Wing Loading / climb rate

I have had a similar question, with a small difference, for many years.

My question is:

"Using only s single glider and changing only the max flying weight - adding ballast shot bags, whatever - will that glider give its pilot a greater potential thermal climb rate when heavier or lighter?"

I am aware that higher weight will alter airspeeds but that is not my curiosity - other than a higher weight will raise stall speed some - which may add difficulties for the heavier glider using very narrow thermals - turn radius varies as the square of true airspeed, etc.

At 23:39 02 February 2017, Jim wrote:
I have had a similar question, with a small difference, for many years.

My question is:

"Using only s single glider and changing only the max flying weight -
addin=
g ballast shot bags, whatever - will that glider give its pilot a greater
p=
otential thermal climb rate when heavier or lighter?"

I am aware that higher weight will alter airspeeds but that is not my
curio=
sity - other than a higher weight will raise stall speed some - which may
a=
dd difficulties for the heavier glider using very narrow thermals - turn
ra=
dius varies as the square of true airspeed, etc.



For any glider increasing the weight will reduce it's climb rate.

On Friday, February 3, 2017 at 11:15:04 AM UTC+3, Tom Claffey wrote:
At 23:39 02 February 2017, Jim wrote:
I have had a similar question, with a small difference, for many years.

My question is:

"Using only s single glider and changing only the max flying weight -
addin=
g ballast shot bags, whatever - will that glider give its pilot a greater
p=
otential thermal climb rate when heavier or lighter?"

I am aware that higher weight will alter airspeeds but that is not my
curio=
sity - other than a higher weight will raise stall speed some - which may
a=
dd difficulties for the heavier glider using very narrow thermals - turn
ra=
dius varies as the square of true airspeed, etc.



For any glider increasing the weight will reduce it's climb rate.

The concept is pretty simple :-)

If you double the weight of a glider you increase all the speeds, including the sink rate, by 40%. So maybe you go from 100 fpm sink to 140 fpm.

If the lift is strong enough that an unballasted glider climbs at 10 knots then the ballasted one will climb at 9.5 knots or so. Maybe worse. Maybe 9 knots. So 5% or 10% slower climb.

But then it gets to run 40% faster at the same glide angle.

You need to factor in the increased thermal speed and larger diameter circles. Unless the core of the thermal is large the climb rate is reduced significantly more than just the glide calculations predict. In the "real world" higher wing loading gives an advantage, but not as much as many think unless you are flying mostly on streets. In the mountains I often do better with a 9.5 to 10 pound wing loading because I can maneuver better and work small diameter thermals.

My curiosity has been about the effect of just gross weight vs. wing loading on the

For example, let's stipulate a thermal providing a vertical force ( I avoid using newtons as the SI unit for force. I've never managed to get comfortable with it.) that would provide +5 kt lift to a glider with a gross weight of 800 lbs and a wing loading of 10 lbs / sqft.. I'm just making this stuff up. I am not trying to be realistic!

Now let's invent another glider with a wing loading of just 5 lbs / sqft. but with the same gross weight as the first glider.

Would the second glider, with a wing loading of just 5 lbs / sqft, get a better climb rate than the first glider since it appears it would need only half the lifting force per square foot of wing than would the first glider?

On Friday, February 3, 2017 at 10:19:00 AM UTC-7, Jim wrote:
My curiosity has been about the effect of just gross weight vs. wing loading on the

For example, let's stipulate a thermal providing a vertical force ( I avoid using newtons as the SI unit for force. I've never managed to get comfortable with it.) that would provide +5 kt lift to a glider with a gross weight of 800 lbs and a wing loading of 10 lbs / sqft.. I'm just making this stuff up. I am not trying to be realistic!

Now let's invent another glider with a wing loading of just 5 lbs / sqft. but with the same gross weight as the first glider.

Would the second glider, with a wing loading of just 5 lbs / sqft, get a better climb rate than the first glider since it appears it would need only half the lifting force per square foot of wing than would the first glider?

Unfortunately it is not that easy. The short answer is the lighter wing loading glider will climb better, just as the heavier will run better. The long answer is they won't fly at the same speed so the lighter wing loading glider has the advantage additionally of working a tighter core.

Thank you Tim. I am beginning to understand it all.

JIm

On Friday, February 3, 2017 at 7:40:25 AM UTC-7, Tim Taylor wrote:
You need to factor in the increased thermal speed and larger diameter circles. Unless the core of the thermal is large the climb rate is reduced significantly more than just the glide calculations predict. In the "real world" higher wing loading gives an advantage, but not as much as many think unless you are flying mostly on streets. In the mountains I often do better with a 9.5 to 10 pound wing loading because I can maneuver better and work small diameter thermals.

Exactly what we have found in Arizona - much depends on the thermal profile and especially the ability to stay in a strong, narrow thermal core.

Mike

On Sunday, February 5, 2017 at 3:24:58 AM UTC+11, Mike the Strike wrote:
On Friday, February 3, 2017 at 7:40:25 AM UTC-7, Tim Taylor wrote:
You need to factor in the increased thermal speed and larger diameter circles. Unless the core of the thermal is large the climb rate is reduced significantly more than just the glide calculations predict. In the "real world" higher wing loading gives an advantage, but not as much as many think unless you are flying mostly on streets. In the mountains I often do better with a 9.5 to 10 pound wing loading because I can maneuver better and work small diameter thermals.

Exactly what we have found in Arizona - much depends on the thermal profile and especially the ability to stay in a strong, narrow thermal core.

Mike

I often feel like on the exceptionally hot and high Australian days, that it feels like I just can't fit in the thermals at high altitudes. Lighter aircraft don't seem to have the same trouble. My theory is that a thermals diameter doesn't vary substantially with height, however due to density altitude/TAS, my thermalling radius does vary substantially. Or at least that's my excuse.

Any thoughts on whether this is true, that the diameter of thermals remains constant at altitude, or widens slower than the circling radius considering TAS?