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alfuller194(at)gmail.com
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 Posted: Mon Jun 05, 2023 11:23 pm Post subject: fuses in series |
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A question regarding the observation below concerning master switch placement [“… A friend of mine crashed his F1 rocket at during a go-around at full throttle and ended up trapped upside down. He could smell the fuel from the damaged wing tank but couldn't reach the master switch. Fortunately the electrical system stayed intact and the fuel never ignited. …”:
Q: Is placing the master switch where it is within reach when the pilot is strapped in a [mostly undocumented] requirement? Should it be?
The comment reminds me of an auto gymkhana where a race-prepped Healey Sprite suffered a broken throttle return spring and the throttle stuck wide open. The car was piloted by the racer’s 16 year-old son, who was belted in with the race harness. When strapped in he couldn’t reach the master off switch, so the car careened around the office building parking lot venue until it left the ‘track’, went into and thru the crowd, and finally dragged one spectator thru the glass curtain wall of the office building – all because the driver couldn’t reach the master off switch when needed. Much serious bodily injury and property damage ensued, and the police cited the youngster for reckless driving [despite the event being caused by a mechanical failure, and on private property as opposed to a public street – but all that is a story for another day].
So – just wondering how much consideration we do or should give to being able to reach controls that could become critical in certain situations.
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All the best,
Al Fuller
From: owner-aeroelectric-list-server(at)matronics.com <owner-aeroelectric-list-server(at)matronics.com> On Behalf Of Sebastien
Sent: Saturday, February 25, 2023 10:35 AM
To: aeroelectric-l. <aeroelectric-list(at)matronics.com>
Subject: Re: Re: fuses in series
We definitely need SOME way to cut electrical power to the aircraft for several different emergency situations. A battery contactor solves this for all but the most sudden and catastrophic situations. A friend of mine crashed his F1 rocket at during a go-around at full throttle and ended up trapped upside down. He could smell the fuel from the damaged wing tank but couldn't reach the master switch. Fortunately the electrical system stayed intact and the fuel never ignited. I don't know of a single crash where a battery fuse could have changed the outcome.
As for current limiters rated for short starting loads, I flew King Airs for years with current limiters. We carried spares because they blew on engine start more than once. Beech eventually replaced them with bus ties.
When Cessna starts producing single engine aircraft with battery fuses, I think it will be worth another look. In the meantime I don't see a benefit to adding odds and ends to a proven system.
On Sat, 25 Feb 2023, 08:38 Matthew S. Whiting, <m.whiting(at)frontier.com (m.whiting(at)frontier.com)> wrote:
| Quote: |
I agree that the likelihood of a direct short of a main battery cable is small. However, it is not zero and the localized heating from such a short could ignite combustibles. As long as the cable is kept away from combustibles, this isn’t an issue.
The difference in current between starting and a significant short is pretty large so viable overcurrent protection is feasible. For example, most engines in EA-B aircraft probably draw 100 amps or less during starting. It takes a fairly large engine to draw 200 amps (think diesel pickup truck or larger). Yes, the initial current when the starter is not turning can be twice or more the normal cranking current, but that is very short duration and is not likely to blow/trip a 200 A fuse or breaker. A short circuit of a battery can easily draw 1000 amps or more which would blow a 200 A fuse fairly quickly.
[img]cid:E2577D00-CEE6-44B3-963B-7FE9316010E4[/img]
VRLAshortCurrentsStorageBatterySystems
PDF Document · 163 KB
[img]cid:22B0F079-6A61-4D4A-B632-9F909E2D9767[/img]
Cessna Flyer Association - Save your Starter
cessnaflyer.org
youtu.be
[/url]
[url=https://youtu.be/d2nPHWNoDSA]
I believe overcurrent protection on a battery is easily accomplished, but I tend to agree with Bob that the likelihood of needing this is small. Then again, you can make a similar argument for the battery contactor. You don’t see these in the automobile world as they are deemed unnecessary and for good reason. One could argue the same for aircraft.
Matt
Sent from my iPad
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On Feb 25, 2023, at 10:23 AM, GLEN MATEJCEK <fly4grins(at)gmail.com> wrote:
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Re: fuses in series
I could see someone following the architecture used in home and building
electrical distribution systems ... |
A couple more data points:
My 1970's VW Rabbit had a fusible link in the battery cable, and I guess I wouldn't be shocked to learn many cars were so equipped without it being general knowledge.
There are transport category aircraft with current limiters geographically distributed around the system to prevent hard faults from taking out the whole system.
No clue if that strategy is based upon crashworthiness considerations, maintenance considerations, corporate history, or some combination.
In my aft-battery RV-8, the fat wire runs through the crushable structure under the cabin floor, making it susceptible to pinching and a hard fault in a crash, especially given the model's tendency to shed its main gear. Not sure the practicality of trying to size a current limiter that would not open under cranking loads but still open with a hard fault. The guestimated risk for me centers on the probability of hitting the planet without knowing it's coming and thereby not getting the master off in time. Given how I operate, I judge that to be a low very order threat and one I can live with.
YMMV-
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nuckolls.bob(at)aeroelect
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| Posted: Wed Jun 07, 2023 8:16 am Post subject: fuses in series |
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| Quote: |
Q: Is placing the master switch where it is within reach when the pilot is strapped in a [mostly undocumented] requirement? Should it be? |
It is a 'requirement'
Here is one of what has to be many hundreds of
publications on the topic:
https://tinyurl.com/mrwzfn64
The real-world is replete with
anecdotal recitations of outcomes arising
from inability to reach a particular control.
Or perhaps the outcome was strongly influenced
by training i.e. recognition and timely
action to mitigation of an anomalous
condition.
Human factors has always been high if not
at the top of the list for risk mitigation.
Individuals with a propensity for worrying
about risks are noteworthy for their desire
to regulate, legislate, design or educate
toward the utopian, risk-free condition.
Sometimes, those efforts have a good
cost/benefit ratio . . . but it's
impossible to address ALL human shortcomings
that go to increased risk. Recall the
fuel selector location on John Denver's
Long-Ez, Dan Lloyd's under-crimped
power distribution terminals, and crews
of the 737MAX aircraft who (when
presented with an un-commanded pitch down on
their aircraft) were TRAINED to search
the emergency procedures check list
for a 'solution'.
Yeah, it seems like a no-brainer that
all critical controls should be suitably
accessible to the pilot under normal and
abnormal conditions of flight.
But it's important for YOU to do your
own FMEA on configuration decisions for
your project. Sitting in the cabin of
your unfinished airplane doing your
'Walter Mitty thing' need not be a
frivilous exercise. Astronauts spent
hours in their simulators practicing,
refining and documenting response to
every possible operational scenario.
Even so, their emergency procedures
manuals were decidedly silent when
it came to dealing with a failed oxygen
system blew out the side of their
spacecraft.
Do the best you know how to do and don't
hesitate to exploit the knowledge and
experience of your peers.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
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