On 9/11/2019 8:11 AM, wrote:
On Wednesday, September 11, 2019 at 10:00:12 AM UTC-4, Senna Van den Bosch
wrote:
I noticed for the first time when flying at speeds above 200 km/h, my
wingtips start to bend down a bit, has anyone ever noticed this? Glider
is a DG-100.

Yep. The twist that helps provide the very docile handling hurts at higher
speeds. The airfoil is not very efficient above 150 or so. Not much reason
to fly very fast. FWIW UH

"What UH said."

Me knowing zero/zip/nada about the DG-100's airfoil choice(s?), reason for the
downward-bend-phenomenon at higher speeds lies in some flavor of
geometric/aerodynamic twist from root to tip, where - in essence - the tip
airfoil is at a lower/reduced angle of incidence (and hence angle of attack)
to the root airfoil...done for the reason UH mentions, i.e. to ensure the root
stalls prior to the tip, helping ensure low-speed behavior is benign. None of
this "sudden tip stalling" excitement to worry about. Twist is a
less-graceless manner of avoiding (say) stall strips often seen inboard on
power planes (e.g. Bonanzas).

At higher speeds (lowering AoA), reversed aerodynamic effects become apparent,
as you've now seen. The tip will reach negative AoA prior to the root. Cool!

If the reason is geometric twist from root-to-tip (i.e. the same airfoil),
sometimes you can actually *see* that by gazing from tip to root along the
apar. Kinda cool, for the wannabe aerodynamicist/designer in you!

Bob W.

---
This email has been checked for viruses by AVG.
https://www.avg.com