3 ms·

No, this is false. The stiffness issue is a second order issue (which is why larger conventional planes actually have LOWER dry mass per passenger than 9 seat p

No, this is false. The stiffness issue is a second order issue (which is why larger conventional planes actually have LOWER dry mass per passenger than 9 seat passenger aircraft) and IT AFFECTS ALL PLANE TYPES, and can be addressed via truss braced wings as I said. There are more important minimum gauge type issues at small scale that tend to dominate and make small scale worse performance than large scale. The claim that larger size in particular is a problem is false. Efficiency, including structural efficiency, actually tends to improve with scale beyond 100 seats. > We sadly cannot make large battery powered airplanes with a usable range and speed unless we get up the gravimetric density. This, again, is often repeated but false from a technical standpoint. 9 seater and 100 seater, for the same range, scale just fine between them and with clean sheet design we can use existing 200-400Wh/kg gravimetric density. Scale. Isn’t. The. Problem. Large planes tend to be used on longer routes, in fact. Smaller planes are needed for their granularity on short routes. The reason we see 9 passenger electric planes first is pretty obvious: cheaper and faster to develop small planes than large. Big aircraft manufacturers are much more risk averse as well. A large new clean sheet aircraft can take literally decades to develop. Not true for small aircraft. And again, generally the granularity of small planes means they’re more useful than large planes for shorter routes. This all reinforces the false notion that there is some technical reason why we “CAN’T” make large electric planes when there really, truly isn’t. For instance, consider the Learjet 70/75. 8 passenger, dry mass of 6 some tonnes. Over 700kg per passenger. 14 passenger Falcon jets do better at about 500kg per passenger. 737 Max8 with 210 passengers gets about 215kg/passenger. So if anything, overall structural efficiency improves with scale! At least up to ~200 passengers. (Caveat is that these are typically private jets with a different seating arrangement... but so are the example electric aircraft. So they'd similarly benefit from scale up to larger seat capacity.)

sudosysgen 5y ago
I think you seriously underestimate the mass of a 100 seater with 500 mile range. The 737 Max8 has a massive advantage over the LearJet of massively lower surface area per passenger. It's not comparable at all. In an electric aircraft where the bottleneck is the battery as far as weight goes this is not a relevant comparison. You have two regimes. One where the dominant factor is structural efficiency is mass. One where the dominant factor is area. You cannot compare the two. It is simply a completely deficient comparison. Do you want an actually correct comparison? Keep the 737 Max 8. Now compare it to a PAC P-750XL, dry mass of 1.6 tons over 9 passengers. That's 181kg per passenger, less than the Max-8. Now that's the aluminium version. The Max-8 uses a massive amount of composites - the composite version of the P-750XL is expected to be significantly lighter still. It's absolutely not a fiction. A 787 Max-8 consumes 18 liters (!!!) of kerosene at >60% thermal efficiency, per passenger, per hour. That's 175kW of useful energy consumption per passenger. To fly one hour at 400Wh/kg assuming 100% energy efficiency you need to add 437 kg of batteries PER PASSENGER.
- Robotbeat 5y ago
  PAC P-750XL Is unpressurized so is able to significantly lower the dry mass per passenger. I noticed this difference while researching the different dry mass numbers. The low speed unpressurized utility aircraft like the P-750XL ARE able to get lower per passenger mass, but the experience is not comparable as they are unpressurized. Among pressurized jet aircraft, the larger jets do universally better per passenger than the smaller. The real key to making electric aircraft feasible is to increase the efficiency dramatically. (Also, jets don’t have >60% thermal efficiency if you use the HHV of the fuel.) just a swap out of the fuel for battery gets you to a few hundred miles of range at best. Enough maybe to compete with the California HSR, but not much more. It’s like how a Tesla Model S is not a battery swapped sedan. It’s a custom clean sheet design. That’s why you can get 400 miles of range in it instead of just 150 miles. Likewise, you need a clean sheet battery electric aircraft design. That’s why the Eviation Alice is able to get significant range. Incorporate 777x-like folding wingtips and possible truss braced high aspect ratio wings, natural laminar flow like sailplanes, you could increase L/D to about double current aircraft. Things like that allow 1000 mile range. Substantial enough for short haul trips, which are about half of all passenger miles.
  - sudosysgen 5y ago
    If you're actually trying to scale aircraft up and down, you can do the math and figure out that a scaled down aircraft will be slower. It's a perfect comparison. A Tesla Model S doesn't have any more weight efficiency than a battery swapped sedan. It's just as heavy as a battery swapped sedan, it's just built to handle the weight better. The main factor in the Alice having a lower L/D is flying at less than half the airspeed and thus drastically reducing parasitic drag. There are no easy gimmes. You're going to have to sacrifice range and speed. So far electric airplanes are somewhat worse than piston aircraft. They will never rival jets until we drastically increase energy density. The turbine efficiency of modern turbojets is actually around 60% and there are turbines with more than that. The overall efficiency is actually lower because of propulsive inefficiency, but electric aircraft have that exact same problem.

