Too much fuel flow???

[Fastcapy]

-----

[Sonex1517]

To head the conversation in a different direction, I am a technical geek.

As a prospective AeroVee builder, I ask where is the data?

I read opinions and experiences in both directions, and about lots of things. In fact, there was a fatal accident years ago on a Jabiru powered Sonex that sounds awfully like a burp, yet all I read is "AeroVee burp."

If the system requires constant adjustment, can we measure or record the data and share it?

So to propose solutions, I ask - how can we, as builders, owners, pilots, and experimenters, make this more of a known quantity? How can we really and truly gather data and facts to compare?

I have little answers to my questions but since our Sonex Builders and Pilots Foundation is devoted to safety and building the community, this looks like something we could try to gather real world factual data on, IF we can find a data set or way to measure it.

Any suggestions?

Robbie Culver
Sonex 1517
N1517S now reserved


Sent from my iPad using Tapatalk HD

[MichaelFarley56]

Great questions Mike. I'll be the first to admit that I'm not anywhere near an expert on the AeroInjector or how to get it "perfect." I've been flying behind mine for almost 2 years and close to 100 hours now, and have to admit it took me a little while to tune things to my satisfaction.

Ultimately, what I've personally found on my engine is that the standard, straight taper on the #2 needle I use isn't quite optimal. Even though it's not terrible, at some point I'm going to experiment with the needle itself a little, just like Jeff Schultz described on his webpage. At this point I'm having good luck by tuning the needle to wide open throttle EGT readings to get them where I want them, and then using the mixture needle for other adjustments. Like the factory and everyone else has said, a small turn on that needle can make a big difference. I wouldn't make more than 1/4 turn adjustments at a time. Also, I do agree that there's a difference between having the cowling on and off. To get a good initial "rough" tune leave the cowling off, but once you're into the fine tuning steps the cowling needs to be in place.

For me personally, my goal is to run my engine at wide open throttle (either in a climb or tied down well) and see my hottest EGT run up to around 1200 degrees. I used to see 1300-1350, but the factory told me that's too lean for climb which I agree with. I'd really like to see 1100-1200 on the climb but things get too rich in cruise and during descent. So, when I tune my needle, that's my goal. It was important for me to lean while flying my Waiex that I couldn't simply push the mixture to full rich for the whole flight like the old Cessna trainers; I generally make a mixture adjustment after every big power change. Leaned for taxi, full rich on takeoff, leaned just a little in cruise, leaned some more during approach, etc. etc.... For me that's not a safety concern, just something to get used to.

I completely understand the concern with this Florida accident and know I don't need to say it, but remember an engine stumble can be a lot of things. Proper fuel delivery can certainly be an issue, but so can the ignition system, spark plugs, air filter, a valve issue, etc. I landed last weekend and did an ignition check as I taxied in since it felt like my engine just wasn't running quite as smooth as normal. Turned out my engine ran really bad on the secondary ignition which I traced to a bad secondary ignition coil. I just installed a new one yesterday and even though I didn't fly, it ran much better during a ground run. Point is, let's be patient on that accident before we jump to conclusions. It may very well have been a carb issue, but at this point we just don't know.

Robbie I couldn't agree more with the need for data. This is going to be a tough one though; I'm not sure how many people can quantify carb issues (or any other issue for that matter). You asked me about "burps" on my AeroVee; I had a lot early on which I ultimately traced to an older style MGL fuel flow sensor causing blockage issues. Once I removed that, I haven't had a single one since.

I wish there was a way to measure this data. The only thing I can come up with to start is to create a poll to see who all is using AeroCarbs/AeroInjectors and see how many people are having or have had issues. It doesn't give us much info though. This is a tough one.

[radfordc]

Mike is dead on.

My aerocarb hasn't been touched in over 6 years, so constant tweeking isn't needed once you get it right. At full throttle on takeoff and climb my EGTs peak around 1300, which might be just a touch lean but hasn't caused any problem that I can see. Naturally, the actual EGT varies depending on weather conditions....cooler in the summer and hotter in the winter. I generally only use full power for a couple of minutes and then reduce rpm a bit for the rest of the climb...this keeps the CHTs below redline. I like to keep my CHTs below 385. At full gross weight when I need all the power available I let the CHTs climb to 410 without worrying too much.

In cruise I maintain rpm at about 3100 (plus or minus 50) and lean the mixture as much as possible until the CHT stabilizes in the 350-375 range. This generally gives an EGT around 1325. My fuel burn is a little under 5 gal/hr at this setting. If I choose to run with a richer mixture I can get the CHTs in the low 300s, but burn more gas doing it and don't think it offers any advantage.

For landing I richen the mixture, but not full rich. My engine doesn't idle well at full rich mixture when its hot. After landing I often lean the mixture to almost idle cutoff to get the smoothest, lowest idle (800-1000 rpm).

