While reading through the Fatal Flight from Bill Hammack, I’ve noticed numerous references on another book – Airship Design by Charles P. Burgess. I couldn’t resist an opportunity and bought a copy. It arrived shortly and I’ve ended up reading it for past 2 months! There were was so much of interesting information related to our project that I’ve lost track of all of them after while, but dedicated to coming back and do at least a minimal review on some highlights – I came with a plan to pick my top 10 highlights.
While plan is laid, I would still like to start with synopsis on the book’s booklet itself: Originally published in 1927, this volume was intended to fill the dual role of textbook for the student of airship design and handbook for the practical engineer. The design of airships, particularly of the rigid type, is mainly a structural problem; and theoretical aerodynamics has nothing like the relative importance which it bears in airplane design. This is to be expected when we consider that the gross lift of an airship depends solely on the specific gravity of the gas and the bulk of the gas container, and not at all on shape or other aerodynamic characteristics which determine the lift of airplanes. … and it is all there!
Now let’s start with our list itself.
1/ Beautiful historical pictures and schematics
This book is full of them. I’m picking up two of them, bu I’ll keep picking more through our list.
2/ Hydrogen vs. Helium lifting performance.
It is well known that weight difference between weight of Hydrogen and Helium is just about 5%. However it is not that apparent how it translates to the gas lifting power. One of the paragraphs in the Size and Performance section covers this topic in a detail clearly stating that usage of Hydrogen increases overall performance of the airship by incredible 54.5% – this roughly translates into larger payload / reach radius / operations ceiling in general.
3/ Testing with models
Imagine 1920s – no computers, 3D visualisation, well … no calculators, no super computers. Pinnacle of the modern technology was mechanical Enigma Machine. What you do? You use wind tunnels to test your aerodynamics, and underwater models for testing all sort of sheering moments and stress forces. Then you’ll come with equations which will describe how all those observations scale up. Then you build it and learn from your mistakes and repeat. Purely amazing!
4/ Venting & Exhaust trunks
Rapid pressure changes caused by the airship’s steep ascend, descend or just gas temperature changes are clearly one of the prime dangers every airship is facing. Practical way to tackle that is to have some good-sized vents which can prevent popping its envelope. Yep, even this is in, including practical calculation example relating to the overall volume.
There is also an equation providing required vent area on the next page together with a description of exhaust trunks for safe Hydrogen venting from gas bags.
5/ Airship size and its performance
You have an airship of a size X and you are designing it to travel with a certain speed, how many horse powers you need? This is called the effect of increased speed – every cyclist has pretty good practical experience with this. With bit of basic calculations and following graphs you’ll know that for your airship being able to carry 16.000lbs payload with speed of 60 knots, you’ll need it to mount it with power plants totalling 1.450Hp.
6/ Slenderness and Elongation
Those two super-important fitness parameters are main parameters coming from airship’s linear dimensions and volume. There parameters have a direct effect on the airship’s performance. This book provides multiple graphs showing these effects, while to my surprise at the end of this chapter it leaves designer free hand as it seems like some of those parameters and their effects are not that clear.
Let me introduce you to the state-of-art materials for building airship in 1920s: duralumin, high-tensile steel and hick cotton, painted with aircraft dope containing aluminium to reduce solar heating for envelope! While doing its job, all these materials are today superseded new ones which are lighter, stronger and overall more reliable than anything they could imagine that time. It is actually surprising how creative and resourceful engineers of their time were.
8/ Airship resistance – skin friction
There are multiple parameters affecting overall airship resistance – ability to efficiently propagate through the air and operate. While all of them are important, the most interesting for me was the skin friction – the tangential force of the air actin upon the surface of body. While there are equations provided with indications on how to get these forces, apparently any coarse buckram, unglazed fabric or any other surface imperfection can have significant impact on this ranging with up to 15% performance penalty. Still it is recommended to keep testing, keep testing and then learn from other projects.
9/ Build your own
Whole chapter (called Steps in Design) is dedicated for engineers to be able to assist them with step-by-step design which will fulfil certain performance requirements. It again recommends to check on other projects for inspiration and learn from them. All main and expected design aspects are covered, while paying detail to its controls, ballast, mooring mechanism and finishing with details on passenger cars.
10/ Common airship fallacies
One of the most interesting and the final chapter of this book – what not to do when you are designing your airship. The book clearly warns not to use following inventions:
a) The vacuum airship
b) Compressing gas or air for ballast
c) Artificial control of super-heat
d) Combined heavier and lighter-than-air craft
e) Channel through hull to reduce resistance
f) Wind screen at mooring mast
You might be not surprised that except one – we’ve been clearly considering all of them in our design! I’ll leave you to guess which one was it. 🙂
And that’s all! Really enjoyed this book as well written and while technical still very readable. It already found its place in our library and inspired several updates to our design. Thank you Mr. Burges, your effort won’t be forgotten!