So you "see" a thermal hit your wing, now what?

[arukum17]

I am beginning to be able to "sense" a thermal hit my plane, but wonder what do when this happens. I have read the books, seen the DVD but still want to hear from the practioners.


Various times, when its sunny and warm I have been in the air and "seen" one Paragon wingtip gently bump from a thermal bubble. Should I:

(a) turn into the thermal in a tight circle?
(b) turn into the thermal in a wide circle?
(I have tried both and I dont seem to hold altitude, like I hope)

After I exit/"lose" the thermal should I move:

(a) upwind
(b) downwind
(c) zigzag around randomly

[rdwoebke]

(a) turn into the thermal in a tight circle?
(b) turn into the thermal in a wide circle?
(I have tried both and I dont seem to hold altitude, like I hope)

This depends on how high you are at the time and how strong the lift is. I tend to turn my Paragon pretty tight. Perhaps 30 foot diameter circles if the plane is at 150 feet high or less. Bigger circles as you get higher (lift tends to get wider with altitude). BTW, I think having the right CG is important to good turning handling. I can give you my Paragon CG, if you like.

After I exit/"lose" the thermal should I move:

(a) upwind
(b) downwind
(c) zigzag around randomly

Normally, most pilots probably don't drift well enough with the lift, so normally for most folks it would be B. What I'd do, is widen up the circle quite a bit, trying to push the glider more downwind than it had been, and see where it seems to be doing with regards to that wide circle then once you found the good area tighten back up.

Ryan

[oscillator]

And once in the thermal, how to make those nice flat turns? I'm assuming you apply opposite aileron to flatten it out. Minimum airspeed is probably a factor too. Often I find my self banked over too far.

[O.L. Adcock]

How do you know it wasn't a sink spot dropping the other wing? :)....Here's what I do..I come off launch and set out on a search direction, typically 45 degrees into any prevailing breeze. Trimmed out for nice smooth straight flight. If I hit a bump, usually the up wind wing, a thermal will bank the aircraft away from the strongest lift. So if the bump rolls the plane left, I'll crank her around hard right. Watch the plane in a turn or two..If it noticeably climbs on one side more then the other you need to recenter toward the climbing side. This takes some planning and proper execution and is where most folks "lose it".....Several ways to do it depending on how good a pilot you are and the agility of your plane. If your plane is pretty agile, as you come around and just as you hit the strongest side, reverse your turn...The thermal is going to fight you on this so you got to crank into it hard. If you don't it'll spit you out. The other way is steepen your bank angle on the sink side and flatten it as you come around 90 degrees to the strong side. These adjustments need to be continuous and agressive to stay as centered as you can, knowing the thermal is constantly trying to spit you out. The higher you are and the more broad the thermal is, the more room for error you have.

Down low the bumps tend to be much smaller and the tighter you have to turn to stay in them and take advantage of them. One mistake here and you'll be landing. As a rule if you are cranked up in a hard thermal turn down low and you aren't losing or gaining very fast, the best bet is to hold what you got. If you try to make recentering corrections, do so using the steepen and shallowing bank angles....It's just too easy to mess up a turn reversal and many ships aren't agile enough to pull it off.

The big thing is being able to make the plane do what you want it to do at the right time in the right place and doing so smoothly. Under 100 feet is where the best practice occures but also the toughest lessons. :)....O.L.

[O.L. Adcock]

Oscilator, "And once in the thermal, how to make those nice flat turns? I'm assuming you apply opposite aileron to flatten it out. Minimum airspeed is probably a factor too. Often I find my self banked over too far."

Yep, that's a big factor and I think some don't take enough time trimming their plane. Most planes will have an angle of bank where they'll roll back level if you let go of the sticks. Increase that angle at some poiint they'll hold that angle...Go beyond that angle and they try to over bank...This is called spiral stability, or lack of it. What happens too is many will have too much rudder mix or not enough aileron throw and authority...That'll cause them to over bank and tuck. Too much or not enough elevator throw or authority effects the turns also. CG doesn't have any direct effect other then it effects your elevator authority. 90% of my "trimming" is for turning quality..If you can't turn, you can't thermal.......O.L.

