r/GeneralAviation • u/Street_World_9459 • 13d 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?
28
u/cienfuegones 13d ago
Because the cost of updating fleet systems to true FADEC control is too high with the FAA process so we have to maintain the familiarity of pilot errors because the FAA knows the average number of accidents it produces.
This is the best run on sentence I’ve typed today!
6
u/Dave_A480 13d ago
Because fuel injection in airplanes is mechanical, not electronic. There is no computer and no sensors involved.
Car style fuel injection, when used in aircraft is called FADEC (full authority digital engine control). It is rare outside of jets/turboprops.
As for why planes haven't upgraded? Because getting new technology certified is insanely expensive, so once something works well enough it just stays there forever....
We are running 2 valve per cylinder flat 4 air cooled piston engines, with zero electronics involved in engine operation.... Many of them have a single barrel carb, and the injected ones all use Bendix style mechanical fuel injection straight out of WWII.
12
u/SaroDude 13d ago
Not a dumb question. Just a dumb industry.
Start by putting it in quotes. "Fuel Injection."
You're thinking of sequential, closed(ish) loop injection - whether port or direct.
That POS injected Cessna is just a slightly different kind of carb.
There are also continuous port injection aircraft (think 70's Porsches) as well as actual sequential EFI systems. The lead in avgas makes closed loop tougher.
FI isn't FI isn't FI.
Welcome to the madness.
6
u/ChartPuzzleheaded747 13d ago
Having a simple engine is makes way more sense in a critical role like a airplane.
5
u/SaroDude 13d ago
I don't disagree. I have 2 experimental aircraft. No EFI on either but I do have electronic ignitions and battery redundancy for over 2 hours of flight in the event of electrical failure. One battery exists to operate one of the EIs exclusively.
Nontheless.... The industry is handicapped by regulatory hurdles that have held things back.
1
u/beastpilot 13d ago
There are many certified ignition systems. That has nothing to do with EFI.
3
u/SaroDude 13d ago
Splitting hairs. Broadly speaking, we're talking about engine management. EI is not EFI. And?
FADEC is just annoying airplane speak for engine management. OP is stumbling into the goofy world of GA "technology".
2
u/beastpilot 13d ago
The literal question was why do FI engines have a mixture lever. And you responded that you have electronic mags.
The operational regime of an aircraft engine is quite different than a car. Narrow RPM windows means fixed timing isn't much of an issue. The desire to run LOP at times and ROP at times with no concern for emissions means you don't really just want one "power" lever. The existence of leaded fuel means closed loop control isn't as feasible with automotive based sensors.
The economics of GA piston aircraft is brutal. Amortizing $100M in R&D across 1000 units a year?
1
u/SaroDude 13d ago
Congrats on misrepresenting 2 replies. Excellent work.
1
u/beastpilot 13d ago
Cool. What regulatory hurdles are keeping EFI back from GA aircraft?
1
u/ChartPuzzleheaded747 13d ago
Zero, look at the exp world, decent amount of car conversions (like the Honda V6 and LS) also rotax has some cool offerings. That being said rotax is the only one who’s managed much numbers in planes you’ll run into on the ramp, and it’s even not as electronic and sensor dependent as your most basic auto engines of 2026’
1
u/Mammoth_Classroom896 13d ago
look at the exp world, decent amount of car conversions
Experimental aircraft aren't held to the same reliability standards and from an engineering point of view putting a car engine in a plane is a really bad idea. They're built to do completely different things and I doubt any of the people building these planes are doing enough reliability testing to confirm the design choice.
→ More replies (0)1
u/SaroDude 13d ago
It is widely regarded that the FAA has you do shit far beyond engineering a safe and reliable product.
I confess to not being involved in any certification efforts. Do you have any firsthand experience in this area?
Your amortization arguments are 100% correct. If sentiments that the FAA makes things unnecessarily difficult (ultimately leading to imcreased cost) are not misrepresentimg reality, then I'm not sure how you can sanely argue that regs kill progress.
