The Lost Zeppelin Returns

Well obviously I was being overly dramatic with the title, because the Zeppelin wasn't "lost," just in storage. The box itself was designed to fit in the bed of my Ford Ranger pickup. The frame was made of 1 inch x 2 inch wood, laminated with white corrugated plastic panels and a hinged door on one end. It's wide enough to have fit both halves of the finished airframe, which itself was intended to be joined together at the flying site with couplers that join the longitudinal girders.

The main rings were made from pieces of 1/16 inch by 1/8 inch thick balsa wood, cut to form a 12-sided polygon. I had drawn a pattern onto white foamcore board for the main rings, laminated with thin plastic film. The balsa pieces were glued in place using CA glue and accelerator, each piece pinned in place. The corners where the pieces joined were reinforced with diamond-shaped gussets of 1/32 inch balsa.

The design of the framework was intended to be inspired by the method employed by the original Zeppelins, which had reinforcing wires prestressed across the polygonal main rings. For my reinforcing "wires" I used thin black sewing thread, the ends of each one tied to a map pin and stretched and laid across opposite vertices of the polygon. Once each thread was in place, I then applied CA glue and accelerator to where each end of the threads touched their corresponding gussets. Once dried, I removed the map pins and cut off the excess thread. This process was repeated for all 12 bracing threads on each main ring.

Being as I started this project in the early 2000s and accurate gram scales were harder to come by, I had to find a way to accurately weigh each component to within one gram resolution. I did this by starting with a bag of 1 gram plastic cube weights, that I had acquired a few years earlier from a science store. I made a scale similar to how a fish scale works, with gram weights on each side. Attaching an item to be weighed to one end of the scale, it would slightly tip to one side and the vertical weighted thread would cross a scale marked in one gram increments. This method enabled me to extrapolate weights to a fraction of a gram.

Using this scale, each main ring weighed about 1.5 grams when completed! I thought that was a good indicator that my design might be light enough to float lighter-than-air, yet be sturdy enough to support the loads required.

I purposefully chose a hull profile that was cylindrical, for the reason that the main rings would be the same diameter and hence make construction easier.

When my business assignment came to an end I'd only completed the middle section of the front half, three gas cell bays long. I had to build a small storage box sturdy enough to withstand being moved back home via my household goods. Once home, I continued working on the framework. To begin assembly of the main rings into a hull shape, I built it vertically, joining the vertices of each main ring with longitudinal girders of 1/8 inch by 1/16 inch balsa.

Continuing with the Zeppelin-inspired design, each rectangular panel formed by the intersection of rings and longitudinals were themselves prestressed with diagonal bracing threads, stretched and glued in place using map pins as I'd done with the rings. This design has proven to be sturdy enough to withstand 21 years of summer heat and winter cold in my brother's garage.

I should pause and explain the difference between a "non-rigid" airship and a Zeppelin-type rigid-airship. You could consider there to be two classes of airship hull: pressure airships and rigid types.

Pressure airships maintain the structural rigidity of the hull from internal pressure of the bouyant gas, assisted by internal air-filled ballonets that can be adjusted as needed. Think of the word "blimp" when referring to these.

The Norge in the Arctic

There was also a sub-category of pressure airship known as "semi-rigid," that in addition to internal gas pressure had a rigid keel attached to the bottom of the envelope, useful for attaching loads like gondolas and engines. These were used in the early 20th century for making larger craft at a time when exotic, synthetic fabrics had not yet been developed. The Italian semi-rigid airship Norge was of this type, that succeeded in flying to the North Pole, in 1926. More recently, the Zeppelin company of Germany (yes, they're still around!) developed a version called the Zeppelin NT (for New Technology) that has an internal framework of aluminum and carbon fiber girders to help support the inflated envelope.

A WW1-era rigid airship

Rigid airships, in contrast, maintain the shape of the hull against aerodynamic and aerostatic forces by a rigid hull, in the case of Zeppelins made from a framework of duralumin girders (an alloy of aluminum) and steel bracing wires. Instead of the entire volume of the hull being filled to completion with gas, the spaces between main rings contained large cylindrical balloons called gas cells. The cells were held by nets that transfered the lift from the cells to the framework. One advantage of this design is a leak in one gas cell wouldn't affect the rest of the craft, and each gas cell wasn't pressurized as was the case with blimps.

The ZMC-2 "Tin Blimp"

There was another version of rigid airship called a metal-clad airship, essentially a monocoque rigid metal gas-tight aluminum skin reinforced with internal metal girders. It was strong enough to support itself without internal gas pressure, but was pressurized for flight. One of these was built for the US Navy, the helium-filled ZMC-2, which flew from 1929 to 1941.

LZ-129 Graf Zeppelin

The most successful rigid airship was the German Graf Zeppelin, that used hydrogen lifting gas and, instead of petrol for its engines, used a gaseous fuel gas contained in separate gas cells below the lifting gas cells. The advantage of this type of fuel was as the craft burned fuel during long flights the airship didn't suffer loss of weight, which in a petrol or diesel-powered craft would have meant valving off lifting gas to remain neutrally bouyant. The Graf made many flights from Germany to Brazil, across the Atlantic to North America, explored the arctic and made a round-the-world flight in 1929. But with the destruction of the Hindenburg in 1937 (and the impending war), the rigid's days were numbered.

The LTA Research Pathfinder 1

More recently, a new rigid airship project has been in the works, called LTA Research,, funded by Google founder Sergie Brin. Its framework is made from carbon fiber and titanium and was given license to fly in October 2023. Though only half of the length of the Hindenburg, the 400-foot-long Pathfinder 1 may be superceded by much larger craft.

I last took a look at my model airship in 2012, documented in this blog article. Since then it's sat in its storage box in my brother's unheated garage, over the hot summers and cold winters. I wasn't certain if those delicate balsa and thread connections would hold up to the stress, but in my initial inspection today it seems to have held up better than I'd hoped for. But the large box and delicate model now take up space in my much smaller garage, which leads to the question of what now?

Proponents of rigid airships have often been called dreamers, with their visions of huge leviathans silently floating in the skies. While we don't know if there's a future for the rigid airship, in my case the dream was much more modest, a small model that could float and be propelled by small motors. Like those other dreamers, I still don't know what'll happen to my dream either.