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RC Gliders, Sailplanes and Slope Soaring Discuss rc gliders,rc sailplanes and slope soaring in this forum. Thermaling techniques, airfoils, tips, etc

First thermal?

Old 01-04-2011, 06:51 PM
  #26  
hound46
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Default RE: First thermal?

Great thread. I'll be rereading it several times. Very informative. We have a ton of buzzards at our flying field. When they come back, I'll have to go share some of their airspace!
Old 01-05-2011, 11:25 AM
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Default RE: First thermal?



It's nice to see that what I wrote is still being appreciated. Thanks to all for the compliments.

Soaring birds are certainly one very valid sign. And there's others. Flocks of swallows or other normally surface skimming birds rising up in a "dogfight" ball of birds that are slashing this way and that in arcs and sudden reversals are hunting for insects that were lifted up in a rising bubble. Get your glider over top of them and you're almost certain to go up. If the dogfight is at low altitude be prepared to circle on a wingtip as the thermal may still be very small. As the model and the birds climb in the thermal you'll find that the birds will open up their group and so can you. And don't be surprised if your model scares them away at some point.

If the conditions are forming BIG thermals that only come by occasionally then it pays to watch the direction of the wind if you have flags or such a bit upwind of you. A shift from "normal" over to the side indicates that lift is to that side and the intake at the base of the thermal is pulling the air that way. Or if you see a flag go limp then there's a thermal just upwind of the flag that is drawing air in and thus killing the local wind speed just in the path of the thermal.

For handlaunch or discus launch you need to be aware of things much more close in. Free flight competitions allow the use of a thermal poles. These are 20'ish foot long extension poles that have a half inchribbon of ultra light silvered mylar about 15 feet long attached to them. The mylar is so light that it faithfully follows the air around it. It'll blow to the sides or even upwind and greatly aid in locating thermals that are coming towards you if mounted about 100 feet upwind of your launch location. Other more natural "sensors" are to watch the air for passing insects or fluff and seeds. If you see them begin to rise well enough then you found a ground level thermal that hasn't broken away yet. Another free flight trick is to harvest some cat tails. Get them when "ripe" and brown and just before they are ready to explode. Wrap then tightly in double layers of newspaper and twist the ends to keep them tight. Allow to dry for a few months. To use them tear off the paper to expose a small portion of the seeds. Tease them with a finger and blow the fluff up into the air. Watch what they do. When you're first learning to follow the signs just follow the fluff around and don't worry too much about flying. But really the time honored way is to just feel the wind for speed and shifts. If you do this with the aid of some cattail fluffies at first and FEEL the wind while using the fluffies as a test of your feelings you can soon develop a feel for what is happening over and around you out to around 100 to 150 feet.

As for climbing with a powered glider as mentioned by vhq2? A few years back with low powered brush motor systems that didn't climb all that fast it was easy. Fly into the wind at an angle that provided a good climb rate. If the wind was up and the model wasn't making enough ground speed to get well upwind reduce the climb angle so that the model reached the desired altitude at around200 to 300 yards upwind of the launch point. The idea being to get the model out horizontally far enoughto where you can see changes in vertical speed while still being in close enough that you can still see the wings bobble while searching for your lift. The low power outputs of those old motors made doing this pretty much the only way that worked.

But with access to a host of cheap and powerful brushless motors that have made it possible for every glider to climb verticallly like a hot liner I don't doubt that lots of pilots are forgetting that the optimum place to be hunting for lift is well upwind so that you can follow the lift longer before getting too far downwind and have to return.

Now in the case of some limited motor run contests you HAVE to climb like mad. But I, for one, find it extremely difficult to hunt for lift when the model is in a narrow cone of air right over my head. The perspective issues make it all but impossible to see if the model is going up or down. So that means you need to punch up, shut off, then transition to level and push upwind at least a short ways so you can see what is going on. But flying upwind means losing some altitude. Some testing would be needed but I suspect that climbing into the wind at more of a 50 to 60 degree angle to make ground upwind while climbing may well result in a better situation. The actual altitude at shut off might not be as high but the model is out in front where you can see thermal effects more easiy and right away.

As for sport flying I feel there's a lot to be gained by putting in a smaller motor or throttling back and climbing at more of a 30 to 45 degree angle into the wind. Now this climb can be done at a high speed if the model will withstand it or a lower power motor and smaller pack can be used to give a sporty but not insane speed in the climb for more delicate models. The goal though is the same in all cases. To arrive at your hunting station upwind and at a height that leaves you looking upwards at a 30 to 40 degree angle and that has the model just close enough to see the wings bobble. As you get better obviously you can move further out. Or on a calm day you may want to keep it back in a little more. And of course following shutoff you'd go into your S pattern hunt mode mentioned in my first post.

