Why Updraft Carbs?
Bob Chilcoat
got away from this type years ago. Apart from the obvious, that there is
more room below the engine on horizontally opposed aircraft engines than
above, are there any other advantages? Disadvantages?
--
Bob (Chief Pilot, White Knuckle Airways - "Always spare landings for every
takeoff")
----------
Tom Cummings
lighter intake manifold. They are nearer the exhaust system for a convenient
carb heat system. They are below the engine to be near or very near the
lowest point in the fuel system. This enables gravity fed systems and
draining of water. Fuel leaks from the updraft carb, gasculator, and fuel
line would not fall on top of the engine.
Tom
"Bob Chilcoat" <view...@erolsREMOVE.com> wrote in message
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Bruce A. Frank
Tom Cummings wrote:
>
Fuel leaks from the updraft carb, gasculator, and fuel
> line would not fall on top of the engine.
> Tom
No, the leakage falls on the cowling and drains back towards the
firewall creating a real hazard in getting out of the burning plane,
whereas the top mounted carb cooks a spot where you can see it before
involving the whole engine compartment and cabin. ;^)
The evolution to the updraft carb precipitated the loss of a very useful
devise ...the choke.
Bruce A. Frank
veed...@postoffice.pacbell.net
Dear Bob,
The main advantage has to do with using gravity to feed fuel to the carb.
With a pump you've got another system to power -- and to fail. But the main
hazard associated with fuel pumps is that most will keep on pumping for so
long as the engine is turning. If you've got a leaking fuel line, the pump
makes sure the fuel gets sprayed around as widely as possible :-)
There are a host of fixes to the pump hazard but for a simple system the
easiest 'fix' is to simply not use a pump.
An oft-heard argument for down-drafts, high mouted side-drafts and so forth is
that they allow shorter intake runners, reducing the lag in throttle
response. But in a constant speed engine, throttle response is not a major
issue. This is another case of applying automotive logic to an aeronautical
situation.
Despite the obvious advantages of a gravity fed carburetion system, it simply
won't work for every application. But as a general rule, if you don't require
a pumped system, leave it out. If you're particular airframe falls into that
gray area between the two I suspect you'll need a few hundred hours of
experience -- including maintenance -- with each configuration before you'll
have enough data to make an informed decision.
-R.S.Hoover
highflyer
>
> Generally, light plane carburetors are updraft designs. Automotive carbs
> got away from this type years ago. Apart from the obvious, that there is
> more room below the engine on horizontally opposed aircraft engines than
> above, are there any other advantages? Disadvantages?
>
>
Carb fuel leaks leak out and not into the engine.
--
HighFlyer
Highflight Aviation Services
John Nocero
"Bob Chilcoat" <view...@erolsREMOVE.com> wrote in message
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David B Brownell
> Wouldn't a downdraft carb sitting atop a warm engine be less likely to ice?
No, because the intake air source is the same, along with the same
pressure drop in the carb throat & venturi.
Also:
Up draft carbs are less likely to flood the engine when pumping the
throttle/accelerator pump.
The fire hazard is of course increased compared to a down draft carb
when pumping the throttle.
Dave Brownell
Ray Toews
the crankcase with gasoline creating a ruined engine and a real fire
situation in the crankcase, an updraft carb engine when flooded (too
much fuel in the combustion chamber) will clear out very quickly
without washing all the oil off the cylinders.
Ray
Dan Thomas
I think an upsraft carb under the engine is less likely to ice
because of the warmed cooling air coming downward off the cylinders.
While the engine is running it's fairly cool up top and hot in the
lower cowl. On the Lycomings I'm familiar with the carb is bolted to
the bottom of the oil pan, and the intake pipes run upward through the
pan and out the side. The pan gets pretty hot and keeps the carb body
warm. The air has to be pretty damp before we see any ice in this
system.
Dan
jerry wass
cylinder[s] and possibly create a hydraulic lock when an attempt is made
to start it--or run out the air vent of the bowl and run all over the
top of the engine--little risky to start.. An updraft just runs out on
the ground .
jim brackett
20,s and 30,s,. What happens when a carbureuter sitting on top of an
engine has a float stick? This was not an uncommon occurrance. hence
the updraft carb.
On 19 Aug 2001 17:28:05 -0700, dan.t...@pbi.ab.ca (Dan Thomas)
wrote:
JCalSifredi
Ever had carb ice in a car? Most probably not.
It can happen. Most usually on hot rods and race cars modified for
cool-air induction. I have had it on a Porsche with Webers and a
modified decklid and on a inline 6 Chevy with Webers (don't laugh) on
a truck running hoodless. But usually, most people don't.
