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The gulf stream would be less efficient, require more passengers and may not be able to land at as many airports.

I think they aim for some kind of long-range air taxi. Small groups which want to travel a long distance from A to B but a very short distance to and from A and B's respective airports. Business trips, most likely.

And probably the plane is no slouch at medium or even short range if it is operated by a non-airline company. Just not "ridiculously efficient".

If it can show real efficiency gains on short travel, it could probably consume the market on flights from major hubs to local, just for being able to cut costs in an area where there's lots of room to do so

For a lot of your questions, I think this thing is going to be marketed for defense purpose as a HALE (high altitude, long endurance) sensor platform that costs significantly less in purchase cost, and operating cost, than a global hawk. There's already companies flying retrofitted King Air and similar for this purpose for the DoD.

If it can carry 500 kilos at 65,000 ft for 24 hours without landing, and not cost a ridiculous amount in dollars per flight hour, that's something pretty unique.

In my totally non expert opinion the undercarriage and very low ground clearance also tell me it's intended to fly from paved strips in pristine condition, which is very different than the rough field capabilities of many single and twin airplanes powered by the PT6 turboprop or one of its derivatives.

That doesn’t really line up with how defense aircraft (or defense anything, for that matter) are financed and designed. Aircraft designs are created as part of a response to a Department of Defense request for proposal and design details are kept highly secret (they won’t even file patents to ensure that no details about the aircraft are leaked). Then the craft are tested from military bases to prevent people taking pictures. Also, a defense craft wouldn’t be seeking FAA approval (the FAA isn’t authorized to regulate military aircraft)

Maybe in the cold war, but these days there are plenty of repurposed civilian aircraft. They just swap out the avionics with some nicer things, add good cameras, and have a useable and proven platform. The airframe details are self-evident enough that they may not be worth keeping secret.

Not all, necessarily, they may have created the design with a HALE market as one of several market possibilities. Companies have self funded r&d projects to build things and then try to sell them to defence markets before. Scaled composites did it with their Ares, and so has embraer with their turboprop ground support plane.

Here's an example of a retrofit of a COTS platform for bespoke sensor platform use.

https://www.thedrive.com/the-war-zone/19921/these-secretive-...

> The propeller is a pusher configuration, which isn't inherently bad, but causes efficiency losses from turbulent air coming off the fuselage.

Teardrop shape greatly reduces turbulent flow behind the fuselage compared to the mainstream tube shape.

I'd like to see how that stacks up and what the actual width of the turbulent flow is.

A slow plane is vastly quicker than any ground based transport so speed is not absolutely vital, 300 mph is not breaking the sound barrier but it is 100 times quicker than being stuck in a traffic jam.

I think the shape looks right rather than odd, in particular the bulbous rather than elongated body. Plus with the straight wings this looks well optimised for low skin friction.

Experience of VW rear engined vehicles tells me there are advantages in having the engine at the back when it comes to noise. I thought the reasons we had the propeller at the front was to have it cool the engine and have the centre of gravity 'right'. This just looks right compared to what has gone on before.

Looking right is not necessarily what you want, we have been stuck too long on what a fast plane should look like. But there is something in aesthetics when it comes to these matters.

Seeing the runway is not necessarily that important, I would prefer a plane that does all the landing itself with no assistance needed. It is not as if a regular jet pilot can see the wheels of the plane when landing.

Do you think the engineers never thought of these things?

I'm sure they have. All of aircraft design is a tradeoff (cue that comic of if each different subteam had their way...). However, I'm not sure they've made the right compromises.

Some of that is due to the secrecy surrounding the aircraft. Especially the overall business strategy is in the shadows.

It's not even clear that this plane is close to the final size.

And to speculate about this strategy, those tradeoffs are valid input.

I don't have an aerospace degree, but I will nonetheless comment on a few of your comments:

Engine cooling: diesel engines need substantially less cooling than petrol engines, hp-for-hp.

Gearbox certification: you are generalizing from one example. Every turboprop has a gearbox. Most helicopters have a "complex" gearbox, coupling two (and sometimes three) engines.

Long propeller shaft: Not really a hard problem. Helicopter tail shafts seem more difficult.

Pusher efficiency: The propeller efficiency will be a bit lower for the reasons you mention, however the overall aerodynamic efficiency is likely to be higher. There are plenty of citations for this.

Pusher noise: Again, you are generalizing from one example (Avanti, in which the source of the noise is largely the turbine exhaust interacting with the propeller blades).

Forward visibility: I suspect they intend to use a camera. Other solutions are possible also. WW2 fighters had no forward visibility on landing.

Landing gear and door, tail strikes: yes, probably "prototype" stage engineering

Coffin corner: The potential problems are a consequence of specific airplane design. They are easy to avoid, though admittedly by sacrificing a smidgin of performance.

High altitude flight: I can't see that thing getting to 65,000 feet with that propeller and those wings... the number was taken from the patent, it seems, and may not have real world significance with the current design.

Overall, I think it is great to see a bit of innovation and experimentation happening in aviation again.

A piston engine at 65,000 feet? That’s unreal.

At that altitude, the turbocharger is doing most of the work.

Which is probably part of the interest/mystique in this project.

"Pusher configurations - especially pusher turboprops like the Piaggio Avanti are noisy"

From a passenger perspective?

Why is this, Aerodynamics?

I would have thought that a pusher configuration would have been a net benefit from a passenger noise POV, and aerodynamics wouldn't make much difference on the ground, would they???

I've never been lucky enough to fly in an Avanti, but the noise comes from the turbine exhaust being interrupted at 2000 RPM times 5 blades per revolution. Other pushers I've heard, such as a Skymaster and Long-EZ also make that noise so it may have more to do with the prop being in turbulent air. It's very distinctive.

Honestly, who flies in class A airspace? Can you even fly IFR in that airspace? Class E ends at FL600. (I just do bug smashers, so not sure what the majors do up in the pressurized space)

I think you’re a little confused. Yes, you can fly IFR in class E airspace. The majority of piston airplanes flying IFR do so in class E (the portion below 18,000 ft). Class E is not uncontrolled.

I’m not sure about what you mean with “who flies in class A airspace?” Most airlines and bizjets cruise in class A because their fuel burn is ridiculous at lower altitudes.

The reason that class A becomes to class E above 60,000 ft is because hardly any planes can fly that high. This plane almost certainly won’t go that high, regardless of what the patent application says.

Edit for clarity on why helix’s comment doesn’t make a ton of sense- airspaces go like this:

FL600 (approx 60k ft) and up: Class E

18k ft to FL600: Class A, only IFR flight is allowed, no VFR (even if the weather is good).

below 18k ft to 700 or 1,200 ft above ground: Class E, except around airports, where it can be Class B (big airport), Class C (medium airport), Class D (small airport with control tower), or still Class E (small airport without control tower).

below 700 or 1,200 ft above the ground: Class G, except around airports. Class G is uncontrolled, but you still have to follow the law- no buzzing residential areas and such. You cannot file an IFR flight plan in Class G space, mainly because ATC can’t reliably see you and prevent collisions with other planes.

Class E is controlled airspace but you can fly VFR without filling a flight plan; you are required to fly at altitudes that are xxx,500 ft so you don’t hit planes flying IFR at the xxx,000 altitudes.

You would have to file an IFR flight plan to get to 65k ft because you would transit Class A airspace during your climb and descent.

It seems logical that if there was available on the market a large number of planes capable of flying between FL600 and FL900, the relevant authorities would simply extend class A higher. At present there's no civilian aircraft whatsoever capable of those altitudes for long duration cruises, so it has been a moot point.