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nuckolls.bob(at)aeroelect
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 Posted: Sat Oct 26, 2013 7:16 pm Post subject: EXP 2 Bus workaround - Master Solenoid Failure |
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At 08:47 PM 10/26/2013, you wrote:
| Quote: | I really enjoy this what-if stuff, so here goes...
I'm referring to Bob's drawing sent out yesterday afternoon,
Z-08_Full.pdf. It appears that people are touching on this issue
but I have not seen it clearly stated.
Given:
1. Stated design goal: To be able to survive any single component
failure w/ little or no drama.
2. Electrically-dependent engine
3. Engine/prop does not windmill, because of some kind of PSRU
|
Turns out not true.
| Quote: | 4. You are flying w/ Engine A switch On
5. Engine B switch Off
Scenario:
1. You are in flight and Main Batt Contactor fails (coil burns up,
loose wire, whatever)
|
Okay . . .
| Quote: | 2. Engine shuts down, prop stops
|
No, the alternator doesn't quite producing just
because the battery is off line. Further, based on
the exchange with Fred/Bob Mc/Bob N I realized that
the Engine source coming from the battery should
be switched by ENG A. Next iteration will show that.
But it's also possible that the pilot would be unaware
of the loss of contactor until the next flight
when turning battery switch on doesn't light things up.
| Quote: | 3. Pilot takes several seconds to gather his thoughts
4. Pilot turns Engine B switch On - power restored to engine systems
except starter
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. . . but engine IS windmilling
| Quote: | 5. Pilot hits starter button to re-light. Starter inop because
failed Main Batt Contactor is in series w/ Starter Contactor.
6. Forced landing
7. Failure to meet design goal - single component failure causes
forced landing 
8. Thanks for playing...
|
inaccurate statement of premises . . .
Bob . . .
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jluckey(at)pacbell.net
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| Posted: Sat Oct 26, 2013 9:01 pm Post subject: EXP 2 Bus workaround - Master Solenoid Failure |
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I believe that some of the installations of the Rotax 912 (and probably other power systems) do not windmill (but the 912 may not be electrically-dependent ).
However, I don't think you can categorically say that ALL engines will windmill. In addition some flight conditions may cause a windmilling prop to stop. A possible scenario: The pilot becomes task saturated on the electrical failure and lets the airspeed bleed down and the prop stops.
Dooh! I forgot about the alternator - BUT - I've never trusted an alternator that was not connected to a battery, therefore I would be reluctant to have that as a fall back.
What about moving the starter feed to the battery side of the master?
-Jeff
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
To: aeroelectric-list(at)matronics.com
Sent: Saturday, October 26, 2013 8:15 PM
Subject: Re: EXP 2 Bus workaround - Master Solenoid Failure
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
At 08:47 PM 10/26/2013, you wrote:
| Quote: | I really enjoy this what-if stuff, so here goes...
I'm referring to Bob's drawing sent out yesterday afternoon, Z-08_Full.pdf. It appears that people are touching on this issue but I have not seen it clearly stated.
Given:
1. Stated design goal: To be able to survive any single component failure w/ little or no drama.
2. Electrically-dependent engine
3. Engine/prop does not windmill, because of some kind of PSRU
|
Turns out not true.
| Quote: | 4. You are flying w/ Engine A switch On
5. Engine B switch Off
Scenario:
1. You are in flight and Main Batt Contactor fails (coil burns up, loose wire, whatever)
|
Okay . . .
| Quote: | 2. Engine shuts down, prop stops
|
No, the alternator doesn't quite producing just
because the battery is off line. Further, based on
the exchange with Fred/Bob Mc/Bob N I realized that
the Engine source coming from the battery should
be switched by ENG A. Next iteration will show that.
But it's also possible that the pilot would be unaware
of the loss of contactor until the next flight
when turning battery switch on doesn't light things up.
| Quote: | 3. Pilot takes several seconds to gather his thoughts
4. Pilot turns Engine B switch On - power restored to engine systems except starter
|
. . . but engine IS windmilling
| Quote: | 5. Pilot hits starter button to re-light. Starter inop because failed Main Batt Contactor is in series w/ Starter Contactor.
6. Forced landing
7. Failure to meet design goal - single component failure causes forced landing
8. Thanks for playing...
|
inaccurate statement of premises . . .
Bob . . .
 ========================
[quote][b]
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BobsV35B(at)aol.com
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| Posted: Sun Oct 27, 2013 1:32 am Post subject: EXP 2 Bus workaround - Master Solenoid Failure |
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Good Morning All,
I have not followed all of this thread, but agree that not all engines windmill like our friendly Continentals and Lycomings. I have about twenty hours flying a Legend Cub powered by the Jabiru engine. It is a nice smooth running engine, but if it runs out of fuel or the mags are shut off, the prop stops!
