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nuckolls.bob(at)aeroelect
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 Posted: Thu Jul 14, 2016 10:12 am Post subject: Contactor orientation |
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I've heard a boat load of narratives and anecdotes
concerning contactor orientation in aircraft. Most
of the 'advice' goes to the 'whisky barrel' style
contactors from White-Rogers and Cole-Hersey. The
first time I recall such a story was a OSH back about
1990 . . . an airshow performer showed up at the
B&C booth to buy a new starter and contactor. Seems
his contactor was stuck and the starter gears chewed
up. He hypothesized that g-loads during his show
teased the contactor closed followed by a welding
of contacts and an engaged starter.
In years since, many more tidbits of sage advice on
contactor orientation have appeared throughout the OBAM
aviation industry. I have yet to put my hands on any
failure of hardware that supports any notion of risk
due to airframe induced g-loads.
The tear-downs I've conducted fall into three primary
categories:
(1) Wear out. Contactor has been in service
a long time. Contacts are worn. No other evidence of
stress such as moisture, broken parts, mis-installation.
I.e. the thing went to end of service life.
(2) Moisture ingress: contacts, springs, plunger,
case badly rusted. See:
http://tinyurl.com/p2x7fbl
(3) Installation/Manufacturing error: Failure to solder
coil wires to terminals, main terminals twisted out
of alignment during torque-down of terminal nuts,
bit of debris between contacts, exposed to gross
external moisture, etc.
If you think about it, the plunger in a starter
contactor mounted on fire wall moves PARALLED to
fuselage axis. Mounted terminals up, it takes
NEGATIVE g's to close contact. A whisky-barrel
battery contactor is already CLOSED any time aircraft
is in motion. A transient cross-feed contactor closure
presents no potential hazard.
In 40+ years of working with these devices, I have
yet to see any evidence that supports the widely
circulated fears for 'correct' contactor orientation
in airplanes. By the way, I've see hundreds of
installations of contactors in TC aircraft for
ALL orientations . . . I've never heard of it being
any kind of 'problem'.
If I were going to posit a bit of advice for orientation
it would be to mount the whisky barrel contactor CAP
DOWN after first PUNCHING a very small hole in the
center of the cap. This is for draining moisture that
MIGHT get inside if the contactor experiences long
periods of condensing moisture and/or splash. Don't
drill the hole . . . you may drop a chip into the
interior.
Having a drain hole can be the bane of your
contactor's existence. See photo series at
http://tinyurl.com/p2x7fbl
Note in particular what appears to be a factory
provided drain hole in pictures 10 and 11. At the
same time, severity and range of rust on the
interior parts along with rust patters on both
sides of the cap suggest that this contactor was
installed DRAIN up.
Short answer: I have yet to identify a justification
for recommending a contactor installation orientation with
a goal of reducing risk to system due to operational
g-loads.
Bob . . .
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ARGOLDMAN(at)aol.com
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| Posted: Thu Jul 14, 2016 10:43 am Post subject: Contactor orientation |
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I am a little confused about your statement,
" If you think about it, the plunger in a starter
contactor mounted on fire wall moves PARALLED to
fuselage axis..".
Although the device moves parallel to the fuselage, that is really a non-issue. even with severe aerobatics. It is when a hard landing occurs that the spring which keeps the contacting mechanism open can be compressed and contact made. The contact mechanism I think a thick washer) and its associated armature have mass. When the aircraft hits the ground it stops its downward movement but momentum makes the contact mechanism and armature continue on its downward movement compressing the spring. Added to that, the aircraft rebounds and not only does the contact mechanism continue to move downward, the shell of the solenoid, being connected to the firewall is now moving upward increasing the possibility that the contactor will contact, until the energy contained in the spring overcomes the closing movement of the contactor---or the contactor actually makes contact, at which the spring disengages it.
Actually, if you look at ACS starter solenoid (contactor) you will see that the terminals are on the top of the "can", the lower part is the electromagnet which pulls the armature (connected to the actual contact device) downward to complete the circuit. It has to be held up (open) by a compression spring.
The pilot will never notice that this happens save for the possibility of damaged gears which will probably be blamed on something else.
