Manned Solar Powered Airplane Aloft 26 Hours!

[Broomstick]

When I first saw this I thought it was talking about a drone - no, this is a solar powered airplane that carries a human pilot on board and was able to sufficiently charge batteries to stay aloft overnight.

PARIS — Slender as a stick insect, a solar-powered experimental airplane with a huge wing span completed its first test flight of more than 24 hours on Thursday, powered overnight by energy collected from the sun during a day aloft over Switzerland.

The organizers said the flight was the longest and highest by a solar-powered craft, reaching an altitude of just over 28,000 feet above sea level, at an average speed of 23 knots, around 25 miles per hour.

The plane — Solar Impulse — landed where it had taken off 26 hours and 9 minutes earlier at Payerne, 30 miles southwest of the capital, Bern, after gliding and looping over the Jura Mountains, its 12,000 solar cells absorbing energy to keep its batteries charged when the sun went down.

The pilot, André Borschberg, 57, a former Swiss air force fighter pilot, flew the plane from a cramped, single-seat cockpit, buffeted by low-level turbulence after takeoff and chilled by low temperatures overnight.

“I’ve been a pilot for 40 years now, but this flight has been the most incredible one of my flying career,” Mr. Borschberg said as he landed, according to a statement from the organizers of the project. “Just sitting there and watching the battery charge level rise and rise thanks to the sun. I have just flown more than 26 hours without using a drop of fuel and without causing any pollution.”

The project’s co-founder, Bertrand Piccard, who himself achieved fame by completing the first nonstop, round-the-world flight by hot air balloon in 1999, embraced the pilot after he landed the plane to the cheers of hundreds of supporters.

“When you took off it was another era,” The Associated Press quoted Mr. Piccard as saying. “You land in a new era where people understand that with renewable energy you can do impossible things.”

The project’s designers had set out to prove that, theoretically at least, the plane with its airliner-size, 210-foot wing span could stay aloft indefinitely, recharging batteries during the day and using the stored power overnight. “We are on the verge of the perpetual flight,” Mr. Piccard said.

The project’s founders say their ambition is for one of their craft to fly around the world using solar power. The propeller-driven Solar Impulse, made of carbon fiber, is powered by four small electric motors and weighs around 3,500 pounds. During its 26-hour flight, the plane reached a maximum speed of 68 knots, or 78 miles per hour, the organizers said.

The seven-year-old project is not designed to replace jet transportation — or its comforts.

Just 17 hours after takeoff, a blog on the project’s Web site reported, “André says he’s feeling great up there.”

It continued: “His only complaints involve little things like a slightly sore back as well as a 10-hour period during which it was minus 20 degrees Celsius in the cockpit.

“That made his drinking water system freeze up and worse of all his iPod batteries die.”

Now, for a private pilot such as myself interested in flying in good weather during the daytime you could probably get by with a smaller power system, which would reduce size and wait. The electric engines are probably quieter than gas or diesel (though there would be some noise still, and also from the props, friction with the wind, etc). This could allow us to fly while causing less disturbance to the neighbors and avoiding criticisms regarding pollution. And, personally, I'd be happy to never have to get leaded gasoline on my hands ever again.

But aside from that - this has all sorts of other potential applications, from UAV's on Earth (well, above Earth, technically) to using these to power exploratory robots on other planets.

[Hawkwings]

Imagine generals salivating at aircraft like Global Hawk, except capable of staying up indefinitely.

I am wondering, though, how topped off the batteries were at the beginning of the flight. Could they have recharged enough during the day to fly through another night?

I'm also wondering about how much the performance would have improved had they gone pilotless. Certainly it could have climbed higher and lost less altitude at night, but would the power demands have dropped significantly?

[Eleas]

Imagine generals salivating at aircraft like Global Hawk, except capable of staying up indefinitely.

I am wondering, though, how topped off the batteries were at the beginning of the flight. Could they have recharged enough during the day to fly through another night?

