Egregoros

Cylindrical batteries: 283wh/kg
Apparently about $10 each, so $83/kWh
36kWh = 127kg (279lb)

A gallon of gas, burned in an aircraft engine, is probably good for about 9.4kWh. So 36kWh is probably equivalent to about 4 gallons of gas.

The clever part is you make a string of batteries and put it inside a carbon fiber tube sealed in with epoxy, and then you have a solid rod. You're not doing anything for tensile strength but for compressive strength this would be amazing.

And tension is the easier force to deal with. Lots of materials like kevlar have incredible tensile strength. Compression is hard because compressive load causes bending. This is quite obvious when you think about it, there exists 400lb test fishing line but you would search to the ends of the earth to find anything as narrow as a fishing line that can hold up 400lb in compression.

But compressive load is really interesting because almost everything has good compressive strength - as long as it's confined inside of a tube. You could fill a carbon fiber tube with playdough and it would have great compressive strength - as long as the playdough is confined and has no holes to ooze out though.

Furthermore, the contents of the tube are placed under "pressure", but not load in the classical sense. Bending and squeezing forces only come into play when an object is not confined.

So making compressive load carriers out of carbon tubes full of batteries seems like a really interesting way to integrate batteries without the entire weight penalty.

> electric was not a viable option

Well, yes and no. You're absolutely right that the weight is bad, it's like 10x as bad. But on the other side of things, something like 2/3rds of the cost of a plane ticket is just going straight to fuel, so if you can find a way to replace that fuel with electricity, you're taking maybe 20-30% off the cost of the flight, so the pot of gold at the end of that rainbow is so rich that you start re-thinking the definition of "viable"...

In terms of actual physics viability, it's "borderline". You can get up in the air for an hour or maybe 2 with electricity, which for a lot of short haul, tourist stuff, etc is potentially enough. And if it's "potentially enough" then it's 100% worth it because of the aforementioned fuel cost...

Now what I'm talking about is that blue thing that runs the length of the wing. That has to be frustratingly strong because the whole airplane hangs off of it. So I'm thinking something like pic 2 with two battery tubes, having periodic spacer tubes, and then the whole thing is wrapped up in carbon fiber like it was a Christmas present - and that outer wrapping prevents the two from racking.

Heart ES-30 is an electric plane (still in development) and it has 200km (124 miles) of range on electric only. However, the outer two engines are turbines, so it can extend flight beyond electric range...

Even if you need to burn gas to complete the flight, using as much electricity as possible is *obviously* a cost savings...

It's not clear from the picture but the wingspan is big for what it is. 31m (101ft) for a 30 seat aircraft, the Boeing 727-800 is 25m (117ft) for 160-180 passengers. Long wings improve efficiency...

So like I said, viability is borderline, but they have something like 250 firm orders from airlines, so like I said, the pot of gold is rich...