The Power of Blimps Rise Again

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It is not your typical cigar but, in its decidedly feminine form (complete with a double helium bag, flat bottom and skirts), this hybrid dirigible is buoyed by both military and civilian contracts. There are hybrid structural designs that cross a rigid frame and an inflated blimp but this Hybrid Air Vehicle also combines properties of an aircraft and a hovercraft.

Hybrid Air Vehicles: A new form of Airship

Why We Like Airships…

Aside from the tremendous potential for adult puns, large objects floating in the sky have a certain appeal to the kid in us. Growing up in NJ, I remember calling to others to come and watch the blimps traveling a few hundred feet above our heads. The Lakehurst Naval-Air Station was not far and we didn’t yet have Snooki or the Sopranos to show us what was “really” interesting in rural NJ. They are huge, yet they float. It is like magic and their slow movement suggests the gentle giant. Perhaps there is also something from our first memories when huge beings seemed to float around and take care of us.

history graph of airship development

What is the History of Lighter than Air Ships?

The history of lighter than air craft started with the first hot air balloon built in 1783. Only two weeks later, the first hydrogen gas balloon was flown. We had to wait until 1852 for a “lighter than air craft that could be steered,” which is the definition for the words “dirigible” and “airship.” By 1899, Ferdinand Zeppelin had designs for the ridged framed dirigible that bears his name. In 1925, the US was the sole supplier of the world’s helium and established a reserve which was only recently liquidated. A helium embargo caused other nations to use hydrogen for their airships, including Germany. The Hindenburg was designed to use helium, but was forced to use hydrogen by the embargo. Hydrogen provides only 8% more lift than helium. After Hindenburg was dropped in flames at Lakehurst, NJ, smaller, cheaper, non-rigid airships known as (b-)limps became the diminishing standard. They were used during WWII to spot the shallow operating submarines of the age.

What “Power” of Blimps? Isn’t that a Dirigible?

All airships, rigid and limp, use the power of buoyancy for lift. This is in contrast to air planes and helicopters which use fuel and wing movement to stay in the air. But airships present a larger frontal area to wind resistance so that the

drag on an airship rises as the square of its speed, while the power required to propel it increases as the cube of the speed. In airplanes, lift and drag increase together with speed, so that for a given lift the drag is effectually constant at any speed, and so the power required only increases linearly with speed until close to the speed of sound.

The bottom line is that a large payload dirigible will use less fuel and move more tonnage per hour producing fewer greenhouse gases for a longer period of time than a cargo jet and the overall cost of the vehicle is cheaper.

A blimp has a gas pressure only up to 2psi higher than the surrounding atmosphere. So, bullet holes tend not to do very much. (The Goodyear blimps get them all the time.) But, at higher speeds (max 80-100mph), the vehicle shape tends to deform. A rigid dirigible can go slightly faster while the hybrid structure (rigid keel only) is a good option between cost and performance. The Zeppelin NT pictured above is a blimp with a rigid keel: a structural hybrid.

All airships use their shape to provide some lift under power (10%+). This helps them to come back to Earth. Hybrid Air Vehicles increase this to about 40% with the remaining 60% from buoyancy. The vehicles also have the potential to add up to 25% vectored thrust for unassisted take-offs and landings. This is where the blimp meets the hovercraft — the reason for the skirts — and is a tremendous advantage over the relatively large ground crew required for a conventional airship. Once landed, the hovercraft capacity is reversed to “suck down” the vehicle to the ground. Paul Bouchard president of Discovery Air Innovations (DAI) based in Canada said, “HAV’s heavy lift and cargo capacity of 50 tonnes at speeds up to 100 knots (185 km/h)… will enable economic development of remote, stranded resources with a low environmental impact… without the need for a runway…”

Military Uses

The HAV can stay on site for up to 21 days and be manned or remotely operated. At altitude, it makes an ideal eye in the sky platform:

A radar mounted on a 30 meter high vessel platform has radio horizon at 19.5 kilometers range, while a radar mounted on an 18000m altitude HAA has radio horizon at 478.1 kilometers range.

It is for this reason the HAV won a $517 million contract with Northrop Grumman to develop the Long-Endurance Multi-intelligence Vehicle (LEMV) for deployment by the U.S. Army to Afghanistan in early 2012. This is part of a long standing DARPA program to develop a Radar Airship with a huge antenna.

It appears as if Professor Sir David King’s prediction cargo and military use for airships is becoming a reality sooner than the 10 years he suggested. Perhaps what was really needed was for an airship to look good rather than overstuffed or a bit lean.

Additional information and sources:

Photo Credits: Main photo of NT Zeppelin ben.fitzgerald via flickr ; all other photo’s HAV

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