Effect of Density Altitude on Crosswinds

[CharlieTango]

In an attempt to answer the OP's question, a 15 kt wind at -5000 and a 15 kt xwind at +5000 DA, the effect would be the same. If you consider the"effect" to mean the amount of drift over time. At -5000 DA, the amount of crab or side slip would be greater. But at + 5000 the ground speed will be higher. So a screw up at + 5000 could be much worse since you would be traveling faster.

Retro,

It is hard for me to think about this in terms of drift over time because the pilot prevents the drift with crosswind technique.

 

[vintage cessna]

Retro,

It is hard for me to think about this in terms of drift over time because the pilot prevents the drift with crosswind technique.

Well, the amount of control inputs to correct for drift on final for a given wind at sea level or 8000 ft will be a function of TAS. If a CT departs and flies a heading at 100 kts TAS with a wind 40 degrees left of the nose, and and a 747 with a TAS of 450 kits does the same thing, after 1 hour, both aircraft will have drifted the exact same distance. But the angle will be much less for the 747 than the CT. So the "effect" of the wind is the same for both aircraft. The amount of drift for someone observing from the 747 is just not as apparent as an observer in the CT.

 

[vintage cessna]

Retro,

It is hard for me to think about this in terms of drift over time because the pilot prevents the drift with crosswind technique.

I don't think you have been saying anything wrong really, just that everyone is not on the same page as far as what "effect" means. It will definitely be different landing at higher DA than lower as far as what the pilot experiences.

 

[Silvaire]

....It is hard for me to think about this in terms of drift over time because the pilot prevents the drift with crosswind technique.

Actually you are always preventing this drift in respect to the ground. That is why the nose of your aircraft is hardly ever pointed at the point to where you are ultimately going. The only times it coincides are when the wind direction is exactly the same or 180 degrees from your course or when you intentionally uncoordinate your flight controls to align your wheels with your ground track over the runway for the purpose of landing.

I understand what you are saying about the air being thinner and all but not for the airplane. It simply travels through the air at a faster rate so that the result is the same. 80 knots of airspeed is 80 knots of airspeed regardless of your altitude.

If anything, and this has been mentioned a number of times, the higher ground speed makes the actual xwind landing more difficult at higher altitudes and DA.

 

[vintage cessna]

Retro,

It is hard for me to think about this in terms of drift over time because the pilot prevents the drift with crosswind technique.

Let me try a different example. Two aircraft are on final at the same distance from the runway for parralell runways. Aircraft on left side has a speed of 120 kts, aircraft on right side has speed of 60 it's. Both aircraft are subject to the same wind and therefor both aircraft will experience the same RATE of drift. Let's say that rate of drift is 10 ft per minute to the right. Let us further say they are on a 2 mile final and neither aircraft corrects for drift. It will take the faster aircraft 1 minute to reach the runway and therefor that acft will touch down 10 ft right of centerline. It will take the slower aircraft 2 minute to reach the runway and will so touch down 20 ft right of centerline. If both aircraft were to correct for drift which aircraft would require the larger crab angle or greater side slip?

 

[CharlieTango]

Let me try a different example. Two aircraft are on final at the same distance from the runway for parralell runways. Aircraft on left side has a speed of 120 kts, aircraft on right side has speed of 60 it's. Both aircraft are subject to the same wind and therefor both aircraft will experience the same RATE of drift. Let's say that rate of drift is 10 ft per minute to the right. Let us further say they are on a 2 mile final and neither aircraft corrects for drift. It will take the faster aircraft 1 minute to reach the runway and therefor that acft will touch down 10 ft right of centerline. It will take the slower aircraft 2 minute to reach the runway and will so touch down 20 ft right of centerline. If both aircraft were to correct for drift which aircraft would require the larger crab angle or greater side slip?

Of course the slower aircraft needs the larger/greater correction. Ok thanks now I can think in terms of rate of drift.

Similar scenario:

Two identical aircraft approaching runway 27, different airports one at sea level other at 8,000' Both airports have 15kt southerly crosswinds producing a 15kt rate of drift. The high DA airport has 74% of the air mass of the sea level airport. Will it take a smaller bank angle, perhaps 74%, to counter the drift due to less air mass?

 

[vintage cessna]

Of course the slower aircraft needs the larger/greater correction. Ok thanks now I can think in terms of rate of drift.

