Dick Johnson methodology for measuring glider performance

[Paul B[_2_]]

Hi

I have read many articles published by Dick Johnson on performance of various gliders, but I cannot find any information on the methodology he used. The closest I have come to is this from Wikipedia "Flight Test Evaluation series starting in 1976, which measured the performance of sailplanes utilizing the measurement methods taught by Dr Raspet and refined by Johnson". I am guessing that it may have been based on this article "Sailplane Performance Evaluation - Soaring May–June, 1947" by dr Raspet, but I was not able to make any further headway.
If anyone can point me to some source I would appreciate it.

Thanks

Paul

[[email protected]]

I thought his articles were all pretty complete.
He had an electrically powered "shaker" on the instrument panel to overcome the internal friction of the altimeter and he had a stopwatch. He flew set airspeeds and recorded the vario readings and altimeter readings while flying.
He did most of his testing in the winter on calm days when the airmass would be most stable.
I think he also had a calibrated airspeed indicator that was connected to a "bomb" that was hung out the window to compute the airspeed/pitot error.

[Paul B[_2_]]

Thanks for reply. That is the general understanding I have from reading his articles. I did not think / realised he recorded vario readings. I guess I was after more specifics, how long has he flown for a particular speed, did he need to correct for altitude, temperature etc. Did he made the calculation from altitude loss in kts, etc. Basically I am after the "method" section in his technique. I recall him writing about three tows to 10000 ft, which may point to quite long legs at a particular speed.

Cheers

Paul

[[email protected]]

Beyond my pay grade.

[Ramy[_2_]]

I would think nowadays performance can be measured much more accurately and easier post flight using analysis software such as SeeYou. Also I believe the true performance of the glider should use GPS altitude and not pressure altitude.

Ramy

[Martin Gregorie[_5_]]

On Mon, 11 Jul 2016 09:08:26 -0700, Ramy wrote:

> I would think nowadays performance can be measured much more accurately
> and easier post flight using analysis software such as SeeYou. Also I
> believe the true performance of the glider should use GPS altitude and
> not pressure altitude.
>
The German Akafliegs (aeronautical groups in their universities) still do
rigourous performance measurements on gliders. You could do a lot worse
than reading their papers and/or contacting them.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Soartech]

I am curious about what pilots see on their post-flight analysis programs (like SeeYou) or in flight tools (like XCsoar) for their average L/D. Does it compare well with the advertised L/D of your ship? Or is it lower (or higher)?
For me, using XCsoar, the figure displayed is often lower than stated in my manual.

[Matt Herron Jr.]

On Monday, July 11, 2016 at 9:46:10 AM UTC-7, Soartech wrote:
> I am curious about what pilots see on their post-flight analysis programs (like SeeYou) or in flight tools (like XCsoar) for their average L/D. Does it compare well with the advertised L/D of your ship? Or is it lower (or higher)?
> For me, using XCsoar, the figure displayed is often lower than stated in my manual.

I usually set "bugs" to 6% degradation to my official polar in SeeYou. Through trial and error, this seems to match what I actually see as performance on final glides. Glider is Ventus C with winglets

Matt

[[email protected]]

On Monday, July 11, 2016 at 11:46:10 AM UTC-5, Soartech wrote:
> I am curious about what pilots see on their post-flight analysis programs (like SeeYou) or in flight tools (like XCsoar) for their average L/D. Does it compare well with the advertised L/D of your ship? Or is it lower (or higher)?
> For me, using XCsoar, the figure displayed is often lower than stated in my manual.

Depends on how good a pilot you are. I'm not happy unless I see interthermal L/D numbers over 60 due to flying energy lines, often much higher than that, if possible negative (gaining alt.). Best polar L/D is meaningless, we never fly straight at that speed.

[Glider RN]

I was fortunate to be able to fly with Dick for his tests on my DG-1000. In the 2 seat glider, I flew and he recorded data.

The altimeter was calibrated against his known standard. The vibrator mentioned earlier was hooked to the altimeter mounting bolts to minimize friction effects. The trailing calibrated airspeed "bomb" was dropped out the vent window to about 25 ft below the glider to be in undisturbed air. These readings were later used to adjust the speeds we were holding on the AS indicator in the glider.

