> > Dave,
> > Having had to deal with many carbs and FI systems over the
> years I
> > would
> > respectfully disagree that carbs are safer. While there is
> higher
> > pressuure fuel in a FI there are systems designed (hoses
and > ends) to > > deal with it. The float valve in any
typical carb is the weak > link. The > > fact that the gas
is pumped in by "only" 6 PSI is little comfort > when > > you
> > have an engine fire. In fact if turned off the FI system
> provides
> less
> > to burn. (No float bowl)
> > Bill Jepson
>
>
> Hi Bill,
> I see your point but the reasoning was more as follows:
> A leaking hose in FI produces a fine mist which, if ignited,
makes > the > cowl a bomb. > A carb leak will more
likely produce a fire, so turn off the fuel > and > remove
the source. > Of course, these are only likely scenarios; the
carb leak because > of a > stuck float valve could also
lead to an explosion; but the high > pressure mist in the FI
example is almost guaranteed to explode. > It was > more
that the explosion was the worry rather than the fire. > >
We have a couple of old bike racers in our club and we spoke at
> length > on this possibility and the general opinion was that
float valves > rarely stuck, and when they did, often the valve
stuck in the > closed > position; cutting off the fuel.
Also the Bing and Mikuni 'caged' > valves > are much more
reliable than the old Amal "free" valves. > > Further to
this debate, in your bike days, how common was a stuck > float
> valve and in what position? > > Thanks for your
valued comments, BR, Dave McC > > Dave, > Older bikes
are a bit of a different subject since gravity feed was >
normally used. We saw both stuck open and stuck closed, the latter
> mostly on machines that had been inactive. With fuel pumps, and
that is > very common now, stuck open is more common.
Usually stuck open float > valves being caused by debris.
Running a good filter reduces this > greatly. > With
respect to the under cowl mist being sure to cause an explosion
I > must say bunk, sorry. Few cars built any time in the last
decade have > had carbs, all are fuel injection. You don't see
sudden fire balls on > the road. It would be just as likely as
with an aircraft with many cars > having extraordinary
under hood temps. Hell if it was common the > resultant
lawsuits would be all over the papers. Additionally the >
number > of leaking and ill-maintained cars would make ANY
comparison to planes > look like a tiny sample of generally
pampered engines. On racing > engines > I would say I have
seen far more mechanical failures than fuel > failures. >
Put more simply, I would say if you are more comfortable with carbs
> RUN THEM. You should remember though that more aircraft
accidents are > attributable to carburator icing than any kind
of fires. FI engines > don't have a problem with icing. I had
the carb on my 172 ice up once > on > a night flight
into Montery, scared the crap out of me honestly. I was >
getting ready to let down for landing and the normal "carb heat
on for > decent" proceedure saved the rookie from further misfortune.
> Bill Jepson
Hi again Bill,
I appreciate your comments ref icing up the 172, I was aboard a
Stinson that dead sticked into a field due to carb icing.
Overturned, I exited on hands and knees!
However, since your last remarks, I had some time with old aircraft
engineers, they say most airplane carbs in use today are Marvel
-Schiebler, MA 3, MA3-4, MA 5 etc or derivatives , all have
floats and float valves and no real history of sticking float
valves. Some time back, 10-15 years, there was a problem with
"sinking" floats, but this was mostly due to corrosion of the
brass float, because of water in the float bowl, the float
developed a hole and sunk; and was fixed by installing "plastic
floats". AD as I recall.
As regards carb icing; this should be called by its correct
name- "Induction Icing". If you introduce gasoline into a a long
runner, you will get icing due to the latent heat of
vaporization; whether it is by carb or by injector, you will
have the possibility of induction icing. Just because the fuel
is "injected" does not make the system ice proof. Injecting fuel
close to the valve, (warm head), all but eliminates the
possibility of icing, but if we inject fuel at the bell mouth,
then we can expect induction icing. A good reason to introduce
fuel into Paul's slide throttle; close to the port.
As regards being 'comfortable' with carbs, I am, - have been
for 40 years; but I am "not comfortable" yet with hi pressure
FI. I have been through the auto wrecking yards quite often over
recent years, I am a hotrodder, and underhood fires are far more
common than you suggest.
BR, Dave McC
I had C172 float sink on me one time. Hard to keep that sucker
running with the leaning knob.
--
Paul Lamar ...No rotor no motor.
For what it's worth, I tend to agree with Dave that there are
probably more engine fires since EFI became widespread.
This is hardly a scientific sample, but two years ago I
witnesses a crash in front of my farm in which a brand new Ford
F-150 pickup smashed into the back of a farm tractor pulling a
trailer. I just happened to be looking out my front window and
there was a huge fireball almost instantly. I bolted out the
front door and sprinted the hundred yards or so down my drive in
my slippers and by the time I got there the truck was completely
engulfed.
My neighbor across the road ran over with a fire extinguisher
and tried to put it out, but there was no chance. By the time
fire crews arrived the truck was completely burned out. The
blaze was huge. Luckily the driver and passenger got out, but
the guy on the tractor wasn't so lucky -- he was fatally injured
on impact.
In the last few years I have seen more cars burning on the side
of the highway. This is something I never saw in years past.
I tried to find some statistical info, but the last NHTSA study
is from 1990. They did find that fire frequency had increased
even then.
http://www.autosafety.org/article.php?scid=96&did=533
<http://www.autosafety.org/article.php?scid=96&did=533>
A more recent article from 2004 appears to suggest that fires
are increasing at a high rate, despite overall safer vehicles.
http://www.autosafety.org/article.php?did=1193&scid=179
<http://www.autosafety.org/article.php?did=1193&scid=179>
It's hard to draw cause and effect conclusions from this, but it
does reinforce my nervousness about flying with an
automotive-derived EFI. Just my personal preference, but I would
rather go with a carb and low-pressure fuel. Paul's slide throttle
carb could be the best bet.
Regards,
Gordon.
Paul,
Uncontrolled electric fuel pumps, as used in many English cars during the
70's, were a real danger. After losing a friend in a car fire, exacerbated by
the electric pump feeding the fire, I developed an impact switch to cut off
the pump in the event of a high G impact. The introduction of engine computer
controlled pumps solved the problem. Of course mechanical fuel pumps do not
have this problem. Backup electric pumps in aircraft are a worry when the
cowl hits the ground. Experience. There is a lot to do on the way down.
Colin Smith
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