Two reasons. Cars have underhood temperatures high enough the air,
even cooled by the venturi, is too hot, and thermal conduction makes
the carb bodies and venturis hot so ice could never stick. On most
American cars you had a V8 with a big cast iron manifold, the carb was
thermally sinked and stayed hot. Even on sixes and fours, you had
heavy manifolding and usually with exhaust passages for the automotive
version of "carb heat". Called a thermal riser.
With modified engines with carbs on tubular manifolding-they can get
cold enough.
My point is, in daily use in stock vehicles it was so rare as to be
unknown to any car mechanic who didn't race or hotrod. (Modern cars
are all EFI.)
The updraft carburetor mounted on the end of a long fabricated
tubular intake, or even on the bottom of the sump (Lycoming), in the
air blast in flight, has this problem in a big way.
Putting the carb on top would also make gravity feed impossible in
many airframes and also hydraulic lock would be a bigger problem. Most
starters won't put enough torque into a locked crank to bend anything
but today most people wouldn't have sense to pull the plugs and pull
it through.
assa9
"JCalSifredi" <siffr...@hotmail.com> wrote in message
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Yer showing yer age, whippersnapper.
Audi had a factory bulletin about how to drill a 10 MM hole in the heat
flapper to keep carb ice from happening.
A *LOT* of them stopped going down the freeway.
assa9
Roger Hamlett
"assa9" <dpi...@yahoo.com> wrote in message
news:toa0kjq...@corp.supernews.com...
The first relates to a long hill in the Pennines UK, where a few years
ago, it was common for cars to 'die' mysteriously when descending the
hill. The local garage had a van 'standing by', and used to turn up
'conveniently' for the poor motorist. He would 'fiddle' under the bonnet
for a few moments, say 'try this', and then the car would miraculously
start. He would take some money for his trouble, and the motorist head on
his/her way. The garage knew of course that these cars were stopping with
carb ice, in the long descent, and simply 'fiddled' to cover the couple of
minutes needed for this to melt...
The second is on how unaware of hydraulic lock some people can be. A local
road flooded recently, and I watched as a car was retrieved from this by
the AA. Having got the car out the other side, they tried to dtart it with
the electric start. There was the sound of an engine 'solid' with water
inside. The AA man then says "your starter has stuck, we'll push start
it", and proceeds three times to try to push start the car, with the
wheels locking solid everytime the clutch was released... I was watching
from the other bank, so couldn't point out that it was fairly obvious that
water had got in through the induction system, and they were trying their
best to do a lot more harm...
Best Wishes
JCalSifredi
cars. the overwhelming majority had V8's and the few sixes had exhaust
and intake on the same side often as not.
Dan Thomas
> Carb ice.
>
> Ever had carb ice in a car? Most probably not.
>
> It can happen. Most usually on hot rods and race cars modified for
> cool-air induction. I have had it on a Porsche with Webers and a
> modified decklid and on a inline 6 Chevy with Webers (don't laugh) on
> a truck running hoodless. But usually, most people don't.
>
Almost all cars using carbs had carb heat. My first car was a
Volkswagen Beetle, and it would ice up often. It took me a while to
figure out howcome it sometimes lost so much power without any good
reason. I had removed some of the "useless" plumbing to make the thing
easier to work on, and in doing so I had removed the hot air hose to
the air cleaner. There was an automatic temperature-sensing bellows in
the air cleaner housing that moved a flapper to turn on "carb heat."
Many American cars used a small temperature-sensitive valve that
opened a small air bleed in a vacuum line to the flapper, and if air
temps dropped into icing range the valve would close, raising vacuum
and pulling the flapper over. There was a tin heat muff over one of
the exhaust manifolds to provide the heated air through an aluminized
paper tube. Lots of guys would turn the lid of the air cleaner over,
creating a big gap around the housing, to let in "lots more air for
more power". They suffered a lot with carb ice. Unless they lived in
Arizona.
Most American carbs also mounted either directly above the
exhaust manifold (sixes) or, in a V-8, had an exhaust channel though
the intake manifold under the carb to keep it warm. This channel would
carbon up and block the heat.
I owned a Ford Courier (Mazda) that had a manual carb heat
valve under the hood on the air cleaner housing. Up for summer, down
for winter. Problem was that carb ice was more common in summer. I
attached a push-pull cable to it for "cockpit" control.
I have had people complain to me that their cars regularly
lose power for no good reason. So much so that they have to pull over
for a bit, and then soon things are OK again. A quick look usually
reveals a disabled or defective carb heating system.
Of course, modern fuel injection systems seldom experience
icing problems.
Dan