seems right to me, the upwind wing will be exposed to the wind before the other 1/2 of your wing. but then again, I dont flare hard without wings level.....
Tim _________________ I have a fever…And the only prescription… is more Cowbell!!
If you want to pick a government to trust....why not this one!
If you're looking for what the result would be, it depends on the conditions and cross wind angle relative to your wing. Very often I have to land crosswind at my home site with a topless wing. Not with the king posted due to better performance at tight places.
My observations are
1. if the conditions are calm nothing really happens
2. if the conditions are mild when flared and touching the ground the wind will rotate you upwind, with the windward wing rotating and dropping faster. To overcome this you'd rather use a very aggresive and fast routine. Meaning get low to the ground, and do everything fast and violent to have control of the airborne/grounded transition. Muscle is necessary here to control the rotation and wheels help.
3. if the conditions are strong, the wing can be slowed down a lot during the end of your final. With little turn input the wind will rotate you upwind and grant you a parachuting landing. Note that slow landings are not advised and are to be avoided. I use this technique at coastal conditions, when the wind is strong and laminar, the LZ is very small and no turbulence is known to be present. For all other LZ's I found that approach no.2 above works best, but its very difficult to keep something or the nose off the ground.
These are my own personal experiences. Conclusion, even if the statement seems technically valid in mind, in practice in all situations one is looking for a wing anchoring in the ground and a 360 rotation with a face in the mud
What you need to picture in your mind is that a wings level aircraft of any kind will track in a straight line (flight path) at any speed above
stall in any wind speed or direction. It doesn't mater whether it is 1" above the ground or 1000'. It can not effect the wings flight path as
long as the wing is maintained in level flight. The control input has told the wing to fly straight & level and that is what it will do. It has no
idea of its ground track or drift if you will. It is our jobs as pilots to manipulate flight path and ground track to get the desired outcome.
The only time that wind direction or speed has 100% control over the wing is at touchdown after the wing has been flared below stall
speed (no more flight path). It is once again up to us as pilots to balance the transition from flight path to ground track. At that point
the wing becomes a leaf in the wind, do nothing to keep the "upwind
wing" down and suffer the same fate.
Life's goal is not to arrive safely at the grave in a well preserved body.
But rather to slide in sideways, totally worn out and broken, shouting
"Holy Crap, WHAT A RIDE !!"
What you need to picture in your mind is that a wings level aircraft of any kind will track in a straight line (flight path) at any speed above
stall in any wind speed or direction.
Only if there's no change in wind velocity. Gusts yaw my Falcon into the wind all the time.
What you need to picture in your mind is that a wings level aircraft of any kind will track in a straight line (flight path) at any speed above
stall in any wind speed or direction.
Only if there's no change in wind velocity. Gusts yaw my Falcon into the wind all the time.
Jesse
Jesse,
If you noticed I did say that "It can not effect the wings flight path as long as the wing is maintained in level flight."
I didn't say it had no effect on bank angle. Any change in bank angle, small or large, will change flight path be it a role or yaw. Our
reaction time is slow enough that some kind of bank angle change will happen. Add in rising terrain, a ragged cloud deck and the first
visual change that we will be aware of will be flight path and the appropriate correction will be added to regain our desired ground track.
Life's goal is not to arrive safely at the grave in a well preserved body.
But rather to slide in sideways, totally worn out and broken, shouting
"Holy Crap, WHAT A RIDE !!"
Crosswind landing, the pilot sets up his approach with some crab angle that keeps the glider moving along a "landing line". There is no sideways airflow over the glider. If the glider's speed is constant and the wind speed is constant, the glider will stay aligned with the landing line without any banking or turning.
Now the pilot allows glider to slow in ground effect. How does this change things?
If the wind is steady (no change in strength or direction), the glider will not tend to automatically yaw or turn into the wind as it slows down. Rather, it will simply start drifting downwind relative to the landing line. There is still no sideways airflow over the glider. Not even a little bit, not even momentarily. In the glider's reference frame-- or more precisely I guess I should say in the reference frame of the airmass-- the only acceleration taking place is that the glider's forward velocity is decreasing. That's all.
Now what? The pilot could simply accept the sideways drift, relative to the landing line, and run sideways relative to the landing line. Or the pilot could turn the glider further into the wind as he slows down, to keep the glider on the landing line. I suggest that we often do this unconsciously-- we are focused on making whatever inputs are needed to stay on the landing line, and we don't notice that we are turning the glider by lowering the upwind wing as we slow down, but we must be, if the glider's heading is changing.
It seems that if we are staying exactly on the landing line, and we are steadily slowing down until the moment of flare, we will end up flaring with the upwind wing low.
I think what is happening in reality is that the rate of slowing is so small, and the required bank angle to stay on the landing line is so small, and the resulting turn rate is also so low, that it's pretty negligible. However that wouldn't mesh with a claim that the nose of the glider is observed to swing rapidly into the wind during the flare.
