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Comment by mmcconnell1618 | Hacker News Reader

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.

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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.

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.

Generally all the weight of the fusaage has to go through the wings anyway so it is structurally more efficient to put weight on the wings in the first place.

And they do that with fuel?! Neat!

Yup.

On a 737 they can put about 8k pounds per wing.

Even little planes like Cessnas have wing tanks.

Wow wow!

Might see planes just a smidge differently now :)

In sailplanes we add up to around 200 litres of water to wing tanks in single-seat gliders (empty weight typically around 280kg) to improve the high speed performance (typically up to 270 km/h these days) and ability to fly comfortably in turbulence.

It's surprising what you can fly formation with, even without an engine [1] :-)

https://www.youtube.com/watch?v=G0icOICQLTc

Dumping (most of the) water before landing:

https://www.youtube.com/watch?v=I4Yv-V7eozk

[1] this particular glider does have a small engine for takeoff, but maximum speed with the engine extended is 180 km/h and here they are flying at 280 km/h.

What a rabbithole this is now :D

That glider next to the world's fastest aircraft (in 1953) dressed up for a fight, how about that.

And they can water the grass...

So several thousand $ to get trained and certified and finally be ready to get towed and soar...

but just a few hundred (California) to try for half an hour behind a pro in the cockpit--oh yeah!

...omg they let you fly the thing for another couple bucks!!!

If it's a pro then they'll be sitting in the back seat so you're in the front seat the same as you will be when you fly solo.

Here's a video of me taking a student for their first lesson:

https://www.youtube.com/watch?v=RDZN21xzsRo

That's in a DG1000, actually this exact one ZK-GGR:

https://www.youtube.com/watch?v=PeueijUoL70

https://www.youtube.com/watch?v=r0ShTUTiqlM

And how that looks from the other end of the rope:

https://www.youtube.com/watch?v=sRxcJR-zipI

And from the door of the hangar (using the runway in the opposite direction). Turn it up!

https://www.youtube.com/watch?v=RUnXuMVhKfs

Coming back to more like the current topic, an electric powered glider:

https://www.youtube.com/watch?v=7F2gS9ENl5k

Also from Stefan's channel, some fun here in New Zealand ... this flight passes just a couple of km from the Lord of the Rings "Weathertop" site (Google maps knows it).

https://www.youtube.com/watch?v=ggz2CzvPNUc

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.

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.

Probably because they intend to sell aircraft, not electric motors.

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.

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.

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.

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.

https://www.latimes.com/business/la-fi-travel-briefcase-unit...

These guys did that / are trying to do:

https://www.weflywright.com/products/motor

But then again, they also ship now stuff for datacenters (facepalm):

https://www.weflywright.com/products/densegen-3750

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