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Old September 23rd 03, 08:09 AM
Peter Duniho
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"Mark Cherry" wrote in message
...
Sorry to be pedantic but, as far as I understand it, 'coefficients' are

physical
constants. In this case, they are characteristics of a particular

airframe.

You're not being pedantic. You're just being wrong. A "coefficient" is
simply a number in an equation. It may or may not be a physical constant,
but in the case of lift, it is not. It varies with the angle of attack, as
does the coefficient of drag.

You can break the coefficient of drag down into its component parts, induced
and parasitic (aka "form" or "friction") drag. But even the parasitic
component changes slightly with angle of attack, simply because of the
change in the cross-section of the airframe presented to the relative wind.
As you noted, the parasitic component changes even more when flying in
uncoordinated flight, such as a slip or skid.

[...] Whilst TAS is fine for dead reckoning navigation
calculations


It's not just fine. It's necessary.

[...] (And when
that stalling speed converges with the highest achievable forward speed in

level
flight, the plane reaches its 'service ceiling').


Wrong again. An airplane's "service ceiling" is defined to be the altitude
at which the climb rate is lower than 100 feet per minute. An airplane's
*absolute* ceiling is the altitude at which the airspeeds corresponding to
best rate of climb (Vy) and best angle of climb (Vx) converge, which is the
altitude beyond which the airplane simply cannot climb. The airspeeds Vx
and Vy, the same at absolute altitude, are well above stall speed.

There IS another altitude that is of importance for airplanes that can climb
especially high and which go particularly fast. That is, the point at which
stall speed and the Mach buffet speed converge. At that altitude, going
slower stalls the airplane and going faster results in Mach buffet. Perhaps
that is what you were thinking of.

[...] The induced drag
coefficient, however, remains a constant, for that particular aircraft.


As I mentioned above, no. The induced drag coefficient changes along with
the lift coefficient, and depends not only on the airfoil, but also on the
angle of attack.

[...] The turbulence of the
stalled portion causes a vibration which the pilot will be able to feel,

as a
warning that a full stall is about to occur and give them time to take

action.

One will experience turbulence *prior* to stall even in an airplane with a
constant angle-of-incidence airfoil. The pre-stall buffet is caused by the
airflow separation, which starts to happen before the actual stalling angle
of attack, along with this turbulent airflow striking the horizontal
stabilizer (the latter happens only in aircraft in which the horizontal
stabilizer is in the path of the airflow coming off of the wing, of course).

Pete