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nuckolls.bob(at)aeroelect
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 Posted: Thu Feb 18, 2016 12:40 pm Post subject: Starter engaged warning lights |
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| Quote: |
Although relatively rare, having the starter and flywheel teeth jam
and break in flight might make for a "stormy night" story  |
Not sure how much of a risk this is.
Every starter I'm aware of has an over-running
clutch built onto the pinion gear shaft. Hangar
myths about stuck pinions back driving a starter
and turning it into a generator are without
merit. Further, the solenoid/contactor configuration
of choice features a robust disengagement mechanism.
The only 'unintentional engagements' I've
heard about over the last 20 years have
involved stuck contactors that kept the pinion
gear electrically engaged. One such case involved
a aerobatic performance airplane at OSH where
the entire routine was performed with the starter
engaged.
While chewed up ring gears and pinons are ugly,
they don't represent much of a hazard to the engine
or airplane.
The strongest prophylactic against these events
are a strong battery and a modern, stick-resistant
contactor.
Most mechanical risk for pinion gear retraction
failure have foundation in poor maintenance . . .
a 'hard stick' is going to be preceded by a series
of tentative sticks. Just keep the shaft clean
and watch the pinion gear teeth for changes
in wear patterns.
Bob . . .
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bakerocb
Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA
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| Posted: Fri Feb 19, 2016 5:24 am Post subject: Starter engaged warning lights |
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2/19/2016
Hello Bob Nuckolls and Fellow Listers, At 12:40:30 PM PST US Bob Nuckolls
wrote: "While chewed up ring gears and pinons are ugly,
they don't represent much of a hazard to the engine or airplane."
(Extracted from Nuckolls entire 12:40:30 PM PST US posting
which is copied below.)
This quoted statement (and the entire premise of his 12:40:30 PM PST US
posting) is based on the configuration of Lycoming engines
with ring gears and pinions external to the engine crankcase. But if the
starter pinion gear and the engaged engine cranking gear are internal
to the engine crankcase, as is the arrangement for some Continental
engines, then considerable engine damage can result from the metal
shards thrown off by a disintegrating starter pinion gear that remains
improperly engaged after the engine is running.
Copied here is an extract from an internet posting
(http://www.pprune.org/archive/index.php/t-467979.html) that discusses this
condition:
"In Continentals, gears do not engage and disengage. The smaller
Continentals, have an over running clutch, which are known to seize. When
this happens, the starter motor is accelerated to a rotational speed far in
excess of the design, and it's probably going to fly apart, and seize. This
is going to cause something in the engine drive line to break. The larger
Continentals employ a worm drive and clutch spring. These are known to seize
and overheat. There are a number of reasons for, and variations on this
failure, which are too much to describe here. In short, a running on motor
in these engines is bad for several reasons, and there are other failures,
which do not involve an energized motor.
So, just because your "starter engaged" warning light is not illuminated (it
probably should be called a "starter energized" warning light), there could
still be a failure of the starter system, which is every bit as serious. Be
"at one" with how your engine should sound and operate just after start. If
it is not right, shut it down, and have the maintainer have a look."
Regardless of the degree or commonality of the risk involved, I stand by my
Tuesday, February 16, 2016 9:24 AM posting and this extract from it:
"So it turns out that the “starter engaged light” is not an absolute
indicator of the starter gear being engaged to
the engine cranking gear or not, but rather is more accurately described as
a “starter contactor frozen (or stuck) in the start position light”."
'OC' Baker
==========================================
Time: 12:40:30 PM PST US
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
Subject: Starter engaged warning lights
| Quote: | Although relatively rare, having the starter and flywheel teeth jam
and break in flight might make for a "stormy night" story
|
Not sure how much of a risk this is.
Every starter I'm aware of has an over-running
clutch built onto the pinion gear shaft. Hangar
myths about stuck pinions back driving a starter
and turning it into a generator are without
merit. Further, the solenoid/contactor configuration
of choice features a robust disengagement mechanism.
The only 'unintentional engagements' I've
heard about over the last 20 years have
involved stuck contactors that kept the pinion
gear electrically engaged. One such case involved
a aerobatic performance airplane at OSH where
the entire routine was performed with the starter
engaged.
While chewed up ring gears and pinons are ugly,
they don't represent much of a hazard to the engine
or airplane.
