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Optimum thermalling speed display



 
 
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  #21  
Old September 28th 12, 02:10 PM posted to rec.aviation.soaring
kirk.stant
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Default Optimum thermalling speed display

On Friday, September 28, 2012 6:30:03 AM UTC-6, Jim White wrote:
Two thoughts on this:



1) There is no substitute for practice.

2) If you need a computer for everything you might as well let the computer

fly the glider. Why have the middleman?


I'm confused, Jim: Do you have a vario in your glider? Or a glide computer? PNA?

How does having real time information on a variable performance value (min sink speed for current conditions) equate to letting the computer fly the glider?

Kirk
  #22  
Old September 28th 12, 03:25 PM posted to rec.aviation.soaring
Evan Ludeman[_4_]
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Default Optimum thermalling speed display

On Friday, September 28, 2012 8:55:30 AM UTC-4, kirk.stant wrote:
On Thursday, September 27, 2012 3:50:35 PM UTC-6, Tim Taylor wrote:



1. Most pilots don't/can't thermal steep enough and can't tell what




bank they are flying even when told how to look at the panel or look




outside the glider.








2. You already have an instrument to tell you optimum speed and bank




to fly, it is the variometer. There is no magic perfect speed to fly




that you can predict ahead of time. Depending on the thermal itself,




I may fly slower or faster than optimum for some equation. All those




factors come down to one number, maximum climb rate! I adjust bank




angle, speed, flap setting, slip, etc until I get the best rate of




climb for each thermal.




Tim, I totally agree about bank angle - steep is good! And I mostly agree on your second point, about varying a bunch of parameters to find what works best in any particular thermal. Where I disagree, probably due to less experience, is that there isn't room for better instumentation to tell the pilot what exactly his glider is doing. Min sink is min sink - it only happens at one angle of attack. That equates to one unique airspeed for every combination of bank angle and wing loading. Think of it as Mcready speed - a wonderful invention, gives the theoretical optimum cruise speed to fly, made cross country faster, etc.. and all our fancy computers give us a variety of indicators on how fast to fly, when to push or pull, audio tones, etc... Of course, a lot of us just use it as a guide and adjust our speed for the conditions at hand, since the bloody black box isn't looking out the window!



I'm just thinking that the equivalent for thermalling might be useful.



Cheers,



Kirk

66


Best climb isn't achieved at minimum sink. Usually (90%), it pays (in climb) to fly slower than (load factor corrected) minimum sink speed. The optimum is going to be very slippery -- it depends as much on the thermal characteristics, turbulence, etc. as it does on glider performance. It's this sort of abstract, complicated, multivariable, analog "computing" that humans can still do better than machines (with enough practice). Enjoy it while it lasts!

-Evan Ludeman / T8
  #23  
Old September 28th 12, 03:39 PM posted to rec.aviation.soaring
[email protected]
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Default Optimum thermalling speed display

Please explain in more detail. Not clear what you mean by "optimum is going to be very slippery." Are you saying that the benefit of slower flight and therefore tighter radius circles outweigh the losses from the higher sink rate? Not trying to be a smart alec, I seriously want to learn from you more experienced guys. thank you.

Robert

On Friday, September 28, 2012 9:25:17 AM UTC-5, Evan Ludeman wrote:

Best climb isn't achieved at minimum sink. Usually (90%), it pays (in climb) to fly slower than (load factor corrected) minimum sink speed. The optimum is going to be very slippery -- it depends as much on the thermal characteristics, turbulence, etc. as it does on glider performance. It's this sort of abstract, complicated, multivariable, analog "computing" that humans can still do better than machines (with enough practice). Enjoy it while it lasts!



-Evan Ludeman / T8


  #24  
Old September 28th 12, 03:48 PM posted to rec.aviation.soaring
Evan Ludeman[_4_]
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Posts: 484
Default Optimum thermalling speed display

Ye Gods, are we top posting or bottom posting in this thread :-)?

"Slippery" in the sense of elusive, ever changing, fiendishly difficult to calculate in real time.

2nd part: Yes, exactly, smaller circle (v min sink) yields better climb in most (classic small, round, columnar, strong at the core) thermals. Uncenterable lift or really huge thermals are typical exceptions.

-Evan Ludeman / T8

On Friday, September 28, 2012 10:39:21 AM UTC-4, (unknown) wrote:
Please explain in more detail. Not clear what you mean by "optimum is going to be very slippery." Are you saying that the benefit of slower flight and therefore tighter radius circles outweigh the losses from the higher sink rate? Not trying to be a smart alec, I seriously want to learn from you more experienced guys. thank you.



Robert



On Friday, September 28, 2012 9:25:17 AM UTC-5, Evan Ludeman wrote:



Best climb isn't achieved at minimum sink. Usually (90%), it pays (in climb) to fly slower than (load factor corrected) minimum sink speed. The optimum is going to be very slippery -- it depends as much on the thermal characteristics, turbulence, etc. as it does on glider performance. It's this sort of abstract, complicated, multivariable, analog "computing" that humans can still do better than machines (with enough practice). Enjoy it while it lasts!