Remember, the glider isn't "feeling" any sideways component in the wind, just because it is slowing down. There is nothing to "weathervane" the glider into the wind. This is is very different from a sailboat, where a change in the boat's speed creates a change in the relative wind direction.
Re the bank angle at the moment of flare-- maybe what we do in practice is keep the wings level and accept the fact that a slight sideways drift will build, relative to the landing line as the glider slows during the flare.
The key point about this "turning" thing, is that it is a very gradual process that takes place during the entire time the glider is slowing down to trim speed. The actual required turn rate is so low, and the required bank angle is so low, that we don't notice that we're not keeping the wings completely level. (I can't say that I've ever noticed it.) But it must be the case that we're not.
I couldn't watch the video, I'll try again later. One thing I suppose that could make a glider tend to "pirouette" during a flare, is if it rises up into the wind gradient into a layer of higher wind speed. This would be equivalent to a sudden increase in wind speed. There would be a (temporary) sideways flow over the glider that would tend to make the glider yaw into the wind, at the same time that it is starting to drift sideways at a faster rate. But if there is wind, are we really flaring hard enough to zoom up significantly into the gradient?
Note that even in this case of zooming up into the gradient, or the case of a sudden increase in wind speed, the glider doesn't "pirouette" far enough to stay exactly on the landing line. At the same time that it is "pirouetting", it is building up some sideways drift relative to the landing line. The sideways flow over the glider can be removed either by the glider yawing into the wind, or by the glider building up more sideways drift relative to the landing line. Which will predominate, surely must depend on things like the amount of cross-sectional area (as seen in a side view) the glider has, and the amount of yaw inertia vs "weathervane" yaw torque.
It wouldn't surprise me if most flex-wing hang gliders have significant positive "effective dihedral" at extreme angles-of-attack, like during the landing flare. In this case, zooming higher up into the gradient would tend to make the glider roll in the downwind direction.
Even if there is no significant upward zoom in the flare, if the pilot allows the upwind wing to be high, then this will also make a roll torque in the downwind direction, because it is higher in the wind gradient than the downwind wing. If we combine this effect with an additional downwind roll torque caused by zooming higher up into the wind gradient, this would be a bad combination. If one wing is higher during the flare, it would seem that it would be better if it is the downwind wing and worse if it is the upwind wing. But level during the flare is probably best?
We'd be most likely to see this "pirouette" due to wind gradient at somewhere like the beach where the wind is smooth and steady and thermal mixing is low and the gradient is strong. At an inland site, we might suspect that a "pirouette" during the flare was simply caused by a sudden gust in the wind at the moment of flare.
One thing is for sure-- in ground handling an a situation with a strong wind gradient-- like at the beach-- we can notice that there is a strong tendency for which ever wing is higher, to keep rising. This is true whether there is a crosswind or not.
Reasons why we don't want the upwind wing to rise-- if we have come to stop and are trying to ground-handle the glider, it might get flipped over. In contrast if the upwind wing is lower and is driven to the ground, that is a stable situation. On the other hand if we are still flying (say we are in the midst of the flare), if the upwind wing rises the flight path is going to curve downwind which raises our ground speed and creates the possibility of an ugly high-energy crash. If the downwind wing rises the flight path is going to curve into the wind which decreases our ground speed and decreases the amount of carnage that may follow. Guess I'm stating the obvious here.
There seems to be a difference in opinion as to whether the glider should be exactly level at the moment of flare or as close as possible, or should be intentionally banked a bit upwind… I don't know that I've done enough landings that involved crosswinds, and also involved substantial flares, to be able to comment. I have a hard time imagining that I would want to flare with the wing banked. Running a crosswind landing on the beach, it seems you would find yourself lowering the upwind wing to prevent the glider from drifting off in the downwind direction as it slows--in the reference frame of the airmass, the glider's path must curve if the glider is to stay on the landing line as the glider slows, and this is true even as the pilot is running out the landing. But I don't recall intentionally banking the glider during such a run-out-- again the required bank angle may be small enough that we don't usually notice, we just do whatever is needed to keep the glider on the landing line. Maybe at some point during the run the sideload could come from our feet not from the banked wing?
It's interesting how a trajectory can be curved in one reference frame and linear in another. We saw this in the paragraph immediately above, and also in the paragraph near the top beginning "if the wind is steady". From both the reference frame of the ground and the reference frame of the airmass, the glider is undergoing an acceleration, but in one reference frame the acceleration creates a curving flight path and in the other reference frame the acceleration creates only a change in the glider's forward speed. Both reference frames (ground-based and airmass-based) are valid inertial reference frames.
What you need to picture in your mind is that a wings level aircraft of any kind will track in a straight line (flight path) at any speed above
stall in any wind speed or direction.
