Quick, quizzie :
Aerodynamic flutter is dependent on True Air Speed (TAS) or Indictaed Air Speed (IAS) ?
True air speed
The resonance (which is what flutter is) is going to be triggered by the actual speed of the airflow i.e. TAS.
But it is marked as IAS on the ASI, because the ASI indicates only IAS. So this puts an implicit limit on the operating ceiling (because, for a constant IAS, TAS goes up as you climb). This is not an issue with non-turbo planes because they can’t climb high enough, but turbo, or turboprop conversions, have a certification issue with this.
My impression is that flutter speed is not constant throughout altitudes. Furthermore Vne (if that was what you were referring to wrt. markings on ASI) is not necessarily be limited by flutter, but may be limited by structural strength.
We’ve had this discussion earlier. Most piston airplanes are Vne limited by aerodynamic forces (frequently wing twisting moment vs tail structure) and thus IAS, because it is IAS that determines all aerodynamic forces.
Whereas most gliders and motorgliders are quite strong but slender aircraft with short wing chords. The slenderness of those makes stiffness a challenge, and the short wing chord reduces the wing’s twisting moment, thus making flutter the limiting element for Vne instead of aerodynamic forces. And as said above, flutter is a function of TAS, not IAS. That explains why my Grob 109 and many other (motor-)gliders have different Vne’s for different altitudes, but when you convert them to TAS, they are the same.
