Dick Johnson methodology for measuring glider performance

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!).

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.

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.