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Solar Impulse

Old 24th Apr 2016, 07:21
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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.

Last edited by ExXB; 24th Apr 2016 at 09:04.
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Old 24th Apr 2016, 23:21
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3 days of single pilot operations, with 20 minute controlled naps. Testing the limits of human performance as much as tech aspects.
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Old 25th Apr 2016, 07:03
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Wing area

Originally Posted by [URL="http://www.pprune.org/members/270458-scuffers"
Scuffers[/URL]]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.
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.

Last edited by RealUlli; 25th Apr 2016 at 07:05. Reason: Fixed style/grammar
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Old 26th Apr 2016, 15:28
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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
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Old 28th Apr 2016, 03:46
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then consider that the Trent 900 is rated at some 80,000Lbf, which roughly equates to ~95Mw (40,000ft @ Mach 0.85)
Can we back up a minute? How did you get from thrust to power here?
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Old 28th Apr 2016, 07:25
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How did you get from thrust to power here?
The OP appears to have multiplied take-off thrust by cruise speed.
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Old 28th Apr 2016, 13:17
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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.
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Old 28th Apr 2016, 16:30
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Originally Posted by Scuffers View Post
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
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.
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Old 28th Apr 2016, 16:43
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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?)
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Old 28th Apr 2016, 16:59
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Originally Posted by Scuffers View Post
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?
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.
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Old 28th Apr 2016, 17:22
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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?
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Old 28th Apr 2016, 19:27
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Originally Posted by Scuffers View Post
Trent is more efficient at 40,000ft than at ground level, they are very much optimised for running at cruise altitude.
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.

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?)
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.

What do you think it's max thrust would be at 40,000ft?
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..
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Old 29th Apr 2016, 07:02
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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.
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Old 29th Apr 2016, 08:18
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Neat approach.

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.
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Old 29th Apr 2016, 08:34
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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.
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Old 2nd May 2016, 14:56
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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.
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Old 4th May 2016, 07:59
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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.
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Old 4th May 2016, 12:38
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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?
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Old 4th May 2016, 13:27
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Slight problem is that the props also need to counteract drag, which is huge for a blimp at any significant speed.
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Old 4th May 2016, 13:30
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Originally Posted by Dubaian View Post
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.
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.
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