Whacks and micro-conditions in xc fields

[Flying Lobster]

Reading the thread on Dan's experience at the Pulpit has got me thinking about conditions we encounter while landing out in fields.

Since I've started training with the Blue Sky "low and slow" scooter method 4 years ago I've had the opportunity to get more familiar with ground level and just above ground level wind phenomenon by virtue of the many hundreds of tows I've done throughout the day. I end up training at fields which might be similar to what we encounter on a typical xc, and most of my tows are for hundreds of feet across a field at altitudes of 10 to 50 feet agl except when a pilot is getting near their H2. Having a glider on a line and pulling it along gives a very good visual as well as pressure/feel indicator of what's going on in the air very close to the ground.

I've developed a couple of theories which you may find useful as "food for thought." Or you may discard them as ravings of a lunatic, if you wish.

I used to think that landing in high winds was the most challenging conditions to land in--but I now believe that light and variable days are really the most challenging and potentially dangerous. On these kinds of days, a sudden and dramatic shift in local surface wind direction can happen without much visual warning by a sudden shift or inflow/outflow of air in the lz air. This could be due to the passing of a thermal--but I think there are other subtle wind conditions besides thermals that can create these kinds of shifts. I've reached this conclusion after frequently observing wind direction indications along the length of a tow that consistently show differences of 90 degrees or more along the length of the tow.

I think these kinds of shifts can happen with even minor shifts in temperature and topography--in other words, eddies of air masses that move laterally in much the same way that thermals get triggered to move vertically off the surface. The presence of high pressure, relatively stable surface to boundary layer air mass seems to enhance this probability.

The obvious question is how to detect and avoid in those few seconds while setting up an approach. The short answer--I dunno! : ) But I think it might help to get an idea of the surrounding topography and set up for an area with the highest probability of consistent direction--or at the very least avoid getting in a downwind/outflow, especially if it's going downhill or in the direction of a treeline, fence etc. In particular, I think fields with gentle rolling terrain, and surrounded by areas of potential heating/cooling sinks are the types of fields that are most prone to these "microflows." The highest part of a field may be the best to land in--but it can also be subject to sudden changes in wind due to an outflow in the area below it--especially if there are lower areas surrounding the high ground. Perhaps diving with speed into a lower or "mid-level" contour might be best as this is the area where most likely cooler air will consistently be flowing into. It might be wise to consider doing this into an uphill even if the wind indicators higher up on approach might show a different prevailing wind direction.

Hopefully this will "trigger" some discussion and observations by more experienced xc pilots.

marc

[RedBaron]

I'm not an XC pilot. I'm not very experienced. But I made the observation that only a very few pilots truly know how to textbook land a glider, and I do not include myself in that short list. Obviously it's unavoidable sometimes to land in a challenging field or in challenging conditions after an XC flight. Obviously there's no sure way to tell when and where the wind direction in the LZ will change 180 degrees. IMO, only perfect landing skills and wheels are somehwat effective in dealing with nasty slopes and switchy winds.

[Matthew]

Wow! This topic came up years ago when people started going XC from Ridgely. And I think it was Fred Permenter who made the same point as Marc. On light wind days there is more of a tendency for the winds to shift around seemingly at random. I know I've landed downwind going XC at Ridgely when moments before the wind was 180 degrees opposite. Wheels saved my ass both times. Both Karen and Paul Tjaden broke an arm landing downwind on L&V days. Karen had wheels but high grass negated them. Don't remember the particulars about Paul.

So for what it's worth-- wheels help.

And as Janni said, practice your landings. The next time you're at the tow park, throw in a couple of pattern tows or truck tow to practice landing.

And when the grass is high in the middle of the Summer, go XC in your paraglider instead of your hang glider. High grass isn't as much of an issue. And if you can run fast, a minor tail wind is easily handled.

Matthew

[Flying Lobster]

The only pilot I know with perfect landings is one that never flies!

marc

[Danny Brotto]

Those "micro" air currents exist even on stronger days. It's just that they are over ridden by the prevailing wings. So a 5 mph tail wind on a L&V day becomes a 5 mph headwind into a 10 mph prevailing wind day.

