The up and down sides of rotors relative to ridges

[son_of_flubber]

Mulling over a wave flight from last October and realized that I'd gotten it into my head (perhaps erroneously) that the up (lift) side of rotor is usually closer to the upwind ridge than the down side (sink) of the rotor. So for example, if I persist in heading closer towards the slope/ridge while in the downside of rotor, that I have a good chance of hitting the up side (lift) of the rotor. In other words, the sink side of the rotor is farther away from the upwind ridge than the lift side.

Now I realize that this situation is chaotic, anything can happen, and that before AGL gets tight, I'd better turn away from the slope and use the tailwind to hastily penetrate the sink that I just flew through and try for the secondary rotor, downwind ridge lift, or land.

But what about my assumption that the lift side of the rotor is generally found between the sink side of the rotor and the upwind ridge? Or does this depend on the particular ridge and the particular day?

And what about a downwind ridge? I've got it into my head that the sink side of the rotor is between the lift side of the rotor and the downwind ridge. There may be a band of ridge lift between the sink side of the rotor and the downwind ridge. Are rules of thumb possible/useful or is this just my limited experience on my local ridges?

[Dan Marotta]

Let's play a game of imagination and visualization.

Start with the upwind ridge on the left side of a piece of paper.
Looking into the paper is like looking to the north. The ridge is on
the west side of the paper and the wind is blowing from left to right.
As the air flows over the ridge top it sinks and then rebounds upward as
the rising air of the primary wave. Visualize it as a sinusoid. The
rotor is under this wave. The left side of the rotor (west) is
generally up while the right side of the rotor (east) is generally
down. If you have the altitude AGL you can generally climb on the
upwind side of the rotor and will get into the smooth laminar lift.
Another ridge downwind can either boost or kill the wave further
downwind. It depends upon wavelength and wind speed.

Personally, I would not penetrate upwind towards the leeward side of a
ridge in high winds hoping to get into the up side of a rotor.

YMMV

On 4/7/2016 6:26 PM, son_of_flubber wrote:
> Mulling over a wave flight from last October and realized that I'd gotten it into my head (perhaps erroneously) that the up (lift) side of rotor is usually closer to the upwind ridge than the down side (sink) of the rotor. So for example, if I persist in heading closer towards the slope/ridge while in the downside of rotor, that I have a good chance of hitting the up side (lift) of the rotor. In other words, the sink side of the rotor is farther away from the upwind ridge than the lift side.
>
> Now I realize that this situation is chaotic, anything can happen, and that before AGL gets tight, I'd better turn away from the slope and use the tailwind to hastily penetrate the sink that I just flew through and try for the secondary rotor, downwind ridge lift, or land.
>
> But what about my assumption that the lift side of the rotor is generally found between the sink side of the rotor and the upwind ridge? Or does this depend on the particular ridge and the particular day?
>
> And what about a downwind ridge? I've got it into my head that the sink side of the rotor is between the lift side of the rotor and the downwind ridge. There may be a band of ridge lift between the sink side of the rotor and the downwind ridge. Are rules of thumb possible/useful or is this just my limited experience on my local ridges?
>

--
Dan, 5J

[BobW]

On 4/7/2016 6:26 PM, son_of_flubber wrote:
> Mulling over a wave flight from last October and realized that I'd gotten
> it into my head (perhaps erroneously) that the up (lift) side of rotor is
> usually closer to the upwind ridge than the down side (sink) of the rotor.
> So for example, if I persist in heading closer towards the slope/ridge
> while in the downside of rotor, that I have a good chance of hitting the up
> side (lift) of the rotor. In other words, the sink side of the rotor is
> farther away from the upwind ridge than the lift side.

That's certainly true along the Front Range of the Rockies in the Boulder, CO,
area.

Atmospheric waves can only exist downwind of the obstruction generating
them...though (IMO) their relationship to geography beneath and downwind of
the generating obstruction doesn't lend itself to accurate, simple,
declarative statements. Atmospheric dynamics along "the Boulder part" of the
Front Range are such that only once did I ever attempt (unsuccessfully; my
wallet gave out) or even need to tow directly into a wave; every other time
has come via thermalling, sometimes in what seemed to be "aligned thermic lift
bands" paralleling the suspected/sometimes-visible wave, other times using
what was unarguably rotor.

<Snip...>
> But what about my assumption that the lift side of the rotor is generally
> found between the sink side of the rotor and the upwind ridge? Or does
> this depend on the particular ridge and the particular day?

I'll be surprised (shocked?) if anyone can point to a rotor that ever lies
UPwind of the wave-generating geographic feature, if that's what you're
wondering about, though that's not to say "your wave" is the first along the
wind's streamlines. If there's genyoowine rotor upwind of "your wave
generating feature" it's coming from another, upstream, feature. FWIW, in the
absence of an upstream wave, don't assume the lower level winds on the upwind
side of the wave-generating feature will be "ridge-lift smooth"...reality
always rules!

