Thanks to Charlie for posting the results of Martin Hollman’s initial calculations for the Lancair IV.  Recall that the original Lancair IV was unpressurized, 2900 pounds, and had no  fuel in the outer parts of the wing.   It grew to 3200 pounds, then 3550, and the  wing ended up wet from tip to tip.  All of these changes  affected Vne.

 

Charlie, do you recall the work done to evaluate flutter when the wing tanks were initially extended?  My recollection is that a lot of us wanted to fill the outer bays as is commonly done now, and so we pooled some money  in the early 90’s and Martin did the analysis.  Results as I recall: the flutter margin was reduced at altitude when the outer fuel bays had fuel in them reducing the initial maximum speed.  However, most of this fuel was burned off during climb and so the effect was minimal unless you forgot to switch tanks during the long climb to 24,000. 

 

Do you suppose this led to the final Vne figure of 274 KIAS that is now painted on our airspeed indicators?  Or do you think Lance et al took Martin’s figures, used them in dive tests to establish Vd, and then divided by 1.1 to get the final figure (since  Vd is usually defined as 1.1 times Vne)? 

 

As for the discussion on HOW Vne is calculated, I suspect a single figure is never actually calculated since so many factors affect the safety of the airplane at the edge of its operating envelope.  I suspect that the manufacturer establishes a  target speed, designs with some reserve (flutter margin, structural margin, compressibility margin, etc.), and then does a dive test to Vd for certification.  Vne is then Vd divided by 1.1.   Details of Part 23 would tell the tale, perhaps.

 

Fred Moreno