Dr. S. B. Battey’s (1893)”Aerial Machine” patent US502168A…

I’ve previously included a link to Dr Battey’s (1893) “Aerial Machine” patent on Google Patents (it was even cited in a 2018 patent!), because it seems to me to share many features with the mysterious airship in the 1896 & 1897 Airship Flaps. I thought it would be useful to post a description of Battey’s patent, particularly its novel propulsion back-end. So… here we go, then.

Battey’s Aerial Machine

Here’s the artist’s impression of Battey’s airship published in Scientific American. The main sections are the streamlined balloon envelope, the wings on the side (for ascending and descending), the gondola below, and the curious-looking propulsion device on the back, all connected via standard Heath Robinson ropes / pulleys / sprockets straight out of every Victorian schoolboy’s My First Engineering Kit.

Battey doesn’t claim anything inventive about the aerodynamic balloon envelope. He describes this as having “the shape of a double cone with the bases united […] preferably made of light sheet metal, such as aluminum”. Internally, the envelope is “strengthened […] by a suitable framework […], preferably composed of vertical and transversely disposed braces”. His innovation is all in his “propellor”…

Battey’s Propellor

What Battey actually “claim[ed] as new and desire[d] to secure by Letters Patent” is his “propellor”, by which he means the mechanism to propel an airship forward. To illustrate this, I’ve grabbed the two relevant figures from his granted patent, cleaned them up (by removing all the arrows and letters), and then annotated the various parts in red using the terms used in the text.

As embodied here, the entire “propellor” mechanism is driven by the ticking of a clockwork mechanism (driven by a clock mainspring), which at regular intervals pushes a piston downwards along a short vertical cylinder. This piston (somehow) drags a nitroglycerin pellet out from the end of a J-shaped magazine feed pipe, and then pushes that pellet downwards towards a firing cup. When the pellet lands in the firing cup, the pellet itself completes a circuit between two wires connected to a battery (not shown), causing the pellet to explode. The shock from the detonation hits the dish-shaped propellor, and so propels the aerial machine forward: the spring beneath the firing cup yields, and so the firing cup is not damaged by the explosion.

Your thoughts, Nick?

Many people’s immediate reaction to this design would be that anyone who would combine a huge airship envelope full of hydrogen with external explosions every few seconds was a suicidal maniac. But knowing a little more about balloon history, I’m not sure that’s entirely fair.

In the 1930s, one of Jean Piccard’s innovations with his Pleiades multi-balloon setup was to attach explosive charges to ropes to release groups of balloons: before that, balloonists had used knives or even pistols to do the same thing, but these were often highly unsatisfactory. At the time, everyone thought Piccard was insane, but it wasn’t many years before just about everyone started copying him. So maybe Dr Battey’s design wasn’t quite so, ummm, batty after all.

The key limitation on the range of Battey’s airship would seem to be how many explosive pellets would fit in the magazine feeder pipe. If a pellet exploded every, say, six seconds, then you’d need ten pellets per minute. Annoyingly, the design doesn’t seem to have any means of stopping the clockwork piston (the only control over the mechanism seems to be to disconnect the battery), so it seems that once started the piston would keep pushing pellets down the cylinder until the magazine was empty.

So… the maximum length of a single flight would be determined by the number of pellets in the magazine. Even taking the dimensions of the magazine broadly as drawn (say, 5cm diameter x 2m tall), its capacity would be about 4,000 cm³ (and unless anyone knows better, I’d guess each explosive pellet would be about 1 cm³ in volume), so around 3500 or so pellets. This would give roughly 350 minutes of flight on a single magazine load, which would seem to be plenty for reasonable length night flights.

But would these nitroglycerin pellets have been powerful enough to propel Battey’s aerial machine at all? The figures given by Wikipedia are 1.6 g/cm³ for density, and 1.488 kilocalories per gram, so a 1 cm³ pellet would contain 2.38 kilocalories of energy. I believe that this is about half the energy density of gasoline, but I would be happy to be corrected.

I suspect the easiest way by far to determine how much power this would produce in practice (without all the losses to heat, light and sound etc) would be to build a test rig, but given that I have precisely zero desire to have the anti-terrorist squad kicking my door down, I’m not going to be doing this. Sorry for not going 100% gonzo on this etc etc.