Jos,
Since I intent to order a Woodcomp propellor soon, I'm very interested
in the cause of the accident.
I'm however still puzzled by your claim that a mechanical failure of the
Woodcomp propellor was the cause of your crash.
I was prepared to wait for the final AAIB report, but now you are
pointing to the quality of the Woodcomp propellor as being the cause of
the accident, I would love to hear the complete story.
You first state that the lack of an end-stop in the Woodcomp propellor
was the cause.
Later on, you blame diodes and relays of inferior quality.
These are two different things. Anyway, as someone else pointed out
already, the accident implies more or less that the propellor control
motor got somehow engaged. A missing end stop was nothing more than a
contributing factor, not the real cause. Since you had the reverse pitch
option, there could not be a mechanical end stop anyway. But even
without the end stop, the prop would have functioned correctly, IF the
prop pitch motor got not erroneously engaged during the flight.
The big question therefor remains: what caused the prop motor to start
cranking the prop to superfine?
Some of us are intrigued by a message from you, written the 19th of may
2007, in which you wrote:
"For reason of simplicity, exactly in a high stress situation (most of
my landings will be :-) ) managed to do away with the change-mode
switch. The 3-pole reverse-unreverse switch now operates a relay, that
changes the mode. This latched and warning labeled switch is IMHO
security enough against accidental operation.
Do you have to wait for full reverse before opening the throttle? Should
i think about an indicator light that indicates the reverse end stop
reached?"
See http://www.europaowners.org/viewtopic.php?t=4276
In a normal setup, you can not engage reverse, without changing the mode
first, and putting power back to idle first. In a standard Woodcomp
setup there are no relays involved at all. You are describing a
modification that bypasses the mode switch by the addition of a relay,
and could potentially switch the prop to full reverse without closing
the throttle first.
Could it be that your safety bypass, consisting of the addition of a
relay, played a role in this accident? Was this the malfunctioning relay
you are referring to? If this single additional relay would fail, could
it all by itself unintentionally power up the pitch control motor?
I hope you understand that I'm confused by your claim that it was just a
missing mechanical end stop that was the main cause of the accident. If
your modification made it easier for the prop pitch motor to
unintentionally start cranking the prop to fine/reverse, it doesn't make
sense to point so strongly to the Woodcomp company as being the cause of
the accident. So far, I have no reasons to believe that a Woodcomp prop,
without reverse option, and without safety bypass, would have a higher
risk than any other prop. There are no statistics that point into that
direction.
I'm not involved in the Woodcomp company, I even don't have a Woodcomp
propellor (yet). Hope you understand that I'm purely technically
interested in the chain of events that led to this tragedy. There might
be something that can be a lesson for us, so we avoid this from
happening again in the future. For the safety of us all, we'd better
stay away from emotions and look purely at the factual data we have. At
this moment, without substantial data, just pointing to Woodcomp as the
cause, is not really convincing, and not sufficient ground to start
talking people into selling their Woodcomp propellors. Just my 2 cents.
--
Frans Veldman
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