Dear Frans.
For the moment i am still willing to believe you honestly still do not
understand
what happened and try to fill in the gaps.
[quote:e2d9de2b1b]
If you throttle back from take-off power to cruise climb, the controller
tries to move the blades to the finest pitch possible, and it is the
task of the endswitches to prevent the blades from moving even further?
[/quote:e2d9de2b1b]
Correct.
[quote:e2d9de2b1b]
With other words, with every throttle move, the blades will always
travel to one of the endstops?
[/quote:e2d9de2b1b]
Of course not, where you did invent that idea now?
The controlers task is to keep the rpm as instructed.
It will move the blades until that selected rpm is reached.
If you would nearly close the throttle it will never reach that rpm, and the
fine
endstop comes into play to prevent the blades from moving into an unflyable
position. Still, even with disabled endstops, due spotwelded contacs,
short-circuited
diode ect, adding power would increase rpm and the blades would return
to a normal pitch. You would never notice what happened. Unless, that underrated
pitch motor, which had been struggling hard to turn to negative pitch, now
has to struggle again to positive pitch under full load and decides that enough
is enough. It burns, blowing the CB.
[quote:e2d9de2b1b]
If this is the case, I can understand how a failed endstop immediately
caused the blades to travel to a non flyable position.
[/quote:e2d9de2b1b]
No you don't
[quote:e2d9de2b1b]
As I'm technically handicapped, I picture the working of the prop and
controller as follows:
Say you fly at 100 knots, and the controller has adjusted the rpm, as
you have demanded, to 5000 rpm. Now, if you reduce throttle slightly,
the controller reduces the pitch somewhat *without fully traveling to
the end stop*, measure the rpm again, evaluate if still below the target
rpm, reducing the pitch a little bit more, evaluate again, and stop when
the engine again is at 5000 rpm. The end switch has not been used in
this scenario, because the prop went never to its finest position in the
first place.[/quote:e2d9de2b1b]
Correct.
[quote:e2d9de2b1b]
Even with the end switches shorted, you won't notice anything.
Until something else goes wrong...
[/quote:e2d9de2b1b]
Like closing the throttle a little bit more.
[quote:e2d9de2b1b]
For a failure, you need an additional factor, something that tries to
move the blades to an even finer pitch *while the rpm is already above
its target*.
[/quote:e2d9de2b1b]
No you don't Just closing the throttle is enough to hang you life on the proper
functioning of the fine end stop.
[quote:e2d9de2b1b]
I'm still looking for a scenario where the rpm can rise to 6200 rpm, the
blades are in super fine, and something is feeding power to the pitch
motor to move the blades even further. What is this "something". Once
[/quote:e2d9de2b1b]
What about opening the thottle to full power because you are low and slow?
[quote:e2d9de2b1b]
again: even with all micro-switches shorted, the pitch motor won't run,
because power is fed only to these switches if something (the
controller, the reverse pitch relay) is sending power to the pitch motor
with the purpose of reducing the pitch. The end switches won't see any
power, shorted or not, unless something tries to move the pitch motor
even further.
[/quote:e2d9de2b1b]
There is no such thing as a reverse pitch relay.
[quote:e2d9de2b1b]It will keep reducing the pitch at any further
reducing of throttle, to keep up the RPM.
[/quote:e2d9de2b1b]
[quote:e2d9de2b1b]Past the desired RPM?
[/quote:e2d9de2b1b]
Again, stage one: I did explain now how the pitch can turn into fine or negative
on any Woodcomp SR 3000 with broken fine endswitches.
Stage two: If the pitch moter burns at that critical point, it can't do anything
to prevent to go past the desired rpm.
[quote:e2d9de2b1b]
Let me spell it out: In a normal situation, when powering back from
take-off power to cruise power, the end/stops/limit switches never come
into play, because the controller cuts the power to the pitch motor long
before the fully finest position is reached.
[/quote:e2d9de2b1b]
Correct, partly.
[quote:e2d9de2b1b]
In order for the limit switches to show their failure, something has to
keep sending power to the prop circuit, now putting all bets on the
limit switches to prevent the prop from going past fully fine. Once
again: I think it is not common practice to cruise along with the prop
in fully fine, so the end switches should never have been exercised. But
something tried to move the blades to fully fine, and apparently even
past fully fine.
[/quote:e2d9de2b1b]
You get the picture.
Just reducing the power under the power needed for the engine to keep the
desired
rpm will make the conmtroller send more "fine" power into the pitch motor.
[quote:e2d9de2b1b]
Now, as I studied the schematics, there are only two power sources for
the prop pitch motor: the controller, and the reverse circuitry. One of
these circuits had to be inadvertently sending power to the pitch motor,
while the rpm was already way up.
[/quote:e2d9de2b1b]
Wrong, you mixing up stage one, how to get the blades over fine pitch, with
stage
two, having burnt the pitch motor. The rpm will not go up, will never reach
desired rpm unless there is enough power added. Adding power, burning the motor
then will overrun the engine.
[quote:e2d9de2b1b]
By definition, the reverse circuitry has to bypass the microswitches,
because its purpose is to intentionally move the blades past fully fine.
That makes the reverse circuitry suspect number one.
If I then read that you have modified the reverse circuit, it is not
difficult to start to wonder if this has had something to do with it.
[/quote:e2d9de2b1b]
Wrong again. The reverse circuitry uses it's own slipring, and has nothing to do
with the fine pitch microswitches. By the way, the diode is there to return
power to the pitch motor with opened micro switches. Not intended nor rated for
spark killing.
[quote:e2d9de2b1b]
If I recall correctly: on the Woodcomp there is a third slip ring, for
adding power to move the prop beyond its normal flying operating range.
This is used for reverse, or feathering. You need to put power on this
ring to feather or go to reverse.
This third ring is not connected to the controller, so the controller is
no longer suspect here.
Normally you put power on this third ring with a safety latched switch.
It appears from your message that you replaced the function of this
switch by a relay.
[/quote:e2d9de2b1b]
I told you that the reverse circuit was switched off, no power, no relay power,
powerless, cold not doing anything, dead, not working, not operating. Safety
latched. It's just not possible for circuits to operate without power. Not in
this world anyhow. I also explained how the pitch ended up super fine. I also
explained why the pitch could not return to normal. Most probably you don't want
to understand the facts, it is much easier to cap your ears.
Last advice:
Find an SR 3000 and have a good look at the components. Google the
specifications
of those life critical parts. Poor water over these microswitches. Run then
pitch motor up and down for an hour or so while restricting the blade movement.
But on the ground please!
Regards,
Jos Okhuijsen
Visit - www.EuropaOwners.org
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