Similar scenario:

Two identical aircraft approaching runway 27, different airports one at sea level other at 8,000' Both airports have 15kt southerly crosswinds producing a 15kt rate of drift. The high DA airport has 74% of the air mass of the sea level airport. Will it take a smaller bank angle, perhaps 74%, to counter the drift due to less air mass?

Less crab angle or side slip for the 8000 ft approach but not becuase the air is less dense. The TAS, and so ground speed also, for the 8000 ft aircraft will be higher than the one at sea level. So just like the two aircraft in my example, the aircraft with the slower ground speed will require more correction becuase it takes longer to cover the same distance. If an airplane is traveling at an IAS of 60 kits at sea level or at 8000 ft, the wing doesn't know the difference., it is subject to the same aerodynamic forces.

 

[Silvaire]

Of course the slower aircraft needs the larger/greater correction. Ok thanks now I can think in terms of rate of drift...

Both airplanes will use the same amount of correction. The only difference is that the slower airplane will apply it for one minute longer because it will be airborne for an additional minute.

 

[vintage cessna]

Unfortunately wrong answer. Both airplanes will use the same amount of correction. The only difference is that the slower airplane will apply it for one minute longer because it will be airborne for an additional minute.

Don't think so. The faster aircraft will require less of a wind correction angle.

 

[CharlieTango]

How do you quantify 'amount of correction'?

Crabbing and slipping seem fundamentally different.

 

[vintage cessna]

How do you quantify 'amount of correction'?

Crabbing and slipping seem fundamentally different.

If you are holding a crab on final to maintain centerline tracking, that is the same as trying to correct for the wind on a cross country and track a course, right? The greater the wind, the more of a wind correction angle you need for a given speed, correct? Get out your E6B and calculate the WCA for a 90 degree 15 kt wind at a TAS of 60 it's and one for 80 kts. Which one has a greater WCA?

 

[vintage cessna]

How do you quantify 'amount of correction'?

Crabbing and slipping seem fundamentally different.

They both have the same effect. The greater the crab angle required, the more bank required in a side slip to achieve the same desired result.

 

[CharlieTango]

They both have the same effect. The greater the crab angle required, the more bank required in a side slip to achieve the same desired result.

For every WCA there is a corresponding bank angle?

 

[whifferdill]

How do you quantify 'amount of correction'?

Crabbing and slipping seem fundamentally different.

I hesitate to contribute here, but crabbing and slipping are identical as far as x-wind "correction" goes. You can track the runway and touch down in a crab rather than a slip in lots of airplanes, but it's just not as easy on the airplane as aligning it in a slip.

Have you considered what actually determines the limit of an airplane's ability to correct for x-wind while touching down aligned with the runway and not drifting? What determines this is how much of a yaw displacement angle the airplane can achieve during a slip without turning from its flight path at any given touchdown speed.

Say you're in a J-3 Cub gliding at 60 mph with your nose pointed at a spot on the ground. Doesn't matter whether the wind is blowing or not. Now put in a slip and see how far you can displace the nose while preventing the airplane from turning from its flight path in either direction. You're still flying along the same ground track as you were before you slipped, you're just seeing how much of a yaw angle the airplane can fly with at that speed.

If that max. yaw angle is 30 degrees from your selected spot on the ground, that means if you are flying down final (not slipping) tracking the runway in a wind that requires a 30 degree crab angle, that the airplane will just barely be able to align its nose with the runway and avoid drifting at touchdown at that speed you tested.

In a slip, ready to touchdown, the airplane is still not feeling any wind force, it is still just flying along a ground track (slipped or not) that causes the airplane to track the runway. You simply slip the airplane to change its ground reference and make for a smoother touchdown...or avoid a ground loop in a tailwheel airplane. It doesn't change anything from the standpoint of "fighting" or "feeling" the x-wind.

If the airplane can't be aligned with the runway and drift stopped, then it simply has insufficient control authority to produce a large enough yaw displacement without turning. That's all you're doing while slipping in a x-wind- causing a yaw displacement. The aileron is only there to keep the airplane from turning due to the rudder input. It's not there to "fight" the wind or force the airplane through the prevailing wind. Landing in a slip still requires the proper flight path through the air such that the airplane tracks the runway.

Crab angle for a given amount of wind does not change whether the density altitude is high or low. If the crab angle doesn't change, then neither does the amount of yaw angle needed to align the airplane at touchdown. I fail to understand how air density affects how much angle of yaw correction is required to land in a given amount of wind...other than the fact that has been mentioned already - your TAS is higher at lower air density, which would lessen - not increase - the crab angle (correction) for a given amount of x-wind.