[O.L. Adcock]

"After I exit/"lose" the thermal should I move:

(a) upwind
(b) downwind
(c) zigzag around randomly"

Ryan is correct, folks tend to not drift down wind with the thermal fast enough so taking a quick look down wind is a good ploy. Many stay with what they thought was a thermal too long also. If you aren't at least maintaining altitude, go find something better. If in searching you haven't found anything, NEVER fly back through the same air you've already flown through.....O.L.

[rdwoebke]

We probably have to be a bit careful here, since we are talking 2 different kinds of planes. Aruk has a Paragon, which is a polyhedral plane with a very floaty airfoil. Mark has an Oraganic, which is a full house wing that is quite a bit flatter.

It seems to me, that poly planes that are nose heavy don't seem to want to carve thermal turns as nicely. They either won't turn as tight or seem to loose altitude more in tight turns.

Ryan

[O.L. Adcock]

Yes Ryan, I was addressing Oscilator which was obviously an aileron ship. The problem with carving turns with a nose heavy ship is lack of elevator aurthoity. Too much authority is just as bad if not more so.....O.L.

[oscillator]

Apologies for the confusion - I figured with a Poly plane the problem would take care of itself - bit it makes sense CG could impact turning on a poly ship (and an aileron ship too). Speed will obviously impact both ships turning performance as well.

But I think the question is the logical follow on to Aruk's original question - assuming you found a thermal, how do you get the most from it? Obviously some elements of the answer may vary slightly for a poly ship vs aileron ship, others will be the same.

Great thread. Thanks!
Mark

[rdwoebke]

I probably like to turn tighter than most, but I find that if I'm making tight turns, I can follow the lift easier. Plus, tight turns give you a more oppertunities to watch the front and back side of the turn (since you are making more turns over a given timeframe), and that can give you better oppertunity to judge if you are following the lift well enough or not.

But, there have been times I'm turning too tight and my timer suggests opening the turn up a bit and then the thing really climbs good.

Ryan

[Hostage-46]

O.L. and Ryan have covered it well, the only thing I can add is it's important to look at the big picture. What is the model doing in the context of any lift indicators. Once you become attuned to subtle changes of wind speed, direction and temperature, you'll be able to guess where the lift is likely. If you can combine your observations of lift indicators with what your model is doing, you're going to see a drastic improvement in your flying. When you're feeling out the boundaries of a thermal and tracking it's movement, and how far they are spaced apart, you can put a plan together for the next flight. Most fields have a "house thermal", if you can figure out what the trigger is, you'll be good to go.

Finally be decisive, if you have a ship that can fly in a wide speed range, take advantage. If you find yourself circling in sink, don't just sit there, DO Something! If you have a decent guess of where there might be lift you stand a better shot at salvaging the sink hole into a save.

[rdwoebke]

That is a good point. I also find it is easiest for me to thermal down wind. If you have a small mylar streamer on your antenna (something the size of say 16 inches of audio cassette tape) then you can watch that and that points towards the thermal. So, if you are down wind and finding yourself not quite in the good lift, glance at the steamer and it might have you go left or right some.

Ryan

[O.L. Adcock]

Mark, IMO, there's only 2 speeds you should ever fly your plane...Minimum sink, and max l/d...Of course it's impossible to accurately do so without eyeballs in the cockpit but some can get pretty good at it. Minimum sink should be our "thermal" speed and it's going to be just above a stall. So close that the least little mistake will result in a stall. Flying at minimum sink will result in the fastest climb. But we can thermal and thermal well at other speeds, as long as the air going up is faster then we're going down, net result is a climb. To make the most out of the weakest lift, slow is the way to go.

Ryan, We get the chance to "see" our thermals some times in the form of dust devils. I agree on days that are calm with little to no prevailing wind, going down wind will take us closer to the thermal if that's what is generating the breeze. Thermals rotate in a large spiral so the core is usually somewhere to the left of straight down wind depending on how far away it is and how much acreage it's covering. Sure fun trying! :)....O.L.

