Best Overall Motorglider available today?

On Thursday, 8 October 2020 at 10:59:09 UTC+1, Tango Whisky wrote:
Idaflieg measurements are never published to the public.

Individuals can get a copy from the Idaflieg polar (but not all the data) on request for a fee no sooner than 5 years after the first flight of the type but you are not allowed to publish them without permission. See:
https://idaflieg.de/?page_id=88

2G wrote on 10/7/2020 9:11 PM:
On Tuesday, October 6, 2020 at 9:48:47 AM UTC-7, Eric Greenwell wrote:
2G wrote on 10/6/2020 8:33 AM:
On Monday, October 5, 2020 at 3:37:33 PM UTC-7, Dave Nadler wrote:
On Sunday, October 4, 2020 at 8:04:18 PM UTC-4, 2G wrote:
The telling difference for was when I did a 30nm glide at Ely in my 26e
with an ASG29; I ended up 3,000ft below him!

Apologies all, I guess Tom's '26 perhaps isn't the "Best Overall Motorglider Available Today"...

Moral of the story: wing loading matters.

Tom

So, you were flying too fast for your wing loading, trying to keep up with the 29?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

No, we were gliding at the same speed, but not flying wingtip to wingtip.

"Wing loading matters": If the gliders had different wing loadings, and that could
have been as much as 3 lb/ft2 (based on the max wing loading each glider is
allowed), one of you was flying at the wrong speed.

The point Jon and I (both 26E owners) are trying make is the 26/29 glide angles
are similar, but the 29 will be faster when ballasted due to it's much higher max
wing loading. Had you flown at a speed appropriate for your 9.3 lb/ft2 max wing
loading, you could have arrived 2000'+ above the ridge, instead of on it,

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

Paul T wrote on 10/7/2020 10:26 PM:
At 04:12 08 October 2020, 2G wrote:
On Tuesday, October 6, 2020 at 1:58:06 PM UTC-7, Eric Greenwell
wrote:
The JS website says it's 60 for the JS1C/21M; 63 for the JS2/21M.

jfitch wrote on 10/6/2020 1:37 PM:
Link? Google produces zero results.
On Tuesday, October 6, 2020 at 1
1:00:06 AM UTC-7, Paul T wrote:
At 15:39 06 October 2020, jfitch wrote:
They are claiming 63:1, that is 7 points higher than AS claim of
56:1. I
th=
ink it is best explained by a mistake in their math. I'd be
interested in
s=
eeing the test data proving it.=20

On Tuesday, October 6, 2020 at 12:53:25 AM UTC-7, Carlo
Orsini
wrote:
Thank you for your first hand infos, those are good news for
me (I
don't
=
understand why they advertise these dimensions in a different
way).
JS2
see=
ms to be a nice project overall. Hard to me to understand
where they
strech=
ed out those +4 points of efficency in 21m, according to their
calculated
p=
olars, compared to ASH31 (yes I know that '31 profiles are a
bit
superseede=
d and the aspect ratio is a factor too but 4 points are a huge
amount!!).
Those two dimensions for the JS2 and the ASH31 are
clearly not
be
compa=
rable - one internal cockpit rim and one external I guess. The
525mm
should=
er width for the JS2 is exactly the same as the quoted figure
for the
JS1
(=
and JS3) and the JS1 cockpit roominess is fully equal to the
ASH26/31
from
=
which it was derived. I have 4 years in a JS1 followed by 2 in
the
ASH
26e
=
and they are so similar that it would be hard to know which
cockpit I
was
i=
n with my eyes closed. Looking at the JS2 cockpit photographs
it
obvious
th=
at its structural cockpit rim design is the same as the 31, 26
and
JS1.
JS
=
do not make small cockpits.
I believe the Idafleig measured a JS1C at 63:1......so the JS2
witH
its
few improvements on the JS1C should achieve that....


Someone might ask them how they came up with these L/D figures
because I
understand that they aren't from actual flight tests.

Tom


THE JS1C TO MY KNOWLEDGE HAS BEEN MEASURED AT 63:1 BY THE
IDAFLEIG IN ITS FLIGHT TESTS- PROBABLY THE MOST RELIABLE WAY
OF MEASURING A GLIDERS POLAR. (I THINK THE JONKERS BOYS
WHERE SUPRISED BY THAT FIGURE AS IT IS RARE FOR A GLIDER TO
EXCEED ITS THEOROTICAL FIGURE -BUT IT DOES HAPPEN.) ALL
MANUFACTURERS FIGURES ARE AT BEST 'THEORETICAL' UNTIL
MEASURED.................. SOME ARE WILDLY OPTIMISTIC - BUT BEST L/D
DOESNT MEAN MUCH THESE DAYS REALLY................. ITS NOT AS
THOUFGH THIS AIRCRAFT AS NOT PROVED ITSELF IN THE CONTEST
ARENA IS IT.......

