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Mark Burton

Joined: 10 Jan 2006
Posts: 74

Posted: Mon Jun 27, 2011 6:35 am Post subject: Re: Woodcomp after Sales Service

Hi,



I have nothing to say re the suitability of the microswitches/diodes used by Woodcomp in the SR3000. However, from what I know about the characteristics of the scimitar bladed SR3000 fitted with either the reversing or feathering options, I feel that they are unlikely to have been the cause of Jos' accident.



Let's consider some facts:



Fact #1 - Woodcomp specified that a 10A circuit breaker should be used with that propeller and I believe that's what was fitted to Jos's aircraft.



Fact #2 - under heavy load (high engine power, pitch motor stalled or moving very slowly), the SR3000 pitch motor is capable of drawing more than 10A.



Fact #3 - Jos's propeller had recently returned from the factory and (Jos, please correct me if I am wrong), had not been checked to see that the fine limit microswitches were correctly set so that the aircraft would be flyable with the pitch stuck on fully fine.



Therefore, it's possible for the C/B to pop simply by applying enough load to the pitch motor. If it pops when the prop is fully fine, expect trouble.



Regards,



Mark



PS - I informed the factory in 2007 that the scimitar bladed SR3000 required an excessive amount of current to go coarse . Nothing came of it.

davidjoyce(at)doctors.org
Guest

Posted: Mon Jun 27, 2011 9:43 am Post subject: Woodcomp after Sales Service

Jos, I am not sure it is helpful to prolong this, but yes I have tested my 

mechanical stop It is strong enough to stop a runaway electric motor I guess 

100hp more powerful than the fitted one and comes into action a degree or 

two past the usual position so still capable of producing reasonable thrust. 

(For those who want to try it is necessary to  isolate the wires to the 

motor by unsoldering them.)

           The microswitch problem was as far as I am aware simply mine. It 

was reported to LAA and to Woodcomp and indeed to you and the europa list, 

and no other such incidents had (or have since as far as I am aware)been 

reported. The side wall of the microswitch parted company because of a 

strange design and this could allow failure of the switch. Newer versions 

have the side wall integral with the entire structure.

          I have nothing to add to my views  on the rain worthiness or the 

general reliability of the design.   Regards, David

---

stephan(at)scassel.se
Guest

Posted: Mon Jun 27, 2011 11:23 am Post subject: Woodcomp after Sales Service

Hi,

  

 I am very pleased with my SR2000 approaching 300 hours. I have one failure  though.

 The company (Jiri) is very supportive. I ordered spare parts in order to  repair the gear box.

 Within 3 days the parts arrived and the prop was back in service 3 days  later.

  

 When or if I need to buy a new prop it will be a WoodComp. Wood and  composite is great combination.

 Low vibration due different materialâ€™s resonance and will save the engine  in event of a prop strike.

  

 It is important to regular service. As it is for all variable pitch  props.

  

 Regards 

 Stephan

 LN-STE mono

   [quote][b]

josok-e

Joined: 29 Jan 2010
Posts: 16
Location: Ivalo Finland

Posted: Mon Jun 27, 2011 11:42 am Post subject: Woodcomp after Sales Service

Hi Mark,



It's a pity Mark, that you have not checked the max DC specification of 

those microswitches. I am afraid they are even more underrated as their 

circuit breaker specification. I am also disappointed that you are not 

willing to comment on my "indoor use only" comment for these switches.

I had tested the prop before when new, and did not test it after the 

repair. Maybe i was convinced that Woodcomp would have done a proper 

job. My mistake. Your scenario of the fatal flight could be possible, or 

not because your controller's pulse ratio would limit the max energy the 

motor would pull on full power.



I think that Paul has now a good picture of the quality of the Woodcomp 

after sales service now. My god, you will need it. When ordering the 

prop from them do not forget to order spare microswitches, spare gears, 

a spare motor spare diodes and ask them if you may change their 

specification to a 20 A circuitbreaker.

Add a full fine to coarse excercise to your checklist, and check before 

every flight that the microswitches are still in one piece. It's a pity 

you will have to unbolt the prop for that, but hey, you have saved a 

couple of thousand.



Regards,



Jos Okhuijsen





27.6.2011 17:35, Mark Burton kirjoitti:

 	  Quote: 	
		   



 Hi,



 I have nothing to say re the suitability of the microswitches/diodes used by Woodcomp in the SR3000. However, from what I know about the characteristics of the scimitar bladed SR3000 fitted with either the reversing or feathering options, I feel that they are unlikely to have been the cause of Jos' accident.



 Let's consider some facts:



 Fact #1 - Woodcomp specified that a 10A circuit breaker should be used with that propeller and I believe that's what was fitted to Jos's aircraft.



 Fact #2 - under heavy load (high engine power, pitch motor stalled or moving very slowly), the SR3000 pitch motor is capable of drawing more than 10A.



