I have a Rocky Mountain Instrument's micro-encoder (no longer availab= le)=20 that is also an air-data computer. Thus, one may display IAS, TAS an= d Mach=20 because the device measures OAT (corrects for compressibility as= TAT)=20 and indicated altitude (after baro correction, also shows Dalt and Palt).&= nbsp;=20 Since modern slick aircraft are all faster than a C172, it would be useful= if=20 the designer/manufacturer would describe limits, like Vne, as IAS, TAS and= =20 Mach. After all, modern glass avionics are certainly capable of=20 calculating, displaying and issuing warnings for these values.

Remember that one of the wing design parameters is the Reynolds numbe= r=20 range (a non-dimensional viscosity measure related to atmospheric composit= ion)=20 in which it is to operate.

Altitude, temperature, composition (moisture, etc.) and speed all hav= e an=20 effect on aircraft performance, structural integrity, flutter, yada,=20 yada....

Scott Krueger AKA Grayhawk

In a message dated 12/9/2009 11:05:41 A.M. Central Standard Time,=20 WeinsweigD@tsnci.com writes:

yes, this whole thing about mach limitting speed= is=20 rather new to me also. i don't really remember being taught about= it in=20 initial or recurrent training(though i do subscribe to grayhawk's theory= of=20 new info requires old info to leave the brain-lol!). what i am=20 understanding from this discussion is that vne for lancairs is indicated= =20 airspeed ie 274 kias for a iv. but the mach speed for a iv= that=20 should not be exceeded due to flutter considerations is 0.57mach ie .57= x=20 761=3D433 mph Tas or 382 kTas. is this correct? still not qu= ite sure=20 why this mach speed is in tas and not ias. but if this is true it= has=20 definite ramifications for a iv or propet particularly during descent.&n= bsp;=20 despite the few flames, this has been an interesting and practical=20 discussion.

david weinsweig
n750dw propjet
178=20 hours

>>> bknotts@buckeye-express.com 12/09/2009 8:1= 2 AM=20 >>>
I haven't seen much on Mmo. In fact, this is the= first=20 time I've heard
of a limiting mach number for the IV-P. My Chi= lton=20 PFD shows any mach
above .35 at the top of the airspeed tape. = I've=20 seen .44 in cruise at
altitude. (I giggled like a little=20 girl.) Now I'm a little concerned
that the "hard" Mmo should= be=20 placarded so as not to exceed it in a
cruise power (usual)=20 descent.

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

Frede= rick=20 Moreno wrote:
>
>
> When Brent Regan and I were= =20 racing his Lancair IV Denver to Oshkosh
> (1996, 97 as I recall),= the=20 descent profile was Mach limited initially
> starting at 27,000= feet=20 using a hard limit of Mach 0.58. This was
> chosen because= the=20 factory aircraft was test flown to Mach 0.6 and we
> did not want= to=20 enter the unknown. This Mach number (I had to compute
> it= in=20 those early days -- no Mach displays then) was held until the
>= IAS=20 built to Vne (274 knots IAS) and this IAS was held to the bottom
>= ; of=20 descent, all occurring at 90-100% power. The maximum cruise speed= =20
> at 27,000 was about 320 knots TAS (corrected for temperature an= d=20
> compressibility effects) and Mach 0.52. As I recall, it only re= quired=20
> 200-300 feet per minute initial descent at the high power setti= ng to=20
> drive the Mach number up to 0.58, so the descent started out ve= ry=20
> flat, and the built up as the air got thicker. I think we= hit=20 Vne at
> about 12-14,000 feet and the maximum descent rate near= the=20 bottom of
> descent was off scale on the VSI. It sounded qu= ite=20 different from
> cruise and caused the hair on the back of the ne= ck to=20 stand up a bit
> particularly since much of the descent was in IM= C.=20
>
>
>
> Key point for you IVP guys: It= does=20 not take much nose down high
> altitudes and high power settings= to=20 push you up to Mmo, the maximum
> allowable Mach=20 number.
>
>
>
> Y'all be careful out=20 there.
>
>
>
> Fred
>
> = =20
>

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