Weathervaning (in the air)

Threefingeredjack said:
Very interesting conversation. I have had the odd occasion to observe vessels at sea from the air both underway and without power. In my experience a vessel drifting without power in wind almost always stays broadside to the wind. Sea anchors were invented ages ago to hold the bows of ships in distress into the wind, and by extension the prevailing seas, to provide a stable ride and to keep the vessel from broaching to. If there is significantly tall superstructure at one end of the hull or the other I might expect the wind to point the vessel, but the rules of stability generally preclude such a design. The area of the hull, waterline to main deck is always the greatest sail area of a vessel. When conducting hoists by helicopter off a disabled vessel we always attempted to get the crew to stream a sea anchor to keep the bow into the sea and wind to reduce rolling and all the attached dangers. Only vessels at anchor will weathervane, as they are attached to a fixed point.
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I think the ship will align itself with the wave troughs, which puts it broadside to the wind. I don't think the wind is affecting the ship nearly as much as the water.

Dan
 
My question is whether the crosswind affect all areas of the plane equally, or if it could push harder on a large rudder than on a cabin cross section and thus have a tendency to weathervane the plane? Flying a plane that is trimmed for a given attitude and then changing the cross wind would change the side forces, it would seem to me. No?
 
jnmeade said:
My question is whether the crosswind affect all areas of the plane equally, or if it could push harder on a large rudder than on a cabin cross section and thus have a tendency to weathervane the plane? Flying a plane that is trimmed for a given attitude and then changing the cross wind would change the side forces, it would seem to me. No?
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Well, sort of, to a certain extent. Aircraft transitioning from one airmass to another will initially be subject to a weathervaning tendency. The aircraft's resistance to this tendency will be a function of the aircraft's mass versus its presented area, i.e., airliners will take longer to "catch up" than a Piper Cub. However, if the airmass in which the aircraft is flying changes direction, the aircraft will be carried with it like a fish in a fish tank which is being carried around and the person carrying it changes direction -- the fish remains alinged with the water even if the water changes direction.
 
Ron Levy said:
However, if the airmass in which the aircraft is flying changes direction, the aircraft will be carried with it like a fish in a fish tank which is being carried around and the person carrying it changes direction -- the fish remains alinged with the water even if the water changes direction.
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It's always entertaining to read folks perspective on mass and inertia...

Your statement would true only if the fish is massless.
 
Lance: I think you are in danger of losing the bet if you didn't condition it. I have had a 172 weathervane into the GUSTY wind around mountains. That was Tim's point about a "steady" wind. If mountains or other terrain cause gusty winds to also shift directions, the airplane (or powered parachute) will turn into the gust, especially if it is sustained.
 
gismo said:
Last week I met the pilot/owner of a two seat powered parachute and I think he might even be a CFI-SP for that category. He insisted that his aircraft will "Weathervane" directly into the wind if you don't touch the "steering" controls while still in the air and that as a result it can be relied on to head directly into the wind by itself for landing in a field. I tried to explain that the craft has no reference to the wind direction unless some portion is in contact with the ground and although he agreed with that he still insisted that the weathervaning tendency was there. I offered to bet him $100 that he was wrong and he actually accepted in front of mutual friends although I wouldn't really take his money if and when he's proven wrong. I suspect that what he's actually experienced is the ease with which a pilot of a slow moving aircraft can visually sense the wind direction and is able to subconsciously steer the ship directly into the wind by such cues. The really unfortunate side of this is that it appears that he's' teaching this untruth to others.
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That is not totally correct. There is a reference with regards to the center of lateral resistance and pressure component to your side slipage against your inertia that you weather vane to since gusts are 15* off low/steady wind direction. It's minor but it exists.
 
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Henning said:
That is not totally correct. There is a reference with regards to the center of lateral resistance and pressure component to your side slipage against your inertia that you weather vane to since gusts are 15* off low/steady wind direction. It's minor but it exists.
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I'm not quite following you here but I would agree that if you fly through a wind shift there will be some "weathervaning", otherwise you'd be flying a continuous slip in the newly entered airmass (assuming the wings remained level, which they probably won't). The gentleman in question insisted that his PPchute would align itself with a steady wind and that's simply not possible because there's no difference between flying through air moving over the ground vs flying in still air with the ground moving underneath.
 
gismo said:
I'm not quite following you here but I would agree that if you fly through a wind shift there will be some "weathervaning", otherwise you'd be flying a continuous slip in the newly entered airmass (assuming the wings remained level, which they probably won't). The gentleman in question insisted that his PPchute would align itself with a steady wind and that's simply not possible because there's no difference between flying through air moving over the ground vs flying in still air with the ground moving underneath.
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Slight effect due to Coriolis but nothing like he's thinking.
 
