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Thermal generating

PostPosted: Sat Mar 17, 2012 10:26 am
by terryJm
Don't try this withought recovery altitude. The low pressure area generated behind and above our wing may be focused into a vortex by a tight 360 app 60 degree bank, leading to an updraft in the center of our turn radii drawing ambiant air from below, possibly creating an artificial lift zone when there are no thermals to take advantage of. I'm welcoming ideas leading to improvement in soaring potential. More later, Terry

Re: Thermal generating

PostPosted: Tue Mar 20, 2012 1:22 pm
by Bob Kuczewski

An artificial thermal trigger ... at altitude!!

Re: Thermal generating

PostPosted: Wed Mar 28, 2012 12:31 pm
by Bill Cummings
Steve Moyes was once quoted as saying, “I just keep circling until I make a thermal.”
This response was to the question about whether or not he sold his soul to the devil to find thermals so low.
Most everyone was sure it was a tongue in cheek statement. --- Not me.

Crop dusters dive at a crop field and make the first pass without releasing their spray to break off any thermals that would carry away their spray --(They know what their doing.)

Sailplane pilots dive at the ground to break off thermals to ascend in. (They know what their doing.)

Several times when low I have tried to start a thermal up by circling above a small knoll (trigger point) in a tilled field as I was sinking out. Far more times than not I got back up and continued on my way. I usually wound up eventually having to turn the other way and circle once I was high enough to safely make the maneuver and not fall out of the thermal. That way I would be turning against the rotation of the thermal.

By the way if you spend one summer flying over the flat fields in central Washington state where almost all thermals are marked with the fine talc like dust that is everywhere in that area you will be convinced that the hemispheric rule has nothing to do with the direction a thermal turns.
Just as many turn counter clockwise as turn clockwise.

I’ve flown there over ten different summers and I took note of the direction that thermals turn and it is a fact beyond any reasonable doubt that the hemispheric rule holds little to no sway over the rotational direction of something as small as a dust devil.

I once watched a pilot sink out and land on the flat farm (dirt) field after he had crossed the Columbia River. He had launched from Chelan Butte, WA.
As he flared a right wing tip vortex turned into a dust devil that saved me from landing with him.

While going cross county following Hwy 2 east toward Spokane, WA I have seen many dust devils start from the back of traveling 18 wheelers.

During the 1985 and again in 1995 Nationals my wife would see me get low and she would drive with the vans right wheels in the loose field dirt and raise the fine powdered dust to mark thermals that saved the flight. (possibly creating thermals too.)

During the Nationals I would hear pilots radio their chase vehicles and ask which way the wind was blowing. :wtf:
I would think, hey dummy were drifting east isn’t that enough for you to make up your mind? :crazy:
Then the driver would stop check and radio back that the wind was out of the south. Until that moment I thought the pilot was just trying to make the driver feel important and boost their ego.

This was my aahaa :idea: :o moment. If the wind was out of the south the thermal was north of the chase vehicle. (Gee but I can be slow learner at times! :roll: )

If you run across a list of pilots that believe that they can trigger a thermal low by circling over a trigger point, put me on that list with them! :thumbup:
PS (Edit) At altitude: Dynamite, Railroad flares over dry grass are two that come to mind.

Re: Thermal generating

PostPosted: Fri Apr 06, 2012 12:33 pm
by Bill Cummings ... 42&bih=612

In my post above I misspoke/mistyped. The phrase I should have used would be Coriolis Effect. Not the hemispheric rule. :oops: :roll: :shh: :wave:

Re: Thermal generating

PostPosted: Sat Apr 07, 2012 9:05 am
by terryJm
Another trick I've learned is that the core of the thermal, having more velocity, is also at a lower pressure, so that if you have enough bank angle it will center the kite in the core. Just like the tennis ball is centered in the air stream of a pressure hose, I'm estimating a 45 degree bank angle or more for this to be effective. Very weak thermals will require flat yawing turns at very low speed, just above stall, only smooth air with out any turbulence may be worked in this way. Please do not experiment new tech. in a gaggle or at too low an altitude. New ideas in altitude gain are appreciated here. Later, Terry

Re: Thermal generating

PostPosted: Mon Apr 09, 2012 12:28 pm
by Bill Cummings
Terry, and Hawks,
Having a good deal of flying from boat towing and later flying over the wheat fields of Washington State this is what I have noticed that many other pilots may not yet have made this same discovery.

When a thermal, dust devil, leaves a bare field of dirt and enters a wheat field many times the thermal will not pick up enough dust to continue to mark itself.

The foot print of the thermal can be tracked, or seen, by following the lighter shade of wheat as the thermal swirls it’s way downwind. It looks like a bright spotlight moving and swirling across the wheat field.

Just the opposite happens when a thermal moves out over a body of water. The foot print of the thermal looks darker than the surrounding water. This dark wind print over water can be seen from many thousands of feet above whereas leaves fluttering as the thermal moves across the top of a grove of trees cannot be seen from much more than about a thousand feet above.