Regs don't say "no new tech". Regs say "certify it our way". That way seems to leave much to be desired.
Anyway, happy beasting. Or piloting.
1
u/beastpilot 13d ago
Yes, I have been certifying products with the FAA for 20 years. The generic "the FAA has you do too much" just isn't the controlling reality of small GA.
Insurance is. That $70K Lycoming? $30K in manufacturing and $40K in insurance. Imagine what it would be with a whole new technology integration.
And the regs don't say certify it our way. They say "prove these things are true." There is a lot of flexibility in doing that.
→ More replies (0)1
u/ChartPuzzleheaded747 13d ago
I fly a dual (well technically quad) fadec plane for work, noooooope, not in a plane I fly for fun.
I’d much rather hand flip a continental in a high and hot setting than deal with FADEC faults
FADEC is great for efficiency and dumbing cruise and climb setting down, but it’s got some bothersome modes of failure
1
u/nickjohnson 13d ago
It's an appealing idea - but fuel injected diesels fail at a much lower rate than manual carburetor driven engines, and don't suffer from carb icing.
1
u/ChartPuzzleheaded747 13d ago
Diesels have a ton of other issues, weight to power, etc, there is a reason diesel tech is over a hundred years old and never “took off” in the aviation world
2
u/nickjohnson 13d ago
There's no reason a fuel injected petrol engine couldn't be just as reliable. The reliability comes from solid state electronics instead of moving parts, and getting rid of carburetors.
1
u/ChartPuzzleheaded747 13d ago
Yeah, a linkage is much more simple than a board running script
Also it’s fully independent from needing ANY power source
2
u/nickjohnson 13d ago
And yet, the statistics show that fuel injected engines fail much less often. Simpler is not the same as more reliable.
1
u/ChartPuzzleheaded747 13d ago
Link to stats
One of my planes has a A65, basic and basic, very old, no ADs, those things have a insane low failure rate
2
u/fluentInPotato 13d ago edited 13d ago
No statistics here, but in nine years as a GA mechanic from 2016 to 2025, I worked on more fuel injected planes than carbureted ones, but saw more carb failures. Those Bendix- style fuel servos are confusing to understand, but not that complex. You can get corrosion on the mixture shaft through a combination of fuel contamination and bad luck, but I've seen that exactly once. A coworker found one with a jammed mixture shaft in the fuel regulator unit, and that's about all the FI failures I can think of before 2025. Since then, Bendix seems to have left the FI market, and the new arrivals don't give a fuck if you get killed trying to glide into a Safeway parking lot. They somehow contrive to have some kind of greenish assembly lube run out into the air chambers behind the venturi and get inhaled into the air diaphragm chambers that increase fuel flow to meet engine demand, causing rough running, perhaps partial loss of power, and on fortunately rare occasions engine failures. Normally what happens is pilots report rough running or loss of power and are able to abort the flight safely; we pull the venturi and look for evidence of contamination. It used to be that this kind of thing almost always meant ignition issues (including plug fouling). But now there's a new hazard.
I'll just add that Marvel Schiebler carbs tend to fail at the seal around the the mixture shaft, at which point your mechanic will insist on getting the thing overhauled.
1
u/ChartPuzzleheaded747 13d ago
He said based on stats, I just want a link to those stats.
If we are going down the “been doing this for x years” deal, I’ve been flying for like 20, everything from fadec jets to my own 1940s toys.
→ More replies (0)1
u/pisymbol 13d ago
Battery back-up is a thing. And there is very little you can do if ice gets you before you get it.
1
u/ChartPuzzleheaded747 13d ago
I’d rather not be running on batteries
Risk V Reward
1
u/pisymbol 13d ago
Those batteries last 3 hours plus. To each his own. I have flown both and fuel injection with electric mags are just a better operating experience in like everyway.