The strongest prophylactic against these events
are a strong battery and a modern, stick-resistant
contactor.
Most mechanical risk for pinion gear retraction
failure have foundation in poor maintenance . . .
a 'hard stick' is going to be preceded by a series
of tentative sticks. Just keep the shaft clean
and watch the pinion gear teeth for changes
in wear patterns.
Bob . . .
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Fri Feb 19, 2016 12:20 pm Post subject: Starter engaged warning lights |
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At 07:22 AM 2/19/2016, you wrote:
| Quote: | --> AeroElectric-List message posted by: "Owen Baker " <bakerocb(at)cox.net>
2/19/2016
Hello Bob Nuckolls and Fellow Listers, At 12:40:30 PM PST US Bob Nuckolls wrote: "While chewed up ring gears and pinons are ugly,
they don't represent much of a hazard to the engine or airplane." (Extracted from Nuckolls entire 12:40:30 PM PST US posting
which is copied below.)
This quoted statement (and the entire premise of his 12:40:30 PM PST US posting) is based on the configuration of Lycoming engines
with ring gears and pinions external to the engine crankcase. But if the starter pinion gear and the engaged engine cranking gear are internal
to the engine crankcase, as is the arrangement for some Continental engines, then considerable engine damage can result from the metal
shards thrown off by a disintegrating starter pinion gear that remains improperly engaged after the engine is running.
Copied here is an extract from an internet posting ( http://www.pprune.org/archive/index.php/t-467979.html) that discusses this condition:
"In Continentals, gears do not engage and disengage. The smaller Continentals, have an over running clutch, which are known to seize. When this happens, the starter motor is accelerated to a rotational speed far in excess of the design, and it's probably going to fly apart, and seize. This is going to cause something in the engine drive line to break. |
Yes, the premise was based on the open-air, ring-gear
configuration common to Lycoming. But if a Continental
starter suffers the event, there's no way one can
sense this condition electrically for operation
of a 'starter engaged' light . . . so while the
condition is rare the risk is not zero . . . and
there's probably not much we can do about it in terms
of annunciating the condition.
Bob . . .
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yellowduckduo(at)gmail.co
Guest
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| Posted: Fri Feb 19, 2016 1:15 pm Post subject: Starter engaged warning lights |
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Sounds like a challenge for a non certified continental owner who is
concerned about this rare scenario.
Surely there is a simple electrical test to the starter side of the
contactor that would determine whether the armature is still rotating
after startup. One could mount a starter in a lathe or drill press and
start experimenting...
Ken
On 19/02/2016 3:17 PM, Robert L. Nuckolls, III wrote:
| Quote: | At 07:22 AM 2/19/2016, you wrote:
>
>
> 2/19/2016
>
> Hello Bob Nuckolls and Fellow Listers, At 12:40:30 PM PST US Bob
> Nuckolls wrote: "While chewed up ring gears and pinons are ugly,
> they don't represent much of a hazard to the engine or
> airplane." (Extracted from Nuckolls entire 12:40:30 PM PST US posting
> which is copied below.)
>
> This quoted statement (and the entire premise of his 12:40:30 PM PST
> US posting) is based on the configuration of Lycoming engines
> with ring gears and pinions external to the engine crankcase. But if
> the starter pinion gear and the engaged engine cranking gear are internal
> to the engine crankcase, as is the arrangement for some Continental
> engines, then considerable engine damage can result from the metal
> shards thrown off by a disintegrating starter pinion gear that
> remains improperly engaged after the engine is running.
>
> Copied here is an extract from an internet posting
> (http://www.pprune.org/archive/index.php/t-467979.html
> <http://www.pprune.org/archive/index.php/t-467979.html>) that
> discusses this condition:
>
> "In Continentals, gears do not engage and disengage. The smaller
> Continentals, have an over running clutch, which are known to seize.
> When this happens, the starter motor is accelerated to a rotational
> speed far in excess of the design, and it's probably going to fly
> apart, and seize. This is going to cause something in the engine
> drive line to break.
Yes, the premise was based on the open-air, ring-gear
configuration common to Lycoming. But if a Continental
starter suffers the event, there's no way one can
sense this condition electrically for operation
of a 'starter engaged' light . . . so while the
condition is rare the risk is not zero . . . and
there's probably not much we can do about it in terms
of annunciating the condition.