>
> And what about a downwind ridge? I've got it into my head that the sink
> side of the rotor is between the lift side of the rotor and the downwind
> ridge. There may be a band of ridge lift between the sink side of the rotor
> and the downwind ridge. Are rules of thumb possible/useful or is this just
> my limited experience on my local ridges?
>

I'm all ears on this question!

Bob W.

[son_of_flubber]

Hoping to clarify, my upwind Ridge A generates the primary. My downwind ridge Ridge B is downwind of Ridge A (and lower in altitude). Secondary wave lift and rotor forms upwind of Ridge B. Oftentimes, ridge lift between the rotor and the ridge.

[son_of_flubber]

On Thursday, April 7, 2016 at 8:56:48 PM UTC-4, BobW wrote:
> On 4/7/2016 6:26 PM, son_of_flubber wrote:
....
> > But what about my assumption that the lift side of the rotor is generally
> > found between the sink side of the rotor and the upwind ridge? Or does
> > this depend on the particular ridge and the particular day?
>
> I'll be surprised (shocked?) if anyone can point to a rotor that ever lies
> UPwind of the wave-generating geographic feature, if that's what you're
> wondering about,...

No. I'm only talking about rotor that is formed downwind of the wave-generating topographic feature (aka Ridge A).

My thinking is that for a wind blowing towards the east, the top of the rotor is also blowing east and the bottom of the rotor is blowing west, so the lift side of the rotor is to the west of the sink side. This is idealized because if the feature causing the wave is convoluted and irregular, all sorts of chaotic interactions can result in unpredictable patterns.

[[email protected]]

S of F, as for other locations I can't comment but for the sierra generated orimary wave, yes your assumptions hold true. As a starving college student who wanted to fly wave as much as possible, I could not affort high tows into the wave so on numerous occasions I would "thermal" the "upwind" rising side of rotor to work my wave into wave. After succeeding a few times I got pretty good at working rotor into wave in the minden nv system.

It always made for an incredably rough ride. The rising portion of the rotor was very small and there were many times what I gained in the few moments of lift, was cancelled out by associated sink. I can remember one time working for more than an hour barely gaining on each gust untill I finaly worked high enough to contact laminar flow. But a poor boy will always find a way. I hope this helps.
Dan

[BobW]

On 4/7/2016 7:54 PM, son_of_flubber wrote:
> On Thursday, April 7, 2016 at 8:56:48 PM UTC-4, BobW wrote:
>> On 4/7/2016 6:26 PM, son_of_flubber wrote:
> ...
>>> But what about my assumption that the lift side of the rotor is
>>> generally found between the sink side of the rotor and the upwind
>>> ridge? Or does this depend on the particular ridge and the particular
>>> day?
>>
>> I'll be surprised (shocked?) if anyone can point to a rotor that ever
>> lies UPwind of the wave-generating geographic feature, if that's what
>> you're wondering about,...
>
> No. I'm only talking about rotor that is formed downwind of the
> wave-generating topographic feature (aka Ridge A).
>
> My thinking is that for a wind blowing towards the east, the top of the
> rotor is also blowing east and the bottom of the rotor is blowing west, so
> the lift side of the rotor is to the west of the sink side. This is
> idealized because if the feature causing the wave is convoluted and
> irregular, all sorts of chaotic interactions can result in unpredictable
> patterns.
>

I may still not be fully understanding what you're puzzling over, but...yes,
rotors revolve with their "top" moving in the same direction of the overall
prevailing stream flow, their "bottom" moving against the large-scale stream
flow, their "back edge" (relative to the prevailing stream flow) moving down
toward the ground, and their "front edge" (relative to the prevailing stream
flow) moving up. Rotor "organization" in my experience is useful more as a
mental concept than as PIC-reality, though - situation/geography permitting -
if you believe yourself in rotor and averaging the wrong direction (i.e.
toward the ground below), moving upwind, against the overall stream flow is
often a useful tactic in striving to change "averagely down" to "averagely
up." In the Boulder, CO, region, some days that was a practical proposition,
others "surely you jest!"

Bob W.

[Jim White[_3_]]

At 00:56 08 April 2016, BobW wrote:
If there's genyoowine rotor upwind of "your wave
>generating feature" it's coming from another, upstream, feature.

If you sail close in to a headland in tidal waters you could well find
eddies in front of the headland. Sort of 'under' the general flow.

Flying a ridge over a quarry filled with water in high winds I have seen
'cats paws' banging on the water. This is surely a rotor effect upwind of
the ridge just like the eddies seen above. I would not, however want to try
to soar on them!

Jim

[Dan Marotta]

The downwind ridge can generate a wave of its own. What I tried to say
earlier is that this second wave (not to be confused with a secondary
peak off of the first wave) can either reinforce or cancel the upwind
wave with the result being either much stronger downwind of the second
ridge or little to nothing at all. There have been books written on
this. A good example is Mark Palmer's "Practical Wave Flying".