 Fact #3 - Jos's propeller had recently returned from the factory and (Jos, please correct me if I am wrong), had not been checked to see that the fine limit microswitches were correctly set so that the aircraft would be flyable with the pitch stuck on fully fine.



 Therefore, it's possible for the C/B to pop simply by applying enough load to the pitch motor. If it pops when the prop is fully fine, expect trouble.



 Regards,



 Mark



 PS - I informed the factory in 2007 that the scimitar bladed SR3000 required an excessive amount of current to go coarse . Nothing came of it.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=344245#344245

nigel henry

Joined: 24 Feb 2011
Posts: 16
Location: oxford uk

Posted: Mon Jun 27, 2011 12:09 pm Post subject: Woodcomp after Sales Service

Well Guys,                do we fit a plank of wood to the front of the Rotax or are there other options I thought 

it was the prop of chose ? who's next and why do the manufactures not take notice of the pilots in the seat  

it all seems to work well tillll ..... and not enough safety margin Options Guys |Options ? 



 	  Quote: 	
		   Date: Mon, 27 Jun 2011 22:38:02 +0300

 From: josok-e(at)ukolo.fi

 To: europa-list(at)matronics.com

 Subject: Re: Re: Woodcomp after Sales Service

 

 --> Europa-List message posted by: Jos Okhuijsen <josok-e(at)ukolo.fi>

 

 Hi Mark,

 

 It's a pity Mark, that you have not checked the max DC specification of 

 those microswitches. I am afraid they are even more underrated as their 

 circuit breaker specification. I am also disappointed that you are not 

 willing to comment on my "indoor use only" comment for these switches.

 I had tested the prop before when new, and did not test it after the 

 repair. Maybe i was convinced that Woodcomp would have done a proper 

 job. My mistake. Your scenario of the fatal flight could be possible, or 

 not because your controller's pulse ratio would limit the max energy the 

 motor would pull on full power.

 

 I think that Paul has now a good picture of the quality of the Woodcomp 

 after sales service now. My god, you will need it. When ordering the 

 prop from them do not forget to order spare microswitches, spare gears, 

 a spare motor spare diodes and ask them if you may change their 

 specification to a 20 A circuitbreaker.

 Add a full fine to coarse excercise to your checklist, and check before 

 every flight that the microswitches are still in one piece. It's a pity 

 you will have to unbolt the prop for that, but hey, you have saved a 

 couple of thousand.

 

 Regards,

 

 Jos Okhuijsen

 

 

 

 

 27.6.2011 17:35, Mark Burton kirjoitti:

 > -->  Europa-List message posted by: "Mark Burton"<markb(at)ordern.com>

 >

 > Hi,

 >

 > I have nothing to say re the suitability of the microswitches/diodes used by Woodcomp in the SR3000. However, from what I know about the characteristics of the scimitar bladed SR3000 fitted with either the reversing or feathering options, I feel that they are unlikely to have been the cause of Jos' accident.

 >

 > Let's consider some facts:

 >

 > Fact #1 - Woodcomp specified that a 10A circuit breaker should be used with that propeller and I believe that's what was fitted to Jos's aircraft.

 >

 > Fact #2 - under heavy load (high engine power, pitch motor stalled or moving very slowly), the SR3000 pitch motor is capable of drawing more than 10A.

 >

 > Fact #3 - Jos's propeller had recently returned from the factory and (Jos, please correct me if I am wrong), had not been checked to see that the fine limit microswitches were correctly set so that the aircraft would be flyable with the pitch stuck on fully fine.

 >

 > Therefore, it's possible for the C/B to pop simply by applying enough load to the pitch motor. If it pops when the prop is fully fine, expect trouble.

 >

 > Regards,

 >

 > Mark

 >

 > PS - I informed the factory in 2007 that the scimitar bladed SR3000 required an excessive amount of current to go coarse . Nothing came of it.

 >

 >

 >

 >

 > Read this topic online here:

 >

 > http://forums.matronics.com/viewtopic.php?p=344245#344245

 >

 >

 >

 >

 >

 >

 >

 >

 >

 >

 

 

 _-=============================================

 _====

 

 

 


	




 		 	   		  

  [quote][b]

kees de bussy

Joined: 16 Jul 2009
Posts: 18
Location: the netherlands

Posted: Mon Jun 27, 2011 12:42 pm Post subject: Re: Woodcomp after Sales Service

Hi all,



I haven flown my Europa with the Woodcomp SR 3000 (with reverse option which is not wired) in many conditions, several times in heavy rain too. Up to now I have not met any problems (prop has approx 220 hrs.) To avoid problems as much as possible I always switch to manual before take-off and landing. This way never a signal will be given to change the pitch in the most critical phases of flight. I feel this way it makes it safer to operate this kind of prop (not only Woodcomp). Back on topic, I only had it checked once by a local dealer because of some play of the blades.



