Why use carburetors on aircraft engines... at all?

Discussion in 'General Experimental Aviation Questions' started by choppergirl, Sep 16, 2016.

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  1. Sep 18, 2016 #41

    Dana

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    Philosophically, a good point, I never thought of it that way.

    But practically, you can fill a fuel tank a lot faster than you can charge your battery on a cross country.

    Dana
     
  2. Sep 18, 2016 #42

    Himat

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    Practicalities and cost.
    What it boils down to when all the flair and subjective considerations are removed. Just changing the battery instead of charging it is quick too, if replacement batteries are available.
     
  3. Sep 24, 2016 #43

    SVSUSteve

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    I wasn't talking about the antiques. I was referring to folks who are building today.

    And, yes, the Amish are a great bunch. I grew up in an area with a few of them and they are wonderful people.
     
  4. Sep 24, 2016 #44

    SVSUSteve

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    Nice ad hominem there TFF. How about you actually rebut it on its face instead of pleading to emotion?

    You presume that I dislike flying. You are incorrect. Granted, I find cruise flight to be as boring as driving down a straight highway but I am not afraid of nor anti-aviation (actually quite the opposite). I just believe that if you have an identified problem that regularly kills people and the "We've always done it this way" approach to managing it doesn't work but have an off the shelf solution for new aircraft, it's foolish to not take it when we have the ability to do so.

    If someone wants to accept the risk for themselves, fine but I do have some reservations about using outdated technology for hauling around innocent and oblivious persons in aircraft because each fatality simply adds to body count that each crash produces that they NIMBY and truly anti-aviation assholes use against us. Let's face it, someone wiping out their kids and wife garners a ton more sympathy and negative publicity than some random pilot punching a hole in a cornfield on his own. My only agenda is to get people to use the leeway we have to advance safety. It's like the old saying about "How about you use your head for something other than a hat rack?".
     
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  5. Sep 24, 2016 #45

    StarJar

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    It's not just antiques. To me, an electrical system on a Hummel Ultra Cruiser, or a Legal Eagle, would be undesirable....Alternator, battery, starter; all heavy stuff. Almost 10% of the empty weight.
     
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  6. Sep 24, 2016 #46

    SVSUSteve

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    True. I stand corrected but I will admit that I don't even think of those planes unless someone mentions them. They simply don't even register on my "radar"....probably because A) I can't think of having seen one in person except at Oshkosh and B) they don't involve any form of flying that has appealed to me in the past ten or fifteen years.
     
  7. Sep 24, 2016 #47

    StarJar

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    Oh that's a shame IMO. I know of some airline pilots who like to fly those type of planes, just to feel in touch with pure and simple aviation.
    The ultralight I have planned, I could cruise it from here at the Mexican/CA border to visit family members in Las Vegas, San Louis Obispo, and Lake Elsinore. I've flown nice comfortable GA planes, but a plane like the Ultra Cruiser, flying lower and slower would be some serious casual fun IMO.
    The trick is to keep that 1/2 VW healthy, and pick your path wisely.
    To each their own, Steve my man.

    Sketch246123948.jpg
     
    Last edited: Sep 24, 2016
  8. Sep 25, 2016 #48

    pictsidhe

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    I've fixed a few carb and EFI vehicles over the years. Carbs are simple, they are usually easier to fix and rarely fail suddenly, broken fuel pumps usually, though they usually last a long time. EFI has a tendency to suddenly stop. Modern EFI is very complex, there are many ways to break it. Something I've seen often is bad wiring or connectors. Intermittent problems can be a real ***** to diagnose. One EFI car, I eventually resorted to taking the wiring harness apart to find the bad wires. I'd be very leery of homemade harnesses from someone without a lot of wiring and electrical experience. Despite all that, I do like EFI cars, when they work, which is most of the time.
     
