Sky Whale II... feasible?

Susheel said:
Also a bit too blowy-uppy.
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Actually no. Not when compared with petrol and other similar hydrocarbons. If there is a leak then the gas will go up and not hang around waiting for a spark. You do not want to be anywhere near a petrol leak. Or even where one has happened recently.
 
dasmiller said:
Okay, I'll bite. Let's look at the solar-powered cruise thing.

The wingspan is ~100 meters, the aspect ratio looks to be ~8, so the total wing area is 1250 sq m. Let's assume the fuselage and tail have about the same area as the wing, so the total area available for solar cells is ~2500 sq m.

Also, let's assume that it's flying very, very high, so that only 5% of the sun's energy is lost in the atmosphere1, so the incident flux is 1.29 kW/sq m. Also, let's assume that we only fly when the sun's at least 60 deg above the horizon2, so our cosine loss is only ~13%. And let's assume our solar cells are 80% efficient.3 2500 x 1.29 x (1-0.05) x 0.866 x 0.8 gives us 2.24 MW to propel our totally-not-crazy airplane.4
Is that enough?

Well, a loaded-without-fuel A380F weighs 402,000 kg. The Sky Whale is much larger, but let's assume it has the same weight.5 A typical airliner has a lift/drag ratio of about 17, but this one has genuine cartoon aerodynamics so let's give it a L/D of 276. 402,000 x 9.8 / 27 gives us 146 kN of drag. To keep up with other airliners, we'll be cruising at about 800 km/hr = 222 meters/sec.

Thus the total power needed to maintain cruise is about 146,000 x 222 = 32.4 MW.

With 2.24 MW available, that means we need our engines to convert electricity to thrust with 1440% efficiency7.

I'm dubious.


1About 17,000 meters/55,000 feet, I think. This is higher than any current airliner but not crazy by itself.

2This will limit flight time based on direction, latitude and season. The best case is near the equator flying west, which will allow up to 5 hr/day of flying. At London's latitude it would be limited to ~2 hours on the best day (June 21) and wouldn't be able to fly at all for 46 weeks of the year (July 15 to May 28)

3Crazy. AFAIK the current world record is 44.4%

4That was sarcasm.

5A little crazy.

6Pretty crazy. That's the same aerodynamic efficiency as Rutan's Voyager.

7Absolute giant mutant batcrap crazy. You shouldn't need to be told this.
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Awesome post! I assume you are an aeronautical engineer?

There is one thing you seem to forgot to have taken into account.

While you did mention height, which increases the efficiency of solar panels higher in the atmosphere, what about the loss of atmosphere that high up, giving the plane less lift, due to lower air pressure? Don't airliners typically consume more fuel, the higher they fly? Wouldn't that necessarily offset that efficiency gain for the solar panels?

Also, what purpose would those three....uuummmm....finger-type-things....at the ends of the wings serve?
 
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RecoveringYuppy said:
I don't think this guy is that wrong. I think he's thinking to use that to recover energy during descent and landing.
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If you're powered by solar energy during cruise, why do you need an extra generator during descent? Sure, there's energy that you could "recover" during descent but what are you going to do with it? It's not like you were carrying around a bunch of empty battery capacity, right? Oh wait, this is just a cartoon, may as well slap some giant weightless battery banks in there. And a small aluminum refinery.
 
Was really hoping thread was referring to this

http://www.canberra100.com.au/programs/the-skywhale-by-patricia-piccinini-/

picture.php
 
steve s said:
Except he's got three on each wingtip. I guess he figured if one is good, three must be better.

Steve S
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He's probably right, if you look at eagles for an example of the same principle in action.
 
RecoveringYuppy said:
I don't think this guy is that wrong. I think he's thinking to use that to recover energy during descent and landing.
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Oh, please. It's more energy-efficient to lose altitude by reducing engine thrust. Unless you're proposing that a commercial passenger jet will make its final approach by means of a power dive. In which case we can rename it "Stuka".
 
ben m said:
If you're powered by solar energy during cruise, why do you need an extra generator during descent? Sure, there's energy that you could "recover" during descent but what are you going to do with it? It's not like you were carrying around a bunch of empty battery capacity, right? Oh wait, this is just a cartoon, may as well slap some giant weightless battery banks in there. And a small aluminum refinery.
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Current planes carry around a lot of rechargable batteries now.
 
WhatRoughBeast said:
Oh, please. It's more energy-efficient to lose altitude by reducing engine thrust. Unless you're proposing that a commercial passenger jet will make its final approach by means of a power dive. In which case we can rename it "Stuka".
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It's more efficient to throw energy away than recover it? Especially when electric motors turn in to to generators so easily? The overall realism of this particular plane may not make sense, but if you've got electric motors you also have electric generators. If it ever makes sense to power a planes engines by electricity it's very likely to be guaranteed that using them to recover energy will also make sense.
 
Don't forget it also harvests microwaves. What with all the microwaves filling the air these days it'll gain power and also clean the air of cancer-inducing microwaves! It's a win-win!!