Keep in mind that I'm not saying that you SHOULDN'T put in a powerful motor system. Just that if you're out for a day of soaring that you don't NEED to climb like a Saturn rocket ALL the time. Instead the idea of throttling back a hair and power up to your hunting station at a slightly more moderate speed that won't flutter the wings should be in your flying vocabulary. Or if it's a hot liner that won't flutter then sure, pedal to the metal and shoot up and upwind at the angle like a bullet. The point is that "over there" is where you want to be for hunting and not right overhead.


Oh, and one last thing. If you're using a bird of prey as your thermal finder watch the bugger for a moment. I've been sucked in twice by birds that were shopping for dinner. They were circling and figure 8'ing in a way that seemed like they were catching a ride when in reality they had radar lock on something in the grass below. I no sooner got over in the same air than they shot for the ground and came up with a mouse in their claws. Of course that left me out in left field with no lift....But that's all just part of the fun

Old 01-05-2011, 11:33 AM
  #28  
vh2q
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Default RE: First thermal?

Well since my name came up I have a related question. I did put a brushless in my Eclipse and now it climbs like a banshee as our resident expert states above. But the power seems to cut in and out (the esc goes cherp cherp) as I am climbing away. I am using a standard FM 72 Tx and Rx ... is this signal glitching because the on board antenna is pointing straight back at me? Or is there something else going on?
Old 01-05-2011, 12:15 PM
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Default RE: First thermal?

Sorry to butt in, but that's most likely what you suspect. Why don't you simply try different antenna directions (tx antenna as well), then you would know for sure?

BMatthews, may I add something to electric gliders? You know I'm weird, I'm still flying my old "brushed" glider with NiCd battery from 2002 because it's still great. It's just not a primitive can motor with a small propeller, but a geared Neodym motor with a big folding prop. Overall efficiency is more than 50%!

My point is that I do just what you describe, climb out upwind for hunting thermals, but the rest might be different. When I crashed my first electric glider in a tree because I followed a bird of prey (which was up and away before I was aware that the thermal had gone) I realized that it might be a bit dumb (just not birdbrained) to let the model go down near the ground where thermals are small and hard to find. At least it seemed to me that the birds of prey stay at some altitude flapping their wings in search for the next thermal. I tried it and it worked well. (Here you may laugh.) (As well as the visual line separation I use to observe since then to avoid trees.)

While I get only 6 minutes of power-on (climb) time from the flight battery at full power (climb), it will be 15 minutes (and more) of floating at level altitude with minimum power. Since my flying site is rather confined I can bridge the time between several thermals drifting across the field and have flights of one hour and much more (what my neck can't stand, though).

Another point: The modern (and cheap) outrunners are still not that efficient (due to still too much rpm), but of course they are much better than the old cheap can motor drives. On the other hand, a true progress is the modern 2.4 radio with back channel. Finally it's affordable to have a variometer in the glider. Even circling overhead you'll notice a thermal, but that's still useless since you don't see the airplane's attitude and can't really control it. The benefit is noticeing the many flimsy (in addition to the few strong) thermals and using them to keep the glider aloft. There were even some cases when birds of prey used my glider as an indicator of thermals.
Old 01-06-2011, 12:18 PM
  #30  
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Default RE: First thermal?

Vh2q, I concur with Ustik's advice on re-orienting the antenna. Start simple and hold your transmitter such that you are not pointing the end of it at the model. That may be all you need to kill the glitches. The signal off a straight whip antenna is a donut shape called a toroid. It generates the strongest signal in a plane that is 90 degrees to the axis of the antenna. So the best signal at the plane will be when you point the whip 90 degrees away. The actual direction doesn't matter so much as the 90 degrees. But to keep it simple at first try pointing the back side of the Tx at the model. And if you are standing near to any chain link fencing or other big metal bearing structures try moving well away from them.

Ustik, I concur with all your thoughts about flying. Including the need for good judgement and restraint when flying low and around obstructions. Better safe than sorry. And yeah, it's great to have the safety net of the motor to just climb back up and scoot over things like trees.

