4 ms·

Even better, these could be generation systems hooked up to an electric motor and energy buffer (battery). Put the prop on the motor, keep the whole transmissio

by FL410 5y ago

Even better, these could be generation systems hooked up to an electric motor and energy buffer (battery). Put the prop on the motor, keep the whole transmission system electric, and stick one or more of these somewhere else making power.

ncmncm 5y ago
You could put a little turbine in a Cessna or Beechcraft driving a generator and little-ish battery, and an electric motor driving the prop, and get the same benefit, but the cost and maybe weight would be higher in a place where both are critical. Still, FAA probably should look into pre-approving such a configuration, too.
- KennyBlanken 5y ago
  Or you can just do what's already done: drive a propeller off the turbine. Which is what's done in turboprop engines, the most efficient airplane propulsion system available. Nothing is more efficient under power; turbines are only inefficient at low power settings (descents, taxiing, etc.)
- sokoloff 5y ago
  There’s no concept of a pre-approval in FAA land. You build an airplane and flight test it in experimental category to gather real-world performance numbers to put into the required format for the operating limitations and pilot operating handbook and get certification of the package based on demonstrated data.
  - ncmncm 5y ago
    That is surely fixable. I.e., there is no constitutional restriction against Congress assigning such a task to some agency. NASA might be best organized, of federal apparatus, to do the work, maybe under a future "General Aviation Revitalization Initiative" authorization, maybe letting contracts for actual development. The problem to be overcome is that nobody private seems to be rich enough to jump through all the regulatory hoops to get a modern engine approved to build modern small aircraft around, no matter how much better one could be. I don't know why a Cessna-size turboprop mill never got to market. Is periodic maintenance and inspection of turbines prohibitively expensive?
    - sokoloff 5y ago
      There’s no real reason to pre-approve something (IMO). You want to certify an airplane? Build and fly a prototype. If you’re capable to build an airplane manufacturing company, you’re capable to make and fly a prototype. For small aircraft turbines: Cessna makes the 208 Caravan. If the 208 is too big, Quest makes the Kodiak and Socata makes the TBM. If someone’s going to pay all the purchase and operating costs to run a PT6 turbine, they might as well drag around a medium-sized airframe. Maintenance and inspection of turbines isn’t prohibitive. Initial purchase price and specific fuel consumption at low altitude is a far greater concern for private operations. Pistons are way more popular simply because of economics. Virtually everything else about turbines is better. If I could afford a turbine, I’d switch to one immediately.
      - ncmncm 5y ago
        If it were that easy, we would not still be flying 70-year-old Lycoming and Continental designs. I interpret the facts on the ground to mean qualifying a new light-aircraft power plant is in practice prohibitively difficult and/or expensive, and needs assistance, maybe even statutory assistance.
        sokoloff 5y ago
        It’s not the regulatory side so much as the total addressable market being quite small. If you build a new light airplane now, you’re looking to steal market share from annual sales figures totaling just over 1300 airframes per year. Worldwide. Ferrari sells almost as many cars in a month as light aircraft are sold in a year. I’m not surprised that people aren’t lining up to compete for those scraps.
        ncmncm 5y ago
        We can speculate about what exactly are all the reasons, but none of it can change the facts. It is a safe bet that if small aircraft got as cheap and performant as is in easy reach of modern engineering and production capabilities, there would be a lot more of them bought and used. Halving cost ought to result in much more than twice the demand. For comparison, we may look at solar panels. There have been no fundamental advances in a long time, but increasing volume triggered by heavy Chinese subsidies kicked the market into a different mode it is still far from settled into. Probably there are lots who would rather general aviation not become a lot more accessible, but that is policy, not fundamental economics.
nradov 5y ago
That sounds heavy. How much would it weigh?
- ncmncm 5y ago
  It doesn't need to weigh much. Idea is that if you can use a battery to boost output power for takeoff and climb out, for that few minutes, you can get along with a much smaller turbine just for cruising than you would need for a turboprop, so is cheaper. And, if the turbine drives a generator directly, it doesn't need the step-down gearing you would need to drive a prop, and you can run the turbine at a constant speed any time it runs at all, more efficiently for that and without gear-train loss. And, it can run on jet-A fuel, which is cheaper per kWh than Avgas. I don't know where a turbine of the right size is in use, that could be re-purposed.

by FL410 5y ago

ncmncm 5y ago

You could put a little turbine in a Cessna or Beechcraft driving a generator and little-ish battery, and an electric motor driving the prop, and get the same benefit, but the cost and maybe weight would be higher in a place where both are critical. Still, FAA probably should look into pre-approving such a configuration, too.

