RE: Europa-List: Woodcomp Propellers

[Karl Heindl <kheindl@msn.com>]

Josok=2C


This is a most fascinating thread and I wish it had never happened. What I 
would lke to ask you is : How much of this is theory and how much is fact ?
 Was the hub recovered intact or did it burn as well ? In particular I woul
d like to know if there really was a motor failure=3B as you know I had two
 motor failures. And I believe you when you say that the motor cannot turn 
the blades at high rpm. These are mickey mouse motors designed for the auto
motive industry. Jiri claims they are Bosch manufacture=2C but mine (they s
ent me 3 different types) all have the name Johnson stamped on it. I believ
e this is a Hongkong company producing millions of these things for the car
 manufacturers.

For that reason I will avoid all pitch changes at high rpm and below 2000 f
eet.


Karl


> Subject: Re: Europa-List: Woodcomp Propellers
> From: josok-e@ukolo.fi
> Date: Thu=2C 19 Mar 2009 20:48:05 +0200
> To: europa-list@matronics.com
> 
> 
> Dear Frans.
> 
> For the moment i am still willing to believe you honestly still do not un
derstand what happened and try to fill in the gaps.
> [quote:e2d9de2b1b]
> If you throttle back from take-off power to cruise climb=2C the controlle
r
> tries to move the blades to the finest pitch possible=2C and it is the
> task of the endswitches to prevent the blades from moving even further?
> [/quote:e2d9de2b1b]
> Correct.
> [quote:e2d9de2b1b]
> With other words=2C with every throttle move=2C the blades will always
> travel to one of the endstops?
> [/quote:e2d9de2b1b]
> Of course not=2C 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=2C an
d the fine endstop comes into play to prevent the blades from moving into a
n unflyable position. Still=2C even with disabled endstops=2C due spotwelde
d contacs=2C short-circuited diode ect=2C adding power would increase rpm a
nd the blades would return to a normal pitch. You would never notice what h
appened. Unless=2C that underrated pitch motor=2C which had been struggling
 hard to turn to negative pitch=2C now has to struggle again to positive pi
tch under full load and decides that enough is enough. It burns=2C blowing 
the CB. 
> [quote:e2d9de2b1b]
> If this is the case=2C 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=2C I picture the working of the prop and
> controller as follows:
> Say you fly at 100 knots=2C and the controller has adjusted the rpm=2C as
> you have demanded=2C to 5000 rpm. Now=2C if you reduce throttle slightly
=2C
> the controller reduces the pitch somewhat *without fully traveling to
> the end stop*=2C measure the rpm again=2C evaluate if still below the tar
get
> rpm=2C reducing the pitch a little bit more=2C evaluate again=2C and stop
 when
> the engine again is at 5000 rpm. The end switch has not been used in
> this scenario=2C because the prop went never to its finest position in th
e
> first place.[/quote:e2d9de2b1b]
> 
> Correct.
> [quote:e2d9de2b1b]
> Even with the end switches shorted=2C 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=2C you need an additional factor=2C 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=2C th
e
> blades are in super fine=2C 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=2C the pitch motor won't run
=2C
> because power is fed only to these switches if something (the
> controller=2C the reverse pitch relay) is sending power to the pitch moto
r
> with the purpose of reducing the pitch. The end switches won't see any
> power=2C shorted or not=2C 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=2C to keep up the RPM.
> [/quote:e2d9de2b1b]
> [quote:e2d9de2b1b]Past the desired RPM?
> [/quote:e2d9de2b1b]
> Again=2C 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=2C it can't do
 anything to prevent to go past the desired rpm. 
> 
> [quote:e2d9de2b1b]
> Let me spell it out: In a normal situation=2C when powering back from
> take-off power to cruise power=2C the end/stops/limit switches never come
> into play=2C because the controller cuts the power to the pitch motor lon
g
> before the fully finest position is reached.
> [/quote:e2d9de2b1b]
> Correct=2C partly. 
> [quote:e2d9de2b1b]
> In order for the limit switches to show their failure=2C something has to
> keep sending power to the prop circuit=2C 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=2C so the end switches should never have been exercised. Bu
t
> something tried to move the blades to fully fine=2C 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 pitc
h motor.
> [quote:e2d9de2b1b]
> Now=2C as I studied the schematics=2C there are only two power sources fo
r
> the prop pitch motor: the controller=2C and the reverse circuitry. One of
> these circuits had to be inadvertently sending power to the pitch motor
=2C
> while the rpm was already way up.
> [/quote:e2d9de2b1b]
> Wrong=2C you mixing up stage one=2C how to get the blades over fine pitch
=2C with stage two=2C having burnt the pitch motor. The rpm will not go up
=2C will never reach desired rpm unless there is enough power added. Adding
 power=2C burning the motor then will overrun the engine. 
> [quote:e2d9de2b1b]
> By definition=2C the reverse circuitry has to bypass the microswitches=2C
> 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=2C 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=2C and has noth
ing to do with the fine pitch microswitches. By the way=2C the diode is the
re to return power to the pitch motor with opened micro switches. Not inten
ded nor rated for spark killing. 
> 
> [quote:e2d9de2b1b]
> If I recall correctly: on the Woodcomp there is a third slip ring=2C for
> adding power to move the prop beyond its normal flying operating range.
> This is used for reverse=2C 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=2C so the controller i
s
> 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=2C no power=2C no re
lay power=2C powerless=2C cold not doing anything=2C dead=2C not working=2C
 not operating. Safety latched. It's just not possible for circuits to oper
ate 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 no
rmal. Most probably you don't want to understand the facts=2C it is much ea
sier to cap your ears. 
> 
> Last advice:
> Find an SR 3000 and have a good look at the components. Google the specif
ications 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 b
lade movement. But on the ground please!
> 
> Regards=2C
> 
> Jos Okhuijsen
> 
> 
> 
> 
> 
> 
> Visit - www.EuropaOwners.org
> 
> 
> 
> 
> 
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