We would tow to 10,000 - 12,000 ft early in the morning in stable air. We then flew at various airspeeds from min sink to high cruise and timed 500 feet changes. Speeds were varied 2.5 kts at the lower speeds, and then every 5 kts at the higher speeds.

The tests were a tremendous learning experience. As we descended and started to encounter any thermals/turbulence, Dick would call of the measurements and we would then take another tow if the high conditions were still favorable. As we got down to about 2500 ft he said there are bumps (actually just wiggles and not workable thermals) so that is it for this flight. Not wanting to waste time, I pulled the spoilers and headed for the airport. He politely asked if he could fly and I said great, maybe I could learn something. He closed the spoilers and tried to work every wiggle while explaining that spoilers burn energy and should be avoided at all costs. Guess I quickly learned to never quit trying.

[Ramy[_2_]]

Unless you fly in completely stable air, the post flight analysis L/D has more to do with the soaring conditions and how well you utilize energy lines, than glider performance.

Ramy

[Soartech]

On Monday, July 11, 2016 at 8:22:38 PM UTC-4, Ramy wrote:
> Unless you fly in completely stable air, the post flight analysis L/D has more to do with the soaring conditions and how well you utilize energy lines, than glider performance.
>
> Ramy

Ramy, Are "energy lines" actually lift streets? That name makes it sound like some sort of mystical experience.

[jfitch]

On Monday, July 11, 2016 at 5:22:38 PM UTC-7, Ramy wrote:
> Unless you fly in completely stable air, the post flight analysis L/D has more to do with the soaring conditions and how well you utilize energy lines, than glider performance.
>
> Ramy

While that is true, flights done from a high tow in early morning stable conditions specifically to measure performance, might be usefully analyzed from logged data. Set the logger to 1 second intervals, pilot comment each change of speed, etc.

You would still need to correct the data to standard atmosphere, which I believe DJ did.

[SoaringXCellence]

Energy lines are not necessarily "lift streets' but rather the selection of a path through the air that results in the least energy lost. Many times a reduction in sinking airmass is the gain.

[Paul B[_2_]]

Hi

Thank you to all that replied. Glider RN and a reply I have received privately, provided all the information I require. To conduct such a test is clearly an exacting endeavor, requiring a thorough preparation.

On the positive side, I have thoroughly enjoyed a flight in utterly still air ( I have not yet experienced wave flight). Also thanks Martin for suggesting Akafliegs, I am sure their method would also be informative.

Cheers

Paul

[Tango Whisky]

The method by Dick Johnson works for gliders with limited performance. Even in "still air conditions", which are typically found in meterological high pressure regions, there are wide-area vertical movements of air. There is no way that the method by DJ can work them out. They are just a few cm/s - so if you try to measure a 1:30 or 1:35 ship, that's not a big deal.

Now, if you are measuring a ship with 1:45, a 5 cm/s air mass movement will give you an error of 7%, or about 3 points.

That's why in Europe, DJ measurements are widely disregarded.

Instead, we have the Idaflieg (which is kind of the federation of Akafliegs) doing their measurements in collaboration with DLR (the German Research Institute for Aerospace). These measurements are based on two key points:
One is a calibrated (the "sacred") glider, which has been an Open Cirrus, then a DG300-17 and now I think it is a Discus 2/18. This glider is measured ynd calibrated extensively (takes about 1-2 years).
Second key point is that the glider to be measured flies in parallal to the calibrated glider, and in the basic form of the measurement, pictures of both gliders are taken after each intervall of flying at a defined speed. By using the (precisely known) fuselage length of the calibrated glider, you can get the vertical distance between the gliders very precisely.

This method gets rid of any air mass movement and is very accurate. It comes at a steep cost though: a calibrated glider (which is used for nothing else), two tow planes to FL120 at 5 p.m., and one of the tow planes flying alongside the gliders during the descent.

Bert
Ventus cM "TW" (measured by Idaflieg to 1:47 ;-) )

[[email protected]]

The problem with the Idaflieg/DLR measurements is that they are not simply made available to the larger public.

There seems to be a kind of secrecy agreement between the Akafliegs/Idaflieg and the (mainly German) sailplane manufacturers to keep the results under wraps for a number of years (at least two, if my information is correct), and even then, you won't find them simply in the soaring press, you'll have to ask them to the Idaflieg...

