CFI candidate lands with side loading

Are you saying that when you're about to touch down with your cross wind correction in and the cross wind picks up and say you are already out of rudder, that the plane won't weathervane into the wind?
Yes, I am. It will be blown downwind, but it won't yaw out of the relative wind such that it proceeds upwind.

Come on Ron, you're making yourself look stupid now.
:rolleyes2:

And yes, on takeoff, an increase in the crosswind force will turn you into the wind. A reduction in wind is not as critical as you can always release and even reverse rudder. When it increases, you only have so much more to give it.
If you're taking off with a wind so strong that it takes full rudder to maintain directional control, you deserve what happens to you. If not, you still have rudder authority remaining to control the yaw.
 
Last edited:
Holy cow this has devolved since last login!!

:rolleyes2:

Why is this so hard? Someone used "weather vane," and it isn't really applicable.

If the wind is variable, the airplane will turn into it (stability and all that) unless countered by equal force.

How's that?
 
Holy cow this has devolved since last login!!

:rolleyes2:

Why is this so hard? Someone used "weather vane," and it isn't really applicable.

If the wind direction is variable, the airplane will turn into it (stability and all that) unless countered by equal force.

How's that?
FTFY.
 
I'm not sure if this is going to help this discussion or not...

Figure 8.1 shows a situation where the airplane’s heading has been disturbed out of its usual alignment with the airflow. There are lots of ways this could happen, including a gust of wind, a momentary uncoordinated deflection of the controls, or whatever.
crab.png

Figure 8.1: Response to a Yaw Angle
In this situation, the relative wind is striking the vertical fin and rudder at an angle. Like any other airfoil, the fin/rudder produces lift in proportion to its angle of attack, so it will produce a force (and therefore a torque) that tends to re-align the airplane with the wind. We say that the airplane has lots of yaw-wise stability.
The colloquial name for yaw-wise stability is “weathervaning tendency”. That is, the airplane tends to align itself with the relative wind, just as a weathervane does. Section 8.12 discusses weathervaning during taxi.
http://www.av8n.com/how/htm/yaw.html

rotations.gif


[FONT=Arial, Helvetica, sans-serif]The yaw axis is defined to be perpendicular to the plane of the wings with its origin at the center of gravity and directed towards the bottom of the aircraft.[/FONT]
http://www.grc.nasa.gov/WWW/K-12/airplane/rotations.html

But now when you start talking about the ground it becomes like the treadmill question. :D
 
That is what seems a little fuzzy to me - textbooks will tell you that in flight, the airplane will yaw around the CG, but a ship in water most definitely does not pivot or yaw around its CG - the pivot point for a ship is a function of the speed of the ship. When dead in the water it is the CG. As the ship starts to pick up speed, that pivot point starts to move forward away from the CG.

All I'll say is that yaw doesn't care one wit about gravity. Yaw cares only about pressure (like any force balance...okay, okay, pressure is not a force but a force over an area). I'm not quite sure how anyone would confuse themselves on this point.
 
If the wind is localized (by which I mean small enough to hit the tail but not the rest of the airplane) - the airplane will pivot around the CG. But if the wind is not localized - the whole airplane moves.

The whole plane will move, but it will also rotate around the lateral CL moment created by having the wing down which is keeping from drifting downwind to begin with.
 
Thank you. Finally. Phew. :)

You'll still yaw around your horizontal component of lift that's keeoing you tracking the runway. You won't go to winsward, but that doesn't matter, you're in the air. Introducing the inflight portion is irrelevant, it's when you're on the ground that you'll hit things.
 
You'll still yaw around your horizontal component of lift that's keeoing you tracking the runway. You won't go to windward, but that doesn't matter, you're in the air. Introducing the inflight portion is irrelevant, it's when you're on the ground that you'll hit things.


You'll likely tend to yaw; how much depends on the nature of the gust and the shape of the airplane. The motion will be about the center of mass. The airplane will also tend to translate downwind (with the gust). Of course, if the pilot can react quickly enough these movements will be minimal. If the gust is sudden and strong enough, though* ...

