Where Fuel Meets Air

His webinars are made possible by the generous support of Aircraft Spruce and specialty home builders and EAA members since 1965. Tonight's presentation, Where Fuel Meets Air, Our Presenter Mike Bush Mike is President of Savvy Aviation, Incorporated author of numerous aviation publications and holds a CFI certificate. P Certified Mechanic with Inspection Authorization Aviation Maintenance Technician of the Year 2008 and EAA Member Mike thank you very much for being with us tonight I'm going to hand over control of the presentation to you good evening Tim good evening everyone, let's begin The title From tonight's presentation, as Tim said, is

where

the

fuel

meets

the gear and we're going to talk about the topic of

fuel

metering, so to start with the basics, you know there are two types of reciprocating engines, spark ignition engines and compression ignition engines.

Compression ignition engines are more commonly called diesel engines and one of the main differences between spark ignition engines and compression ignition or diesel engines is that in diesel engines the fuel is injected directly into the combustion chamber. , but in the case of spark ignition engines, the vast majority of us fly behind us, the fuel has to be mixed with air and then a mixture of air and fuel is introduced into the cylinder

where

It's ignited by a spark plug, so what we're going to talk about is how that fuel-air mixture comes about and the process of creating a fuel-air-air-fuel mixture floating around with your coffee maker wherever you want to say it is called metering now.

Basically, there is a fairly narrow range of air/fuel ratios that will keep our engines running on basically anything that is leaner than 18 parts air to one part fuel and, by weight, are too lean to burn and Anything richer than about eight parts air to one part fuel is too rich to burn if you drink a bucket of gasoline. Throw a match in, the match goes out because it is too rich to burn between eight to one and 12 to one. The mixture will burn but it will not produce significant energy. You could light a torch with it, but you can.

I don't really run an engine, so the mixtures that are capable of combustion are between 12 to 1 on the rich side and 18 to 1 on the lean side and, again, that's the air-fuel ratio by weight and the mixtures that basically they were interested in the ones that we actually use in our engines are in the range of 30 and a half 14 15 16 to 1 about 15 to 1 14 point 7 to 1 to be exact, it is what is called stoichiometric or the mixture chemically correct that corresponds to GT peaks that we normally run richer than that for takeoff and climb and some of us, like me, run leaner than that, we run thin in a peak for cruise and other phases of flight, but we have to have mixtures somewhere within that general area of ​​14 15 16 to 1 air fuel to power ratio in order for it to ultimately work and produce significant power, now the traditional way to get that air fuel mixture is something called carburetor.

The word carburetor comes from the French verb car beret, which actually means to add carbon to something or in the context of an engine. to add volatile hydrocarbons and that is the device that has historically and traditionally been used. It's not the only way we'll talk about it, but it's the traditional way engines have done this job of measuring to mix the right amount. fuel with air The first carburetors that were developed in the late 19th century were typically called evaporative carburetors. They use drips or wicks or similar mechanisms to allow the fuel to evaporate into a stream of air and that stream of air is then fed to the engine and because gasoline is probably quite volatile, it's not difficult to get it to evaporate when you go through a lot of air on him.

This was kind of a cool old diagram from a patent application from 1902, patent application for an evaporative carburetor, um, however, evaporative carburetors didn't. It doesn't run well unless the engine was operated at a constant rpm and power setting because if you were varying the engine speed or power setting, the carburetor didn't have the intelligence to vary the amount of fuel to correspond to the amount. of air that the engine was breathing to maintain a mixture in the fuel range, so evaporative carburetors generally worked only if the engine was running well, only if the engine was at constant rpm and power settings, and in fact, if you think In some of the really, really old World War I airplanes, they didn't really have a throttle.

You turned the engine on and off with the ignition at the beginning of the 20th century, which brought the development of what are called proportional carbonate carburetors, that is, carburetors that have the ability to measure the volume of air that the engine breathes and measure the proper amount of fuel in that airflow to maintain the proper air-fuel ratio that was sought and there were many of these metering carburetors developed this one, this image on the The screen is an old Hobson Beardmore zenith Bendix Stromberg carburetor. We'll look at Stromberg carburetors a little later, but the vast majority of contemporary GA engines, particularly the flat engines, the horizontally opposed engines that fly in the fleet now use a carburetor called a wonder, a marbled Hibbler carburetor.

It is by far the most common carburetor and is used by GA. It is a fairly old design. It was invented by a guy named George Gabler and Bert Pierce. Bert Pierce actually had a company called Marvel and he's actually the guy who invented Marvel Mystery Oil for a little trivia there and that's why the carburetors called Marvel's a blur because the co-inventor and the carburetor were originally developed by these two types for use in Indy racing cars and was used in Indianapolis racing cars from 1911 to 1935 and a variant of that racing carburetor was developed as an aircraft carburetor and continued to develop and is now the dominant carburetor in use by GA piston currently, the Gabler marble property has a carburetor.

It changed hands many times here are some of the companies that owned it, bore warner and then they sold it to Fassett who sold it to zenith precision. Airmotive had the rights to the Marvel Schaller carburetor for a long time and then they ended up becoming bellari carburetors and Finally in 2011 the design was acquired by a company called Marvel Shea Blurr LLC and that is the owner of the carburetor today. If you go to Marvel Marvel Gabler com, you will find their website. Now we'll spend a little time going over the basics. Marvel Scheidler carburetor design there are many different variants, but they all use the same basic design, they are floating type carburetors, most of them, but not all of them are high draft carburetors, this diagram, this cutaway diagram, is a kind of A simplified scheme is an updraft carburetor, which means that air enters at the bottom of the carburetor and exits at the top, so this is a carburetor designed to be mounted under an engine, at the bottom of a motor.

