Crosswinds!

[TomVal]

Originally Posted by Ed_Wischmeyer

Time for me to be the stick in the mud again.

Unless there's some dire emergency, why push your luck? Suppose you get away with 24 knots xwind, but the next time you try it, you bend your airplane. Is that a win?

And for the rest of the folks who celebrate crosswind machismo, why is that worth celebrating? And will that tempt folks to try things beyond their skill level? Are scared pilots, bent airplanes and occasional bashed pilot worth it?

C'mon, guys, man up.

Ed

Ed,

I am in your court on this one. With a 30 kt ground speed on final, what is the effect on aircraft performance if the headwind suddenly shifts or drops to lets say 5 kts. Whether you are flying a RV-12 or 747...the negative effects on IAS and lift are the same except the 747 may have more reserve power to recover.

Tom

[rocketman1988]

But that 747 has far more inertia, and may NOT be able to recover a 30kt shear...in fact, most carriers have a stabilized approach criteria that mandates a go around if not within specified criteria. We use +/-15 knots for shears...

[TomVal]

Originally Posted by rocketman1988

But that 747 has far more inertia, and may NOT be able to recover a 30kt shear...in fact, most carriers have a stabilized approach criteria that mandates a go around if not within specified criteria. We use +/-15 knots for shears...

Agree...just tried to keep it simple.

Tom

[rongawer]

Originally Posted by TomVal

Ed,

I am in your court on this one. With a 30 kt ground speed on final, what is the effect on aircraft performance if the headwind suddenly shifts or drops to lets say 5 kts. Whether you are flying a RV-12 or 747...the negative effects on IAS and lift are the same except the 747 may have more reserve power to recover.

Tom

Hmm... even though ground speed is 30KT, the aircraft was still flying at 65KIAS and performance is the same relative to the wind it's flying in. And a strong headwind is very different than wind shear. If the headwind was physically able to suddenly stop, the aircraft ground speed would suddenly be 65KIAS and the margin above stall is unchanged. This is very different than varying aircraft approach speed at 1.2 vs 1.3 Vso in KIAS for additional margin above stall, something that you might apply for variations in wind gust - such as the rule of thumb "half the gust". The 747 referenced would still be using KIAS, not ground speed, for regulating approach speed.

When I share my experiences, while they may be perceived as expressions of "machismo", they are really just provided for the edification of the reader.

If you are uncertain of your outcome on final then, by all means, go around - or consider going somewhere else to land. If you land and then look back and say to yourself, "whew, I'm glad I made that one!", then you probably ARE on the verge of bending metal the next time. However, for this recent experience I provided, there was no question on the outcome and I provided detail so that others may be able to use those details as a reference to how their landings are working out and as an update to what I've learned since previous posts in my RV12 - not as a challenge.

Using the crab method, you're able get into ground effect without the cross-controlled effects that a forward slip creates. It does require practice and good timing, but once mastered, is a very effective way to land in XW and reflects my military training. With the heavy XW, when I did insert left rudder to align the aircraft with the runway, effectively forcing the right gear onto the runway, I still had some rudder control remaining (it was not at the stop), which is why I said the aircraft may be able to hand a couple more knots. It's important to know the limits of the aircraft - and the pilot's as well - which may not be the same.

As I stated previously, the landing was really a non-event. Taxiing was much more difficult and likely why Van's recently lowered the total wind max for ground operations from 35 to 30KT.

[Ed_Wischmeyer]

Uh, no...

If you're flying at 65 KIAS, 35 knots headwind component and hence 30 knots ground speed, and the wind abruptly stops, you're suddenly at 30 KIAS. Oops!

[rongawer]

Originally Posted by Ed_Wischmeyer

Uh, no...

If you're flying at 65 KIAS, 35 knots headwind component and hence 30 knots ground speed, and the wind abruptly stops, you're suddenly at 30 KIAS. Oops!

Ed, if you’re in your boat going 20kt downstream and the current is going 5 kt, then you’re going 25KT relative to the shore line - or ground. If you simply turn around and maintain that same 20KT of weigh on the boat, you will now be going 15KT relative to shore - you’re traveling in the current. The same principle is true flying in the air. If you’re flying 65KIAS into a 35KT HW, your ground speed is 30KT. If you turn around, you’re now going 95KT ground speed, but still flying the same 65KIAS within the air. If the wind, or body of air - which is a fluid much like the river, you’re flying in, were to stop, you would still be going 65KIAS within the body of air as your airspeed is relative to the volume surrounding the airframe, not relative to the air volume and the ground.

[Kyle Boatright]

Originally Posted by rongawer

Ed, I?m not sure where to start with this...but here goes... if you?re in your boat going 20kt downstream and the current is going 5 kt, then your going 25KT relative to the shore line - or ground. If you simply turn around and maintain that same 20KT of weigh on the boat, you will now be going 15KT relative to shore - you?re traveling in the current. The same is flying in the air. If you?re flying 65KIAS into a 35KT HW, your ground speed is 30KT, if you turn around, you?re now going 95KT ground speed but still flying the same 65KIAS within the air. If the wind, or body of air you?re flying in, were to stop, you would still be going 65KIAS within the body of air.

Not really. There's momentum to consider. The problem with gusty conditions is that gusts can be sharp enough that your IAS fluctuates almost as much as the gusts do. If we're talking about a 35 knot wind shear (or sudden onset gust), the airplane would have to accelerate 35 knots to maintain airspeed. That's gonna take a few seconds.

[rongawer]

Originally Posted by Kyle Boatright

Not really. There's momentum to consider. The problem with gusty conditions is that gusts can be sharp enough that your IAS fluctuates almost as much as the gusts do. If we're talking about a 35 knot wind shear (or sudden onset gust), the airplane would have to accelerate 35 knots to maintain airspeed. That's gonna take a few seconds.

It’s all about the relative wind. I included a link below for discussion. However, wind shear and wind gusts are different than a steady head wind. These topics are being merged and should not be.

Speaking relative to the wind, regardless of how the wind speed slows or increases, the aircraft speed within the volume of that wind will be unchanged. Relative to the ground, it has changed.

https://en.m.wikipedia.org/wiki/Relative_wind

When you’re on final and you see IAS fluctuating, that is because the aircraft speed itself is fluctuating within the wind, most likely due to pitch or power changes, but not a result of the wind speed changes.

[N456TS]

Originally Posted by Ed_Wischmeyer

Time for me to be the stick in the mud again.

Unless there's some dire emergency, why push your luck? Suppose you get away with 24 knots xwind, but the next time you try it, you bend your airplane. Is that a win?

And for the rest of the folks who celebrate crosswind machismo, why is that worth celebrating? And will that tempt folks to try things beyond their skill level? Are scared pilots, bent airplanes and occasional bashed pilot worth it?

C'mon, guys, man up.

Ed

Rongawer, thank you for posting your experience. Unfortunately, some keyboard cowboys like to ironically create machismo posts criticizing your valuable input. Despite his very clear intent on doing so, I hope Ed's post doesn't discourage any future posts of anyone.

[Kyle Boatright]

Originally Posted by rongawer

It?s all about the relative wind. I included a link below for discussion. However, wind shear and wind gusts are different than a steady head wind. These topics are being merged and should not be.

Speaking relative to the wind, regardless of how the wind speed slows or increases, the aircraft speed within the volume of that wind will be unchanged. Relative to the ground, it has changed.

https://en.m.wikipedia.org/wiki/Relative_wind

When you?re on final and you see IAS fluctuating, that is because the aircraft speed itself is fluctuating within the wind, most likely due to pitch or power changes, but not a result of the wind speed changes.

You're right about there being a difference between steady winds and variable winds. With a 30 knot steady wind, it might just be easier to land across the runway. With gusts, you're subject to the vagaries of the winds. They may drop you, balloon you, or whatever. Windshear is probably the most extreme example of rapidly changing winds.

Think about why Delta crashed an L-1011 at DFW in windshear.. The wind changed from a headwind to a tailwind almost instantly and the aircraft couldn't accelerate quickly enough to avoid sinking into the ground despite using maximum power. Clearly, airspeed changed substantially because of the changing winds.