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Kellym
Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ
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 Posted: Fri Oct 06, 2006 6:26 am Post subject: Why fuel cutoff? |
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I'd infer the reason has a lot to do with the fact that airplane engines
have magnetos and a big old prop out front that doesn't take much effort
to move. When is the last time you moved your auto engine with one hand?
When is the last time you worried about your car starting if you moved
the engine? If you kill the engine with the mag switch you will have
fuel in the cylinders, and if a mag isn't fully grounded, someone moves
the prop, and presto, instant unintended start and whatever is in the
way of the prop gets sliced and diced.
linn Walters wrote:
| Quote: | Dean, I share your frustration. Thanks to the Feds, we have to put up
with antiquated engines because it costs too much to certify new ones,
and the lawyers have inferred that if an improvement is made, then the
original was flawed. Homebuilts are the only solution. Car engines
have all the newest technology ... are far more efficient, have better
power to weight ratios, and far better tolerances. I really have to
agree .... magneto's belong on lawnmowers!!! However, they're dirt
simple and if taken care of .... hardly ever fail. I like that.
Electronic ignition is more efficient ..... but is still prone to
failures like any other electronic gadget. I don't really like that.
Working in the electronics industry all my life has made me very
wary!!! KISS is important to me, and adding dual backut everythings
just doesn't give me a warm fuzzy feeling. But I digress.
I believe the biggest difference between car engines and airplane
engines is the way we operate them. The only way your car sits in the
garage for weeks on end is when your job takes you out of town!!! I
run the dog-crap out of my Pitts engine ..... and often .....so I
don't worry about internal rust and corrosion because I run it often.
If you flew every day, then you'd probably never have any problems
related to shutting the engine down with the mag switch. I was given
that reason for having an idle cutoff on the mixture and accepted it.
It's plausible to me. So, I ask you ..... do you have a better
reason?? Lycoming says a lot of things relating to their engines that
I think come from a severe case of CYA. This could be one of them.
Until I find good. meaningful data to suggest otherwise, I'll hold on
to this "urban legend".
Linn
do not archive.
DEAN PSIROPOULOS wrote:
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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD |
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FLYaDIVE(at)aol.com
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| Posted: Fri Oct 06, 2006 8:50 am Post subject: Why fuel cutoff? |
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In a message dated 10/6/2006 10:28:24 AM Eastern Standard Time, kellym(at)aviating.com writes:
| Quote: | So, I ask you ..... do you have a better
| Quote: | reason?? Lycoming says a lot of things relating to their engines that
I think come from a severe case of CYA. This could be one of them.
Until I find good. meaningful data to suggest otherwise, I'll hold on
to this "urban legend".
Linn |
================================
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Hi Linn:
I would think there are three reasons to have a fuel cutoff:
1 - If you have your wits about you ... Just before the crash you shut off the fuel so as not to fuel the fire.
2 - Since many planes with two tanks manage their fuel with a fuel selector switch and that switch is located in the cockpit it may just help if there is a fuel leak in the cockpit or engine fire.
3 - It is probably an FAA requirement.
But, as for the KISS ME principal, why not eliminate all fuel lines in the cockpit and run the lines directly to the boost pump and engine forward of the firewall. Do away with the switch completely. I know, I know ... Fuel management and fuel contamination.
Barry
"Chop'd Liver"
[quote][b]
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pitts_pilot(at)bellsouth.
Guest
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| Posted: Fri Oct 06, 2006 8:50 am Post subject: Why fuel cutoff? |
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Good point Kelly! I know two 'victims' of prop strikes after shutdown
with the mixture. One lost a thumb, and the other spent weeks in the
hospital recovering from a blade across the top of his head. In this
one, he just braced his hand on the prop to look into the intake ....
and the impulse fired ..... on a hot engine. I treat mags like guns
..... they're always loaded and ready to fire!!! I just don't trust
them to always be grounded. Both my buddies were in a hurry and didn't
switch the mags off when they got out of the plane. Another one of my
learning experiences.
Linn
Kelly McMullen wrote:
| Quote: |
I'd infer the reason has a lot to do with the fact that airplane
engines have magnetos and a big old prop out front that doesn't take
much effort to move. When is the last time you moved your auto engine
with one hand? When is the last time you worried about your car
starting if you moved the engine? If you kill the engine with the
mag switch you will have fuel in the cylinders, and if a mag isn't
fully grounded, someone moves the prop, and presto, instant unintended
start and whatever is in the way of the prop gets sliced and diced.
linn Walters wrote:
> Dean, I share your frustration. Thanks to the Feds, we have to put
> up with antiquated engines because it costs too much to certify new
> ones, and the lawyers have inferred that if an improvement is made,
> then the original was flawed. Homebuilts are the only solution. Car
> engines have all the newest technology ... are far more efficient,
> have better power to weight ratios, and far better tolerances. I
> really have to agree .... magneto's belong on lawnmowers!!! However,
> they're dirt simple and if taken care of .... hardly ever fail. I
> like that. Electronic ignition is more efficient ..... but is still
> prone to failures like any other electronic gadget. I don't really
> like that. Working in the electronics industry all my life has made
> me very wary!!! KISS is important to me, and adding dual backut
> everythings just doesn't give me a warm fuzzy feeling. But I digress.
>
> I believe the biggest difference between car engines and airplane
> engines is the way we operate them. The only way your car sits in
> the garage for weeks on end is when your job takes you out of
> town!!! I run the dog-crap out of my Pitts engine ..... and often
> .....so I don't worry about internal rust and corrosion because I run
> it often. If you flew every day, then you'd probably never have any
> problems related to shutting the engine down with the mag switch. I
> was given that reason for having an idle cutoff on the mixture and
> accepted it. It's plausible to me. So, I ask you ..... do you have
> a better reason?? Lycoming says a lot of things relating to their
> engines that I think come from a severe case of CYA. This could be
> one of them. Until I find good. meaningful data to suggest
> otherwise, I'll hold on to this "urban legend".
> Linn
> do not archive.
> DEAN PSIROPOULOS wrote:
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