The German (and other) manufacturers no longer publish the polars of new sailplanes in the flight manual either (fear of being proven too optimistic?).. So if you want to calibrate a flight computer, you have to guess what the true polar might be.

That's why, however imperfect, the Johnson measurements have been widely disseminated in the past. They were readily available: as soon as they were published in Soaring, they were translated and published in the international soaring press... much to the chagrin of most manufacturers, because they usually were worse than the claimed values (yes, manufacturers used to put an "official" polar in the flight manual in the old days!).

[Paul B[_2_]]

Thanks Bert

That is all well and good if you are in Europe, have connection to Akaflieg and want to spend a lot of money. I guess it may make sense to review a glider, but it simply is not practical elsewhere. So I guess if you wish to obtain a reasonable measurements you may as well use the best method available that fits the conditions where one flies. I have not yet verified your assertion regarding the error with your stated parameters regarding the vertical movement of the airmass one is flying through. Nor am I a good enough meteorologist to know how likely is it that the whole airmass would be uniformly moving up a down over a distance required to loose 1000ft over flat lands without wind that may cause sheerwave.


Finally, I would think that enough people with requisite knowledge looked at Dick J work, yet there is not a great deal of criticisms floating about. But as you say, Concordia may not be a suitable candidate.

Cheers

Paul

[Bruce Hoult]

On Tuesday, July 12, 2016 at 7:58:20 PM UTC+12, wrote:
> The problem with the Idaflieg/DLR measurements is that they are not simply made available to the larger public.
>
> There seems to be a kind of secrecy agreement between the Akafliegs/Idaflieg and the (mainly German) sailplane manufacturers to keep the results under wraps for a number of years (at least two, if my information is correct), and even then, you won't find them simply in the soaring press, you'll have to ask them to the Idaflieg...
>
> The German (and other) manufacturers no longer publish the polars of new sailplanes in the flight manual either (fear of being proven too optimistic?). So if you want to calibrate a flight computer, you have to guess what the true polar might be.
>
> That's why, however imperfect, the Johnson measurements have been widely disseminated in the past. They were readily available: as soon as they were published in Soaring, they were translated and published in the international soaring press... much to the chagrin of most manufacturers, because they usually were worse than the claimed values (yes, manufacturers used to put an "official" polar in the flight manual in the old days!).

The good news is that it is not actually necessary to know the precise performance of your particular glider or even glider type in order to fly it close enough to optimally. Any roughly similar polar (and they are all roughly similar in a given class) will do the job. The information you want is "how fast should I fly" and that is neither very critical (+/- 5 knots is fine) nor very different from one glider to another.

What does vary is the total height loss over an extended run e.g. a final glide. I don't think there's any option but to see if you consistently come out above or below your expected height loss and use that to make a correction in the programmed polar.

[Tango Whisky]

The air mass in an anticyclone generally sinks over its whole area. That's what generates the wind which turns clockwise around an anticyclone (northern hemisphere).

I agree that just for programming the polar into the flight computer, the actual precision does not matter much.

As to the Idaflieg measurements - there is no secrecy involved. Manufacturers put their gliders at disposition for those measurements, and no data will be published in the first two years. This stems from the times of Nimbus 3 vs ASW22 - with people looking only at best L/D, one of the two gliders being published with 2 points more would have made the other manufacturer go bankrupt.

The data is not published anywhere. If you're interested in a measurement of your type of glider, you send Idaflieg a request by email. If it exists, they will send you a paper copy, and a bill of about 10-15 Euros.

