This is the only article of original substance on the internet, everyone else copied pieces from it. I still can't find an answer (or even anyone asking the question): How does it land?
There's no landing gear, it takes off from a dolly, and it's only designed to stay up for 'months at a time.' Does this mean it needs extensive repairs after it crash lands on runways that are half its width? The ScanEagle UAS also has no landing gear but is small enough to be caught by a cable mid-air [1].
Having no journalists present for their test launch and only getting officially produced videos and non-critical reposts is not enough.
I believe it summons a Tesla Uber on Autopilot(tm) with a proper roof rack to drive down the runway, and wafts down upon it and then they roll on into the hangar together.
I would speculate that it lands on skids. Skids are pretty lightweight and will do fine for landing, but you need a lot of power to take off with them unless you're on ice or snow.
(You know your landing gear is up when it takes full power to taxi.)
good call. The U2 has only gears in the center and "skids" on the wings, trying to get as slow as possible before they are needed (an some muscle car following for guidance). https://youtu.be/hxFz6ImB8fI?t=165
With a sea level low speed capability of staying airborne at 25mph, I suspect even given it's huge size and delicate construction - getting it down to a few feet off the ground and slowing down till it stalls, just like nearly all model gliders do, would be practical. If you look carefully at image #3 in the gallery - it looks like they've got tubular metal skids under each motor pod. I'd guess that's what they land on.
They write "The automatic landing algorithm also performed well, tracking the glide path and centerline with expected accuracy."
That's very little to go by, but this plane likely can fly very slowly. I guess they plan to glide it almost into ground, stall it to further decrease speed, and then 'crash' it in some fairly soft spot. Alternatively, they could land it on top of that dolly, but that might be more of a challenge.
It seems to follow the Stanford Swift aerodynamic philosophy: low taper and winglets.
This is different from the recent NASA Prandtl-d aircraft which is of the Horten paradigm: lots of taper and no winglets.
It's possible the former is a lot easier to build, because of constant chord, especially as a solar powered platform.
With batteries you can distribute the weight very well so designing for things like wing root moment might not be the defining thing, instead some re complex aeroelastic design criteria.
Very fascinating to see this resurgence of flying wing again, popping up in many other places too.
I have no clue about half of the things you just said. Can you guide us, the ones with less knowledge about aerodynamics-- to some resources which we can watch/read? (preferably online and free, of course :) )
Basically in a wing, there's overpressure on the bottom and underpressure at the top. This is all good. But it causes a problem at the wingtip, the air escapes and goes from bottom to top. The tip vortex. Does not contribute to lift, causes drag, so is bad.
So you can put a vertical winglet there to diminish the tip vortex, or to extract thrust from it. Or you can extend the wing but make it have a lower angle of attack near the tip, again extracting thrust, basically a horizontal winglet if you will.
Then there's the issue of stability. A plane is stable when, if you increase the angle of attack, the rearward lifting surfaces have more increase in negative nose down moment than the positive nose up moment of the forward lifting surfaces. So the aircraft tends to correct itself (move back to lower angle of attack).
In an ordinary plane it means a wing near the center of gravity and a tail with a lower angle of set incidence far behind.
In a canard, the center of gravity must be between the wings and the front wing must be set in a higher incidence.
In a flying wing it means sweepback and twist: the outer portion of the wing must act as a tail. The outer portion must be twisted nose down so it has a lower angle of incidence.
Flying wing design is harder since there are more functions it must do than in a more conventional plane.
That is a really really short version of it. It didn't mention positive moment airfoils etc.
Does it not include balloons? They want surface area, slow movement, and the ability to operate on little to no energy. Wouldn't a large, permanent balloon filled with helium and sized to perfectly offset the weight of the aircraft be better? It seems like it would be easier just make it neutral buoyancy than to try to constantly provide lift.
Yes, I'd like to see an evaluation of different designs.
Why not multiple balloons attached to the ground (to overcome wind drift), at not too high altitude, perhaps interconnected by line-of-sight communication.
But not too slow. You need to be able to stay on station when there is a wind. You would need some sort of powered airship. To be better than a wing it would have to have less drag.
I don't think that's it's "cruise speed", I think that's it's minimum flight speed.