Regards,



Kees de Bussy

Europa XS TG, PH-SBR

kheindl(at)msn.com
Guest

Posted: Mon Jun 27, 2011 1:20 pm Post subject: Woodcomp after Sales Service

Kees,



You are a very wise man. Forget about automatic pitch control below 1000 feet. I have been doing the same after my own and Jos's experience. I will never trust an electric prop again. But I wanted variable pitch and feathering for gliding mode. 

But the original question from Paul was about support, not whether the make was any good. That seems to have improved, at least in Europe, but the problem I pointed out is still there: There is only one person to talk to. If he is not there and he goes on frequent sales trips and there are long holidays, not to mention sick leave, then your support is one big zero.

And I still say that the pitch motor is not up to the job after two failures. An electric motor should never fail.

They are off-the-shelf items from another company and were designed to power electric tools for Bosch and Dremel etc. 

Karl





 	  Quote: 	
		   Subject: Re: Woodcomp after Sales Service

 From: keesdebussy(at)hotmail.com

 Date: Mon, 27 Jun 2011 13:42:52 -0700

 To: europa-list(at)matronics.com

 

 --> Europa-List message posted by: "kees de bussy" <keesdebussy(at)hotmail.com>

 

 Hi all,

 

 I haven flown my Europa with the Woodcomp SR 3000 (with reverse option which is not wired) in many conditions, several times in heavy rain too. Up to now I have not met any problems (prop has approx 220 hrs.) To avoid problems as much as possible I always switch to manual before take-off and landing. This way never a signal will be given to change the pitch in the most critical phases of flight. I feel this way it makes it safer to operate this kind of prop (not only Woodcomp). Back on topic, I only had it checked once by a local dealer because of some play of the blades.

 

 Regards,

 

 Kees de Bussy

 Europa XS TG, PH-SBR

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=344288#344288

 

 

 

 

======================

&gt================
	


 	  Quote: 	
		   

 

 


	




 		 	   		  

  [quote][b]

frans(at)privatepilots.nl
Guest

Posted: Mon Jun 27, 2011 1:42 pm Post subject: Woodcomp after Sales Service

On 06/27/2011 09:38 PM, Jos Okhuijsen wrote:

 	  Quote: 	
		   It's a pity Mark, that you have not checked the max DC specification of

 those microswitches.


	


The max DC specification of the switches is of little value. Max DC is

mainly limited by the opening arc of the switches under load. In normal

situations, the limit switches are never opened as the controller cuts

the power long before the limit is reached. These switches are just

sitting there all their life closed, waiting for a controller failure

which is unlikely to happen anyway.



In a previous statement you claimed that the run away was caused by

failed micro switches. This is similar as claiming that you have had a

trim servo run away because of a failing end stop in the trim servo.

Such a claim would ignore the fact that the trim servo can only run

away, with or without end stop, if something keeps feeding power to it

after it reached the desired position. It would require a faulty cockpit

switch or faulty pilot in addition. Similary: Your situation, even with

shorted micro switches, could only occur if the controller or some other

circuitry was failing at the same time: something was delivering power

to the prop while it was already over the target RPM. Even then, this

would never let the CB pop. There is only one controller and it can not

give power to two opposite directions at the same time whatever failure

mode you can devise.



Someone asked whether you had modified the circuitry and you denied

that. However in the archive (before the accident) I found a message

where you wrote that you had the reverse circuitry modified to simplify

the process of entering reverse (which is cumbersome in the original

setup but maybe there was a reason for that), and if I recall it

correctly a relay was used to switch the controller and feed power to

the reverse ring of the prop at the same time.



If this modified circuitry failed, it would explain fully what happened:

While feeding unwanted power to the reverse ring of the prop the prop

could reach 0 or negative angle because the reverse slip ring  bypasses

the limit switches (for logical reasons) AND the controller at the same

time, and the CB would pop if the controller tried to reverse the engine

polarity.



The whole story of short circuited limit switches does not explain the

problems in any way. I would be confident to operate the airplane with

shorted limit switches AND shorted or busted diodes, as these items are

never used while the controller is working properly.



The function of the diodes is to allow the motor to run in the other

direction once one of the limit switches opened (otherwise you could

never recover from reaching the prop limit as the limit switch cuts ALL

power to the prop). In normal operation the diodes are never used.

Neither shorting them or opening them would affect the normal operation

of the prop. Again, whether these diodes are fully up to specs wouldn't

matter at all in normal situations as it is unlikely that any current

will ever flow through them.



Your situation further differs from standard configurations by using the

scimitar blades, which are not pitch bias neutral under load but have

strong aerodynamic resistance in one pitch direction. It could well be

possible that changing the pitch in one way caused excessive current,

while in the other direction the aerodynamic loads would try to changing

the pitch even further, and maybe drive the blades over the limit

causing the limit switches to open. And in such a situation it might be

possible that the limit switches finally give up the ghost (but

logically they would burn through and open up, making it impossible to

change the pitch from there). Again, even in this scenario it would not

lead to pitch run aways and popping CB's, but just to a prop which

doesn't respond anymore to pitch change commands.