Marvell cable also has some side draft carburetors that are designed to mount on the back of the rim and the draft ones are called ma Cirie alpha mic and the side draft ones are called che Hotel alpha for horizontal but most of them They are updraft and that's what we'll look at now, the carburetors are essentially similar in design it's just directional only, the air flows a little differently so let's take a quick look at the various parts and pieces that make this carburetor works correctly. The carburetor basically has two main subsections, one called the flow chamber and another called the throttle body.

The float chamber basically works just like a toilet tank if you have ever worked on a toilet that has a float operated valve. in it to regulate the water level in the tank, this is more or less the way the float chamber and carburetor work. Obviously, if you're lucky, there's a hundred low levels of lead in that chamber and not water, but the fuel comes in through an inlet. It passes through a filter and then its flow into the float chamber is regulated by a needle valve which is operated by a float and as the chamber fills it raises the float and closes the needle valve and maintains the fuel level. at a desired level in the float chamber, as the fuel in that chamber is used, the float drops and a lot more fuel comes in to maintain the level in the float chamber, so that's pretty simple, the other one.

Part of the carburetor is the throttle body and the throttle body basically allows the air flow to the engine to pass through this throttle. Oh, throttle valve that's connected to the throttle control in the cockpit, so when you move the throttle in and out, it turns this. this butterfly and opens or closes it and regulates the amount of air flow that the engine must breathe on the side of the throttle body is a venturi and the venturi is a narrowing of the throttle body and this is due to the Bernoulli effect that creates . a low pressure area and how low the pressure is is a function of how much airflow goes through the carburetor and the venturi is what allows the carburetor to sense how much airflow goes through it, so the Venturi creates a low pressure area or suction if you want, the amount of suction is a function of the amount of airflow passing through the throttle body and strategically located within that area of ​​the venturi is a nozzle. discharge which is connected to the fuel from the float chamber and because the pressure inside the Venturi is less than the air pressure inside the float chamber.

Fuel is sucked from the float chamber through the nozzle and atomized into the air flow. The faster the airflow moves through the throttle body, the greater the suction and the more fuel it ends up being. aspirated through the nozzle that is what makes the carburetor proportional. It is through this venturi arrangement that it is able to measure the amount of air flow and provide an amount of fuel that is proportional to that air flow to maintain a constant air and fuel mixture. That's the basics. The basics of the carburetor, we'll talk about some little extra features.

Firstly there is an air bleeder which is a passage and the air at the top of the float chamber allows the air to mix with the fuel as it exits. As it is drawn through the discharge nozzle to aerate the fuel and make it atomize a little more efficiently in the air flow, there is a mixture needle which is another needle valve which in this case is controlled by the mixture control of The cockpit that allows you to regulate the speed at which fuel is allowed to flow to the discharge nozzle opens and closes that little passage that goes from the float chamber to the discharge nozzle, so it gives you some control over What will the mix be?

One problem with these carburetors is that when you rev ​​the engine to idle and the throttle closes, there is very little air flow through the carburetor, so there is very little suction and very little fuel is drawn into the intake stream. air; In fact, there is so little fuel that the engine, unable to idle, will shut down when you close the throttle, so it is necessary to add a little more fuel when the throttle is closed and that is accomplished by something called the throttle circuit. Idling, is another fuel path that allows fuel to pass through. a second small nozzle that is downstream of the throttle plate instead of upstream where the main discharge nozzle is and if you think about it, when the engine is idling and the throttle is closed there is very little air flow through the air flow through the carburetor, so there is very little suction at the lesion, but there is lots and lots of suction downstream of that closed throttle plate because the engine is desperately gasping for air and creating lots of suction, it's so if you have a manifold pressure gauge when the engine is idling, the manifold pressure gauge is very, very low, which indicates that there is a lot of suction in the net intake manifold, so it is that suction that is It is used to draw some additional fuel through this idle circuit and provide enough fuel for the engine to run smoothly.

The diagram came from an old marble carburetor manual, so excuse the quality of the graphic, but it shows that little idle wastegate on the downstream side of the throttle belt and also shows that there is another needle valve. in that circuit that allows you to adjust the amount of fuel that the engine receives when it is idling, that is the idle mixture control and the way we adjust it is with an enginehot, we leave it at idle and then very slowly pull the mixture control from full deck to idle cut and if the idle mixture is adjusted correctly you should get a small rpm increase of 25 to 50 rpm before it the engine becomes so lean that the engine shuts down.

If you don't get a 25 to 50 rpm boost, then the idle mixture is too lean and you need to open the needle valve a little with a small adjusting screw. If you get a boost of more than 50 rpm it means the idle is making your bit too rich and you need to close that needle valve to provide a slightly leaner idle mixture, but this is how we adjust the idle mixture by doing a Idle RPM increase test normally which should be done with the engine warm. Some of these carburetors also have something called an economizer circuit that provides a little extra fuel when the throttle is wide open to provide an extra rich mixture for takeoff, not all carbs have that other little gadget that some of the carbs have, but not all it's something called an accelerator pump, it's a small plunger style pump that is connected to the linkage and the design of the throttle so that if you suddenly open the throttle from closed throttle to open throttle very very quickly for example , when cornering, for example, if the accelerator pump will inject a little extra fuel at the end of the discharge. nozzle to prevent the engine from stumbling when accelerating quickly.

Good pilot technique says that you should not open the throttle quickly, you should make all throttle movements smoothly, but sometimes that happens and if we suddenly push the throttle quickly, we don't do it. I don't want the engine to stall, so the accelerator pump is there to provide a little burst of extra rich mixture during quick accelerations to keep the engine from stumbling, so that's pretty much all the little details of the carburetor design. marble one thing to mention that although the carburetor is a proportional carburetor, if you think about how it works, what it measures is the volume of air and it is putting in a proportional amount of fuel volume, to equal the air volume, that's what which is measured by suction and venturi, but the air-fuel ratio is actually a ratio that is by weight, not volume, so it is affected by the density of the air and, as you ascend to higher altitudes and the air density decreases, the carburetor will not do so automatically.