I'm also wondering about how much the performance would have improved had they gone pilotless. Certainly it could have climbed higher and lost less altitude at night, but would the power demands have dropped significantly?

As long as microfractures exist, the airframe is always going to have a shelf life. And that, IIRC, is fairly unavoidable when aluminium is the mix.

[Broomstick]

Of course - removing the pilot would have removed at least 100 lbs of weight (call it 50 kg, very roughly) assuming some of the pilot's mass is replaced with electronics. Even in a 3,500 lbs airplane removing 100 lbs of weight will make a notable difference in performance... but you know, sometimes you want a human on board (or sometimes the human wants on board). Less weight means less demands on power. I don't have the math to calculate the savings exactly, but yes, they would be significant.

We already have solar-powered drones that can stay aloft indefinitely - being efficient enough to carry a sack of meat along and still stay up 26 hours, that's the new impressive feat here.

[Broomstick]

As long as microfractures exist, the airframe is always going to have a shelf life. And that, IIRC, is fairly unavoidable when aluminium is the mix.

Actually, Solar Impulse is mostly carbon fiber (re-read article) and anyhow, ALL airframe materials are subject to eventual deterioration and thus all airframes have a "shelf life". At least aluminum "microfractures" are easier to detect than those in a carbon fiber airframe.

[Eleas]

As long as microfractures exist, the airframe is always going to have a shelf life. And that, IIRC, is fairly unavoidable when aluminium is the mix.

Actually, Solar Impulse is mostly carbon fiber (re-read article) and anyhow, ALL airframe materials are subject to eventual deterioration and thus all airframes have a "shelf life". At least aluminum "microfractures" are easier to detect than those in a carbon fiber airframe.

Pardon, I shouldn't have shot off my mouth, being a layman in matters of aviation. I've been given the impression that aluminium is a bit of an oddity in its tendency to develop fractures from continuous wear, and somehow it stuck in my mind.

[Broomstick]

I'm sorry if that came off at all snarky - I didn't mean it to.

Everything eventually breaks, and everything differs in how that happens. Wood, for example, starts to show visible wear and even splinter/fray. I'm not sure how steel breaks down over time - there have been a few steel planes, but not many. Aluminum, when they started using it, took aviation somewhat by surprise in that it did differ somewhat in the pattern of breakdown, leading to a few tragic accidents, but mostly we've got a handle on that now. Composites are wonderful in many ways, but they can fracture in ways that you can't see, and we haven't worked out a really great way to detect them yet (that I know about - things are always changing). Metals can, too, but we've got ways to detect those tiny problems before catastrophic failure... largely because we've been using them longer and have had more time to research the problem.

I'm a pilot, I just fly the things - we have people far more conversant with the engineering involved who, if they are so inclined, can no doubt fill us in on this with more detail.

[adam_grif]

There's going to be some issues when you want to strap on big sensor suites and missiles though, right? Just in weight terms? Those things aren't light.

[Temujin]

Imagine generals salivating at aircraft like Global Hawk, except capable of staying up indefinitely.

I do remember seeing some concepts for both UAV and manned aircraft like this in recent years, and as Broomstick mentioned, a UAV for Mars exploration.

[Mr Bean]

There's going to be some issues when you want to strap on big sensor suites and missiles though, right? Just in weight terms? Those things aren't light.

Remove the pilot make this thing a drone full of camera/passive sensor equipment and you might get 24 hour dwell times out of it un-manned. I'd love to have something like that for say... border security since the next step in law enforcement seems to be getting UAV's of their own. You won't be able to strap bombs to something like this. But there's nothing thats says you can't simply use it for target identification and leave the bomb tossing to linked in artillery or other aircraft.

[Eleas]

I'm sorry if that came off at all snarky - I didn't mean it to.

No worries. It's truthfully less about you and more about my own signal-to-noise ratio. Lately, it's been in apparent decline, and that worries me. So when I get sloppy, I take it harder than I should.