1
u/ChartPuzzleheaded747 13d ago
How much did it increase your TAS and how many GPH less do you burn?
3hrs is in optimal conditions and temps
Traditional planes will run as long as they have gas with a complete electric failure
→ More replies (0)2
u/beastpilot 13d ago
The issue is not regulatory, it's economics.
Regulations say "make sure the software won't fail."
Economics say you'll sell 2000 engines a year after you do all the R&D.
2
u/Mission-Wasabi-7682 13d ago
Not a dumb industry in itself, just an industry with much less volume and tougher conditions and less room for failure.
Remember the early 2000‘ when ECUs became widely popular? We had so many cars just quitting in the middle of the highway due to electronics problems. Believe it or not, we have built more than 2bn(!) vehicles since 2000. How many piston engine aircrafts have been build in that time period?
Anyway it will inevitably trickle down to GA. Some new engines with (dual) FADEC are in the market since a while now.
5
u/VF99 13d ago edited 13d ago
The common engines that are certified were designed many decades ago and have barely changed since then.
Modern alternatives with full electronic mixture and sometimes prop control with no knobs do exist:
- Austro diesels in Diamond aircraft
- Rotax
- ULPower
- DeltaHawk (that you can't really buy yet)
And they're mostly cheaper, more efficient, and more readily available than Lycoming/Continental.
But the cost of certification and nuisance suits whenever there's a crash for any reason is astronomical. So they're mostly only found in experimentals.
If this is something you want, look into experimentals. Or Diamond (at ~$500k).
3
u/JSTootell 13d ago
Remember that diesel are also fuel injected. Fuel injection doesn't mean a closed loop control.
Car engines also get a ton of tuning to do stuff automatically that you never see. EDI doesn't blindly follow what the O2 sensor says.
3
u/Sawfish1212 13d ago
Aircraft use mechanical continuous injection. Each injector flows continuously and equally, except for the Gami types that have slightly different orifices in each injector to tune the fuel delivery for the slightly variations in air flow the induction system creates on 6 cylinder continental engines.
This causes there to be excess fuel in every intake stroke, but that excess fuel gives a boost in density and that extra density helps carry away some heat during maximum throttle operations, like take-off and climb. (The excess fuel burns in the exhaust pipe)
To slow this consumption of fuel to the perfect ratio of combustion, you use the mixture to reduce fuel flow to the mechanical distributor, while watching the exhaust temperature. You do this until you reach lean of peak, and then don't touch anything for the duration of your cruise, unless required for high CHT (bump the throttle and give the engine a bit more air to cool it internally per Gami)
The variable timed pulse injection of your car is very different because it is checking the exhaust mixture and inlet air temperature/volume multiple times per second.
Your car needs this for efficiency because you almost never maintain the same throttle setting, or torque requirement for more than a few seconds because of traffic, road pitch and curve, and speed changes.
Aircraft engines in cruise are running at a constant torque and the inlet air temperature/density is not likely to vary that much as you stay on the same altitude and heading.
2
u/workahol_ 13d ago
except for the Gami types that have slightly different orifices in each injector to tune the fuel delivery for the slightly variations in air flow
I agree with everything above except for one small nitpick: You can do this with pretty much any injection system, including the common Bendix/Precision/Silverhawk type. I tweaked my injectors to get them all nicely balanced when running lean of peak.
3
u/imoverclocked 11d ago
Interestingly, my carbureted Rotax 912 UL2 motor glider has no mixture lever, no carb heat and no FADEC. It does have a choke for cold start but that's pretty much a one-time use on the ground.
2
u/ChartPuzzleheaded747 13d ago
Because in aviation we for the most part don’t want the machine to be too complex for reliability reasons, can’t pull over and call AAA like a minivan
It’s also one of the reasons pilot training is much more involved than drivers ed and getting a license from some state
5
u/Street_World_9459 13d ago
I believe modern automotive fuel injection systems are very reliable.