(I also see the similarity with Thunderbird 2)
 
Jebus Christ, I don't think S.H.I.E.L.D. has that kind of technology.
 
ben m said:
Let me rewrite the article very slightly.
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Great post !


elgarak said:
And sustainable fusion power is 10 years in the future, and has been for the last three decades or so. :D
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Hmm - it's been just over the horizon for at least 40 years.


MikeG said:
The designer forgot to mention that it is mostly filled with helium and is actually just a glorified dirigible.
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I worked on a high altitude unmanned dirigible program at one point. Solar powered, w/ batteries and really huge compared to this toy. It really is practical to consider, but only b/c the 'lift' is free.

dasmiller said:
...
With 2.24 MW available, that means we need our engines to convert electricity to thrust with 1440% efficiency7.

I'm dubious.
...
7Absolute giant mutant batcrap crazy. You shouldn't need to be told this.[/SIZE]
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Great post and thanks for the back of the envelope numbers.


WhatRoughBeast said:
Oh my sweet Lord. Look, anybody who suggests (as the link does) that "The aircraft would also be fitted with a rear engine that would double as a wind turbine" is clearly having problems dealing with reality. The missing piece of technology is apparently a perpetual motion machine.
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No. It suggests the engine is electric and during slow-down, descent, and landing can recoup energy - just like w/ regenerative breaking an an electric car. This issue is not so much a technology problem as an economic one - is the cost of this tiny energy recovery practical considering costs.


rjh01 said:
Hydrogen is a good fuel. It has a lot of energy per kilogram. Only trouble is that the kilogram takes up a lot of space. Plus you need a good way to produce it in bulk.
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Plus you need a cheap way to store it, which is a huge deal. Hydrogen embrittles common metals as it diffuses into the metal, so the prototype vehicles use very expensive carbon fiber lined tanks, and the econ analysis suggest the price of those isn't likely to improve.

========


As usually these "Green flights of fancy" fail to distinguish the issue of pollution from energy conservation. I think any rational view of a better future include far more per capital energy across the planet, but less pollution.
 
rjh01 said:
Those are common on modern aircraft. Without them air would circulate around the end of the wings decreasing lift.

Here is a article about them I found http://www.airspacemag.com/flight-today/how-things-work-winglets-2468375/?no-ist
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Well, yeah. I get that. But does the specific design of of the flinger-like winglets on the "sky whale II" actually do anything more than the normal winglets on planes today?

Those winglets serve the same purpose as the winglets on the ends of spoilers on race cars. It keeps the vehicle steady on the road surface at fast speeds. Just never saw anything even like those fingers on so much as a concept other than for the hypothetical Sky Whale II design.

MikeG said:
He's probably right, if you look at eagles for an example of the same principle in action.
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But plane wings don't flap up-and-down like eagle's wings.
 
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Nihilianth said:
Awesome post! I assume you are an aeronautical engineer?
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Yes.

While you did mention height, which increases the efficiency of solar panels higher in the atmosphere, what about the loss of atmosphere that high up, giving the plane less lift, due to lower air pressure?
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Keep in mind that a plane that weighs X kg needs X kg of lift for level flight, whether it's at 17,000 m or at sea level. I know that seems obvious, but it's surprising how often people forget about it. The airplane won't have less lift at 17,000 m; it'll just use a different combination of lift coefficient and speed to get X kg.

Also keep in mind that while the lower density is reducing the maximum lift, it's also reducing the drag.

Airliners are generally optimized for cruise, so I assumed that the quoted L/D ratio (17) for a 747 was the cruise L/D.

Don't airliners typically consume more fuel, the higher they fly? Wouldn't that necessarily offset that efficiency gain for the solar panels?
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Not necessarily. There are a number of things going on. At low altitude, an aircraft can fly slower while still generating enough lift to stay up, so the minimum power needed is lower at low altitude. But if the plane is going fast, then parasite drag will dominate, and it's much worse at low altitude than high altitude. If an airliner could cruise at 800 km/h at sea level, I suspect that the fuel consumption would be atrocious.
 
dasmiller said:
Yes.



Keep in mind that a plane that weighs X kg needs X kg of lift for level flight, whether it's at 17,000 m or at sea level. I know that seems obvious, but it's surprising how often people forget about it. The airplane won't have less lift at 17,000 m; it'll just use a different combination of lift coefficient and speed to get X kg.

Also keep in mind that while the lower density is reducing the maximum lift, it's also reducing the drag.

Airliners are generally optimized for cruise, so I assumed that the quoted L/D ratio (17) for a 747 was the cruise L/D.



Not necessarily. There are a number of things going on. At low altitude, an aircraft can fly slower while still generating enough lift to stay up, so the minimum power needed is lower at low altitude. But if the plane is going fast, then parasite drag will dominate, and it's much worse at low altitude than high altitude. If an airliner could cruise at 800 km/h at sea level, I suspect that the fuel consumption would be atrocious.
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I understand. So the proper altitude for cruising speed is optimized for maximum fuel efficiency, already taking air density/drag into consideration.

Thank you for answering my post. Greatly appreciated. :)
 
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