Best Overall Motorglider available today?

Reynolds numbers do make a difference, but it would be a *very* unusual airfoil that changed that much over such a small change in Re. The Jonkers published polar is peculiar in many ways.

I did reach out to both Ideflug and Jonkers about any data they had on tests, got acknowledgment of the requests but no response from either.

On Thursday, November 19, 2020 at 6:59:29 AM UTC-8, wrote:
On 11/19/2020 8:35 AM, Eric Greenwell wrote:
How odd the 63:1 only occurs at the high wing loading in 21M, and not at
the minimum wing loading, where the L/D is essentially the same for the
18M and 21M wings.
Not odd at all. Reynolds number changes make a big difference especially
with tiny chord. IIRC the original Ventus 15m increased LD 2 points with
ballast, and could not change wingloading as much as modern gliders.

Dave Nadler wrote on 11/19/2020 6:59 AM:
On 11/19/2020 8:35 AM, Eric Greenwell wrote:
How odd the 63:1 only occurs at the high wing loading in 21M, and not at the minimum wing
loading, where the L/D is essentially the same for the 18M and 21M wings.

Not odd at all. Reynolds number changes make a big difference especially with tiny chord. IIRC
the original Ventus 15m increased LD 2 points with ballast, and could not change wingloading as
much as modern gliders.


This does not seem to be about wing loading, as the chart shows the 18/21 versions at the same
wing loading, so I repeat: It's still odd that adding 10' to the span does not significantly
change the performance at any speed except in the lowest few knots of the polar.

If it's Reynolds number that's important: Shouldn't the 21 M wing have more feet of wider chord
than the 18M wing, and shouldn't we expect it to do better, just based on 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...ad-the-guide-1

On Thu, 19 Nov 2020 08:23:43 -0800, Eric Greenwell wrote:

Dave Nadler wrote on 11/19/2020 6:59 AM:
On 11/19/2020 8:35 AM, Eric Greenwell wrote:
How odd the 63:1 only occurs at the high wing loading in 21M, and not
at the minimum wing loading, where the L/D is essentially the same for
the 18M and 21M wings.

Not odd at all. Reynolds number changes make a big difference
especially with tiny chord. IIRC the original Ventus 15m increased LD 2
points with ballast, and could not change wingloading as much as modern
gliders.


This does not seem to be about wing loading, as the chart shows the
18/21 versions at the same wing loading, so I repeat: It's still odd
that adding 10' to the span does not significantly change the
performance at any speed except in the lowest few knots of the polar.

If it's Reynolds number that's important: Shouldn't the 21 M wing have
more feet of wider chord than the 18M wing, and shouldn't we expect it
to do better, just based on that?

Aspect ratio is also beneficial and will increase the overall L/D ratio
at a given airspeed if the wing section and wing loading are unchanged.


--
--
Martin | martin at
Gregorie | gregorie dot org

Martin Gregorie wrote on 11/19/2020 9:01 AM:
On Thu, 19 Nov 2020 08:23:43 -0800, Eric Greenwell wrote:

Dave Nadler wrote on 11/19/2020 6:59 AM:
On 11/19/2020 8:35 AM, Eric Greenwell wrote:
How odd the 63:1 only occurs at the high wing loading in 21M, and not
at the minimum wing loading, where the L/D is essentially the same for
the 18M and 21M wings.

Not odd at all. Reynolds number changes make a big difference
especially with tiny chord. IIRC the original Ventus 15m increased LD 2
points with ballast, and could not change wingloading as much as modern
gliders.


This does not seem to be about wing loading, as the chart shows the
18/21 versions at the same wing loading, so I repeat: It's still odd
that adding 10' to the span does not significantly change the
performance at any speed except in the lowest few knots of the polar.

If it's Reynolds number that's important: Shouldn't the 21 M wing have
more feet of wider chord than the 18M wing, and shouldn't we expect it
to do better, just based on that?

Aspect ratio is also beneficial and will increase the overall L/D ratio
at a given airspeed if the wing section and wing loading are unchanged.

Exactly! And yet, despite an aspect ratio of 36 (21 M) vs 29 (18 M), the 21 M performance is
almost identical, according to the chart. How can that be?

--
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

Not to hijack this interesting thread either, but for anyone who is leaning towards getting in to a self-launcher, I just listed my DG-400 on wings and wheels.
It is serial# 104, built in 1984. I flew it this past season and am upgrading to a Schleicher self-launcher.