Feel that and reduce the weight of the fuel that's being dispensed, which has to be done manually with a manual mixture control and you know, like we talked about, there's a mixture control lever on the carburetor and it operates that little needle valve that gives you manually control the mixture but it is a manual function in that sense, the carburetor is not automatic because it is proportional to volume but what we need is proportional to weight so we have to adjust the carburetor mixture manually to take into account the altitude. There are actually some airplane carburetors, mostly onions, that have automatic mixture controls where there is an aneroid that senses altitude, but the wonderful Scheidler carburetors don't do that, so almost all of our piston GA airplanes have them. manual mixture control, so at least All flow type carburetors now, like the Marvel cable or virtually any other type of floating carburetor, have several inherent limitations.

First of all, if you think about it, they won't work very well in negative key maneuvers because the float chamber depends on gravity, so if you fly upside down this probably isn't the best measurement system in the world for your airplane. The second problem is that they are susceptible to carburetor icing in the venturi area and throttle plate. of the throttle body and that's because the air, as it passes through the throttle body and sprays fuel, that fuel evaporates and causes evaporative cooling of the air flow, just like you might use a swamp cooler to cool. an RFA and therefore if the air is humid and cooled by evaporation in the carburetor it can end up forming ice which can be a problem, it is a big problem on some engines like the Continental Oh 470 series which is in the Cessna 182 and some.

Other aircraft, Navy aircraft, etc., are famous for being very prone to carbohydrate ice. Carbureted Lycomings tend to be more resistant to carb icing because their carburetor is bolted to the engine's oil pan, so there's plenty of engine. By keeping the carburetor hot, icing can form in the carburetor and Lycoming, of course, doesn't happen as often as if you were flying a Continental Oh 470. Also, if you think about it, it's possible, but it's a little tricky. make one of these carburetors work with turbocharged engines where pressurized air is pumped into the engine because you would also have to reference the float chamber with pressurized air.

It is doable and there are actually a small handful of turbocharged engines that use these flow carburetors the Cessna TR 182 comes to mind it has a lycoming oh five forty with the turbocharger hanging in front of the marble table a carburetor but there aren't many in Generally, it's not very easy to get these carburetors to work properly with turbocharging, here's a good picture I just wanted to show to illustrate where the car ice forms. If you have ice in one of these carburetors, ice will tend to form in the venturi portion of the throttle body as well. at the throttle plate and as I mentioned, certain engines are more vulnerable to this than other engines, so how do we fix these various problems that these carburetors have, the car problem, the turbocharger problem, etc.?

Well, one solution is something called a boost carburetor. A boost carburetor is a carburetor where the discharge nozzle is downstream of the throttle valve instead of upstream, so fuel is injected into the airstream after of the throttle and after any venturi. Boost carburetors usually have a venturi because they need suction to feel how much air is passing through them, but they spray the fuel later in the game, after the air has passed through the venturi and the throttle valve. for evaporative cooling to occur. downstream of those things and no ice will form in the venturi or throttle bell now, to be able to do that you need some kind of system since you don't have a turi suction to suck. fuel through the discharge nozzle, you must pump fuel through the discharge nozzle and you must have some type of system to regulate the amount of fuel that is pumped to that nozzle and do it in a way that is proportional to the air flow , so First of all, it's a little complicated.

First, a pressure carburetor needs pressure, so it requires a fuel pump. You can't run a pressure carburetor with a gravity feed system and it requires a fairly complicated metering system that senses airflow and adjusts fuel flow. For the correct amount of fuel to come out, a proportional amount of fuel comes out of the discharge nozzle. This is a cutaway diagram of a pressure carburetor called a Stromberg pressure carburetor or Bendix Stromberg PS, these were popular during World War II and are still in use. In some radial engine aircraft, in fact, they are even used. I think there are some older Cessna 310s that had one of these things before they went to fuel injection, so let's take a look at how it works.

I don't have many of these in the GA fleet anymore, but it's a useful exercise to figure out how they work because it will lead to fuel injection, so anyway, the key to pressure carburetors is that the fuel is discharged backwaters. down the venturi and throttle body butterfly instead of upstream which eliminates the icing problem and for that to work there has to be a fuel pump that pumps pressurized fuel to the carburetor and then a regulator that determines how much fuel to send out of the discharge. mouthpiece, so I said that's where all the magic happens, we'll take a quick look at how the magic works and in this thing, if you look inside that little yellow box, you'll see that there are four chambers and they're marked B, D and C.

Here's a little expansion of that and kind of a schematic diagram of how it works. It is a four chamber regulator. Chambers A and B have air. Chambers C and D have fuel. There are two diaphragms in the system, one between the two fuel chambers and one between the two air chambers. Here's a quick overview of how it works. The throttle body has some little things called impact tubes. You will see them at the top. On the right side of this slide the bump tubes are like little pitot tubes that sense the airflow coming into the throttle body and therefore the airflow is then there is a venturi and there are some little ports Venturi suction pumps that experience suction and increase suction. the faster the air flow, the impact air from the Pitot tubes enters chamber A, the Venturi section enters chamber B and the difference between them, which is a function of the amount of air flow that passes through through the throttle body, it bypasses that little diaphragm. between a and B deflects it to the right so the more airflow there is the greater the force to the right and that diaphragm is connected to a small horizontal rod as you can see in the diagram on the other side of the system they are these two fuels.

