yes,  this whole thing about mach limitting speed is rather new to me also.  i don't really remember being taught about it in initial or recurrent training(though i do subscribe to grayhawk's theory of new info requires old info to leave the brain-lol!).  what i am understanding from this discussion is that vne for lancairs is indicated  airspeed ie 274 kias for a iv.  but the mach speed  for a iv that should not be exceeded due to flutter considerations is 0.57mach ie .57 x 761=433 mph Tas or 382 kTas.  is this correct?  still not quite sure why this mach speed is in tas and not ias.  but if this is true it has definite ramifications for a iv or propet particularly during descent.  despite the few flames, this has been an interesting and practical discussion.

david weinsweig
n750dw propjet
178 hours


>>> bknotts@buckeye-express.com 12/09/2009 8:12 AM >>>
I haven't seen much on Mmo.  In fact, this is the first time I've heard
of a limiting mach number for the IV-P.  My Chilton PFD shows any mach
above .35 at the top of the airspeed tape.  I've seen .44 in cruise at
altitude.  (I giggled like a little girl.)  Now I'm a little concerned
that the "hard" Mmo should be placarded so as not to exceed it in a
cruise power (usual) descent.

Barry Knotts
N4XE, LIV-P, Conti TSIO-550

Frederick Moreno wrote:
>
>  
> When Brent Regan and I were racing his Lancair IV Denver to Oshkosh
> (1996, 97 as I recall), the descent profile was Mach limited initially
> starting at 27,000 feet using a hard limit of Mach 0.58.  This was
> chosen because the factory aircraft was test flown to Mach 0.6 and we
> did not want to enter the unknown.  This Mach number (I had to compute
> it in those early days -- no Mach displays then) was held until the
> IAS built to Vne (274 knots IAS) and this IAS was held to the bottom
> of descent, all occurring at 90-100% power. The  maximum cruise speed
> at 27,000 was about 320 knots TAS (corrected for temperature and
> compressibility effects) and Mach 0.52. As I recall, it only required
> 200-300 feet per minute initial descent at the high power setting to
> drive the Mach number up to 0.58, so the descent started out very
> flat, and the built up as the air got thicker.  I think we hit Vne at
> about 12-14,000 feet and the maximum descent rate near the bottom of
> descent was off scale on the VSI.  It sounded quite different from
> cruise and caused the hair on the back of the neck to stand up a bit
> particularly since much of the descent was in IMC.
>
>  
>
> Key point for you IVP guys: It does not take much nose down high
> altitudes and high power settings to push you up to Mmo, the maximum
> allowable Mach number.
>
>  
>
> Y'all be careful out there.
>
>  
>
> Fred
>
>  
>