Jaybird180
Final Approach
Deal.
Pattern Work Question
- Thread starter MDeitch1976
- Start date
Deal.
MDeitch1976
Line Up and Wait
jpower
Cleared for Takeoff
Heh that happend to me on my checkride. I was demonstrating my emergency procedures, and he had broken my engine right over an airport. I was of course super high, because we had just been doing the cross country stuff, and I did a 360 out on long final. When I tried to add flaps, he said "flaps are broken." He reminded me that he wanted to see a forward slip at some point, so I figured "why not!" and slipped it all the way down long final from about 1500 AGL. Great fun! Took it out of the slip right over the threshold at about 5 AGL.
Captain
Final Approach
Two points:
1. I have no idea what this weathervaning is you guys are talking about. If you push hard on the rudder and then let go the plane weathervanes back into the wind. Short of that it's made up.
2. When on final with the runway in sight I don't use any fancy gadgets to tell me the winds or hold centreline. I stay exactly on centreline and if winds change I make corrections, but I do not come off the centreline. It's like walking down a balance beam. You don't wait until you're falling to make a correction. Instead, the instant the gymnast perceives movement corrections are made...constantly. Holding centreline is just like that.
1. I have no idea what this weathervaning is you guys are talking about. If you push hard on the rudder and then let go the plane weathervanes back into the wind. Short of that it's made up.
2. When on final with the runway in sight I don't use any fancy gadgets to tell me the winds or hold centreline. I stay exactly on centreline and if winds change I make corrections, but I do not come off the centreline. It's like walking down a balance beam. You don't wait until you're falling to make a correction. Instead, the instant the gymnast perceives movement corrections are made...constantly. Holding centreline is just like that.
MDeitch1976
Line Up and Wait
I know in the little Piper Sport I am learning in, if there is a crosswind when I leave the ground, the airplane weathervanes into the wind, or you could say naturally crabs into the wind.
alfadog
Final Approach
Yes, it weathervanes into the relative wind, exactly as designed. There seems to be this idea floating around that the airplane in the moving air mass will turn upwind as a taildragger want to do on the ground (or any airplane, just more of an issue in a tw). Of course, on the ground, that is because the center of resistance to the wind (centroid of side surface area) is well behind the point of contact between the mains and the ground causing a force couple that will yaw the airplane. The only inflight "weathervaning" I can imagine would be a transient condition as you pass a horizontal wind shear boundary and your momentum briefly causes a tendency to yaw. Do not know if it actually is perceptible, though.
Jaybird180
Final Approach
So what are we arguing about??? Crabbing and weathervaning (IMO) are interchangeable terms, and it does happen. Because the airplane at altitude is traveling faster than the wind drift, it causes the relative wind to reduce the perceived crab angle, but nonetheless it's still there.
Captain
Final Approach
Yes, I get that too in every plane I've ever flown. I chalk it up to the control inputs you have when taking off into a crosswind (normally ailerons turned toward the wind) and the fact that the elevator flies before the wing. As a result the nose wheel lifts off first (or tail wheel) while the mains are still on the ground. At this point the plane does weather-vane as contact is still made with the ground.
alfadog
Final Approach
No, probably not perceptibly, and, er, no.
alfadog
Final Approach
Sorry if I came across snarky. Actually, I think that you have just put your finger on the source of your misconception. Crabbing and weathervaning are definitely not interchangeable terms.
Crabbing means to fly a heading different from your desired ground track to compensate for the wind. It is something the pilot initiates and is simply a direction taken through the air. The airplane does not "know" what direction the wind is moving in a crab, only the pilot knows (maybe LOL). There is no part of the airplane that is resisting the airmass' ability to translate* the aircraft relative to the ground. You just compensate for the translation with a crab angle.
Weathervaning is the tendency of the airplane to be literally blown into the wind. It is something the pilot is usually opposing. The airplane "knows" as in "is reacting to" the direction the wind is moving. In order for weathervaning to occur there must be some part of the airplane that is resisting the translation caused by the wind hitting the side of the airplane. That is the gear touching the ground. It resists translation and since the centroid of wind resistance is behind the gear, you get rotation into the wind.
*Translation (physics), movement that changes the position of an object, moving every point the same distance in the same direction, without rotation, reflection or change in size
Captain
Final Approach
MDeitch1976
Line Up and Wait
How close the angle of the natural tendency of the plane weathervaning to the crab angle? Once weathervaned, if I level the wings, would that be close to the correct cran angle?
Jaybird180
Final Approach
I tend to favor flying Xwind approaches using the crab-kickout method and establish the slip after roundout. IOW, I correct for the crab, because I no longer want it. I did not create it, the wind did.
How does crab differ from weathervaning?
How does crab differ from weathervaning?
Are you trolling?
Weathervaning is what happens when an object ATTACHED TO THE GROUND aligns itself with the wind. This happens because objects attached to the ground cannot move with the wind. This means the wind "pushes" on them, causing them to align with the wind. "Weathervaning" is what a windsock and all the boats anchored in the lake do when the wind is blowing.
Crab is not remotely related to weathervaning. Crab is simply the difference between the direction an airplane's nose is pointing, and its PATH ALONG THE GROUND. There is NO weathervaning happening when an airplane is crabbing. Crab angle does not exist because the wind pushes on the airplane and turns it into the wind.
You can fly an airplane pointed 90 degrees from the direction the wind is blowing. Never will the wind try to rotate the airplane to be aligned with the wind direction. It cannot do this in the air. It can do it when an airplane is on the GROUND, but that is something totally different.
Are we getting any warmer?
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MDeitch1976
Line Up and Wait
I tend to favor flying Xwind approaches using the crab-kickout method and establish the slip after roundout. IOW, I correct for the crab, because I no longer want it. I did not create it, the wind did.
How does crab differ from weathervaning?
Terminology. The crab is intentional. Weather vane is caused by the wind.
alfadog
Final Approach
I tend to favor flying Xwind approaches using the crab-kickout method and establish the slip after roundout. IOW, I correct for the crab, because I no longer want it. I did not create it, the wind did.
How does crab differ from weathervaning?
Really? I just told you.
alfadog
Final Approach
I would say the difference goes well beyond semantics.
alfadog
Final Approach
You were just along for the ride, huh?
Yep, not remotely related.
MDeitch1976
Line Up and Wait
I retract the Terminology word from my prior post. This should then become a more accurate statement.
By intentional, I meant desired/input from the pilot.
Jaybird180
Final Approach
No, but your mother is.
Seriously, It seems that you didn't read this thread. This is the thread that casused me to search and find the other one.
I got it now. But the point I was making above is that you don't have to be an ass about it.
But thank you. Learning has occurred.
Then I apologize. It seemed you were being deliberately obtuse. If not, then again...
Jaybird180
Final Approach
Obtuse maybe, deliberately no.