Danny Brotto

[Kurt Hirrlinger]

Because I don't waste a lot of time soaring all over creation like you guys,
I get more practice @ launch & arrest. That's the ticket.

[Paul Tjaden]

Marc is absolutely right regarding the dangers of flying in L and V conditions. I would much rather land in winds bordering on the high side of safe. If it's cranking, just keep your speed way up all the way to a few feet above the ground so that you slice through any gradient and have good control. Obviously, you should try to stay well downwind of any obstacles or tree lines, too.

I'll not attempt to second guess Marc or anyone else regarding what micro meteorology causes the wind direction changes but we all know it happens and it's not just a problem with XC. Nearly all of my flying is flatland flying and even if I go XC, I usually fly triangles or out and backs and end up back at Quest if I'm lucky. On L and V days my stomach starts twitching as soon as I arrive back at the field and start watching the wind sock as it casually swings to and fro, sometimes hanging like it is in severe need of viagra and other times looking like an oversexed teenager. I guess it's good to have a windsock but it has screwed me so many times by switching at the last second that I almost wish it was not there. I don't have much advice as to how to deal with this problem with the possible exception of trying not to land while a thermal is close by. If you know a thermal is working in the area, try to wait until it is downwind of your intended landing area. Thermals pull in air from around them and that should serve to increase your head wind rather than cancel it out.

Regarding my broken humerus caused by a bad landing on an XC out of Ridgely: Winds were not strong that day but they were probably strong enough to override most micro meteorology. I'm certain a strong thermal was kicking off near the SE edge of the field I landed in due to the way the grass was being blown around. I tried to hook it but was unable due to my low altitude so I headed up wind, away from the turbulence, to land. My ground speed didn't seem extreme so I don't think I was down wind but I got slammed into the ground unexpectedly before I could flare. Maybe I was just too close to the thermal that was kicking off and I got dumped out the edge? Maybe my landing skills weren't up to snuff? I HAVE worked on them with Kevin since then and I still wish they were better. I did have wheels but they were those skinny "hot wheels" and the ground was soft so they didn't help at all.

Paul

[Danny Brotto]

or tumbling around?

The traditional model of a thermal releasing is that it sucks air from all around. We've all seen that happen when multiple streamers around a field all point from oposite directions. The more compeling model is the wind "packet" that tumbles across a field around and around like a tumbleweed. Larry Tudor described this in HG mag about 10 years ago. This is being discussed in a thread on the Oz Report forum. Encountering one of these tumbleweed air gusts could drive a hapless pilot into the ground.

Danny Brotto

[RedBaron]

Provided your landing field is not a swamp and without obstacles, and you do have wheels deserving of their names, I'd suggest treating every midday summer landing as an emergency landing expecting the worst possible outcome, i.e. a broken femur or two. I find staying prone until you eat dirt safer than going upright after turn onto final. It A) allows you to fly as fast with as much control as possible and if B) ground effect yet again proves to be but a theory your glider will take the impact rather than your legs and arms. Lot's of horizontal speed will decrease the force of the impact. If it turns out you worried over nothing you can still transition and flare or run it out or gently belly it in.

[Flying Lobster]

Provided your landing field is not a swamp and without obstacles, and you do have wheels deserving of their names, I'd suggest treating every midday summer landing as an emergency landing expecting the worst possible outcome, i.e. a broken femur or two. I find staying prone until you eat dirt safer than going upright after turn onto final. It A) allows you to fly as fast with as much control as possible and if B) ground effect yet again proves to be but a theory your glider will take the impact rather than your legs and arms. Lot's of horizontal speed will decrease the force of the impact. If it turns out you worried over nothing you can still transition and flare or run it out or gently belly it in.

Hmmm...how does increased speed decrease impact force? You sure about that?

marc

[Flying Lobster]

... other times looking like an oversexed teenager. I guess it's good to have a windsock but it has screwed me so many times by switching at the last second that I almost wish it was not there. ...
Paul

You mean the windsock was pointing straight up into the air? Now THAT must of been one heck of a thermal! I've also heard Quest has one of the few radio-controlled windsocks around

Seriously--ever notice how the hotshots down there like to squeeze it in by doing final over the lake and between the pool and hangers? And they seem to always pull it off. Makes ya wonder, eh?

marc

[Flying Lobster]

or tumbling around?