[AMBeck]

Just a little amplification on the excellent comments above. In the east, with it's weak lift low down, you need a reasonably light ship to learn to work thermals. Most 2 meter poly ships should be no heavier than 35 oz., and 32 is a lot better. You can add weight later as you learn, fly on breezier days and want higher zoomies.

In general, as a novice at soaring, you'll be flying faster than best L/D when you hit lift. Most novices tend to fly too fast. The first thing to do is slow down. Minimum sink speed will result in the smallest circles, but anything between best L/D and minimum sink is good to start. You'll think you're hanging on the hairy edge of a stall. Practice!

Once the turn is established, you need to come in with a little up elevator, or speed will increase and your circles will get big quickly. Remember, you are using some of your wing's lift to turn the plane. That lift has to be replaced with more angle of attack, which means back stick.

Get your model trimmed properly! If your CG is too far forward, you'll need too much up elevator. That has several bad effects. It increases tail load, which is the same as increasing your sailplanes weight. It decreases dynamic pitch stability, so when you do stall in lift, you'll be chasing the stall rather than getting back into the lift. And, the negative lift at the tail increases induced drag.

If you are flying a poly 2 meter, maintain a shallow bank and use airspeed control to keep your circles tight. The bottom tends to drop out with smaller ships in steep turns. A steep turning open model looks great in lift, but a steep turning 2 meter is coming down unless the lift is strong.

Of course, if you are flying a nice, light 2 meter, be careful of getting too far downwind, especially if you're not climbing well. You might not be able to get back.

Hope that helps.

[Bryan Quick]

Flat turns- Guys, I have to disagree. In order to fly the most efficiently, you must bank your plane. Make sure your turns are coordinated to minimize your slip. Slip equals drag equals inefficient. Uncouple your rudder from the ailerons and fly it with another axis on your radio.

In order to turn, you must bank your wings to produce lift in the direction you want to turn. The higher the bank angle, the smaller the turn radius. If you need to fly a small circle to stay in the lift, you must also do it efficiently. Use your rudder to minimize the slip angle and keep your plane efficient.

Bryan

[oscillator]

O.L. - I agree min sink is just over stall, and is where you want to be in a thermal. Of course, those of us new to the TD game often find the ship going too fast (or too slow and stalling) and thus are learning to stay on top of the trim.

Finding best L/D speed is something I have no clue how to accomplish - without being in an instrumented cockpit or data linked model. How does one make an educated guess at best L/D in the RC world?

[schrederman]

Flat turns... I have to agree with Brian. A coordinated turn = efficiency. The WING turns the airplane... not the fuselage or the rudder. The VERY best thing someone that's trying to learn to thermal can do is go buy a ride in a real sailplane... preferrably when there's some good lift. Tell the instructor what you're trying to accomplish... and take an airsick bag... :eek: ... I can't tell you the number of times I've thermalled up through people trying to make "flat turns"... in R/C and flying the real thing. I've done lots of turning at 60 degrees of bank with the stick bouncing off the backstop, and the vario pegged. It unnerves some folks to have someone turning inside them and going up 400' per minute faster. :D

With an RES plane, the story's the same. An aileron ship will have to be coordinated by the flyer, using rudder and ailerons together. But the RES ship will pretty much coordinate itself, as an effect of the polyhedral and rudder. I regularly thermal my Houston Hawks at high angles of bank and lots of elevator.

If you do buy a ride, pay attention to how much aileron and rudder is being used, and how much back stick he's holding... and most important, how much bank angle he's holding. Don't look down the wing at the ground. Look out at the horizon to see the bank angle. Again, tell the instructor what you're trying to learn from the flight or he'll putz around making 10 degree banks to keep you from puking in the airplane... On second thought, take 3 airsick bags... :eek: :eek: :eek: ... If they get full, take off your tennis shoe... Don't puke in the glider... :o

Pardon the rant... Flat turns is a pet peeve... :p

Jack

[O.L. Adcock]

Oscilator, I'm not sure either other then we have experts that tell us with this airfoil or that we need to reflex XX degrees for best L/D...Without very good testing is dead air conditions, I don't know of anyway to know for sure. The ship I'm flying now is still pretty darned fast with surfaces in neutral or even deflexed a bit so I only use the reflex setting when I want to play! :) L/D might get better reflexed and flying a little faster but profile drag and skin drag still goes up by the square of the velocity and kills sink rate no matter how you slice it. I can screw up all the good qualities of a plane with poor decisions faster then the good qualities can bale me out! :)....O.L.