I'm not so much in agreement about the motors though. But maybe for different reasons than you stated. Yes, brushed motors were efficient from a watts in to watts out standpoint. And they got better when the rare earth magnets came in. But the brushes were always a weak point that contributed to the effective resistance and limited the amount of power that could be fed to the motor. And then there was the WEIGHT!The new stuff has such a better power to weight ratio that it's almost silly. Old to new comparisons of motors of the same peak continuous power show that brushless motors are anywhere from 1/2 to 1/3 the weight of the equivalent brushed motor.

My best hot windbrushed05 stylebuggy motor with rare earth magnets was capable of around 30 amps on 7.2 volts before it would self destruct. Mind you at that power level it had a rather short brush life. The motor weighed a solid7 oz. And more like 8.5 with the gear box on it to let me turn a 10 inch prop. I can geta brushless outrunner that has a Kv suited to that same 10x6 prop and is rated for the same or more power that is literally 1/3 of that total weight. And add in the power to weight advantages of Lipos and other current battery technology and it's a winning situation all around. I've been meaning to upgrade two of my well used electric models from brushed to brushless for some time. Between the direct weight loss of the equipment and the ability to remove the tail weight I had to put into both I expect to lose 8 to 10 oz by doing this conversion. This is the motor and battery weight differences and the removal of the separate small flight pack and tail weight in each case. As a side benefit I'll be shifting from the 38 to 40 watts per lb in the brushed versions up to around 70 watts per lb with the lighter brushless instlallations by using motors that in addtion to being light will be generating almost twice the power. And this does not even take into consideration gains in friction losses by elimination of the gear boxes.

While I have not done the sailplane and old timer conversions yet Idid convert a sport model over. I replaced that hot buggy motor and gearbox when the box blew up and Icould not find a replacement with an Eflite Park 480. I ran it on the same 8 cell Nimh packs that Iused to run the brushed motor with. Using the same 10x6 prop I immediately noticed that it pulled vertical for longer and was overall a better climbing model and faster in level flight. And flight duration improved as well. Shortly after that swap I bought a wattmeter. The old brushed motor had a max ground current of 26 amps. The new 480 was only drawing 19 amps. All this was from the same old packs on the same model. The only change being the motor, which I had to mount on the front of the mount instead of the rear like the old one to keep balance, which lowered the weight by about 2 oz or so. So I got better performance for less current. Is it any wonder I can't agree with your thinking that the old stuff compares well with the new? Oh, and the model went from a gearbox growl in flight that sounded like a muffled glow engine to whisper quiet. Obviously the gear box was using up some of the power.

Nope, I don't see going back to or staying with brushed motors for myself. In fact I gave away my horde of brushed motors and ESC's to someone that wanted to play with them.
Old 01-06-2011, 03:44 PM
  #31  
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Default RE: First thermal?

Sorry, I admitted that I'm weird, I just wanted to explain why I stick to the brushed drive. I've had no problems in 8 years, not even with weight. It makes no sense to exchange the motor and the ESC (which are still perfectly good) because replacing the 7-cell NiCd (which has to be replaced sometime, anyway) by a 2s A123 would save much more weight (12 oz compared to 2.5 oz). Energy/weight of A123 is 4 times that of NiCd. Yes, the motor with gear weighs 6.5 oz, max. efficiency is 79% (good brushes), the gear costs 5% of power. The alternative would have been a geared brushless inrunner. The efficiency gain of the 14x8 prop (75% max. eff.) turning only 4800 rpm is bigger that that of a gearless and brushless outrunner turning faster. But yes, an outrunner turning a bit "too fast" is much better than an old drive because the better battery outweighs the slightly lesser efficiency. I didn't want to split hairs, sorry again.

Actually, I somehow belittled the modern drive to all the more emphasize the benefits of a variometer. It's worth three modern drives in terms of flight time.

The new batteries have changed our world even more than brushless motors. The first electric gliders had only a switch for the motor (no ESC), and sometimes I think that's why modern electric gliders are flown likewise, that is flown to some altitude at full power, then gliding power-off to quite low altitude, and that again and again until the battery is exhausted (or the pilot). Meseems that is wasting the battery's energy.

Wouldn't it be better to climb to an altitude with good prospects for thermals, say 200 ft or even up to 500 ft, and use the drive only to hold the model there as long as no thermal is found? My glider could climb full-power for 6.5 minutes, but if only hauled to my thermalling base level it can stay there for 20 to 30 minutes at 1/4 power (to give you the correct figures). If I replace the NiCd by a still lighter A123 battery, I get 60 minutes floating time, enough for staying aloft for the whole afternoon and getting a stiff neck for days.