Frans

rlborger(at)mac.com
Guest

Posted: Mon Jun 27, 2011 1:48 pm Post subject: Woodcomp after Sales Service

Richard,



If you want a constant speed prop, the prop of choice for many folks is the Airmaster propeller with their AC200F controller as recommended by Europa.  It's not perfect but it does extremely well and they are always working to improve on it.  They have their original 3 blade system with Warp Drive blades for either the 80/100 HP or 115+ HP engines as well as their new 2 blade system with blades from Sensenich.  Their own controller works quite well.  They have hub configurations available for most engines that folks stuff in the front of their Europas (Europii?)  They have a long history of working with Europa and Europa builders.  I find them most responsive and supportive of their products.  

Unfortunately, they are located in New Zealand which is on the other side of the earth, quite literally, from the U.K. and most of the remaining Europa population.  Shipping back and forth is a bugger.  Local reps, like Europa in the U.K. and Bud Yerly in the U.S.A. can help.  

In most cases their props seem a bit under-bladed for our application, so they might not wring out the last HP of efficiency but they used to push my Europa, back when it was still a monowheel, along at a solid 140 kts TAS (at) 4.0 - 4.5 gph at about a 75% cruise power setting.  I'm still about a week from flying the tri-gear conversion so I can't speak for it at this time.  

A final issue is the response time of the prop to a rapid throttle advance.  It can be slower than desired producing a momentary exceed of the takeoff RPM.  You can soon learn to compensate for this simply by not advancing the throttle as rapidly allowing the prop to keep up.

They have an excellent web site at http://www.airmasterpropellers.com/Products.aspx with support and information on their AP332 and AP420 prop packages as well as hubs, blades, Controllers, spinners, extensions & hardware.  Should you have any questions Martin, the owner, is the guy on the other end who will respond.  

I suggest you look into Airmaster before you commit to another prop manufacturer.

Blue skies & tailwinds,

 Bob Borger

Europa Kit #A221 N914XL, XS Tri-Gear, Intercooled 914, Airmaster C/S Prop

http://www.europaowners.org/forums/gallery2.php?g2_itemId=60232

http://www.biplaneforumgallery.com/index.php?cat=10046

Europa Flying!

3705 Lynchburg Dr.

Corinth, TX  76208

Home:  940-497-2123

Cel:  817-992-1117



 

 

On Jun 27, 2011, at 15:06, nigel henry wrote:

 	  Quote: 	
		  Well Guys,                do we fit a plank of wood to the front of the Rotax or are there other options I thought 

it was the prop of chose ? who's next and why do the manufactures not take notice of the pilots in the seat  

it all seems to work well tillll ..... and not enough safety margin Options Guys |Options ?

Mark Burton

Joined: 10 Jan 2006
Posts: 74

Posted: Mon Jun 27, 2011 3:09 pm Post subject: Re: Woodcomp after Sales Service

OK, let's put our thinking caps on and ponder switches and diodes.



We're only concerned here with the operation of the fine pitch limit switch and its associated diode (incidentally, the SR3000 has two fine limit switches and diodes in series so failures 1-4 described below have to occur to both switches/diodes, likely?)



When the pitch is being reduced, the switch is carrying the current and the diode is reverse biased. The current level is not high and well within the breaking capability of the switch so it should open as expected and the pitch freezes on the fine limit (+ some overrun).



Assuming that the switch has operated as it should, the pitch will now be fully fine. When the controller next commands the pitch to go coarse, the switch is already open so the diode will have to carry the current. That current can be large as it's basically the pitch motor stall current (initially around 25-30A, falling quickly as the motor spins up). Now the diode is only rated for 5A continuous current but it has a good pulse capability (check the data sheet) so it probably won't fail (we will talk about what happens if the diode fails next) - assuming the diode did not fail and the pitch motor is actually moving, the switch will close shortly afterwards. Exactly how much current will flow through the switch is difficult to predict because we don't know how much the motor has spun up so it could be quite a lot - mind you, there's only around 1V across the switch (the diode drop) so I should think the switch could hack it OK (perhaps with a reduced life).



Now, let's consider some failure modes:



1 - the diode fails open circuit - in this case, when the switch opens as the pitch goes fully fine the pitch will freeze at that point (+ some overrun) and when the controller tries to coarsen the pitch nothing will happen because the switch is open and the diode is open too. Therefore, the end result will be the prop will be stuck in fully fine. But, this would not cause the C/B to pop.



2 - the diode fails short circuit - in this case when the switch opens as the prop reaches fully fine, the pitch motor keeps going and will drive the pitch all the way to reverse position (and the reverse switch would operate). If the controller subsequently tried to coarsen the pitch, it would succeed unless the diode decided the current was too much and died in which case the pitch would freeze. Now as it has been reported that the pitch of the prop was not in the reverse position this probably didn't happen. Again, the C/B would not blow.



3 - the switch fails open circuit - the pitch will not be able to reduce, only coarsen. C/B still intact.



