Finding Thermals (Gambler)

[Vito]

I had always figured that flying a DLG over a black parking lot on a hot day was almost sure to find thermals. I just spent several hours at the shore in Georgia flying my Gambler under these conditions and only found weak rising air. A 1 minute flight was rare with a max of just over 90 seconds. I tried:
- waiting for the afternoon sun (~95 degrees) to provide direct sun,
- still air and some breeze
- adjusting my CG with a coin (from the tip of the nose to 1 inch behind the spar) to see if I was missing something.
I also spent a few hours on an open fairway of a golf course. The sand traps were painfully hot but 1:30 was the max flight time.
Any thoughts on what I am doing wrong? Am I looking for thermals in all the wrong places?
The CG bothers me a bit. I set the plane up in the shop to be a bit behind the spar. I will see where it is with the coin the furthest back.
Thoughts would be appreciated
Vito

[dave_beardsley]

few things to remember....

Thermals don't happen just because its hot outside. Its the DIFFERENCE in temp between ground and sky that get things moving, not just a hot afternoon. In fact, you can have a very frustrating day of thermaling at 4:00pm on a 90+ degree day, of the night time temp only drops 20-30 degrees, and the air has been stagnant for a while. By 4:00pm on a day like that, the air will be very flat…. Lame but true.

Around my area, I find the max thermal activity between about 10:00 am and 2:00 pm. After 2:00, the ground and sky temps start to even out a bit, and the thermal cycle is MUCH longer. Each location is a bit different. In hot dry area’s thermals will still cycle frequently later in the afternoon.

One of the reasons Estrella Sailport (in Az) (http://www.azsoaring.com/) is so popular among full scale guys is because of the huge temp swings between night and day. In that desert climate night temps will drop 30+ each night

Don’t fly over anything wet (like freshly water lawns). A good idea is to find a dark colored field, or a black parking lot, next to green grass. Head out about 10:00ish, get things trimmed out and ready to go, except to see big thermals kicking off by 11:30-12:00.

Its also helpful to fly near something that will easily blow in the wind, like long tall grass, lightweight tree limbs etc. As the thermals pass by, these objects will literally "point" to the thermal as the cool air gets pulled into the thermal. You can use these ground signs to help learn where the thermal is.

Look for tiny birds circling low(ish) they are eating bugs that get sucked up in thermals.

If you suspect the thermal cycle is working, use your stop watch to time the intervals between thermals blowing through the area. If the cycle is ~5 min, you'll know when to launch....

Best thing you can do...
Get the "old buzzard goes soaring" book, and order Paul’s video - here
http://www.radiocarbonart.com/Pages/asecthermalmain.html

hope this helps -

[Vito]

Dave,
That does help. I guess I proved what you already knew. I remember reading somewhere that thermals tend to break off new obstructions like trees and hedgerows. I tried that and didn't find more thermals but risked a climb to retrieve my plane. I suspect that the whole area was baked in the sun and there was minimal difference to spawn thermals. I also suspect that my lame launches kept the plane below them.
Thanks
Vito

[John Gallagher]

There are days when there is a layer of stable air at ground level. This inversion level may be a couple of hundred feet high.

http://www.newton.dep.anl.gov/newton/askasci/1993/general/GEN021.HTM
http://en.wikipedia.org/wiki/Thermal_inversion

[Thermalin]

I also have a gambler and experienced the same thing the other day... hot hot hot but only weak thermals.. enough to basically maintain altitude... On other days I can catch rising air blindfolded..... "yeah it's hard.. it's the hard that makes it great... if it was easy.. everybody would be doing it... (tom hanks).
Mike

[jester1a]

Vito,
Weren't you the one that also invested in a slingshot? How did you fare with it?
I see you went with a Gambler- a good choice.

JESTER

[Daemon]

A hot parking lot is not always the best place to look for thermals
although it may trigger them when they form elsewhere.
Yes it creates a strong heat differential between air near the ground
and above it, but it's almost too much. The air gets so hot so fast,
that it just rises immediately in small unuseable pops, like throwing water
on a frying pan.
A thermal needs some organization and horizontal inflow. You need the air
near the ground to be heated evenly and a little less quickly. That warm
air will start to rise naturally, but usually it doesn't form a
useable thermal until it moves horizontally into something that disrupts its
flow like a building, treeline, or some other trigger like a road.
The trigger will cause what was fairly slowly rising air to start rising
more quickly, and as it does, it'll start pulling in the other warm air
horizontally at its base and this creates an organized thermal column,
which you can detect by the change in horizontal direction of
the wind at ground level. The thermal column shuts off when the
horizontal inflow exhausts the supply of warm air, but you may still
be able to catch the bubble of rising air up high.

So what you're looking for, for instance, would be a dry dirt/grass
field, and downwind of it, a row of trees, or a road or the parking lot
you started with. When the warm air from that field drifts
downwind into any of those triggers, that's where you might
expect to find the thermal. One place I've been very successful with
my DLG works like this.. A dry field. Downwind is a treeline.
Crosswind is a street, and on the other side of the street, a supermarket
building with rock covered roof, and on the other side of that
the parking lot. I usually catch the thermals somewhere over the field
or near the trees (sometimes able to slope the treeline waiting for a thermal
to arrive), and then I'll range out upwind and crosswind often catching more
thermals over the supermarket and above a nearby 4 way intersection.
With a 14.5oz DLG I've had several 35-40 minute flights there.
Unfortunately they constructed a huge new building in the middle of
the field a while back, and I haven't flown there recently to see how
that building has affected the wind and thermals.

