Jim's a retired USAF test pilot, so I'm sure understands all the intricacies of flying near Vne.

I'm not an aerodynamicist so here's my lay understanding. A glider's Vne is the true airspeed as indicated IAS at typically 3000m. If I recall, my ASH-26E redline was 146 KIAS which worked out to 160-ish TAS. The chart Schleicher provides for Vne above 3000m drops the IAS to keep the TAS at or below 160.

My ASW-27 chart is:
10K 151 knots
16.5K 133 knots
23K 119 knots
etc...

In the '26 I flew a 100 km triangle in wave between 14 and 18K MSL so limited my IAS to a conservative 120 knots, which I maintained nearly the whole time. The achieved speed for the triangle was a bit over 130 knots. So TAS is your friend even below 18K!

If repeating this in the '27 I would again use 120 as a "safe" Vne for below 18K.

5Z

On Wednesday, September 21, 2016 at 6:59:10 PM UTC-7, howard banks wrote:
Every glider flight manual I studied made it clear that the flight tested limits laid out applied up to 3000 meters ... over that you are relying on a combination of theory, over-design, excessive build over required standards, and it always seemed to me good fortune. I have no idea if such applied to the Arcus M used by Payne.