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By JanB
#150381
Of course at the beach we land crosswind all the time. Dropping the downwind wing is bad, dropping the upwind wing is (generally speaking) harmless.

Image

Here I was aiming to land on the spot, I thought it was quite a good landing. I was pretty surprised when I saw the photo, looks terrible, doesn't it!

Cheers,
Jan
Last edited by JanB on Sat Nov 07, 2009 4:18 pm, edited 1 time in total.
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By AIRTHUG
#150406
jimrooney wrote: Surely someone's got a Dense Pages book handy.
I looked through the "Hang Gliding Training Manual" and couldn't find the diagram I'm thinking of, so it's either another book, or it was a magazine article...
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By pjwings
#150415
Well, this thread has been awesome. I feel that I am well prepared for cross wind landings. I guess I'll never know what actually caused my wings to shift of level while in ground effect though. Was it an unconscious 'correction' to try and fly the ground instead of the air? Was it turbulence? Was it a mild case of PIO? Fact is, while flying I always entered a unique kind of state of focus. My brain is in charge of monitoring traffic, watching the conditions, maintaining and adjusting my flight path, setting up landings, etc. while my body does all the actual flying of the glider all by itself. As a result I typically don't remember exactly what happened at any given point unless of course it is something highly unexpected.

Which all brings me to my next point... I've got to get a camera. Having the video is soooo awesome. I want to be more like $!>< when I grow up :mrgreen:

So, how are those GoPro HDs treating people?
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By Aeschna
#151485
Which all brings me to my next point... I've got to get a camera. Having the video is soooo awesome. I want to be more like $!>< when I grow up
I've been training with $!>< at MFP and the GoPro has definitely helped him to iron out problems. Every time I blow yet another landing he urges me to get one. So, tops on my Xmas list ...

I might catch up to $!><'s flight skills, but I'll never match his video "production values."
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By DMarley
#397618
AIRTHUG wrote:
jimrooney wrote: Surely someone's got a Dense Pages book handy.
I looked through the "Hang Gliding Training Manual" and couldn't find the diagram I'm thinking of, so it's either another book, or it was a magazine article...
Sorry to be dragging up a thread that is quite dated, but cross-wind landing technique hasn't changed much, and the wind is still fickle. :)
Here is the Dennis Pagen article that Ryan was referring to:
http://www.eastbayhanggliding.com/wp-co ... s-1of2.pdf
Hope this helps someone!
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By Karl_A
#397620
I don't have enough brain power to understand what Dennis Pagen writes so my method of crosswind landings has to be very simple: I'm going to drop a tip so I make sure it's the upwind tip that drops.
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By miraclepieco
#397680
An old thread on a subject that always bears repeating.

As one ground skims on final the glider's speed is high enough that the crosswind component is a smaller percentage of the forward speed, so the crosswind is comparatively irrelevant. As speed slows however, the cross becomes a greater factor. My technique is to ignore the crosswind while ground skimming, then as the glider slows to the flare point it will naturally began to turn into the cross. Allow it to do so. Now, being more windward, your ground speed will diminish and you can flare normally.
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By aeroexperiments
#397690
* Why does the crosswind suddenly affect the glider just because the glider's airspeed has decreased?

* I see this post is from 2009 so never mind...
AIRTHUG wrote:worth mentioning- while the glider is flying, crosswind is pretty much irrelevant.

When you flare and stop the glider (relative to the ground), now the crosswind is effecting the glider. It's typical that, when you flare, your upwind wingtip will drop. You can flare a little asymetrically if you'd like, or just let it drop

[youtube]http://www.youtube.com/watch?v=d16dFOppUFk[/youtube]
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By aeroexperiments
#397691
* Ok this one is from a few hours ago, not 2009-- that's better.

* Rodger, there's no reason that the glider should turn into the wind just because the airspeed is decreasing. Rather, the flight path and ground track should curve downwind, with no change in heading. All this assuming no pilot input.

* On the other hand if the pilot is making steering inputs as needed to stay on a linear ground track, he'll cause the glider to turn upwind-- the heading will change in the upwind direction. Some amount of bank in the upwind direction will be required to make this happen.

* This may be the explanation for an observed tendency for the upwind wing to drop during the flare-- the glider was already slightly banked when the flare was initiated, because the pilot was consciously or unconsciously trying to keep the glider flying along a linear ground track as the airspeed decreased.

* As hang glider pilots we lack the sort of straightforward "gunsight" heading refererence that you have when seated on the centerline of a single-seat or tandem-seating airplane or sailplane, so we are often MUCH more aware of the direction of the ground track than the actual heading of the aircraft. This can cause some confusion as to the fundamental dynamics at play.

