4 ms·

avgas is more expensive doe

mistercow 13y ago
Yeah, where I am, it's about 5/3 as expensive. The upper bound improvement factor you can get over driving due to flying in a straight line is 2/sqrt(2), so your best case cost-equivalent efficiency is about 11 mpg.
- mikeash 13y ago
  The upper bound is infinite if you fly a route with no road equivalent, for example to an island. Even sticking to a single landmass, you can get arbitrarily high, as roads can be extremely indirect in some cases.
- mahyarm 13y ago
  This is why I'm excited about electric airplanes and driverless cars. A GA electric airplane has about 1/10th the energy cost of an avgas one. The cost of avgas is what discourages me from owning an airplane.
  - sokoloff 13y ago
    In most cases, avgas will be under half your total expenses for the year. You have to fly well over the average utilization for gas to dominate over maintenance, insurance, hangar, database updates/charts, etc. Even at 100 flight hours/year in a thirsty airplane, you'll spend maybe $10K on fuel. It would take a very simple airplane, hangared very cheaply, and no abnormal maintenance events for the year, for those other costs to be under $10K. Few privately owned planes fly even 100 hours per year, and most of the non-fuel costs are largely fixed, meaning you pay them all just to fly the "first hour" and then subsequent hours just cost fuel and a small wear-related maintenance allocation. Airplanes are cheap to buy, but not cheap to fly. The cost of gas hurts, but doesn't dominate in my experience (owning three airplanes over 15 years, and flying my family on most of our domestic travel east of the Mississippi).
    - leoedin 13y ago
      You're not taking into account the vastly simpler design of an electric aircraft. An electrically propelled aircraft will have maintenance requirements similar to a glider. Fewer engine overhauls and much simpler procedures means significantly reduced cost.
      - sokoloff 13y ago
        I don't think you're taking into account the vastly increased battery maintenance, inspection and capacity testing that will be required. Yes, you'll save a lot on not maintaining a piston IC engine. You'll give some of that back in inspection processes to ensure that you don't have 95% of the range that you think you have. If you run of out power in a Leaf or a Tesla, it's overwhelmingly likely that the car will come to rest on a piece of pavement and intact. If you run out of juice in an electric airplane, you turn into a glider, and it's far from assured that you'll end up at an airport or on pavement. I'm not scare-mongering, but that's the point of view the FAA will take on inspection and testing requirements for electric storage systems to achieve equivalent level of safety. I know when I add 40 gallons into my left tank (beyond the unusable fuel) that I have added 40 gallons of range. I need some similar assurance for battery capacity. (again, it's not me, but the FAA.) Just have a look at the annual inspection requirements for ELT and starting batteries for piston airplanes. And those are not propulsion systems. The batteries that run the AHRS in the G1000 and Aspen systems are also onerous and those batteries are crazy expensive relative to their capacity. I can see electrics working for flight school airplanes, especially if they can get the 80% recharge time down under 2 hours. I don't see them as practical for cross-country travel anytime soon without advances in battery tech; those are inevitable, but I don't see them displacing liquid organic fuels in my flying career for 1000nm legs.
        mahyarm 13y ago
        I would think inspecting & maintaining the actual capacity of the battery would be part of the automated charging system. It would be recorded to a fine a amount of detail. Most airplanes have a more predictable energy consumption model than a typical consumer car also, and since the typical pilot is more sophisticated, can afford to show a more complicated energy display for more accurate energy consumption and range assumptions. Electric aircraft currently would be very useful for people who live on an island or island cluster or want to do frequent short hop flights. For example Hawaii, the Caribbean, Indonesia, the Philippines, Seattle and the near by gulf islands, etc. I can take a ferry boat for 3 hours at scheduled times or I can hop on my plane for 30 minutes at any practical time at the same cost really changes things for island dwellers. I could live on an island and theoretically commute to work every day for 45minutes of total travel time. Going to Tahoe every weekend wont be a big deal, etc. It would be also useful for future automated air taxis, since the energy costs would soon dwarf the cost of everything else in those situations.

Yeah, where I am, it's about 5/3 as expensive. The upper bound improvement factor you can get over driving due to flying in a straight line is 2/sqrt(2), so your best case cost-equivalent efficiency is about 11 mpg.

mikeash 13y ago
The upper bound is infinite if you fly a route with no road equivalent, for example to an island. Even sticking to a single landmass, you can get arbitrarily high, as roads can be extremely indirect in some cases.
mahyarm 13y ago
This is why I'm excited about electric airplanes and driverless cars. A GA electric airplane has about 1/10th the energy cost of an avgas one. The cost of avgas is what discourages me from owning an airplane.
- sokoloff 13y ago
  In most cases, avgas will be under half your total expenses for the year. You have to fly well over the average utilization for gas to dominate over maintenance, insurance, hangar, database updates/charts, etc. Even at 100 flight hours/year in a thirsty airplane, you'll spend maybe $10K on fuel. It would take a very simple airplane, hangared very cheaply, and no abnormal maintenance events for the year, for those other costs to be under $10K. Few privately owned planes fly even 100 hours per year, and most of the non-fuel costs are largely fixed, meaning you pay them all just to fly the "first hour" and then subsequent hours just cost fuel and a small wear-related maintenance allocation. Airplanes are cheap to buy, but not cheap to fly. The cost of gas hurts, but doesn't dominate in my experience (owning three airplanes over 15 years, and flying my family on most of our domestic travel east of the Mississippi).
  - leoedin 13y ago
    You're not taking into account the vastly simpler design of an electric aircraft. An electrically propelled aircraft will have maintenance requirements similar to a glider. Fewer engine overhauls and much simpler procedures means significantly reduced cost.
    - sokoloff 13y ago
      I don't think you're taking into account the vastly increased battery maintenance, inspection and capacity testing that will be required. Yes, you'll save a lot on not maintaining a piston IC engine. You'll give some of that back in inspection processes to ensure that you don't have 95% of the range that you think you have. If you run of out power in a Leaf or a Tesla, it's overwhelmingly likely that the car will come to rest on a piece of pavement and intact. If you run out of juice in an electric airplane, you turn into a glider, and it's far from assured that you'll end up at an airport or on pavement. I'm not scare-mongering, but that's the point of view the FAA will take on inspection and testing requirements for electric storage systems to achieve equivalent level of safety. I know when I add 40 gallons into my left tank (beyond the unusable fuel) that I have added 40 gallons of range. I need some similar assurance for battery capacity. (again, it's not me, but the FAA.) Just have a look at the annual inspection requirements for ELT and starting batteries for piston airplanes. And those are not propulsion systems. The batteries that run the AHRS in the G1000 and Aspen systems are also onerous and those batteries are crazy expensive relative to their capacity. I can see electrics working for flight school airplanes, especially if they can get the 80% recharge time down under 2 hours. I don't see them as practical for cross-country travel anytime soon without advances in battery tech; those are inevitable, but I don't see them displacing liquid organic fuels in my flying career for 1000nm legs.
      - mahyarm 13y ago
        I would think inspecting & maintaining the actual capacity of the battery would be part of the automated charging system. It would be recorded to a fine a amount of detail. Most airplanes have a more predictable energy consumption model than a typical consumer car also, and since the typical pilot is more sophisticated, can afford to show a more complicated energy display for more accurate energy consumption and range assumptions. Electric aircraft currently would be very useful for people who live on an island or island cluster or want to do frequent short hop flights. For example Hawaii, the Caribbean, Indonesia, the Philippines, Seattle and the near by gulf islands, etc. I can take a ferry boat for 3 hours at scheduled times or I can hop on my plane for 30 minutes at any practical time at the same cost really changes things for island dwellers. I could live on an island and theoretically commute to work every day for 45minutes of total travel time. Going to Tahoe every weekend wont be a big deal, etc. It would be also useful for future automated air taxis, since the energy costs would soon dwarf the cost of everything else in those situations.