Fall/winter thermal?

[catman529]

I haven't done much research on thermals - can there be significant thermal activity during the cold months? If so, I assume the weather conditions and time of day would be similar to those in the summer?

[Andy W]

Absolutely. It's all about relative temps, not absolute. Air still rises and falls..
..a

[Tuomo]

...and in winter clouds ofter hang at very low altitude. Try going out in an almost raining/snowing weather... A totally new experience for rc-soaring: you can work the wing bottoms like the full scale boys do :)

[rdwoebke]

Catman,

There are thermals on just about every day of the year.

You can figure that there will be thermals from about 2 hours after sunrise to perhaps an hour or less before sunset. Although some days the thermals are very weak. On many days, the best thermal flying starts about 10 AM and will last until 2 or 3 pm.

I have worked thermals every month of the year, and I live in Indiana. I made a nice 12 minute thermal flight with my Paragon on January 20 of 2007. And on January 27 of this year I had a nice 10 minute flight of my Allegro Lite.

Ryan

[Kenny Sharp]

Same here...thermals year round.

[rdeis]

Round the clock, too. I've found lift in the dark.

[catman529]

OK thanks everyone, that answers my question perfectly.

Thermals in the dark? Would that be heat rising from the earth after the air temp cools down?

[rdeis]

Bubbles work the same way as in the daytime: parts of the ground are warmer than others, and the air over the warmer spots will move up and blow away, drawing cooler air in beneath it.

In the daytime that's usually because some parts of the ground heat up more readily, at night it's usually because some parts cool more readily.

[lincoln]

I've caught thermals after sunset in the winter flying off a frozen lake. They don't always act the way you'd expect. I'm going to miss that lake. DLG flying a 3 minute walk from where I used to live.

[catman529]

Even off a frozen lake...I never would have guessed you would find thermal activity in a place like that.

[ozmo01]

I like the polyester ones..... oh not thermal under wear, Ok :p

Often on days when the night /day temps very more you get good thermal action. This is often the case in the fall and winter so thermals can be good.
On those summer days when the previous night was HOT the difference in temps can be very little and LESS thermal activity is sometimes the case.
Summer sun is more intense however but a great day flying in the fall is not so hard to do! Less sweating isn't to tought to take either.

[lincoln]

DLG off a frozen lake is hazerdous. I must have slipped and fallen down 10 times while launching. But I seem to fall well for a guy my size. Particularly if I'm holding a tx so I can't reach out my hand and bust it.

If there's loose snow it will mark the really strong stuff.

[catman529]

It's not cold enough down here to freeze the lakes so I wont have to worry...now I think I'm gonna do some research and find out how/where to find thermals year-round. I know I've caught a couple with my previous scratchbuilt (powered) planes, at the top of a hill in our neighborhood. It might have been wind blowing up the hill but I don't usually get much lift from that spot. I think it was this past spring, maybe last fall..can't remember exactly, but I did notice the thermal and it wasn't stationary.

[Kenny Sharp]

It's not cold enough down here to freeze the lakes so I wont have to worry...now I think I'm gonna do some research and find out how/where to find thermals year-round. I know I've caught a couple with my previous scratchbuilt (powered) planes, at the top of a hill in our neighborhood. It might have been wind blowing up the hill but I don't usually get much lift from that spot. I think it was this past spring, maybe last fall..can't remember exactly, but I did notice the thermal and it wasn't stationary.

Maybe you should look into some of Paul Natons' DVDs.
He has a couple of great ones that cover thermals and lift...as well as how to find them and stay in them.
Lots of good info. try www.Radiocarbonart.com

[Forest Flyer]

Fall thermaling is usually very good. October is my favorite month for thermaling. And as others have pointed-out, thermals can be found all year. I do indeed fly all year, and I have found decent thermals in air temps in the single digits Fahrenheit. The main problem is the big increase in wind during the winter...