* In many cases, keeping the glider flying along a linear ground track is an excellent way to keep the wings level. Not so if we are bleeding off airspeed in a strong crosswind! If we are bleeding off airspeed in a strong crosswind, and we want to keep the wings level, we need to either observe the actual bank angle and make sure it remains zero, or we need to observe the glider's actual heading and keep it constant. Either method will keep the wings level. Either method requires a significantly different control input than would be needed to keep the glider flying along a linear ground track. Either method requires more deliberate attention-- even if less actual control input-- than would be needed to keep the glider flying along a linear ground track.

* The wind gradient can also be important. If the glider descends into a lighter crosswind, the nose ought to tend to swing AWAY from the crosswind, not into the crosswind. If this is not happening, it is probably due to a pilot steering input in the upwind direction, as noted above.

Steve

miraclepieco wrote:An old thread on a subject that always bears repeating.

As one ground skims on final the glider's speed is high enough that the crosswind component is a smaller percentage of the forward speed, so the crosswind is comparatively irrelevant. As speed slows however, the cross becomes a greater factor. My technique is to ignore the crosswind while ground skimming, then as the glider slows to the flare point it will naturally began to turn into the cross. Allow it to do so. Now, being more windward, your ground speed will diminish and you can flare normally.
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By aeroexperiments
#397692
JanB wrote:Of course at the beach we land crosswind all the time. Dropping the downwind wing is bad, dropping the upwind wing is (generally speaking) harmless.
Makes sense-- in smooth coastal air there is often a strong wind gradient near the ground, creating a strong tendency for the glider to roll to a steeper bank angle whenever the wings are not level. (Whichever wing is higher experiences more airspeed and generates more lift.) If I'm going to accidentally slam a wingtip into the ground, I'd much rather it be the upwind wingtip than the downwind wingtip! If the glider comes to rest with the upwind wingtip on the ground, nothing bad is going to happen...

Steve
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By adyr
#397694
Crosswind landing due of terrain, it is sloped on the wind direction:

[youtube]http://www.youtube.com/watch?v=am5w6seglmo[/youtube]

The wind was blowing straight from the right of the landing path. It was not very strong, but strong enough to pose problems when turning the glider after landing.
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By DMarley
#397701
As usual, I believe Jim Rooney has condensed the whole thing down into an easy-to-follow exercise. Keep the wings level, with lots of airspeed before rotation into ground-effect, then keep the wings level.


This is a student with a very slow approach for the conditions in my opinion, but the vid does a good job documenting the cross wind gradient effects.
https://www.youtube.com/watch?v=NbBg3ChfVIs
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By brian scharp
#397703
jimrooney wrote:That wing drop bit is not due to cross wind. It is due to you adjusting to the effects of cross wind.... normally, it's trying (often unconsciously) to fly straight down a path. In simpler terms, you're wings are not level.
aeroexperiments wrote:* This may be the explanation for an observed tendency for the upwind wing to drop during the flare-- the glider was already slightly banked when the flare was initiated, because the pilot was consciously or unconsciously trying to keep the glider flying along a linear ground track as the airspeed decreased.
Bingos. When landing on the beach the wind is pretty much 90 degrees cross where I land. Usually I'd make an effort to land into wind, but there the beach is steep and narrow enough that if you tried there'd be a good chance you'd end up in the surf. I make a final that parallels the beach and stick to it. It's never presented a problem in a variety of wind speeds.
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By Wonder Boy
#397719
The glider doesnt know there is a crosswind until your feet touch the ground....
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By miraclepieco
#397725
aeroexperiments wrote:
* Rodger, there's no reason that the glider should turn into the wind just because the airspeed is decreasing. Rather, the flight path and ground track should curve downwind, with no change in heading. All this assuming no pilot input.
Steve,

Have you never noticed the obvious tendency of a swept-wing hang glider to "weather vane" into the wind? The glider tends to turn more into the wind as its speed diminishes because as the glider slows, the crosswind component becomes a greater percentage of the glider's speed, thus has an increasing affect on its ground track. Much as I loathe Dense Pages, he has covered this topic exhaustively in his publications, mostly as it relates to crosswind launches, but it also is quite pertinent to crosswind landings.
OMG, I can't believe you are sucking me into your eternal vortex of endless theoretical discussions :shock: :surrender: :ahh: :oops: :-o
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By aeroexperiments
#397728
Rodger, I suspect you are wrong about your comments re Pagen. I've noticed some errors he has made but don't recall that one being among them. Can you cite me a specific page?

The thing is, as long as the pilot's feet are off the ground, the glider has no idea what direction the wind is blowing. The "weathervane" effect (which we could also call "yaw stability" or "directional stability" is very real but only pertains to the "felt" / "apparent" / "relative" wind, not the external meteorological wind. The glider knows about changes in apparent wind due to dropping down through a gradient (shear), and also knows about the roll torque exerted by a wind gradient when the glider is banked so that one wing is high in a stronger flow and one wing is low in a weaker flow, but those are both different from knowing the direction the wind is blowing in a more general sense.