-Evan Ludeman / T8

  #25  
Old September 28th 12, 08:13 PM posted to rec.aviation.soaring
Grider Pirate[_2_]
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Default Optimum thermalling speed display

On Sep 28, 7:48*am, Evan Ludeman wrote:
Ye Gods, are we top posting or bottom posting in this thread :-)?

"Slippery" in the sense of elusive, ever changing, fiendishly difficult to calculate in real time.

2nd part: Yes, exactly, smaller circle (v min sink) yields better climb in most (classic small, round, columnar, strong at the core) thermals. *Uncenterable lift or really huge thermals are typical exceptions.

-Evan Ludeman / T8



On Friday, September 28, 2012 10:39:21 AM UTC-4, (unknown) wrote:
Please explain in *more detail. *Not clear what you mean by "optimum is going to be very slippery." *Are you saying that the benefit of slower flight and therefore tighter radius circles outweigh the losses from the higher sink rate? *Not trying to be a smart alec, I seriously want to learn from you more experienced guys. thank you.


Robert


On Friday, September 28, 2012 9:25:17 AM UTC-5, Evan Ludeman wrote:


Best climb isn't achieved at minimum sink. *Usually (90%), it pays (in climb) to fly slower than (load factor corrected) minimum sink speed. *The optimum is going to be very slippery -- it depends as much on the thermal characteristics, turbulence, etc. as it does on glider performance. *It's this sort of abstract, complicated, multivariable, analog "computing" that humans can still do better than machines (with enough practice). *Enjoy it while it lasts!


-Evan Ludeman / T8- Hide quoted text -


- Show quoted text -


The key point Evan makes (and I totally agree!) is that the strongest
lift is closest to the the center of a thermal, so flying slower
smaller diameter spirals will increase climb rate even though the
increased bank decreases the vertical component of lift. I had
opportunity to fly with some paragliders (with JS ) and even though
the paraglider min-sink isn't good, they outclimbed us because they
can fly such a small circle, and stay in the strongest lift.
  #26  
Old September 29th 12, 07:23 AM posted to rec.aviation.soaring
Jim Wallis[_2_]
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Default Optimum thermalling speed display

So is the target bank angle always 45 degrees (with slowest safe speed for
that bank) or would you give up bank angle to slow down more i.e. focus on
speed control. Which gives you the tightest circle?

- Jim






The key point Evan makes (and I totally agree!) is that the strongest
lift is closest to the the center of a thermal, so flying slower
smaller diameter spirals will increase climb rate even though the
increased bank decreases the vertical component of lift. I had
opportunity to fly with some paragliders (with JS ) and even though
the paraglider min-sink isn't good, they outclimbed us because they
can fly such a small circle, and stay in the strongest lift.


  #27  
Old September 29th 12, 03:49 PM posted to rec.aviation.soaring
kirk.stant
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Posts: 1,260
Default Optimum thermalling speed display

Evan,

I wonder if there has been a study done on tradeoffs between sink rate and circle size. Of course, the problem is that thermals are not very consistent...

And just to make things clear, I also vary my speed and bank angle until I find what I think is the best climb.

But I disagree that the best speed cannot be somewhat quantified. Stall is obviously the slowest - and that speed changes based on at least two variables. How far above stall - up to CL max, or perhaps even faster in a tight, turbulent thermal at 60 degrees of bank) is optimum? Without knowing what stall speed or min sink is, you are guessing or relying on experience or glider feedback. If you are not experienced, or your glide does not give much feedback, you are left with guessing - probably on the high side because of all the "stall spin" stories you have read here on RAS.

So if it is easy to display, in real time, what stall/min sink/Cl max is at your current flight condition, that data helps calibrate your "experience" quicker.

I find it amusing that we are raving about new technology varios and debating the relative merits of PNA thermal centering displays, while the airspeed cue we display in the cockpit to use all the new info is still just a mechanical airspeed indicator. Some gliders talk a lot, so that monitoring the airspeed is not very necessary. Others, like my ls6, have very little change in feel from the stall up to ridiculously high thermalling speeds - only the nose position relative to the horizon is a givaway to how fast I'm flying, once trimmed up. So the technique of pulling till you feel the stall buffet and easing off doesn't work very well!

Anyway- interesting discussion.

Cheers - gotta go give a glider ride.

Kirk
66

  #28  
Old September 29th 12, 04:37 PM posted to rec.aviation.soaring
Eric Greenwell[_4_]
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Default Optimum thermalling speed display

On 9/29/2012 7:49 AM, kirk.stant wrote:
So the technique of pulling till you feel the stall buffet and easing
off doesn't work very well!


