Dick Johnson methodology for measuring glider performance

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"

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

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"

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!!!

Originally Posted by

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