But, even at my pretty southerly latitude here at about 40 deg. N, thermals do get noticeably weaker and more sparse within about plus/minus three weeks of the winter solstice (Dec. 21). I’ve experienced this effect every winter. You can, however, get decent lift around the solstice when the air is unstable and the sun is shining.

I’m not sure how strong this mid-winter thermal lull would be in Tennessee.

FF

[scaflock]

Winter thermals are usually weaker than those during the rest of the year but they do exist. The Radio Carbon Art DVDs point out a very good reason for this. The angle of the sun is lower at that time of year so it doesn't warm the ground as much or as quickly. Hence it does not create as great a difference in temp as it will in the summer.

If you really want to learn the details of thermals, I highly recommend the DVD series from RCA. Lots of tricks in them to help beginners learn to read the air as well as some great footage of planes in filght.

Jeff

[steelhead]

As stated before, YES, there are thermals in winter.

Rising and falling air happen whenever there a temperature difference.

Never been near a frozen lake, but I'll have to try flying over one one day:) Seen some mighty large frozen puddles though!

I've found that melted rooftops make great sun energy catchers when there is snow on the ground. Rooftops catch and store the heat, then slowly transfer it to the airmass and small thermals start forming bigger thermals.

Dont forget to play with catapult launched FREE FLIGHT gliders in the winter. Chasing those things down will keep you warm, and teach you about winter thermals!

Have fun!

Dean

[Tuomo]

Frozen lake is not much different from large fields etc. In winter also ground is frozen :D And if there is snow, it is propable that the ground and lake ice are equally covered with it.

I fly often on frozen lakes. Classic bubble like thermals, where tight circling in called for, are extremely rare. Usually I look for difference between lake ice and surrounding terrain, or difference between ice close to the shore and in the middle of the lake. Also wave type lift is very common.

Winter thermals certainly happen, but in summer time thermal flying is 10x more fun.

[catman529]

Steelhead - I've got 4 Zing Wing gliders hanging on my wall waiting to fly again. I've only had one thermal once or twice as I don't fly them often...but it is fun chasing them down.

I'll be looking for sources of heat when I fly...that is, surfaces that absorb and radiate heat from the sun. I build and fly solar balloons (www.solar-balloons.com) so I've got plenty of experience with dark surfaces absorbing and radiating solar heat... :)

Again, thanks everyone for the info. I'm planning an 8ft span blue Dow foam glider, 2 channel (elevator & rudder) that I will either build a crude bungee from bike inner tubes :p for launching or discus launch by hand. I'll probably build it (brace the wings, that is) so it can be discus launched anyway in case the bungee doesn't work out :rolleyes: I have been saving inner tubes, I rike my bike a lot and the universal tubes I use are more stretchy than the single-size tubes.

[lincoln]

You don't necessarily have to brace the wing, actually. You can run a small rope to the tow hook, hold a loop in that rope with a couple of fingers, and control the wing tip with a couple of other fingers and your thumb. I've launched my Ava that way, although I didn't go for full effort as it got scary fast. The rope falls off as soon as you launch.

But a high start is better because you get higher.

BTW, if you're going to fly off a frozen lake, be sure to consult with the locals and stay away from the inlet and outlet, or any other place the water might be moving and thin out the ice.
Steelhead - I've got 4 Zing Wing gliders hanging on my wall waiting to fly again. I've only had one thermal once or twice as I don't fly them often...but it is fun chasing them down.

I'll be looking for sources of heat when I fly...that is, surfaces that absorb and radiate heat from the sun. I build and fly solar balloons (www.solar-balloons.com) so I've got plenty of experience with dark surfaces absorbing and radiating solar heat... :)

Again, thanks everyone for the info. I'm planning an 8ft span blue Dow foam glider, 2 channel (elevator & rudder) that I will either build a crude bungee from bike inner tubes :p for launching or discus launch by hand. I'll probably build it (brace the wings, that is) so it can be discus launched anyway in case the bungee doesn't work out :rolleyes: I have been saving inner tubes, I rike my bike a lot and the universal tubes I use are more stretchy than the single-size tubes.

