Shute devotes a good deal to this in "Slide Rule" so all I can do is provide perhaps a little more illumination for the non-technical. The R100 was a massive engineering project. It was 709 feet long, 133 feet in diameter with an actual displacement of 156 tons. The engine power was 4,200 horsepower with a maximum speed of 80 miles per hour and a cruising speed of 71.5 miles per hour.
So here were Vickers, contracted to build an airship to a certain budget, and to meet a required specification using only their own resources. Under these circumstances the first thing to do is to assess the specification - are there any impossible or conflicting requirements ? (there were not). Secondly, if you have limited resources, what existing technology can be used in the project. You simply do not have the money to go and design new items for the airship.
The R100 was a dirigible airship. That is, it had a skeleton which was covered by a fabric outer skin. The skeleton is a structure which consists of hoops varying from large diameter in the middle to smaller diameters at the ends and these hoops are connected by members running along the length of the ship . It is this skeleton that gives the ship its overall shape and, like the human skeleton, takes all the forces imposed upon it. This structure has to be both strong and rigid but it also has to be as light as possible. The construction method used, thought up by Barnes Wallis, was to make the structural elements by winding aluminium strip into tube as a helix, joined together by riveting . So that you can make the structural elements the right size, you need to know, pretty accurately, the forces that they have to bear. This is what Shute and his team of calculators did in the design stages of the R100. Of course there were no computers available in the early twenties so all the number crunching was done by hand using slide rules and jotting the results down in tables of figures. This is what he describes in the pages of "Slide Rule" when he goes into some detail on the calculations for one of the main rings of the R100 structure. In technical parlance he describes analysing what is termed a "statically indeterminate structure" In mathematical terms there are more unknowns than equations that can be written for them. In these sorts of cases you have to start by guessing some of the values and then working through the equations to see if the results add up. If not, you adjust your guessed values and go through it all again, probably many times, until all the results agree. All this took a team of calculators days and weeks ( It is interesting to note that, using a modern structural analysis program on a current digital computer, the specific problem detailed in "Slide Rule" could be set up and analysed in detail by one person probably in a couple of days !). It as said that the structural strength of the R100 was five times greater than that of any airship built in Britain prior to 1924.
The framework of R100 is shown in Fig.1 and it is the analysis of the multi-sided ring girders that Shute is describing in "Slide Rule". If you look closely you can see two men sitting on the top of the ring probably some 70 or 80 feet above floor level, no wonder they had to have a head for heights!
They had to have faith in their calculations - Vickers did not have the money to build expensive test sections and rigs to back up the calculations. One example Shute gives is that of the steering the R100. Their calculations indicated that the rudders should be able to be turned by the helm wheel using mechanical control alone. They could not afford the weight of a servo motor to help move the rudders. Yet their confidence in what they were doing was undermined when they learned that Cardington was proposing to fit just such a servo motor. In the end their confidence was borne out - a servo motor was not needed and the airship could indeed be manoeuvred by "hand power" alone. So, as another great contemporary engineer [2] wrote, "the pen is mightier than the spanner".
Another aspect of the R100 engineering approach was not to re-invent the wheel. If an existing piece of equipment was available then it was used. Examples included the valves for the gasbags. These were bought from the Zeppelin works in Germany and were obviously tried and tested. Had airship work continued then (Shute comments) Vickers would have made them under license. After some abortive development works on engines which, as Shute points out, was sold off, they decided to buy commercially available Rolls Royce petrol engines.
Shute was promoted to Deputy Chief Engineer of the R100 project. In fact due to Barnes Wallis' absence through illness, Shute was effectively the Chief Engineer and the man on the spot who had to make the decisions.
Fig.2 shows the lounge of the R100 Airship showing how luxurious, for its day, the accommodation was [3].
Incidentally helium was not used either on the R100 or R101 since it was "not commercially available except in the U.S. where its export is prohibited" [3]. Hydrogen was made on site and piped into the gasbags. Hydrogen is of course very flammable and was the gas used in the German Hindenburg Airship which caught fire at Lakenhurst airfield in 1937. A recent television programme on the Hindenburg disaster ascribed the cause to the paint used on the outer skin of the Hindenburg. This recalled to my mind a passage from "Slide Rule" where, on a visit to Cardington, Shute is shown a piece of the outer fabric from R101 where the dope used had made the fabric very friable. Perhaps this was a contributory cause to the R101 tragedy as with the Hindenburg [4].
