General airship question: advantages and disadvantages of size?

Question

Airships are cool, and one of the only vehicles that benefits of the square cube law as it can carry more weight if it has more volume of lifting gas. This got me thinking about what other advantages abd disadvantages you get based on an Airships size. What benefits are there to having a small airship versus a large one? What benefits does a large airship have over a small one?

To get a singular answer I want to focus on a general comparison:

What are the advantages and disadvantages of a large airship compared to a small airship?

To illustrate what I'm after, I would like to know the differences in capacity, short/Mid/long-range flight, maneuversbility during different weather etc.

Answer 1

The most obvious answer to your question is lifting capacity.

At the end of the day, with the exception of drones that are designed to be as small as possible while lifting a set weight (usually a camera), aircraft are designed and built to lift as much as they possibly can. The point of that is the same reason that cargo ships are getting bigger and bigger now that cargo has been standardised around the shipping container; carrying more units means that the fuel and time (read as wages for crew) required to do so is spread across more paying customers, or at least more freight. This is the reason for planes like the Airbus A380; if you have enough passengers per day to fly two (say) 747 jumbo jets to the same destination, then ultimately having a single plane that can carry them all makes sense even if it uses 150% of the fuel as you're still doubling the fares you can charge and you only pay for one air crew on a single flight.

To that end, meet the Lockheed Martin LMH1, a prototype for a new range of heavy cargo airships. According to the article, this prototype can carry 20 tonnes of cargo and 19 passengers, but future models could be scaled up to carry up to 500 tonnes, albeit with 800m lengths.

The fact that a company like Lockheed Martin is investing in large scale airships even as proofs of concept tells you that there is a commercial benefit to these designs. If you're moving cameras around, then going small makes sense. But these things can carry (say) massive amounts of cargo through impassible terrain for instance to supply people cut off by floods, forest fires and any other manner of natural disaster. For that reason alone, it seems like a good idea to go large on airships.

Answer 2

Disadvantages of size will be grouped around housekeeping:

• Hangars are more scarce,
• mooring is more difficult,
• repairs are complicated by increasing lack of facilities.
• Volumes involved (bladder, cargo, fuel) become a headache, i.e. ingress and egress happens through areas (square) while the mass is governed by cube, so the mass flow needs to get higher, or you need linearly more time for related actions: fueling, loading/unloading, filling/deflating
• Market is smaller for bigger things.
• Accidents grow more catastrophic (economically: how to haul the carcass back?, victims/damage: one leaky bladder just suffocated a whole village/ one runaway 10km zepplin just got caught against the NY skyline in a storm, toppling the lot).
• While the airship has no problems supporting it's size, the cargo is not necessarily so sturdy - many supermassive things (supertankers etc.) are built to be supported on a wide area (water, ground), not from individual hardpoints. So the airship needs cradles for that, and techniques to get the cargo onto them.

Advantages of size will group around technical issues - At same ratio of power to lift (which is not true irl, large blimps usually are relatively weaker, because you can get away with it (qed), economics at work) bigger is better in :

• handling (air forces needing to be overcome scale with either length or area), both only growing in square with size, while lift (~power, remember) goes as cube
• resilience (lifiting gas is lost over the surface (square) and available in volume (cube); Crew is bigger, so more redundancy;)
• range, (corrolary of the other points)
• speed, (Reynolds number grows with linear size)
• acceleration (as lift/power is defined as equal, the only variable is air resistance, going back to square/cube)
• lift (most obvious last - but also note that this burns you on the economics: if you are capable of lifting a refinery, lifting a petrol truck will not cover the bills, and fetching petrol trucks weighing as much as a refinery will mostly generate overhead).

Adv./Disadv.? - Note Not sure how to class this one: As your lift grows by cube, the 'attachment area' for loads only grows by square. If we now think about all the super massive things that humans built (industrial plants, skyscrapers, ...) they usually are not simply 'scaled up' from smaller versions (an industrial plant my be 1km wide, 50 m high, so scaling it down to the 10m length of a garage, it would be only 0.5 m high; Skysrapers would be chubby smokestacks if scaled to the size of a family home) - so the reality of 'things our giga-airship might carry' is not centered around stuff whose mass goes as the cube of their length; On the other hand, our giga-airship is not real either, so it might be disingenous to assume that in a world of such ships there would be no 'scaled-up fuel truck'-kinda-refinery in need of carrying - and that would be a problem because our airship would have the raw lift, but would be unable to link to the refinery because of insufficient area to put tow-lines.