[[email protected]]

On Tuesday, July 12, 2016 at 7:45:32 AM UTC+1, Tango Whisky wrote:
> The method by Dick Johnson works for gliders with limited performance. Even in "still air conditions", which are typically found in meterological high pressure regions, there are wide-area vertical movements of air. There is no way that the method by DJ can work them out. They are just a few cm/s - so if you try to measure a 1:30 or 1:35 ship, that's not a big deal.
>
> Now, if you are measuring a ship with 1:45, a 5 cm/s air mass movement will give you an error of 7%, or about 3 points.
>
> That's why in Europe, DJ measurements are widely disregarded.
>
> Instead, we have the Idaflieg (which is kind of the federation of Akafliegs) doing their measurements in collaboration with DLR (the German Research Institute for Aerospace). These measurements are based on two key points:
> One is a calibrated (the "sacred") glider, which has been an Open Cirrus, then a DG300-17 and now I think it is a Discus 2/18. This glider is measured ynd calibrated extensively (takes about 1-2 years).
> Second key point is that the glider to be measured flies in parallal to the calibrated glider, and in the basic form of the measurement, pictures of both gliders are taken after each intervall of flying at a defined speed. By using the (precisely known) fuselage length of the calibrated glider, you can get the vertical distance between the gliders very precisely.
>
> This method gets rid of any air mass movement and is very accurate. It comes at a steep cost though: a calibrated glider (which is used for nothing else), two tow planes to FL120 at 5 p.m., and one of the tow planes flying alongside the gliders during the descent.
>
> Bert
> Ventus cM "TW" (measured by Idaflieg to 1:47 ;-) )

I don't disagree with this post but I would say that, overall, DJ's testing was good at pointing out the gliders that performed particularly well compared with its competitors - and this was often confirmed by the choices of top competition pilots. Example: ASW20 versus Mini Nimbus and LS3a.

John Galloway

[[email protected]]

<<I don't disagree with this post but I would say that, overall, DJ's testing was good at pointing out the gliders that performed particularly well compared with its competitors - and this was often confirmed by the choices of top competition pilots. Example: ASW20 versus Mini Nimbus and LS3a. >>

It worked the other way, too. When DJ tested the ASW 20 and LS-3 (not the later LS-3a), they both had remarkable, essentially equal performance. This was confirmed by those who flew the two gliders in that first year or two (ours was delivered in 1978). For a brief period, they were equally favored by competition pilots in the U.S.

Then the rush to the ASW 20 began. At first this was a bit baffling. Except for the higher wing weight of the LS-3, what was there about the '20 that seemed to capture so many pilots' favor? Then it became evident that the two types were no longer equal. They still climbed together but the '20 had an advantage in glide.

I profiled the top surface of my LS-3 wings and discovered a "flat spot" where post curing had apparently shrunk the wing over the spar cap. Building up this flat spot fully restored the glide performance, equally dramatically compared with other types as well as other LS-3s. A few owners (e.g., Jim Cox, IIRC) went even further, building up the leading edge where the profile was apparently a bit too blunt compared with the published coordinates as well as fixing the flat spot, with similarly impressive results.

But by that point, not only had time passed the LS-3 by but DJ's tests of the LS-3a seemed to indicate that the later version had inferior glide performance right out of the box, allegedly because of a thicker profile caused by the molds not being completely stable (see heated exchange of letters in "Soaring" mag about that time). My own impression was that the early LS-3a gliders were quite good, but that impression didn't last.

In any case, the reputation of the LS-3 remains today as inferior to the original ASW 20a despite DJ's original published test.

Chip Bearden
ASW 24 "JB"

[ZZ]

Before Richard Johnson's passing, I was communicating with him regarding a glider performance test (an ASW20) and he was kind enough to send me some Excel spreadsheets showing the parameters that he was focusing on. As expected, he used KTAS for the glide performance calculations. What caught me by surprise was his glide calculations used computed TRUE SINK as well. This might have made sense to me if he was measuring vertical speed with a rate instrument but unless I am mistaken, he measured sink rate using an altimeter and a stop watch.

I did not get the chance to ask him about this.

Nevertheless, he is missed.
Paul
ZZ

[[email protected]]

> That is all well and good if you are in Europe, have connection to Akaflieg and want to spend a lot of money.
I did order the results for my Pilatus B4, and the cost was 10 euros. I do not call that "a lot of money" :-)

[Andreas Maurer]

On Tue, 12 Jul 2016 10:04:30 -0700 (PDT),
wrote:


>It worked the other way, too. When DJ tested the ASW 20 and LS-3 (not the later LS-3a), they both had remarkable, essentially equal performance. This was confirmed by those who flew the two gliders in that first year or two (ours was delivered in 1978). For a brief period, they were equally favored by competition pilots in the U.S.
>
>Then the rush to the ASW 20 began. At first this was a bit baffling. Except for the higher wing weight of the LS-3, what was there about the '20 that seemed to capture so many pilots' favor?