The traditional model of a thermal releasing is that it sucks air from all around. We've all seen that happen when multiple streamers around a field all point from oposite directions. The more compeling model is the wind "packet" that tumbles across a field around and around like a tumbleweed. Larry Tudor described this in HG mag about 10 years ago. This is being discussed in a thread on the Oz Report forum. Encountering one of these tumbleweed air gusts could drive a hapless pilot into the ground.

Danny Brotto

I had a discussion with LT at the time about that whack--he made it sound like no matter how good you think you are there are "ground dragons" out there that can punch your ticket unexpectedly. In particular, he mentioned that even a huge flat field with no obvious obstructions to create mechanical turbulence can still yield one of these "turbo-tumbleweeds."

The phenomenon I observe at the field I train at isn't so much a sudden, temporary shift--which I would guess is more likely associated with a thermal passing or other parcel of temporary turbulence, but rather a fairly consistent difference in wind flow over a very small area in the same lz.

marc

[Dan T]

It's very refreshing to see a reasoned discussion, respectful of the opinions of others on here. It would be nice to see some of the consistently good landers weigh in on the subject. How do they do it?

They ones I see consistently make good landings burn it in, then flair with enough retained energy to permit the glider come up and stop itself. Wish I could do that consistently. Kevin Carter's description several months back is the best flair timing advice I've heard. I recall that it is essentially fly the approach fast, let the glider slow down without dropping once it is in the 2 foot or so ground effect, then flair promptly once it is no longer possible to keep the glider from sinking.

One thing I'm pretty sure of, more speed means more momentum. I believe more momentum means more inertia, i.e. more resistance to changes in velocity resulting from the influence of a given amount of outside impulse force. That would seem to improve the chances that we could absorb a very short duration impulse force without getting knocked akilter.

Any other takes on it?

Dan T

[Flying Lobster]

Respectful? We'll have to fix that.

Your mama uses weaklinks!

marc

[Kurt Hirrlinger]

I like to use most of the speed my Falcon has and staying prone til ground effect @ 4-5 feet. I also like manly wheels, although in some situations they act like brakes. By the way, I weaklinked your mamma last night.

[mcgowantk]

I think this is a great discussion too.

However, I have to say that I don't think I have ever landed with a tail wind when flying XC. I have experienced my share of poor landings, but generally my poor landings start with poor approaches, causing me to be too low and slow on approach, causing difficultly in balancing the wings when low on final, and then not being ready to flare with enough energy to stop the glider. I don't remember ever seeing or having a bad landing after a strong flare. So good approaches and strong flares can correct for a lot. I believe with a no-step flare, a 3-5 mph tail wind can be handled by running it out.

Regarding wind direction, I spend a lot of time watching ground wind indicators while flying XC. Those indicators help locate thermals, are a good source of info on the weather patterns, and help when I am landing. Like everyone else, I look for what ever wind indicators are around and try to land as near as possible to them to minimize surprises. That being said, I often correct my landing direction on final by 15-30 degrees to account for the apparent wind direction. I have even done 180 degree turns to head back into the wind when I felt the wind was from the opposite direction than I anticipated. And winds do shift around during the day. For example, at the ECC’s this year, the wind in my LZ came from every direction of the compass during the hour I was there; however, it was strongest and most often in the prevailing direction. On another flight at the Pulpit a few weeks ago, I adjusted my landing direction by 90 degrees while on final because there was a 10-15 mph south wind, not the nw wind that I saw aloft. Having the ability to adjust your final into the wind and pull off a strong flare arises from doing good approaches and landing toward the middle of large fields where you have the ability to start your final with lots of altitude and change directions while on final.