You may well hit things while in the air. Windsocks, hangars, parked or taxiing airplanes, etc.

IIRC the original issue was "giving away" the centerline. I wouldn't. There's an increased chance of being "moved" into something solid.


* (Happened to me at St. Maarten a couple of weeks ago. Fortunately I was over the centerline - recovery was easy).
 
Last edited by a moderator:
All I'll say is that yaw doesn't care one wit about gravity. Yaw cares only about pressure (like any force balance...okay, okay, pressure is not a force but a force over an area). I'm not quite sure how anyone would confuse themselves on this point.

What you say about pressure makes sense and jives with over 15 years of personal experience driving large steel objects through the water. The confusion comes from things like what Everskyward posted - published by NASA that claims the yaw rotation is around the CG.

I think what Henning is describing about the center of lift makes a little more sense.
 
things like what Everskyward posted - published by NASA that claims the yaw rotation is around the CG.

It is (in flight), although the combination of rotation, translation, and your frame of reference may make this less than apparent.

This issue is tangential though; we can agree that you'll yaw somewhat (maybe very little, maybe not) and will translate with the change of wind.
 
Last edited by a moderator:
Ok, for the sake of further threadjacking, let's try a different direction - curious as to those who advocate sticking to the centerline at all costs vs taking the diagonal.

How many who insist on the centerline are tailwheel pilots?
 
Ok, for the sake of further threadjacking, let's try a different direction - curious as to those who advocate sticking to the centerline at all costs vs taking the diagonal.

How many who insist on the centerline are tailwheel pilots?


I place the upwind wheel on the centerline when landing on the hard stuff.

It helps with slight drift detection.
 
What you say about pressure makes sense and jives with over 15 years of personal experience driving large steel objects through the water. The confusion comes from things like what Everskyward posted - published by NASA that claims the yaw rotation is around the CG.

I think what Henning is describing about the center of lift makes a little more sense.

One thing about it, fluid flow is fluid flow. Years ago a coworker described sea trials of the John Shaw MODU. The wind definitely would weathervane that puppy since the drilling mast wasn't set in the center of the rig. Not quite the same as an aircraft since two fluids (air & water) were involved.

I think Henning is more on the right track than my original post about a lever arm to the center of pressure. I'm sure that center of mass (what folks are calling center of gravity) is relevent since the aircraft wants to align center of pressure and center of mass. The question to me is what's the "alignment" with relative to the wind? Anyway, the wing lift vector factoring into the alignment sounds plausable. I also think there is going to be some pressure from wind on the side of the aircraft and the result of that pressure will have a non-uniform distribution.

I think we've all probably felt aircraft turn into the wind while in flight. The only real question is why?
 
Ok, for the sake of further threadjacking, let's try a different direction - curious as to those who advocate sticking to the centerline at all costs vs taking the diagonal.

How many who insist on the centerline are tailwheel pilots?

We've already talked about the diagonal thing - it's help is negligible when it comes to reducing x-wind component. I like centerline and I fly tailwheels. I've landed in enough wind to cause the airplane to be skidded sideways on rollout toward the downwind edge of the runway, even with full aileron into the wind. Have also had gusts weathervane the plane a bit on rollout causing movement toward the upwind edge of the runway. I don't see why you wouldn't want the centerline so that in either case, you'll have time to correct or go around before getting dangerously close to the edge of the runway.
 
If you're in the air, the effect of a crosswind gust on yaw is insigificant, but the effect on lateral drift is proportional to the size of the gust. But no matter what, the airplane will be blown downwind, so if you're angling across the runway with the downwind wheel near the runway edge to take advantage of that [extremely small] diagonal effect, your downwind wheel is going to be pushed over the edge until you complete your correction for the gust. If you touch down at that point, all the weathervaning in the world won't fix the drag differential between the wheel on the runway and the wheel off the runway, and you're going to find yourself in a very unhappy place.