Everything eventually breaks, and everything differs in how that happens. Wood, for example, starts to show visible wear and even splinter/fray. I'm not sure how steel breaks down over time - there have been a few steel planes, but not many. Aluminum, when they started using it, took aviation somewhat by surprise in that it did differ somewhat in the pattern of breakdown, leading to a few tragic accidents, but mostly we've got a handle on that now. Composites are wonderful in many ways, but they can fracture in ways that you can't see, and we haven't worked out a really great way to detect them yet (that I know about - things are always changing). Metals can, too, but we've got ways to detect those tiny problems before catastrophic failure... largely because we've been using them longer and have had more time to research the problem.

I'm a pilot, I just fly the things - we have people far more conversant with the engineering involved who, if they are so inclined, can no doubt fill us in on this with more detail.

This is fascinating. Are there ever hybrid planes (i.e., for instance, wooden structure reinforced by a metal spine, or something like it)?

[Darmalus]

Imagine generals salivating at aircraft like Global Hawk, except capable of staying up indefinitely.

I do remember seeing some concepts for both UAV and manned aircraft like this in recent years, and as Broomstick mentioned, a UAV for Mars exploration.

I wonder what such an aircraft would look like on Mars. The air is dreadfully thin and the sunlight is weaker, but gravity is weaker as well. But those challenges pale before surviving the continent sized dust storms that crop up from time to time.

[Hawkwings]

Hmm, a quick googling seems to show that the only indefinite-endurance drones we've got are currently fairly small, certainly nothing on this scale.

Also, the BBC says that the plane had three hours of battery power left at morning. Of course it also says that this is the highest flight by a solar powered plane (Helios flew at 90,000+ ft) soI'd like to see where they're getting this information.

Cracks in composites are very hard to find, comparatively. I know that they use several forms of acoustic examination. When the part is initially constructed, they put it in a rig and shoot a high pressure stream of water at it, then methodically sweep it back and forth over the part and listen for changes in the sound coming off, which could indicate defects. They also use ultrasound for this. Anyways, I meant "indefinite" as in "not limited by fuel". Of course they're still going to have to bring it back to do maintenance and whatnot.

Yes, staying aloft overnight with 100 lbs of extraneous cargo is quite impressive. If an aircraft like this were put into military use, I predict that it would strictly be an observation craft, and probably not as versatile as the Global Hawk. It's much bigger, more fragile, slower, flies lower, and can't carry as much. Its only upside is that it can stay in the air longer. For roles like examining oil pipelines and border patrol and such, it's going to be pretty good, if a bit overkill. You don't need something this big to do that.

[Broomstick]

This is fascinating. Are there ever hybrid planes (i.e., for instance, wooden structure reinforced by a metal spine, or something like it)?

Oh, sure - I've flown ones like that. The Bellanca Citabria I did my tailwheel training in, for instance. The fuselage had a steel and aluminum "skeleton" but the wings were entirely wooden. The Bellanca SuperDecathlon had that same type of construction in a full aerobatic airplane. Come to think of it - so did the Stearman, metal fuselage structure (overlaid with cloth) and wooden wings. Some of the ultralight/sportplanes I've flown were mixed composite and aluminum. And for the past couple decades Airbus and Boeing passenger airliners and big cargo planes have been a mix of metal and composite. Nothing unusual in such mixed construction - as my examples show, it dates back to at least the 1940's (the Stearman) and if anything is becoming more common.

Really, it was the era of nearly all aluminum airplanes - roughly the 1950's through the 1980's - that was the anomaly.

[Broomstick]

Imagine generals salivating at aircraft like Global Hawk, except capable of staying up indefinitely.

I do remember seeing some concepts for both UAV and manned aircraft like this in recent years, and as Broomstick mentioned, a UAV for Mars exploration.

I wonder what such an aircraft would look like on Mars. The air is dreadfully thin and the sunlight is weaker, but gravity is weaker as well. But those challenges pale before surviving the continent sized dust storms that crop up from time to time.