[catman529]

I'll go with the highstart (like I said, I'm making it with inner tubes) and I'll definitely try your rope discus method. I never thought of it before but it makes sense. Thanks!

[catman529]

Forgot to mention I cut out the wings this morning. Will need to brace them though, being 4 feet long each, they bend from their own weight when held at the ends. I'll probably build something with bamboo skewers as that's about the best thing I have.

[ronmeister]

Absolutely. It's all about relative temps, not absolute. Air still rises and falls..
..a
I figure I'm a little SOL in that sense.
I'm here, going to school at UND, where at times the temperature won't go above -25 for over a week at a time :p


Ron

[lincoln]

From your description, it sounds like you would ONLY be able to launch with a high start, and only after you reinforced the wing. The discus launch with a rope doesn't require that you add special reinforcing to the tip, but it does require a strong wing, and for that you need spars.

Strongly suggest that you find some wood strips to reinforce the wing with, instead of bamboo skewers. Sources that come to mind:
-those wooden pieces in the bottom of roll up shades
-wooden moldings that they sell at lumber places
-slats from a busted bamboo rake

even stronger might be fiberglass driveway marker poles, though you might want to sand them into rectangles.

If you have a saw you can cut fine spars from lumber.

IN any case, with wood spars make sure the grain is quite straight.

You will need to sand slots or something that are quite straight. ANd glue securely with no gaps.

White foam wouldn't be strong enough anyway.

You can taper the spars so they're only large in the middle, and they don't have to run all the way to the tips.

[lincoln]

At that temperature, I'm sure you have thermal generators all over the place. They're called chimneys.

Now it'll just be a matter of whether you can stay warm for a while.

(Yes, I once used a thermal generated by a furnace from a house, but it went away when the thermostat turned the furnace off. It was only 25F above 0, so the furnace didn't have to be on all the time.)
I figure I'm a little SOL in that sense.
I'm here, going to school at UND, where at times the temperature won't go above -25 for over a week at a time :p


Ron

[lincoln]

Hope this shows up better on your computer than the one I'm using now:
http://www.rcsoaring.com/media/avadlg.wmv

[Forest Flyer]

I figure I'm a little SOL in that sense.
I'm here, going to school at UND, where at times the temperature won't go above -25 for over a week at a time :p


Ron
I’m sure that there are thermals at -25 F. The main problem would be staying warm while sitting still. And if you figure out how to stay warm while flying at that temperature, I’d like to hear about it! I also suppose that battery voltage might be a problem at -25 F, but maybe NiCd packs would work. Some airframes might also not like that temperature.

A couple of years ago, in a thread on this general topic, the coldest sailplane-flying temps reported were consistently a bit below 0 F or about -20 C. That low-temp cut-off was determined mainly by comfort rather than other reasons.

FF

[glidermang]

FWIW: the neat thing I have found about DLG is that it encourages (me, at least) to experiment. And thus I have found lift in the strangest places and at the strangest times.

Some of the strange places/times have already been mentioned (frozen lake, after dark, etc.) I saw a 3-minute flight last summer in falling rain, and once I saw Joe Wurts fly along a line of barbecue grills.

True cold (below freezing) gets into comfort and battery issues, and I can't talk to those. If someone tells me nicads and nmHd have issues in cold, I'd believe them. I experienced some of those issues with a prototype UAV in Minneapolis, in February - we taped chemical hand warmers to the various battery packs before we rolled out at each flight.

However, I have NEVER experienced truly still air, and am glad to launch one of my DLGs most anytime, anywhere. That's part of the fun, to find out what's happening.

Yours, Greg

[catman529]

I'll probably brace my wings with 2 rows of skewers tied together tightly. I want the wings to come off for easier transportation, so I'll have to have some sort of removable spar or something of the like.