When the pilot's feet are off the ground, there is no general tendency to weathervane to point into the external, meteorological wind. Even when the glider is slowing down in the presence of a strong crosswind.

When the pilot is running out a landing, the situation is totally different, as long as he running on surface where his feet exert some traction, rather than on ice. I didn't mean any of my comments to pertain the running-out-a-landing case.

PS-- want to read comments by someone who is absolutely, positively convinced that an aircraft tends to turn DOWNWIND rather than upwind? Read this thread on a model airplane internet page-- http://www.rcgroups.com/forums/showthre ... mass-(wind!) . Things start getting weird around post #12. The specific turning-downwind comments start at post #21 and then see many subsequent posts by same poster.

It takes all kinds...

Steve
miraclepieco wrote:
aeroexperiments wrote:
* Rodger, there's no reason that the glider should turn into the wind just because the airspeed is decreasing. Rather, the flight path and ground track should curve downwind, with no change in heading. All this assuming no pilot input.
Steve,

Have you never noticed the obvious tendency of a swept-wing hang glider to "weather vane" into the wind?

The glider tends to turn more into the wind as its speed diminishes because as the glider slows, the crosswind component becomes a greater percentage of the glider's speed, thus has an increasing affect on its ground track.

Much as I loathe Dense Pages, he has covered this topic exhaustively in his publications, mostly as it relates to crosswind launches, but it also is quite pertinent to crosswind landings.

OMG, I can't believe you are sucking me into your eternal vortex of endless theoretical discussions :surrender:
Last edited by aeroexperiments on Mon Apr 17, 2017 10:02 pm, edited 1 time in total.
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By NMERider
#397729
DMarley wrote:Here is a very nice cross wind landing in perfectly laminar conditions - an onshore breeze. The landing starts at 3:54.
https://www.youtube.com/watch?v=2rjP3xC-DhA
Sadly, 99% of crosswind landings for me and others I've witnessed happen in thermic and turbulent conditions rather than laminar, coastal conditions. This brings with it the risk of ground loops, turtles and assorted glider damage. There is an easy way of negotiating this predicament by coming in with good speed on skim and moon-walking the glider to a controlled stop rather than being suckered into the myth that flaring the glider to a stop is generally a good thing. This doesn't tend to be one of those times.
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By miraclepieco
#397730
aeroexperiments wrote:Rodger, I suspect you are wrong about your comments re Pagen. I've noticed some errors he has made but don't recall that one being among them. Can you cite me a specific page?
I recall the text clearly but don't remember if it was in one of his books or in a magazine article. The subject was crosswind takeoffs and how the cross component becomes less as the pilot's running speed increases (moral: run fast on crosswind takeoffs). Yes, I have caught Dense Pages in blatant cases of conclusion jumping and he has very much lost credibility with me, so I will happily surrender all my old Pagen books and articles to look it up yourself.
aeroexperiments wrote:The thing is, as long as the pilot's feet are off the ground, the glider has no idea what direction the wind is blowing. The "weathervane" effect (which we could also call "yaw stability" or "directional stability" is very real but only pertains to the "felt" / "apparent" / "relative" wind, not the external meteorological wind.


A hang glider "weathervanes" whether it's on the ground or in the air. It's just that when it's on the ground it is more apparent because you can actually FEEL the feedback through your feet and arm muscles. In the air it's more subtle, but the phenomenon is there nonetheless - albeit less because, again, it is a smaller percentage of the glider's overall speed. I suspect it's the same tendency pilots' utilize when they say they allow their glider's nose to "hunt" for thermals.
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By NMERider
#397731
miraclepieco wrote:....A hang glider "weathervanes" whether it's on the ground or in the air. It's just that when it's on the ground it is more apparent because you can actually FEEL the feedback through your feet and arm muscles. In the air it's more subtle, but the phenomenon is there nonetheless - albeit less because, again, it is a smaller percentage of the glider's overall speed. I suspect it's the same tendency pilots' utilize when they say they allow their glider's nose to "hunt" for thermals.
Yaw stability in the air and weather-vaning on the ground are two different things but easily confused. Weather-vaning occur relative to a fixed pivot axis attached to the Earth or other fixed object such as a sailplane canopy. Yaw stability occurs relative to the center of mass of a body in flight. It is entirely possible to have both yaw stability and weather-vaning occur simultaneously around an identical axis but they are distinctly different phenomenon.

Since you mentioned crosswind take-offs and reverse weather-vaning, here is an example from last week: https://youtu.be/Ueq7CDIwUhY
Here, the glider weather-vanes to the right while on the ground then yaws to direction of flight once airborne. The first effect is weather-vaning and the second effect is yaw stability. Similar but different. One happens around the center of mass while the other happens around a fixed pivot point on the Earth.

Capice?