Best Overall Motorglider available today?

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

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

At 21:12 08 October 2020, Eric Greenwell wrote:
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 relati=
ve 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 th=
an 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 wro=
ng 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 gre=
atly mistaken.
Idaflieg has refined its procedure for over 40 years, and
it is a hug=
e 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 th=
ink a Discus 2c 18m) in parallel up to 10'000+ ft very early
in the morni=
ng on a day without convection and fly in free flight at the
various spee=
d points.. One of the tow planes takes pictures along, with
the refernce =
glider's fuselage length as the measure for the difference in
altitude wh=
ich will gradually develop, and the reference glider's polar as
the base =
line. Typically, multiple flights on different days are
conducted in orde=
r to get a decent set of data points. Nowadays, this is
assisted by diffe=
rential GPS data.

If you try to do measurements without a reference
glider, you can't a=
void air movements influencing the measurement (on a high
pressure day wi=
thout 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 dis=
trust hearsay of the results of those measurements.

Idaflieg will never publish data for a specific reason:
Such data cou=
ld be used for commercial purposes by the manufacturer, or
by their compe=
titors (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)=
=2E Using data for commercial purposes would lead to a
situation were 5 y=
ears down the road, manufacturers would be very reluctant
to put their gl=
iders at disposition for measurements (and they are usually
put at dispos=
ition by the manufacturers to give them a chance that this
would be the s=
erial number with the best shape ever). Idaflieg is about
science, not pu=
blicity, and its driven by the students of the various Akafliegs.

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

Bert
Ventus cM "TW"
Ex-Akaflieg Braunschweig

Le jeudi 8 octobre 2020 =E0 16:17:30 UTC+2, Eric
Greenwell a =E9crit =
:
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. Jonk=
ers can, and
likely has, easily do comparison glides itself, to
confirm the perfo=
rmance of
their gliders. Since they stay with the 60:1
specification, why not =
accept their
numbers?
Which gliders have wildly optimistic best L/Ds?
--=20
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...cations/downlo
ad-the=
-guide-1
=20
I don't understand the focus on best LD but when you are
dealing with v=
ery 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 wi=
th an 18m V3 or ASG29? Judging from Open Class contest
results its only=
relevant competitor is the EB29
=20
My mistake: I looked at the wrong chart on their website.
The JS1C/21M (t=
he 60:1=20
glider) should be compared to other 21M gliders, of course. I
agree the f=
ull polar=20
is important when estimating contest performance, but the
max L/D is ofte=
n a good=20
indication of the rest of the polar for modern sailplanes.

--=20
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...cations/downlo
ad-th=
e-guide-1

As I understand it, the Js1 only really beats other gliders
when the wing loading is high.At one point I was considering
buying one and talking with the agent about the benefits of the
21 M tips.
Their opinion was 21 M was often slower than a well blasted
18. I looked at the polars and was frankly baffled.
At that time they were only fitting panels and enclosures for
jet engines that still had not been certified.
I opted to save a lot of money and buy a second hand
Ventus2ct which I love but has hardly flown this year because
of Covid.(could of rented a light twin for less by the hour!!!)

You bunch of ******* don't believe anything do you, argue amongst
yourselves, thats what you are good at , if you don't want to believe it
fine.