It should also be remembered that a prop stuck in a coarse setting can
be an issue as well. To this end it is worth checking that the aircraft
can climb away safely from a go-around at short finals at low speed in
this condition.
I flew C-130s for 9 years and without doubt the propellers with their
control systems were studied more closely than any other technical
aspect of the aircraft. On this aircraft there are 6 different safety
features that are designed to limit the rpm of the engine. This was
particularly important for an engine/prop combination that was designed
to run at constant speed. On the RAF C-130s the engines produced about
5000shp each and the propeller angle could reach 55 degrees in the
cruise and keeping the rpm within the 98-102%rpm limit needed some high
quality engineering. The incident below whilst not relevant to the
Europa might make interesting reading.
An Orion aircraft (which uses the same engine/prop combination as the
C-130) had a very testing incident which makes one aware that, even
after many years of trouble free operation, it is possible to get into
a situation where a prop can bite. In this case the crew was flying in
a naval military exercise many miles offshore. This entailed a long
transit at high level, a significant amount of time of slow flight at
low level, followed by another high level transit back to their base.
The problem came when a fault in one of the propeller control systems
caused an outboard prop to pitch lock during the low level phase of the
flight. This is one of the safety features to prevent the prop going
too fine. However because of the power/altitude/speed combination the
prop was stuck in low pitch. This isnt normally a problem as the
engine speed can be contained by continuing to fly at a low TAS. It
still takes the total attention of one crew member using the throttle
to keep the rpm within limits. However in this case, to be able to
reach the nearest airfield, the aircraft needed to climb as it had
insufficient range at low altitude. The crew was faced with the choice
of a premeditated ditching or to intentionally increase the TAS by
climbing and accept the risk catastrophic failure as the prop was
forced into an overspeed situation. They decided to choose the latter.
The highest rpm that the safety features can normally cope with is
108%. As they climbed the prop rpm increased until finally the engine
and propeller broke away from their mountings. Afterwards this was
calculated to have happened at about 170%rpm. Fortunately the
engine/prop combination fell away without damaging the aircraft. The
crew managed to continue their flight to a safe landing.
When William Mills first flew into my strip with the first Woodcomp
prop with beta range capability I had a chat with him about the dangers
of props that can operate in the beta range. I thought it a risky
feature which was totally unnecessary on the Europa. As Jos found, even
in forward fine pitch the situation can very quickly become
uncontrollable should something go wrong.
I would suggest that owners of Europas with VP props may like to check
that the settings for the mechanical stops for both low and high pitch
on their propellers enable safe low speed flight.
Nigel Charles
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