Air density is a far more significant factor than gravity when it comes to flight. The gain from lighter Martian gravity in no way compensates for it's (by human standards) nearly non-existent atmosphere.

However, aircraft have been developed for Mars. They are invariably very light with enormous wing area by Earth standards. It is certainly possible to fly in the Martian atmosphere, but it's like flying at 100,000 feet above the Earth. In fact, that's about where they've been testing one proposed Martian flyer lately, including testing its mechanism to unfold and self-deploy.

Being able to use solar power for such a vehicle would be immensely helpful, as it would eliminate the need to carry chemical fuel, not to mention the problems of burning fuel in a thin, oxygen-poor atmosphere. One of the reason we got as much as we did out of the Mars Rovers is because of solar power, a solar powered Mars aircraft might do equally well.

[Sea Skimmer]

Pardon, I shouldn't have shot off my mouth, being a layman in matters of aviation. I've been given the impression that aluminium is a bit of an oddity in its tendency to develop fractures from continuous wear, and somehow it stuck in my mind.

Basically the way it works Aauminum has a fatigue life, which means even when an aircraft is sitting on the ground its lifespan is slowly wasting away from stress under its own weight. Of course actually flying is much worse. In contrast steel has a fatigue point, beyond which it has limited fatigue life, but under which it can be subject to external stress but will basically least forever as long as it’s protected from corrosion. This is why we can expect steel things like large buildings and bridges to last hundreds of years, but planes only have lives measured in thousands of hours (in typical operations you’ll break the plane from flying it long before that ground stress actually matters). Carbon fiber is a lot like aluminum, but as people have mentioned it tends to crack internally and out of sight; then catastrophically fail without any other warning.

As for solar powered recon planes, the military and DARPA have projects for that falling out the ass. The trouble is for a useful recon plane you don’t just need enough power to fly, you need enough power to fly and operate the sensors and the radio to send out the data (manned or not). That extra power consumption makes life a lot more difficult, and means that most military projects need to use fuel cells to store power for nighttime, not batteries, which is of course much more complicated. You also need enough engine power to cope with less then ideal weather and winds. But batteries get better every day, which is what made this flight possible, and they’ve got a long way to go before we max out how much energy they can deal with.

Course you also need a battery which can not only provide the power for once night, but for many nights to make the idea economical, and batteries loose capacity the more they cycle.

[Broomstick]

Also, the BBC says that the plane had three hours of battery power left at morning. Of course it also says that this is the highest flight by a solar powered plane (Helios flew at 90,000+ ft) soI'd like to see where they're getting this information.

Probably meant by a manned solar powered airplane. Media editing is not what it used to be.

Yes, staying aloft overnight with 100 lbs of extraneous cargo is quite impressive. If an aircraft like this were put into military use, I predict that it would strictly be an observation craft, and probably not as versatile as the Global Hawk. It's much bigger, more fragile, slower, flies lower, and can't carry as much. Its only upside is that it can stay in the air longer. For roles like examining oil pipelines and border patrol and such, it's going to be pretty good, if a bit overkill. You don't need something this big to do that.

Compare the SR-71 with the U-2 spyplane, the latter of which was comparatively bigger in wingspan, more fragile, slower, and couldn't carry as much - both were useful. As for the Solar Impulse - the limiting factor here for altitude was almost certainly the human pilot and not the aircraft! Flight about 30,000 feet for any significant length of time requires a pressurized suit or cockpit even with 100% oxygen supplied to the pilot, and given the size/weight of this thing they may not have had that at all.

The problem with using it as a UAV for things like pipeline and border patrol is that the see-and-avoid technology for UAV's is still pretty much shit these days, and that's low enough to interfere with other air traffic. With no worries about fuel you might as well put a human being in the cockpit for those assignments rather than flying it remotely, where you'd still have a human you have to pay to do the flying.

With many of the current airplanes used for low-level stuff like pipeline inspection fuel costs can be 2/3 to 3/4 of hourly operating costs (when they use helicopters it costs 3-4 times as much per hour, but I have no idea what percentage fuel costs are with those). Even if initially the solar power system added some cost to the airplane not needing to shell out for petro-fuel could quickly make up the difference.