It is very hard for me to believe Jonkers calculations are in error by 5% (which
is a lot!), so I suspect the error is the Idaflieg measurement. Jonkers can, and
likely has, easily do comparison glides itself, to confirm the performance of
their gliders. Since they stay with the 60:1 specification, why not accept their
numbers?
Which gliders have wildly optimistic best L/Ds?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

From Gren Seibels' book "After All:"

"MANUFACTURER'S POLAR- An exercise in creative mathematics, embellished with artistic prevarication; a gaudy package of high hopes, bound with a ribbon of fantasy; proclaimed as Gospel by the perpetrators, accepted as such by the feeble-minded and soaring pilots."

If you think that inflight measurements are easy to make, you are greatly mistaken.
Idaflieg has refined its procedure for over 40 years, and it is a huge effort:
You have to tow the glider to be measured, and a calibrated reference glider (formerly an Open Cirrus, then a DG300 modified to 17 m, now I think a Discus 2c 18m) in parallel up to 10'000+ ft very early in the morning on a day without convection and fly in free flight at the various speed points. One of the tow planes takes pictures along, with the refernce glider's fuselage length as the measure for the difference in altitude which will gradually develop, and the reference glider's polar as the base line. Typically, multiple flights on different days are conducted in order to get a decent set of data points. Nowadays, this is assisted by differential GPS data.

If you try to do measurements without a reference glider, you can't avoid air movements influencing the measurement (on a high pressure day without convection settled in, the airmass is sinking ever so slighly, and 3 cm/s will make for a huge difference at an L/D of 60.

So no, I wouldn't distrust the Idaflieg measurements, but I would distrust hearsay of the results of those measurements.

Idaflieg will never publish data for a specific reason: Such data could be used for commercial purposes by the manufacturer, or by their competitors (in the 80's, Nimbus 3 ans ASW22 have never been measured because the result would have risked to put one of the companies out of business). Using data for commercial purposes would lead to a situation were 5 years down the road, manufacturers would be very reluctant to put their gliders at disposition for measurements (and they are usually put at disposition by the manufacturers to give them a chance that this would be the serial number with the best shape ever). Idaflieg is about science, not publicity, and its driven by the students of the various Akafliegs.

And yes, you can contact them on their webpage and inquire about specific models, and they'll send you a hardcopy for 10 Euros per set. You are not allowed to spread it - they have no handle on that, but if it happend, nobody would get any copies anymore.

Bert
Ventus cM "TW"
Ex-Akaflieg Braunschweig

Le jeudi 8 octobre 2020 Ã* 16:17:30 UTC+2, Eric Greenwell a écritÂ*:
It is very hard for me to believe Jonkers calculations are in error by 5% (which
is a lot!), so I suspect the error is the Idaflieg measurement. Jonkers can, and
likely has, easily do comparison glides itself, to confirm the performance of
their gliders. Since they stay with the 60:1 specification, why not accept their
numbers?
Which gliders have wildly optimistic best L/Ds?
--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

In science, extraordinary claims require extraordinary proof. On older designs, we have the published Dick Johnson's reports. While his methodology was not problem free, it was objective, independent, consistent, repeatable, and fully documented.

On Wednesday, October 7, 2020 at 10:30:06 PM UTC-7, Paul T wrote:
At 04:12 08 October 2020, 2G wrote:
On Tuesday, October 6, 2020 at 1:58:06 PM UTC-7, Eric Greenwell
wrote:
The JS website says it's 60 for the JS1C/21M; 63 for the JS2/21M.

jfitch wrote on 10/6/2020 1:37 PM:
Link? Google produces zero results.
On Tuesday, October 6, 2020 at 1
1:00:06 AM UTC-7, Paul T wrote:
At 15:39 06 October 2020, jfitch wrote:
They are claiming 63:1, that is 7 points higher than AS claim of
56:1. I
th=
ink it is best explained by a mistake in their math. I'd be
interested in
s=
eeing the test data proving it.=20