If you you're taking off, and the wheels are still on the ground, yes, the airplane will tend to weathervane into the wind. If you're using that diagonal trick near the downwind edge, that yaw could be enough to push your tailwheel off the runway. If not, it could get you pointed across the runway at an even bigger angle than you planned, and now you're headed for the other edge.

All in all, both the FAA and I are pretty well convinced that the right way to takeoff and land is aiming to keep the runway center between your mains, even if we can't convince Henning otherwise.
 
If you're using that diagonal trick near the downwind edge, that yaw could be enough to push your tailwheel off the runway. If not, it could get you pointed across the runway at an even bigger angle than you planned, and now you're headed for the other edge.
If someone is that bad of a pilot, then starting out on the centerline isn't going to provide any better success. The outcome would be the same no matter what technique they use.
 
I have very little time in taildraggers but I have enough to know that you can't see much, if anything, out the front when the tail is on the ground. It seems that it would be more difficult to judge the proper diagonal angle by looking out the side. :dunno:
 
I have very little time in taildraggers but I have enough to know that you can't see much, if anything, out the front when the tail is on the ground. It seems that it would be more difficult to judge the proper diagonal angle by looking out the side. :dunno:

They are different: Cubs and T-Craft have less forward vis than Aeroncas.

Still, the key to knowing where you are vertically as well as laterally is the view out the side.

Lindbergh only had a 10 O'clock view out the Spirit, but the rest of us have 1030-11 or so.
 
Still, the key to knowing where you are vertically as well as laterally is the view out the side.
That is what I am saying. If you are lined up with the runway the view out the side will be symmetrical. If you are flying at an angle it seems that it would be more difficult to judge the proper one by just looking out the sides.
 
If someone is that bad of a pilot, then starting out on the centerline isn't going to provide any better success. The outcome would be the same no matter what technique they use.
Are you suggesting there's no difference between zero margin for error and 25+ feet of margin for error? If so, I beg to differ. While I think I'm a pretty good pilot, I know I can't hold zero tracking error on a crosswind takeoff in any light plane, whether it be tailwheel or nosewheel (steerable or free-castering).
 
Last edited:
That is what I am saying. If you are lined up with the runway the view out the side will be symmetrical. If you are flying at an angle it seems that it would be more difficult to judge the proper one by just looking out the sides.


Hmmm...

Many paved strips are too wide (75' and more) since I'm seated pretty low in a three point attitude in the Chief.

I did notice a lack of perspective first time I landed at KCKB (150' wide). I landed astride centerline -- dumb -- no reference for drift.

Since then on wide runways I usually land between centerline and edge (windy conditions) or with upwind wheel on centerline (lighter winds).

When I land on grass I usually use the mower lines. Absent that, all I have is distance from the runway edge.

I haven't done the curved landing yet. I'm not that good in the Chief yet. I've done curved takeoffs, and that worked out well.

I've done "use all available runway" takeoffs and landings in extreme crosswinds with heavier singles (A36) and that works pretty well, too.
 
If you you're taking off, and the wheels are still on the ground, yes, the airplane will tend to weathervane into the wind. If you're using that diagonal trick near the downwind edge, that yaw could be enough to push your tailwheel off the runway. If not, it could get you pointed across the runway at an even bigger angle than you planned, and now you're headed for the other edge.
Remember, we're not talking about a 10KT crosswind. We're talking about significant winds probably in excess of 25KTs. I the kinds of aircraft being discussed, you don't need much runway to take off or land, and any way you can reduce that crosswind DOES help. Any wind strong enough to take your tailwheel off the edge of the runway is also likely to be enough to make you groundloop if you religiously hold the centerline. That same wind, is probably strong enough, that if you go to the edge of the runway, you can "fly" it at a standstill, and get off the ground long before you run off the opposite edge at an angle. You can practically hold the Cub's tail up in the air at a standstill if the brakes are tight in a 25-30KT wind. You'd be foolhardy to try and do that with a strong wind off to the side, but if you pointed the nose into the wind, aileron down, you should be able to get off the runway in good order very quickly.

