Jos,
I typed Frans instead of you Jos for the congrats....No excuse...In a
rush to another Eagle Scout Board of Review and didn't proof my work.
Too many irons in the fire today.
Sorry, I was only generally commenting on electric reverse pitch props,
and did not intend to segregate the SR3000. Beta control props
normally do not have a mechanical fine pitch stop (without a lot of
mechanical do dads and overrides) because the prop must go from fine to
flat to negative to operate. In my Air Force career I never flew
C-130's but did see that they have quite a system of hydro-mechanical
and operational restrictions on reverse thrust for safety. A great deal
of operational and emergency training covered all the failure modes. I
wish our light plane industry did the same.
Re reading my post, I did not intend to say any particular prop
manufacturer is more reputable than any other. I believe they all try
to give the best product they can for a competitive price. Buyer be
ware is generally not a factor in aviation, as nearly all manufacturers
are sensitive to feedback on their products and their clients safety.
As far as the motors in an electric prop, it does amaze me how little
power it takes to move the prop blade given the mechanical advantage.
During a troubleshooting test, I have run a 7 amp test battery
completely flat running the Airmaster from fine to feather and back to
test how long it takes for a feathered gliding position to fine pitch
power transition and to try and see how quick the prop can respond from
the fine stop at 10 degrees min to the normal full power pitch of about
19 degrees (depending on blade length) and the motor never got hot or
squawked, and neither did the controller. If you're smooth on the
throttle and don't jamb the throttle from idle to full, it keeps pace
nicely.
For the guys looking for props, especially when they have never flown
constant speed props, we need to share our experiences. But for those
searching for info, they need to understand the operational and
emergency response necessary for the eventual equipment malfunction,
then through personal training and emergency procedure training keep
their skills up in the event of failure. Of course I'd rather be lucky
than good any day, but you can't always trust to luck.
Hydraulic props are not without their problems either... But that is
another subject for another day.
Good night,
Bud
----- Original Message -----
From: josok<mailto:josok-e@ukolo.fi>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Thursday, March 19, 2009 9:10 PM
Subject: Re: Europa-List: Constant Speed Prop and failure modes.
<josok-e@ukolo.fi<mailto:josok-e@ukolo.fi>>
Thanks for the clear story Bud,
[quote:022a4d2f87]The Airmaster has a dedicated manual control which
bypasses everything to give you electric pitch control and a mechanical
stop. Propellers, such as the Woodcomp, with Beta (reversing) do not
have mechanical stops, only electric. [/quote:022a4d2f87]
Just one correction: The SR 3000 does not have mechanical stops, not
on any non-reversable or feathering either.
[quote:022a4d2f87]A number of aircraft were lost in the 30's because
of runaway props. Consequently reputable manufactures make sure they
have manual backups and mechanical stops to prevent aircraft
loss.[/quote:022a4d2f87]
And i might add that manual backup does not help if the pitch motor
belongs in a toy car.
Regards,
Jos Okhuijsen
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