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I'd be interested to know how this might size up to the new British heavy-lift airship, Airlander 10: https://www.hybridairvehicles....

Call that an airship, or something, please. Even though this picture reminds me of a very flexible girlfriend of mine.

Would it be at all feasible to cover the top of this thing with thin and semi-flexible solar panels? If Solar Impulse can make it around the planet using just the solar energy hitting its thin little lifting surfaces then surely the surface area of this magnificent flying backside should be able to gather enough energy to shove it across the sky, right?

Going off the Airlander 10 specs:

The vehicle is powered by "4 x 325 hp" diesel engines, for a combined peak power of about 960 kW. Most vehicles do not cruise at peak power continuously, so I will estimate the average power requirement at half of that: 480 kW. (This ratio would be approximately correct for a large subsonic jet; if someone knows what it should be for a diesel-powered lifting-body airship instead, please leave a comment.)

The useful surface area of the Airlander 10 is approximately [92 m long] * [43.5 m wide] = [4000 m^2]. (The exact number depends upon the latitude, the time of day, and the craft's heading, but it turns out that its shape is such that the answer doesn't change much, except near the poles.) Peak solar irradiance (direct sunlight at high noon) at ground level is about 1 kW / m^2, and current thin film solar panels are under 15% efficient. Solar power conversion circuitry is around 90% efficient, and an appropriate electric motor with its controller is about 88% efficient. Therefore, a maximum of [4000 m^2] * [1kW / m^2] * [15%] * [90%] * [88%] = [475 kW] of shaft power could be generated by solar-electric means.

So, a solar-powered Airlander 10 could work - but not very well. Under ideal daylight conditions, it could fly about as well as the hydrocarbon-powered version. However, airships are sufficiently slow and long-range that they are expected to routinely fly through the night. Thus, the average power available must be at least cut in half, to 238 kW. Cloud shadowing (airships can fly over some clouds, but far from all) and dust will further reduce that number.

Additionally, a solar-powered airship needs to carry heavy batteries in order to avoid catastrophic power loss when passing through clouds. One hour's worth of lithium-ion power would mass [475 kW*h] / [86% charge/discharge efficiency] / [200 W*h / kg] / [80% - 20% depth of discharge range limit] = [4600 kg]. As the total mass of the Airlander 10 is only 20 metric tons, it cannot carry much more battery power than that without cutting into the payload.

At cruise, nearly all of the Airlander 10's power is devoted to fighting drag. Since subsonic drag scales with the square of airspeed, a solar-powered version could quadruple its battery-powered run time by halving its speed. (It can't really go any slower than that though, as it needs to be able to overcome typical headwinds to be useful.) Four hours of battery time is still woefully inadequate for an overnight flight though, so a solar-powered version would be limited to daytime flights only, and consequently to overland flights only.

TLDR: A solar-powered version of this airship is possible, but it would be considerably slower and incapable of crossing oceans. Supplemental charging on the ground wouldn't help much at all.

Looked to me at first like a giant nut-sack, like, from underneath.
Head-on, I see booty fillin' really tight pants.

> For cargo though I'd have thought something like this would be better:
> http://www.hybridairvehicles.com/ [hybridairvehicles.com]

For a forward firebase? Are you kidding? That thing would be constantly shot full of holes. Worthless for the purposes described in the article.

Now, for a rear area base that doesn't come under fire that thing would be great!

That's about 3 hours of flight time. So people avoid the chopper for 3 hours and then come back after it runs our of fuel and goes away.

You need boots on the ground to hold something.

For cargo though I'd have thought something like this would be better:
http://www.hybridairvehicles.com/

http://www.hybridairvehicles.com/

The US military is buying half a billion dollars worth of kit from them... Or rather through Northrop Grumman.

http://www.flightglobal.com/news/articles/video-northrop-grumman-wins-race-to-revive-hybrid-airships-with-517-million-order-343259/