BTW, an inversion does not mean that there isn't low level
thermal activity. Quite the contrary. It just means that somewhere
above you is warm air that'll cause warm air from the ground to stop
rising eventually. A typical summer day here starts with an inversion
with low level cool air from the night before, below warm air from the
day before. Warm air from the ground rises all day long filling the space
below the inversion cap until somewhere middle of the afternoon there's
enough hot air below the inversion that some of it finally pushes through
and you see clouds start forming very quickly, and if there's
enough stored energy they may turn into thunderstorms. For the
most part you can't have thunderstorms without starting the day
with an inversion. The trick is to get out at the right time of day
when the cap has risen or is about to break and you'll find some
great lift.

ian

[Vito]

Jester,
Yup I bought a Slingshot. I have had several problems getting it flying and it seemed to suffer some on landing. The removable nosecone and the internals would breakup on landing. It also got a crease in the wing from what seemed like a pretty minor drop from a tree. If I kept trying to learn with it, nothing would be left in short order. It is much heavier than the Gambler and I figured that I better learn something that is more robust. Its hard to figure that the open bay balsa plan is more durable, but it is. I recently reinforced the nosecone and the inner supports on the Slingshot and it is waiting for me to get skills or courage to try again.
As far as thermals go, I seem to do better over a bean field on a windy day that in south Georgia on a hot cloudless day. Not what I expected, but it makes sense.
Vito

[jester1a]

I was very disappointed myself. Mine folded at the top of a launch with only nosecone/ servo mount damage previously. Jochen said it was almost impossible but there you are! Alan is MUCH better to deal with and supports his Gambler+ almost to excess ( a good thing). The Gambler+ should teach you about low level thermals nicely- if you suspect you are on the side of one ( one wing rising), get back there with an efficient turn and give it a few circles. If you are holding altitude or rising, continue- thermals near the ground are very light and , IMHO, strengthen as they go higher. I've struggled at 5-20 ft for minutes and then started rising easily many times. At least this is working for me.

JESTER

[Vito]

Jester,
I mentioned the height thing in my original post. I got the sense that if I could get more height on the launch, I would be better off. I found an elevated tee on a golf course that was closed for maintenance. It probably added 30 feet to my launch and that was when I got the 90 second flight. Lots of fluttering and hopping but it stayed up there. If the wind reversed, I could have sloped there.
I am back in the northeast and just got back from flying my Lil Bird off a high start. It is so much easier to stay aloft when you start at 300 feet. I will be flinging the Gambler over the weekend and think the cut wheatfields will provide better thermals than that Georgia heat. Its easier on me too.
Vito

[carrinsr]

Gentlemen;

For what it's worth, I fly R/C sailplanes via winch launch only, and for thermal duration only...nothing more, nothing less -- so far. I've been at it for about 30 years now. So let me share a few things I've learned from this, here in Northeastern Florida.

Check the weather report for high pressure/low pressure and predominant wind direction and speed where you intend to fly. Check your regional weather conditions as close in time to your actual flying time as possible.

If you're near the center of a high pressure area, just go play golf. It has been my experience that thermals are far greater in number in low pressure areas. If the wind will be in excess of 15 mph, just go bowling. Winds above 15 mph means thermals will be hard to stay in, and difficult to gain any appreciable altitude in. At least that's the way it appears here in NE FL.

If these two conditions do not exist, then besides the obvious things to watch when you're ready to launch (such as tall grass/bugs/birds, etc.), pay attention to wind direction. I'll explain why next.

Think of thermals as small tornados with a lot *repeat* lot less intensity...smaller at or near ground level and getting larger with altitude. Depending on wind speed they do bend with the wind, with the smaller area part of the thermal (at or near ground level) being the further most up wind part of the thermal. For instance, in a five mile per hour wind with you standing in the center of the thermal, the wind may become calm where you are standing, and the rest of the thermal will be down wind from you...the higher in altitude the further down wind.

For instance: a) If the wind is normally blowing steadily from East to West and you're standing in calm air, then you're most likely standing in the center of the lowest part of the thermal, and the rest of the thermal will be to your West. b) If the wind is normally blowing steadily from East to West and the wind has shifted from North to South, then a thermal will almost always be to your South. In other words, wind which suddenly blows contrary to the direction of prevailing winds is probably being drawn into a thermal, and therefore the wind is blowing in the direction of the thermal.

Thermals generally assist in the building of cloud formations, particularly clumulus clouds, even at night, and contrary to what many believed for decades, even over open water. They're even stronger at night, but there are fewer of them. However, I don't fly RC sailplanes at night anyway. So..... (o:

If you've found a thermal and then you lose it, do two things. 1) If the thermal was down wind from you, put the wind directly to your back. 2) The thermal you lost (unless it was just a bubble and not a real thermal) is probably rising toward the base of a cloud that is building. So put your sailplane directly in line between where you are on the ground and the nearest cloud where you were last in the thermal. Unless you already have lots of altitude don't try to find it by zig zaging away from you, but instead zig zag toward you. No sense in getting so far down wind you lose a sailplane! NOT worth it! Land safely so you can launch again!

Finally, don't be AFRAID of altitude. That's what will keep you flying from one cloud or thermal to the next, for great time aloft! Personally speaking, I expect to fly for at least an hour every time I find my first thermal, and I would (and almost always could) fly longer except for my concern for battery drainage. No joke! But just remember, the smaller your sailplane becomes in your field of vision the greater the importance of NOT taking your eyes off it! You may be SURPRISED how just a little glance away can cause you to lose it! I cannot stress this point enough!

Happy Soaring!

David