Double-Hybrid Airship

So I've been thinking about airships lately. If you've read my previous post about (actually) building flying cities, you'll know that this isn't a new idea.

I think I first thought about building a hybrid airship about six or seven years ago. It was a passing fancy: develop a set of plans or kit for building a small personal dirigible. And that's about as far as it got. Dirigible means steerable. Like a Zeppelin- which also has a rigid frame.

Airships are the quintessential romantic conveyance. They show up in alternate history, steam punk, technopunk (okay, Nebuchadnezzar was a "hovercraft"- same idea). Mummy movies. Final Fantasy games. Oh, and the Teddy Ruxpin cartoons back in the '80s. Great epicadventure, unbearable singing. And, of course, Up.

So I'm definitely not the only one who has picked up on this theme. And yet, there are no airships anymore. Sure, the DoD is fielding some radar platforms. There's the Goodyear Blimp. And don't forget hot air ballooning. That's pretty close to the spirit in question.

I was talking with a friend a couple weeks ago. I think our conversation started with a mention of Balloon Boy, and whether it was plausible to actually build such a craft. I started to think about it. The things we talked about were more to do with the spirit of the idea. I started to think about it in practical terms.

The question, as it turns out, isn't how big you build an airship, but how small. Small is cheap. Cheap is attainable. It's easy to imagine a multi-million dollar project that would be guaranteed to fly by virtue of its volume of helium. It's not so easy to imagine getting off the ground on several hundred thousand.

The airship you see in these pictures is actually more of a lifting body aircraft than it is a hybrid airship. It gets less than half of its lift from helium. To achieve the shape, it is built like a omni-directional suspension bridge. There's a open-topped box at its center that is comprised of four tent poles. These are held apart by a pair of horizontal girders that run from nose to tail. They're built like a construction crane (only much lighter).

To the left and right there are several more girders that define the lateral dimensions. Attached to these is a kind of vertical stabilizer that is in place to prevent the air moving over the lifting body from sliding sideways. Hence they are called slip limiters.

The whole aircraft weighs a little less than 16,000 lbs of dead weight. It is a little over 100' long and 80' wide- not counting the roll-control wings. The internal volume of its lifting gas is about 120,000 cubic feet. The cabin is around 1000 square feet of usable space. It uses a single diesel and a set of super capacitors to power all four ducted fans. The capacitors would power the burst of thrust needed to get airborne. After that, aerodynamic lift would take over. Ducted fans are actually more efficient a low speed- less than 100mph. This airship would max out at about 50mph.

Parts of the lower surface would consist of transparent Tefzel, allowing passengers to look straight down, through a Tefzel window- and transparent helium- at the ground below. And the ground would never be very far away. The cabin would be unpressurized. It would solar heated (like a greenhouse) and actively cooled using air conditioners. Parts of the airship's top surface would be covered with lightweight, thin-film photovoltaics. It's conceivable that the aircraft could cruise on solar power alone- albeit at minimal speed. Because of its low speed and enormous area, it might actually be able to achieve meaningful lift from thermal activity. A soaring airship. In such a mode, the ducted fans would be used for extremely tight maneuvering, not for forward thrust.

The amount of usable cabin space would be on par with that of a 50' sailing yacht. It would be capable of landing and taking off from water. Because it would be heavier than air, it would need to be anchored, but not hangered when not in flight.

It would take off at about 20mph.

The airship could be flown using aerodynamic controls. Yaw would be managed with the twin rudders attached to the aft ends of the slip limiters. Angle of attack would be managed with the substantial elevator at the aft end of the main body. Roll would be managed via the side wings.

The internal gas volume would be separated into a number of chambers by a super thin layer of Mylar. Once airborne, the craft would be able to maintain flight even if all of its lifting gas were lost (assuming that the wing surface is mostly intact.)

Here's my Facebook page on the subject. Same thing, presented differently.