Reno-based Valkyrie Systems Aerospace has received a research grant from the US Air Force to develop its HoverJet Guardian, which combines electric VTOL and high-speed jet cruise with amphibious and hovercraft capabilities:
The VTOL system appears to use a quadcopter layout, with four props (or perhaps eight mounted coaxially) hiding in holes in its fat wings. These get it off the ground in relatively civilized fashion, but then a pair of Pratt & Whitney 545c turbofan engines take over, adding a combined 8,200 pounds of horizontal thrust to the mix.
The result, claims Valkyrie, is a cruise speed of 340 mph (547 km/h), a transonic top sprint speed of 700 mph (1,127 km/h), and a whopping 15 hours of endurance at altitudes up to 40,000 feet (12,192 m).
This is no small bird. Measuring 24 x 30 x 6 ft (7.3 x 9.1 x 1.8 m), it’ll weigh 4,200 lb (1,905 kg) empty. Add fuel, a pilot and/or up to 2,000 lb (907 kg) of cargo, and that little VTOL system will have to lift the Guardian at a maximum takeoff weight of 12,000 lb (5,443 kg).
That’s considerably heavier, say, than the Joby S4, which is said to be around 8,820 lb (4,000 kg), and it uses fewer, smaller propellers. So those props are going to have to work hard. On the other hand, since it’ll run primarily on jet fuel, energy storage won’t be an issue at all, and the electric systems can be tuned for high power rather than efficiency.
High-speed VTOL is not all these things bring to the table, either. The Guardian, and its smaller brother, the Eagle UAV, are apparently capable of landing on water, and offering “three modes of operation: aircraft, hovercraft and amphibious.”
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.
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.)
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.
Of course, which is why global logistics are all handled by airplane, and not ships, trains, and trucks…
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..
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.