The fuel from the fuel pump chambers goes to chamber D, that's called ungauged fuel pressure, which is just the fuel pressure from the pump. Fuel also goes from the pump to chamber C, but passes through a metering orifice that restricts the amount of fuel and causes a pressure. falls and the more fuel is drawn out, pressure not measured at D, we have fuel pressure measured at C and the difference between those two causes the diaphragm to apply a counterclockwise force on the small rod proportional to the amount of fuel flow. passing through the system, we have an air flow force pulling the rod to the right, we have a fuel flow force pulling the rod to the left and those two forces balance each other and reach equilibrium at a position that represents the optimal air and fuel mixture and that rod operates a small fuel metering valve that controls how much fuel will go to the fuel nozzles to the fuel discharge nozzle on the top of the throttle body, so it's a little complicated take a lot complicated, these carburetors require a little bit of high maintenance, they have a lot of moving parts and a lot of diaphragms that can leak and things like that, but it's a pretty complicated system, but what it does is it provides a metering of fuel to a fuel nozzle. discharge that is placed downstream of the venturi and a throttle butterfly so that the carburetor does not form ice.

Now there are some much simpler pressure carburetors that are not normally called pressure carburetors, they are called throttle body injection, but it is kind of synonymous and there are a couple of units that are quite popular on experimental aircraft or one from Rotech, one from Ellison and a couple of others that you can see. The images are much simpler than that Stromberg unit, but they basically accomplish the same thing. They inject fuel proportional to the airflow downstream of the throttle plate, and as far as I know, none of these units are certified. I'm not sure what the issues would be with certifying them since I say they do require fuel.

They pump if they don't have fuel pressure, of course the engine shuts down, so that may be a hindrance to too easy a certification, but anyway, these things are called throttle body injectors and effectively they are pressure carburetors, now the pressure carburetor throttle body. The injector is resolved and does not tend to freeze. They work fine with turbocharging if you want to use it that way, but one problem they don't solve is the fact that once the air/fuel mixture leaves one of these. things, whether it's a normal carburetor pressure carburetor throttle body injector, the air/fuel mixture has to go through a bunch of induction pipes to get from the throttle body to whatever type of metering device we're on. using even the intake ports of the cylinders and that induction pipe tends to make twists and turns and you have air with a lot of little droplets of fuel trying to get through those twists and turns, the air makes the twists and turns very easy, but the fuel does not tend to want to rotate so that there is centrifugal separation practically every time the manifold rotates and the result is that with any of these systems the distribution of the mixture between the cylinders is somewhat less than perfect,It is better in some engines than others, depending on how symmetrical and complicated or asymmetrical and complicated the induction system topology is, but you will not get perfect mixture distribution, that is, all cylinders will not work exactly with the same mixture.

This is more important today than it used to be because we tend to run aggressively lean and peaky mixes and stuff, and those who do that require the mix distribution to be very close to perfect, but still We have this problem with the induction system that causes poor mixture distribution now there are two ways to solve that problem: one is to create an induction system with tubes that are as short and straight as possible with a minimum number of twists and turns in In that sense, most carburetors like Cummings are much better than many carbureted Continentals because the Lycoming engine tends to have the carburetor right in the center of the oil pan with induction tubes radiating in a fairly symmetrical manner. , almost perfectly symmetrical, four-cylinder four, like combing a little. a little less than six cylinders and some of the Continental engines that have the carburetor in the rear and run the induction system through horizontal runners and vertical risers, have a big problem with centrifugal separation and like in a Cessna 182 that had one for many years, the rear cylinders always run lean, the front cylinders always run rich and it's just the nature of how the engine is designed, but another solution and a solution that has become more popular is to not inject fuel into the body Not everything is injected before the throttle plate like a carburetor, it is not injected after the throttle plate like a boost or TBI carburetor does, but instead the fuel is injected directly into the intake ports of each cylinder that way, you're pretty much guaranteed that we're going to have a nearly perfect mixture distribution in all the cylinders and if it doesn't, you can adjust the individual nozzles to make sure it's perfect, which makes your distribution perfect. , so an injection system you know looks like this, it has a kind of air and fuel control unit. similar to how we looked at say the booster carburetor, but instead of the fuel going to a discharge, a center discharge nozzle on the throttle body goes to a flow divider or Matt Fold, there are several different names for he, colloquial colloquialisms.

Often called a spider valve, it is usually located on top of the engine and divides the fuel into 4 or 6 equal portions and sends each portion through a small fuel line to a fuel nozzle that is located right at the port. intake port of each individual cylinder, so all those induction pipes now just have air running through them instead of an air/fuel mixture and the fuel is added to the air at the last minute in the cylinder intake port just outside the intake valve again. We are not injecting the fuel into the combustion chamber like a diesel, but instead we are injecting it into the airflow in the intake port just outside the intake valve, which allows for a more even distribution of the fuel, obviously, this system does too.

It is immune to carburetor icing. Works great with turbo charging. It has many advantages. There are two main systems currently in use or were used widely in the GA fleet, one is called Bendix RSA system and the other is called Continental Continuous Flow Fuel Injection system, the Bendix RSA system is used in all fuel injected engines like Cummings and in a small handful of odd continental engines that use that system in the vast majority of almost all fuel injected continental engines. Other than those, some of our weirdos use the Continental system, so let me quickly go over each of those two systems.

The Bendix RSA system is actually practically a second cousin to the Bendix Stromberg PS boost carburetor. It's actually a I think it's a direct descendant of it and it has a ton of things in common, which is why I spent so much time talking about the Stromberg PS carburetor because I won't have to talk about all that stuff again. now, but basically the Bendix RS system has a throttle body that has a throttle valve, it has a shock scoop which is like those shock tubes and the boost carburetor which is basically a pitot tube located in the middle.