4 - the switch fails short circuit - similar to 2 above, pitch could go to reverse. C/B still a happy bunny.



5 - there is a short circuit from one of the switches/diodes/wires to ground - now this is interesting: it could  make the pitch go to the reverse position and then when the controller tried to move the pitch the other way it would blow the C/B. But as it's already been stated that the pitch was near the flyable region that makes this scenario unlikely but not impossible. 



So, from what we know about the accident, the only one of these failures that could have occurred is a short from one of the pitch motor drive wires to ground (either the wire itself or a switch/diode/motor failure). Is that likely, I don't know, but I reckon you could poor a bucket of water into a microswitch and it's not going to conduct substantial amounts of current to ground (sea water would conduct better).



So, Jos, that's why I don't have much to say about the quality of the diodes and switches because apart from them physically flying apart and causing a short circuit to ground, I can't see how they could be responsible for the reported chain of events. 



Regards,



Mark

josok-e

Joined: 29 Jan 2010
Posts: 16
Location: Ivalo Finland

Posted: Mon Jun 27, 2011 3:27 pm Post subject: Woodcomp after Sales Service

Hi Frans

As usual, you haven't got a clue, and your arguments limp.

In your explanation you could do away with a lot of things around your 

airplane, because if everyting goes well, you will not need them. Like 

fuses, circuitbrakers, a second fuel pump, not needed in normal 

circimstances. Maybe toys instead.

In very normal life the controller will run until the limit switches are 

opened. Thats why they are there. If you don't understand that go and 

ask somebody, i am tired of explaning basic stuff to somebody who is not 

interested anyway.

The rest of your answer is total rubbish, can't even bother.

Is there somebody out there who can explain to this poor soul how it is 

supposed to work?

Regards,

Jos

28.6.2011 0:39, Frans Veldman kirjoitti:

 	  Quote: 	

 On 06/27/2011 09:38 PM, Jos Okhuijsen wrote:

> It's a pity Mark, that you have not checked the max DC specification of

> those microswitches.

 The max DC specification of the switches is of little value. Max DC is

 mainly limited by the opening arc of the switches under load. In normal

 situations, the limit switches are never opened as the controller cuts

 the power long before the limit is reached. These switches are just

 sitting there all their life closed, waiting for a controller failure

 which is unlikely to happen anyway.

 In a previous statement you claimed that the run away was caused by

 failed micro switches. This is similar as claiming that you have had a

 trim servo run away because of a failing end stop in the trim servo.

 Such a claim would ignore the fact that the trim servo can only run

 away, with or without end stop, if something keeps feeding power to it

 after it reached the desired position. It would require a faulty cockpit

 switch or faulty pilot in addition. Similary: Your situation, even with

 shorted micro switches, could only occur if the controller or some other

 circuitry was failing at the same time: something was delivering power

 to the prop while it was already over the target RPM. Even then, this

 would never let the CB pop. There is only one controller and it can not

 give power to two opposite directions at the same time whatever failure

 mode you can devise.

 Someone asked whether you had modified the circuitry and you denied

 that. However in the archive (before the accident) I found a message

 where you wrote that you had the reverse circuitry modified to simplify

 the process of entering reverse (which is cumbersome in the original

 setup but maybe there was a reason for that), and if I recall it

 correctly a relay was used to switch the controller and feed power to

 the reverse ring of the prop at the same time.

 If this modified circuitry failed, it would explain fully what happened:

 While feeding unwanted power to the reverse ring of the prop the prop

 could reach 0 or negative angle because the reverse slip ring  bypasses

 the limit switches (for logical reasons) AND the controller at the same

 time, and the CB would pop if the controller tried to reverse the engine

 polarity.

 The whole story of short circuited limit switches does not explain the

 problems in any way. I would be confident to operate the airplane with

 shorted limit switches AND shorted or busted diodes, as these items are

 never used while the controller is working properly.

 The function of the diodes is to allow the motor to run in the other

 direction once one of the limit switches opened (otherwise you could

 never recover from reaching the prop limit as the limit switch cuts ALL

 power to the prop). In normal operation the diodes are never used.

 Neither shorting them or opening them would affect the normal operation

 of the prop. Again, whether these diodes are fully up to specs wouldn't

 matter at all in normal situations as it is unlikely that any current

 will ever flow through them.

 Your situation further differs from standard configurations by using the

 scimitar blades, which are not pitch bias neutral under load but have

 strong aerodynamic resistance in one pitch direction. It could well be

 possible that changing the pitch in one way caused excessive current,

 while in the other direction the aerodynamic loads would try to changing

 the pitch even further, and maybe drive the blades over the limit

 causing the limit switches to open. And in such a situation it might be

 possible that the limit switches finally give up the ghost (but

 logically they would burn through and open up, making it impossible to

 change the pitch from there). Again, even in this scenario it would not

 lead to pitch run aways and popping CB's, but just to a prop which

 doesn't respond anymore to pitch change commands.

