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As David says there is definitely a groove and a limiting stop in Williams
prop - photos herewith..
I have just sent it back to Woodcomp for them to shorten the length of the
groove so the blades can't travel beyond the fine setting (ie: into reverse
pitch).
It isnt clear but the end stops are 6mm allen head bolts through the front
hub. These slot into the grooves limiting the blade travel.
It should be fairly obvious that if a prop is capable of going into reverse
pitch, a physical end stop wont prevent the blades going into a dangerous
condition if the servo motor continues to run past the fine setting.
Presumably that is the reason there is a backup microswitch which should cut
off the power if the primary switch fails.
However both the fine setting switches will be over ridden if the control
circuitry initiates reverse pitch !!! One assumes this would not normally
happen unless the reverse pitch switch was engaged (ie: by the pilot).
Carl Pattinson
----- Original Message -----
From: "David Joyce" <davidjoyce@doctors.org.uk>
Sent: Thursday, March 26, 2009 4:42 PM
Subject: Re: Europa-List: Woodcomp Propellers
>
> <davidjoyce@doctors.org.uk>
>
> Jos I suspect you had your mind on other things! Carl Pattinson has been
> requested by the LAA to modify the mechanical end stop of his prop to stop
> it being able to go into reverse. He has the prop from William Mills
> aircraft, which happens not to have been on William's plane when he
> crashed. It is one of the earliest SR3000s. Carl has recently dismantled
> it and the mechanical end stop is there, taking the form of a stud
> sliding in a groove, with the length of the groove determining the
> mechanically possible pitch range.
> Regards, David Joyce, G-XSDJ
> ----- Original Message -----
> From: "josok" <josok-e@ukolo.fi>
> To: <europa-list@matronics.com>
> Sent: Wednesday, March 25, 2009 7:13 PM
> Subject: Re: Europa-List: Woodcomp Propellers
>
>
>>
>> David and All,
>>
>> Probably i am the only one who has ever opened an SR 3000 hub. There are
>> no mechanical endstops. Not on the end of any travel movements. Maybe
>> added later, that i don't know.
>>
>> The micro switches are not suitable for outdoor use. That point is left
>> out.
>>
>> The rating of the micro switches, if 16A? is probably for AC. DC ratings
>> are usually 1/4 to 1/3 of that. Left out. Why two in series? Doubt about
>> the quality? Left out.
>>
>> If the normal working current range of the motor is 4 A, the stall
>> current, or startup current, is about 5 times higher. That stall current,
>> startup current probably is over 20 A for a very short period.
>> Specifications of diodes are for peak currents too. Peak current, even
>> glitches break semiconductors. So any time the (fine) endstop micro
>> switches are opened, the reverse current, momentarely up to 20 A will fry
>> a 5 A diode easily. Left out.
>>
>> If the diode is short circuited, there is no electrical endstop working.
>> If there would be a mechanical endstop, the motor could fry because it
>> would be blocked. Left out.
>>
>> So David, please ask some more questions? I do very well understand, that
>> you are not an outsider, as the person who got the first SR 3000 approved
>> by the PFA. I am not either, so that could balance things out. Your
>> interest seems to be to flatten issues with the Woodcomp SR3000, mine is
>> to warn about the product, and maybe save lifes.
>>
>> Regards,
>>
>> Jos Okhuijsen
>>
>>
>>
>>
>>
>>
>> Visit - www.EuropaOwners.org
>>
>>
>>
>>
>>
>>
>>
>>
>
>
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