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Solar Impulse

Old 22nd Apr 2016, 18:08
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Solar Impulse

Just over one day into the journey to Mountain View CA and over 1/3 of the distance. Go André!

Solar Impulse - 9th Leg from Hawaii to Mountain View, CA
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Old 23rd Apr 2016, 01:58
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Well the flight has definitely shown that there is no future in solar 'powered' flight as currently implemented as a cargo or pax carrying system. Give it a little time. I read a book from the 1900's that said there was no future in aircraft in warfare as at best they could only carry two people. So perhaps in 80 years or so .....
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Old 23rd Apr 2016, 07:56
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Personally, I think it's a total waste of time/money.

even if you could make solar panels 100% efficient, they are simply not going to generate enough power for anything significant to fly.

so, you're back to batteries/capacitors/etc. to store enough energy.

to put this in context, best current LiPo cells have a power density of ~0.5 MJ/kg (and that's without any casings/interconnects/management/etc.

compare this with A1 Jet at ~42.80 MJ/kg.

then factor in that the LiPo will still have the same mass as a flat battery as a fully charged one unlike burning off A1.
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Old 23rd Apr 2016, 09:14
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If the pilot needs to take exercise anyway, why can't they connect some pedals to a hand/foot generator for a little extra juice? Surely useful in an emergency, even possibly the difference between life and death.


Is the need to prove it can be done SOLELY on solar power so overriding?
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Old 23rd Apr 2016, 09:18
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From an aviation perspective - interesting.

From all other perspectives an embarrassing failure that proves the green dream will cripple the real world.

How can that money have been approved.

$20 Million Bailout ?$170 Million Solar Impulse 2 Flight To Be Completed ? After More Than One Year!
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Old 23rd Apr 2016, 09:24
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Most people laughed at the Wright brothers 'wasting their time and money' . I refer you to Ian W post above!
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Old 23rd Apr 2016, 11:58
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If you don't try you can never move forward

Sure it hasn't been acording to plan but it's still pretty amazing - we're just at the start of portable electrical power - I supect it will be pretty important in 50 years
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Old 23rd Apr 2016, 12:22
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Originally Posted by sagan
From an aviation perspective - interesting.

From all other perspectives an embarrassing failure that proves the green dream will cripple the real world.
You sound like one of the balloon operators when told about the wright flyer. "Interesting. But with an endurance of just a few seconds, just useless."

We all know how that turned out.

For example, I can imagine a large orbital solar power station that beams down microwave energy along the Atlantic crossing corridors, the aircraft carrying just enough batteries to take off and land, in flight just using the beamed energy.

Another option might be extremely efficient flying wing planes with a solar panel surface (assuming 100% efficiency, a flying wing the size of an A380 could generate several megawatts of power, probably enough to stay aloft).

We're not quite there yet, but I don't see why we shouldn't get there at some point.
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Old 23rd Apr 2016, 13:06
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Like the Wright Flyer and others, it's a "proof of concept" flight, and as such can be considered a success.
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Old 23rd Apr 2016, 13:47
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For example, I can imagine a large orbital solar power station that beams down microwave energy along the Atlantic crossing corridors, the aircraft carrying just enough batteries to take off and land, in flight just using the beamed energy.
So can I.

Now calculate the level of emissions that would be created in getting the "large orbital solar power station" into orbit in the first place (BTW assuming today's level of air traffic how many of those would be needed), and maintaining it once there......
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Old 23rd Apr 2016, 13:48
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Originally Posted by RealUlli
You sound like one of the balloon operators when told about the wright flyer. "Interesting. But with an endurance of just a few seconds, just useless."

We all know how that turned out.

For example, I can imagine a large orbital solar power station that beams down microwave energy along the Atlantic crossing corridors, the aircraft carrying just enough batteries to take off and land, in flight just using the beamed energy.

Another option might be extremely efficient flying wing planes with a solar panel surface (assuming 100% efficiency, a flying wing the size of an A380 could generate several megawatts of power, probably enough to stay aloft).

We're not quite there yet, but I don't see why we shouldn't get there at some point.
Look, all well and good, but unless you plan on changing the laws of physics, simply not going to happen.

big as the A380 wing topside is, it's never going to be big enough for anything like a megawatt of power from solar.

Now, at best, solar is ~1,000W/M2, so if you had a mythical 100% efficient solar cell array the size of the A380 wings (some 845 M2) then assuming your A380 is directly beneath the sun, on the equator, you only have some 0.85Mw to start with, and as soon as said plane (it may well be slightly better at 40,000 ft, but not by a massive factor).

