An interpretation of Jules Verne’s heavier-than-air airship from 1886:

It is possible, in the real world not fiction, to land a plane on an airship. From an airship buff website:

The United States Navy airships U.S.S. Akron (ZRS-4) and U.S.S. Macon (ZRS-5) were designed for long-range scouting in support of fleet operations. Often referred to as flying aircraft carriers, each of the helium-inflated airships carried F9C-2 Curtiss Sparrowhawk biplanes which could be launched and recovered in flight, greatly extending the range over which the Akron and Macon could scout the open ocean for enemy vessels.

An F9C-2 captures the trapeze aboard Macon in 1933

Why am I telling you this fun fact about cutting-edge aviation technology in 1932?

On the beach the other day, I came across an article in the regional newspaper Sur about a small Malaga company called Mesurex  that makes software for in-flight refuelling. Catching the drogue at the end of the boom is still a severe test of pilot skill, but it’s becoming automated and easier. Which leads them to suggest that civilian airliners could also be refuelled in flight. Allowing nonstop flights from say London to Auckland, saving as lot of fuel. Their main customer is Airbus Military, so I assume they know what they are doing, and the proposal is technically credible.

So I fell to musing about refuelling electric airplanes. They work. Airbus have flown, and plan to sell, a two-seater basic trainer. It’s not a flimsy tour de force like Solar Impulse, but a normal plane with batteries running an electric fan for propulsion. They are working on a commuter plane. The problem, as with electric cars, is range.

If you can refuel planes in flight with kerosene, you can do it with electricity. The cable has to take a massive current for a fast charging rate. This could be a difficulty so let’s assume it away, like Leonardo, to get to the bit he would have liked.

This is where I had my beach brainwave – before the tinto de verano, not after. There is an infinite supply of electrical fuel aloft in the form of sunlight. All you need is a big area of solar panels to catch it with. For a plane capable of useful work, the available surface area isn’t enough. But an airship is big – in fact the limitation on size is ground handling. You can add thin-film solar panels ad lib by towing them like advertising banners. A big solar airship is a possible airborne recharging station.

The US Navy showed in the 1930s that docking a plane with an airship is perfectly feasible. So an electric airliner could just dock to recharge? The snag here is matching the speeds. Dirigibles have such a large cross-section that the practical upper speed limit is, according to Wikipedia, about 160 kph. A Cessna takes off and lands at much less, around 100 kph. But modern commercial jet airliners need 250 kph.

You could always redesign the airliners to have drastically lower stalling speeds, meaning bigger wings or biplanes. There would presumably be penalties for this in cruising speed and weight, so the numbers might not pan out.

There is another solution, even more Leonardo-y. The giant airship is designed to stay aloft for months. You need a shuttle to ferry the crew and maintenance workers to and from the ground. So make the shuttle the refuelling intermediary. It need only bridge the speed range between the airship’s 150 kph and the airliner’s 250 kph, plus carrying the weight of the superbattery or capacitors (another assumed can-opener), which you remove for the ground runs. This is a design challenge, but a much narrower one. The Akron’s and Macon’s Sparrowhawks (max 284 kph) already spanned the speed range.

The batteries would be too heavy? If you can get them on the airliner, you can put them on the airship or shuttle. So if electric planes are feasible, so is in-flight refuelling.

Now tell me. Is this plan any more out to lunch than the USSS Akron and Macon? Both airships crashed, but through pilot error and design flaws in the structure, not their aircraft complement. The line was discontinued because the airships were sitting ducks to enemy warplanes, not because the concept didn’t work. When radar came along, for which they would have been well suited, it was too late to rethink. My scheme may not be workable, but it’s not a visionary fantasy like Leonardo’s wooden helicopter.

The next post will be on something I know a little more about, which will not be a hard promise to keep.