SonexBuilders.net

As suggested by the moderation in the “Flying over the Sierra Thread”, we should split off the AeroCarb/AeroInjector topic in its own thread given the subject regularly pops up in other threads.
So here it is, the big AeroCarb/AeroInjector thread.

I would very much like to hear from ALL people on this forum flying behind, or ever having flown behind an AeroCarb/AeroInjector, both POSITIVE AND NEGATIVE experiences/opinions.

I've attached a poll to the topic as well.

Personally I have not flown behind my AeroCarb so I'm not voting myself in the topic, however, I’ll quote my post from the other thread which pretty much explains where I stand on the subject:

I have an AeroCarb and I am very aware many people struggle to get it running right.
However, I also know there are many, many, many more who don't have issues with it and they are usually much less vocal (busy flying probably).
I personally still like the simplicity of the setup and no other carb beats the AeroCarb on that, so I am going to try my AeroCarb and see how it goes.
But, I'm not going to put tens of hours into it though, what you save in simplicity in setup is lost in many hours fiddling with the thing trying to get it to run right.
If I can't get it to run right following the instructions within a reasonable time frame, I'll get a Rotec and turn the AeroCarb into an ashtray or something.

Deleted

I have just over sixty hours on my jab 3300 with aerocarb and have no issues with it. It took four adjustments during the first five hours to get it adjusted. I have not had to readjust for summer or winter flying but I do see higher egt's in colder weather due to running leaner. My fuel system is exaclty as described in the Jabiru engine installation manual with the exception of the the line from the fuel valve to the gascolator is steel braided teflon hose instead of the hard line.

Granted I only have about 10 hours behind my aerocarb but so far so good. I have only had to make two adjustments from the factory recomended initial setting. One was after the first flight when I found it needed to be a bit richer to keep the EGT's down and a second adjustment when the weather turned cold. I did have an issue with the needle wanting to move when I tightened down the set screw but the factory provided a very simple solution that fixed the problem.

The complaints with the aerocarb that I have seen seem to be foucused on trying to get it to run a perfect mixture at all power and atlitude settings and not necessarily issues with it failing in flight or keeping the engine from starting. The simplicity of the aerocarb tends to make it so that it is a very reliable carb (once the engine starts it wants to keep running) but very hard to get setup so you don't have to use the mixture when flying. Personally I set the carb just a bit on the rich side and then adjust as needed when flying by using the mixture knob. I imagine you would see some of the same behaviors of being too lean or too rich at different power settings in an old cessna if you put CHT and EGT digital readouts on all cylinders on those engines as well. It is just that we never had this type of technology back then so we blissfully flew around either burning more gas than needed or toasting our exhaust valves. If there is one thing the sonex has taught me it is what the mixture knob is for and how to use it.

Keith

My Onex 107 Tricycle has been flying 50 hours with the Aeroinjector and I have been working to get it tuned in most of that time. I started with the #2 needle, as delivered, and it worked as per the book setup for the first 20 hours. Then it went lean at the top end and I had to change up to the #2 1/2 needle. The problem with both needles was when the top end, wot, was adjusted for max rpm the idle was so rich I had to adjust the mixture almost to cutoff to get a smooth idle. Throw in a case of the burps and it was a handful to keep running.
Obviously, the #2 and #2 1/2 needles are not linier with the slide opening and adjusting in small increments was not working. I pulled the needle holder out and started measuring. I found that my needle holder had .025 play in the ball joint. That is nearly 1/2 turn of the 3/8 X 16 set screw. They are suggesting 1/8 of a turn, .0075 adjustments here. A new needle holder was made using a disc on the end instead of a ball so the play/clearance could be eliminated. That fixed one problem. Next was the needle taper. A builder in Florida suggested trying the #3 needle. Richer? Really? I did, and found that I could adjust for a perfect idle first, with a small amount of mixture adjustment left, and then work on wot with small adjustments. I'm not sure the quality control of the needles is that great. The overall length of my four needles varied .040 along with the position of the taper in relation to the needle holder. I couldn't measure the taper it's self. It's important to mark the bottom of the needle with a file to accuratly start the first installation. A wide felt marker is not good enough. I, like the builder in Florida, find the #3 needle to be more linear with the slide opening than the "leaner" needles. When it is adjusted for a smooth idle there is enough left at the top end for the higher rpms. I think the variation in dimensional control of the needle holders and needles is the contributing problem with the varity of tuning frustrations we are having.

I built ONEX 350NX and have 20 hrs on it so far. I took the aero-injector out of the box installed it as per- manual never touched the needle that came installed from the factory it performs just fine.
The only thing I've had to adjust is the idle stop, still playing with it to get set at 900- 1000 rpm.The other thing, I went with a bigger K-N airfilter after trying a K-N filter the same size as the paper
factory filter as i couldn't get the 3000 RPM on climb-out.Same problem with the paper filter.With the bigger K-N I'm now getting the 3000 RPM on climb-out. So you can say I'm happy with the aero-injector.