[Hawkwings]

Just for an example of how important air density is...

The Solar Impulse climbed to 8700m during the day. The air density at that altitude is about 0.483435 kg/m^3
At night, the plane glided down to 1500m, where it tooled around overnight. The air density at that altitude is about 1.058067 kg/m^3

The endurance of an airplane depends linearly on the air density, meaning that by dropping down to 1500m altitude, the pilot doubled his endurance.*

*disclaimer: This is assuming flight at constant altitude and lift coefficient, which may not exactly have been the case.

[Broomstick]

Pardon, I shouldn't have shot off my mouth, being a layman in matters of aviation. I've been given the impression that aluminium is a bit of an oddity in its tendency to develop fractures from continuous wear, and somehow it stuck in my mind.

Basically the way it works Aauminum has a fatigue life, which means even when an aircraft is sitting on the ground its lifespan is slowly wasting away from stress under its own weight. Of course actually flying is much worse. In contrast steel has a fatigue point, beyond which it has limited fatigue life, but under which it can be subject to external stress but will basically least forever as long as it’s protected from corrosion. This is why we can expect steel things like large buildings and bridges to last hundreds of years, but planes only have lives measured in thousands of hours (in typical operations you’ll break the plane from flying it long before that ground stress actually matters). Carbon fiber is a lot like aluminum, but as people have mentioned it tends to crack internally and out of sight; then catastrophically fail without any other warning.

Just to add to the fun - some composites have issues with both UV - meaning sitting out in the sunlight degrades your airplane unless you are very careful in coatings, and even then you have to immediately fix any wear on the coating (friction with the air alone, must less dust, rain, etc., will wear away any aircraft skin). ALL composite aircraft are ALWAYS painted - they have to be, and the higher they fly the more important that is, because the higher you go the more intense the UV. Small composite aircraft are usually hangared. For those that aren't, or for taking extended trips, there are aircraft covers available to provide added protection when not in flight. Commercial airlines... I assume maintaining the coating is part of regular maintenance.

Some composites also have temperature issues - the Diamond Eclipse I flew had dire warnings (by which I mean words like "YOU WILL DIE" featured in the cautions regarding consequences for screwing up) about the main spar getting above a certain temperature and said spar was equipped with sensors which had to be checked prior to flight. It's a real bummer if your airplane heats up on a hot summer day and turns the main spar into a limp noodle.

Not that any material is safe - those of us who fly cloth covered airplanes are cautioned not only about the expected hazards, such as tears from sharp objects (a reg from 1922 that was still on the books when I started flying in the 1990's prohibited wearing spurs in the cockpit - you just know there's a hell of a story behind that one!) but also that, for some inexplicable reason, cows LOVE to eat the skin off airplanes. Even more than goats love to eat it, apparently, but then, goats are famous for eating anything. Apparently, a small heard of dairy cattle can strip the skin off a vintage plane in a matter of minutes if they've a mind to do so. Given that such planes are most often flown in rural America these days that is not entirely a trivial concern.

What this boils down to is that nothing is perfect and all aircraft involve compromises.

[Hawkwings]

Broomstick:

Of course the U-2 was less capable than the SR-71 in terms of speed, range, ceiling, payload, etc. However, they were built for vastly different missions, and the U-2 could still carry a sizable payload of cameras. I'm simply saying that if it takes this enormous of a solar aircraft to simply get 100 lbs into the air, it's not going to be terribly useful for the kind of applications that surveillance aircraft are currently used for.

Good point about the pilot's limitations on altitude. Apparently max altitude for the Solar Impulse is around 12,000m.

Re: UAVs and collision avoidance, is there an altitude below which private small craft typically do not fly? If so, fly the UAVs under this altitude. I can't imagine patrolling the border in a vast expanse of desert you would run into much terrain avoidance issues. As for oil pipes, well, that's getting trickier. More navigation hardware needed then, maps and positioning systems.