Happy Skies,
Old Bob
In a message dated 10/27/2013 3:32:26 A.M. Central Daylight Time, jluckey(at)pacbell.net writes:
| Quote: |
I believe that some of the installations of the Rotax 912 (and probably other power systems) do not windmill (but the 912 may not be electrically-dependent ).
However, I don't think you can categorically say that ALL engines will windmill. In addition some flight conditions may cause a windmilling prop to stop. A possible scenario: The pilot becomes task saturated on the electrical failure and lets the airspeed bleed down and the prop stops.
Dooh! I forgot about the alternator - BUT - I've never trusted an alternator that was not connected to a battery, therefore I would be reluctant to have that as a fall back.
What about moving the starter feed to the battery side of the master?
-Jeff
|
[quote][b]
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klehman(at)albedo.net
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| Posted: Sun Oct 27, 2013 6:19 am Post subject: EXP 2 Bus workaround - Master Solenoid Failure |
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Old Bob
Just curious whether you've tried it and whether it was the 4, 6, or 8
cylinder jab? (You probably have tried it or talked to someone who has
if you posted it.)
There were lots of opinions that my geared setup would not windmill but
it most certainly does. More opinions than facts as is often the case on
the internet. For sure there are some known engines/reduction units that
do not windmill.
(break)
I like the concept of minimal connections and components in the truly
essential engine circuits so I like feeding them directly from battery
busses. Engine stoppage occurs far more often than the need to kill
every last electric circuit in a dire emergency. (I'm sure that a
significant percentage of engine out landings/crashes occur with the
battery master still on anyway). I favor feeding "keep it running"
engine circuits directly from battery busses. Sure, route backups
through the master if one wishes but not primary circuits. Then
regardless of windmilling, I see little need to wire such that an engine
can be cranked with the master off or with a failed battery contactor.
That caters to multiple failures and raises other safety concerns IMO.
Ken
On 27/10/2013 5:31 AM, BobsV35B(at)aol.com wrote:
| Quote: | Good Morning All,
I have not followed all of this thread, but agree that not all engines
windmill like our friendly Continentals and Lycomings. I have about
twenty hours flying a Legend Cub powered by the Jabiru engine. It is a
nice smooth running engine, but if it runs out of fuel or the mags are
shut off, the prop stops!
Happy Skies,
Old Bob
In a message dated 10/27/2013 3:32:26 A.M. Central Daylight Time,
jluckey(at)pacbell.net writes:
I believe that some of the installations of the Rotax 912 (and
probably other power systems) do not windmill (but the 912 may not
be electrically-dependent ).
However, I don't think you can categorically say that ALL engines
will windmill. In addition some flight conditions may cause a
windmilling prop to stop. A possible scenario: The pilot becomes
task saturated on the electrical failure and lets the airspeed bleed
down and the prop stops.
Dooh! I forgot about the alternator - BUT - I've never trusted an
alternator that was not connected to a battery, therefore I would be
reluctant to have that as a fall back.
What about moving the starter feed to the battery side of the master?
-Jeff
|
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BobsV35B(at)aol.com
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| Posted: Sun Oct 27, 2013 6:54 am Post subject: EXP 2 Bus workaround - Master Solenoid Failure |
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Good Morning Ken
You wrote:
"Just curious whether you've tried it and whether it was the 4, 6, or 8
cylinder jab? (You probably have tried it or talked to someone who has
if you posted it.)"
I flew the airplane over twenty hours in less than a week flying off a lot of the required time for an experimental category airplane. It was at the factory in Texas, so I did have the factory folks to help with any difficulties encountered.
The runways were long and the traffic was nil so I had no hesitation to do things that would cause the engine to quit. I never had to make a "forced" landing as the starter always worked, but I did shut off the fuel at least once just to check how well it would restart. Same for shutting off the ignition. It also quit at low speeds if the idle RPM was set on the low side.
To get a nice short Cub style three point landing, the idle RPM had to be so low that the engine would quit and the prop would stop turning well before touchdown. I do not recall the exact airspeed at which the prop would stop, but it was not much below sixty mph. It has been over five years since I did that test flying.
That was the only feature of the Jabiru install that I really did not care for. If it were up to me, I would have used the O-200 Continental or an O- 320 Lycoming.
The high idle made for longer than necessary ground roll out and/or excessive use of the brakes.
It is a 6 cylinder 3300 Jabiru with the BMW carburetor.
Happy Skies,
Old Bob
[quote][b]
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