"mise en drapeau" to put a flag
la bière biensur !!!
Bon copier coller ca donne ca :
It controls the ADJUSTABLE-PITCH Propeller
A constant-speed propeller is the most common type of
adjustable-pitch propeller. The main advantage of a
constant-speed propeller is that it converts a high
percentage of brake horsepower (BHP) into thrust
horsepower (THP) over a wide range of r.p.m. and
airspeed combinations. A constant-speed propeller is
more efficient than other propellers because it allows
selection of the most efficient engine r.p.m. for the
given conditions.
An airplane with a constant-speed propeller has two
controls—the throttle and the propeller control. The
throttle controls power output, and the propeller
control regulates engine r.p.m. and, in turn, propeller
r.p.m., which is registered on the tachometer.
Once a specific r.p.m. is selected, a governor
automatically adjusts the propeller blade angle as
necessary to maintain the selected r.p.m. For example,
after setting the desired r.p.m. during cruising flight, an
increase in airspeed or decrease in propeller load will
cause the propeller blade angle to increase as necessary
to maintain the selected r.p.m. A reduction in airspeed
or increase in propeller load will cause the propeller
blade angle to decrease.
The range of possible blade angles for a constant-speed
propeller is the propeller’s constant-speed range and is
defined by the high and low pitch stops. As long as the
propeller blade angle is within the constant-speed range
and not against either pitch stop, a constant engine
r.p.m. will be maintained. However, once the propeller
blades contact a pitch stop, the engine r.p.m. will
increase or decrease as appropriate, with changes in
airspeed and propeller load. For example, once a
specific r.p.m. has been selected, if aircraft speed
decreases enough to rotate the propeller blades until
they contact the low pitch stop, any further decrease in
airspeed will cause engine r.p.m. to decrease the same
way as if a fixed-pitch propeller were installed. The
same holds true when an airplane equipped with a
constant-speed propeller accelerates to a faster
airspeed. As the aircraft accelerates, the propeller blade
angle increases to maintain the selected r.p.m. until the
high pitch stop is reached. Once this occurs, the blade
angle cannot increase any further and engine
r.p.m. increases.
On airplanes that are equipped with a constant-speed
propeller, power output is controlled by the throttle and
indicated by a manifold pressure gauge. The gauge
measures the absolute pressure of the fuel/air mixture
inside the intake manifold and is more correctly a
measure of manifold absolute pressure (MAP). At a
constant r.p.m. and altitude, the amount of power
produced is directly related to the fuel/air flow being
delivered to the combustion chamber. As you increase
the throttle setting, more fuel and air is flowing to the
engine; therefore, MAP increases. When the engine is
not running, the manifold pressure gauge indicates
ambient air pressure (i.e., 29.92 in. Hg). When the
engine is started, the manifold pressure indication will
decrease to a value less than ambient pressure (i.e., idle
at 12 in. Hg). Correspondingly, engine failure or power
loss is indicated on the manifold gauge as an increase
in manifold pressure to a value corresponding to the
ambient air pressure at the altitude where the failure
occurred.
The manifold pressure gauge is color-coded to indicate
the engine’s operating range. The face of the manifold
pressure gauge contains a green arc to show the normal
operating range, and a red radial line to indicate the
upper limit of manifold pressure.
For any given r.p.m., there is a manifold pressure that
should not be exceeded. If manifold pressure is
excessive for a given r.p.m., the pressure within the
cylinders could be exceeded, thus placing undue stress
on the cylinders. If repeated too frequently, this stress
could weaken the cylinder components, and eventually
cause engine failure.
You can avoid conditions that could overstress the
cylinders by being constantly aware of the r.p.m.,
especially when increasing the manifold pressure.
Conform to the manufacturer’s recommendations for
power settings of a particular engine so as to maintain
the proper relationship between manifold pressure
and r.p.m.
When both manifold pressure and r.p.m. need to be
changed, avoid engine overstress by making power
adjustments in the proper order:
When power settings are being decreased, reduce
manifold pressure before reducing r.p.m. If r.p.m. is
reduced before manifold pressure, manifold
pressure will automatically increase and possibly
exceed the manufacturer’s tolerances.
When power settings are being increased,
reverse the order—increase r.p.m. first, then
manifold pressure.
To prevent damage to radial engines, operating time
at maximum r.p.m. and manifold pressure must be
held to a minimum, and operation at maximum
r.p.m. and low manifold pressure must be avoided.
Under normal operating conditions, the most severe
wear, fatigue, and damage to high performance
reciprocating engines occurs at high r.p.m. and low
manifold pressure.
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