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#11
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Greg, you did a fine job of putting these articles up
and the effort is greatly appreciated. I read them all and found useful information in all of them. I was not putting down anyones pilot report. But... Give ten pilots the opportunity to fly a new ship and you will get ten different pilot reports, each will have his own opinion depending on a variety of things, including experience, skill or ability, weight, etc. All of these pilot reports are subjective, Wheras I believe Dick Johnson's flight reports are more OBJECTIVE. Backed up by flight tests with measured and recorded results. They feature polars and numbers relating real world results. Over the years, manufacturers have consistantly given their L/D numbers to be 1 or 2 points higher than was revealed after Mr. Johnson tested a production craft. Dick Johnson has established his credibility among glider pilots by being very independant in his testing. My issue is with the claimed L/D of the Sparrowhawk. I was hoping to see an independent review of this sailplane with polars. Willie |
#12
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Willie wrote:
My issue is with the claimed L/D of the Sparrowhawk. I was hoping to see an independent review of this sailplane with polars. The tests have been done, it was discussed at the SSA convention. It hasn't been published in Soaring, yet, so it is no surprise it isn't online. |
#13
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Earlier, Marc Ramsey wrote:
The tests have been done, it was discussed at the SSA convention. It hasn't been published in Soaring, yet, so it is no surprise it isn't online. Hmmm. I was pretty sure I did see it in Soaring. Now I'd better go check. |
#14
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Willie wrote:
All of these pilot reports are subjective, Wheras I believe Dick Johnson's flight reports are more OBJECTIVE. Backed up by flight tests with measured and recorded results. They feature polars and numbers relating real world results. Even Dick will tell you that a flight test is not exactly "real world results". How many contests or soaring flights are flown in dead calm conditions at steady speeds? The early ASW 24 is an interesting example of this, as it tested well, but did not climb well in mid-afternoon turbulence. Later models changed the airfoil slightly, showing no change in flight testing, but definitely improving the climb. Another example back in the '80s from Schleicher is the ASW 20, which outdid the Ventus in dolphin style flying, but not in straight steady glides. One glide suffered separation in pull-ups, the other did not. Even ensuring these "dead calm" conditions is a major problem, which is why the Alafliegs use a very carefully tested comparison sailplane to fly with the glider they are testing, instead of trying to measure actual sink rates. Also, as Dick has explained in the past, his results are not based entirely on objective criteria, but involve some "educated guessing" about which points to ignore and exactly where to draw the curve through points that are kept. As you might expect, not all aerodynamicists or sailplane designers agree with this approach! The point I'm slowly making is it sounds like you may be giving too much weight to Dick's flight tests, instead of considering it just one of a number of ways of evaluating a glider's performance in the _real_ world. This is definitely more difficult to do with a new glider whose small numbers mean there isn't much real world flying you can examine. The people at Windward Performance tell me they believe the calculated value of 36:1 is reasonable, based on informal glide testing against several other types of gliders in the 35+ L/D range. I don't know if this practical for you, but if I were seriously interested in a SparrowHawk, I'd try to arrange to fly one, or to fly along side one in glider with the performance I'd want it to have (Std Cirrus? Std Libelle?). Great Western Soaring might be the place to do this, since they are a SparrowHak dealer and will have a SparrowHawk there, and maybe other sailplanes to rent for the comparison. A couple days there would be money well spent when considering the purchase of a new sailplane. -- Change "netto" to "net" to email me directly Eric Greenwell Washington State USA |
#15
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On 28 Apr 2005 20:19:15 GMT, John Galloway
wrote: Well - there's a thing -as a non SSA UK pilot for years until yesterday I could get straight to the Johnson flight tests (including yesterday the newly posted ones) and then today all of a sudden I can't. http://www.ssa.org/Magazines/Johnson.asp Anyone got a new link? The wayback machine web site has som of them - http://web.archive.org/web/200402141...es/Johnson.asp Chris |
#16
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At 10:30 02 May 2005, Chris Rowland wrote:
On 28 Apr 2005 20:19:15 GMT, John Galloway wrote: Well - there's a thing -as a non SSA UK pilot for years until yesterday I could get straight to the Johnson flight tests (including yesterday the newly posted ones) and then today all of a sudden I can't. http://www.ssa.org/Magazines/Johnson.asp Anyone got a new link? The wayback machine web site has som of them - http://web.archive.org/web/200402141....ssa.org/Magaz ines/Johnson.asp Chris Chris, Thanks. That's a good archive site that I knew nothing about - and it gets me back to what I could previously access. I still feel that it is a shame that the SSA have decided to deny general web access to all of the Johnson tests at the time they have posted some more recent ones. The are a unique resource of independent data. No polars are ever going to be totally true but Dick Johnson has a record of picking up quite few valid performance issues over the years. DFVLR polars are surprisingly smooth, surprisingly better at higher speeds than Johnson's, don't show individual flap polars, and are available only by individual purchase 2 years after measurement or in manufacturers manuals. I always use Dick Johnson's data (if available) for glide computers. John Galloway |
#17
