We’ve done this before – examples.
The lead in 100LL makes it impossible to use an oxygen sensor for automatic leaning. One would have to lean for peak EGT, but that is a non monotonic curve so a different and more complicated technique is needed. These have been developed for various things e.g. extracting the max power from a solar panel.
Ultimately, as with so much in GA, the market will vote to not bother because anybody even half smart can use the magic red lever 
Same with electronic ignition. And those less than half smart pay the extra, which is what always happens in life
172driver wrote:
The Rotax 912s in the Tecnam P2006T have automatic mixture control, there is no mixture lever (or other control) in the cockpit. They do, however, have chokes which are engaged for cold starting on the ground.
That’s a description of Bing constant velocity (CV) motorcycle carbs used on the 912 since the ‘80s, not FADEC. The CV design concept was originated by SU in the UK and has been used widely since the 1920s. It does have a degree of automatic mixture control but I’m surprised it is enough to provide for operation in a twin engined plane with what must be a pretty high ceiling. Web surfing indicates that the P2006T does regularly have carb ice in some people’s service but that the carb heat is effective.
Mooney_Driver wrote:
The automotive industry has been going with automated mixture for decades. Last time I saw a choke was a while ago… At least that should be possible.
What a modern carburettor or fuel injection system in an automotive setting tries to do is maintain close to stoichiometric combustion over a range of different throttle/speed/power situations.
Whether automated or manual, that is not the same thing at all as the mixture adjustment we perform with air-cooled aero engines. With our engines we run well rich of stoichiometric for take-off because the air-cooled design simply could not dissipate the heat generated by full-throttle sea-level stoichiometric operation (which would also tend to make them ping).
Automotive engines spend relatively little time at high power outputs and generally have liquid cooling systems able to absorb any amount of heat the engine might need to dissipate from its cylinder head(s), as well as variable ignition timing.
So when people say their car does the mixture automatically, they are only half right because unlike an aeroplane pilot it is automatically setting the same mixture (or nearly the same mixture) all the time (or nearly all the time). An automatic mixture system for a Lyco/Conti would need to do more than that.
Incidentally, the C90 in our PA17 happens to have ‘auto mixture’. The mixture control arm on the carburettor is wire locked full-rich because no-one ever bothered to set it up with a cable.
Graham wrote:
Incidentally, the C90 in our PA17 happens to have ‘auto mixture’. The mixture control arm on the carburettor is wire locked full-rich because no-one ever bothered to set it up with a cable.
Very common on Stromberg carbs used on early Continental engines, largely because the mixture control is an unconventional half effort controlling float bowl air pressure. It can FWIW be made to function acceptably for cruise flight leaning should you ever have the need. A detented push-pull control makes it easier because the sensitivity is high and the response time slow. I used it on my Luscombe because it otherwise ran very rich at its 10K ft absolute ceiling.
I’ve done a substantial amount of work on motorcycle electronic fuel injection, map tuning etc. 1990s era digital systems used on air cooled engines included a crude altitude compensation chart that subtracted fuel uniformly under all conditions of throttle and rpm with increasing altitude, as measured by an absolute pressure transducer. It works but not to the degree of fidelity or reliability required for aircraft. The fuel map is similarly offset as a function of ambient temp and CHT. The three factors plus some others interact and the result is a bit approximate in comparison to what we can do manually in aircraft. The compromise that makes it work is to run mostly a little rich. One of the main reasons motorcycles have largely moved to liquid cooling is to provide a useable cylinder head temperature signal in the form of a single coolant temperature sensor. Once you start going down this road the complexity piles up and you end up with a car engine, which despite my current involvement in car style engines being used in aircraft is not at all what I want in my own plane.
As Peter points out, there is a difference between spending somebody else’s money and spending your own. For the latter and for decades of long term ownership, the market says simple is good.
Silvaire wrote:
Very common on Stromberg carbs used on early Continental engines, largely because the mixture control is an unconventional half effort controlling float bowl air pressure. It can FWIW be made to function acceptably for cruise flight leaning should you ever have the need. A detented push-pull control makes it easier because the sensitivity is high and the response time slow. I used it on my Luscombe because it otherwise ran very rich at its 10K ft absolute ceiling.
Ours actually has a Marvel-Schebler carburettor.
Putting in a mixture control cable is on my to-do list.
The Marvel would serve the C90 a lot better with the mixture control working. What one would guess happened on your Vagabond is that it came with a Stromberg, with mixture wired as some Stormbergs were from the factory, and no cockpit mixture control. Piper was trying to save every penny on those planes. Then when somebody installed the Marvel they didn’t want to bother with installing the cockpit control.
Oh come on folks, stop tinkering on the nano level with your leaning stuff 
Look what Sabine puts on the table and let’s get these excellent brains on this forum to get to work on a big scale. If we win, it goes to Peter, so EuroGA can run without any kind contributions well in to the next century, if there are people around to read it.
Btw, I always enjoy Sabine’s work. No nonsense and numbers based arguments.
Malibuflyer wrote:
I’m not aware of any car that has a manual override for the automated mixture.
No, because it doesn’t need it. On the rest, Graham has explained what actually goes on there.
On the airplane side, Rotax does too. Without fall back I believe, so the question is if you actually need it.
Energy Ration per Earth-Human? If you want to use more than your allocation, you must buy it from someone who doesn’t need it.
eBay might handle the exchange.
I’ve been criticized for my Carbon Capture activity – letting the weeds and grass grow in my garden.
It isn’t difficult to come up with a simple leaning mechanism which sort of does something.
Like the fuel servos which have the extra diaphragm for altitude compensation, and which occassionally stop the engine (with a very rich cut) when the diaphragm perforates… the pilot has to know about it and rapidly reach for the mixture lever and lean it right back.
In the Rotax market, few will notice or care if a plane gets to FL100 when it could do FL120. But if you want a system which optimises the performance – say the difference between achieving FL160 and FL180 – then the only thing which would beat the mixture lever would be a proper “ECU”, software controlled.