 

[Silvaire]

Don't think so. The faster aircraft will require less of a wind correction angle.

Yup, I stand corrected - basic wind triangle again

 

[vintage cessna]

For every WCA there is a corresponding bank angle?

I think there is a general correlation. Flying an LSA in a stiff crosswind, I find it easier to track centerline in a crab rather than a slip, then slip it just before touchdown to avoid side load. Wind usually deminishes the lower you get, so the slip won't be as severe as on final.

 

[vintage cessna]

People learning to fly, like everything else, won't remember everything. So an instructor tries to emphasize the most important details. As far as less or more WCA or side slip at high altitude landings, that is not really important. You just naturally correct as needed to maintain centerline.

What is important for the student to remember is that at high altitude landings , even though the IAS is the same as low altitude airports, the aircraft will be touching down at higher and potentially more dangerous ground speeds.

 

[FastEddieB]

As far as less or more WCA or side slip at high altitude landings, that is not really important. You just naturally correct as needed to maintain centerline.

I think one takeaway from this thread is that even if this proposed effect is real, it must be really, really small for most pilots to never have noticed it.

Further, I don't recall it ever coming up in training materials, so the powers that be also seem to be either ignoring or downplaying it as a factor to be dealt with.

Interesting discussion nonetheless.

 

[Silvaire]

I think one takeaway from this thread is that even if this proposed effect is real, it must be really, really small for most pilots to never have noticed it...

I think it is completely overshadowed by the very real and noticeable increase in ground speed at higher altitudes that has a more profound effect on the difficulty of executing the xwind landing than an imperceptible decrease in the force of the wind. Yes, the air is thinner but as has been pointed out numerous times the aircraft is moving at a faster speed so that what it feels in regards to the air is no different than at sea level.

 

[FastEddieB]

Well, at least if I ever have to do a 100k crosswind landing on Mars, at least I'll have thought about it beforehand!

 

[CharlieTango]

I'm still stuck on this thinking:

I'm in a slipping configuration in order to maintain alignment and track the center-line.

With a 15kt 90* crosswind I do have sideways velocity but relative to the relative wind not relative to the ground. When it comes to aileron input sufficient to track centerline how can the air mass density not play a part? If shear is present and the 15kts changes to 20kts I need more aileron to counter that acceleration.

According to this conversation I should then consider the WCA at 20kts, convert to bank angle and realize that the mass/density of this accelerating crosswind is playing no part.

 

[vintage cessna]

I'm still stuck on this thinking:

I'm in a slipping configuration in order to maintain alignment and track the center-line.

With a 15kt 90* crosswind I do have sideways velocity but relative to the relative wind not relative to the ground. When it comes to aileron input sufficient to track centerline how can the air mass density not play a part? If shear is present and the 15kts changes to 20kts I need more aileron to counter that acceleration.

According to this conversation I should then consider the WCA at 20kts, convert to bank angle and realize that the mass/density of this accelerating crosswind is playing no part.

In a side slip you do have lateral movement reference the ground. The aircraft will move in the direction of the lowered wing, off setting the drift. That is why you lower the wing into the wind. Otherwise you could slip in either direction and it wouldn't matter.



The air density doesn't matter. If your POH says approach at 60 kts IAS, that is for any density altitude. To achieve 60 kts IAS at 8000 ft would require the plane to move faster in the air than at sea level. Since you are moving faster at 8000 ft the resulting air pressure on the wings and flight control surfaces is the same as 60 kits IAS at sea level.

All this stuff is in the FAA Airplane Flying Handbook, a good source to review every now and then.

 

[CharlieTango]

In a side slip you do have lateral movement reference the ground. The aircraft will move in the direction of the lowered wing, off setting the drift. That is why you lower the wing into the wind. Otherwise you could slip in either direction and it wouldn't matter.



The air density doesn't matter. If your POH says approach at 60 kts IAS, that is for any density altitude. To achieve 60 kts IAS at 8000 ft would require the plane to move faster in the air than at sea level. Since you are moving faster at 8000 ft the resulting air pressure on the wings and flight control surfaces is the same as 60 kits IAS at sea level.

All this stuff is in the FAA Airplane Flying Handbook, a good source to review every now and then.

I think you are answering a different question than the one I am attempting to ask. You are telling my why I use the same IAS for approach/landing at altitude and I am essentially asking the same thing as the OP.