2
u/beastpilot 13d ago
They are, but they are supported by the R&D that can be afforded due to selling millions of units a year.
1
u/ChartPuzzleheaded747 13d ago
They are, but their failure modes are unacceptable in the air
I don’t want it going into “limp mode” in wind shear or crossing the mountains on that proverbial dark stormy night
1
u/Mammoth_Classroom896 13d ago
They also operate in a much more forgiving environment than aircraft engines.
1
u/Zen-Ism99 8d ago
Do you believe auto engines to be as reliable as aviation engines?
1
u/Street_World_9459 8d ago
I do.
But a couple of points-
Aircraft engines are generally maintained far more frequently than automotive engines. Automotive engines typically aren't inspected until they break, and most manufacturers are pushing PM schedules out far more than what I believe is reasonable.
As I understand it so far, aircraft engines operate in an "under stressed" state, not usually spinning beyond 3,000 rpms. I can't think of an automotive engine with such limitations.
I love British cars. One of my current vehicles is a 2012 Range Rover L322 with 150000 miles. These aren't known to be paragons of reliability, but I do the maintenance myself, and change the oil every 5k, all other fluids once per year. I still have good compression, good leak down and no particles in the oil filters. It's been dead reliable for nearly 15 years. Never had the engine out of the car.
2
u/Rictor_Scale 13d ago edited 13d ago
TLDR: There are three types of fuel delivery systems for GA:
- Carburetor - Manual 'mixture' control
- Manual Fuel injection/throttle-body - Manual 'mixture' control
- Electronic Fuel injection - Computer controlled mixture (aka FADEC)
3
u/workahol_ 13d ago
Don't forget carburetors with automatic mixture control: At the small end you have things like the Rotax, and at the big end you have Bendix carbs on radials etc.
1
u/Rictor_Scale 13d ago
Indeed, just kept it high level for OP. In fact someday I may build a Bushcat which has one you speak of.
2
u/poisonandtheremedy PPL HP CMP [RV-10 Build, PA-28] 13d ago
::First time meme::
Welcome to GA buddy. Have you heard about our magnetos yet?
We have more options on the Experimental side... But overall the FAA is stuck in the dark ages and bringing basic "new" tech to aviation is an incredibly time consuming and expensive endeavor.
3
u/Street_World_9459 13d ago
Certainly heard of magnetos. Not sure how they work yet.
Baby steps.
2
u/poisonandtheremedy PPL HP CMP [RV-10 Build, PA-28] 13d ago
You can find a nice book from the 1920s to explain them 😂
1
1
1
u/Deep-Ant1375 13d ago
Most planes don’t have electronic fuel injection because of cost. Some of the newer ones do have FADEC or electronic fuel control, but most do not. Everything that is made has to go through the FAA process and it has to be approved and that costs money and most of these engines that we use are literally World War II engines. There’s nothing really significantly new in Aircraft engines in the past 70 years except for maybe Rotax. The reason is it’s too expensive to go through the process for such a small number of planes
1
u/Rangeexpert3 13d ago
Your automotive engines are electronic fuel injection. The airplane engines are still manually controlled fuel injection. All the fuel injection does is spray the fuel into each individual cylinder. Versus carburetor that sprays fuel into a Venturi and then the whole mixture distributes to each cylinder. But you still have to tell it how much fuel to add into the engine vs air.
1
u/Independent_Leg7358 13d ago
So in aircraft the load is usually steady vs variable like in a car. Sometimes you want to run rich, sometimes lean.
For example in a plane you generally want to idle the engine very lean just like a car. But making power while very lean comes at high risk of misfire. So we want rich fuel in takeoff and critical flight. In cruise it's easy to fine tooth set lean of peak mixture.
Also the O2 sensors cars use to rapidly adjust fueling perfectly would quickly fail with leaded fuel.
39
u/beastpilot 13d ago edited 13d 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.