Disproportionate Wind Effect

I just took off in the B777-300ER from RPPL on Runway 6. I had winds 180@6KT, so barely any crosswind. I rotated at a usual speed using the usual flaps. I was rather heavy, about 200,000 pounds of fuel, as I’m heading all the way to Vancouver this evening.

As I rotated, I was being pushed to the right side pretty heavily. I was not turning my device nor moving the rudder, so the only logical explanation is the wind.

In real life, a few knots of wind wouldn’t have this effect on a heavy 777, right? Is this just something wonky with the IF physics, or am I missing something?

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I just tried this and the plane more or less didn’t move at all (it deflected like 1 degree off center but even with 0 rudder correction it was fine). Maybe it was a 1 time thing? Big gust? Not sure.

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Could be a fluke. When I land, I’ll post a screen recording of my replay to show the issue.

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Can you show a video of your takeoff as well ?

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The factors that may make a difference in how much you notice it: how fast you rotate (how quick you change pitch angle), your IAS at rotation, and whether, as you are accelerating to rotate speed, you are more neutral to forward with pressure on the yoke vs neutral to back with pressure (if you don’t keep the nose “stuck down” you start yawing before rotation).

I had substantial side yaw (compare two images below) by selecting among the above conditions to maximize its effect, even with that low crosswind speed.

I assume you meant RPLL, runway 6, 6knt crosswind (on the slider though it shows 5 kts here), about the same fuel load (though I cranked up the pax and cargo; but I tried it lighter too).

After calibrating and being careful not to deflect aileron or rudder:

edit: I tried lower weight (MLW), and max throttle, but lingered slightly with my rotation rate perhaps, and the change in yaw angle was still around 8 degrees.

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Looking at the HUD the wind looks like it’s coming slightly from behind the plane. Maybe this was the cause of Morts plane deflecting off the runway? I understand that some planes can takeoff and land with a maximum tailwind of 7 kts.

Between the heading of 62 degrees when pointed straight down runway 06, and the wind coming out of 180 degrees, the wind angle forward is 180-62-90=28 degrees.

So the wind is blowing at an angle of 28 degrees forward from a direct crosswind.

By taking the trigonometric sine of that angle, you get the effective percentage of forward wind (from the total wind).

Multiply that percentage times the 5kts:

5kts x sine (28 degrees) =

5 x 47% (in other words, the sine of 28 degrees is .47) = 2.4 kts

2.4 kts, I’m sure you’ll agree is too tiny to make a difference.

When we talk of “tailwind component”, that’s what the 2.4kts is. As opposed to the total wind speed being 5 kts.

(putting 5 or 6 kts for the wind doesn’t affect the conclusion)

But the bigger sense of whether somewhat of a tailwind matters, is to just test it out in solo.

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Also worth mentioning is yaw vs drift. While maybe the drift from a small crosswind component could seem benign, if the yaw proceeds for long enough (rotational motion from torque - from the tail’s exposure to the crosswind), the aircraft is being turned onto a different (more sideways) course with amplifies the sensation of drift (you’ve added a component of motion sideways, or perpendicular, to the runway heading).

How did you get this much deflection? I can’t get this much track difference unless I’m at 20+ knots in which case the FPV is way off.

Edit: I guess if you take 10+ seconds to rotate it could, but it’s such a gentle effect I highly doubt a post would be made about it.

Notice my second screenshot I’m testing with the throttle at 87, so I may have taken longer with rotation out of caution.

But other than that, if you consider the 787, it may seem it wants to yaw early. But that’s really about how firmly you have the nosewheel down during a crosswind takeoff roll.

For the 777, if you calibrate and have trim at zero, the nose is more “stuck” down than the 787 under similar conditions (you kind of have to purposely push the 787 nose down).

But you can kind of get that 787 effect for the 777 if you start with a good amount of positive trim and/or you have unknowingly (or knowingly) moved your device pitch angle back a bit from where you calibrated it. (I didn’t test for the right mix of back pressure and trim to get this result so much as assess by feel that my nose was near the “unstuck” point)

To reproduce a good amount of yaw, just making sure the nosewheel is free to yaw early gives the significant yaw angle result, even if I don’t rotate so slowly.

Over time I’ve replied to countless topics about the nose drifting, and a fair portion of those mention winds not being strong. Just the weight of the number of topics dealing with this seems to suggest it’s something frequently puzzling others.

