If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#211
|
|||
|
|||
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. |
#212
|
|||
|
|||
Best Overall Motorglider available today?
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 |
#213
|
|||
|
|||
Best Overall Motorglider available today?
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 |
#214
|
|||
|
|||
Best Overall Motorglider available today?
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 |
#215
|
|||
|
|||
Best Overall Motorglider available today?
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 |
#216
|
|||
|
|||
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. |
#217
|
|||
|
|||
Quote:
:-) Colin |
#218
|
|||
|
|||
Best Overall Motorglider available today?
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. |
#219
|
|||
|
|||
Best Overall Motorglider available today?
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. |
#220
|
|||
|
|||
Best Overall Motorglider available today?
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 |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
ASW 20C Motorglider | Nick Kennedy[_3_] | Soaring | 3 | February 7th 19 12:17 PM |
FS: DG-400 Motorglider | 2G | Soaring | 0 | September 20th 13 02:32 PM |
IFR in motorglider? | cp | Soaring | 28 | March 9th 08 01:02 AM |
Motorglider Tug | Ray Lovinggood | Soaring | 21 | November 13th 04 05:06 AM |
motorglider | KsiTau | Soaring | 0 | September 4th 04 09:10 AM |