying Handbook can be accessed here:
http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/airplane_handbook/

[aeromed202]

I've read several sources agreeing that this is an FS9 intrinsic issue. For all the work and marvelous results the game offers, they didn't quite get the effect right or maybe couldn't. I have had some luck with certain aircraft cfg edits to improve things, the caveat being they may make other behaviors worse. In small amounts, increasing yaw stability and/or yaw MOI, moving the main gear contact points aft, or the empty weight CG position toward the nose, all for tricycle gear aircraft can help reduce nose wheel drift while on the ground. These can be evaluated one at a time after saving the original, basically season to taste.

[stuartcox]

There's a bit of human nature at play too... it's a $50 computer program so it is easy to think like the carpenter who blames his tools... (that should get lots of hate mail :running: )


Not from me anyway...!

Thanks for your interesting input and the links. Well appreciated!
A very interesting read. I have spent hours with my Dad and Uncle in a Cherokee and Bonanza , but never experienced anything like the MS 'real' weather.
As you say, it's a cheap program, not a real life simulation, so it has it's limitations.

Unfortunately in FS9 the ground roll commands are opposite to this FAA demonstration until airbourne.

84745

Thanks, Stuart

[fliger747]

FSX is better in the surface friction department, an improvement but not perfect. FS9 has to high of a braking friction coefficient and about no lateral friction. Planes slide sideways and do all sorts of unusual things. FSX has a better balance between the two, but is total off with say skis on snow which they model like glare ice. T

[uniform7]

Ok, I installed FS9 on my other computer (laptop) Default everything. Set up flight with live weather, same issue. Set up flight user defined no wind OK. Set up user defined 16 knot winds, plane blown off runway. Main sim computer(see my specs) replaced magdec.blg file no help. Tried entire default modules folder no help. Gather it's in default program something to do with the wind factor. When I take off I will just keep my hand on the stick. What else can be done? I am still open for ideas cause sometimes I like to sit back with full throttle and watch the aircraft fly itself which, I have been told is what it will do and all a landing is well, a controlled crash.