KennyBlanken 5y ago
Or you can just do what's already done: drive a propeller off the turbine. Which is what's done in turboprop engines, the most efficient airplane propulsion system available. Nothing is more efficient under power; turbines are only inefficient at low power settings (descents, taxiing, etc.)
sokoloff 5y ago
There’s no concept of a pre-approval in FAA land. You build an airplane and flight test it in experimental category to gather real-world performance numbers to put into the required format for the operating limitations and pilot operating handbook and get certification of the package based on demonstrated data.
- ncmncm 5y ago
  That is surely fixable. I.e., there is no constitutional restriction against Congress assigning such a task to some agency. NASA might be best organized, of federal apparatus, to do the work, maybe under a future "General Aviation Revitalization Initiative" authorization, maybe letting contracts for actual development. The problem to be overcome is that nobody private seems to be rich enough to jump through all the regulatory hoops to get a modern engine approved to build modern small aircraft around, no matter how much better one could be. I don't know why a Cessna-size turboprop mill never got to market. Is periodic maintenance and inspection of turbines prohibitively expensive?
  - sokoloff 5y ago
    There’s no real reason to pre-approve something (IMO). You want to certify an airplane? Build and fly a prototype. If you’re capable to build an airplane manufacturing company, you’re capable to make and fly a prototype. For small aircraft turbines: Cessna makes the 208 Caravan. If the 208 is too big, Quest makes the Kodiak and Socata makes the TBM. If someone’s going to pay all the purchase and operating costs to run a PT6 turbine, they might as well drag around a medium-sized airframe. Maintenance and inspection of turbines isn’t prohibitive. Initial purchase price and specific fuel consumption at low altitude is a far greater concern for private operations. Pistons are way more popular simply because of economics. Virtually everything else about turbines is better. If I could afford a turbine, I’d switch to one immediately.
    - ncmncm 5y ago
      If it were that easy, we would not still be flying 70-year-old Lycoming and Continental designs. I interpret the facts on the ground to mean qualifying a new light-aircraft power plant is in practice prohibitively difficult and/or expensive, and needs assistance, maybe even statutory assistance.
      - sokoloff 5y ago
        It’s not the regulatory side so much as the total addressable market being quite small. If you build a new light airplane now, you’re looking to steal market share from annual sales figures totaling just over 1300 airframes per year. Worldwide. Ferrari sells almost as many cars in a month as light aircraft are sold in a year. I’m not surprised that people aren’t lining up to compete for those scraps.
        ncmncm 5y ago
        We can speculate about what exactly are all the reasons, but none of it can change the facts. It is a safe bet that if small aircraft got as cheap and performant as is in easy reach of modern engineering and production capabilities, there would be a lot more of them bought and used. Halving cost ought to result in much more than twice the demand. For comparison, we may look at solar panels. There have been no fundamental advances in a long time, but increasing volume triggered by heavy Chinese subsidies kicked the market into a different mode it is still far from settled into. Probably there are lots who would rather general aviation not become a lot more accessible, but that is policy, not fundamental economics.

nradov 5y ago

That sounds heavy. How much would it weigh?

ncmncm 5y ago
It doesn't need to weigh much. Idea is that if you can use a battery to boost output power for takeoff and climb out, for that few minutes, you can get along with a much smaller turbine just for cruising than you would need for a turboprop, so is cheaper. And, if the turbine drives a generator directly, it doesn't need the step-down gearing you would need to drive a prop, and you can run the turbine at a constant speed any time it runs at all, more efficiently for that and without gear-train loss. And, it can run on jet-A fuel, which is cheaper per kWh than Avgas. I don't know where a turbine of the right size is in use, that could be re-purposed.