How can the density not play a part when considering how much aileron input is required to counter a crosswind at a DA 10,000' lower? We have talked about the difficulty of calculating sideways velocity in the slip configuration, we know more aileron is needed to counter an increasing crosswind, how can the density of that increasing crosswind not be a factor? Everyone admits there is less correction needed at altitude and it is evident when comparing WCAs. I think comparing WCAs is one way of seeing it and considering the density difference is another.

 

[whifferdill]

In a side slip you do have lateral movement reference the ground. The aircraft will move in the direction of the lowered wing, off setting the drift. That is why you lower the wing into the wind. Otherwise you could slip in either direction and it wouldn't matter.

This is incorrect as well, similar to Charlie Tango's thoughts. We need forget about "side" slip vs. forward slip. Slip is slip. Slipping does not cause the airplane's flight path to move sideways. It simply causes a misalignment in yaw attitude. Flight path does not change. Go mess around in no wind conditions and transition from coordinated flight to a slip and back - in both directions. The airplane doesn't start drifting left or right of your flight path during a slip. If it does, then you are doing a slipping turn, not a constant flight path slip required when landing in a x-wind.

You could be tracking the runway, crabbed down final in a x-wind, and then put in a slip in either direction. You will still be tracking the runway, but in one direction the airplane will be aligned with the runway, and in the other direction, you will simply be more misaligned than you were during the crab in coordinated flight.

The bank angle during a slip is not to move the airplane sideways into the wind. It's only to keep the airplane from turning in the direction of your slipped rudder input. We do not want the airplane to turn. All we are doing when going from a crab to a slip is misaligning the nose so that the landing will be smoother. Aileron is used to keep from turning. If you are drifting, it's not because you don't have enough aileron, it's because your flight path is not sufficiently into the wind. Aileron would need to be used to turn the airplane's flight path more into the wind, not create more "lateral movement". Once sufficiently turned into the wind, you use the amount of rudder required to align the airplane, along with sufficient aileron to keep the rudder input from turning the airplane downwind.

So think about this - you are in your J-3 Cub gliding down final in zero wind - aligned with and tracking the runway. Now you put in a big slip. You are still tracking the runway, just as you were before the slip. So then, what exactly is your "lateral" speed through the air now? There is none. The airplane does not start moving to the left of the runway track unless you are turning. It is physically impossible to move an airplane "laterally" through the air at a constant heading. It is only possible to turn the airplane, which causes your heading to change.

 

[vintage cessna]

I think you are answering a different question than the one I am attempting to ask. You are telling my why I use the same IAS for approach/landing at altitude and I am essentially asking the same thing as the OP.

How can the density not play a part when considering how much aileron input is required to counter a crosswind at a DA 10,000' lower? We have talked about the difficulty of calculating sideways velocity in the slip configuration, we know more aileron is needed to counter an increasing crosswind, how can the density of that increasing crosswind not be a factor? Everyone admits there is less correction needed at altitude and it is evident when comparing WCAs. I think comparing WCAs is one way of seeing it and considering the density difference is another.

Ok, first a gust is actually a shear, a sudden change in the velocity or direction of the wind. What happens when you encounter a gust while landing? You have a sudden increase in airspeed causing the plane to float or climb, then when it ceases the airplane wants to drop. Doesn't matter what your altitude is. Whether you need more or less WCA for a given wind speed an any altitude is just a function of TAS, higher the speed less correction needed. If your airplane is moving through the air at 60 kts IAS, the air density the airplane feels is the same regardless of altitude. At 60 kts IAS at any altitude the amount of input for any flight control surface to achieve similar results is the same. Otherwise, your controls would feel real sloppy at 60 kts IAS when landing at 8000 ft.

 

[Silvaire]

...How can the density not play a part when considering how much aileron input is required to counter a crosswind at a DA 10,000' lower? ...

Because as far as the aileron is concerned there is no difference in the air density. If you are going 60 knots through the air you are going 60 knots period, doesn't matter what altitude or DA is. You are moving faster through the thinner air to achieve 60 knots.

This has been explained numerous times in this thread, stop beating yourself to death over it.

 

[vintage cessna]

This is incorrect as well. We need forget about "side" slip vs. forward slip. Slip is slip. Slipping does not cause the airplane's flight path to move sideways. It simply causes a misalignment in yaw attitude. Flight path does not change. Go mess around in no wind conditions and transition from coordinated flight to a slip and back - in both directions. The airplane doesn't start drifting left or right of your flight path during a slip. If it does, then you are doing a slipping turn, not a constant flight path slip required when landing in a x-wind.

