Comments on: US Air Force backs Valkyrie’s high-speed, amphibious jet-powered eVTOL

By: Jim

Jim — Wed, 16 Mar 2022 06:30:32 +0000

It sounds ridiculous, but it’s true. There are significant flight envelopes where an ideal air vehicle is more efficient than a comparable ground vehicle. And one of them is small passenger vehicles.

You’re right about Musk.

By: Sam J.

Sam J. — Wed, 16 Mar 2022 02:18:20 +0000

Jim says, “The energy lost to rolling resistance plus friction of any ground vehicle with tires is inherently and ineradicably greater than the energy lost to air resistance plus gravity of an optimal flying vehicle.”

I don’t think this is even close to right. An airplane is actually continuously throwing air down at a pressure and volume to equal the weight of the aircraft. A truck is not doing that. It has friction but it doesn’t have to throw it’s weight in energy down into the ground.

Rail is even more efficient. Truck tires lose a good deal of energy to flexing that is lost in heat but trains roll with very little friction. (Noting, most of the losses in trucks on the highway are from air friction).

There may be though a way that planes can be very efficient. Musk has hinted at this, although he has not publicly spelled it out. If you have electric planes, they will get more efficient as they go higher into thinner atmosphere. If you could rapidly go to a very high altitude, go at high speed in thin air, then coast down, it may very well be that it would be more efficient than trucks or trains. The rapid travel in thin air means that the plane would only have to support it’s weight for a greatly reduced time. Lowering energy cost. Maybe, even more efficient than boats, but not likely for boats.

His Starship will be vastly more efficient than planes over long distances..

By: Pseudo-Chrysostom

Pseudo-Chrysostom — Tue, 15 Mar 2022 12:43:49 +0000

Of course, which is why global logistics are all handled by airplane, and not ships, trains, and trucks…

By: Jim

Jim — Tue, 15 Mar 2022 07:48:04 +0000

The energy lost to rolling resistance plus friction of any ground vehicle with tires is inherently and ineradicably greater than the energy lost to air resistance plus gravity of an optimal flying vehicle.

By: Pseudo-Chrysostom

Pseudo-Chrysostom — Mon, 14 Mar 2022 02:52:47 +0000

Ground vehicles have the advantage of their weight being supported by the ground. You just have to get them rolling with low resistance.

A flying vehicle, on the other hand, needs to carry it’s own weight, which can be an issue that compounds exponentially. This is a fundamental problem with attempts at ‘battery powered’ aircraft. The power density of carbon-hydrogen bonds, in their various forms, is hard to beat. (And especially hard to beat with the same convenience.)

By: Ezra

Ezra — Sun, 13 Mar 2022 12:57:22 +0000

Objects, especially those touted to do it all, can usually do everything only in a mediocre manner. If that.

This eVSTOL just sounds too good to be true.