So where are you going to get "several megawatts of power" from?

this is not about a technology needing development so much as the physics simply don't stack up.

then consider that the Trent 900 is rated at some 80,000Lbf, which roughly equates to ~95Mw (40,000ft @ Mach 0.85) and the A380 has 4 of them.
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Old 23rd Apr 2016, 14:59
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That Trent 900 will be putting out 25% or less of its full rated thrust in cruise at 40,000'.

So, while the engineering of converting that electricity to usable thrust is a considerable challenge, it is not "impossible" to get a significant percentage of power used from solar. Also, solar could more feasibly serve the electrical load on an aircraft, reducing the drag on the engines from the generators.

Might it be cost effective? Not yet. It it possible in the foreseeable future? YES!
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Old 23rd Apr 2016, 15:44
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That Trent 900 will be putting out 25% or less of its full rated thrust in cruise at 40,000'.
It it possible in the foreseeable future? YES!
95Mw is 95Mw. If the wing area can only provide .85Mw you are still less than 1% of the way there. That is nowhere near a "significant percentage" is it? It is probably less than the allowed shortfall between individual Trent 900s due to wear and tear.

And that 0.85% is with a 100% efficient solar cell and the entire wing area remaining at right angles to the sun.

So you need either a wing that is 120 times bigger or to turn the sun up a hundred and twenty fold. And never to fly at night, nor need to take off or go around (need 4 times that much power to do that). Factor in pv cell efficiency and make it perhaps 300 times bigger. Are you getting the picture?
Oh, and only ever fly wings level within the tropics at noon.

Why/how is it hard to see that maths and physics fundamentally prevent this happening?

Huge span ultra lightweight long endurance RPVs perhaps. Transport? No. Never from on board PV cells. Can't happen.
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Old 23rd Apr 2016, 16:25
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Perhaps we are all missing the point, after all we tend to think of applicability in our own sphere of experience. Clearly this technology will not be outperforming turbofans anytime soon. But as a drone ?
Remember well that the predator/reaper met stiff resistance in traditional flying circles during the early days, until those on high realized that it had the ability to linger in an area of interest for 20+ hours. A developed version of this technology could be put to a similar use. Whilst it would be nice to think of benign applications, were I to place a small wager it would go on a military role.
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Old 23rd Apr 2016, 16:27
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Coming up to sunrise on day 3. 83% of the journey done.

Every journey begins with a single step, and that money comes from private sources.
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Old 23rd Apr 2016, 18:38
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Originally Posted by Teddy Robinson
Perhaps we are all missing the point, after all we tend to think of applicability in our own sphere of experience. Clearly this technology will not be outperforming turbofans anytime soon. But as a drone ?
Remember well that the predator/reaper met stiff resistance in traditional flying circles during the early days, until those on high realized that it had the ability to linger in an area of interest for 20+ hours. A developed version of this technology could be put to a similar use. Whilst it would be nice to think of benign applications, were I to place a small wager it would go on a military role.
well, yes and no,

the point of a drone is to be small, inconspicuous, remote etc, ie, the predators etc, they have bugger all wing area, thus to make them viable as solar powered, you would need wings the size of a Vulcan or the like, at which point, they would be far from inconspicuous and a pretty easy target!

then consider what happens when the sun goes down or cloud cover comes over?

Look, it's not about lack of belief in technology, it's simply a matter of physics, yes you can make a solar powered plane, but it will be usless for any practical purpose that we use planes for now.

Same goes for battery powered flight, yes it's obviously possible, but until battery (or capacitor) tech increased power density by a factor of 20+, it's simply not practical for anything other than toys and expensive demo's.

Next somebody will pop up and claim Hydrogen fuel cells are the answer - in which case I will point them at the issues around them at any major scale, and also where does Hydrogen come from (commercially).
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Old 23rd Apr 2016, 23:07
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Obviously this is a stunt. Stunts are important in the development of new technologies, because they're a way of pushing the limits of the possible in a quasi-sporting mode (i.e., to hell with the expense), and getting publicity.

Fossil fuels will be necessary for aviation for the foreseeable; therefore all the more need to replace fossil fuels wherever possible elsewhere, so that total greenhouse emissions can go down while still keeping air transport possible (I do know greenies who are opposed to aviation, and motor cars, and growth: but they're really puritans, and there are plenty of others who are actually just concerned about the environment). Solar Explorer may have some impact here, just as car racing has some impact on the vehicles we drive.

So yes, this has got bugger all to do with practical aviation directly; but it might have some indirect benefit.
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Old 24th Apr 2016, 01:34
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Looking at the live feed from post #1... Why is he flying West again? perhaps too early for film crews... Close to Golden Gate Bridge.
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Old 24th Apr 2016, 01:51
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Check this out - actually with some innovations, hybrid makes the most sense...

https://www.youtube.com/watch?v=w5t8VdLpsOA
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Old 24th Apr 2016, 02:45
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We like the look of that! Go RR...
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