The important question is
How many buses is a 35m wingspan
Defence kit megalith BAE Systems is working on a drone that "has the potential to fly for up to a year before needing maintenance", in a challenge to Airbus' Zephyr being trialled by the Ministry of Defence. The Phasa-35 drone, under development by Hampshire-based firm Prismatic with the backing of BAE Systems, is intended to …
I'm curious as to why the Airbus example couldn't do a whole year, I'd have thought if you can survive 45 diurnal cycles then you've got the solar and battery tech sorted to effectively stay up indefinitely.
I mean stand fast doing it somewhere extreme like North of the Arctic circle.
Back in the early spy satellite days, they did exactly that: Corona (satellite)
I would guess the batteries.
The nominal rating on a given cell is not an absolute, it's a value that it will maintain over a given number of charge-discharge cycles.
I am guessing that the Airbus unit is using older cell design and thrashing the snot out of them, hence the short lifespan.
I am guessing that the Airbus unit is using older cell design and thrashing the snot out of them, hence the short lifespan.
Yeah, by the looks of it the Zephyr uses Lithium-Sulphur, the Prisma is Li-Ion.
That said, the comparison in the article is a bit unfair and lacking in context.
The Zephyr is a 25m wingspan aircraft that weighs ~50-60kg.
The Prismatic is a 35m aircraft that weighs ~150kg.
Shocker, an aircraft that weighs 3 times as much has found an extra 10kg of payload capacity! One would assume that the extra wingspan/solar panel area and enlarged vehicle allows them to generate more lift and thrash a larger pool of cells less hard.
The next generation of Airbus (Zephyr-T) is getting a stretched wing and touting "year round operations" though not until 2020, so it seems like Prismatic have made the jump straight to the big-brother configuration and leap-frogged Airbus instead of working up through smaller demonstrators.
It's a good question. If I had to guess, i'd say something on the aircraft is only rated for around about a thousand hours in service (~42 days) with a 10% leeway before it has to have a routine service (which brings you to 1100h /24 = 45.8 days)
I also suspect that there is a difference between being able to build something that can in theory stay aloft for that long, and building something that the Civil Aviation Authority (or Military Aviation Authority) will let you fly for that long without a routine service to check for airframe fatiuge/damage.
Or maybe i'm just cynical after being exposed to salesmen for too long. In short, one firm has hardware that flies. The other firm has vapourware that they promise that they could build, and should somebody pay them to do so then it could/should have the performance claimed in their advert.
"routine service to check for airframe fatiuge/damage."
ISTR that the biggest concern for airframes is pressure cycles. On a long flight duration drone A) there's no pressure cycling to speak of. B) there's probably no pressure vessel C) there's no self-loading cargo to complain if the pressure vessel fails.
Running an engine for a year straight might raise some concerns, but continuous-duty electrical motors are a thing that exists.
Those wings look ace at gliding, and gliders are brilliant at losing height slowly. The best competition gliders lose height at 100 ft/minute.
I'm too lazy to do real research, so let's assume the thin air at that height means it loses height at 200 ft/minute instead. Don't argue. The god of 'pluck random multipliers from thin air' decrees this lazy logic is sound.
Let's also assume it's allowed to descend from 70,000 feet to 30,000 before some officious minion requires it to land. That will take 3 hours 20 minutes which offers a useful 'buffer' during the night, should the batteries have too little boogie juice to run the engine.
Then the sun rises and it can climb back up to 70,000 ft during the day.
Perhaps it's something along those lines which determines the operational time? The battery tech means it loses a little height each day, and eventually officious minion number one gets to press the big flight abort button.
I wouldn't put too much importance in the headline picture; apart from the high aspect-ratio wings, which are to be expected, the only other significant detail it shows is probably incorrect - I can't think of any good reason why the props have been placed so far out on the wings, and quite a few reasons why they shouldn't be placed there.
That would imply the sorts of people they want to watch with this kind of much, much cheaper kit have weapons capable of detecting and hitting the thing....
Even if they do, it's still alot cheaper to lose compaired to a U2. Also, comparable platforms are already in use but don't have the longevity (think predator or watchkeeper drones) without being lost constantly.... so I'd rather say you're missing the mission profile thinking that it'd be doing high risk spy jobs rather than keeping watch on local nut jobs with guns.
This isn't warzone tech, I'd predict it's mainly going to be used for ubiquitous monitoring on domestic populations. Much cheaper and lower profile than using police helicopters for the job.
It's a pity they're so focussed on the surveillance role, the platform might also be useful for comms. Think satellite phones, but much, much cheaper to run.
"Much cheaper and lower profile than using police helicopters for the job."
I wonder how much the camera/lens combo weighs that could replace a low altitude police chopper and still get the same close up detail? Not to mention the gear for night vision, ie honking bright search lights.
"Even if they do, it's still alot cheaper to lose compaired to a U2. Also, comparable platforms are already in use but don't have the longevity (think predator or watchkeeper drones) without being lost constantly.... so I'd rather say you're missing the mission profile thinking that it'd be doing high risk spy jobs rather than keeping watch on local nut jobs with guns."
And with the EU spat over Galileo, it does make one wonder if a fleet of these could be tasked as a SatNav (equivalent) system at significantly lower initial and running costs. It'd probably need a few ground stations so the aircraft can get their own locations. Not much use for overseas adventures though.
With this kind of payload mass and flying at these altitudes, this system is designed to carry communication equipment and little else. Fast communications / internet with no ground infrastructure is the goal. Earth observation payloads (visible light, hyper spectral, radar, lidar) are too heavy, and cloud cover will often obscure the line of sight (except for Radar).
If the goal had been surveillance, then the system would have ended up looking a lot more like the U2.
Clouds. At 55-70,000' there's a lot of weather beneath you so the chances of being able to see what you're interested in are pretty low in London, and not great in LA with the coastal fog and/or smog. For long-term surveillance it's not a major issue, for real time following car chases and the like it makes it a non-starter.