  9. Oct 4, 2016 #49

    Billrsv4

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    Ok, I will first admit that I didn't read every post in this thread, but wanted to mention that there are several mistaken statements in the original few posts. First, the comment that a car is ok for a carb since it remains in one orientation. NOTHING could be more incorrect. Cars have body roll, and g-loading in corners both of which lean the fuel in the float bowl the WRONG WAY. The reason most modern car carbs have such small float bowls is to control fuel slosh. Fuel injection typically is insensitive to orientation. The funny thing is that a plane or a motorcycle lean into corners. (The plane obviously can't be doing a negitive g manouver) Both planes and motorcycles in normal operation are easier on carbs than a car! Fuel injections vary as to how they are controlled. A modern EFI or engine management system is controlled by a computer and the operation requires an electrical system, and an on-board battery. This isn't a problem for almost any self-starting aircraft. It is adviseable that if you go to a fully electronic system to carry at least a small back-up battery, that isn't always hooked into the electrical system. That can keep you running when your alternator fails. I'm sure other posters have mentioned this. The other type of fuel injection is the type normally found on a certified aircraft engine. Mechanical fuel injection. I won't describe this in detail other than to mention that unless you buy some incredibly expensive racing car system it isn't very discreet. They call these things "dribble" or "drool" sytems. The "injectors" are really just nozzles and all of them inject all the time. Most are just an orifice (jet) and a screen to spread the spray in the port. Many contain no valving at all, which is why when hot and parked on the ramp they can boil the fuel in the feed lines and flood the engine causing the hot start problems they are so well known for. Carbs are simple to understand and since they have been around so long they are well sorted out. Their biggest problem is icing. Since the fuel is mixed into the air and evaporates it cools the intake and all us pilots with carbs know to use the carb heat at low throttle openings like landing RIGHT? FI of all types are usually immune to the icing problem.
    The thing is carbs are so cheap! They can be complex to produce but they make the things by the millions (or at least they used to) so the tooling was paid for in 1931. If your fuel pump keeps some gas in the things the power difference at wide open throttle is just a bit lower than the FI systems, (at least the cruder aircraft type), So if you want to sell your engine cheaper you just buy a carb from one of many manufacturers. It almost always comes down to money.
    Bill
     
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  10. Oct 4, 2016 #50

    Aesquire

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    After banging my head against the wall, and spending money to keep the computer in my Caravan ( Dodge, a car, not a plane ) happy, I'm becoming very prejudiced about foolproof, easy to use, electronic engine controls. Admittedly it's not A&P money, but it was unplanned. I got off lightly. A hundred bucks for "smoke testing" ( which in my mind is when you throw power to a freshly wired circuit to see if you messed up ) and a firmware upgrade. Then 3 days later, a pleasant return of the check engine light. The dealer comped me the labor, and only charged me for a new gas cap.

    Yes, the gas cap on a modern car is an integral part of the emissions control system, and after 150,000 miles, the gasket gets old and no longer seals good enough to make the computer ( and the EPA ) happy.

    The gas cap is also a vital part of an aircraft's noise maker's system too. A quick look at FAA incident records will show it's not a freak problem.

    So I'm looking hard at used trucks for my next car that are old enough that they have systems I can actually fix.

    Apropos the OP, a carb works without power. Even if you aren't going for a no-electrical-system aircraft, a Carb, like a Honey badger, don't care if your battery ran down on short final. Or crossing Lake Superior. Or the Pacific.

    The mechanical fuel injection used on Lycoming & Continental engines also don't care. The disadvantage is weight and lots of money. Depending on how many miles you fly there may be enough fuel savings from a well tuned injection system ( with Gami injectors, for example ) and an every cylinder monitoring system, to pay for the difference. ( But it's a LOT of hours ) If your motivation is smoother running and no carb ice, then the cost/benefit is up to you, enjoy.

    Electronic systems, FADAEC, etc, are, like modern cars, wonderful. Reducing pilot workload is nice. But despite decades of development, the small number of units sold make these systems bleeding edge, and lack the robust nature of a mechanical system. ( which is why it's taking so long. ) By all means feel free to go that direction, but be certain you understand the build requirements of a modern electrical system.

    What pitiful wiring skills I have picked up on Ultralights isn't in the same hemisphere as the quality you want for a modern electronic plane. ( But I am avidly studying those skills )

    And if you want to mock a comparison of a Quicksilver MX to a RV-10 set up for hard IFR, feel free, but I remind you in both planes, "pull stick back to make houses smaller, pull back more to make houses bigger" and when the pilot cooling fan gets quiet in each, you sweat, and hope you remembered to always look for a place to glide to a landing.
     
  11. Oct 5, 2016 #51

    VFR-on-top

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    A key point worth making twice. For cars and planes.
     