Charlie Radford, N168SX

[fastj22]

Getting back to the original question of flow and pressure. I'm no engineer, but I don't think having 35 gal/hour flow vs say 20 gal/hour will increase pressure. Its a gravity feed system so the pressure is dictated by that. Both flows will choke down to the inlet on the carb anyways, which I if I recall is 1/8 NPT.

One thing that did give me fits when I was initially tuning my Aerocarb was I accidentally installed the needle backwards (flat side towards filter) once. That really made the engine run poorly at anything above half throttle. Took a while to figure that out with a few calls to Kerry.

[radfordc]

So, a thought that crossed my mind was that maybe since the aeroinjector is not flow regulated that I may be drowning the carb with fuel. At higher rpms the engine can digest it, but at the lower rpms it is flooding it out causing a really rich mixture.

The Aerocarb does have a flow regulator. It's the mixture control. I does exactly what you want it to do...reduce the flow of fuel into the carb when less fuel is needed. The Aerocarb has been described as a sophisticated fuel leak...somewhat accurate.

With a gravity flow system, the fuel pressure at the carb depends on the fuel "head" in the tank. The flow rate depends on how large a tube the gas is flowing through. If the fuel hose were several inches in diameter the fuel flow would be 100s of gal/hr.

I was thinking I could test this out by running it with the fuel valve in a semi closed state, but with another winter storm and then at least another week of frigid temps I won't get to it for awhile and thought I would get some opinions here beforehand.

How does closing the fuel valve partially differ from closing the mixture valve?

[radfordc]

I guess I don't mind leaning a bit on taxi and at cruise. But I didn't realize I was going to have to chase the thing all over the place all the time. I have experience in a lot of aircraft and while have had to lean out at taxi I have never seen one that needs to be chased all over the place during all phases of flight.

It seems that the Aerocarb is demanding more of your attention than you want to deal with. There are certainly options. Check out Great Plains Aircraft: http://www.greatplainsas.com/sccarb.html $430 (and a new carb heat system) and your troubles are over. You can probably sell the Aerocarb for most of what it cost.

I looked for what a Rotec TBI cost and they don't list it. Maybe its: If you have to ask you can't afford it?

One of the first links under a Google search for the Rotec carb is an NTSB accident report that says: "A witness reported that he spoke to the pilot shortly before the accident. He stated that the pilot was going to fly the accident airplane on a maintenance test flight because he had recently installed a throttle body fuel injection system in place of the original carburetor. The pilot had also installed new engine baffles and a Vans RV-4 intake scoop.

The witness observed the pilot conduct the pre-takeoff and engine run-up procedures. He reported that the engine hesitated and failed to run up to full RPM on the first attempt. The engine “went flat and lost RPM” on the second attempt. He reported that the third run-up was successful and the engine attained full RPM. He reported the takeoff roll was normal with the engine developing full power. The airplane rotated normally and climbed straight ahead to about 500 – 600 feet above ground level (agl). The airplane entered a left crosswind turn. The witness reported that he observed a “brief puff” of dark, black smoke coming from the exhaust. The airplane, which was now about 1/2 mile from the airport, started to lose altitude as it continued in a left turn. The airplane continued in a left bank until it was headed in a westerly direction. The witness stated, “The aircraft entered a full stall, probably 150 to 200 feet off the ground.”

[Fastcapy]

-----

[rizzz]

Talking about Jeff Shultz, and the AeroInjector.
If you look at the pictures of his latest Sonex build #1374, he did go with the AeroInjector,
at least that means that he was happy enough with his first AeroInjector to choose one again for his second Sonex.

There isn't much explanation with the photo's of his second build but from what I can see it looks like he hasn't put a gascolator in this time, he did have one in his first Sonex.
This picture is straight from his website, here is a drain point visible but no gascolator:

[radfordc]

Also, thats where my thinking that limiting the flow into the carb may help. It would limit the amount of fuel into the carb and would maybe not require the mixture needle to be so far closed right on the edge of cut-off. Like you said restricting the diameter of the hose reduces flow from the tank, So brings my train of thought that if i restrict flow into the carb I can keep the mixture needle open a tad more on the low end.

If you restrict the fuel flow to the carb to make the idle leaner it will also make the top end leaner at the same time. You would have to juggle both the mixture control and the fuel valve at the same time.

The correct thing to do is to find a needle that provides the proper full throttle mixture while also providing an acceptable idle mixture. Most folks say that its necessary to have the idle mixture somewhat rich...but it sounds like yours is way too much. You might consider buying some new needles and see if one of them does better. It's just possible that all needles have some small variations that make one better than the other. Or you could do the trick of adding solder to the portion of the needle that controls the idle and then begin filing the solder away in small increments until you get the sweet spot.