For new pilots trying to enter these thermals, that can be seen leaving a footprint on the ground, I tell them to lead the thermal to the downwind side. If they ask me, by how much they should lead the thermal to intersect it I tell them this:
Stand up and move one of your hands about a foot away from your leg. That is the angle to be downwind of the thermals foot print on the ground. Strong wind days it will of course need a greater angle. This is just a starting reference point for them.

Just like putting some “English” (spin) on a ping pong ball, tennis ball, or baseball a person can make the path of the ball curve or tack off of the direction the ball was thrown. (Oh yes, you can be seated and finish reading now.)

The same thing happens as a spinning thermal is being blown downwind.

The thermal will not blow straight downwind but tack off to the left or the right of the winds course line depending on the thermals rotation (spin/“English”).
This will also make the thermal lean to the left or right as it tacks its way slightly off of the downwind course line.

So If you are flying downwind to the next thermal and the foot print or dust near the ground gives you an indication of which way the thermal is rotating, clockwise or counter clockwise, this will tell you which way left or right of the footprint you need to fly to intersect the leaning invisible thermal at your altitude.

Darn it! ---- :oops: I’ve got to get out more! :? I used to know which way to search for the thermal above its footprint as it moved downwind depending on its rotation and now I can’t remember! :oops: :oops:
I guess you will have to sort this out yourselves.
Let’s see now ---if a ping pong ball has right “English” on it and it curves left---then a thermal blowing down wind would go------???? :?:
Darn it!
Oh well! It was a lot of fun back when I figured it out for myself so I wouldn’t want to spoil the fun for everyone else.

Re: Thermal generating

PostPosted: Mon Apr 09, 2012 12:31 pm
by miguel
Back when I was a young pup, I tried this technique. High bank angles made the trees get bigger more quickly than low bank angles. I came up with a name for this technique. I called it corkscrew to the ground. I learned early on not to do this.

Re: Thermal generating

PostPosted: Mon Apr 09, 2012 5:56 pm
by Bill Cummings
Terry I agree with you.
It is my opinion that the air moving up at the core of the thermal is moving upward around two/thirds faster than the air inside and close to the edge of the thermal.

It is further my opinion that the writer that told of the force of the air increasing in a logarithmic fashion when the air speed increases each unit of measurement, as in, going from 2mph to 4mph the lifting force isn’t simply doubled it is quadrupled, I believe this author is correct.

It is my experience that dry, desert, high pressure, days make very small diameter thermals than those I have experienced in Florida, Minnesota, or other areas with higher relative humidity. The humid thermals in Minnesota and Florida get big and I can boat around with big flat turns. Here in New Mexico I advocate doing a 12 second 360 degree turn which gives about a 60 degree bank angle just to keep from falling out of most the thermal.

I’ve watched Jonathon Dietch (sp?) in his videos at Youtube: NMERider, doing 10 second, three hundred and sixty degree turns, out on the west coast.

10 and 12 second 360 degree turns is what I mean when I say stand it on the wingtip and auger up through the middle of all the flat turning riff raff.

Of course at higher altitudes in New Mexico I am able to make bigger circles and not fall out of the thermal.

I used to believe and fly like all the sailplane books said to fly but an article in HG years ago had a story in it that so much as said that was hog wash and to bank it up and beam out. I tried it and have stayed with that style of thermaling ever since.

If you haven’t tried it, the next time you are circling in a good thermal and doing well try moving in closer to the core with tighter turns. There is most often a much better climb rate banked up to 60 degrees than doing flat turns that take twenty five to thirty seconds to do one complete turn.

Of course the ACP (Ace Comp. Pilots) will tell you, “big flat turns” just like they use to tell me that you never, never want to fly over a dust devil. (A.C.P. S.O.B.’s)

Maybe someone has an idea I haven’t tried yet and I’m still learning and willing to give anything a try to get high. (Now knock that off. I don’t mean that kind of high. :angel: )

Re: Thermal generating

PostPosted: Tue Apr 10, 2012 12:42 pm
by terryJm
Miguel, I've had that problem also, however; due to my timid push out, I wasn't making efficient turns. Current instruction tech does not address coordinated bank angle turns. Just leaning left produces a left turn, pushing out aggressively coordinates the turn to stop the downward spiral, producing an efficient, high banked turn. Air speed in this turn is greater, and must be maintained to prevent stalling the inner wing. Our sink rate will be greater than level flight, but the thermal moving up will more than compensate. The sky is vast, with much to be aware of, I'm only beginning to learn how little I know. The spiral dive is the fastest way to loose altitude when you need too, Hoolies & Wangs are also effective at getting on the ground. Enough for now, some of you experts are welcome to offer tips if you're not too proud! Later, Terry

Re: Thermal generating

PostPosted: Mon Apr 16, 2012 8:31 am
by terryJm
Thanks Bill, for you'r detailed description on visualising thermal activity, most other pilots arn't seeing these clues, or looking for them. They seem to think my ideas are too incredable to be usefull, However, I've seen thermals of different colors depending on the source. It is still easy to be surprised by the invisable ones, and go over the falls on the back side. Sometimes a 270 will get me back in after loosing one and a reversal might catch it, but most often there is another in reach. Your posts have been the most informative, and incourageing further discussion on the fascinating subject of soaring! Later, Terry