Hi Wolfgang,

I would be surprised if we have an aeronautical engineer in the group that specializes in determining Vne for composite aircraft.  I believe that it combines at least two specialties, materials science and structural engineering - maybe more.

From this most recent thread, and from others on this and other forums, I gather that Vne is determined by many things:

- Indicated airspeed causing compression loads on one or more areas of the aircraft that exceed their compressibility strength, or causing flutter on control surfaces, doors, or even unsecured aircraft skin
- Mach number likewise creating unusual stresses
- True airspeed, for reasons I don't understand

All of this has to be factored together with every kind of materials strength (tensile; compressibility, torsional, fatigue, others?) including layup alignment factors of the original glass (affects at least torsional strength in given angles of twist); balance; harmonics; aircraft stability and controllability (at least one aircraft I know had Vne set because it ran out of elevator authority at high speed); and probably many more factors I'm unaware of.

I'm quite certain that Lance used at minimum some baseline modeling to set conservative Vne numbers - the proof of that is the lack of Vne related accidents.  I'm also quite certain that given a supercomputer using the latest models (finite element analysis?) that a more accurate Vne could be established, and also equally certain that because of the inherent variability of fiberglass construction that relying on such a model would be dangerous.

So what I'm saying is, Vne for a Lancair is probably somewhat science and somewhat art (because of the variability of fiber and resin).  Even if you personally choose to be a test pilot and test YOUR airplane up to 500KIAS successfully it is no guarantee that any other Lancair will perform similarly.

For me, I'll stick to the published Vne unless some emergency (UFO chasing me?) causes me to exceed it.

Cheers,

Bill Reister


Wolfgang wrote:

So . . . am I to conclude that there's nobody on the list that can identify how Vne is determined ?

With all the experience of posters on this list, I'm surprised to say the least.

Is this black magic art or is there some real formula/procedure ?

All I've seen here so far is "is that meadured in IAS, TAS OR Mach ?" or "what is the speed for xxx airframe ?".

. . . but nothing about how the number comes to be.

 

Wolfgang