 Frans

josok-e

Joined: 29 Jan 2010
Posts: 16
Location: Ivalo Finland

Posted: Mon Jun 27, 2011 4:13 pm Post subject: Woodcomp after Sales Service

Hi Mark,



Excellent work.

And probably more understandable for the crowd then what i manage to 

explain.

My guess is number 5, and i think i can make that plausible.

I have been finding and replacing faulty microswitches in an industrial 

environment, and the cause of the failure was usually water ingress in 

the switches. What happens is that the water, which only has to be one 

drop, boils between the contacts in a flash. The metal vaporizes and 

forms a conductor on the insulation. The steam breaks the housing, with 

could then hang the contacts up the mounting. Very much like the 

microswith David describes. It sounds like you would need a lot of power 

for that, but don't forget, these are microswitches, it's all very light 

and feeble. An open contact could be 0.1 of a mil.

I think what happened is that the controller run the prop fine. The fine 

limit microswitch(es) opened, exploded and shorted to ground. The 

controller reversed to increase pitch and the breaker popped.

You don't mention Ivor's narrow escape with a broken motor, which looks 

a lot like mine, with the difference that he had speed and altitude. The 

investigator told me that the motor was loose in the spinner but he 

blames that to the impact.



I still don't understand your willingsness to accept a 5 A diode, which 

has to endure regularly 15 A. It could work in a toy car, but is not 

acceptable in an airplane. You a talking about pulse load, In my book a 

pulse is microseconds, a reversing motor will take considerately more 

time. Does somebody have the typenumbers of the old and newer 

microswitches? From memory the AC to DC max current  is about 5 to one, 

which would ask for 75 AC switches. I bet they are 6 A 



Regards,



Jos



28.6.2011 2:09, Mark Burton kirjoitti:

 	  Quote: 	
		   



 OK, let's put our thinking caps on and ponder switches and diodes.



 We're only concerned here with the operation of the fine pitch limit switch and its associated diode (incidentally, the SR3000 has two fine limit switches and diodes in series so failures 1-4 described below have to occur to both switches/diodes, likely?)



 When the pitch is being reduced, the switch is carrying the current and the diode is reverse biased. The current level is not high and well within the breaking capability of the switch so it should open as expected and the pitch freezes on the fine limit (+ some overrun).



 Assuming that the switch has operated as it should, the pitch will now be fully fine. When the controller next commands the pitch to go coarse, the switch is already open so the diode will have to carry the current. That current can be large as it's basically the pitch motor stall current (initially around 25-30A, falling quickly as the motor spins up). Now the diode is only rated for 5A continuous current but it has a good pulse capability (check the data sheet) so it probably won't fail (we will talk about what happens if the diode fails next) - assuming the diode did not fail and the pitch motor is actually moving, the switch will close shortly afterwards. Exactly how much current will flow through the switch is difficult to predict because we don't know how much the motor has spun up so it could be quite a lot - mind you, there's only around 1V across the switch (the diode drop) so I should think the switch could hack it OK (perhaps with a reduced life).



 Now, let's consider some failure modes:



 1 - the diode fails open circuit - in this case, when the switch opens as the pitch goes fully fine the pitch will freeze at that point (+ some overrun) and when the controller tries to coarsen the pitch nothing will happen because the switch is open and the diode is open too. Therefore, the end result will be the prop will be stuck in fully fine. But, this would not cause the C/B to pop.



 2 - the diode fails short circuit - in this case when the switch opens as the prop reaches fully fine, the pitch motor keeps going and will drive the pitch all the way to reverse position (and the reverse switch would operate). If the controller subsequently tried to coarsen the pitch, it would succeed unless the diode decided the current was too much and died in which case the pitch would freeze. Now as it has been reported that the pitch of the prop was not in the reverse position this probably didn't happen. Again, the C/B would not blow.



 3 - the switch fails open circuit - the pitch will not be able to reduce, only coarsen. C/B still intact.



 4 - the switch fails short circuit - similar to 2 above, pitch could go to reverse. C/B still a happy bunny.



 5 - there is a short circuit from one of the switches/diodes/wires to ground - now this is interesting: it could  make the pitch go to the reverse position and then when the controller tried to move the pitch the other way it would blow the C/B. But as it's already been stated that the pitch was near the flyable region that makes this scenario unlikely but not impossible.



 So, from what we know about the accident, the only one of these failures that could have occurred is a short from one of the pitch motor drive wires to ground (either the wire itself or a switch/diode/motor failure). Is that likely, I don't know, but I reckon you could poor a bucket of water into a microswitch and it's not going to conduct substantial amounts of current to ground (sea water would conduct better).



 So, Jos, that's why I don't have much to say about the quality of the diodes and switches because apart from them physically flying apart and causing a short circuit to ground, I can't see how they could be responsible for the reported chain of events.