Rich
In a message dated 7/14/2016 11:13:32 A.M. Pacific Daylight Time, nuckolls.bob(at)aeroelectric.com writes:
| Quote: | I've heard a boat load of narratives and anecdotes
concerning contactor orientation in aircraft. Most
of the 'advice' goes to the 'whisky barrel' style
contactors from White-Rogers and Cole-Hersey. The
first time I recall such a story was a OSH back about
1990 . . . an airshow performer showed up at the
B&C booth to buy a new starter and contactor. Seems
his contactor was stuck and the starter gears chewed
up. He hypothesized that g-loads during his show
teased the contactor closed followed by a welding
of contacts and an engaged starter.
In years since, many more tidbits of sage advice on
contactor orientation have appeared throughout the OBAM
aviation industry. I have yet to put my hands on any
failure of hardware that supports any notion of risk
due to airframe induced g-loads.
The tear-downs I've conducted fall into three primary
categories:
(1) Wear out. Contactor has been in service
a long time. Contacts are worn. No other evidence of
stress such as moisture, broken parts, mis-installation.
I.e. the thing went to end of service life.
(2) Moisture ingress: contacts, springs, plunger,
case badly rusted. See:
http://tinyurl.com/p2x7fbl
(3) Installation/Manufacturing error: Failure to solder
coil wires to terminals, main terminals twisted out
of alignment during torque-down of terminal nuts,
bit of debris between contacts, exposed to gross
external moisture, etc.
If you think about it, the plunger in a starter
contactor mounted on fire wall moves PARALLED to
fuselage axis. Mounted terminals up, it takes
NEGATIVE g's to close contact. A whisky-barrel
battery contactor is already CLOSED any time aircraft
is in motion. A transient cross-feed contactor closure
presents no potential hazard.
In 40+ years of working with these devices, I have
yet to see any evidence that supports the widely
circulated fears for 'correct' contactor orientation
in airplanes. By the way, I've see hundreds of
installations of contactors in TC aircraft for
ALL orientations . . . I've never heard of it being
any kind of 'problem'.
If I were going to posit a bit of advice for orientation
it would be to mount the whisky barrel contactor CAP
DOWN after first PUNCHING a very small hole in the
center of the cap. This is for draining moisture that
MIGHT get inside if the contactor experiences long
periods of condensing moisture and/or splash. Don't
drill the hole . . . you may drop a chip into the
interior.
Having a drain hole can be the bane of your
contactor's existence. See photo series at
http://tinyurl.com/p2x7fbl
Note in particular what appears to be a factory
provided drain hole in pictures 10 and 11. At the
same time, severity and range of rust on the
interior parts along with rust patters on both
sides of the cap suggest that this contactor was
installed DRAIN up.
Short answer: I have yet to identify a justification
for recommending a contactor installation orientation with
a goal of reducing risk to system due to operational
g-loads.
Bob . . . |
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nuckolls.bob(at)aeroelect
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| Posted: Thu Jul 14, 2016 3:10 pm Post subject: Contactor orientation |
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| Quote: | At 01:37 PM 7/14/2016, you wrote:
I am a little confused about your statement,
" If you think about it, the plunger in a starter
contactor mounted on fire wall moves PARALLED to
fuselage axis..".
Although the device moves parallel to the fuselage, that is really a non-issue. even with severe aerobatics. It is when a hard landing occurs that the spring which keeps the contacting mechanism open can be compressed and contact made. |
Okay, the plunger mass moves along the longitudinal
axis of the aircraft. All the flight dynamics plots
I've observed speak to really big loads along Z-axis,
this is the one that breaks the wings off. What is
the forcing function that accelerates the fuselage
along the X-axis with any degree of robustness in
a 'hard' landing?
| Quote: | | The contact mechanism I think a thick washer) |
Not exactly . . .
[img]cid:.0[/img]
| Quote: | | and its associated armature have mass. |
Yes, but even less than the legacy whisky-barrel
contactor . . .