Many gliders, like my ASH 26 E, the DG 800, and others, have a "flat
spot" in the airfoil lift drag curve, and climb better in "turbulent"
thermals when flown significantly faster than just above the stall
buffet. An indicator would be especially helpful for these gliders.
Also, even the stall buffet is hard to detect above about 40 degrees
bank, at least with my CG.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
  #29  
Old September 29th 12, 05:19 PM posted to rec.aviation.soaring
[email protected]
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Posts: 2,124
Default Optimum thermalling speed display

On Saturday, September 29, 2012 2:30:04 AM UTC-4, Jim Wallis wrote:
So is the target bank angle always 45 degrees (with slowest safe speed for that bank) or would you give up bank angle to slow down more i.e. focus on speed control. Which gives you the tightest circle? - Jim The key point Evan makes (and I totally agree!) is that the strongest lift is closest to the the center of a thermal, so flying slower smaller diameter spirals will increase climb rate even though the increased bank decreases the vertical component of lift. I had opportunity to fly with some paragliders (with JS ) and even though the paraglider min-sink isn't good, they outclimbed us because they can fly such a small circle, and stay in the strongest lift.


There is no "always". The bank angle for best climb must take into acoount sink rate of the glider as well as the gradient of thermal strength with respect to thermal size. Then throw in that many thermals are not round and require bank changes. Add to this that, as bank changes, speed should change slightly, while anticipating the next gust or slacking of lift. And, just to make it a bit more complicated, avoid the angle of attack where the lift vs angle of attack gradient is unfavorable.
Funny how flying for a week or so in concentrated manner makes this easier to do.
UH
  #30  
Old September 29th 12, 06:34 PM posted to rec.aviation.soaring
Evan Ludeman[_4_]
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Posts: 484
Default Optimum thermalling speed display

On Saturday, September 29, 2012 10:49:36 AM UTC-4, kirk.stant wrote:
Evan,



I wonder if there has been a study done on tradeoffs between sink rate and circle size. Of course, the problem is that thermals are not very consistent...



And just to make things clear, I also vary my speed and bank angle until I find what I think is the best climb.



But I disagree that the best speed cannot be somewhat quantified. Stall is obviously the slowest - and that speed changes based on at least two variables. How far above stall - up to CL max, or perhaps even faster in a tight, turbulent thermal at 60 degrees of bank) is optimum? Without knowing what stall speed or min sink is, you are guessing or relying on experience or glider feedback. If you are not experienced, or your glide does not give much feedback, you are left with guessing - probably on the high side because of all the "stall spin" stories you have read here on RAS.



So if it is easy to display, in real time, what stall/min sink/Cl max is at your current flight condition, that data helps calibrate your "experience" quicker.



I find it amusing that we are raving about new technology varios and debating the relative merits of PNA thermal centering displays, while the airspeed cue we display in the cockpit to use all the new info is still just a mechanical airspeed indicator. Some gliders talk a lot, so that monitoring the airspeed is not very necessary. Others, like my ls6, have very little change in feel from the stall up to ridiculously high thermalling speeds - only the nose position relative to the horizon is a givaway to how fast I'm flying, once trimmed up. So the technique of pulling till you feel the stall buffet and easing off doesn't work very well!



Anyway- interesting discussion.



Cheers - gotta go give a glider ride.



Kirk

66


The LS-6 is a much loved glider, what gives? My 20 gives plenty of feedback. Here's how I train T8's pilot: instrument covers. Climb to top of convection, cover everything but altimeter and averager, no audio. Great for back to basics.

As far as calculating the optimum way to climb, we do trade studies several times a year. We call 'em "contests" :-). I find them effective.

Seriously, given an accurate mathematical description of any given thermal, any given sailplane, you could of course, find an optimum. That's been hashed out for simple cases in Reichmann, other places. It's probably all valid, but it puts me to sleep.

As far as Nav instruments and all the rest... well, I've tried a bunch. On the ClearNav team since June (end user and part time associate, just to be clear). Like that a lot. I've tried the thermal assistants in various devices to see what they do. I found one of them useful for a while a couple of years ago (WinPilot) until I discovered my real problem was a buggy, jumpy electric vario (with smooth nmea output so the thermal assistant worked fine). With the vario problem solved I no longer have any use for that stuff.

What I like about the CN is speed of info acquisition. Glance, and done. It doesn't try to tell me how to fly, I'm not going to have to hassle with anyone about an AHRS disabled mode, it doesn't show me pictures of off field landing sites, it doesn't have the amazing in flight statistical analysis of thermals and wind that some other devices do. While I found the statistics useful (or thought I did)... the statistic I really like is that is that I fly one helluva lot better in competition on CN than I do on anything else. I don't think that was a fluke. It was simply figuring out a Nav setup that doesn't get in my way.

-Evan Ludeman / T8

PS Cheers, got to go to a birthday party (it's raining, no loss :-))

 




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