Ryan
 
Last edited:
Remember, we're not talking about a 10KT crosswind. We're talking about significant winds probably in excess of 25KTs. I the kinds of aircraft being discussed, you don't need much runway to take off or land, and any way you can reduce that crosswind DOES help.
In my opinion, the diagonal trick doesn't help nearly as much as it takes away margin for error or deviation.

Any wind strong enough to take your tailwheel off the edge of the runway is also likely to be enough to make you groundloop if you religiously hold the centerline.
If that's true, you'll groundloop off the diagonal method too, unless you think 3 degrees of wind direction change is significant -- and the numbers say it's not.
 
If that's true, you'll groundloop off the diagonal method too, unless you think 3 degrees of wind direction change is significant -- and the numbers say it's not.
It's not 3 degrees. More like 10-15 or better depending on the winds and the aircraft's capabilities...

Ryan
 
We've already talked about the diagonal thing - it's help is negligible when it comes to reducing x-wind component. I like centerline and I fly tailwheels. I've landed in enough wind to cause the airplane to be skidded sideways on rollout toward the downwind edge of the runway, even with full aileron into the wind. Have also had gusts weathervane the plane a bit on rollout causing movement toward the upwind edge of the runway. I don't see why you wouldn't want the centerline so that in either case, you'll have time to correct or go around before getting dangerously close to the edge of the runway.

+1.

I would go with the centerline, and I'm a tailwheel pilot. Of course, home base for the tailwheel is narrower than the wingspan of the Citabria if I'm landing on pavement, so diagonal is completely worthless. If the winds are that bad, I'd just land on the grass part of 15, which is between two large stands of big trees. There'd be some hellacious turbulence a bit off the ground, but they'd cut the crosswind down to size for the actual landing.
 
Guess this would explain why I actually have a harder time greasing the landings at 150' wide KAPF vs. 100' wide KMKY.
 
How wide is the runway? How long is your takeoff roll?
Well, for instance, on two of the grass runways I use, I could probably get off in 6-800' with no wind and the field is 100' wide. With a significant enough crosswind to have issues, you could easily half the distance. I'm not saying that you should use a diagonal in normal circumstances by any means, just pointing out that if you're limited to a single runway and a significant crosswind, it's a technique that could help. Also, on the grass, there IS NO centerline. The centerline is an arbitrary device rightfully used to help with precision. Do I normally land on the centerline, of course - hopefully within 3-6 inches. I just spent a week beating that into a student's head.

Ryan
 
Well, for instance, on two of the grass runways I use, I could probably get off in 6-800' with no wind and the field is 100' wide.

Even reducing your takeoff roll to 500', doing the diagonal thing gives you only 11.5º which is not going to reduce your crosswind component by much unless the wind is <30º off runway heading. If it's a direct crosswind, your takeoff roll will also not be changed by much until its magnitude allows you to do a takeoff run at 45º or more to the runway, which means the wind needs to reduce your takeoff roll to 140 feet or less, meaning its magnitude is roughly 3/4 of your takeoff speed, in which case you're probably not even going to be able to make it to the runway in the first place.

I'm not saying that you should use a diagonal in normal circumstances by any means, just pointing out that if you're limited to a single runway and a significant crosswind, it's a technique that could help.

The only time you're limited to a single runway is if you ran out of gas.

Also, on the grass, there IS NO centerline. The centerline is an arbitrary device rightfully used to help with precision.

Yes, but even on grass, you should generally be landing somewhere close to the middle of the runway.
 
It's not 3 degrees. More like 10-15 or better depending on the winds and the aircraft's capabilities...
For it to be 15 degrees, the runway would have to be over 200 feet wide with a takeoff roll of less than 800 feet. Try again, unless you're operating out of MacDill AFB.
 
Yes, but even on grass, you should generally be landing somewhere close to the middle of the runway.


While you usually want to have as much room on the right as you do on the left, it ain't always so.

For example, the grass "runway" at KFWQ sports a couple of big drainage grates and a big hole:

http://www.bing.com/maps/?v=2&cp=qq...80&sty=b&where1=Monongahela&q=monongahela, pa

Hard to see on that view, but the grass strip is north of 8/26. I shade a bit right when landing on grass 26, as any drifting left could end up in the grates. The right side is taller grass and a bit upslope so little danger drifting that way.
 
