In article ,
"John Carrier" writes:

Top Posting fixed, to improve following teh context

"Peter Stickney" wrote in message
...
In article ,
"Mortimer Schnerd, RN" writes:
Ian MacLure wrote:
Operationally its irrlevant because the FAA limits speed below 10K
ft to 250Kts IIRC.
As to the actual max speed attainable at low altitude, I believe
you
have it correct.


Agreed. Thicker air equals lower speed. FAA equals even lower speed.

Not necessarily - thicker air also = much more thrust. It's all pretty
much a wash, with a transonic airplane. Usually the TAS in units/time
(mph, kts, km/hr) is higher, but the Mach Number's a bit lower. *The
Speed of Sound is proportional to absolute temperature. It's warmer
near the surface, so there's more mph/Mach Number.

Generally not true. Indicated airspeed top end is usually highest at low
altitude, but true airspeed capability will rise with increased altitude.
This all assumes no airframe structural limit, which is frequently below the
aircraft's capabilities in commercial designs.

John, I have to respectfully disagree. While I don't have the
specifics for a 757 or 767, here's a list of the thrust/drag limits
(Which often exceed the published flight limits) for a number of
similarly performing transonic military aircraft. The data sources
are teh Standard Aircraft Characteristics for each aircraft, which
uses the same flight test data used to create the Pilot's Handbooks
and NATOPS.
All are Standard Day conditions

Sea Level 35,000' Notes
Vmax Vmax Mmax Vmax Vmax Mmax (Placard Limits, etc.)
KTAS KEAS KTAS KEAS
F-86H 600 600 0.91 545 304 0.94
B-47E 545 545 0.83 485 270 0.85 Lim. 425 KEAS/M 0.86
B-57B 521 521 0.79 475 262 0.83 Lim. 500 KEAS/M 0.83
A-3A 545 545 0.83 510 284 0.89
AV-8B 575 575 0.87 528 294 0.92
S-3A 430 430 0.65 443 324 0.72 Vmax is at 20,000'

Of all the examples, the S-3 comes eth closest to, say, an airliner,
with its fat body and high bypass engines. Even so, there isn't much
difference. The thing driving drag the most is Mach Number. (The drag
rise due to compressibility getting going) Since Mach 1 is about 85
Kts lower at 35,000' than it is at Sea Level, It's not too surprising
that you'll have more knots in hand at low altitudes.


--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster