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I have practical market experience on building a two passenger electrical aircraft and trying to market it, what I found is that "range anxiety" is a real issue

by elmar 10y ago

I have practical market experience on building a two passenger electrical aircraft and trying to market it, what I found is that "range anxiety" is a real issue for pilots and the market today for electrical planes is really limited to trainers, so we decided to modify our aircraft to an hybrid configuration.

paulmd 10y ago
As a private pilot: yes, you absolutely do not want to be landing on empty. Range is the same thing as endurance, and endurance means you have options when things don't go your way. Endurance is already a concern even on conventional motors - your average Cessna 150 only has a useful payload of 344 lbs with full fuel tanks. If you want to put two people in it, you're not taking off with full tanks, especially once you account for possibly thinner air above sea level or due to warm temperatures. You need to keep a minimum (!) 30 minute reserve of fuel for VFR. The 150 has a 4-hour max endurance with full tanks. Usually you get less, because that doesn't include full-throttle time for takeoffs/climb. So if you take out half the gas (buying yourself another 76 lbs of payload) you've actually removed about 3/4 of the useful range of the aircraft. The same problem applies to battery-driven electric aircraft - extra weight kills endurance, and compensating for this causes a death spiral. Twin-engine aircraft are really the way to fix this, but they're more expensive to get certified for, more expensive to run, more expensive to insure, etc. I'm a big fan of the Diamond DA42, twin diesels are cool as hell and it's totally nuts how slowly they sip fuel. The other thing not mentioned in the article is that with batteries, as you drain them the output voltage also drops. That translates into reduced torque/power, and possibly an aircraft with different handling characteristics in stall situations. Conventional engines will deliver 100% power on-demand right up until they're out of gas.
- vvanders 10y ago
  The voltage droop isn't as bad as you'd think, I don't get limited power until I'm below 10% in our Tesla 85D. Even "full throttle" for most electric motors isn't near the max C rating(because amps = heat = power loss). The rest of the stuff thought, yeah that's an issue and I feel like one of the areas where Fuel Cells might actually be applicable(you don't have the long-term leakage/storage/fueling issues as with cars).
  - paulmd 10y ago
    An aircraft can't afford to be hauling around 2-3x as much battery as is actually necessary to fly, as is common in electric cars. I can assure you than when an electric airplane is at the limit of its range, its performance characteristics will change in a negative way. Electric planes are already at a 100x disadvantage in terms of Specific Energy - liquid fuels (JP-1 jet fuel or gasoline) contain about 46 MJ/kg while Li-ion batteries contain about 0.36-0.875 MJ/kg. They cannot afford to make that a 300x disadvantage. It doesn't work in terms of lift. As someone else posted in a thread, electric power already takes you from a 900 mile range to a 150 mile range. 50 miles is not acceptable because you're talking <30 minutes of endurance including takeoff, and you have zero safety margin if something should go wrong.

by elmar 10y ago

paulmd 10y ago

As a private pilot: yes, you absolutely do not want to be landing on empty. Range is the same thing as endurance, and endurance means you have options when things don't go your way. Endurance is already a concern even on conventional motors - your average Cessna 150 only has a useful payload of 344 lbs with full fuel tanks. If you want to put two people in it, you're not taking off with full tanks, especially once you account for possibly thinner air above sea level or due to warm temperatures. You need to keep a minimum (!) 30 minute reserve of fuel for VFR. The 150 has a 4-hour max endurance with full tanks. Usually you get less, because that doesn't include full-throttle time for takeoffs/climb. So if you take out half the gas (buying yourself another 76 lbs of payload) you've actually removed about 3/4 of the useful range of the aircraft. The same problem applies to battery-driven electric aircraft - extra weight kills endurance, and compensating for this causes a death spiral. Twin-engine aircraft are really the way to fix this, but they're more expensive to get certified for, more expensive to run, more expensive to insure, etc. I'm a big fan of the Diamond DA42, twin diesels are cool as hell and it's totally nuts how slowly they sip fuel. The other thing not mentioned in the article is that with batteries, as you drain them the output voltage also drops. That translates into reduced torque/power, and possibly an aircraft with different handling characteristics in stall situations. Conventional engines will deliver 100% power on-demand right up until they're out of gas.

vvanders 10y ago
The voltage droop isn't as bad as you'd think, I don't get limited power until I'm below 10% in our Tesla 85D. Even "full throttle" for most electric motors isn't near the max C rating(because amps = heat = power loss). The rest of the stuff thought, yeah that's an issue and I feel like one of the areas where Fuel Cells might actually be applicable(you don't have the long-term leakage/storage/fueling issues as with cars).
- paulmd 10y ago
  An aircraft can't afford to be hauling around 2-3x as much battery as is actually necessary to fly, as is common in electric cars. I can assure you than when an electric airplane is at the limit of its range, its performance characteristics will change in a negative way. Electric planes are already at a 100x disadvantage in terms of Specific Energy - liquid fuels (JP-1 jet fuel or gasoline) contain about 46 MJ/kg while Li-ion batteries contain about 0.36-0.875 MJ/kg. They cannot afford to make that a 300x disadvantage. It doesn't work in terms of lift. As someone else posted in a thread, electric power already takes you from a 900 mile range to a 150 mile range. 50 miles is not acceptable because you're talking <30 minutes of endurance including takeoff, and you have zero safety margin if something should go wrong.