Henry

Exactly! And yet, despite an aspect ratio of 36 (21 M) vs 29 (18 M), the 21 M performance is
almost identical, according to the chart. How can that be?

--
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[/quote]

Hi - The polar graph on the JS website starts at a higher airspeed than most others - the major performance difference between spans occurs around the thermalling speed region which is missing in the graph. I can attest from flying JS1's in both spans against others that there is very little noticable performance difference at similar wingloadings at cruise speeds.
That said I believe the ballasted 21m JS1 is an underrated weapon and the JS2 will be even better. The JS5 will be in a class of its own.

Originally Posted by Eric Greenwell[_4_]

Dave Nadler wrote on 11/19/2020 6:59 AM:
On 11/19/2020 8:35 AM, Eric Greenwell wrote:
How odd the 63:1 only occurs at the high wing loading in 21M, and not at the minimum wing
loading, where the L/D is essentially the same for the 18M and 21M wings.

Not odd at all. Reynolds number changes make a big difference especially with tiny chord. IIRC
the original Ventus 15m increased LD 2 points with ballast, and could not change wingloading as
much as modern gliders.


This does not seem to be about wing loading, as the chart shows the 18/21 versions at the same
wing loading, so I repeat: It's still odd that adding 10' to the span does not significantly
change the performance at any speed except in the lowest few knots of the polar.

If it's Reynolds number that's important: Shouldn't the 21 M wing have more feet of wider chord
than the 18M wing, and shouldn't we expect it to do better, just based on 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...ad-the-guide-1

The max wing loadings shown on the polar chart differ by c. 5 kg/m² so that fits with what is shown as does the equal min wing loadings

:-) Colin

At 12:13 19 November 2020, Paul T wrote:
For all you non-believers and skeptics that did not believe the JS1 had

been measured by the Idafleig at 63:1 please see the latest posting on th

Jonkers website regarding the JS2. Your really not as smart as you thin
you
are.



Apologies, should have said FB page(although the article should also be on

their website)- the article by Segelfleigen magazine on the JS2
acknowledges that Idafleig measured the JS1C at 63:1 as you where
previously informed off, but had to have a massive debate decrying the
fact.
Hopefully some of you have the intellect to read German.

At 07:25 20 November 2020, Paul T wrote:
At 12:13 19 November 2020, Paul T wrote:
For all you non-believers and skeptics that did not believe
the JS1 had
been measured by the Idafleig at 63:1 please see the latest
posting on the Jonkers website regarding the JS2. Your really
not as smart as you think you are.

Apologies, should have said FB page(although the article should
also be on
their website)- the article by Segelfleigen magazine on the JS2
acknowledges that Idafleig measured the JS1C at 63:1 as you where
previously informed off, but had to have a massive debate decrying th
fact.
Hopefully some of you have the intellect to read German.

Doubtless some of us, including some of the native English
speakers, *do* have the intellect to understand German. Had you
shown any aptitude for spelling, syntax and semantics, we might
have been more stung by your insulting tone.

I'll allow you the absurd "sKeptical", as I suppose that you
are American or Canadian. But not
"Idafleig" for "Idaflieg",
"Segelfleigen" for "Segelfliegen",
"Your really not ..." for "You're ...", and
"you where ... informed off" for "were" and "of" (which
latter should not have been dangling at the end of the clause).
Nor "non-believers and skeptics that ..." which, in addition to
the glaring tautology, was grammatically incorrect in using "that"
where "who" was required.

May I recommend the Biblical advice:
"First cast out the beam out of thine own eye"?
J.

Paul T wrote on 11/19/2020 11:25 PM:
At 12:13 19 November 2020, Paul T wrote:
For all you non-believers and skeptics that did not believe the JS1 had

been measured by the Idafleig at 63:1 please see the latest posting on th

Jonkers website regarding the JS2. Your really not as smart as you thin
you
are.



Apologies, should have said FB page(although the article should also be on

their website)- the article by Segelfleigen magazine on the JS2
acknowledges that Idafleig measured the JS1C at 63:1 as you where
previously informed off, but had to have a massive debate decrying the
fact.
Hopefully some of you have the intellect to read German.

I, like most of the people on this forum, do have the intellect to read German, but not the
training or the motivation. Why not translate crucial paragraph(s) for us?

--
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