Ok, i'll try to answer the questions asked. Some of them have been asked and
anwered
before, and i hope these answers will be consistent with what was mentioned
before :-) Latest news from the accident investigator was 3 weeks ago, where
he told me that he wanted to finish the report within a week. Maybe there are
new delays.
Why did the prop run into super fine pitch?
I took off normally, full throttle, prop controller in the take-off position.
Everythinjg
fine. At 500 ft above ground i switched the controller to cruise and
throttled back. The controller adjusted the blades to 4350, my last descent
cruise. I had forgotten to adjust the controller to 5000 rpm, my normal slow
climb
cruise. As a result the map went beyond an acceptable value. So i throttled
down more, and at the same time toggled the controller to 5000 rpm. This caused
the blades to turn more fine. Probably against the fine endstop position,
if that endstop had been functional. At that very moment the tower instructed
the formation to switch frequencies, although i was still on crosswind, and
number 3 probaly still on upwind. While changing frequencies i noticed that my
number one was disappearing fast, added more power and noticed 6200 rpm and no
thrust, 50 knots airspeed The blades were obviously in super fine. Also the
prop CB had popped. Resetting the CB resulted in the
controller showing boot messages as normal, and the CB popped again. Because
the
controller booted normally, it is clear that there was no sc in there, and
the controller only did what is was supposed to do: Turn fine to increase the
demanded rpm, (fine endstop being the end of travel) turn coarse to reduce to
demanded rpm. Most probably the pitch motor had burnt. It could not cope with
turning the blades at this high rpm. That the propellor was of a reversible
version
had nothing to do with the events. All components that played a role are
present in any SR 3000. To resume: !st Endstops did not work, Woodcomp supplied
component failure. 2nd: Motor burnt
The electrical components in the propeller are not suitable for the task. The
end-stop
microswitches are for indoor use, and not suitable to withstand weather
influences. Most probably their DC amp rating is much lower then the current
drawn by the motor. The diode across the switches is of a 5 A type, where the
pitch motor can draw + 15A. The motor, for which i could not find any
specifications,
looks to be a 6 V type. Suitable for either very short tem useage or
pcm control lower then 50 %. Woodcomp had repaired the prop. After the repair
i had to increase the pcm ratio from 40% to 80% to make the pitch motor run.
Either
the mechanism was turning far more difficult, or the motor specifications
had been changed. With the repared propellor came some parts, gears, and also
a used motor. As usual with Woodcomp, there was no explanation or specification.
As stated before: There is no mechanical endstop in the SR 3000 (Thanks David
for
the addition) Not in any Woodcomp 3000, being "normal", reverse or feathering.
Proper working of the fine endstop relies only on proper working of the
electrical
circuit. This circuit, contradictory what David states, is NOT double.
it relies on a single, underrated diode!. There are 2 fine endstops
microswitches,
probably because their rating is insufficient. As any electrical engineer
can tell you, doubling contacts does not double the switching capacity. Reason
being that one will always be earlier. There will be NO indication that either
the microswitches or the diode has failed, until also the motor burns and
you are in superfine pitch at 500 feet and at 50 knots :-(
Yes, also Rotax engines have failed, the difference is, ,that there are no
underrated
or misplaced components to point a finger at. There is proper documentation,
and proper follow-up for anything that may cause a problem. The best Woodcomp
came up with was to "No support for 3rd party controllers" That they are
also the only supplier not contacting me after the accident does not make me
happy either.
Its only fair to admit my own mistakes. As an electrical engineer i should not
have accepted the electrical setup of the prop. I should have known better. I
should not have acepted their offer to repair the propellor. I should not have
acceped the needed change in pcm without further explanation. I should have
adjusted
the cruise rpm before take-off. Maybe i should not have flown in rain.
I should not have accepted the frequency change while still taking off.
There were fields within range, if i would not have been distracted.
If you keep flying with a SR 3000: Please add a fine endstop check to you
checklist
for every take-off.
Kind Regards,
Jos Okhuijsen
Visit - www.EuropaOwners.org
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