In the throttle body, this can be seen in this diagram, the airflow goes from top to bottom instead of bottom to top, it has a venturi that provides a suction that is proportional to the amount of airflow and it has a paddle that provides such proportional pressure. amount of air flow and it has a throttle valve as usual, so it's kind of the throttle body is almost exactly the same as the Bendix Traum bird pressure carburetor, except there's no wastegate and then It has a fuel chamber. pressure regulator which is practically a second cousin to the four chamber fuel pressure regulator which is on the Stromberg pressure carburetor and we know how it works and it takes two air chambers for the fuel chambers and it uses pressurized air from the co-op impacts. and vacuum from the venturi and fuel from the pump and metered fuel that comes from the pump through a metering orifice and does all its push-pull magic in the little tube and delivers the correct amount of fuel, but in this case instead After the fuel goes to a discharge nozzle on the throttle body, it goes to a flow divider valve.

Continental tends to call it a manifold, as Homing tends to call it a flow divider. Val, but it's the same thing dividing the fuel into four six pieces and sending the pieces to the fuel injector nozzles. There is a mixture control valve that is usually attached to the side of the throttle body and has both throttle and mixture control inputs, so it allows manual adjustment of the mixture. Some versions of the Bendix RSA system that actually have automatic mixture control where there is an aneroid element mounted inside the throttle body that senses the density of the air and automatically adjusts the mixture so it doesn't have to be adjusted manually.

I don't come across many of those, but it's a pretty sophisticated system, very smart. Look, it's the kind of thing that nowadays you'd really like to do with a microprocessor and a bunch of sensors, but this was all designed in the '60s and it does everything with mechanical things and diaphragms and holes and stuff, it's amazing that they were able to create a system that is so smart again, the downside is that it's complicated, pretty high maintenance and If you have a problem with this system you pretty much have to take the fuel servo out and send it to a specialized shop. fuel meter you can set it up on a flow bench, test it and replace all the little ones. diaphragms and all the rings and so on, that's not something a mechanic in the field can do, it's a really specialized task, the Continental system is much simpler, much sillier so to speak, but much easier to maintain on the field without having to send things.

It doesn't actually measure airflow into the engine. It doesn't have impact blades or Venturi Zoar air chambers or diaphragms or anything like that. It's a really stupid system, so to speak, it works remarkably well, but when? Continental designed this system instead of trying to measure the amount of airflow entering the engine and then calculating or determining how much fuel should go with that airflow. It uses an approximation of how much airflow goes to the engines, it actually measures it and the approximation is something like this: If we know the RPM at which the engine spins and we know the throttle position that limits the airflow, then we can calculate what the airflow must have been.

We're not actually measuring it, we're just. deducing it from two variables of rpm and throttle position this is how the Continental system works and results in a much lower parts count so basically the way this system works is there is a fuel pump driven by the engine , it's a positive displacement vane pump that puts it has a fuel pressure that is proportional to the engine rpm, it has a little adjustable bypass valve for the idle end, so that if the airplane is, I mean, if the engine revs back to 600 rpm, it dumps a little extra fuel over what it normally would so the engine doesn't stall the same way an idle circuit does, but it basically generates a fuel pressure that is proportional to engine rpm, that fuel pressure then enters a fuel control unit that the fuel control unit simply has.

It has two valves, one that is connected to the mixture control and another that is connected to the accelerator butterfly and the fuel control unit regulates the part of that fuel that comes out of the pump and that must go to the engine and sends the rest. of the fuel back to the pump through a fuel return line and that's all there is to metering, no diaphragms, no impingement tubes, it's really a very, very crude system, very simple, but It actually works surprisingly well, the fuel and throttle body is just a tube with a throttle butterfly, it doesn't have a venturi, it doesn't have any kind of sensing of anything, it's just a tube with a throttle butterfly and that's it. fuel coming out of that fuel control. unit, which is a really fancy name for something, just has two valves to manually control the valves, which is called metered fuel pressure, which again is a function of engine rpm, throttle position, and throttle position. mix, and it goes to the manifold valve and it is divided into four or six pieces and they are sent to the fuel nozzles and that's it, that is the Continental system, a very simple system, the two good things about the Continental System, is like I say, it's a very dumb system but it's extremely reliable because it has a very low part count and it's its field. adjustable almost very, very rarely do you have to send something back for rework you can you can adjust it in the field it has four or five different adjustments that can be made to adjust the idle rpm idle mixture idle fuel pressure maximum power fuel pressure is It's very, very field adjustable and if anything you know half of it and you improve it and fine tune it, so it's a different approach.

It's a much dumber approach than the Bendix RSA system. Now I mentioned that you know it really would be. It would be nice if all this was done with the microprocessor and the sensors and stuff, and in the '90s, both continental homing and homing invested a lot of money in trying to do that, creating what are called FADEC or control systems. total authority digital engine like homing. system called epic epi. See, they did it in partnership with unison, the people who used to own slick magneto, the system didn't go anywhere, as far as I know, it's kind of a silent death.

Continental acquired a company called Eros Ants and that made for a pretty complicated fadec system. It's continental about the company taking the system through certification and rebranding it from Aero sans to power link. It is Continental's Power Link fadec system. In fact, they certified it on a lot of engines, but almost no one is using it in the best way. As far as I know, about the only airplane that uses this system is a small two-seat trainer called the Liberty XL. Thanks, nice little plane using a continental IO 240 engine with I guess it's called IO F 240 f. it's for Fadec and it has this Fay platform, but other than that FADEC hasn't been a commercial success at all and whether Continental continues with this is anyone's guess, but the hope is that in the future there will be more and more engines. will be converted to theta ik control, there are several experimental FedEx systems flying on Humboldt aircraft and it remains to be seen what happens with a certified engine in this area.

I think I'll stop here, the, the, the other. The sub kick I'd love to talk about is Diesel's, but we'll save that for another webinar, so Tim, that's all I'm going to cover tonight. We can open it from Singh for some questions. Very good, Mark, Hi Mike, interesting presentation, very, very interesting, thank you. We have some interesting questions that have already arrived, so let's get into it. Walt asks why their various updraft side draft carburetors, etc., is it just a fitment issue inside the engine compartment? Yes. that's exactly what an updraft carburetor is, which is what most of them are designed to mount under the engine and which works well for most single engine airplanes, for airplanes where the engine compartment doesn't It can be so deep and for some twins. when they try to keep the cell motor nice and flat toFor aerodynamic purposes it may be advantageous to mount the carburetor behind the engine rather than under the engine and in that case a side draft carburetor works better as I say, the wonderful Kevlar does both sides. draft and draft models, but updraft models are much more commonly seen.