Clark1961 said:
How does one go about baptizing a fish? And where do they keep the holy water?
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It seems there was this Protestant gentlemen, who was the sole non-Catholic in his tightly-knit neighborhood. He got on well with his neighbors, except during Lent. Yea, while his neighbors endured all manner of fish products every Friday, he, not being bound by the Lenten anti-meat clause, would barbecue all manner of beef products at the same time. The neighbors, being Good Catholics™, did not bemoan their meatless state, they instead sought to convert their neighbor to the Catholic faith.


Verily it came to pass that this man was confirmed, and while being confirmed, the Bishop declared "You were born a Protestant, you were raised a Protestant, you are now a Catholic". The Bishop, and the gathered neighbors, declared this good indeed.


Lent once again came to this now fully Catholic neighborhood. The first Friday of Lent, wouldn't you know that the newly confirmed Catholic set out a huge honking side of beef on his barbecue grill. As the delicious aroma of flame-broiled beef wafted through the neighborhood, his neighbors, who thought they had solved his Lenten Beef Tendencies by having him convert, peered over their fences. What they saw was a ritualistic blessing of the beef, as he chanted "You were born a Steer, you were raised a Steer, you are now a Fish".
 
It seems to me that weathervaning is related to the observer's point of view. I have flown at altitude and observed the nose of the aircraft being misaligned with the direction of travel as observed from the pilot's seat using the ground as a fixed reference. I was convinced that weathervaning is trus. I can now see how there could be observational errors.

Similarly while in the pattern I have been the observer on the ground and watched pilots correct for x-winds.

I'll have to do more thinking about this...
 
Jaybird180 said:
It seems to me that weathervaning is related to the observer's point of view. I have flown at altitude and observed the nose of the aircraft being misaligned with the direction of travel as observed from the pilot's seat using the ground as a fixed reference. I was convinced that weathervaning is trus. I can now see how there could be observational errors.

Similarly while in the pattern I have been the observer on the ground and watched pilots correct for x-winds.

I'll have to do more thinking about this...
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Please...not this again. You observed (in the air and on the ground) crab angle, not weathervaning. Weathervaning is a what a windsock does. Airplanes don't do that in the air.
 
Okay then I accept your change in terminology. All the same conceptually, right?
 
RoscoeT said:
Please...not this again. You observed (in the air and on the ground) crab angle, not weathervaning. Weathervaning is a what a windsock does. Airplanes don't do that in the air.
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Actually, they will - but only when transitioning from one air mass to another that is moving in a different direction (wind shear). It's got to be a pretty good change to notice it though...
 
airguy said:
Actually, they will - but only when transitioning from one air mass to another that is moving in a different direction (wind shear). It's got to be a pretty good change to notice it though...
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And it's momentary.

Dan
 
gismo said:
That's exactly correct. In the air there's no difference between being in a stationary body of air with the ground moving underneath vs in an airmass that's moving over the ground. And if you can grasp that concept it's fairly easy to recognize that the ground moving under the air shouldn't have any effect on your direction relative to the air since all is still where you are.
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Stick your hand out the window and tell me what you feel
 
RoscoeT said:
Please...not this again. You observed (in the air and on the ground) crab angle, not weathervaning. Weathervaning is a what a windsock does. Airplanes don't do that in the air.
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Agreed, but he does have a point when he says observational errors. It sure could LOOK like the plane was weathervaning.
 
What happens if a parachutist tries to land on a treadmill? :devil:
 
gismo said:
I'm not quite following you here but I would agree that if you fly through a wind shift there will be some "weathervaning", otherwise you'd be flying a continuous slip in the newly entered airmass (assuming the wings remained level, which they probably won't). The gentleman in question insisted that his PPchute would align itself with a steady wind and that's simply not possible because there's no difference between flying through air moving over the ground vs flying in still air with the ground moving underneath.
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So did the test to discover who's right ever take place?
 
