Word of advice on making use of thermals?

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mac
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Postby mac » Wed Jun 07, 2006 1:17 pm

OXO wrote:Anyway, who uses ft/sec in gliders?


Nearly OT question:

I understand from radio msgs during races that people gauge lift in knots.
I use metrical system, but AFAIK 1 knot = 1 mile per hour. What is the reson to use that scale? I mean: in a thermal you spend some minutes, not hours... And height is measured in feet, if I am not wrong...

I just wonder why not to use a vario with a scale expressing furlongs per week, then! ;)
Last edited by mac on Thu Jun 08, 2006 2:04 am, edited 1 time in total.
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OXO
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Postby OXO » Wed Jun 07, 2006 1:22 pm

1 knot = 1 nautical mile per hour. Not the same at all.

1 knot is 101.33 ft/minute or 0.5147 m/s.

I don't know why we use knots. feet/minute makes much more sense. :roll:
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Sommersprosse
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Postby Sommersprosse » Thu Jun 08, 2006 7:58 pm

and meters per sec again makes much more sense...

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Postby tatali0n » Fri Jun 09, 2006 10:57 am

Only if you're measuring your height in meters. Which always struck me as an odd thing to do. I'd rather think of myself as being at 3200' (or near enough) rather than 1000m :wink:

As for knots vs ft/min; given that 1 knot of lift is pretty damn close to 100' per minute, I've always figured the two to be pretty much interchangable. So if you're measuring your height in feet (as any respectable gentleman is obviously going to do :P ) then it makes perfect sense to measure your climb or sink in knots.
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Postby LP » Sun Jan 14, 2007 12:09 pm

I looked through the thread quickly and saw speeds of 50 to 55 knots recommended.

If have missed something I apologize.

My question is, 50 to 55 knots seams a little slow to me, I am usually going around 65 knots, am I flying to fast?

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Postby OXO » Sun Jan 14, 2007 12:37 pm

Dr_Sprocket wrote:I looked through the thread quickly and saw speeds of 50 to 55 knots recommended.

If have missed something I apologize.

My question is, 50 to 55 knots seams a little slow to me, I am usually going around 65 knots, am I flying to fast?


Probably.

You want to fly as slow as possible, as this reduces the diameter of your turns and puts you closer to the core of the thermal, therefore, more lift !

But - the lowest speed you can fly at depends upon the angle of bank (actually the load factor, but bank angle is good enough), the amount of water ballast you are carrying, and the type of glider.

If you have a force feedback joystick, you will feel the pre stall buffet if you are flying too slow - just fly 3 knots faster than the buffet.

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Postby LP » Sun Jan 14, 2007 2:38 pm

Force feedback joystick?

No, but I guess I deserve a new toy, I will get one!

[SUGC] Calum
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Postby [SUGC] Calum » Sat Jan 05, 2008 2:52 pm

LP- i think generally you want to fly slower in lift so you spend more time in it.. if you press right ctrl button to switch the vario over to the other function, it tells you how fast you should be flying in air with that vertical speed. you know when your going through lift as it suddenly tells you you are flying to fast! and visa versa for sink

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Postby LP » Wed Jul 02, 2008 9:36 pm

Yeah, I have noticed that about the vario and figured that’s what it was. I was mainly concerned with the speed to fly wile circling in a thermal.

Since my last post Sun Jan 14, 2007 I have realized quite an advantage by trying to fly slower in thermals as you guys recommended. I don’t think flying slowly to make smaller circles is true. What I think is happening is now I am flying closer to minimum sink and going up faster. I can circle tighter by speeding up a bit but that does not seam to work as well as just getting the speed down.

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Postby LP » Wed Jul 02, 2008 9:46 pm

I have a new question about thermals that come off the tops of mountains with wind blowing up the mountain too. I have noticed that the thermal stays in one place and does not drift with the wind for sometimes a long way above the top of the mountain. I sometimes fly these “stationary” thermals with s turns.

I have also noticed that when approaching cloud base wile circling in a thermal that the thermal moves around.

What I am wondering is this the same in real life or some quirk of the sim?

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Icarus
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Postby Icarus » Thu Jul 03, 2008 6:31 am

It's a simple calculation, speed of air going up minus speed of glider going down = climb rate. The lowest speed your glider will go down is the "minimum sink speed", so the closer to that speed you can fly the faster you will climb.

Don't think about flying thermal circles in terms of fast or slow. Think about what diameter circle you need to fly to stay in the best lift. If you fly that same diameter circling turn faster you need a greater angle of bank to keep the circling diameter the same...(it stands to reason that flying faster you need a higher rate of turn to maintain the diameter). Doing this reduces the vertical lift component (vector) so reduces your climb rate. You would only fly faster if you had to....like if you had ballast on board, or if it was rough and you needed more control authority.

The optimum bank angle for thermalling in most cases in RL appears to be around 45-50 degrees. This is where the best compromise between climbing in the best lift (core) and trading off sink rate with higher bank angle seems to be. Try and find a gliders "circling polar" and you'll see what I mean. I can't speak to the thermal model in Condor though, and the thermals generally seem to be wide enough in our general flying to allow lower bank angles.

If you really want to discuss thermals, have a look at the thread called The Great Online Thermal Debate....

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Arie2c
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thermal

Postby Arie2c » Fri Aug 29, 2008 12:32 pm

Henk,

In het echt houden wij zon en windkant van de wolk aan om het stijgen te zoeken, weet alleen niet goed of dit in condor ook zo werkt.

Als je een wolk aanvliegt moet je vlak voor je er onder vliegt naar boven kijken dan zie meestal de wolk roteren, heb daar al vaak stijgen gehad.

Succes en misschien tot online.

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velaskez
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Re:

Postby velaskez » Sun Jun 14, 2009 3:26 am

tatali0n wrote:Only if you're measuring your height in meters. Which always struck me as an odd thing to do. I'd rather think of myself as being at 3200' (or near enough) rather than 1000m :wink:


Yeah...but it feels like you're falling like a rock, when you look at vario in ft :P Especially if you flown earlier on metric system.
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Didivolk66
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Re: Word of advice on making use of thermals?

Postby Didivolk66 » Sat Jan 09, 2010 4:55 am

Hi Guys
I'm still relatively new to virtual soaring. My active time flying is nearly 50y back. This is an old post but maybe somebody still looking like me. The best short advice of effective thermalling I think is from Kai Gertsen: Introduction to cross country soaring.
I can't attach the file because pdf is not allowed. But here is the web site: www.flsc.org/Xcountry/Kai_Intro_XC.pdf Its a nice easy to read and understand 40pg booklet. Have fun
Didi
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