Donald wonders if a fuel injected engine has an accelerator pump. No, I've never seen an accelerator pump or anything like that on a fuel injected engine, but again, the reason. for an accelerator pump is that when you pour the calls into the fuel, you're turning me into shit, you know three feet away from where it's needed and it takes a while to go through all the pipes to get to the cylinders. With fuel injection, the fuel is sent exactly where it is needed, so there is really no delay when you accelerate in a fuel injected engine, the fuel is there immediately.

Thomas wonders: Does hobli fuel injection eliminate the need for manual guidance? When banking at altitude, there is generally a version of the Continental System that is called that has a fuel pump that is an altitude compensating fuel pump. It was actually developed for the beach for use in bonanzas and barons and the fuel pump has an aneroid dome that senses ambient pressure and automatically adjusts the fuel pump output to compensate for altitude or outside ambient pressure that varies with the altitude. That system turned out to have some problems and Beech had some recriminations and decided they wanted to go back to the old manually tilted stuff, so it only appeared for a few years in Beach's production and then cooled off.

It wasn't actually a bad system, but they had some problems with it, but most continental systems and all As far as I know, Bendix RSA systems, that's not all, but most Bendix RSA systems have have to be manually adjusted with altitude. We mentioned that there is a version of the Bendix RSA system that has altitude compensation. Actually, I haven't. crash into it, but there must be some aircraft that uses it, but I haven't broken into it and there is a version of the Continental System that has an altitude compensation fuel pump and occasionally you run into that, but most systems fuel injection valves have to be manually adjusted to the altitude hmm.

Marty wonders why fuel injected engines are so hard to hot start. That is a good question. My personal experience is that if you know the correct starting procedure, they are not that picky, but I know a lot of people have problems with not starting the engine and the main reason is that they tend to flood the engine, put too much fuel in it with gas engines. fuel injection when you, when you prime the engine, you prime it by applying pressure and squirting fuel through the fuel, not the fuel injector nozzles, and it's very, very easy to flood a fuel injected engine if you're too generous with it. the primer.

I have a rule myself and I've been flying fuel injected airplanes for about forty years, but I have a rule. that I developed, which never primes the engine unless the propeller is spinning. I never prime first and then crank because it's too easy to flood the engine so I always start cranking the engine and then gradually apply some fuel and when the fuel to air ratio reaches that magic number the engine cranks and if it does You do it that way it's much harder to flood the engine, but I think it's mostly a pilot technique. A couple of people have asked us about the Rotax 912.

The Bing engine and carburetor they have and the Jabiru engines which have a large carburetor and no mixture controls. I'm wondering if you could talk a little bit about its design. No, that's above my pay grade. I don't know anything about the Jabiru. engines, except you have to stand upside down. I know that the Rotax engines with the Bing carburetor have those carburetors that run automatically and sense ambient pressure and there is no mixture control in the cabin and of course, Of course Rotax is moving more and more towards injection engines with control gradual and I think that most of the engines sold today are the series with electronic injection systems, but no, I really can't go. in more details, it never worked on a Rotex powered airplane, so I don't have any, no blood on my hands in the Rotex department.

Scott is now wondering why a Bendix fuel injector still needs manual mixture control if it is already metering fuel. based on airflow changes, again, it's the same reason we talked about the carburetor, what it measures is the volume of air through the carburetor, not the weight of the air through the carburetor, and to maintain a constant mixture, it should be proportional to weight rather than volume, unless there is some type of aneroid that compensates the air pressure in order to calculate the air density, whether it is a Bendix RSA injection system, a Stromberg pressure carburetor or a simple flow type. carburetor those things are proportional in terms of volume but not in terms of weight and the difference between volume and weight is basically the density of the air that varies with altitude, so we have to delimit them manually, except for the relatively small number of systems that that have automatic tilt with some type of animal assist system, Timothy asks how often or how you can tell when a carburetor needs a good check, when, when it starts, when the engine starts to run rough and shows signs of being a fuel. related problem, it's probably time to consider checking the carburetor.

I mean, the first thing you want to do is make sure there are no induction leaks and that the idle mixture is adjusted correctly on these carbs, pretty much the only adjustment is idle. mix the rest, you can't really adjust it and if you have removed it, you know the obvious cause of the leaks and idle mixture jesseman and the engine is still having fuel related problems, then it's time to take the carburetor out and send it away. take it to a fuel metering location, you can put it on a flow bench and find out what's going on with it.

Darrell wonders what can be done with a stock carburetor that runs too lean at full throttle, even with a mixture set to full rich. I mean, the first thing you need to do is make sure the fuel pressure at the carburetor inlet is within specifications. I mean, it's possible that there is some kind of problem with the fuel system, whether it's a faulty fuel pump or some kind. of restriction in the fuel lines or whatever, if the fuel pressure at the carburetor inlet is what it should be, then all you can do is send the carburetor and have them install it on a bench so they can adjust the jet size of the main jet and the carburetor, but you can't really do it very well in the field, it's the kind of thing that requires a flow bench to get right, so you really need to send the carburetor to Kent. wondering about continental fuel injection, you explained that the engine fuel pump senses rpm, how does this work with the backup electric fuel pump?

Well it doesn't work with the rear backup electric fuel pump and if the only time you would use the backup pump The fuel pump works fine on many continental systems, on many of them the auxiliary electric pump is a two speed pump with a low speed position, a high speed position, and a low speed position, does not provide enough fuel pressure to operate. the motor on is only there for steam suppression but the high speed position of some of the auxiliary pumps and if it is just a single speed pump then the only speed is high and it is there simply as a backup in case of the engine pushes the fuel.

