How a Carburetor Works

[History]

I hope it’s ok to post this link,,,,,,? I know most of you are gurus and understand how a carburetor meters and mixes fuel with air. I’m sure some guys on here work with their minds and not their hands, or in my case, my back Here’s an interesting video that shows how a carburetor in general works. I believe that even you gurus will enjoy it.

https://youtu.be/toVfvRhWbj8

[kbinde2]

One description I had heard, and the concept had stuck with me..

"Like the action of sipping that first sip of hot coffee", the coffee cup in this case portraying the float bowl, the coffee liquid (gas), the vacuum created by the sipping action simply follows the carburetor throat assembly and intake manifold functions.. more gas needed, take a deeper sip of coffee.

Simple explanation for my simple mind I guess..kb

[Patrick L.]

Good ole Daniel Bernoulli and his famous principal. Same reason an airplane flies.

[History]

Originally Posted by Patrick L.

Good ole Daniel Bernoulli and his famous principal. Same reason an airplane flies.

When my instructor asked me if I knew how a wing created lift and he proceeded to tell me the top of the wing, I was like whaaaaaaaaaaat? Until that point I had always thought it was the bottom of the wing. Of course only going to the tenth grade had to play into it.

[rotorwrench]

Lift depends both the upper and lower surfaces of a wing. Thrust also has a hand in the mix. A brick will fly with enough thrust applied. A clean airfoil will lift with almost no thrust. Gravity and wind currents will sustain lift on a glider wing but it still takes a tow to get it off the ground.

The venturi effect is more about divergent & convergent ducts and how they affect pressure of a flow of gas through that duct. The Bernoulli effect is a way to take advantage of the venturi to affect a fluid that is introduced to that pressure change.

[Big hammer]

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Originally Posted by History

When my instructor asked me if I knew how a wing created lift and he proceeded to tell me the top of the wing, I was like whaaaaaaaaaaat? Until that point I had always thought it was the bottom of the wing. Of course only going to the tenth grade had to play into it.

The good old days learning to fly an airplane! My instructor drew a airfoil with the 4 arrows and asked me what they where “ lift, gravity,drag, thrust “ he asked how that I knew that ? I’ve been reading this and that. Ok lets go flying ! not many words from him after that. The very most fun was unusual attitudes under the hood and then flying back to the airport under the hood and then removing the hood on short final and landing!

[kbinde2]

Lift, Drag.. Under the Hood (Foggles).. Lining up on final, my first was almost as far off course as this thread is becoming.!
Sorry.. just couldn't resist this morning.! kb

[slatgrille]

When I taught Tech. Ed. (shop, Industrial Arts for you older guys), I introduced the principles of flight by having the kids blow across the top of a piece of paper as it sagged in their hand= lift, rapidly 'swinging a backhand' with an open palm vertical to the ground= drag (feeling the air on said palm), gravity is self explanatory, and thrust is 'pull' or 'push' gaining speed.....

Speaking of carb function.....drove my RPU around the neighborhood for its maiden voyage yesterday with no issues. Started it this afternoon and all it will do is idle. Once the pedal begins to depress, she starves for fuel and quits (unless I just let it idle). Before removing the good rebuilt Marvel (Renner's), I think I'll check the gas cap...if I'm not mistaken, I don't think it has 3 vent holes inside it, yet it's worked so far before today. Maybe I tightened it too much???

Craig

[History]

Slatgrille, let us know what you find to be the problem.

[Bob Bidonde]

rotorwrench,
Nice explanation of how Bernoulli used the Venturi Effect in fluid mechanics.

[nkaminar]

The downward deflection of the air is what makes airplanes fly. Otherwise they could not fly upside down.

The venturi does not provide correct air/fuel ratio throughout the speed range. That is why the compensator is there in the Zenith and other mechanisms in other carburetors. The SU has a needle that controls fuel flow as the cylinder rises. The old Model T carburetors had ball valves that opened to let more air in at high speed.

[Patrick L.]

Give the basic simple explanation and people get picky picky picky. [smiley face].
Its all about pressure differential.

[rotorwrench]

Most all carburetors have some form of air mixing before the fuel is introduced to the low pressure areas of the carburetor throat and venturi. The idle circuit has to exit at the low pressure area of the throttle valve in the throat but that only works at idle.

The printed carb in the video doesn't have any form of jet or air mixing for good atomization since it's just a port into the venturi. It illustrates Bernoulli's principle OK but it's not a very controllable example of a carburetor. The high speed video slowed down shows how the fluid just sort of barfs out of the port in the venturi when the cylinder is on the intake stroke.

[History]

I’d like to see the same thing on a v12.

[slatgrille]

History, it was debris in the main jet. Took off the bottom plug (drain?) and blew air through it. Thought I saw an 'object' fly out under pressure. Easy fix. Man, those carbs are simple! I also have a Zenith 2, and a 'Zenith clone' type Tillotson, but prefer the Marvel.

Craig

[rotorwrench]

Marvel Schebler and Tillotson were both divisions of Borg Warner Corp.

[History]

Awesome!!

Originally Posted by slatgrille

History, it was debris in the main jet. Took off the bottom plug (drain?) and blew air through it. Thought I saw an 'object' fly out under pressure. Easy fix. Man, those carbs are simple! I also have a Zenith 2, and a 'Zenith clone' type Tillotson, but prefer the Marvel.

Craig

[BillCNC]

Originally Posted by rotorwrench

Lift depends both the upper and lower surfaces of a wing. Thrust also has a hand in the mix. A brick will fly with enough thrust applied. A clean airfoil will lift with almost no thrust. Gravity and wind currents will sustain lift on a glider wing but it still takes a tow to get it off the ground.

Correct,

The benefit of an airfoil is efficiency at the intended speed of flight.

Power can over come most efficiency short comings. At that point, it becomes AOA (angle of attack) Between power and AOA, that's when your brick will fly up to a point. At a certain point, you have to ditch the propeller and go with Jet power. Otherwise you'll have torque issues vs wingspan vs prop diameter vs blade count. Throttle to fast, and you could be inverted quickly in the opposite direction of the engine rotation even with full aileron deflection.

Sailplanes can fly for free forever with the right conditions. I took one of my competition TD Oly-650's sloping a little while back.

Wait, this is about carburetors, ... never mind.

Regards
Bill

[nkaminar]

Here is my 30 town sedan with my Playboy Senior, a 30's vintage freeflight gasoline powered model airplane converted to radio control and electric power. Great for catching thermals. Wing span is 6 feet.

[nkaminar]

Today I went to the Martin Auto Museum here in Phoenix. They had the first Benz car, a three wheel affair with a horizontal flywheel, 1885. The carburetor consisted of a tank of gasoline that had hot air bubbled through it, the air heated by the exhaust. This fuel vapor rich air was mixed with other air to get the right air/fuel ratio. A valve on the added air is accessible to the operator to control the mixture. I did not see a throttle. I think the added air valve was closed down to get the car started. I suspect that white gas would work the best as the original probably used straight benzine.