Nope.
Vne is 90% of Vd (as opposed to Vmo which is 80% of Vd). Vd is the maximum demonstrated dive speed. If the manufacturer determines that this speed is not a constant CAS value, then there must be a means of determining the correct value at changing altitudes.
Reference: (as of April 28, 2009)
FAR 23.1545 Airspeed indicator.
(c) If Vne or Vno vary with altitude, there must be means to indicate to the pilot the appropriate limitations throughout the operating altitude range.
In other words, if there is no indication on the airspeed indicator or pilot's operating handbook showing that Vne varies with altitude, than it is limited by CAS,
NOT TAS. This is the case with most certificated light aircraft.
As a pilot who was first trained as an aerospace engineer, and one who has experience with both relatively high altitude flying and extensive experience with gliders, the oversimplifications about TAS and flutter made by the VAF community always bother me. First off, flutter is NOT always the limitation driving Vd. In fact most often maximum dynamic pressure is the limitation upon which Vd is based (a point which has been clearly stated by other posters).
In gliders, which have a relatively torsionally flexible structure, and which are sometimes flown to altitudes far beyond what most RV's will ever see, flutter CAN be a concern at high altitudes. In this case, the aircraft manual will have a table showing the maximum airspeed versus altitude. Most of the time, the table will not even start until above 20,000 ft. Even above this altitude, close inspection will show that the speed limit does NOT correspond to a constant TAS (the maximum TAS increases with altitude, while the maximum IAS decreases with altitude).
Because the subject of aeroelasticity (flutter) is so complex, often only generalities are discussed. This means casual readers will know that harmonics required to achieve flutter depend on TAS, the harmonics can be adjusted or reduced by various mass ballancing techniques, etc. However, flutter also requires that the fluid flow have enough energy to excite the harmonic, which means it also depends somewhat on dynamic pressure. How important the actual airspeed is relative to the dynamic pressure depends on so many factors that a determination is well beyond the capacity of most of the homebuilder community.
Our confusion with the flutter issue stems from people operating RV's outside of the operating envelope originally designed for them, and Van's reaction to this. Since Van's Aircraft does not have the resources to determine flutter envelopes for all of their aircraft, and any such envelope would only be pertinant to an aircraft with exactly the same mass ballance and stiffness as the test aircraft (not many homebuilts would be close enough for the envelope to be relevent), they make no attempt to do so. Instead, they take the absolute safest course from an engineering standpoint: If you know the aircraft will not have a flutter problem if operated at or below the published Vne at sea level, and if the maximum true airspeed for no flutter operation increases at an unknown rate with increasing altitude, then you can make the blanket statement about flying the airplane at a TAS below the maximum TAS at sea level and you will be CERTAIN that no flutter will occur at higher altitudes.
This assertation on the part of Van's makes perfect sense, and I have to agree with the reason they do this. However, do not jump to conclusions. The following conclusions are all incorrect and do not logically follow from Van's stated position:
1) All aircraft are limited by True Airspeed rather than Indicated (or more correctly Calibrated) airspeed - False! Most are not.
2) The True Airspeed at which flutter will be triggered is independant of altitude - False! The maximum no-flutter TAS will increase with altitude, but without extensive analysis no one knows by exactly how much.
3) All RV's will flutter if the maximum TAS value at sea level is exceeded - False! Most are probably capable of some reasonably large margin above the maximum dynamic pressure limit designed into them, but no one knows by how much, and actual testing can be EXTREMELY hazardous.
I do not advocate flying your airplane outside of its safe limits. Maintaining a TAS in your RV below the maximum TAS at sea level will always be a safe thing to do. But please do not conclude that this limitation is common to all aircraft, or even all RV's.
Pat
