Wind on ground...

[Anatoli-Kagari9]

I know that some time ago ground wind started being reported to a reference 30ft AGL ( ~10m AGL ) according to RL METAR data, but irrespective from this, and although I am aware the physics model applies a reduction due to friction as the aircraft approaches the surface, I find that even setting extreme winds and turbulence, that have as result the mission starting at the ramp due to excessive values, thruth is I am still able to taxi at low to moderate speeds without "feeling" any x-wind effects.

 

It all comes to play during takeoff roll,, as speed crosses a given threshold, and then, all of a sudden, if there's an x-wind component it really kicks in.

 

I get the idea that just as MFS / FS2020 now does, DCS nill any axial wind component up to a certain speed ( on ground ) to make taxinng only as difficult as the prp effects ( if using sucjh modules ) can make it ?

 

Any one shares this thought ?

[Mars Exulte]

I haven't put extreme winds before, so can't comment too much on what it does/doesn't do on the ground. I know there is a multiplier to wind speeds at the 10m point, if I remember, like it's 5ms on the ground but 20ms at 10m or something along those lines. You can see it really clearly if you pop smoke or something that drifts up, you'll see it shear sharply at a specific point in height. I'm uncertain if this is strictly AGL or ASL, though.

 

Tldr it wouldn't surprise me if it simply doesn't factor in at lower speeds on the ground itself.

[Anatoli-Kagari9]

zhukov032186, thx for your comments, and yes apart from the reduction due to drag effect near ground, I guess they further reduce the axial wind components for low speed taxi operations, maybe to simplify  ( ? )

 

Would rather prefer to have it as an option, as well as more intense weather effects such as wind shear and turbulence.

 

Maybe this will arrive after the new weather visuals.

 

[Anatoli-Kagari9]

Also checked an old effect I once brought to discussion about the way the P51D reacted to x-wind during takeoff.

 

Just noticed it's even worst in the P 47 D...

 

Pick the takeoff quick mission and edit in the Mission Editor.

 

Set a 90º x-wind at, say, 39 kts from either port or startboard.

 

Save your mission "As" to give it a different name and not ovewrite the original one... Go flying...

 

First you will start fro the Ramp because the aerodrome will be closed due to wind out of operational limits, yet you will be able to taxi to the runway, and not a big deal provided you don't taxi too fast. You don't have to worry about the x-wind during taxi at all !

 

Then as you lock your tailwheel for takeoff, and start the takeoff run, your aircraft will drift, and actually the nose will turn downwind instead of upwind due to weathervane !

 

This stops as you reach takeoff / rotation speed and then the aircraft starts to properly weathervane, as it should have right from the beginning  I believe ( ? )

 

The justification given by the Devs is the deflected propwash hitting the downwind wing and tail surfaces creating a higher lift and associated induced drag, plus other effects over the tail, thus causing this initial  "reverse weathervane" when takeoff power is applied and propwash is at it's maximal values...

 

Very strange

Edited February 8, 2021 by jcomm

[Mars Exulte]

Can't really comment on that. If they're saying it's deliberate, I am not knowledgable enough to argue with them. I know enough to follow reasoning and I've seen enough stuff that sounds ''odd'' turn out to be accurate, so it's certainly possible. Aerodynamics is complicated stuff, and not all of it is particularly intuitive (area rule, imo, basic 101 stuff, but not obvious either). On the other hand I've seen enough DCS glitches (MiG-15 control surfaces going haywire when stationary but ok when moving, for example) to know that's ALSO a possibility in some instances.

 

I think the team knows their stuff for the most part, and I think that what (common) people think reality is and what it actually is are often two different things in these complex topics, so I lean in their favor most the time.

[Anatoli-Kagari9]

Indeed a complex one, and I remember having discussed it with Yo-Yo along a big thread I started, maybe around 2017, on this very same subject.

 

One day I found a nice article that looked like it described the effect ( the aircraft wanting to veer downwind side at initial takeoff power application under strong x-wind ) but that was about the only reference to it I ever found.

 

OTOH, I do think that DCS ground physics are designed to soften the wind effects on ground at taxi speeds...

[sLYFa]

Try the Mi-8. You will very much notice wind effects as soon as your rotors start turning.

[Anatoli-Kagari9]

Thx for the suggestion sLYFa !

 

Rotary wing are probably modelled differently ( ? )

[Dragon1-1]

I think this might be an attempt to simulate how the wind near the ground is greatly weakened by buildings and so on. I noticed this with RC aircraft, no matter how wimpy the wind feels on the ground, once you go above a few meters, it usually becomes rather substantial. I'm pretty sure DCS implementation is oversimplified, especially if you try to get very high winds near the ground, but the gist of it is correct.

[Ironhand]

On 2/7/2021 at 6:46 PM, jcomm said:

First you will start fro the Ramp because the aerodrome will be closed due to wind out of operational limits, yet you will be able to taxi to the runway, and not a big deal provided you don't taxi too fast. You don't have to worry about the x-wind during taxi at all !

 

Then as you lock your tailwheel for takeoff, and start the takeoff run, your aircraft will drift, and actually the nose will turn downwind instead of upwind due to weathervane !

 

This stops as you reach takeoff / rotation speed and then the aircraft starts to properly weathervane, as it should have right from the beginning  I believe ( ? )

This hasn't been my experience, though I don't fly any of the prop aircraft regularly enough to be proficient. In the aircraft I do fly, if I set the crosswind to 15m/s, I will definitely notice a weather vaning effect into the wind, if I I allow my taxi speed to increase. And there is most definitely a weathervaning effect during the takeoff roll. Beyond that, takeoff works as you'd expect it to.

 

You may not experience much effect when taxing slowly simply because you are in a multi-ton aircraft as opposed to a relatively lightweight general aviation aircraft like a Cessna 172.

[Anatoli-Kagari9]

Thx for your comments Ironhand,

 

and, it makes sense for jet's regarding that weird effect that appears to "plague" only the props, where the aircraft initially goes opposite what it should, as you apply takeoff power.

 

Say, you're on the P51D or the P47, you have a 30 kts wind from  your left ( port side ) and you apply takeoff power...

 

As your takeoff roll starts, these aircraft will actually want to head downwind ( to the right / downwind ) requiring even into wind rudder and away from wind aileron !

 

Only as you gain more speed and approach rotation will the expected weathervane effect come to play and the nose start pointing to the left.

[Ironhand]

On 2/9/2021 at 9:13 AM, jcomm said:

...Say, you're on the P51D or the P47, you have a 30 kts wind from  your left ( port side ) and you apply takeoff power...

 

As your takeoff roll starts, these aircraft will actually want to head downwind ( to the right / downwind ) requiring even into wind rudder and away from wind aileron !

 

Only as you gain more speed and approach rotation will the expected weathervane effect come to play and the nose start pointing to the left.

So I actually tried it in the P-47 (I own it...just don’t have the time to use it). Once with the crosswind (15m/s) from the right and once from the left. Taxiing down to the runway each time provided two very different experiences. So there is definitely an effect, even when taxiing.

 

As far as the takeoff roll is concerned, in both cases, the nose moved downwind as I started my roll and, then, eased upwind as my speed continued to increase. There was no abruptness to the shift. All except the first part felt normal to me. If Yo-Yo says the initial movement of the nose downwind is due to the prop wash on the aircraft, I’d be willing to accept that explanation.

 

Edit: To clarify, I had the wind set to 15m/s but set not quite to perpendicular to the runway. So the actual crosswind component was probably closer to 13 or 14m/s for takeoff. Still a hefty amount.

Edited February 10, 2021 by Ironhand