I guess people found out about the extreme loss of performance of a
wet or dirty LS-3 and spreat the word...


Cheers
Andreas

[Dave Nadler]

On Tuesday, July 12, 2016 at 2:45:32 AM UTC-4, Tango Whisky wrote:
> The method by Dick Johnson works for gliders with limited performance.
> Even in "still air conditions", which are typically found in meterological
> high pressure regions, there are wide-area vertical movements of air.
> There is no way that the method by DJ can work them out...

In addition to airmass movement, there are a couple other serious problems
with the methods used:

1) The CG of the plane was not controlled.
- what is the effect of forward vs. aft CG on max LD?
- what popular plane was measured with a very low LD due to above?
Discuss amongst yourselves...

2) The number of (and selection of) datapoints is not adequate
Discuss amongst yourselves...



> ...That's why in Europe, DJ measurements are widely disregarded.

Yup.

[[email protected]]

On Thursday, July 14, 2016 at 9:00:22 AM UTC-5, Dave Nadler wrote:
> On Tuesday, July 12, 2016 at 2:45:32 AM UTC-4, Tango Whisky wrote:
> > The method by Dick Johnson works for gliders with limited performance.
> > Even in "still air conditions", which are typically found in meterological
> > high pressure regions, there are wide-area vertical movements of air.
> > There is no way that the method by DJ can work them out...
>
> In addition to airmass movement, there are a couple other serious problems
> with the methods used:
>
> 1) The CG of the plane was not controlled.
> - what is the effect of forward vs. aft CG on max LD?
> - what popular plane was measured with a very low LD due to above?
> Discuss amongst yourselves...
>
> 2) The number of (and selection of) datapoints is not adequate
> Discuss amongst yourselves...
>
>
>
> > ...That's why in Europe, DJ measurements are widely disregarded.
>
> Yup.

For reference see Paul Bikle's "Polars of Eight" in Soaring magazine.

[Soartech]

Dave Nadler said
> 1) The CG of the plane was not controlled.
> - what is the effect of forward vs. aft CG on max LD?
> - what popular plane was measured with a very low LD due to above?
> Discuss amongst yourselves...

So what is the typical percentage change in L/D from full forward CG to maximum rearward CG?
Is it a huge change (>10%) or minor change? I have no idea.

[[email protected]]

> I guess people found out about the extreme loss of performance of a
> wet or dirty LS-3 and spreat the word...
>
>
> Cheers
> Andreas

Indeed, many gliders from that era that used the same family of airfoils suffered thusly, perhaps none so reputed as the PIK 20. But I think the impact here in the U.S. was more from occasional rain than from the bugs that seem more a problem in Europe. Those of us who campaigned LS-3s here often left the wings sanded to a satin finish--without wax--so the rain would spread rather than bead up, which seemed to help significantly. 400 grit seemed about right although one top pilot left his at 220 grit--and joked about having to sand the occasional bugs off each day. :)

Just before I sold mine, I contoured the wings and polished them up, then flew a last contest that took me into rain one day. Nothing evil happened. I'd since heard from a PIK driver that using more positive flap than usual and flying a bit slower helped cure the "falling out of the sky" phenomenon for which PIKs were infamous. It seemed to work well for the LS-3, too.

To the question of CG position, I flew mine with the CG at the aft end of the range. That seemed to yield the best performance, the only negative being somewhat more pitch sensitivity in rough thermals.

Chip Bearden
ASW 24 "JB"

[Charlie M. (UH & 002 owner/pilot)]

My "non engineering" comment is..... A similar airfoil was used on the PIK-20, SGS-135 and others.
When clean, it worked well.
When dirty (bugs, dust, rain) the bottom dropped out.

Common cure was:
-sand to 45* of chord with 600 grit
-wipe D-tube with liquid dish soap and let dry

Sanding allowed a turbulent boundary layer, soap sheeted water, thus killing drag!

Long final glide in a "20" with others into Mifflin, a 1-35 (highly modified) showed the drag gain when we hit rain showers, he had a tough time, we made slight adjustments to final glide.