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  12. Oct 5, 2016 #52

    Himat

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    Then give me a system where I can check all connections and wiring before I hook a PC or other computer to the terminal port and run diagnostic software. After that I can always use a multimeter to check voltages and power or a oscilloscope to check signals.;)
     
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  13. Oct 5, 2016 #53

    rv6ejguy

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    Our EFI has full time diagnostics right on screen as shown below:

    em5a.jpg

    In this case, it shows the engine temp sensor has failed. Nothing else to plug in, no other diagnostic software to run. Dirt simple. You could also run the internal data logging software (shown below) hooked to a PC which shows all sensors plus AFR, injector duty cycle to aid in tuning or diagnosis. Not much guesswork unlike with carbs.

    log22.jpg

    I've seen plenty of people screw around with carbs for hours trying to fix a problem on a so called "simple" device. Most people working on them really don't understand exactly how they work, they just feel good that they can take it apart and blow out some passages, hoping it will fix their problem.

    The nice thing about good EFI is it just works and works and works with virtually no maintenance outside of checking the fuel filters annually.
     
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  14. Oct 5, 2016 #54

    Turd Ferguson

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    You can actually fix the evaporative or EVAP system on a car (without a smoke machine and without the dealer's smokescreen, a.k.a. firmware update). It's not complicated but does take time and effort to understand how it works and where the various components are located.

    EVAP systems have been installed since the '70's so there is a practical limit in trying to find a vehicle without it.
     
  15. Oct 5, 2016 #55

    nerobro

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    Ain't that the truth. Worse than that, the typical explanation of carbs is wrong, so if you try to research the subject, you're assaulting yourself with lots of awfuly wrong information. And for some reason, carb manufacturers seem.... well I can only assume they KNOW, EXACTLY, what each passage on a carb does, but why isn't there documentation easily available? I'd expect that would make them a lot of money....
     
  16. Oct 5, 2016 #56

    rv6ejguy

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    I'd add that some carbs are indeed pretty simple while others like many Webers and copies thereof are not (I used to be a Weber dealer and tuner in my past life).

    The day of the carb is quickly drawing to a close on many engines in many applications from small 2 strokes to mid range and up aircraft engines to almost every automotive engine built today. Only some very low hp engines are being factory fitted with carbs these days. It's your preference if you want to fly with a carb but the writing is on the wall in the OEM worlds and the retrofit aviation market. Our aircraft ECU sales have quadrupled in the last 5 years or so for Rotax, Jabiru, Honda, Continental and Lycoming engines primarily.
     
  17. Oct 5, 2016 #57

    Himat

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    That is even better!
    Much simpler to work on than a carburettor.
     
  18. Oct 5, 2016 #58

    Swampyankee

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    One rather obvious reason that carburetors are dying in so many places is cost: modern electronics can be incredibly cheap: even thirty years ago, a digital electronic timer for a toaster cost less than a mechanical one. A single point EFI system -- throttle-body injection -- would need two or so sensors: an air mass flow valve and a throttle position sensor, and an electronically controlled fuel metering valve. In OEM quantities, the price of this setup could be under $10. The control system would have a look-up table to control fuel flow, via the metering valve, based on air mass flow and throttle position. Essentially, this is all a carburetor does.
     
  19. Oct 5, 2016 #59

    Vigilant1

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    Well, I was on the other side of the issue with >my< Caravan, a 1984 with a Mitsubishi 4-banger. It had a carburetor, but with more bypasses, overrides, vacuum-operated bells-and-whistles and other whatnot that any FI system would have been easier to fix.
    I was intrigued by a dual setup I heard Joe Horvath at Revmaster was trying out. It was one of his Revflow "carburetors" that also had an FI injector plumbed into the throat of the carb. You could run the FI as the primary system with the fuel to his carb shut off, but if you pulled open the mixture knob for his carb and flipped a switch turning off the FI, you were running again in a heartbeat on a totally independent system. Seemed pretty bulletproof and totally redundant, and as those carbs are dirt simple to begin with and not very expensive (about $425), it could be a practical approach to addressing a very rare potential issue. I suppose it would be no more trouble to do the same with an AeroInjector.
     
  20. Oct 6, 2016 #60

    rv6ejguy

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    You don't really need a TPS if you have a mass flow meter but you'll have problems with cold starting if you don't have an engine temp sensor. $10, I don't think so. $100 at the OEM quantity level of 50,000 units maybe if you don't count engineering and development time. You'll need wiring, a drive circuit for the injector, fuel pump, regulator etc.
     

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