That's what I adopted from the birds of prey and what I think is good motorglider tactics. At full power you don't notice any thermal, but floating around at minimum power you'll notice any thermal just as well as when gliding, even flimsy thermals with the variometer.
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Old 02-11-2011, 12:26 PM
  #32  
Lee Sherwood
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Default RE: First thermal?

My first thermal was large, I doubt that I would have recovered the plane withouy the help of an experieced glider pilot . Then that first summer I lost two Ascent gliders from not being able to get them out of the thermals. That was the point were I realized I had better learn safe glider flying. I still have the most problems with 2 m. gliders with out flaps or even ailerons If I can not convert them to spoilerons!! B Willams thoughts are written in a wonderful way, thank you for your sailplane and wrtiting skills!! Lee Sherwood
Old 02-24-2011, 11:31 PM
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invertedthoughts
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Default RE: First thermal?

Bmatthews, from a rookie glow plane pilot and aspiring glider pilot I wholeheartedly recommend you write a book. (if you haven't already done so that is)
Old 03-11-2011, 05:34 AM
  #34  
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Default RE: First thermal?

My first thermal was a small encounter, I remember flying the tracks back and forth across the field, at one point I saw the wiggle of the wings. I never found it again on that flight, the next flight I launched and headed just a little ahead of it, I got rocked out hard, so I cut around and caught it this time. All I knew was to keep the bank shallow and keep circling, since I used an upstart, I maybe had 150~200' of launch altitude... When I fell out of it I was higher than 700' roughly. I was hooked, that flight lasted over 30 minutes, to the point where your wishing it would come down because your eyes are watering and your neck hurts from looking up for so long. It's my opinion that if you want to be a better pilot then you need to fly a glider, it teaches you so much more than any engine powered plane could. Your reward is directly equal to flight times, the better you get, the longer your flights will be. Thermaling is a skill, reading the surroundings and the terrain, looking for birds flying in one area and feeding is a big clue, the smaller flying insects get sucked up into thermals and the birds will feed on that vortex of insects while doing the least amount of work flying.
Old 03-11-2011, 11:23 AM
  #35  
evlwevl
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Default RE: First thermal?

You always remember your first thermal even if you weren't looking for one. About 12 years ago a friend and I purchased vectored thrust planes that was supposed to guarantee some actual sticktime to beginners. They relied on 2 small motors handling Left/Right banking and a cambered wing for lift. To climb, you held both motors on, and to descend you just didn't touch anything and the plane would glide down by itself because there was no rudder or elevator. We launched these together at about 100 ft up or so we noticed that they were sort of rocking back and forth we kept asking each other, are you climbing? We both said no, but we noticed the planes circling around kept getting smaller. This continued till we realized we were out of range and had no control. We were at the mercy of the thermal gods as the planes continued to get smaller and smaller and drift along so we followed them downwind. After a while of sweating it out, my friend just gave up and threw down his controller. I continued trying to work the sticks and eventually we got control back and all I could do was just continue turning downwind and hope I didn't hit another thermal. I ended up landing about 40 ft up in a tree and knocked the plane down with a pine cone. I still remember that day like it was yesterday. That was the day my obsession started.
Old 02-26-2020, 05:42 PM
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i know this is an old thread but just wanted to share even micro sized gliders can catch thermals, given the right conditions and right weight class, the Feather˛ is around 47grams AUW, wing span of 28.5" inches.






Old 06-10-2020, 04:45 AM
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Lots of great advice here. I'd add that the position of thermals can sometimes be deduced. There are broadly speaking two types, so-called "blue thermals" where there's no cumiliform cloud above - with these it's merely a matter of luck running into one, recognising the uncommanded roll out of the thermal, and rolling in the opposite direction to commence "centering". Mostly, however, thermals are inferable if they have cumulus above. If you draw a line into wind from the base of the cumulus to your position over the ground, you will generally find a thermal upwind of that line. A really strong thermal may result in a lighter colour area in the centre of the base of the cumulus.

From an RC point of view, timing of the launch is going to be absolutely critical, as if you launch too early, or too late, you'll be launching into "sink". If you're flying within 10 miles of a coastline, the stronger the thermal activity, the more likely a sea-breeze will kill the thermals stone-dead. *I was once one of 17 gliders than all landed at the same field within a few minutes when just sea-breeze occurred. Amazingly we all missed each other on what became a very challenging landing for later gliders.

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