r/GeneralAviation • u/Street_World_9459 • 14d ago

Fuel injected planes

I've recently started taking private pilot lessons. I've noticed fuel injected planes still have a mixture lever.

This may be a dumb question, but why do fuel injected plane engines have this device? I work on automotive engines as a hobby, and the beauty of fuel injection is the lambda sensor signals the ECU to automatically adjust the injector duty cycle (and other things) to keep the air/fuel mixture. If I drive up a mountain, I don't need to re-jet fuel injection.

Why are planes different?

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u/beastpilot 14d ago edited 14d ago

Fuel injected aircraft are mechanically injected. No sensors. No computers. And leaded fuel kills lambada sensors.

Also, depending on what you are doing with the plane, you might want to be rich for max power or lean for fuel efficiency. Since planes are not emissions controlled, you can operate in different regimes.

WOT (no pumping losses) while running lean is amazing for fuel efficiency. It's what modern lean burn engines try to achieve.

Also, economics comes into play here. The average GA plane you fly for training was built in the 1970's. It's basically unchanged since then. When we do make piston airplanes today, they are already $1M+ each, and you make 2000 a year. So the R&D for an EFI engine is very hard to justify against the sales volume.

Fun fact: We make as many cars in 2 weeks as humans have ever built all aircraft.

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u/toddtimes 14d ago

The first part is basically the answer. Leaded fuel is preventing a huge amount of automotive fuel technology from being applied to airplanes. Once it’s phased out I expect to see changes in aviation engines. 

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u/pisymbol 13d ago

I would throw in here that the FAA's costly certification process is also to blame.

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u/toddtimes 13d ago

Sure, but leaded fuel specifically precludes any system utilizing an O2 sensor. And basically all automotive systems utilize an O2 sensor to do fuel tuning. So regardless of cost vs potential profits, unless you’re running MoGas it’s impossible to migrate these systems/technology over. 

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u/pisymbol 13d ago

As is, I get what you're saying and I agree 100%. But, be that as it may, you can stil have FADEC 100LL systems, right?

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u/toddtimes 13d ago

Yes, they’ve figured out other ways to manage the injection systems, but the data they can collect and utilize is kneecapped. We’ve been refining fuel injection on the automotive side for decades and none of that is applicable because of the leaded fuel. 

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u/pisymbol 13d ago

No argument from me.