So, that airfoil can be good clean,but really sucks when dirty. No, you DON'T want a high gloss finish!!!

[Ventus_a]

I guess people found out about the extreme loss of performance of a
wet or dirty LS-3 and spreat the word...


Cheers
Andreas

Indeed, many gliders from that era that used the same family of airfoils suffered thusly, perhaps none so reputed as the PIK 20. But I think the impact here in the U.S. was more from occasional rain than from the bugs that seem more a problem in Europe. Those of us who campaigned LS-3s here often left the wings sanded to a satin finish--without wax--so the rain would spread rather than bead up, which seemed to help significantly. 400 grit seemed about right although one top pilot left his at 220 grit--and joked about having to sand the occasional bugs off each day. :)

Just before I sold mine, I contoured the wings and polished them up, then flew a last contest that took me into rain one day. Nothing evil happened. I'd since heard from a PIK driver that using more positive flap than usual and flying a bit slower helped cure the "falling out of the sky" phenomenon for which PIKs were infamous. It seemed to work well for the LS-3, too.

To the question of CG position, I flew mine with the CG at the aft end of the range. That seemed to yield the best performance, the only negative being somewhat more pitch sensitivity in rough thermals.

Chip Bearden
ASW 24 "JB"

Hi

FWIW I used to have a share in a Janus and I too found that having some extra positive of flap and flying a little slower helped to avoid the plummeting when wet. No hard figures to verify that but the airframe shaking went away as well so more comfortable for the poor old pilot.

:-) Colin

[Eric Greenwell[_4_]]

wrote on 7/12/2016 8:26 AM:
> I don't disagree with this post but I would say that, overall, DJ's
> testing was good at pointing out the gliders that performed
> particularly well compared with its competitors - and this was often
> confirmed by the choices of top competition pilots. Example: ASW20
> versus Mini Nimbus and LS3a.

One of the flaws in DJ's method (and the Akafliegs) is it doesn't test
the performance dynamically; ie, while dolphin soaring or flying in
turbulent air and thermals.

I once noticed the superior dolphin ability of my ASW 20 vs a Venus
while we were under clouds, quickly gaining on him. As soon as we
started a 10 mile glide in the blue, he slowly rose above me, over 800'
or so by the time we got to the next cloud.

The early ASW24, and others with that generation of airfoils (like my
ASH 26E), showed the problems induced by a "flat spot" in the L/D curve
when the air isn't smooth.

For competition purposes, I suggest competitions are the best test for a
glider. For recreational purposes, ultimate performance is unimportant
compared the other features of the glider.

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

https://sites.google.com/site/motorgliders/publications/download-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

[Eric Greenwell[_4_]]

ZZ wrote on 7/12/2016 9:00 PM:
> What caught me by surprise was his glide calculations used computed
> TRUE SINK as well. This might have made sense to me if he was
> measuring vertical speed with a rate instrument but unless I am
> mistaken, he measured sink rate using an altimeter and a stop watch.

Since the altimeter (properly corrected) would give true altitude loss,
and the stop watch would give true duration, I think (altitude
loss)/(duration) would give true sink rate.

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

https://sites.google.com/site/motorgliders/publications/download-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

[[email protected]]

I was fortunate to have assisted DJ in testing several gliders and he/we did measure sink rate by timing descents. Typically in 1,000 ft increments. Also, we/he did several flights for critical data points and threw out data from flights that obviously suffered from atmospheric or data anomalies. Data points from the remaining flights were manually averaged to create the finished polar. And, he did normalize the data to sea level, standard atmosphere, and TAS conditions. There was at least one article in Soaring in which he published the formulas. Interestingly, when I first analyzed data and created graphs using Lotus 1-2-3 (does that age me or what??), Dick suggested I was wasting my time as he trusted calculators and graphs created manually more. I'm pleased to see he eventually accepted Excel outputs.

[Paul B[_2_]]

Thank you for your reply. Fortunately couple of very helpful individuals supplied virtually all the info I needed and I was able to do my tests. Despite few individuals casting doubts on the methodology, I was able to get enough data points that allowed to get a line of best fit with all the points pretty much on that line. Also the sink rates at relevant speeds matched factory sink rates. An interesting exercise anyway.

Paul