I'm very grateful to Mark and William for helping to publicise the
consequences of failure of a variable pitch control.
I asked Francis Donaldson of the PFA for advice on the settings for VP
props, and he immediately sent me a copy of the instructions he had issued
last year in connection with a Permit to Test. In this case it was for a
Europa/Rotax/Kremen 2000 set up, but the principles would apply generally.
I have extracted the following, including some general points regarding
installation, cooling and balancing which may be helpful as guidance to
others who may not yet have reached the testing stage:
For this engine/prop installation the stops must be set so that:
a. With the propeller in fully fine, with full throttle set the engine
should not overspeed (ie not exceed 5800) when 'static' on the ground or
when climbing out at the normal climb speed for best angle of climb.
(JAR-VLA 33 (c)(i) refers). We recommend it is set up so that it cannot
exceed 5800 rpm, at full throttle, at a climb speed less than 80 kts.
b. With the propeller pitch in fully coarse, during a glide at Vne with
throttle closed (provided this has no detrimental effect on the engine) the
engine must not exceed 110% of the maximum permitted continuous speed, ie
1.1 x 5500 = 6050 rpm (JAR-VLA 33 (c)(II) refers).
c. With the propeller pitch fully coarse, the aeroplane must demonstrate an
ability to safely go-around, flaps and undercarriage down, and provide a
positive rate of climb,(300 ft/min) with the aeroplane at max gross weight,
under ISA conditions.
This latter is a PFA-imposed requirement which is in recognition of the fact
that this VP propeller has a relatively crude pitch changing control system
in which the reliability of the pitch change system has yet to be
satisfactorily proven in service.
The propeller pitch control must be clearly identified as to function and
sense, and clearly distinguished from the other cockpit controls to avoid
any possibility of confusion. Do not put it directly alongside the pitch
trim switch for example. JAR-VLA 781 requires that propeller controls should
be orientated such that forward motion acts to increase engine rpm ie to
reduce propeller pitch. Ideally the switch should be characteristically
different in shape to the switches for other equipment.
You will need to check not only that the propeller gives satisfactory climb
and cruise performance but also that the engine cooling is not adversely
effected. The cooling may be influenced due to the load applied to the
engine by the prop being different. The VP prop allows the engine to produce
more power, in doing so it creates more waste heat.
The cooling may also be affected by the airflow around the propeller hub and
spinner, particularly if the cooling air intakes are in this area. Removal
of a spinner can upset the airflow, as can a propeller with a large hub or
round shank blade roots which can effectively block the engine cooling inlet
airflow.
You must also check for signs of vibration or buffetting throughout the rpm
range and in all phases of ground running as well as in flight. This may may
result if the natural frequency of vibration of the engine on its mount
rubbers, or the tail surfaces or fuselage, or of the engine/gearbox coupling
should happen to couple in an unfortunate way with the resonant frequency of
the propeller blades in bending, or the aerodynamic buffet coming from the
slipstream. It may also indicate that the propeller (or possibly the
spinner) is out of track or out of balance. Good results have been reported
---From dynamically balancing propellers on Europas, at least one balancing
company advertises in 'Popular Flying'.
Fly safely
Mike
Europa Club Safety Officer
safety@europaclub.org.uk
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