Still-air turbulence

[Tim Wescott]

Lately I've been getting a lot of opportunities lately to fly in cold, dry, still air.  Today conditions were bad enough that we were hitting turbulence two or three laps after finishing a maneuver, and stepping backwards while maneuvering was mandatory, not optional.

I notice that, for me at least, I have much more problems with turbulence in the round maneuvers rather than the square ones.  This could just be because I'm still not hitting my corners in exactly the same places every time, or it could be because I'm too busy cornering to notice the wingwazzles the plane makes in turbulence -- I'm wondering if this is your experience also.

Given just how bad things were today, I'm also wondering what (other than still air, obviously) makes for the worst still-air turbulence -- does it seem to be worst at low density altitudes (low, cold, dry), high density altitudes (high, hot & wet), or does it just go with the deadest air being the worst?

[RknRusty]

Now y'all have me worried about dead calm air, though I can remember only one day in the past year that was all that calm. I suppose I should practice staying out of my wake just in case it ever happens. That one day when it was calm, I had to do more back peddling than usual to keep my inept Shoestring tight. To make matters worse, I was pretty inept at the time too. Just having moved up from 1/2A, I was accustomed to being wary of the wind. Now I have learned that the wind can be my friend.

Rusty

[Steve Helmick]

When there is essentially no wind, there can still be thermal activity, even in freezing cold & calm conditions. Where there's a "thermal" (updraft), there's at least one "downdraft". The "infill" and "outflow" is light, but can come at you from all directions, even from the "downwind" direction. You may think you're backing away from the turbulence, but it can follow you, if the thermal's infill is making it come your direction. Maybe that's what happened to Tim? Happened to me at NW CL Regionals in 2011. Yes, it's exciting! Isn't that why we do this? 

Howard and Keith Varley put out "thermal poles" like it's a FF contest. Very often, the streamers point 90* apart, sometimes more, or point at eachother from opposite sides of the circle! That makes things really interesting. It's also why Paul and Howard fly fairly fast. It's what you gotta do when the turbulence is bad. Doing it all the time helps with your timing. That is, if you don't run short of reflexes at a bad moment. Rusty, definitely be cautious in calm conditions, 'cause wake turbulence can be very much like flying into a vacuum.  Steve   

[Tim Wescott]

Maybe that's what happened to Tim?

On Tuesday we were pretty much reliably whacking into turbulence right where it had happened before.  It was cold, with heavy clouds, and barely any discernible wind.  There were a few times when you could discern some drift, either on the back of your neck or in your buddy's exhaust cloud, but we were still whacking into turbulence right where the last maneuver was.

There were several times for both of us that the plane was jinking in the turbulence on the first or second lap after a series of maneuvers.

I've had that happen to me before, in isolated cases, and I've had considerable "dead air" flights in the last month or so.  Tuesday was the first time that I've spent an entire morning flying totally dead air.

[tom brightbill]

Steve, maybe you can help with this-
What Tim and I were wondering about was of possibly due to the density of the air, 30* and foggy overhead, that the turbulence was greater and/or not dissipating as it does on warmer days. Maybe there's no more to it than that?
Thanks,
Tom
(The other c/l guy near Oregon City)

[Steve Helmick]

Steve, maybe you can help with this-
What Tim and I were wondering about was of possibly due to the density of the air, 30* and foggy overhead, that the turbulence was greater and/or not dissipating as it does on warmer days. Maybe there's no more to it than that?
Thanks,
Tom
(The other c/l guy near Oregon City)

Just as a guess, the denser the air, the longer the patch of turbulence would rotate around? I've noticed the same thing, and recall just this Autumn hitting wake turbulence in level flight, where no trick had been done on any previous lap. One could speculate that this turbulence was from some other cause, but it didn't seem likely at the time. Quite possibly, that patch of turbulence migrated from where a trick had been done. A ball of evil air, if you will. This is a good time to adjourn the meeting, to await a better day. 

Strange stuff does happen. You being a glider flier, Tom...one time a bunch of us F1A & F1B guys met at Harts Lake Prairie and flew for a German Postal contest. We agreed to fly one at a time, so no piggybacking. One plane in the air at a time. We also agreed that we'd fly in hour long rounds, tho we didn't have to do either. We had, as I recall, four flying F1A's and two flying F1B's, so 6 flights...a lot in an hour. Turned out that we all flew in one thermal. For two consecutive rounds...same thermal. If I remember right, it was a nice Autumn day, and retrieves were about 100'-200' or less.  A very extraordinary experience. We placed very high, if we didn't win it outright.

I've previously mentioned flying F1A at the Sierra Eagles' field near Rancho Cordova, CA. This one day, up to about 50', the wind was blowing one direction, rather gently, but above 50', the wind was blowing 180* opposite and quite a bit stronger. My solution was to start towing 'upwind', sprint to get the glider up to full line length, and reverse field, trying to keep it above 50' as I circle towed and searched for lift.  I wish I could remember if that was '79 or '81. Freaky! It would have been very ugly to fly stunt in that situation.  Steve

[RknRusty]

Steve, maybe you can help with this-
What Tim and I were wondering about was of possibly due to the density of the air, 30* and foggy overhead, that the turbulence was greater and/or not dissipating as it does on warmer days. Maybe there's no more to it than that?
Thanks,
Tom
(The other c/l guy near Oregon City)

On warmer days I expect there are more convection currents moving the air around, even if there is otherwise no wind.
Rusty