[Sea Skimmer]

Compare the SR-71 with the U-2 spyplane, the latter of which was comparatively bigger in wingspan, more fragile, slower, and couldn't carry as much - both were useful. As for the Solar Impulse - the limiting factor here for altitude was almost certainly the human pilot and not the aircraft! Flight about 30,000 feet for any significant length of time requires a pressurized suit or cockpit even with 100% oxygen supplied to the pilot, and given the size/weight of this thing they may not have had that at all.

The sensor payload on the SR-71 and U-2 are about the same at 3,500lb. The difference between the planes is really just one of loiter time vs. penetration time. Global Hawk has about the same payload too, no surprise about that. Thousands of B-17 crews flew well enough at 30-32,000 feet without needing pressurization, and the higher flying B-29 almost always went into combat with the pressurization turned off to avoid the risk of explosive decompression. Certainly its harsh, but it can very much be done for long missions.

The problem with using it as a UAV for things like pipeline and border patrol is that the see-and-avoid technology for UAV's is still pretty much shit these days, and that's low enough to interfere with other air traffic. With no worries about fuel you might as well put a human being in the cockpit for those assignments rather than flying it remotely, where you'd still have a human you have to pay to do the flying.

The military is finally getting close to fielding a solution to that, in the form of a very compact (small book sized) MMW radar with enough resolution to detect birds and power lines about 1 mile away, other aircraft much further. Supposedly the complete system is going to be light enough that RQ-7 Shadow with a gross weight of only around 350lb can carry one, so it'd be an option on just about anything civilians are likely to want to build. I would not expect anyone would want a micro drone for pipeline inspections ect.... simply because it would be so vulnerable to the weather and wind. The military doesn't really care that its micro drones crash all the time, it can afford to just treat them like rounds of ammo.

[Broomstick]

Of course the U-2 was less capable than the SR-71 in terms of speed, range, ceiling, payload, etc. However, they were built for vastly different missions, and the U-2 could still carry a sizable payload of cameras. I'm simply saying that if it takes this enormous of a solar aircraft to simply get 100 lbs into the air, it's not going to be terribly useful for the kind of applications that surveillance aircraft are currently used for.

The pilot in question was probably closer to 200 lbs - I just assumed that if you replaced the pilot you'd have to add some hardware and WAG'd a number. I suspect the usable payload for this thing is actually greater than just 1 human pilot or equivalent weight, but I don't know enough to actually make a reasonable guess at the true limit. Just to clarify things.

Anyhow - my point was sort of that not every military mission requires bombs and guns. There is certainly a niche for this.

Re: UAVs and collision avoidance, is there an altitude below which private small craft typically do not fly?

No.

Well, it's recommended you stay 1000 feet or higher (about 300 meters) but that's largely due to obstacles likes trees, towers, buildings, powerlines... in remote areas (like much of what needs border patroling) legally you can fly an inch off the deck as long as you don't hit anything. Me, I've flown as low as a couple hundred feet - or just a couple feet - when I've felt it was a safe situation to do so.

Basically, anywhere low-level flight is prohibited it's due to safety reasons that most likely would apply to UAV's as much as private aircraft. That whole "two physical objects can't occupy the same point in spacetime" thing.

I will add that is the rule in the United States - things may well be different elsewhere, and in some cases almost certainly are.

I can't imagine patrolling the border in a vast expanse of desert you would run into much terrain avoidance issues.

No - just cactus. And the Southwestern Desert of the US and Mexico does have some of the world's largest cacti....

As for oil pipes, well, that's getting trickier. More navigation hardware needed then, maps and positioning systems.

Still not good enough - there are these things called "birds" that don't file flight plans, don't carry transponders, and don't read the regs. Hitting one is a Bad Thing. At night, you not only have nocturnal birds, you have bats. One of the guys at my local airport hit a bat landing at night - almost crashed the airplane, it ripped one of the wheels half off, tens of thousands in damage... Fortunately, his insurance covered it.