One thing I keep experiencing is rotors off tree lines, etc. I need to remember more often to land in the middle of the field or as far downwind of the tree as possible to minimize turbulence, even though that means walking a bit farther after landing. Finding a field where you can land uphill is a bonus. I would never intentionally land downhill. If things go that bad I would try very desperately to land cross wind. I have trouble judging the steepness of LZs from the air. If it looked slightly downhill, it could be too down hill to be landable.

Although I suppose there are dragons out there that would make anybody crash, I believe those conditions occur pretty infrequently. In my experience, my poor landings have usually had an obvious cause. I would focus on developing the skills necessary to routinely have strong flares and adopting approach techniques that provide you with options to deal with wind shifts that become apparent while on final.

Tom McGowan

[Flying Lobster]

Very good points Tom, especially the whole set-up approach quality and leaving one's self room for change on final.

I have to admit I've been nailed more than once by ending up going downwind VERY fast and low on final, I certainly need to work on my approach assessments and downwind technique.

marc

[deveil]

It's very refreshing to see a reasoned discussion, respectful of the opinions of others on here. It would be nice to see. . .
Dan T

the post by "mcgowantk" in the 'day at cumberland' thread was also gold, in many regards - IMHO

sincerely,
the 'peanut gallery'

[deveil]

- after a case of getting turned while on low approach to High Rock LZ, I took instruction and rebuilt my landing approach technique.
Key points:
* SPEED, SPEED, SPEED - remember there's a big wind gradient down in that hole - so "AIRSPEED, AIRSPEED, AIRSPEED" - forget about groundspeed (easy to say, hard to do)
*keep both hands on the control bar even though your legs are out of the harness and you are "upright" - all the way into ground effect
* then transition to downtubes, minimizing the inevitable pop-up as you lose pitch authority
* wait for speed to decay, testing with slight pitchups
* if you think it might be time to flare - IT'S TIME TO FLARE - do not delay further
* have your hands up on the downtubes at the level of your ears and throw a huge one (UP/not out)** as quickly and decisively as you can
* quick and decisive ** will limit the amount of pop-up - but if you do, hold the flair and use your shock absorbers (knees)
- Hugh

**(my emphasis)

Turbulent landing position? . . . One hand up on down tube and one hand down on base tube when you transition. Stay there until well into ground effect and almost ready to flare. Keeps you from popping up the nose when transitioning.
Matthew

with matthew's emphasis (the more upright position also gives more drag when you need it), that which hugh did a good job of articulating pretty much nails it. (IMHO)

[deveil]

. . . bills hill, young gal working on her H-II, glider (newly repaired i think was the situation) with the hang point Extremely forward - such that when the bar was in the "neutral" position (no bar pressure) the glider was flying screaming fast - discovered when an experienced pilot (king newman, same weight) test flew it later (it scared the pants off him also).
she did a sled ride that probably set a record for time from launch to lz (treetop the whole way). anyhow, screaming in on final (scared to death, i might add), she threw a Textbook, Kick-butt flare at that thing and, i swear, we watched that glider travel 50 ft. with it's nose pointed straight up and it never climbed an inch! it was as if she was riding a drogue shute to a perfect two pointer. that image always stuck with me - reinforced for me the effectiveness of a well executed flair.
(well, two cents doesn't buy you what it used to does it )

[markc]

One thing I keep experiencing is rotors off tree lines, etc.
Tom McGowan

Just to add another experience to this thread, although it relates to
a primary rather than an XC landing field....

I've flown in some fairly strong conditions at Woodstock in the past
couple years. On two occasions when winds were strong enough out of
the WSW/SW that I've elected to land across the crest of the LZ
(rather than the usual uphill final), my landings were far less than pretty.

For both, I did S-turns over the north treeline, followed by a turn onto
final at about 1.5X-tree height.

On the more recent, I dropped out of the sky like a rock, did a
touch-and-go off the wheels (winter, the ground was frozen), pulled in,
and then bellied-in. It happened FAST. I went from maybe 50' over the
ground to wheel-touch in... 2 seconds? Fast enough that I can't be sure
of the details, wish I had video.

Maybe it was plain-and-simple gradient, and I was flying too slow for
the conditions. Yup, could be.

