What is magical about a 45 degree bank?

I know that a 45 degree bank is useful for flying small circles and staying in small thermals, but is there something special about a 45 degree bank compared to say a 50 degree bank?

For example, does the designer intend for the glider to do something special at 45 degrees? Is the glider designed to balance aerodynamic forces in a particular harmony at a precise 45 degree bank?

On Saturday, October 5, 2013 12:48:27 PM UTC-5, son_of_flubber wrote:
I know that a 45 degree bank is useful for flying small circles and staying in small thermals, but is there something special about a 45 degree bank compared to say a 50 degree bank?



For example, does the designer intend for the glider to do something special at 45 degrees? Is the glider designed to balance aerodynamic forces in a particular harmony at a precise 45 degree bank?

Simple: the tan 45 deg is = 1 so you are #1, A-OK, top of the world, #1 flying ace, you get the drift! (don't drift when thermaling)
On the other side, the tan of 30 and 60 deg is a mess, don't go there!
Seriously, there seems to be a sweet spot around 45 deg where the radius flown at our thermaling speeds is keeping us closest to the high-climb values found at the center of the thermal without the penalty of higher wingloading and resulting higher stall speeds and overall higher sink at bank angles 50 deg.
Not sure this was helpful...
Herb

I see Herb is just as frustrated as I am that it's raining...

The magic of 45 degrees is that if you tell someone to thermal at 45, they'll probably thermal at 35 - 40 which is really the optimum most of the time, at least over the soggy midwest!

John Cochrane

On Saturday, October 5, 2013 10:48:27 AM UTC-7, son_of_flubber wrote:
I know that a 45 degree bank is useful for flying small circles and staying in small thermals, but is there something special about a 45 degree bank compared to say a 50 degree bank?



For example, does the designer intend for the glider to do something special at 45 degrees? Is the glider designed to balance aerodynamic forces in a particular harmony at a precise 45 degree bank?

"The proper angle of bank in a thermal is one which yields the fastest average rate of climb" --Jim Indrebro--

Obvious, but often overlooked metric. Every thermal is different, airspeed is a factor, airplane, etc., etc.

Matt

On Saturday, October 5, 2013 1:48:27 PM UTC-4, son_of_flubber wrote:
I know that a 45 degree bank is useful for flying small circles and staying in small thermals, but is there something special about a 45 degree bank compared to say a 50 degree bank? For example, does the designer intend for the glider to do something special at 45 degrees? Is the glider designed to balance aerodynamic forces in a particular harmony at a precise 45 degree bank?

Over time we have learned that the best climb rate tends to be when the optimum trade off between circling diameter and sink rate increase caused by banking in achieved. This turns out to be right around 40 degrees. Most people over estimate their bank angle. When they think they are 45 degrees, more likely they are just over 30. Only rarely does more than 45 improve climb.. The key is tighten till the climb rate is steadily best and stick with it..
Most gliders, left alone to spiral, will settle in around 30 degrees from my experience.
FWIW
UH

Hi, there is a very descriptive book by Markus Lisken and Ulf Gerber called
Radio Control Thermal Gliding, that uses some very complex mathematics to
investigate the best possible thermaling practice.

In it's comparison of various birds, it concludes that Buzzards are better
thermalers than Sea-gulls, because they have a lower Wing Aspect Ratio
(6:1 cf 12:1.) and are able to make tighter turns into the middle of the
lift. It quotes.. 'These wing shapes clearly show that a design to give
minimal sink in no way concur with a design for maximum climb rate'.

So your K8 might outperform a ASW29 in a small diameter thermal.

On Sun, 06 Oct 2013 08:15:31 +0000, Peter Higgs wrote:

Hi, there is a very descriptive book by Markus Lisken and Ulf Gerber
called Radio Control Thermal Gliding, that uses some very complex
mathematics to investigate the best possible thermaling practice.

In it's comparison of various birds, it concludes that Buzzards are
better thermalers than Sea-gulls, because they have a lower Wing Aspect
Ratio (6:1 cf 12:1.) and are able to make tighter turns into the middle
of the lift. It quotes.. 'These wing shapes clearly show that a design
to give minimal sink in no way concur with a design for maximum climb
rate'.

I watched a medium sized buzzard-shaped raptor at Wiener Neustadt the
other day as it picked up lift at 50-60ft over the apron and climbed
away. It went up like a rocket in a very small corkscrew spiral, not more
than 3 times its own span and using under 40 degrees bank.

Try doing that in any current sailplane!



--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Nothing magical about 45 degree angle of bank. For any given angle of
bank, turn radius varies with the square of (true) airspeed. For the
gliders we are mostly used to and average sized and velocity gradient
thermals, 45 degrees is often about right. For a vintage type with a
stalling speed of 30 knots, circling at 30 degrees of bank, or even less,
at 35 knots may be better, for a heavily ballasted modern type, in a small
thermal, 60 degrees or even more may be best (better to dump the water
unless your pretty sure of finding bigger thermals later). How much bank
to use in a particular thermal is one of the most important and hardest
learned skills.

At 17:48 05 October 2013, son_of_flubber wrote:
I know that a 45 degree bank is useful for flying small circles and
staying
in small thermals, but is there something special about a 45 degree bank
compared to say a 50 degree bank?

For example, does the designer intend for the glider to do something
special at 45 degrees? Is the glider designed to balance aerodynamic
forces in a particular harmony at a precise 45 degree bank?

Thank you for the recommendations made here. I've just ordered copies of:

"Fundamentals of Sailplane Design" by Fred Thomas.

"Radio Control Thermal Gliding" by Markus Lisken and Ulf Gerber

Good reading for the winter ahead.

Maybe lots of inside rudder...?? ;-P


"Martin Gregorie" wrote in message
...
On Sun, 06 Oct 2013 08:15:31 +0000, Peter Higgs wrote:

Hi, there is a very descriptive book by Markus Lisken and Ulf Gerber
called Radio Control Thermal Gliding, that uses some very complex
mathematics to investigate the best possible thermaling practice.

In it's comparison of various birds, it concludes that Buzzards are
better thermalers than Sea-gulls, because they have a lower Wing Aspect
Ratio (6:1 cf 12:1.) and are able to make tighter turns into the middle
of the lift. It quotes.. 'These wing shapes clearly show that a design
to give minimal sink in no way concur with a design for maximum climb
rate'.

I watched a medium sized buzzard-shaped raptor at Wiener Neustadt the
other day as it picked up lift at 50-60ft over the apron and climbed
away. It went up like a rocket in a very small corkscrew spiral, not more
than 3 times its own span and using under 40 degrees bank.

Try doing that in any current sailplane!



--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |