Free flighters use a number of methods to locate thermals - a fresh haircut, sensitive skin on the back of the leg, cat-tail fluff, dust in the air - and, some folks claim they can even 'see' a thermal.
The use of soap bubbles is particularly effective, and it will only cost you about $1.00 to try it out. A small bottle of bubble stuff even comes with a 'bubble wand'. What you are looking for is upward moving air. If the bubbles just drift around or fall to the ground, wait a while and try again. You will learn to judge the strength of the lift by how fast the bubbles rise. Sometimes one can see the bubbles spiraling up very quickly.
Toy stores offer hand-cranked bubble 'machines' fairly often, and some of these machines can be electrified with a small motor and some leftover gears from a clock or a toy. Here's one I made some years ago:
As this is written in December, 2002, Radio Shack has released a bubble machine as part of their 'party equipment' line. The stock number is 42-3081 and the retail price is US $29.95. It runs on 2 AA cells, or an included AC adapter.
Here's a copy of the drawing that comes with the machine - note that the wheel of rings rotates through a bubble fluid reservoir, with a fan blowing through each ring in turn to make bubbles.
And here's a picture of the Radio Shack bubble machine in action:
Super bubble stuff
Mix up this 'Super bubble stuff' to use with a toy-store bubble wand or a 'bubble
machine' sometimes found in toy stores.
1. 1/3 Joy - 2/3 water
2. Mix Joy/water half and half with Mickey Mouse or Snoopy bubble fluid. (Brand name of toy store bubble fluid is not important.)
3. Add glycerine: 1 cup/gallon; 8 oz/64 oz; ratio of one to eight.
The resulting bubbles will be very tough - bubbles made from this mix have been found lying on the ground 1/2 mile from their origin. When you think there might be a thermal, make some bubbles. If there's lift, the bubbles will rise. At times, you may see the bubbles spiral upward in the core of the thermal. If you're launching a Hand Launched Glider (HLG), get downwind 50' or so for launch.
[formula is from: the late Toni White (Mrs. Bob White); about 1970]
New Information About Super Bubble Stuff
[from tests in January '03]
Here's an exchange of emails - Tom Curphey was confused by the glycerine proportions noted above - because there are 128 ounces in a gallon!
From: email@example.com (Tom Curphey)
In a message dated 1/3/03 8:52:27 AM US Mountain Standard Time,
<< Any idea which is the correct proportions for the glycerine to J/w/S mix?
Well, you see, you've just figured out why they don't trust me in the kitchen!
I'd suggest a small-quantity test. Just get one of the small bottles of bubble stuff - that's 'maybe' 8 ounces? Anyhow - mix up a 1 to 16 batch and try it out. In the quiet of one's home, bubbles made with glycerine exhibit
the properties we're after - toughness and longevity, and they tend to get bigger than straight bubble fluid. They also exhibit a really strange phenonmenon. Slowly blow a bubble [use the wand from the small bottle] about
6" across. As it floats around, poke it with pencil or finger. The bubbles I've blown this way make a sound as they pop - and then, if you watch carefully, the skin stuff collapses away from the hole, collects on the opposite side - and falls to the floor! If you get this result, then 1 to 16 is OK, If not, then try the stronger mix.
Let me know how this works out for you - I can post your results with the formula. BTW - does your Radio Shack machine seem to want to blow bubbles 30-40 deg away from straight out? Mine does. Have only tried this one with> the fluid that came with it - and, it may work differently outside.
Many thanks for your reply and pardon my delay in answering. It took me awhile to round up the time and materials to do the necessary "scientific" study, but here are the results, for what they are worth.
First off, I noticed the same two things you did with the Radio Shack machine. The bubbles came out sideways and there were a certain proportion of misfires, i.e. a wand went by the fan, but no bubbles emerged (you mentioned this on the FFML, as I recall). These preliminary experiments were conducted with the fluid which came with the machine. However, I think this fluid is garbage. It seemed to work OK the first time I tried it, but the second time (New Years Eve, of course!), the percent of misfires rose to close to 100%. I was concerned that the machine was defective, but subsequent experience suggests that the fluid was bad. The only explanation I can come up with is that it might have been due to the fact that I recycled the fluid from the first try and possibly this contaminated the lot, maybe from plasticizers leached out from the unit during the first trial.
Anyway, I made a trip to my local Walmart, that purveyor to the modeling trade, and procured a bottle of "Mr. Bubbles" in the "Super Economy Size". With a bottle of Joy from the supermarket and glycerine from the
lab (I am an organic chemist), I locked the door to my lab to prevent embarassing interruptions, and ran the experiments. Some of the observations are somewhat subjective, but I did try to use as an objective measure the time it took for the machine to produce 10 misfires. Here are the results:
1. Water/Joy in a 2:1 ratio (by volume) produced 10 misfires in 9 seconds, which is close to 100% misfires, essentially useless.
2. Water/Joy/glycerine, prepared using 8 volumes of the 2:1 water/Joy to 1 volume of glycerine. I wanted to see what effect the glycerine might have. The numerical results were actually a bit worse than the straight water/Joy combination, with 10 misfires in 8 seconds, but the difference is probably well within experimental error.
3. Mr Bubbles, straight up. A very nice stream of bubbles with about 80 seconds required for 10 misfires.
4. Mr. Bubbles/glycerine in an 8:1 (by volume) ratio. Still curious about the glycerine. The results were about the same as straight Mr. Bubbles, or possibly slightly worse, with 10 misfires in 73 seconds.
5. Mr. Bubbles/water/Joy in a 3:2:1 ratio (by volume). This is the recipe you recommended, but without the glycerine. The results were quite dramatic! Almost no misfires. I gave up when, after 4 min operation, I had counted only three or four misfires, and those seemed to occur mostly at the beginning of the run.
6. The 3:2:1 Mr. Bubbles/water/Joy combination mixed 8:1 with glycerine, which is your recipe. This was even better then the mixture without the glycerine. The number of misfires was lower, although measurement was a bit difficult because of the low frequency. What surprised me more was that the bubbles formed from this mixture definitely traveled further before bursting than the combination without glycerine. Some of them made it almost all the way across the lab before hitting the floor and bursting. The only explanation I can come
up with for this, is that the weight of bubble film per volume of bubble must be less with the glycerine than without it. The bubbles are therefore "lighter" and so travel further before reaching the floor.
Why glycerine would have this effect, I cannot figure out, but it does seem to be the case.
7. The same as in 6, but with the glycerine reduced to 16:1. Not too surprisingly, this mixture was intermediate between the 8:1 combination and the stuff without glycerine, showing a low percent of misfires, but not quite the range of the 8:1 combination.
The grand conclusion is that the recipe you gave, assuming an 8:1 glycerine ratio rather than a 16:1 ratio, is the best of the combinations tried. One big disappointment though, was that I could not reproduce the phenomina you mentioned concerning the collapsing bubbles. Even with the best 8:1 combination, I did not hear a pop and
the films burst too fast for me to see the retraction you mentioned.
One other observation was that with a good bubble mixture, the bubbles seemed to emerge more nearly straight out from the machine. I suspect
this is because the bubbles were larger, stayed on the wands longer, and therefore were swept fully across the fan area before coming loose.
I guess I can unlock the door now!