sudosysgen 5y ago

I think you seriously underestimate the mass of a 100 seater with 500 mile range. The 737 Max8 has a massive advantage over the LearJet of massively lower surface area per passenger. It's not comparable at all. In an electric aircraft where the bottleneck is the battery as far as weight goes this is not a relevant comparison. You have two regimes. One where the dominant factor is structural efficiency is mass. One where the dominant factor is area. You cannot compare the two. It is simply a completely deficient comparison. Do you want an actually correct comparison? Keep the 737 Max 8. Now compare it to a PAC P-750XL, dry mass of 1.6 tons over 9 passengers. That's 181kg per passenger, less than the Max-8. Now that's the aluminium version. The Max-8 uses a massive amount of composites - the composite version of the P-750XL is expected to be significantly lighter still. It's absolutely not a fiction. A 787 Max-8 consumes 18 liters (!!!) of kerosene at >60% thermal efficiency, per passenger, per hour. That's 175kW of useful energy consumption per passenger. To fly one hour at 400Wh/kg assuming 100% energy efficiency you need to add 437 kg of batteries PER PASSENGER.

Robotbeat 5y ago
PAC P-750XL Is unpressurized so is able to significantly lower the dry mass per passenger. I noticed this difference while researching the different dry mass numbers. The low speed unpressurized utility aircraft like the P-750XL ARE able to get lower per passenger mass, but the experience is not comparable as they are unpressurized. Among pressurized jet aircraft, the larger jets do universally better per passenger than the smaller. The real key to making electric aircraft feasible is to increase the efficiency dramatically. (Also, jets don’t have >60% thermal efficiency if you use the HHV of the fuel.) just a swap out of the fuel for battery gets you to a few hundred miles of range at best. Enough maybe to compete with the California HSR, but not much more. It’s like how a Tesla Model S is not a battery swapped sedan. It’s a custom clean sheet design. That’s why you can get 400 miles of range in it instead of just 150 miles. Likewise, you need a clean sheet battery electric aircraft design. That’s why the Eviation Alice is able to get significant range. Incorporate 777x-like folding wingtips and possible truss braced high aspect ratio wings, natural laminar flow like sailplanes, you could increase L/D to about double current aircraft. Things like that allow 1000 mile range. Substantial enough for short haul trips, which are about half of all passenger miles.
- sudosysgen 5y ago
  If you're actually trying to scale aircraft up and down, you can do the math and figure out that a scaled down aircraft will be slower. It's a perfect comparison. A Tesla Model S doesn't have any more weight efficiency than a battery swapped sedan. It's just as heavy as a battery swapped sedan, it's just built to handle the weight better. The main factor in the Alice having a lower L/D is flying at less than half the airspeed and thus drastically reducing parasitic drag. There are no easy gimmes. You're going to have to sacrifice range and speed. So far electric airplanes are somewhat worse than piston aircraft. They will never rival jets until we drastically increase energy density. The turbine efficiency of modern turbojets is actually around 60% and there are turbines with more than that. The overall efficiency is actually lower because of propulsive inefficiency, but electric aircraft have that exact same problem.