You could be tracking the runway, crabbed down final in a x-wind, and then put in a slip in either direction. You will still be tracking the runway, but in one direction the airplane will be aligned with the runway, and in the other direction, you will simply be more misaligned than you were during the crab in coordinated flight.



The bank angle during a slip is not to move the airplane sideways into the wind. It's only to keep the airplane from turning in the direction of your slipped rudder input. We do not want the airplane to turn. All we are doing when going from a crab to a slip is misaligning the nose so that the landing will be smoother. Aileron is used to keep from turning. If you are drifting, it's not because you don't have enough aileron, it's because your flight path is not sufficiently into the wind. Aileron would need to be used to turn the airplane's flight path more into the wind, not create more "lateral movement". One sufficiently turned into the wind, you use the amount of rudder required to align the airplane, along with sufficient aileron to keep the rudder input from turning the airplane downwind.

So think about this - you are in your J-3 Cub gliding down final in zero wind - aligned with and tracking the runway. Now you put in a big slip. You are still tracking the runway, just as you were before the slip. So then, what exactly is your "lateral" speed through the air now? There is none. The airplane does not start moving to the left of the runway track unless you are turning. It is physically impossible to move an airplane "laterally" through the air at a constant heading. It is only possible to turn the airplane, which causes your heading to change.

You should call the FAA and let them know.

 

[whifferdill]

You should call the FAA and let them know.

What? That airplanes don't fly laterally through the air without turning? This is simple stuff. Take a model airplane and throw it laterally though the air. What happens? Its vertical fin and CG location cause the nose to turn in the direction you threw it. Airplanes can't move sideways through the air without changing heading. Again, a simple yaw misalignment with the relative wind does not mean the airplane is moving sideways through the air. In no wind conditions, it would be easy to prove sideways movement is possible, but nobody will ever be able to capture video of this. Would of course need to be done in both directions to show that it's not just wind drift.

This concept really is at the crux of CT's misunderstandings.

 

[Silvaire]

...It is physically impossible to move an airplane "laterally" through the air at a constant heading....

How on Earth do you land in a crosswind if it's "physically impossible" to do so?

 

[vintage cessna]

What? That airplanes don't fly laterally through the air without turning? This is simple stuff. Take a model airplane and throw it laterally though the air. What happens? Its vertical fin and CG location cause the nose to turn in the direction you threw it. Airplanes can't move sideways through the air without changing heading. Again, a simple yaw misalignment with the relative wind does not mean the airplane is moving sideways through the air. In no wind conditions, it would be easy to prove sideways movement is possible, but nobody will ever be able to capture video of this. Would of course need to be done in both directions to show that it's not just wind drift.

This concept really is at the crux of CT's misunderstandings.

If what you are saying is true, then landing on one wheel in a side slip would still result in drifting and side load. We're you taught to slip in the direction the wind is coming from?

Go to the FAA Airplane Flying Handbook pg 8-10 and see what is says, then write the FAA and let them know they have published incorrect information.

 

[whifferdill]

How on Earth do you land in a crosswind if it's "physically impossible" to do so?

I've explained it as best I can. To me, "laterally through air" means that you have changed your flight path without changing your heading. If you consider going from coordinated flight to a slip without changing your flight path to result in "lateral" movement, then I guess we have a semantics breakdown. To me, unless the flight path changes, there is no "lateral" movement - you just have a yaw misalignment wit the relative wind.

 

[CharlieTango]

Obviously everything in this thread can't be correct. I am however seeing things from more than one perspective.

whifferdill's last post makes me realize that when I drift with aileron even if it looks to me like I am simply drifting latterly into the crosswind that I am transitioning into and out of a slipping turn, good lesson thanks.

Ultimately I reject the idea that a crosswind never impacts my aircraft from the side. If 3 things are true there is a crosswind component impacting the side of my aircraft.

1) I am landing in a crosswind
2) I am maintaining the runway heading
3) I am slipping (presenting my fuselage to the relative wind)

The classic definition of a slip 'presenting the fuselage to the relative wind' says it pretty clearly.

 

[Silvaire]

... If you consider going from coordinated flight to a slip without changing your flight path to result in "lateral" movement, then I guess we have a semantics breakdown...

No, I think you have "air" and "ground" mixed up because a slip is definitely a lateral movement through the air.

