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

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 .....

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.

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?

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!

Most people laughed at the Wright brothers 'wasting their time and money' . I refer you to Ian W post above!

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

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.

Like the Wright Flyer and others, it's a "proof of concept" flight, and as such can be considered a success.

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......

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.

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!

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.

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.

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.

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).

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.

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.

Check this out - actually with some innovations, hybrid makes the most sense...
 

We like the look of that! Go RR...

Apparently winds are delaying the landing.

Great picture of it over the bridge. http://www.bbc.co.uk/news/science-environment-36122618

Edited to add: She's landed now.

3 days of single pilot operations, with 20 minute controlled naps. Testing the limits of human performance as much as tech aspects.

Wing area
 

Ok, thanks for the numbers. (I'm sorry I didn't look them up myself)

I wasn't thinking about getting an A380 to fly on solar. That's obviously impossible. What I'm imagining is more like a giant flying wing that carries much less, has the same wing span as the A380 but a much deeper wing, e.g. 80m wide, 40m long, carrying maybe 20 metric tons of stuff (maybe less - I'm just guessing things). That gives 3200 m2, yielding 3.2 MW.

This kind of plane would be much slower than a conventional plane, with extremely low wing loading.

What I don't know is, will passengers accept travel times in excess of 24 hours? In conventional planes, space for seats is expensive. In that hypothetical plane, space will not be a problem, weight will be. (And of course, flying through the night... ;-))

Crew block time will be a problem, I'm not quite sure how to overcome that. Fully automatic will be out, since I imagine the plane will need minders, unless you want it to look like a subway car in a poor city after a while. The cost structure will change for sure.

However, the main question remains - can a plane like that be made to fly? I really don't know if that is feasible. Probably not alone.

As an example for area, RAF Coltishall has just been converted to a solar farm, just under 50MW at peak generation (i.e half an engine).

http://www.edp24.co.uk/polopoly_fs/1..._630/image.jpg

Can we back up a minute? How did you get from thrust to power here?

The OP appears to have multiplied take-off thrust by cruise speed. :O

Not quite.

read this:

Aerospaceweb.org | Ask Us - Convert Thrust to Horsepower

and I picked 80,000Lbs as it's broadly the mid-spec for the Trent 900

As an aside the Rolls-Royce MT30 genset is rated at 40Mw and is based on the Trent 800 core, if you then take into account different duty cycle ratings and inefficiencies of the Aero engine vs. genset, it actually stacks up about right.

I think you need to read that example more carefully.

It calculates, based on NASA data, that a 747-200 in the cruise generates around 16 MW per engine.

The Trent 900 develops roughly one-and-a-half times as much thrust as the JT9D, so around 24 MW per engine.

who said anything about at cruise power?

Yes, at cruise, the Trent is probably at ~24Mw, however, what would it be if you push the throttles forward all the way?

(Or are you suggesting that the engines never have to be run at anything above cruise power?)

If you really believe that you can get 80,000 lbf out of a Trent in the cruise at 40,000 ft, I would get on the phone to Derby and Toulouse straight away and let them in on the secret.

really?

Trent is more efficient at 40,000ft than at ground level, they are very much optimised for running at cruise altitude.

So, A380 at 40,000ft loses an engine, does it fall out the sky or do the other three make up the loss in thrust? (How about if it loses 2 engines?)

What do you think it's max thrust would be at 40,000ft?

Well that depends how you define "efficiency" - if you use SFC as a measure, it's roughly twice as good on the ground at takeoff thrust compared to the value in the cruise. In fact you could argue that the engine is optimised for getting the aircraft off the ground in the first place. :O

No, of course it doesn't fall out of the sky.

A loss of two engines on an A380 or 747 (roughly analogous to losing one engine on a twin) would necessitate the remaining engines producing double their normal cruise thrust if the same airspeed and altitude were to be maintained.

But, as you will have seen from the article you quoted, normal cruise thrust is about a quarter of T/O thrust, so even doubling that will only equate to around 50% of the latter.

In lbf? I don't know. MCT is normally expressed in terms of N1 or EPR, rather than lbf.

But think about it - if an engine was capable of producing SL take-off thrust at 40,000 feet then it would mean that a 747/A380 could maintain height and speed on one engine, which it clearly can't..

L/D of about 20. Weight is 500 000 kg, thus 5 000 000 N.
Trust requied is 5MN/20=250kN. Cruise speed of 250 m/s results in 62.5 MW.

Neat approach. :ok:

Dividing that per-aircraft value by 4 gives a per-engine figure of around 16 MW in the cruise.

Interestingly, that's almost identical to NASA's value for the 747/JT9D - maybe they did their sums with a Shuttle on top. :O

L/D of 20 is a bit optimistic at Mach 0.8. About 16 is probably more realistic, so it would be 20MW per engine.

Two hours into next sector

Solar Impulse - 10th Leg from San Francisco to Phoenix

Goodbye Silicon Valley!
André Borschberg took off on May 2nd 12:03UTC from San Francisco to Phoenix, Arizona. Si2 spent a week in California after Bertrand Piccard's 3-day flight that marked the completion of the Pacific Crossing. It was a great opportunity to meet with the public and Silicon Valley's tech companies, to spread the #futureisclean message. The flight is expected to take 16 hours and 23 minutes, crossing 720 miles over the Mojave Desert and will arrive in Phoenix Goodyear Airport at around 4:23AM UTC.

Re funding - an earlier poster says it's private? Don't think so. Most (if not all...?) of it is from Masdar / Mubadala - which are Abu Dhabi Govt organisations.

What about getting this solar power on a blimp? Like a hybrid car, the buoyancy of the gas cancels out weight for passengers/cargo/equipment and the solar cells power props for momentum?

Slight problem is that the props also need to counteract drag, which is huge for a blimp at any significant speed.

Here's a list of their partners Solar Impulse RTW. Not all are large financial contributors - for example ICAO gave no money, but technical assistance. IATA gave a small bit of cash, etc. The Swiss government, gave them access to a disused hangar at Payerne.

No doubt the UAE contributed a lot of money. That's what they had to do for the 'prestige' of being the origin/destination.