I have 40 hours on a Jabiru 2200 Sonex fitted with an earlier Aerocarb. It uses the lighter flex cable for pull open operation on the aerovee throttle quadrant. (current flex cable is a little thicker)
Mixture is a vernier control.
It took about 4 flights to get it adjusted where I was happy with it. It was too lean to begin with and has been progressively richened to keep EGTs under control. It could probably go another 1/8-1/4 turn richer. Idle is no problem at present.. probably why it needs to be a bit richer!
At present on takeoff the fuel flow is about 21 litres per hour at 3100 rpm. The throttle often needs to be backed off a little if the EGTs get too high.
In cruise I have been leaning to 15-16 litres per hour at 2750-2850 rpm for around 100-105 Kts IAS.
Last weekend with OAT 30°C at 3500' feet I had a couple of hiccups when leaned a little too much (about 15 litres per hour).
Richening a little solved that.
I have steel braided line throughout, with fire sleeve, an Usher gascolator and a Red Fuel cube transducer. The fuel drip tray below the carb and a heat shield around the red cube is covered with reflective heat shield. I also use a hot air box with a larger K&N filter.
A small NACA vent on the left hand cowl ports air to the lower corner where the air filter and gascolator sit. A larger opening under the gascolator with a small deflector helps pull that air out of the cowl past the unit.
I have used the hot air box on occasion even though its not technically required, just a bit of insurance on a long idle descent on a humid conditions.
The biggest problem I have is heat soak after sitting on the ground post flight.
It can take some judicious mixture work to get started again if its still hot under the bonnet.
Park brake on, throttle cracked a little more than usual, and push the mixture in whilst cranking usually gets it going.
All in all I am very happy with my setup.

Hey guys,

I put some thoughts down regarding this topic. It drags on for a while, so I apologize in advance for the length.

Jeff

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I've tuned several AeroCarbs and AeroInjectors, both my own and others, and have formulated a few conclusions over time. First off, small things make a big difference. Because of this, it' s very difficult to compare people's experiences directly because their setups often contain numerous small differences that may be having major impacts on their ability to tune.

The list of "small things" that comes to mind includes:

- Fuel system specifics (line routing, gascolator or filter, proximity of the fuel line to the exhaust pipes, location of the flow sensor). I think the best thing you can do is to simplify the routing as much as possible and keep flow rate as high as possible (i.e. reduce constrictions). Pay attention to the FWF instructions Sonex publishes (no high spots in line, no place for vapor to form or collect, consider ditching the gascolator). The fuel flow sensor location seems to cause trouble as well. I mount mine right after the tank shutoff valve and it reads perfectly and stays cool there, as opposed to mounting it close to the carb where it vibrates, heats up, and may collect vapor).

- Cowling setup (size of inlets, "smoothness" of intake openings, size of the exhaust openings, extra openings like NACA vents, internal blast tubes, size of the oil cooler inlet) - the cowling specifics affect the airflow inside the cowl, which has a big impact on the carb itself. High or low pressure into the carb throat affects airflow into the engine, and thus mixture. A "hot bubble" that sits over the carb or fuel line can heat soak the line, create burps or change mixtures at random times. Too much pressure in the lower part of the cowl (i.e. extra inlets, oversized oil cooler inlet, or too small exhaust outlets) stifles cooling flow and messes up the carb (this is frustrating because it will tune fine on the ground but change tuning once in flight).

- Air filter (size and type, clean vs dirty, even high vs low density altitude). Sonex recommends tuning without the filter. If you get it tuned right without a filter, then add the filter and things change, you probably need to change something to improve airflow thru the filter.

- Needle selection (old brass needles that came with the early AeroCarbs vs the new SS needles, diameter of the needles, diameter of the orifice in the slide itself, "smoothness" of the taper cut into the needle). I've measured several old needles and some of them mic smaller than the newer SS needles. This will make tuning hard because a sloppy fit of the needle in the orifice will always allow fuel to flow around the perimeter of the needle itself, making the engine run rich at idle. The quality of the taper also matters - a rough "step" where the taper begins, milling ridges in the machined surface, or other "imperfections" will change how fuel flows through the carb. Don't believe me? Take two needles of the same value and slightly modify one (sand or polish the surface, round over a corner or two, something seemingly small and innocent) and you'll see that that needle will tune differently. The new AeroInjectors use a nylon (?) bushing insert at the orifice to provide a tighter more consistent fit around the needle. The carb is difficult to tune if the fit between the orifice and needle is "sloppy", say from the wear of a few hundred hours run time and vibration.

