Dick Johnson methodology for measuring glider performance

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

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.

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

Beyond my pay grade.

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

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 |

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.

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

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.

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.