On Tuesday, October 6, 2020 at 12:53:25 AM UTC-7, Carlo
Orsini
wrote:
Thank you for your first hand infos, those are good news for
me (I
don't
=
understand why they advertise these dimensions in a different
way).
JS2
see=
ms to be a nice project overall. Hard to me to understand
where they
strech=
ed out those +4 points of efficency in 21m, according to their
calculated
p=
olars, compared to ASH31 (yes I know that '31 profiles are a
bit
superseede=
d and the aspect ratio is a factor too but 4 points are a huge
amount!!).
Those two dimensions for the JS2 and the ASH31 are
clearly not
be
compa=
rable - one internal cockpit rim and one external I guess. The
525mm
should=
er width for the JS2 is exactly the same as the quoted figure
for the
JS1
(=
and JS3) and the JS1 cockpit roominess is fully equal to the
ASH26/31
from
=
which it was derived. I have 4 years in a JS1 followed by 2 in
the
ASH
26e
=
and they are so similar that it would be hard to know which
cockpit I
was
i=
n with my eyes closed. Looking at the JS2 cockpit photographs
it
obvious
th=
at its structural cockpit rim design is the same as the 31, 26
and
JS1.
JS
=
do not make small cockpits.
I believe the Idafleig measured a JS1C at 63:1......so the JS2
witH
its
few improvements on the JS1C should achieve that....



--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email
me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorg.../download-the-
guide-1

Someone might ask them how they came up with these L/D figures
because I
understand that they aren't from actual flight tests.

Tom
THE JS1C TO MY KNOWLEDGE HAS BEEN MEASURED AT 63:1 BY THE
IDAFLEIG IN ITS FLIGHT TESTS- PROBABLY THE MOST RELIABLE WAY
OF MEASURING A GLIDERS POLAR. (I THINK THE JONKERS BOYS
WHERE SUPRISED BY THAT FIGURE AS IT IS RARE FOR A GLIDER TO
EXCEED ITS THEOROTICAL FIGURE -BUT IT DOES HAPPEN.) ALL
MANUFACTURERS FIGURES ARE AT BEST 'THEORETICAL' UNTIL
MEASURED.................. SOME ARE WILDLY OPTIMISTIC - BUT BEST L/D
DOESNT MEAN MUCH THESE DAYS REALLY................. ITS NOT AS
THOUFGH THIS AIRCRAFT AS NOT PROVED ITSELF IN THE CONTEST
ARENA IS IT.......

I was talking about comparison flights to determine performance relative to their
competitors, not absolute L/D measurements. If the JS1C is really a 63:1 glider,
they can relatively easily determine that it's significantly better than an ASG29,
Ventus 3, ASH 31. etc, by borrowing several of those gliders and doing the tests.
They do not need a calibrated glider for this type of test.

Do you find it easy to believe Jonkers calculations of max L/D are wrong and low
by 5%? I think they would have corrected their calculations by now if they
believed the Idaflieg's measurement of 63, so that the numbers for the JS2 would
be accurate, yet that is specified at only 63.

Tango Whisky wrote on 10/8/2020 8:45 AM:
If you think that inflight measurements are easy to make, you are greatly mistaken.
Idaflieg has refined its procedure for over 40 years, and it is a huge effort:
You have to tow the glider to be measured, and a calibrated reference glider (formerly an Open Cirrus, then a DG300 modified to 17 m, now I think a Discus 2c 18m) in parallel up to 10'000+ ft very early in the morning on a day without convection and fly in free flight at the various speed points. One of the tow planes takes pictures along, with the refernce glider's fuselage length as the measure for the difference in altitude which will gradually develop, and the reference glider's polar as the base line. Typically, multiple flights on different days are conducted in order to get a decent set of data points. Nowadays, this is assisted by differential GPS data.

If you try to do measurements without a reference glider, you can't avoid air movements influencing the measurement (on a high pressure day without convection settled in, the airmass is sinking ever so slighly, and 3 cm/s will make for a huge difference at an L/D of 60.

So no, I wouldn't distrust the Idaflieg measurements, but I would distrust hearsay of the results of those measurements.

Idaflieg will never publish data for a specific reason: Such data could be used for commercial purposes by the manufacturer, or by their competitors (in the 80's, Nimbus 3 ans ASW22 have never been measured because the result would have risked to put one of the companies out of business). Using data for commercial purposes would lead to a situation were 5 years down the road, manufacturers would be very reluctant to put their gliders at disposition for measurements (and they are usually put at disposition by the manufacturers to give them a chance that this would be the serial number with the best shape ever). Idaflieg is about science, not publicity, and its driven by the students of the various Akafliegs.

And yes, you can contact them on their webpage and inquire about specific models, and they'll send you a hardcopy for 10 Euros per set. You are not allowed to spread it - they have no handle on that, but if it happend, nobody would get any copies anymore.

