This past weekend I was running the new motor at a fast idle in my mostly 1923 Runabout and noticed a sweat over the old carbie:
In aviation we have a control to introduce heat into the inlet track while descending at low power settings. The problem is that at high vacuum settings, the carb can develop internal icing and then the motor will loose power and run rough, just as My Problem Child did this weekend running in the yard.
Here in SoCal we normally do not expect to see carb ice, the climate is generally too dry but we had it last weekend. Has anyone else had any experience with a T carb icing up? Was it only that it was running at a fast idle? Descending a long hill at low power settings ought to induce the same condition on the road . . .
Put your Carb. Pipe on. Problem solved.
I've had carb ice in several old cars here in the NW.
I've gotten used to pulling the carb heat by habit every little while and have gotten a big surprise a few times when the ol' 170 almost died trying to burn the water.
Here is an icing chart. Low power at moderate speed is most likely to show ice. The chart shows even at over 86F and 20% humidity that light icing is possible under low load. This is serious stuff when it comes to aircraft but not a big deal in a vehicle that travels on the surface or the earth.
Here in the sunny south we have that problem. I have had cars that would not drive because of it. Runs fine at idle, hit 20MPH and they would not run. Put on the HOT AIR PIPE and the problem is fixed.
Also: Has anyone had problems with the repro pipes fitting? Thanks, Dan.
I would not care to run a hot air pipe unless it could be switched off like an airplane. The Model T needs all 20 of those ponies!
We were driving to the Thanksgiving parade last year when the car started running bad. The closer we got to the parade the worse the car ran. Got to our spot and opened my hood and found the carburetor all iced up. I use the hot air pipe now.
Dan, yes the repops need much bending to get them to fit.
Ice is more likely to accumulate at a fixed throttle setting, like in an airplane or a Model T. Frequently varying throttle position is one of the few advantages of that evil foot feed.
Warm air contains and holds more water than cooler air does. Air going through a carburetor looses 70 degrees f. in the process. So 100 degree warm moist air drops to 30 and the water freezes. In airplanes you change the color of the seats. In a car you simply pull over to the side of the road and let it warm up.
You don't have carb ice. You have condensation on the outside of the intake manifold.
He who dreams of being a pilot wakes up with his joy stick in hand.
"You don't have carb ice. You have condensation on the outside of the intake manifold."
Are you sure about that? I took the external condensation and rough running as a pretty good indication of carb ice. Had I been flying I would have pulled on the carb heat.
Ralph, it was largely at a fixed throttle setting as I was spending time looking at and listening to the new motor and doing things like changing the mixture & spark settings to see if I could smooth it out.
would a small butterfly valve fix both problems within the heat pipe itself??,allowing for cooler air and heated air when higher humidity at the pull of a wire........carb heat......
Here is the most ice I ever got on my carb, mid winter, snowy day, no carb preheat pipe, ran like a champ, same as always. YMMV
I do frequently get a little condensation as in Paul's photo. Never any performance issue though.
Here in Texas it is normally humid and normally there is always condensation on the outside of the intake manifold. Its a don't care thing, expected, normal, and no reason to consider there is a problem.
I don't quite understand the thought behind putting on the pre-heater will cut down on the HP unless it's because the fuel air density is changed if the humidity is low (that part I can understand). The air flow should be about the same with or with out it on. Carbs like the early Zenith had a built in port just a head of the choke that could be opened in warm weather to get cooler air in. If the weather calls for it I run mine, today would be a good day to have it on. About 60 and rain! Too much humidity!
You pull in the same volume of air with or without the heater. However the density of hot air is less then cold air so you get less oxygen and less bang for your buck with hot air. In an ideal world, you should have a manual control to add heat when needed not not add heat when not needed.
condensation there every time I drive here in Ellenton fl. freaks people out when they ask to look under your hood and you grab it. and scream loud. belly laughs.
I suspect that we have a bit of frost in the intake many times and don't realize it because it hasn't gotten bad enough to be a problem. But every once in a while it happens. Surely Henry Ford wouldn't have made and installed heat pipes if he didn't think they were necessary.