 Regards,



 Mark





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=344300#344300

frans(at)privatepilots.nl
Guest

Posted: Tue Jun 28, 2011 6:33 am Post subject: Woodcomp after Sales Service

On 06/28/2011 01:24 AM, Jos Okhuijsen wrote:

 	  Quote: 	
		   Hi Frans

 As usual, you haven't got a clue, and your arguments limp.


	


Interesting to see then that my arguments are supported by Mark Burton

(manufacturer of the controller) and some others.

Your arguments limp, because numerous people have now tried to explain

that faulty microswitches can not be responsible for your crash, and you

still haven't got the clue.



 	  Quote: 	
		   In very normal life the controller will run until the limit switches are

 opened.


	


Wrong again. The controller will run until the target RPM has been

reached. It has nothing to do with micro-switches at all. If a micro

switch opens when you reach the desired RPM then there is a grave error

in the whole setup. It is similar to trying to trim the airplane and the

trim servo reaches its end and cuts the power. If you have to trim the

airplane always to the end limiter, you'd better start checking a few

things. The micro switches should only open if for some reason the

controller tries to move the pitch outside the designed area.



 	  Quote: 	
		   Is there somebody out there who can explain to this poor soul how it is

 supposed to work?


	


There are numerous people now trying to explain a few basic things, like

that broken micro switches can never cause the CB to blow and/or make

the prop go into a non-flyable state. Maybe you should read more

carefully what these people are trying to explain.



Frans

kingsnjan(at)westnet.com.
Guest

Posted: Wed Jun 29, 2011 2:54 am Post subject: Woodcomp after Sales Service

---

frans(at)privatepilots.nl
Guest

Posted: Wed Jun 29, 2011 4:23 am Post subject: Woodcomp after Sales Service

On 06/29/2011 12:51 PM, Kingsley Hurst wrote:

 	  Quote: 	
		   As I understand it, the 1V across the switch would only be present while

 the switch is still open and on the closing of the switch, is it correct

 to say that ALL of the current (whatever that might be) would then flow

 through the switch (assuming closed switch has minute or zero

 resistance) notwithstanding the diode is still forward biased?


	


That is also my thought.

But let me explain a bit about switches and AC and DC currents.

It is often said that for DC applications the switches need to have a

higher current rating than for AC applications.

The reason is this: If we look in slow motion to the process of opening

a switch, a small arc will form just at the moment of opening. With AC,

the arc extinguishes automatically when the current goes through the

null when alternating. With DC, the arc will continue to exist until

either the contacts are spaced out far enough, or when the source of the

DC is taken away.

While the contacts are closed, or during closing, the current rating is

the same for AC and DC. It is the opening of the contacts which is the

limiting factor for DC applications.



So, in the scenario Mark is describing, excessive current over the

offical DC rating of the switch has no consequences.



Furthermore, in the application of Woodcomp propellers with either

feathering or resversing options, it isn't actually DC which is fed to

the controller. The controller uses PWM (Pulse Width Modulation) to

control the prop, and it is the ratio between the pulses and pauses that

determines how fast the pitch changes. This pulsing DC behaves, as far

as the micro-switch is concerned, exactly as AC, because the DC is

interrupted periodically and any arc when opening will extinguish in a

few milli-seconds.

So, in this application with PWM you can use the micro-switches to their

max AC-current rating. The lower max DC-rating doesn't apply here.



And finally, I like to restate that the controller and prop form

together a RPM-controlled closed loop, and the limiter micro-switches

will never open as the controller will cut the power to the prop when

the target RPM has been established. Only in faulty setups the

micro-switches will open. Such a fault could be a setup error, like a

too powerfull engine which overrevs even with the prop fully coarse, and

the controller will subsequently try to move the pitch coarser than the

design limit of the prop. Another failure mode would be a faulty

controller, i.e. a controller that keeps feeding power to the prop after

the target RPM has been reached. A faulty micro-switch will consequently

only reveal itself when something else goes wrong in addition.



 	  Quote: 	
		   In this case, I would have considered the diode to have already died

 when it short circuited . . . .


	


There are multiple ways of dying... I'm pretty sure that Mark meant that

after short circuiting the diode might blow like a fuse and go open circuit.



Frans

jan_de_jong(at)casema.nl
Guest

Posted: Wed Jun 29, 2011 6:01 am Post subject: Woodcomp after Sales Service

Hi Frans.



In the section below you describe PWM with a pulse width of less than 

100% - thus running the motor at less than full speed.

This surprises me as electric full speed pitch change is slow compared 

to hydraulic pitch change already.

Is there ever a reason to slow the electric motor down?

 	  Quote: 	
		   Furthermore, in the application of Woodcomp propellers with either

 feathering or resversing options, it isn't actually DC which is fed to

 the controller. The controller uses PWM (Pulse Width Modulation) to

 control the prop, and it is the ratio between the pulses and pauses that

 determines how fast the pitch changes. This pulsing DC behaves, as far

 as the micro-switch is concerned, exactly as AC, because the DC is

 interrupted periodically and any arc when opening will extinguish in a

 few milli-seconds.