Only if there's no change in wind velocity. Gusts yaw my Falcon into the wind all the time.
Jesse
Is this when you're at 6000ft or just when you're 2ft off the deck?
Pete _________________ The Harem:
Atos VQ11
Seedwings Funky 15
My observations are
...
3. if the conditions are strong, the wing can be slowed down a lot during the end of your final. With little turn input the wind will rotate you upwind and grant you a parachuting landing. Note that slow landings are not advised and are to be avoided. I use this technique at coastal conditions, when the wind is strong and laminar, the LZ is very small and no turbulence is known to be present. For all other LZ's I found that approach no.2 above works best, but its very difficult to keep something or the nose off the ground.
NMErider posted a good video of this to the Oz Report Forum: look at the landing at 4:00. http://www.youtube.com/watch?v=2rjP3xC-DhA&t=3m45s . At least I think that's what we're talking about. It's only a very mild flare. It's "parachuting" in the sense that ground speed is near zero but the airspeed is nowhere as low as in a full flare. I don't want to get into arguments about what is a "flare", so for the sake of discussion we'll call the end of the landing in the video a flare. You can call it whatever else you want, that's fine too.
I flubbed up my answers to this topic over several days of posting so here is a better answer with some of the bugs worked out.
If the glider is flying at a constant speed, it only needs to be aimed upwind of the landing line at some constant angle to stay on the landing line. This is called "crabbing" and involves no sideways flow over the glider.
If the glider slows while holding a constant heading, it will start drifting to the downwind side of the landing line. There is still no sideways flow over the glider.
If pilot makes whatever steering inputs are needed to stay on the landing line as the glider slows, he'll find himself commanding a bank in the upwind direction. This may or may not be noticeable among whatever other steering inputs are needed to deal with whatever turbulence may be present. In the smooth air in the video, the bank is very noticeable, shortly before the flare. There is still no sideways flow over the glider.
The pilot is turning the glider upwind to stay on the landing line as the glider slows. The turn is accomplished by banking--whether the pilot is consciously aware of it or not.
Therefore staying on the landing line in a crosswind as the glider slows, will involve a bank, and will tend to lead the pilot to flare while banked.
In the flare, airspeed rapidly decreases. For any given bank angle, the turn rate increases as the airspeed decreases. Therefore the turn rate really picks up during the flare-- we see the glider turn rapidly into the wind.
There is still essentially no sideways flow over the glider. It would be a misconception to say that the glider is "feeling" the wind and "weathervaning".
There's no relationship that guarantees the glider will turn exactly enough to end up pointing exactly into the wind just as the pilot's feet touch the ground, so far as I can figure, but it sure worked out nice in this video.
In practical terms, just maneuvering as needed to stay on the landing line in a crosswind really does tend to make the glider turn into the wind during the flare. Because the flare is performed in a bank. As the airspeed slows, the turn rate increases, and the glider's heading ends up swinging quite rapidly in the upwind direction as the airspeed.
We could do the same maneuver at altitude, ignoring the ground track, flying in any direction. The glider would always turn in the direction of the bank. The direction of the wind would be irrelevant. (I'm not recommending actually carrying out a full flare at altitude, it's just a thought experiment.)
It looks to me like the "flare" in the video is extremely mild. As one would expect in windy conditions. I don't think you would want to do a vigorous flare while banked, wind or no wind. But I could be wrong-- anyone have more video to shed more light?
Another way to land in the same crosswind would be to not bank the wing at all, and accept that the glider is going to start drifting more and more sideways (downwind) relative to the landing line as it slows and the initial heading (crab angle) is no longer adequate. It will especially drift sideways during the flare, as the airspeed drops to near zero. None of this will involved any heading change or sideways airflow over the glider.
I'm not advocating flaring while banked in general, just talking about the specific case of what is described in #3 in the quote above, and what is happening in the video around 4:00. Smooth coastal conditions may be key to making this work well?
An interesting point in all this is that just observing that the glider is travelling in a constant, linear direction over the ground is not a guarantee that the wings are level. In hang gliders I think we tend to judge bank largely by whether or not we are travelling in a straight line over the ground or travelling in a changing direction, but this is not really always adequate. If we are slowing down while wings-level, the ground track will curve in the downwind direction; if the ground track is straight as we slow down, the wings are not level. In the above video, if the pilot needed to perform a really vigorous flare for some reason (brick wall coming up fast), might it be better if he recognized that he was banked (though travelling in a straight line over the ground), and rolled the glider closer to level before flaring? I don't know the answer to this for certain but I suspect it might be.
There are some interesting (to me) points there such as how the glider's track can be curved in one reference frame but linear in another reference frame, and how the drag vector can act to turn (curve) the path of travel as the glider slows, as viewed from the ground reference frame, if the glider is not banked.
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