But I've landed in high-gradient conditions before, and *usually* I can
tell what's going on as I fly through it. "You damn well better pull in
right now butthead!".

There was no such moment on that flight though, just "Ground, meet
Mark; Mark, meet ground." Really lucky to have gotten out of that one
with no damage to glider or self.

Although my post is off-topic of the original, just wanted to remind
people to treat upwind treelines in strong conditions with the utmost
respect! Keep that speed up... And even if you do, be prepared for a
wild ride.

And of course, remember that choosing to fly in strong conditions means
that you could be assuming a higher level of risk (though it depends
on the exact nature of the launch, your chosen LZ, gust factor, etc etc).

MarkC

[bustedwing2]

I believe with a no-step flare, a 3-5 mph tail wind can be handled by running it out.Copied from the thread,I'm perplexed,how does one run out a no-step flare? RichB

[Ashley Groves]

Pretty Good Topic, I'll throw my 2 cents worth in even though people are sick of the topic.

Take time to set up and plan out an approach. Part of the planning is a brief thought of various options and outs (can I turn left, can I turn Right) as you may want to refine your plan as things proceed. I tend to pick a "spot" for spot landing, but I often adjust my spot, sometimes several times during a landing. Sometimes, when face with RLF, you have limited spot adjustments and I will do more to keep a spot.

I am much happier when I pick a good landing spot that leaves me with a long walk than with a bad landing spot that leaves me a short walk.

I find (for me) the most common problem on landing is pilot mentality. If you believe you will crash, you will be right, you will crash, no matter how benign the conditions. (alas, if only the opposite were true). I have had an X-C landing where I get it into my head that I am coming in down wind, pile into a giant flat field, only to discover I was going into the wind the whole time. I have seen similar examples with other pilots.

*For X-C I will often take an uphill if I can.
*Also pick open areas with lots of outs if possible.
*Avoid upwind rotor (It can extend quite a distance) if possible.

Example: Once, I flew X-C and came into a new field. As I was dropping into ground effect it became apparent the field was not level as I had thought but sloped downhill and there were trees and barbed wire at the far side. I turned cross wind/ cross slope. I tried to make a shallow banked curve, but alas I dragged a wing tip. I did an ungainly ground loop, but no equipment or bodily harm. Initially I was pissed, but later reflection I decided that was a pretty good outcome for the possibilities.

Example: My last landing was X-C. I set up my approach like an idiot. I picked a spot with a shorter walk, but limited run out space and obstacles, (but plenty big enough to land in).

As I came in my landing field was eaten away quicker than I had planned. (Some thermal lift came in at the last minute, kept me bouyant, sent me down wind, and stupidly I left my VG on to boot). I was hesitant to make heavy swooping S turns due to obstacles. I came in, and flared hard. Being down wind with VG, I ran hard and had a fairly gentle whack (yes, you can land downwind, just flare hard and run), but I had less than ten feet to the trees from where I stopped. It definitely could have been far worse, but there was no reason why I couldn't have had a nice landing, or at least a whack in a more open area with less risk.

"You can't prevent everything, but you can prevent most things." would be my summation.

[deveil]

I believe with a no-step flare, a 3-5 mph tail wind can be handled by running it out.Copied from the thread,I'm perplexed,how does one run out a no-step flare? RichB

i guess the point would be: if one decided to go hunt barr, one would get himself a darn good barr rifle, probably a good side arm, a sturdy knife, a well thought out plan-B, be very familiar and well practiced with them all, talk to all the barr hunters he could find, and maybe take a few barr wrestling lessons. then 'play it by ear' - depending on the mood of the barr.

or, as stated in another fashion:

. . . I've landed in high-gradient conditions before, and *usually* I can tell what's going on as I fly through it. "You damn well better pull in right now butthead!".

There was no such moment on that flight though, just "Ground, meet
Mark; Mark, meet ground." Really lucky to have gotten out of that one
with no damage to glider or self.

. . . just wanted to remind people to treat upwind treelines in strong conditions with the utmost respect! Keep that speed up... And even if you do, be prepared for a wild ride.

[RedBaron]

Landing a hang glider kinda sucks, doesn't it?