In 50 years of general aviation flying I have had perceptible carb ice only twice. Once was on takeoff roll after a prolonged period of idling waiting for my turn for the runway. Pretty easy to understand there. The second time was in a steady cruise on a nice, clear day. After pulling the carb heat to clear the ice I returned the control to the off position. The ice came right back. After clearing it the second time I played with the control to see how much heat it took to stop the ice formation. Took maybe half travel on the control.
Coincidentally, I just finished watching a PBS showing of a 2009 Canadian documentary on the first Broken Arrow - a crash with a nuke onboard. It was a B-36 headed from Fairbanks to Ft. Worth in 1950 that encountered "severe carb icing" just off the BC coast, causing 3 of the six recip engines to burn up. 12 crew bailed out and were rescued, but five were never found. I wonder if it was really carb icing, or intakes clogged by ice?
The USAF found it on a ridge in BC four years later, and went in and blew up the mostly intact airplane. There are still lots of questions the USAF has never answered, like: Did it really have a live nuke? Had the crew dropped the bomb undetected in the Pacific? Did the USAF remove the plutonium ball in 1954 before blowing up the plane using mostly the bomb's own high explosive? Was the plutonium ball still in its bird cage in 2009 when they confiscated it from a collector who had plundered it from the site?
Great story by the Canadians.
You're probably correct, the term carb icing is really kind of a misnomer. The real problem with carb icing is the intake gets clogged by ice.
You got me thinking of the scene from the movie The Spirt of St. Louis. When the plane ices up and the carb chokes on the ice. Great movie.
Read the Ford service manual. It tells you to remove the heat pipe in warm weather. The heat pipe was there because of crappy gas that would not vaporize properly. Not because of carb ice.
The dynamometer has proven removing the carb heat pipe increases horsepower significantly.
Jim, I meant carb icing was probably a misnomer in the case of the B-36. Maybe it wasn't. I don't know where you got that diagram, but it doesn't jibe with the training I've had. Fuel injected engines don't ice up, because there is no carb venturi to distort with ice. Think of a venturi as an airplane's wing turned outside in.
A curiosity of air is its trait of cooling when its density is reduced, and heating when compressed. . That's how refrigerators work. . Refrigerant is pumped at high pressure into a radiator that releases heat, then through a restrictor valve that reduces the pressure (vacuum), at which point it enters the ice box, and absorbs heat from the box's contents. . Refrigerant condenses to liquid in the compression stage, and evaporates in the vacuum stage, creating additional heat transfer.
Common carburetors have a venturi whose purpose is to create an area of low pressure (vacuum), into which fuel is sucked and vaporized. . Even at WOT (wide open throttle), there has to be a vacuum in the carb for it to work. . This pressure drop can cause a temperature drop of up to 70 degrees F, depending on carburetor design, and other factors. . The actual drop in any carb will vary, depending on temperature and humidity of the incoming air, as well as characteristics of the fuel itself.
Carb ice becomes a nuisance when it builds up at the downstream end of the venturi, and changes the shape of the venturi to something much less aerodynamic. . At that point, the sucking of fuel becomes inefficient, and the engine starves for fuel, and starts running rough.
In light aircraft, the FAA teaches that the ideal conditions for carb icing are high humidity and about 60 degrees F, at partial throttle. . They teach you to habitually apply carb heat when reducing power to descend. . I found their advice right on the mark when I got carb icing at partial throttle 3,500 feet on a cool, partly cloudy morning in our 100 HP Continental powered Cessna 150. . That was on my first unsupervised solo...
As an FAA Airframe and Powerplant mechanic with Inspection Authorization (IA) I can tell you that what you are saying has merit within the context of aircraft operation. However it is misplaced in this case.
Ah, I knew it was tempting fate to post so many times without sour grapes from you, Royce. Especially so after my highlighting the Toyota foot feed fiascos.
Do you mean to say puddle carbs don't have venturis? Real carbs do. As I stated above, cars with hand throttles are more like airplanes where the throttle setting can be the same for extended periods, leading to icing if conditions merit.
A carburetor with a smaller venturi is more prone to "icing" that one with a larger venturi. A Stromberg OF will build frost on the outside of the area ahead of the venturi and the lower portion of the intake manifold when conditions are right. I don't know how much frost builds on the inside but I know you can see water if you remove the carb and look inside the intake and the end of the carb. Other carbs with small venturi also do this.