Bert
Ventus cM "TW"
Ex-Akaflieg Braunschweig

Le jeudi 8 octobre 2020 à 16:17:30 UTC+2, Eric Greenwell a écrit*:
It is very hard for me to believe Jonkers calculations are in error by 5% (which
is a lot!), so I suspect the error is the Idaflieg measurement. Jonkers can, and
likely has, easily do comparison glides itself, to confirm the performance of
their gliders. Since they stay with the 60:1 specification, why not accept their
numbers?
Which gliders have wildly optimistic best L/Ds?
--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

Very interesting information Bert, thanks for sharing.
Mana

On Thursday, October 8, 2020 at 5:45:36 PM UTC+2, Tango Whisky wrote:
If you think that inflight measurements are easy to make, you are greatly mistaken.
Idaflieg has refined its procedure for over 40 years, and it is a huge effort:
You have to tow the glider to be measured, and a calibrated reference glider (formerly an Open Cirrus, then a DG300 modified to 17 m, now I think a Discus 2c 18m) in parallel up to 10'000+ ft very early in the morning on a day without convection and fly in free flight at the various speed points. One of the tow planes takes pictures along, with the refernce glider's fuselage length as the measure for the difference in altitude which will gradually develop, and the reference glider's polar as the base line. Typically, multiple flights on different days are conducted in order to get a decent set of data points. Nowadays, this is assisted by differential GPS data.

If you try to do measurements without a reference glider, you can't avoid air movements influencing the measurement (on a high pressure day without convection settled in, the airmass is sinking ever so slighly, and 3 cm/s will make for a huge difference at an L/D of 60.

So no, I wouldn't distrust the Idaflieg measurements, but I would distrust hearsay of the results of those measurements.

Idaflieg will never publish data for a specific reason: Such data could be used for commercial purposes by the manufacturer, or by their competitors (in the 80's, Nimbus 3 ans ASW22 have never been measured because the result would have risked to put one of the companies out of business). Using data for commercial purposes would lead to a situation were 5 years down the road, manufacturers would be very reluctant to put their gliders at disposition for measurements (and they are usually put at disposition by the manufacturers to give them a chance that this would be the serial number with the best shape ever). Idaflieg is about science, not publicity, and its driven by the students of the various Akafliegs.

And yes, you can contact them on their webpage and inquire about specific models, and they'll send you a hardcopy for 10 Euros per set. You are not allowed to spread it - they have no handle on that, but if it happend, nobody would get any copies anymore.

On Thursday, 8 October 2020 at 19:39:27 UTC+1, Eric Greenwell wrote:
I was talking about comparison flights to determine performance relative to their
competitors, not absolute L/D measurements. If the JS1C is really a 63:1 glider,
they can relatively easily determine that it's significantly better than an ASG29,
Ventus 3, ASH 31. etc, by borrowing several of those gliders and doing the tests.
They do not need a calibrated glider for this type of test.

Do you find it easy to believe Jonkers calculations of max L/D are wrong and low
by 5%? I think they would have corrected their calculations by now if they
believed the Idaflieg's measurement of 63, so that the numbers for the JS2 would
be accurate, yet that is specified at only 63.
Tango Whisky wrote on 10/8/2020 8:45 AM:
If you think that inflight measurements are easy to make, you are greatly mistaken.
Idaflieg has refined its procedure for over 40 years, and it is a huge effort:
You have to tow the glider to be measured, and a calibrated reference glider (formerly an Open Cirrus, then a DG300 modified to 17 m, now I think a Discus 2c 18m) in parallel up to 10'000+ ft very early in the morning on a day without convection and fly in free flight at the various speed points.. One of the tow planes takes pictures along, with the refernce glider's fuselage length as the measure for the difference in altitude which will gradually develop, and the reference glider's polar as the base line. Typically, multiple flights on different days are conducted in order to get a decent set of data points. Nowadays, this is assisted by differential GPS data.

If you try to do measurements without a reference glider, you can't avoid air movements influencing the measurement (on a high pressure day without convection settled in, the airmass is sinking ever so slighly, and 3 cm/s will make for a huge difference at an L/D of 60.

So no, I wouldn't distrust the Idaflieg measurements, but I would distrust hearsay of the results of those measurements.

Idaflieg will never publish data for a specific reason: Such data could be used for commercial purposes by the manufacturer, or by their competitors (in the 80's, Nimbus 3 ans ASW22 have never been measured because the result would have risked to put one of the companies out of business). Using data for commercial purposes would lead to a situation were 5 years down the road, manufacturers would be very reluctant to put their gliders at disposition for measurements (and they are usually put at disposition by the manufacturers to give them a chance that this would be the serial number with the best shape ever). Idaflieg is about science, not publicity, and its driven by the students of the various Akafliegs.