The pump, the pump failed, but the engine-driven fuel pump, by the way, almost never fails. Those pumps are as bulletproof as you can get, but in the event that the fuel pump fails, the engine will run off the electric pump. however, the electric one, but if you're running the engine with the electric pump and something we do in the simulator all the time, well, when I used to do my flight training on flight safety, they simulated driven fuel pump failures. by the engine, which As I said, never happened in the real airplane and you would have to fly with the electric pump, but since the electric pump can't detect the engine rpm, you will end up getting too active on the mixture control if you reduce the rpm.

You also have to pull back the mixture control or the engine will flood because it doesn't know the electric pump doesn't know the RPM dropped the same way the engine driven pump does, so the answer is basically you drive it all manually if you are using just the electric car, the good news is that never happens because I literally have almost never heard of a continental engine turbine pump failing, there was a Cessna twin accident. of the Grand Canyon that occurred many, many years ago and it was not actually a pump failure, but the shaft that drove the pump became disengaged from the pump and there was an announcement to make sure that all the shafts were replaced with the correct ones and but it never happens so it's not really a problem.

Marc wonders. I have a Marvel Schebler ma - 4 - 5 carb on a Lycoming O-360 at 4M during wide open throttle with the Ox fuel pump on. I have noticed the fuel pressure. it is lower than in reduced power cruise settings on takeoff I see about 2 to 3 psi and in cruise I see 4 to 5 psi with the Ox pump off why is there such a difference in fuel pressure? I can't answer that question, it's, it's, it's A function of the porter pump, the engine's turbine pump has a check valve that if so, if the porter pump generates more fuel pressure than the driven pump through the engine, then the fuel from the ox pump can pass through the engine unobstructed. pump driven, carbs are not particularly sensitive to fuel pressure as long as the fuel pressure reaches the minimum, that's all you need because the carburetor has this needle valve that regulates the amount of fuel flow into the carburetor. float chamber and has the minimum fuel pressure it needs, but anything above that is just gravy, so as long as the fuel pressure doesn't drop below the bottom of the green, you know, I wouldn't really worry . about the fuel pressure going down or up a little when you turn on the pump motor pan, I mean the electric pump.

James asks what vapor lock is and what causes it affects carbureted engines, they are only injected. Vapor blocking is basically where a line that is supposed to contain liquid fuel lines up with evaporated fuel vapors and if the line, if that line, for example, is a line that provides fuel to a pump, the pumps are designed to pump liquid, no It doesn't pump gasoline very well, so the pump may stop pumping if there is vapor in the fuel lines going to the fuel nozzles, the engine may stumble, it's more of a problem with injected engines only because There are many more fuel lines in injection engines and in particular injection engines tend to have fuel lines that run through the top of the engine to the flow divider and then exit the flow divided by all the nozzles and Upstairs is a pretty warm spot, especially when the airplane is sitting on the ground and you're trying to start it, it can be a problem with any airplane, it tends to be more of a problem with fuel injected airplanes and the solution, first of all , is anytime there is a fuel line. in a hot area, put some type of heat shield over it to keep the fuel line cool and secondly, if you experience vapor lock in flight, do something to force liquid fuel into that line, turn on a pump For example, a Cessna 210 has a fairly famous vapor lock problem where there are a few header tanks and the route of each of them on each side of the cabin that can be filled with foam and if the tank is filled with fawni the engine shuts down due to April blocking and the solution on the 210 is to simply switch to the opposite side where the tank is not full of foam so either switch tanks or turn on a pump booster or both to solve the problem, but it tends to This will happen more on fuel injected airplanes just because there are more places for the vapor to lock in to form my fuel injected airplanes, just more pipes and stuff.

Brant wonders if the fuel filter in the carb fuel ball area will be in service at 8am? m. Q, yes, and Richard wonders, is there a monitored fuel injection system?electronically in the future for certified airplanes similar to our cars? Well the arrow and the one I guess is now called Powerlink is very similar to two car systems so it doesn't use a continuous flow. fuel nozzles that have a small electric solenoid and therefore the fuel is injected at just the right time instead of continuously and everything is controlled by microprocessors and such that also control the ignition and vary the timing and everything That's like that, so the eros ants system or the Cannell Powerlink system is the closest thing to a car type system, as we are currently discussing here from Larry, he only says that the initial Bonanza are models 47 to 56 with the e 22 5- The engine 8 has a pressure carburetor and a question from Donald, so let's go back, no, no, no, sorry.

Walt's question, how critical is the fuel delivery pressure for a pressurized carburetor on the 35 Bonanza? I don't know the exact specifications. which is obviously much more critical than for a flow carburetor because the pressure carburetor doesn't really have any type of fuel reserve, the windshield wiper does have a floating carburetor, it depends on the continuous pressure of the fuel. All I have to do is look it up in the type of certificate data sheet to find out what the minimum fuel inlet pressure is. I can probably do this easily since I can write the certificate data sheet for the motor.

Yeah, Donald says let's get back to everyone else's question. What is his technique for starting a fuel injected engine right after shutting it off for gas. What I don't know well, it differs if it is Bendix RSA or Continental. I fly, you know, a Continental-powered airplane, by the way, in my experience. The worst time and in terms of warm start is not right after turning it off, but about 20 minutes after turning it off. If you turn off the engine and then turn it on immediately, things haven't had a chance to warm up, but if you turn it off at the self-service pump and take 20 minutes to pump fuel into your plane, then turn it back on, that's the worst condition and there are many different tricks to improve hot starting, for example if you have a bonanza that you want you want to open the hood doors to let the heat out if you have an airplane that only has a fuel filler door on the top of the hood, it is a good idea to open the fuel filler door again to allow hot air to escape if you can choose which direction to park the airplane if it has flaps, it is good to park one tail into the wind, which is the direction Opposite where most people normally park for airflow. through the calibration fins and moves through the engine compartment in the opposite direction as it does in flight from the bottom of the engine to the top of the engine to expel hot air above the engine through the air inlets at the front. of the colony with the Continental system, if you are really deeply soaked in heat, the trick with Continental engines is to bring the mixture control to idle, put the throttle to the floor and then run the boost pump on high for about half a minute , that?

