On Mon, 27 Aug 2018 05:48:06 -0700, Mark Williams wrote:

I have a share in a Peg 90. I feel that over 65/70kt the LD really drops
off, though, I don't have evidence for this and hope it's higher What
do others think?

From memory, best glide for a peg 90 is 55kts, so anything up to 70kts
won't loose you much height. Its been a while, but IIRC we generally
thought that up to 80-85 kts was OK but height tended to slip away if we
went much faster (and the equivalent number for a Discus 1 was 90kts).

FWIW my Std Libelle runs at 70kts without much height loss and it doesn't
come down all that fast at 80kts.

But don't take my word for it, if your vario can calculate glide ratio
and has a super netto mode[1] (my SDI C4 does and its 'cruise' mode is
super netto) have a play round next time you're reasonably high in calm,
minimal lift conditions. You should find that you can guestimate a usable
polar by flying at, say, 60, 70, 80, 90, 100kts and noting the glide
ratio on the vario when the super netto mode shows zero.

If your vario won't do that, in minimal lift conditions try flying at
these speeds for one or two minutes each with your logger running,
preferably at 1 second intervals. Then calculating the glide ratio from
the IGC log file for each of these segments. It will be a bit of a faff,
but should be doable.

[1] super netto mode adds the glider sink rate (calculated from the polar
you put into the vario) to the TE value, to show what the air mass is
doing, so a zero super-netto reading should mean the air mass isn't
rising or sinking.

For an actual example of what a Peg 90 can do in early evening air, read
this:

https://www.gregorie.org/gliding/200...nals/day8.html

The second to last paragraph in this story (just above the plotted trace)
describes the final glide, 40 km back home starting from 5300 ft, in what
felt like very calm air: no noticeable lift or sink and only a bit of
cross-track drift.


--
Martin | martin at
Gregorie | gregorie dot org