 

[vintage cessna]

I've explained it as best I can. To me, "laterally through air" means that you have changed your flight path without changing your heading. If you consider going from coordinated flight to a slip without changing your flight path to result in "lateral" movement, then I guess we have a semantics breakdown. To me, unless the flight path changes, there is no "lateral" movement - you just have a yaw misalignment wit the relative wind.

Your flight path won't move in the direction of the slip unless you have slipped it too much. Unless you want to start paying me, I'm done.

 

[whifferdill]

If what you are saying is true, then landing on one wheel in a side slip would still result in drifting and side load.

I think we're having a communication problem. I don't understand how you deduced this from my statements. You only drift if your flight path is not sufficiently into the wind. If you were tracking the runway in a crab with no drift, you will still be tracking the runway without drift when you put in the slip.

 

[whifferdill]

No, I think you have "air" and "ground" mixed up because a slip is definitely a lateral movement through the air.

Then we have a semantics issue, rather than one of us suffering from flawed logic. To me, moving sideways would be like trucking along in flight and all of a sudden causing the airplane's flight path to start moving in a different direction without changing the alignment of the airplane - like a car shifting lanes without any amount of turning of the vehicle. Airplanes can't do that.

I only brought this up to (attempt to) point out the flaw in thinking of an airplane as having to fight the air laterally when landing in a x-wind. CT was using this flawed logic to explain that higher wind density would require more x-wind correction. We're 166 posts in, and nobody agrees with that. This tangent is just a semantics confusion, I think.

 

[RotorDude]

This is incorrect as well, similar to Charlie Tango's thoughts. We need forget about "side" slip vs. forward slip. Slip is slip. Slipping does not cause the airplane's flight path to move sideways. It simply causes a misalignment in yaw attitude. Flight path does not change. Go mess around in no wind conditions and transition from coordinated flight to a slip and back - in both directions. The airplane doesn't start drifting left or right of your flight path during a slip. If it does, then you are doing a slipping turn, not a constant flight path slip required when landing in a x-wind.

You could be tracking the runway, crabbed down final in a x-wind, and then put in a slip in either direction. You will still be tracking the runway, but in one direction the airplane will be aligned with the runway, and in the other direction, you will simply be more misaligned than you were during the crab in coordinated flight.

The bank angle during a slip is not to move the airplane sideways into the wind. It's only to keep the airplane from turning in the direction of your slipped rudder input. We do not want the airplane to turn. All we are doing when going from a crab to a slip is misaligning the nose so that the landing will be smoother. Aileron is used to keep from turning. If you are drifting, it's not because you don't have enough aileron, it's because your flight path is not sufficiently into the wind. Aileron would need to be used to turn the airplane's flight path more into the wind, not create more "lateral movement". Once sufficiently turned into the wind, you use the amount of rudder required to align the airplane, along with sufficient aileron to keep the rudder input from turning the airplane downwind.

So think about this - you are in your J-3 Cub gliding down final in zero wind - aligned with and tracking the runway. Now you put in a big slip. You are still tracking the runway, just as you were before the slip. So then, what exactly is your "lateral" speed through the air now? There is none. The airplane does not start moving to the left of the runway track unless you are turning. It is physically impossible to move an airplane "laterally" through the air at a constant heading. It is only possible to turn the airplane, which causes your heading to change.

This is absolutely correct.
Of course "heading" in this case is the direction the aircraft is moving in, not the indication on the DG, since the latter will have an offset if we are in a slip.

And interestingly, even a helicopter that can easily move sideways in no-wind conditions relative to its nose, is still always moving forward relative to its heading, as defined by the direction the airframe is moving.

 

[dtuuri]

To me, "laterally through air" means that you have changed your flight path without changing your heading.

Yes, a sideslip. I used to have students sideslip from being aligned with the runway lights on one side to the other while maintaining runway heading. Not possible you say?

dtuuri

 

[vintage cessna]

I guess this is the reason I no longer have a plane on lease back. The students weren't a big problem, it was the supposedly trained pilots pounding the hell out of the airplane.

 

[Silvaire]

...I only brought this up to (attempt to) point out the flaw in thinking of an airplane as having to fight the air laterally when landing in a x-wind. ... This tangent is just a semantics confusion, I think.

No, I don't think so.

You are approaching the runway, on track in coordinated flight and your nose is 30 degrees off the runway heading to the left because of the xwind.

You now enter a slip by pointing the nose along the runway in preparation for landing.

The wind is still moving laterally in relation to the runway however you are not. So how can you not be moving laterally through the air?

This is pretty basic stuff.