I think you reversed the usage of the terms, Jeff. Angle of incidence is
built into the airplane and angle of attack is a variable, as you say,
per airspeed & density, that refers to the wing related to the relative
wind. What you describe happens with gliders at high altitudes as well,
with no consideration of power. Due to low air density, to maintain an
indicated airspeed the nose must be higher than at lower altitudes to
increase the wing's angle of attack, to get the appropriate amount of
lift in the thinner air. Flying higher and higher, things become more
and more like slow flight.
On 3/16/2020 9:12 PM, Jeff Scott via KRnet wrote:
John, your statement is correct.
Cruising at higher altitudes usually creates a situation where you are flying
at a higher Angle of Incidence. Pilots often times incorrectly interpret the
higher deck angle as AOA rather than AOI. The higher angle of incidence is not
created by altitude itself, but is created by the lower amount of power
available from a normally aspirated engine at a higher altitude for a given
throttle setting and thus typically leaves you flying at a lower indicated
airspeed. The lower indicated airspeed creates a higher angle of incidence for
a given throttle setting at higher altitudes. It's a more complicated way of
saying that at higher altitudes, the nose is usually a bit higher than while
flying at lower altitudes. People take that basic truth for flying behind
normally aspirated engines, then apply the wrong term by interpreting it as AOA
rather than AOI.
That should make it about as clear as mud. :o)
-Jeff Scott
Arkansas Ozarks
Sent: Monday, March 16, 2020 at 9:39 PM
From: "John Martindale via KRnet" <krnet@list.krnet.org>
To: 'KRnet' <krnet@list.krnet.org>
Cc: "John Martindale" <john_martind...@bigpond.com>
Subject: Re: KR> Dan Diehl's comment to Lee
"cruising at higher altitudes lowers the AofA for a given indicated
airspeed".
I think the above statement is incorrect.
The weight of an aircraft and lift required to support it does not change
with altitude. Lift is proportional to airspeed, AoA, density and wing
design....the basic lift formula we are taught as students.
Therefore for a "given airspeed" and weight and wing design that we cannot
alter in flight, as density decreases with altitude, AoA must be increased
up until the aircraft ceiling is reached when the AoA reaches the stall
angle.
It is only if power is increased to increase the given speed that the AoA
can be reduced.
Pleased to be corrected.
John
John Martindale
Unit 39
40 Solitary Islands Way
Sapphire Beach NSW 2450
Australia
m:0403 432179
email:john_martind...@bigpond.com
snip
Just thinking out loud here . . . but if angle of attack decreases with an
increase of indicated airspeed, and also with a decrease in air density . .
. cruising at higher altitudes lowers the AofA for a given indicated
airspeed,
snip.
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