On 4/7/2016 7:39 PM, son_of_flubber wrote:
> Hoping to clarify, my upwind Ridge A generates the primary. My downwind ridge Ridge B is downwind of Ridge A (and lower in altitude). Secondary wave lift and rotor forms upwind of Ridge B. Oftentimes, ridge lift between the rotor and the ridge.

--
Dan, 5J

[Dan Marotta]

My thinking is that for a wind blowing towards the east, the top of the
rotor is also blowing east and the bottom of the rotor is blowing west,
so the lift side of the rotor is to the west of the sink side. This is
idealized because if the feature causing the wave is convoluted and
irregular, all sorts of chaotic interactions can result in unpredictable
patterns.
That's right, and I don't think it can be predicted, hence my original
position that I would not penetrate upwind looking for the up side of
the rotor unless I had plenty of altitude AGL and a place to bail out
(figuratively). I have personally worked rotor up into wave an several
occasions, but I've always had at least 5K' AGL when I did it. This is
the nature of western flying.
--
Dan, 5J

[Michael Opitz]

At 16:40 08 April 2016, Dan Marotta wrote:
>My thinking is that for a wind blowing towards the east, the top of
the
>rotor is also blowing east and the bottom of the rotor is blowing
west,
>so the lift side of the rotor is to the west of the sink side. This is
>idealized because if the feature causing the wave is convoluted
and
>irregular, all sorts of chaotic interactions can result in
unpredictable
>patterns.
>That's right, and I don't think it can be predicted, hence my
original
>position that I would not penetrate upwind looking for the up side
of
>the rotor unless I had plenty of altitude AGL and a place to bail out
>(figuratively). I have personally worked rotor up into wave an
several
>occasions, but I've always had at least 5K' AGL when I did it. This
is
>the nature of western flying.
>--
>Dan, 5J
>
I think Dan is right in the fact that there are a lot of variables which
will affect the issue. Mt. Washington in NH is set up similar to what
SOF describes. A high mountain in the west, a sharp V shaped
valley with the Wildcat ski area (lower mountain top) just to the
east. Oct 8, 1966 was the first day of modern wave exploration
there. Four of us got our Diamond altitudes that day. We didn't
know a whole lot about wave, and we operated from the North
Conway airport 23 miles to the south. Alan MacNichol towed us 23
miles through the continuous rotor of the Moat Mountains to get to
Pinkham Notch right in the middle of the valley. We were at about
4200' MSL which was ~2K' below the top of Mt Washington, and
about 2K' AGL. With the L-19 in a 45 left bank, and my 1-26 going
45 right, (both with full opposite control inputs), I released because
there was no other option. I was lucky. After turning right 270
degrees with full controls against, I finally came into the wind and
leveled out. The vario was pegged at over 1500 fpm up, and I was
spit upwards into the wave, where I cut the climb off at 24K' due to
airspace limits at the time. I landed after 1.5 hours and briefed a
fellow club member who had just showed up with his Ka-6. He
experienced the same tow, but was in heavy sink on release. He
dove for the Wildcat ridge thinking it would work. It didn't. The
rotor was going down-slope there. He wound up thrown into the
trees while trying to land in the ski area parking lot. Luckily, he
walked away, but I had to go get the Ka-6 pieces out of the woods
that afternoon. I think that wind speed and atmospheric conditions
will make the size / strength / location of the rotor vary, and that
will directly affect if the downwind ridge is working or not. I, for
one, would not bank on it working.....IMHO.....FWIW.....

[[email protected]]

Sometimes the rotor goes all the way down to the ground. I was leading a regional at Sugarbush, VT years ago when I arrived back 10 minutes early on a turn area task. The ridge was working OK so, like a chump--er, champion--I continued another few miles to the next turn.

Unfortunately the turn was out in front of the ridge, which--at that point--was stepped, with a lower front ridge and a higher back ridge. Out I went into the valley upwind a few miles to tag the turn (my second big mistake). On way back, it was obvious I would not have enough altitude to safely get to the back ridge with a margin to escape the high valley between the two ridges if the sink I was in didn't abate. No matter, I rolled in over the front ridge and turned north.

More sink! And rough. I must not be close enough. I slid in tighter to the slope. It was really rough now but I was still going down. I could see the leaves being thrashed wildly on the slope. Wind. It MUST be going up! Nope.

By this point I was sinking below ridgetop height and getting pretty upset with the theory of ridge lift, the unfairness of life, and the prospect of going from 1st to last place in one flight. I flew around the corner where the front ridge turned into the main ridge hoping desperately that the different angle might produce different results. No way. Eventually (actually, very quickly) I picked a good field.

Nearby was Kai Gertsen, with his extraordinary skills. When we finally regrouped, we agreed we'd fallen victim to rotor from the upwind mountain. The ridge had been working as I flew south so I hadn't known or worried about it. But the minute I came off that higher back ridge, I was in sink and turbulence and it went literally into the trees on the lower front ridge. Lesson learned. Yes, we were two of the only non-finishers. And, no, it didn't help that I wasn't the only one. :)

Chip Bearden