[Phoebusflyer]

Finding best L/D speed is something I have no clue how to accomplish - without being in an instrumented cockpit or data linked model. How does one make an educated guess at best L/D in the RC world?[/QUOTE]

finding best L/D is not really hard. As for an RC plane, just ease the nose down and pick the speed up until you see the plane flatten out. When adding more down trim increases the down angle of the ship, you have gone past the best L/D. Believe it or not, on most ships, best L/D will occur closer to minimum sink speed than you would believe. Mostly, you need to fly your plane in straight lines across your field of vision on a day (or evening) when the air is stable with no wind or lift. Play with the trim until you see your plane go up on step. It will be like watching a fast speed boat that has been wallowing along and then applies the right amount of power and up it goes and away it goes. I got to really fly my BOT this weekend, and there is no doubt about it when she hits her best L/D. She loves to fly fast and she flys slow very well, as when thermaling. Like I said, you can see when the plane hits its best L/D, it will fly flatter than it will at any other speed.

[oscillator]

Great tip! So sounds like I need 2 trim speeds - one slightly before stall, and one slightly before she starts to noticeably nose down. Sounds easy enough.

[AMBeck]

Sorry, I didn't get my point out clearly. You are right, the turn MUST be coordinated. What I meant was to use minimum (coordinated) bank and get a tight turn by flying as slowly as practical. You can get a tight turn in two ways, lots of bank and speed, or less bank and slower speed. This is how 1-26s outclimb fast glass. They thermal at 30-35 MPH and stay in the strong core, often with a modest bank angle, while the glass is cranked up on a wingtip, going faster and sinking faster, even though they are more efficient. (My old Ka-6 was great at that, especially in weak conditions!)

Jack, I agree with you, once you learn to thermal. When you're trying to learn to work lift down low and in weak conditions, throwing the ship around is the last thing you want to be doing. SMOOTH & SLOW is the key to low saves. A novice's first thermals will be low saves, for them, even though you and I wouldn't necessarily fly them that way.

As for getting the minimum sink and best L/D speeds, you do that with attitude flying. Put your plane in the correct attitude, and it will fly the correct speed. To find the correct attitude, go to your local football field and do a bunch of hand launches. Try to do every launch the same. What fuselage attitude (nose up/down) gives the best distance? That's your best L/D. Now do the same with the nose a little higher. What attitude gives the best duration? That's minimum sink. Now, when you are trying to get away in weak lift, put the fuselage in the minimum sink attitude and you will fly minimum sink. By the way, this works no matter how much ballast you've loaded up. The speeds will change, but the attitudes for minimum sink and best L/D will stay the same. Flaps make life more interesting, since they change both AoA and fuselage attitude. However, once you've mapped the attitudes for each flap setting, they will always work.

By the way, I was the spin instructor at our field and use to teach spins using the flat turn entry (which is the way lots of full size sailplane pilots get killed, flat turns to final). Hold off bank, hurry the turn with rudder and hold the nose on the horizon with elevator. About the time all the controls hit the stops, you'll be looking straight down at the ground twirling madly about (even in an "unspinnable" 2-33. ASK-21s needed the tail weights though). 9 out of 10 students will yank the stick hard back into the corner as the stall breaks. If, as a full size sailplane pilot, you haven't experienced this, you need to find a spin qualified instructor and try it. I never had a student get all the way sick doing this, but most were pretty shaky after we landed.

[schrederman]

Spins are FFUUUUNNNN!!!!!! yeah right... :eek: :eek: Ask me about my spin training sometime. :eek: :eek:

You're right... bankin' and crankin down low ain't for the novice... nor the weak of heart... I sure love it :D

Jack

[O.L. Adcock]

Allen, that's the way I've been doing it but never seen anything in writting so was just a guess. Jack, sounds like your introduction to spins was similar to mine! :).....O.L.