[Admiral Valdemar]

I remember my university was researching nuclear powered UAVs for military recon for DSTL and DARPA, but that would be a lot harder to pull off than solar cells, not technical terms, just that bugbear of nukes being involved.

I'm also reminded of an episode of the hi-tech drama Bugs where micro-UAVs were used for assassination. Little turbine powered craft the size of a dragonfly with a nerve toxin soaked needle. Though at those scales, an ornithopter would be far more efficient, if you can make one that's as agile as the many invertebrates out there.

I also wonder how this solar aircraft would be improved with the latest PV cell designs and a better energy storage medium such as a supercapacitor or micro-flywheel. Course, cost-to-weight benefit ratio is quite slim here.

[Hawkwings]

Ripped a wheel half-off? I find that pretty hard to believe, considering that the landing gear is supposed to be one of (if not the) strongest part of the airplane, and a bat weighs not that much. What sort of plane was he flying? And at about what speed?

Anyways, regarding birdstrikes, they become exponentially more dangerous as velocity increases, correct? (by KE=1/2mv^2) So it would seem that to alleviate birdstrike issues, you'd want your UAV to fly slower, not to mention have a strong leading edge. When I'm picturing my Border Patrol UAV, I see an electric powered craft no heavier than a couple hundred pounds, with a normal cruise velocity of 50mph or so. And yes, if a big goose got into a fight with it, both flyers would probably be hurting afterwards. But with the rarity of bird strikes, would this really be a huge issue?

[Broomstick]

Ripped a wheel half-off? I find that pretty hard to believe, considering that the landing gear is supposed to be one of (if not the) strongest part of the airplane, and a bat weighs not that much. What sort of plane was he flying? And at about what speed?

The bat strike was essentially in just the right spot to cause maximal damage. It was a retractable gear Cessna Cardinal, about slightly under the weight of Solar Impulse, and the landing gear took a hit as it was deploying, approach speeds around 70-90 mph (I forget what it was, exactly, but that would be right for that size/power plant of airplane).

Anyways, regarding birdstrikes, they become exponentially more dangerous as velocity increases, correct? (by KE=1/2mv^2) So it would seem that to alleviate birdstrike issues, you'd want your UAV to fly slower, not to mention have a strong leading edge. When I'm picturing my Border Patrol UAV, I see an electric powered craft no heavier than a couple hundred pounds, with a normal cruise velocity of 50mph or so. And yes, if a big goose got into a fight with it, both flyers would probably be hurting afterwards. But with the rarity of bird strikes, would this really be a huge issue?

Yes. It's a huge issue. Bird strikes aren't nearly as rare as we'd like, although MOST of the time the pilot lands without injury (damage to the airplane, however, is almost inevitable)

Doesn't have to be a big bird - a chickadee is quite capable of punching through the windshield of a general aviation airplane (of course, the birds dies in those circumstances). A bird hitting a prop blade can easily take out the prop (typical prop speeds are 1000 - 9000 rpm, depending on airplane, powerplant, etc. with, contrary to expectation, some of the slower airplanes having the higher rpm's because of their powerplants)

Remember - a goose can take down an Airbus, and compared to an Airbus, a goose is a lot smaller than, say, a sparrow compared to a UAV or Solar Impulse. (By the way - geese have been spotted at 30,000 feet before on migrations. There's a species that flies over Mt. Everest on a regular basis around 35,000 feet. If you want to get above the birds you may have to go higher than you think).

Think about it - how large a bird are you will to have flung at YOUR head at 50 mph? I'd expect a hummingbird would hurt pretty damn bad. Hell - I got a gash across my forehead that had half the side of my face covered in blood by the time I got down from hitting a BUG at those speeds open cockpit. (I think it was a dragonfly, but never got a good look at it and there wasn't really anything left afterward).

Yeah, avoiding critters is sort of important. It's not an insurmountable problem, but it is a problem.