[img]cid:.1[/img]
| Quote: | | When the aircraft hits the ground it stops its downward movement but momentum makes the contact mechanism and armature continue on its downward movement compressing the spring. |
Actually, aircraft Z-axis acceleration is at 90 degrees
to the contractor's stroke axis.
| Quote: | | Added to that, the aircraft rebounds and not only does the contact mechanism continue to move downward, the shell of the solenoid, being connected to the firewall is now moving upward increasing the possibility that the contactor will contact, until the energy contained in the spring overcomes the closing movement of the contactor---or the contactor actually makes contact, at which the spring disengages it. |
Assuming contactor closure CAN be achieved with
airframe g-loads . . . what do you suppose the
duration of closure might be? What is the delay
between first application of power to a starter
until the pinion gear is extended and gears make
contact? Assuming they do make 'contact' what is
the behavior of starter's parts?
Contactor closure times are at best measured in
tens of millisonde. Time from first energization
of starter to gear tooth engagement is many tens
of milliseconds . . . perhaps as much as 200. When
the ring gear tries to drive the starter pinion,
the output shaft will spin ahead of motor velocity
due to the starter's built in over-run clutch.
| Quote: |
Actually, if you look at ACS starter solenoid (contactor) you will see that the terminals are on the top of the "can", the lower part is the electromagnet which pulls the armature (connected to the actual contact device) downward to complete the circuit. It has to be held up (open) by a compression spring. |
If you study the disassembly photos of an exemplar
contactor at . . .
http://tinyurl.com/o5turon
Energizing this style of contactor LIFTS the armature
and pushes a very light moving contact up against
the inside of the dome which mounts the contact
studs. The return spring resides between the stationary
contacts.
| Quote: |
The pilot will never notice that this happens save for the
possibility of damaged gears which will probably be blamed
on something else. |
You're right. The pilot who bought a new starter
and contactor at OSH was unaware that his starter
had probably been engaged for the duration of his
performance . . . not because of some transient
g-loading but more likely from contact welding
promoted by low battery voltage.
G-loading to contactor mounted on the fire wall
isn't even on the right axis for moving the
contactor's inner workings. Even if the contactor
were mounted upside down . . . maintained a Z-axis
g-load induced contact for an interval needed to get the
pinion gears extended is problematic.
Bob . . .
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Jim Baker
Joined: 30 Mar 2006
Posts: 181
Location: Sayre, PA
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| Posted: Thu Jul 14, 2016 5:59 pm Post subject: Contactor orientation |
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Not sure if I can find it again but Cessna Pilots Assn had an article on contactors and orientation about a year ago. One of the interesting quirks was the mention of a mislabeled contactor that was routinely installed incorrectly at the factory resulting in several instances of starter engagement many years after the install. I'll see if I can find it again.
Jim Baker
405 426 5377
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nuckolls.bob(at)aeroelect
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| Posted: Thu Jul 14, 2016 7:52 pm Post subject: Contactor orientation |
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At 08:50 PM 7/14/2016, you wrote:
| Quote: | --> AeroElectric-List message posted by: Jim Baker <jimbaker(at)npacc.net>
Not sure if I can find it again but Cessna Pilots Assn had an article on contactors and orientation about a year ago. One of the interesting quirks was the mention of a mislabeled contactor that was routinely installed incorrectly at the factory resulting in several instances of starter engagement many years after the install. I'll see if I can find it again. |
Super! I've got good G2 at Cessna . . . it will
be interesting to see which parts were involved.
Bob . . .
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racerjerry
Joined: 15 Dec 2009
Posts: 202
Location: Deer Park, NY
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| Posted: Fri Jul 15, 2016 4:00 am Post subject: Re: Contactor orientation |
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Jim Baker, the CPA contactor article you are looking for appeared in the April 2015 issue of their magazine.
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Jim Baker
Joined: 30 Mar 2006
Posts: 181
Location: Sayre, PA
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| Posted: Fri Jul 15, 2016 7:16 am Post subject: Contactor orientation |
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Thanks! Makes it easy now. Jim Baker [url=tel:4054265377]405 426 5377[/url]--
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Jim Baker
Joined: 30 Mar 2006
Posts: 181
Location: Sayre, PA
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| Posted: Fri Jul 15, 2016 12:27 pm Post subject: Contactor orientation |
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Well, that made it easy. Thanks!
Jim Baker
405 426 5377
--
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