> > > > 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
> > > > pressure 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 carburetor 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 Monterey, scared the crap out of me honestly.
> > I was
> > > getting ready to let down for landing and the normal "carb heat
> > on for
> > > decent" procedure 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 under hood 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
> >
> >
> > 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
> >
> >
> > 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, Gordon, Anyone
> what will it take to adapt a Marvel -Schiebler, MA 3, MA3-4, MA 5
> etc or derivative
> to our engine? Also my uncle has been a police officer for some
> 35yrs and I think
> you will learn with a little insurance research that the increasing
> car fires are
> intentionally set by it's owner usually to avoid paying the enormously
> high car payments
> that at the time of the purchase seemed perfectly acceptable to the
> buyer, call it
> buyers remorse by fire.
>
> One other thing I would like to mention the injection units
> in cars use the lowest cost hoses and hardware to assemble there
> system. Now a guy
> like me using only aircraft grade materials to build my FI system
> will more than
> likely never experience a problem if done correctly. Aeroquip
> fittings and braided
> fuel lines are not something you find in most automobile FI systems.
> Look at the
> stock fuel rail you got with your 13b are you kidding me?
>
> As far as a race
> application goes lets not forget those are conditions that far
> exceed what
> your engine will see in an airplane (I think). Seems that most
> engines that
> are in a race environment are expected to perform beyond it's limits
> or close
> to it. I just want to use race proven products and have my engine
> perform
> exceptionally well, not necessarily pushing the bounds of it's
> performance
> envelope, by using extruded fuel rails, AN fittings, safety wire
> ,and braided
> hoses to contain the fuel pressures, I think is a sure way to reduce
> most
> fire issues, even under regular driving conditions.
> (Just thinking out loud).
>
> Here is a drawing of what I have come up with to get rid of the fuel
> rail.
> I will make a few of these next week. I want to copy the "dare I
say it"
> Lycomings way of FI, using stainless fuel lines and a fuel spider.
> The drawing
> you see here is of a holder that incases the injector. The top cap
> attaches to
> the lower section of the holder using (3) 8-32 allen screws safety
> wired together.
> there is a bore hole in the top cap for the injector O-ring. The top
> cap has a
> threaded stud machined into it for the attaching fuel line. These
> will allow me
> to attach my injectors anywhere on my manifold and they don't have
> to be in line
> like if the injector were attached to a fuel rail.
>
> Tony
>
>
> Tony,
>
> Getting rid of the fuel rails is a good idea, but how do you handle
> the return flow ?
>
> I like the mechanical FI used in piston aircraft engines better than
> EFI, but the high pressure pumps add pilot workload. You have to
> manage that boost pump a lot of the time and in an emergency that
> can be the killer. More than a few accidents have been caused by
> improper use of the boost pump.
>
> Personally, I'll take the carb. I suppose you could make a
> Marvel-Schebler work, but you would need to orient your manifold in
> an updraft position. But why bother, the Ellison is a better carb
> and can be oriented any direction. Plus it gives a bit more manifold
> pressure.
>
> Regards,
>
> Gordon.
>
Gordon
I was thinking of using a spider? I think that is what they are
called, that's how Lycoming does it. right?????
So to use the ellison do I just make an intake plenum? and bolt
it on?
Tony
Yes, I see what you mean -- have the return flow coming out of the
spider same as in the fuel rail.
To use the Ellison, you would need a plenum. That means you would
have to do some fabrication to come up with an intake manifold. With
four to six runners, this is not a trivial project, I think.
The other choice is to bore out the P-ports and then you only have
two runners. Put on Paul's slide throttle carb and there you go. I
like this idea a lot.
I would also cobble together a flywheel magneto. That would make for
a very simple aircraft engine with not too many failure modes for
spark and fuel.
Regards,
Gordon.
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