Dick Johnson methodology for measuring glider performance

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.

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.

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

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.

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.

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

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/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf

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.

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