Our airport is at about 4000 feet with usual morning humidity and lots for mornings at 50-60 degrees in the summer. Carb heat is necessary on older carbureted aircraft engines here or you can suddenly lose power on landing. SOP is to pull the carb heat when you turn the base leg for the runway whether needed or not. It was obvious in my 152, not so obvious in my Tri Pacer with an O-320 or the later Pacer with the 0-360. For awhile I had an old Stinson Station Wagon with a Franklin 220/220 in it that didn't seem to care one way or the other but the 152 did.
Part of my flight training was to not pull carb heat and do some touch and goes to see how the engine reacted. We have a mile and a half of runway so there was time to deal with it. Flying in the mountains was another part of it where a lot of guys will pull some carb heat if you are floating down a lee side with reduced power. Me too. Might not be necessary but that's what I was taught to do.
"than", not "that"
lots "of" mornings. Not enough coffee yet.
I just looked back at the photo I posted earlier and find it interesting that the visible ice on the outer surfaces (who knows about the inside) starts at the manifold and not on the carb itself where the venturi is located.
I run a heat pipe on both of our T's and I've still experienced what I believe to be carb icing on at least one occasion. I had driven the TT to a car show about 15 miles away at about 25 mph. When I slowed to turn into the car show, the engine started running really rough. Upon parking and opening the hood, the outside of the carb and/or manifold (Don't remember now which it was or both) was frosted up pretty bad. I can only assume the inside was just as bad or worse.
I believe the phenomenon has more than one cause. I assume the primary reason is the reduction in temperature due to the reduction of air pressure caused by the Bernoulli Effect in the venturi, but the evaporation of fuel will cause a reduction in temperature as well.
Bernoulli's principleFrom Wikipedia, the free encyclopedia
Jump to: navigation, search This article is about Bernoulli's principle and Bernoulli's equation in fluid dynamics. For Bernoulli's theorem in probability, see law of large numbers. For an unrelated topic in ordinary differential equations, see Bernoulli differential equation.
A flow of air into a venturi meter. The kinetic energy increases at the expense of the fluid pressure, as shown by the difference in height of the two columns of water.Continuum mechanics
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In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. Bernoulli's principle is named after the Swiss scientist Daniel Bernoulli who published his principle in his book Hydrodynamica in 1738.
Bernoulli's principle can be applied to various types of fluid flow, resulting in what is loosely denoted as Bernoulli's equation. In fact, there are different forms of the Bernoulli equation for different types of flow. The simple form of Bernoulli's principle is valid for incompressible flows (e.g. most liquid flows) and also for compressible flows (e.g. gases) moving at low Mach numbers (usually less than 0.3). More advanced forms may in some cases be applied to compressible flows at higher Mach numbers (see the derivations of the Bernoulli equation).
Bernoulli's principle can be derived from the principle of conservation of energy. This states that, in a steady flow, the sum of all forms of mechanical energy in a fluid along a streamline is the same at all points on that streamline. This requires that the sum of kinetic energy and potential energy remain constant. Thus an increase in the speed of the fluid occurs proportionately with an increase in both its dynamic pressure and kinetic energy, and a decrease in its static pressure and potential energy. If the fluid is flowing out of a reservoir, the sum of all forms of energy is the same on all streamlines because in a reservoir the energy per unit volume (the sum of pressure and gravitational potential ñ g h) is the same everywhere.
Bernoulli's principle can also be derived directly from Newton's 2nd law. If a small volume of fluid is flowing horizontally from a region of high pressure to a region of low pressure, then there is more pressure behind than in front. This gives a net force on the volume, accelerating it along the streamline.
Fluid particles are subject only to pressure and their own weight. If a fluid is flowing horizontally and along a section of a streamline, where the speed increases it can only be because the fluid on that section has moved from a region of higher pressure to a region of lower pressure; and if its speed decreases, it can only be because it has moved from a region of lower pressure to a region of higher pressure. Consequently, within a fluid flowing horizontally, the highest speed occurs where the pressure is lowest, and the lowest speed occurs where the pressure is highest.
LOL Mike Taylor, that's HILARIOUS. Definitely going to start doing that when people ask me about my speedster.