Vne

On Sunday, November 10, 2019 at 7:02:57 AM UTC-8, Echo wrote:
Haven't read that, would be an interesting one though. I'd always been under the impression Vne is a flutter protection speed. That's why it's a TAS that doesn't change with weight like Va. Wouldn't be surprised if it was from some old math though.

I always thought Vne was an operational limit to airworthiness, usually derived from the flutter speed. Also that flutter speed was an odd power function of altitude (because it varies somewhat with density but not as fast as IAS, therefore TAS is safe). Also that it is an oscillatory phenomena which depends on the stiffness, mass, and forcing function - so practically does depend on weight (or at least mass), particularly of the wings but secondarily the fuselage. But that function would be way too complicated to put on the placard or even into regulations so no change is assumed.

I also didn't think it was required to air test flutter speed anymore, but could be calculated with mass, stiffness, and CFD codes.

jfitch wrote on 11/10/2019 5:11 PM:
On Sunday, November 10, 2019 at 7:02:57 AM UTC-8, Echo wrote:
Haven't read that, would be an interesting one though. I'd always been under
the impression Vne is a flutter protection speed. That's why it's a TAS that
doesn't change with weight like Va. Wouldn't be surprised if it was from
some old math though.

I always thought Vne was an operational limit to airworthiness, usually derived
from the flutter speed. Also that flutter speed was an odd power function of
altitude (because it varies somewhat with density but not as fast as IAS,
therefore TAS is safe). Also that it is an oscillatory phenomena which depends
on the stiffness, mass, and forcing function - so practically does depend on
weight (or at least mass), particularly of the wings but secondarily the
fuselage. But that function would be way too complicated to put on the placard
or even into regulations so no change is assumed.

I also didn't think it was required to air test flutter speed anymore, but
could be calculated with mass, stiffness, and CFD codes.

Ground vibration testing can also aid in determining flutter characteristics. I
don't know what is required of our gliders. The Perlan 2 glider underwent
substantial amounts of ground vibration testing, and it's flight envelope is
gradually extended by in-flight vibration testing, at various altitudes and
speeds, to corroborate the ground testing results. The vibration is supplied by
eccentric, electric motor driven weights built into the wings.

--
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