For it to be 15 degrees, the runway would have to be over 200 feet wide with a takeoff roll of less than 800 feet. Try again, unless you're operating out of MacDill AFB.


The early part of the roll has the greatest curve. It straightens out as speed builds up control effectiveness and the x-wind vector is a smaller.
 
The early part of the roll has the greatest curve. It straightens out as speed builds up control effectiveness and the x-wind vector is a smaller.
Exactly....as the speed builds up, you need less correction so the ground path is more of an arc.
 
Even reducing your takeoff roll to 500', doing the diagonal thing gives you only 11.5º which is not going to reduce your crosswind component by much unless the wind is <30º off runway heading.

Might want to check a x-wind component graph - for a 30 degree/20 kt x-wind compared to a 40 deg/20 kt x-wind is about a 5 kt diff in x-wind component. I would not call that an insignificant amount.
 
Might want to check a x-wind component graph - for a 30 degree/20 kt x-wind compared to a 40 deg/20 kt x-wind is about a 5 kt diff in x-wind component. I would not call that an insignificant amount.
I probably wouldn't start using an angle until it got to be 20-25+ KTS of crosswind. At that point, the Cub's airspeed on short final would be between 45 and 55 KTS - with a groundspeed of 30 KTS or less, and the ground roll would be very, very short. I've flown it in winds so strong that I was able to takeoff, climb out over the runway, slow down and drift backwards, and land - all without any significant change in heading.

Ryan
 
Might want to check a x-wind component graph - for a 30 degree/20 kt x-wind compared to a 40 deg/20 kt x-wind is about a 5 kt diff in x-wind component. I would not call that an insignificant amount.

No need for a component graph, only a unit circle. There will be a 28% difference between 30 and 40, a 46% difference between 20 and 30, and a 97% difference between 10 and 20. So, call it <45º if you wish. In a direct crosswind (or anything within about 30º of it) that's not howling enough to allow you to land across the runway straight into it, the diagonal is not going to give you a significant advantage, especially compared to the loss of any room for error.

Now, a curved takeoff, I can buy into - You'll quickly be on the centerline and have more control authority when the wind is to your side, and you are going to start out traveling towards the centerline.

But a purely diagonal landing doesn't give you much advantage unless the headwind component is greater than the crosswind component. If you do a curved landing, you are on the edge of the runway for most of the landing roll, with no margin for error.

You might as well do the curved landing touching down on the centerline, because you'll still have half the runway to turn into the wind if necessary when you lose the control authority to stay straight, you still have half the runway as your margin for error, and you only "lose" half the width of the runway for your into-the-wind portion of the landing roll.

But, seriously, in winds that bad - What the hell are you doing out flying anyway? :dunno:
 
But, seriously, in winds that bad - What the hell are you doing out flying anyway? :dunno:
20 kts 30-40 degrees off the runway was a pretty typical wind in New England where I did my PPL and TW endorsement. With most ga planes having a max demonstrated x-wind component, again, I'll take a 5 kt reduction in x-wind component.
 
20 kts 30-40 degrees off the runway was a pretty typical wind in New England where I did my PPL and TW endorsement. With most ga planes having a max demonstrated x-wind component, again, I'll take a 5 kt reduction in x-wind component.

I never said I wouldn't fly in 20 knots 30-40 off the runway - That's only a 10~14 knot crosswind component. Heck, I'd do that in the Citabria in a heartbeat.

20 knots direct crosswind - I'll do that too. 30-35, I'd rather be in the 182.

I don't think even 20 knots of direct crosswind is justification for doing anything funky on the landing. If you can't land an airplane on the centerline in a 20-knot crosswind... :frown2:

I'm thinking in this discussion about crosswinds in the 40-60 knot range. A 20-knot crosswind just does not require any special technique other than that which is taught to all student pilots. :dunno:
 
Back
Top