Comment by mmcconnell1618

12 hours ago

Interesting decision to build the whole aircraft instead of the propulsion system only. I wonder what the decision process was between retrofit of existing turboprop frame vs. build from the ground up? I would expect the level of effort and certification to be much higher building from scratch even though you get complete control.

21 comments

mmcconnell1618

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imoverclocked  11 hours ago

Aircraft design is very intricate. Change the CG, break the whole system.

Fuel is often placed in wings because adding/burning fuel from your center of lift means your CG doesn't significantly change through a flight and you spend less on pumping fuel within the aircraft. With batteries, you are looking at a constant mass from the beginning of the flight to the end... so you can place it anywhere. Electric motors are orders of magnitude lighter than jet engines. Also, you don't need to pump electrons against gravity so placing all of that weight lower has handling/performance advantages.

By using an airframe shape that is well known, they are reducing risk and appealing to existing pilots. By building it from the ground-up, they are taking advantage of differences between the tech.

eg: all of that weight in the fuselage instead of the wings means that rolling is going to be much more nimble. Yaw might be affected as well, depending on the placement/moment of the batteries.

MBCook  12 hours ago

It may be too hard to do a good retrofit. If you basically have to tear the entire plane apart and rebuild and recertify it to put batteries in the right places, maybe the costs aren’t worth it for potential customers.

I know many planes use their wings as fuel tanks but given the weight of batteries maybe that doesn’t work.

I agree it’s interesting. Not a small undertaking.

cpach  2 hours ago

There are probably multiple reasons for doing so. I imagine some reasons are business risk, freedom to innovate, freedom to take a holistic perspective and improving the possibilites for raising capital.

If you build only the propulsion system you would be 100% dependent of existing aircraft companies, which are heavily invested in jet engines. It would probably be much harder to innovate and make good design choices in such a setting.

woods42  11 hours ago

I think an interesting aspect is that on normal aircraft fuel tanks have to be near the center of lift to maintain weight and balance as fuel is burned off. When using batteries, this is not really a concern, and I would think might lead to some more interesting designs. To be sure, if there is space in the wing, awesome - the batteries can now also be used as ballast though too if required.

  • rbanffy  10 hours ago

    Wings can also be excellent for heat rejection - in-wing batteries have a lot of surface per unit of volume and are constantly exposed to low temperatures.

    Which may result in them being too cold and you needing to spend power heating them, so someone needs to do the math on that.

lbriner  12 hours ago

Judging by the seats, perhaps making it as light as possible. Existing airframes are relatively light but let's be honest, they aren't trying to save 500g here and there when they have massive jet engines to get everything airborne.

  • lefra  11 hours ago

    I discussed with people working on aircraft components, and my understanding is that weight is a constant obsession for them. Propose a new system to Airbus/Boeing, and the first question they'll ask is "how much does it weight?"

    Every kg saved is a kg more of freight that can be transported (or a little less fuel used to keep the plane in the air); save 500g for each seat of a 200-seat plane, and you can put one more paying passenger in the cabin.

    • notahacker  11 hours ago

      Agreed. But for related reasons, aircraft aren't really designed for either the structural robustness or balance to deal with big heavy batteries, which is what motivated the clean sheet design.