In the context of Challenge #3, they talk about Aquila's "25mph" speed comparing it to a commercial airliner at "200mph" - that's about takeoff speed for a 747, which then goes on to cruise at somewhere around 700mph, so if the Aquila has a similar operating flight envelope you'd expect a "cruise" speed of perhaps 80-90mph.
Also, it's entirely possible the Aquila is designed to have a wider efficient flight envelope that a 747, which a) was mostly designed using the best aerodynamics available in the 50s/60s, b) is limited by the sound barrier at the top of it's speed range (it'd hit Mach1 at ~750mph and things go strange aerodynamically there), and c) needs to be highly optimised for air-breathing jet engine fuel efficiency - which requires some tradeoffs electric power isn't constrained by (the thin cold air at 70,000feet doesn't change the power output of an electric motor the way it does a kerosine-burning jet).
It's wind shear. Wind at altitude tends to travel at right angles to the pressure gradient, as the coriolis force does its thing. Wind near the ground tends to travel directly from high pressure to low pressure, because of friction with the ground. That friction also tends to slow it down. Net result, it's common for wind to turn and increase in speed as you go up.
The article says that it cruises at an altitude where the air density is 10x less than at sea level. Lift is proportional to density and to the square of speed, so it would need to go about 3x faster to generate the same amount of lift at altitude, or about 75MPH.
That the stall speed at altitude (give or take). 75 mph winds aren't uncommon at altitude, but that might work to their advantage to loiter. I've hovered my dad's Cessna before to take pictures and such when the headwind is there, so they should be able to take advantage of that as well.
Hydrogen really isn't all that bad. It's used lots in industry/academia as a process gas, in normal rooms, in processes that involve high temperatures, mixtures of chemicals etc.
Total brand confusion. There is already a well established manufacturer of light aircraft called Aquila[1]. My initial thought was that they'd launched a new model.
It would be pretty high up, although still reachable by fighters.
I doubt people in a friendly country would shoot it down, although I could certainly see Iran having issues of someone flying one along the border providing "free" Internet to people inside their borders. No doubt they would be able to successfully jam it's electronics.
Perhaps more worrisome would be having these things fall out of the sky. Being a long as they are, structural failure by suddenly overloading the wing might turn them into the moral equivalent of the Maple Seed of Doom[1] on their way down. Probably reasonably low risk in rural areas but something to think about if they are taking off from airports in Kansas city for example to fly out over the great plains.
It's that latter bit that makes me even more curious. In the write ups so far, both the 'project loon' and the Aquila videos suggest this very expensive piece of equipment is going to be flying over sparsely populated areas to provide Internet. But with so few customers how do you cover the cost? Simple economics would suggest you'd want to fly it over a really densely populated city, then you would have a huge addressable market rather than over the corn fields of Iowa or the back roads of Oklahoma.
It suggests to me that its easier to spend a million dollars operating a couple of these over a small town than it is to get permission to pull a fiber along the power grid. The latter is more of a policy issue rather than a technology issue though.
If you are operating over a large and crowded area you are going to be facing more competition for customers (from competitors that can use the population density to justify the initial build costs of better infra) and you are also going to be facing more spectrum competition and interference. While flying over the corn fields of Iowa may not seem too useful, each plane could have a relatively large footprint and could also be used to enable a lot of non-urban IoT applications. Sell bulk bandwidth to precision farming equipment shops, mobile applications in the area, and households poorly served by old copper telco infra. Not necessarily huge bucks, but you could probably do it at a cost that would crush competing data providers in that plane's footprint and lock up a nice little revenue stream.
So this plane is supposed to fly continuously without landing gear?
I hope they considered poor flying conditions lasting for weeks in their model, things like heavy rain for a couple of weeks or even hurricanes. Sometimes there's a good reason why the Internet is not yet available somewhere.
There's no landing gear, it takes off from a dolly, and it's only designed to stay up for 'months at a time.' Does this mean it needs extensive repairs after it crash lands on runways that are half its width? The ScanEagle UAS also has no landing gear but is small enough to be caught by a cable mid-air [1].
Having no journalists present for their test launch and only getting officially produced videos and non-critical reposts is not enough.
[1] https://www.youtube.com/watch?v=w88uCC2Jv48