Bob . . .
|
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Fri Feb 19, 2016 4:42 pm Post subject: Starter engaged warning lights |
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At 03:14 PM 2/19/2016, you wrote:
| Quote: | --> AeroElectric-List message posted by: C&K <yellowduckduo(at)gmail.com>
Sounds like a challenge for a non certified continental owner who is concerned about this rare scenario.
Surely there is a simple electrical test to the starter side of the contactor that would determine whether the armature is still rotating after startup. One could mount a starter in a lathe or drill press and start experimenting...
Ken |
Might not be that complicated. ANY non-zero
voltage on that terminal after start-button
release is reason to believe the starter
motor is still spinning. I'll pray over that
that idea a bit . . . but I think the bill
of materials is under a dollar.
Bob . . .
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rv8builder
Joined: 02 Jan 2009
Posts: 56
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| Posted: Sat Feb 20, 2016 6:01 am Post subject: Starter engaged warning lights |
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I added this feature to my RV-8 as omage to my former life as a Captain on a Dehavilland DHC-8 where the first item on the after-start check list was "START LIGHT -- OUT"!!
Dale
On Thursday, February 18, 2016, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | | Quote: |
Although relatively rare, having the starter and flywheel teeth jam
and break in flight might make for a "stormy night" story |
Not sure how much of a risk this is.
Every starter I'm aware of has an over-running
clutch built onto the pinion gear shaft. Hangar
myths about stuck pinions back driving a starter
and turning it into a generator are without
merit. Further, the solenoid/contactor configuration
of choice features a robust disengagement mechanism.
The only 'unintentional engagements' I've
heard about over the last 20 years have
involved stuck contactors that kept the pinion
gear electrically engaged. One such case involved
a aerobatic performance airplane at OSH where
the entire routine was performed with the starter
engaged.
While chewed up ring gears and pinons are ugly,
they don't represent much of a hazard to the engine
or airplane.
The strongest prophylactic against these events
are a strong battery and a modern, stick-resistant
contactor.
Most mechanical risk for pinion gear retraction
failure have foundation in poor maintenance . . .
a 'hard stick' is going to be preceded by a series
of tentative sticks. Just keep the shaft clean
and watch the pinion gear teeth for changes
in wear patterns.
Bob . . .
|
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_________________
Dale |
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Sat Feb 20, 2016 8:55 am Post subject: Starter engaged warning lights |
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At 07:59 AM 2/20/2016, you wrote:
| Quote: | I added this feature to my RV-8 as omage to my former life as a Captain on a Dehavilland DHC-8 where the first item on the after-start check list was "START LIGHT -- OUT"!!
Dale |
Little different breed of cat there. On many turbine
aircraft, the starter contactor on a series/shunt
starter-generator needs to be confirmed open before
a second contactor grabs armature output at the
other end of the series field winding which is used
only for starting.
In this case, the starter-generator is always
geared to the engine.
That light is driven by a micro-switch built into
the contactor's engagement hardware that verifies
the contacts are open thereby extinguishing the
light. Having that contactor stuck shut when the
circuit is re-configured for generator service
makes for some unhandy current flows in some
rather fat wires.
"Unhandy" current flows in fat wires can be a
real PITA . . .
Bob . . .
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rv8builder
Joined: 02 Jan 2009
Posts: 56
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| Posted: Sat Feb 20, 2016 9:31 am Post subject: Starter engaged warning lights |
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Oh I agree Bob. I have no idea what the current inrush is when one of
those starters is engaged, but it has to be a bunch. The lights would dim
briefly when a starter was engaged and that was with the APU DC gen on line
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_________________
Dale |
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Sat Feb 20, 2016 10:07 am Post subject: Starter engaged warning lights |
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At 11:29 AM 2/20/2016, you wrote:
| Quote: | Oh I agree Bob. I have no idea what the current inrush is when one of those starters is engaged, but it has to be a bunch. The lights would dim briefly when a starter was engaged and that was with the APU DC gen on line.
As I said, I added it more for nostalgia then anything else. |
Understand. Inrush on a turbine engine is typically
1000A . . . Here's a plot taken from a Beech 400
(Beechjet/MU300) . . . real contact welder!
[img]cid:7.1.0.9.0.20160220115115.07420e28(at)aeroelectric.com.0[/img]
Thanks for the expansion!
Bob . . .
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