- Technique. Everyone has their preferred technique to tell whether their carb is running rich or lean, and it can vary quite a bit. You can't go with just one or two indicators (like plug color, max RPM, black exhaust or smoke, EGT, EGT rise on leaning, or general feel of the engine), you need to consider multiple indicators and merge them all into a comprehensive assessment of where you are in the tuning range. Consider the case of being *very* rich. You go to WOT and see your EGT's going over redline. You conclude that you are overly lean because of the high temps, and you richen even further. Had you confirmed with something else (leaned the mixture knob while at WOT, observed smoothness and max RPM while doing so), you might reach a different conclusion, like the excessively rich mixture is still burning in the exhaust manifold and that's why the EGT's are high.

Best thing to do while tuning is to play with the mixture knob at various throttle settings (idle, 1-2 mid-range settings, WOT) and see how the engine reacts. If you get overly lean the engine will cut out abruptly. If you can lean the knob by 50% and see the engine running better or no real visible change, you're likely still rich. If the engine cuts out before you reach the 50% point, you might be close to the sweet-spot and have to proceed carefully.

The reason for this requires some visualization. The mixture lever is like a rotating ball valve. As the valve is rotated fuel flow is reduced, but not in a linear fashion. The first portion (0-25%) of the mixture throw has little effect on flow, and is somewhat linear in response. Then as the mixture is further rotated (25%-60%), it starts to choke the flow down in a somewhat linear in response. The last portion of the throw rapidly cuts off flow to almost nothing. It's almost impossible to find the exact right amount of leaning when you are in the last portion of the mixture throw because it tends to go from OK-flow to not-enough with just the smallest change.

So here's my abbreviated tuning method. Start with the recommended needle (#2.5 AeroVee, #3 Jabiru 3300). Inspect it carefully for manufacturing defects and how it fits into the orifice in the carb body. Make sure when you re-install it in the carb that you set it like the manual states (flat towards the engine, set screw in the proper location and tight). Lock the needle carrier with the set screw, and note whether the carrier "creeps" when you tighten the set screw (you have to watch the needle carefully to tell if it's happening). Once all this is done, then install the carb onto the engine. Run the engine at idle or slightly higher rpm and lean with the mixture knob. It's almost certainly rich, but note how much you have to lean the knob to get it running decently, and when the engine cuts out (ideally around the 75% point of the mixture knob throw, at slightly higher than idle rpm). Repeat this for a mid-rpm point and note the smooth-running point and cut-out point. You may need to lean slightly (1/8 turn) just to get to this point if you can still lean past 75% or so without cutting out). Only then try to run a high rpm or WOT. Got to WOT and then note the max rpm. Then lean the mixture knob and note the response (rpm increase, smoothness increase, or cut out point). It won't take more than a few seconds to make these observations and determine if you are still rich at WOT. Adjust the needle by 1/8 turn (or less if you're getting close) and try again. When you get to the point that you only need to lean by 25% or so before the engine starts to bog down or cut out, you're getting close and might be ready to high-speed-taxi test / fly it to further assess. If at any point running at WOT that you can't lean the engine slightly to improve things and smooth things out, you might be too lean already and need to re-assess. The final fine-tuning will come after a few test flights.

The AeroCarb / AeroInjector is a simple device, but you can't expect it to be totally automatic. You trade the operational simplicity of a bing/zenith/marvel (where you don't really touch it in flight) for the dirt-simple mechanics of the aerocarb and the ability to lean easily in flight. The aerocarb works with gravity flow, resists ice, is easy to mount on the engine and feed air into (no air box, carb heat, cobra head), and is inexpensive. Is it perfect? No. But it does work well if you understand it and eliminate potential problems before hand.

Jeff,

One of the concerns I have with the aeroinjector is that even with all the research and experience you've had with it, your engine quit on your first flight(s) on short final. I haven't watched your video recently, but I seem to remember you commenting that the engine stopping was not unexpected.

It would be great if you could explain why you thought that might happen, and how you corrected it before subsequent flights.

Right now I'm considering spending approx $1000 on a rotec TBI that I may not need in hopes of preventing such a thing. At this point it seems like a small price to pay for safey, and time spent....if time spent tuning a carb is valued in dollars.

Sorry if I've mis-stated the facts. I look forward to being set straight.

Paul

Hi All,

I have a aerocarb on my Jab 3300. After initial flights, I did spend a quality weekend or two taking a new needle and following in the footsteps of others to shape it so that I have a good idle and that I don't melt EGT wise at take off WOT. This step made all the difference for me. I also found I needed more travel out of my throttle quad to let enough fuel in mixture wise and I learned quite a lot through the process. Patience is a virtue.

Mine starts in cold weather and in warm weather no matter what. It is scary it starts so well. Once configured, it is just sort of works for me. I do have to richen/lean a little across summer and winter and that is fine.

I think you just need to accept its strength and weaknesses, but it seems to work fine for me.

Cheers,

Andrew
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