5.5 Overspeed Warning
It is possible to overspeed the propeller by rapid throttle
advancement. Therefore, always adjust the power and RPM
lever slowly and smoothly to avoid the possibility of
overspeed.
The 400A propeller is rated for an absolute
maximum 2,700 RPM.
The maximum rated RPM of the propeller is something to be
taken very seriously and often is not by many pilots. All Whirl
Wind propellers are designed with a conservative safety factor
based on the maximum RPM of 2,700. The centrifugal blade
forces are a squared function of RPM. For example, 2,700
RPM has double the blade centrifugal force than that of 2,000
RPM. Considering this relationship what could be perceived
as a small 10% over speed will result in a 21% increase in
blade centrifugal force loads. Therefore even a small increase
in RPM over the maximum limit will quickly diminish the
propeller’s structural safety factor. It is critical to always follow
the propeller’s RPM limitations and over speed inspection
procedures as detailed below.
If an overspeed occurs:
Overspeed Occurrence
Required Action
up to 110 % of the max RPM
A 50 hours inspection must be
performed immediately by a certified
A&P mechanic
111% to 120% of the max
RPM
A mandatory teardown inspection at
the factory is required
above 121% of the max RPM
No further use of the propeller is
permitted! The propeller must be
returned to the factory for
inspection.
5-4