 So, in this application with PWM you can use the micro-switches to their

 max AC-current rating. The lower max DC-rating doesn't apply here.

   

Jan

frans(at)privatepilots.nl
Guest

Posted: Wed Jun 29, 2011 6:40 am Post subject: Woodcomp after Sales Service

On 06/29/2011 03:58 PM, Jan de Jong wrote:



 	  Quote: 	
		   In the section below you describe PWM with a pulse width of less than

 100% - thus running the motor at less than full speed.

 This surprises me as electric full speed pitch change is slow compared

 to hydraulic pitch change already.

 Is there ever a reason to slow the electric motor down?


	


I'm sure Mark Burton can answer this question better. But as I

understand the operation is that with large RPM mismatches the motor is

fed with a higher duty cycle, and with smaller RPM mismatches the motor

is run more slowly, to avoid pitch hunting and overshoots. At full speed

the motor runs out for a considerable time after cutting the power, so

correcting small RPM changes can only be done with a very slow running

pitch change motor.



Do not underestimate the speed of the woodcomp pitch motor: It will go

from fully fine to fully coarse within one second. This only applies to

the propellers with reverse or feather options.



I have not much experience with hydraulic props, but the one I have

flown was considerably slower and more instable than my Woodcomp/Smart

combination.



Frans

josok-e

Joined: 29 Jan 2010
Posts: 16
Location: Ivalo Finland

Posted: Sun Jul 03, 2011 1:56 am Post subject: Woodcomp after Sales Service

The good news is, that this will be my last contribution to the     list. After this message i will unsuscribe, and withdraw from the     Europa community. I will not go again through the horror caused by a     failing prop.

     The one question remaining is which Woodcomp SR3000 was tested by     the LAA?

     

     The following are quotes from private messages from Woodcomp owners     in no particular order.

     

     "I think I was wrong in my guess that the pitch might have gone past     the normal fine limit as the defective switch was the back up one."

     

     "I have heard of a Woodcomp prop stripping off some of its carbon     fibre sheathing in heavy rain, but having said that probably the     majority of the guys that I have flown with (& my own plane)     have Woodcomp props that have shown absolutely no effect.     "

     

     "but yes I have tested my mechanical stop It is strong enough to     stop a runaway electric motor I guess 100hp more powerful than the     fitted one and comes into action a degree or two past the usual     position so still capable of producing reasonable thrust"

     

     "Jos, I thought I would bring you up to date with the prop. On     taking off 

     the motor I found that the drive gear that is on the end of the     motor drive 

     shaft was not on the shaft. Instead it was inside the hub, loose."

     

     "Incidentally there are mechanical stops on each of my blades in the     form of a bolt which projects into a groove in the blade root. The     range is limited from 9 to 29 degrees as measured at the very tip.     You can see from the picture of mine (with the loose bolts) and an     earlier factory one, that they have not always had this feature"

     

     "On each occasion they replaced almost everything that       showed any signs of wear. Brushes, gears, micro switches, wiring       etc and the blades when returned could be mistaken for new"

       

     "Found that one spinner screw was missing and gota complete     new spinner fastening set free of charge"

     

     "I had two motor failures, and now always carry a spare"

     

     "More recently like last year I mentioned a small amount of play in     my blade set, and they sent me a kit f.o.c.     for the hub. It was an upgrade consisting of different gears       and spring washers, which I installed myself and everything seems       fine now."

       

       "someone having some teeth break on the gearing that determines       the pitch angle of each blade and this was promptly dealt with by       Woodcomp  replacing it  both on new models and retrospectively       with a slightly heavier version of the gears"

       

       "I had my           SR3000 motor burn out which took my pitch to fully fine and on           to the stops"

           

           "since my propeller return to service I make a point           of flying it manually  if the           conditions are poor"

           

           "I am very pleased with my SR2000 approaching       300 hours. I have one failure though"

       

       "To avoid problems as much as possible I always switch to manual       before take-off and landing"

       

     

     "Back on topic, I only had it checked once by a local dealer because     of some play of the blades"

     

     "Forget about automatic pitch control below 1000 feet"

     

     "I am also not convinced that Woodcomp engineering is really robust"

     

     "We made the special propeller for David"

     

     "Do not underestimate the speed of the woodcomp pitch motor: It will     go from fully fine to fully coarse within one second"

     

     Regards,

     

     Jos

     

     

     

      [quote][b]

grahamsingleton(at)btinte
Guest

Posted: Sun Jul 03, 2011 2:34 pm Post subject: Woodcomp after Sales Service

Don't change your email address Jos, no doubt some of us will want to talk to you again

regards 

and thanks for all you've done for the forum

Graham

From: Jos Okhuijsen <josok-e(at)ukolo.fi>

To: europa-list(at)matronics.com; andy.draper(at)laa.uk.com

Sent: Sunday, 3 July, 2011 10:53:01

Subject: Re: Re: Woodcomp after Sales Service

 



    

 [quote][b]

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