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Interesting! Once airborne, an aircraft is easy to move, just as a boat in water. One man can make a 300000kg barge travel at nearly 1km/h on a canal, so obviously, 6kt xwind must be corrected, even without being conscious of it, at takeoff, for it amounts to much more force than a single man when applied to the tail of an aircraft.

@AndrewWu
I exchanged messages with a 777 pilot. Besides emphasizing aileron mostly neutral (because if ailerons deflect beyond 5-10 degrees, spoilers deploy to assist bank which increases drag - a no go on takeoff roll), they said “we still have yaw tendency at light winds. You do feel more pressure on one side than the other. Rudder is your friend.”

And btw, after testing a bit more, I think the screen shot comparison I had above was the more extreme result: You’ve got to get the nose up a bit asap* (which is contrary to irl. Check out near the middle of this about holding the nose down is standard practice: Learn To handle A Boeing 737 in severe crosswind. Takeoff (youtube.com)) And I was also likely more subdued with rotation rate (as mention before).

*this means that, paradoxically, using lots of trim to assist in rotation, may actually increase the sensation that the aircraft wants to go off the runway during light crosswinds.

edit: as a side note, avoiding excessive bank input on large commercial aircraft during crosswind operations near the ground (because of the spoiler deployment issue) appears to be quite universal? @ToasterStroodie I think brought it up for the A380 during crosswind takeoffs/landings, and Official source info on the topic: "Aircraft 380 tilts upon landing" extended that to the entire airbus family of aircraft I believe. And the YouTube video link above for the 737 talks about the same thing for that smaller Boeing aircraft as did the 777 pilot I mentioned did for that aircraft. (something I obviously didn’t know…also, avoiding an engine runway strike is something you don’t worry about in a high wing cessna)

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Indeed, airliners avoid aileron correction for the reasons you mentionned, but the rudder definitely is needed I’d say from 4 to 5kt crosswind element, even on big planes.

The effect of a slow or fast rotation on yaw might be down to the speed at which the aircraft actually leaves the ground, for it is the ratio between the crosswind element and the forward airspeed which matters here (if I am right…?). The yaw angle diminishes as the aircraft gains speed with a constant crosswind component.

I’m not sure the ratio makes the difference, as opposed to whether:

1)the weathervaning (yaw motion) has been completed (the wind component perpendicular to the direction the aircraft points has gone to zero), or

2)the aircraft has completely accelerated laterally to be in synch with the wind drift (cancelling out lateral wind force by fully drifting with the wind).

So as long as there remains a transverse wind component the aircraft will continue to yaw and drift. The yaw and drift motion are both competing to remove the transverse force.

Irrespective of the forward speed, any transverse wind will continue these compensating motions.

You are right!
Actually maybe only the decreasing density makes a 6kt xwind imperceptible at cruise level?

I disagree, I think you are right:) That is, depending on exactly what we both mean:

When you are at a much higher speed, say even at cruise (though the air may be less dense, the IAS is proportional to the effective dynamic pressure at play that will act on the tail and side of the aircraft, in contrast to TAS), and you get a sudden change, say 40 kts in cross wind component, the high dynamic pressure should considerably resist yaw from the force of that crosswind change on the tail.

So, translation (drift) “catch up” will dominate over weathervaning “catch up” in removing the transverse force. I believe that’s true anyway.

So actually, I think you have to be correct.

And that will also cause increasing yaw stability as you accelerate through take-off. So, how much it stabilizes the transverse movement (from the combination of drift, and yawing the course travelled) at those range of speeds during the takeoff roll, is a good question.

You have all these things competing with the crosswind component: yaw competing with drift to remove the crosswind force, and (as you pointed out) increasing dynamic pressure from forward speed tending to lessen the yaw contribution to that, as forward speed increases.

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Extremely sorry for the delay - here is a video of the takeoff in question.

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Thanks for showing. The first thing I notice is you indeed have neutral rudder until some delay after the yaw commences.

The yaw appears consistent with light crosswind as mentioned in the discussions.

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Ok, thank you for all the help and insight you provided @adit !

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It is equally nice to be approved or disapproved by you here. I am old enough to have understood a few things, among which the following three are important :

  • I have been wrong in my statements about 50% of the time in my life! ;

  • I sincerly try my best not to fall below that figure;

  • Aviation is indeed a steep and never ending learning curve!

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