That video was great. It seemed to catch some rising air right after the launch, then it flew around and caught a good thermal. That's probably about the size my glider will be, except that mine isn't going to have any dihedral (that's strange isnt it? :rolleyes: )

[lincoln]

Even aileron gliders fly better with a little dihedral, and skewers are not going to cut it on an 8 foot wingspan glider. Unless you live in Antarctica, if you take the time you would use to bundle the skewers and search for wood strips, you can find something much better. If you have a friend who has a table saw and a two by four (or any other nice, straight grained piece of spruce or doug fir, or even basswood) you will be all set.

Strongly suggest you look over the plans at charlesriverrc.org or someplace else to get an idea how to do two or three piece wings.

[lincoln]

BTW, I tried making high starts with weird stuff when I was starting the hobby. DIdn't work. High start latex isn't anything like inner tube butyl. On the other hand, I suppose if you find a high end bike shop where they toss out lots of busted latex bike inner tubes, that might be ok. But those latex tubes are rare.

[catman529]

My highstart worked (without extra line attached) on a delta kite. Hopefully it will be strong enough to pull up an 8 footer. If not, I'll try cutting the strips a little wider. If the highstart never turns out well, I'll just learn to discus launch.

And come to think of it, since my glider won't have ailerons I may want to add dihedral to the wings. I can't see a rudder as being the best way to correct the roll of any plane.

[lincoln]

My highstart worked (without extra line attached) on a delta kite. Hopefully it will be strong enough to pull up an 8 footer. If not, I'll try cutting the strips a little wider. If the highstart never turns out well, I'll just learn to discus launch.

And come to think of it, since my glider won't have ailerons I may want to add dihedral to the wings. I can't see a rudder as being the best way to correct the roll of any plane.
It's a heck of a lot better than nothing, unless you have no dihedral. If your time is worth anything, consider whether it might be worth it to get materials that are a little nicer. Also consider that you may not want to reinvent EVERYTHING. THere's lots of design info out there to start with, such as the plans I mentioned before.

[catman529]

I'm on a tight budget and don't want to put any money into this plane - just build it with what I have. I'm putting my money into my C-130 which still needs 2 more motors, bigger batt and more props. That plane comes first as far as money goes. This glider is just a bit of an experiment and I hope it works. I'll definitely build some dihedral into the wings.

[rdwoebke]

Why don't you share with us what you are planning on building and then perhaps post some pictures and we can make suggestions/offer help.

Ryan

[Libelle201B]

I remember way back in the late 60's a builder/flyer from Norway I think, came out with his "Ghost" series of sailplanes. They were all of built-up construction, very sleek, with highly cambered airfoils. Absolutely beautiful sailplanes! Anyways, I guess he wanted and found a solution for those cold weather thermal days :)

[catman529]

Why don't you share with us what you are planning on building and then perhaps post some pictures and we can make suggestions/offer help.

Ryan
Sorry I've neglected to post any pics or detailed info. It's not a project I'm taking too seriously. But I will probably start a thread (prob in the sailplanes forum) when it's done or at least almost done.

[Libelle201B]

I'll probably brace my wings with 2 rows of skewers tied together tightly. I want the wings to come off for easier transportation, so I'll have to have some sort of removable spar or something of the like.

That video was great. It seemed to catch some rising air right after the launch, then it flew around and caught a good thermal. That's probably about the size my glider will be, except that mine isn't going to have any dihedral (that's strange isnt it? :rolleyes: ) I don't know about all you others, but this is starting to look like a joke to me, no offense intended. :rolleyes:

[FrogChief]

I don't know about all you others, but this is starting to look like a joke to me, no offense intended. :rolleyes:


Or a recipe for how to make the most crap-tastic sailplane of all time... :cool:

[catman529]

yup but it's going to fly :p

I would like some advice though. The wings are 4ft wide each, 1/2" blue styrofoam from Lowe's. I am carving some sort of "airfoil" by cutting on an angle along the leading and trailing edge - the cut angle of the latter will be shallower, if you know what I mean. Basically I'm making the wings more aerodynamic. What kind of stress can I expect on the wings during a discus launch or regular flight? Should I just get some basswood or what for bracing. I'd like some general advice on sailplanes of this size, as I haven't made any plane this big before. What are some important things I should know for larger planes?