What it does is pass cold fuel from the fuel tanks through the pump through the fuel control unit, it will not reach the engine because the mixture controls the idle cut, so one hundred percent of the fuel it will basically return through the return lines. back to the pump to cool it down, then back to the tank and if you run it that way for about half a minute it will basically cool everything in the system except the line that goes from the fuel control unit to the manifold. valve the nozzles to bleed most of the vapor from the system and then at that point you turn the mixture control to full rich and give the boost pump a little beep right up to the point where you start to see a little bit of boost pressure. fuel and that cleans the line to the manifold valve and then you turn it on, don't use anything. prime because it will flood it and that is an almost surefire technique for hot starting a deep heat injected Continental like a Cummings.

I don't have that much experience with Lycoming injected engines that normally start with the mixture control at idle. cut anyway and then once the engine catches you you quickly advance the mixture control to keep the engine running but I'm not that adept at not starting with lycoming because I've been flying a little higher for a long time, what? OK? Roberts wonders if Holman recommends cleaning injectors every 200 hours for leaded fuel. Is it appropriate or is there a risk of contaminating the injector? It is best to monitor cylinder head temperatures to determine when it is best to clean the injectors.

I have researched that topic in some depth. so I can say with some authority that if you have a digital engine monitor with CNG and egt probes on each cylinder, my advice is to never call out the fuel nozzles unless the engine monitor indicates that you have a clogged fuel nozzle. 10 In order not to get dirty over time, there is a very good reason for them to have a very good solvent running through them practically 24/7 when the plane is ready and my experience is that the The vast majority of the time, a fuel nozzle becomes partially or completely clogged.

It occurs shortly after maintenance and is a maintenance where the fuel system was opened for some reason or another and some foreign material entered the fuel system. When the fuel system is closed, there are three successive levels of filtration. of the fuel there is a kind of coarse filter in the pickup in the tank, there is a finer filter in the gas silencer here and there is a super super fine filter in the fuel control unit, so any particles that are in the fuel will be trapped. on one of those filters and it's not going to reach the nozzles, if something is clogging them it's probably because there's a rubber hose very, very late in the system that's falling apart internally or, more commonly, because a mechanic Disassembled something in the fuel system. and I accidentally allowed some grease or something that shouldn't be there to get into the fuel system and I have had two serious nozzle clogging problems on my 3/10 in the 30 years I have owned that airplane.

Both happened right after maintenance, I never had a problem other than that, so my advice is to leave the fuel nozzles alone unless they show some indication on the engine monitor that you have a cylinder that is running too lean. Near the end here, let's answer Bill's question: can there be a fuel injection and icing system around the venturi? First of all, not in the continent system. There is no venturi in the appendix. RSA system. There is a venturi. It's not as deep as we say. event areas in the carburetor and is upstream of where the fuel is, so there will be no icing.

Airplanes are now being injected that have the potential to generate impact ice, for example, in my Cessna. 310, the induction air from the engines passes through some large holes in the leading edge of the short wings and that air then forms a right angle band to exit to the engines and if I'm flying through moisture. Right there, at the right temperature, ice can develop in those ducts and I actually had a case where I had an ice buildup there and I had an altitude change to melt it, it's not very common, but there is something equivalent. to carbohydrate icing, which is icing that is induced through evaporative cooling of the fuel, it is there, it is possible to get some ice and inject and inject aircraft, but it is very, very rare and the conditions have to be exactly right for Mike's, please take a moment and share your final thoughts with everyone who has tuned in.

I saw over 600 in our spotlight here, great turnout, interesting topic, outstanding, that's fantastic, as always, if you're not. I'm already on my mailing list, sign up for the newsletter by going to Savvy Aviation Comm and hit a little button to subscribe to the newsletter at the top of the screen or stick around for the post-webinar survey that Tim is going to post and check out . Either way, you will join our mailing list, we send a monthly newsletter with all kinds of maintenance-oriented material. The manifesto for my first book, which came out just before AirVenture 2014, is still available on Amazon and my second book, I'm very happy. to announce it's almost finished I'm working on the alphabetical index at the end it's a monster it's a 500 page book and it should be on sale on Amazon June 4th and it will definitely be available at AirVenture this year what was my goal for the last one year, it's been a lot of work and finally the next one, the next three webinars and I got the date wrong, Tim, we decided to change the date from July 4th and it was the 8th, right on the 10th, so they were actually going to celebrate it on Tuesday the 10th, ok, sorry, I should have changed that slide, but June 6 and July 10, please ignore what's on the slide and then Tim doesn't know. about this yet, but on my August webinar we usually push it back a week because the first Wednesday in August I'm still soaking my head in AirVenture, so I've got it scheduled for August 8, Tim, unless you want to negotiate a change That sounds good to me, ok, so take note of that.

I'll send you the little blurb about what it will be about, but those are the next ones and that's all I have. I'm delighted that we had 600 people and this was a benefit fund webinar. Thanks, Mike. It was a fun webinar, very informative and educational for me. I know a lot of people commented. Excellent webinar. Thank you very much for providing us with this information. To everyone who tuned in tonight, thank you so much for joining us. We hope to have you next week when Professor Paul Shuck will talk about the four forces of flight, the magic of flight anyway, have a great night everyone, thank you all so much for Tuning in thank you all so much, see you next month comes.