And yes, you can contact them on their webpage and inquire about specific models, and they'll send you a hardcopy for 10 Euros per set. You are not allowed to spread it - they have no handle on that, but if it happend, nobody would get any copies anymore.

Bert
Ventus cM "TW"
Ex-Akaflieg Braunschweig

Le jeudi 8 octobre 2020 Ã* 16:17:30 UTC+2, Eric Greenwell a écrit :
It is very hard for me to believe Jonkers calculations are in error by 5% (which
is a lot!), so I suspect the error is the Idaflieg measurement. Jonkers can, and
likely has, easily do comparison glides itself, to confirm the performance of
their gliders. Since they stay with the 60:1 specification, why not accept their
numbers?
Which gliders have wildly optimistic best L/Ds?
--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

I don't understand the focus on best LD but when you are dealing with very high performance gliders the difference in sink rate for a difference of 3 points is tiny. Even so why compare a 60:1 (or ?63:1) 21m JS1c with an 18m V3 or ASG29? Judging from Open Class contest results its only relevant competitor is the EB29

John Galloway wrote on 10/8/2020 1:09 PM:
On Thursday, 8 October 2020 at 19:39:27 UTC+1, Eric Greenwell wrote:
I was talking about comparison flights to determine performance relative to their
competitors, not absolute L/D measurements. If the JS1C is really a 63:1 glider,
they can relatively easily determine that it's significantly better than an ASG29,
Ventus 3, ASH 31. etc, by borrowing several of those gliders and doing the tests.
They do not need a calibrated glider for this type of test.

Do you find it easy to believe Jonkers calculations of max L/D are wrong and low
by 5%? I think they would have corrected their calculations by now if they
believed the Idaflieg's measurement of 63, so that the numbers for the JS2 would
be accurate, yet that is specified at only 63.
Tango Whisky wrote on 10/8/2020 8:45 AM:
If you think that inflight measurements are easy to make, you are greatly mistaken.
Idaflieg has refined its procedure for over 40 years, and it is a huge effort:
You have to tow the glider to be measured, and a calibrated reference glider (formerly an Open Cirrus, then a DG300 modified to 17 m, now I think a Discus 2c 18m) in parallel up to 10'000+ ft very early in the morning on a day without convection and fly in free flight at the various speed points.. One of the tow planes takes pictures along, with the refernce glider's fuselage length as the measure for the difference in altitude which will gradually develop, and the reference glider's polar as the base line. Typically, multiple flights on different days are conducted in order to get a decent set of data points. Nowadays, this is assisted by differential GPS data.

If you try to do measurements without a reference glider, you can't avoid air movements influencing the measurement (on a high pressure day without convection settled in, the airmass is sinking ever so slighly, and 3 cm/s will make for a huge difference at an L/D of 60.

So no, I wouldn't distrust the Idaflieg measurements, but I would distrust hearsay of the results of those measurements.

Idaflieg will never publish data for a specific reason: Such data could be used for commercial purposes by the manufacturer, or by their competitors (in the 80's, Nimbus 3 ans ASW22 have never been measured because the result would have risked to put one of the companies out of business). Using data for commercial purposes would lead to a situation were 5 years down the road, manufacturers would be very reluctant to put their gliders at disposition for measurements (and they are usually put at disposition by the manufacturers to give them a chance that this would be the serial number with the best shape ever). Idaflieg is about science, not publicity, and its driven by the students of the various Akafliegs.

And yes, you can contact them on their webpage and inquire about specific models, and they'll send you a hardcopy for 10 Euros per set. You are not allowed to spread it - they have no handle on that, but if it happend, nobody would get any copies anymore.

Bert
Ventus cM "TW"
Ex-Akaflieg Braunschweig

Le jeudi 8 octobre 2020 à 16:17:30 UTC+2, Eric Greenwell a écrit :
It is very hard for me to believe Jonkers calculations are in error by 5% (which
is a lot!), so I suspect the error is the Idaflieg measurement. Jonkers can, and
likely has, easily do comparison glides itself, to confirm the performance of
their gliders. Since they stay with the 60:1 specification, why not accept their
numbers?
Which gliders have wildly optimistic best L/Ds?
--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

I don't understand the focus on best LD but when you are dealing with very high performance gliders the difference in sink rate for a difference of 3 points is tiny. Even so why compare a 60:1 (or ?63:1) 21m JS1c with an 18m V3 or ASG29? Judging from Open Class contest results its only relevant competitor is the EB29

My mistake: I looked at the wrong chart on their website. The JS1C/21M (the 60:1
glider) should be compared to other 21M gliders, of course. I agree the full polar
is important when estimating contest performance, but the max L/D is often a good
indication of the rest of the polar for modern sailplanes.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1