[rdwoebke]

I once had a similar plane to what you are making, but instead of blue foam it was white EPS foam. I'll have to dig up the remains of that wing to figure out what the spar was. I want to say it was a piece of plywood at just the very center glued in a slot in the wing. Otherwise it was just foam, no covering or anything.

You might think about hot wiring the foam to get an airfoil. You could download the plans for the Allegro Lite perhaps as a start and then just use the root center section and ends of the center section and make two 4 foot wings via hot wire. You could make a hot wire cutter for about $3.00 using some picture hanging wire, some rolled steel 3/16 rod, and some wood. Power could simply be any 12 volt battery you happen to have around, perhaps a lantern battery, gel cell, lawn mower battery, etc. You get a friend and you mark lines on the templates and then each person is one one side of the cut and you try to count out 1, 2, 3, etc. to keep in pace with each other. Works OK enough and you'd have a better foil than the sanding. And probably less mess!

Ryan

[lincoln]

LOTS of stress on a discus launch. That's why we keep trying to get you to use better spars. Look at some glider plans. You don't need to make it as strong as one of Drela's designs, but it needs to be strong. If you don't want to pay for wood, I'm sure you can find some if you keep your eyes open. 1/2" thick foam is awfully thin for an 8 foot wing that doesn't use carbon.

I think an old style 8 foot glider might have a wing that's 7/8" thick at the root, with 3/8" X 1/8" or 3/16" spruce spars top and bottom, and some shear web in between, but I'm not sure that would hold up to a discus launch. The foam might work as a shear web. Also, you'd probably need to have something to provide some torsional stiffness. Maybe packing tape on the inner half? I'm assuming you use the rope trick to launch this thing, though a high start would be gentler.

If you found a 3 foot wooden yardstick with very straight grain, you could probably make most or all of your spars from that. However, lots of them have crooked grain.
yup but it's going to fly :p

I would like some advice though. The wings are 4ft wide each, 1/2" blue styrofoam from Lowe's. I am carving some sort of "airfoil" by cutting on an angle along the leading and trailing edge - the cut angle of the latter will be shallower, if you know what I mean. Basically I'm making the wings more aerodynamic. What kind of stress can I expect on the wings during a discus launch or regular flight? Should I just get some basswood or what for bracing. I'd like some general advice on sailplanes of this size, as I haven't made any plane this big before. What are some important things I should know for larger planes?

[catman529]

Thanks for the advice. I'll see what kind of spar method I can come up with and hope it works. If I discus launch it will definitely be with the rope trick. I'll try the highstart as well, but I'm not sure if it will be strong enough to haul an 8 foot glider...but it's worth a try.

[catman529]

I don't know if anyone is still interested - but I finished the airframe and it's ready for the guts. I braced the wings with bamboo skewers and packing tape :D No dihedral, the wings just kind of flex up a little when it's in flight :rolleyes:

The test throws show that it flies very well. I'll have to see how it turns out when I put it on my redneck histart, if that's even strong enough to pull the plane into the air. I might try hand-launching from a slope as well. I'm not sure if any part of the plane is strong enough for a discus launch, because the wings can come apart for transportation and aren't secured very well (but should stay in during a normal flight)

Hopefully this will work, at least for a little while. If it turns out to fly well, I will start a build log thread w/ pictures and videos for all who are interested in an 8-foot by 1/2" styrofoam skewer-braced wing that flies :D

We'll see how flying tests the plane. I hope the more-than-usual flexibility of the wings won't cause too much of a problem. They don't seem like they will break easily though.