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The Idaflieg/DLR measurement data is available only after 2 years (except
when a manufacturer agrees to an earlier date) because manufacturer do actually trust these polars - and a bad polar for a particular glider could make the company go belly up... The Idaflieg measurement setup is much more sophisticated than any private individual could afford, and I would always Idaflieg data if I had a choice. BTW, my Idaflieg polar for the ASW20 does show individual flap settings... -- Bert Willing ASW20 "TW" "John Galloway" a écrit dans le message de news: ... At 10:30 02 May 2005, Chris Rowland wrote: On 28 Apr 2005 20:19:15 GMT, John Galloway wrote: No polars are ever going to be totally true but Dick Johnson has a record of picking up quite few valid performance issues over the years. DFVLR polars are surprisingly smooth, surprisingly better at higher speeds than Johnson's, don't show individual flap polars, and are available only by individual purchase 2 years after measurement or in manufacturers manuals. I always use Dick Johnson's data (if available) for glide computers. John Galloway |
#18
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I've been watching Dick Johnson's reports for several decades. The usual
pattern is for a new glider to be produced with a claimed L/D that is significantly higher than what results from Dick's testing. The manufacturer will sometimes pick on dick's methodology and claim that it doesn't show everything about the glider in question or is somehow unfair. Much later, when the glider is no longer in production, the general opinion will be that Dick was dead on with the original report. Dick's methodology is the best there is given limited budgets. Even so, the results are far better than what could be reasonably expected which is a tribute to Dick's skill as an engineer and pilot. A great benefit is that the same methodology has been consistently and meticulously applied to a huge number of gliders over a very long time so there is a lot of data to compare and consequently a lot of confidence in the results. We all owe a great debt to Dick and the TSA for the years of work they have done testing gliders. Bill Daniels "John Galloway" wrote in message ... At 10:30 02 May 2005, Chris Rowland wrote: On 28 Apr 2005 20:19:15 GMT, John Galloway wrote: Well - there's a thing -as a non SSA UK pilot for years until yesterday I could get straight to the Johnson flight tests (including yesterday the newly posted ones) and then today all of a sudden I can't. http://www.ssa.org/Magazines/Johnson.asp Anyone got a new link? The wayback machine web site has som of them - http://web.archive.org/web/200402141....ssa.org/Magaz ines/Johnson.asp Chris Chris, Thanks. That's a good archive site that I knew nothing about - and it gets me back to what I could previously access. I still feel that it is a shame that the SSA have decided to deny general web access to all of the Johnson tests at the time they have posted some more recent ones. The are a unique resource of independent data. No polars are ever going to be totally true but Dick Johnson has a record of picking up quite few valid performance issues over the years. DFVLR polars are surprisingly smooth, surprisingly better at higher speeds than Johnson's, don't show individual flap polars, and are available only by individual purchase 2 years after measurement or in manufacturers manuals. I always use Dick Johnson's data (if available) for glide computers. John Galloway |
#19
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I agree.
At 17:30 02 May 2005, Bill Daniels wrote: I've been watching Dick Johnson's reports for several decades. The usual pattern is for a new glider to be produced with a claimed L/D that is significantly higher than what results from Dick's testing. The manufacturer will sometimes pick on dick's methodology and claim that it doesn't show everything about the glider in question or is somehow unfair. Much later, when the glider is no longer in production, the general opinion will be that Dick was dead on with the original report. Dick's methodology is the best there is given limited budgets. Even so, the results are far better than what could be reasonably expected which is a tribute to Dick's skill as an engineer and pilot. A great benefit is that the same methodology has been consistently and meticulously applied to a huge number of gliders over a very long time so there is a lot of data to compare and consequently a lot of confidence in the results. We all owe a great debt to Dick and the TSA for the years of work they have done testing gliders. Bill Daniels 'John Galloway' wrote in message ... At 10:30 02 May 2005, Chris Rowland wrote: On 28 Apr 2005 20:19:15 GMT, John Galloway wrote: Well - there's a thing -as a non SSA UK pilot for years until yesterday I could get straight to the Johnson flight tests (including yesterday the newly posted ones) and then today all of a sudden I can't. http://www.ssa.org/Magazines/Johnson.asp Anyone got a new link? The wayback machine web site has som of them - http://web.archive.org/web/200402141...w.ssa.org/Maga z ines/Johnson.asp Chris Chris, Thanks. That's a good archive site that I knew nothing about - and it gets me back to what I could previously access. I still feel that it is a shame that the SSA have decided to deny general web access to all of the Johnson tests at the time they have posted some more recent ones. The are a unique resource of independent data. No polars are ever going to be totally true but Dick Johnson has a record of picking up quite few valid performance issues over the years. DFVLR polars are surprisingly smooth, surprisingly better at higher speeds than Johnson's, don't show individual flap polars, and are available only by individual purchase 2 years after measurement or in manufacturers manuals. I always use Dick Johnson's data (if available) for glide computers. John Galloway |
#20
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Is the Idaflieg/DLR measurement data available on the web somewhere?
I hear complaints about Dick's measurements but know of no other sources of info. at the moment I'd like to see the info for the Mosquito 303B Chris |
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