Jaybird180 said:
Stick your hand out the window and tell me what you feel
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Are you serious? You seem to have a fundamental failure to comprehend the fact that airplanes don't "feel" wind like we do, standing on the ground. Airplanes will weathervane on the ground, not in the air. If you stick your hand out of the airplane, you are not feeling "wind". WIND is the air that moves relative to the ground. Objects suspended in the air do not "feel" the wind, they move with it. That is what gismo meant by everything being still up there. Ever been in a hot air balloon? It feels still, even though it could be blowing 20KT. And if you can tell me which way and how strong the wind is blowing by sticking your hand out of an airplane, then you've just defeated the laws of physics.
 
RoscoeT said:
Are you serious? You seem to have a fundamental failure to comprehend the fact that airplanes don't "feel" wind like we do, standing on the ground. Airplanes will weathervane on the ground, not in the air. If you stick your hand out of the airplane, you are not feeling "wind". WIND is the air that moves relative to the ground. Objects suspended in the air do not "feel" the wind, they move with it. That is what gismo meant by everything being still up there. Ever been in a hot air balloon? It feels still, even though it could be blowing 20KT. And if you can tell me which way and how strong the wind is blowing by sticking your hand out of an airplane, then you've just defeated the laws of physics.
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Never been in a balloon, sorry. But I'm begging to ask if a dirigible (airship) weathervanes, considering that it has a tail.
 
Jaybird180 said:
Never been in a balloon, sorry. But I'm begging to ask if a dirigible (airship) weathervanes, considering that it has a tail.
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There is nothing unique about a dirigible. Yeah, it'll weathervane...when tied to the ground - just like anything else. In the air, it doesn't act any differently from any other aircraft, and will not "weathervane" into the wind.
 
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RoscoeT said:
There is nothing unique about a dirigible. Yeah, it'll weathervane...when tied to the ground - just like anything else. In the air, it doesn't act any differently from any other aircraft, and will not "weathervane" into the wind.
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Is that theory or do you have practical knowledge and/or proof?
 
I've seen the goodyear blimp travel cross wind at low altitude with out any rudder input to maintain the direction of travel, as would be required if it weathervaned.
 
Jaybird180 said:
Is that theory or do you have practical knowledge and/or proof?
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You've not told us what force or combination of forces would induce the blimp (or the airplane) to turn from its given path in a homogeneous body of moving air in order to align itself upwind in reference to the ground. E.g. airmass (wind) is from 180 at 20 kt. Blimp is moving 090 at 10 kt. Why would it turn?
 
Jaybird180 said:
Is that theory or do you have practical knowledge and/or proof?
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The proof is the laws of physics. They do not make exceptions for dirigibles. Not sure what's so difficult about this concept. What makes a dirigible any different from an airplane in the air? The physics are no different. You know they have r/c dirigibles. I'll pay you back for it if you observe weathervaning. You still don't seem to understand that objects in the air move WITH the airmass. This is as fundamental as airspeed vs. groundspeed. Do you understand airspeed/groundspeed? Are you even a pilot? Have you ever flown a x-wind landing? In flight, do you need to hold rudder to keep the airplane from being turned into the wind while flying final in a x-wind? No, you don't. Just because a dirigible is lighter than air does not change the laws of physics. I can't explain it any better. There's a reason nobody is chiming in saying that dirigibles and aircraft weathervane in the air. Do you have an instructor? Maybe spend some ground time reviewing some basics.
 
To answer Alfa's question in terms Roscoe can understand:

That big thingie at the back of the aeroplane that sticks way up in the air...whatever that thing is called...when the wind blows, it hits the side of it...and it doesn't like it, so it shys away from it and it makes the front of the plane...where the twirly thing is...it makes that thing go straight.
 
Jaybird180 said:
To answer Alfa's question in terms Roscoe can understand:

That big thingie at the back of the aeroplane that sticks way up in the air...whatever that thing is called...when the wind blows, it hits the side of it...and it doesn't like it, so it shys away from it and it makes the front of the plane...where the twirly thing is...it makes that thing go straight.
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OMG!

:popcorn:
 
If you ride in a hot air balloon you might get the idea. You can be at 500agl moving at 20kts over the ground with zero apparent wind. Kind of a strange feeling.


In the balloon, when you land in a breeze, it feels like there is no wind. As in, if you lit a big fat cigar, the smoke would go straight up above your head. When you hit the ground and stop, you will feel wind on your face, and your cigar smoke will go blowing away.
 
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