Slipping the Bonds
by George Paterson
Many years ago, as part of my engineering course in college, we spent some time on a subject called dimensional analysis, which explains how you can use models to predict the behaviour of full-sized prototype structures. We bridge engineers use this occasionally, particularly to predict the stability of big suspension bridges. The famous collapse of the bridge that spanned the narrows from the mainland to Tacoma island in Washington State testifies to the importance of doing wind-tunnel tests on models of such bridges, and getting the analysis of the data right.
Similar scaling problems arise in model aircraft. Typically this affects airflow needed for the engine, and the size of the rudder and elevators may need to be bigger than true-to-scale. Of course, model makers don't do the complex maths; they simply know from experience how big the engine intakes need to be to get satisfactory performance from their motors.
Recently, while preparing the text for my recent Vampire presentation, I was re-reading sections of my two main reference books on the early jet planes, “The Jet Pioneers” by Glyn Jones, and “Die ersten Strahlflugzeuge der Welt” (The world's first jet aircraft) by Wolfgang Wagner. I spotted a short section in Wagner describing the Henschel Hs 132, the first jet dive bomber, the V-1 prototype of which was about to begin flight testing when the Soviet Army over-ran the Henschel facility. Wagner says that flight tests were made under Soviet supervision, but that no record of the flights had yet (1989) been found.
I did a search for information and images of the Hs 132, and found several model builds from kits by RS models, as well as video of a flight by a free flight (FF) model; the model is about 2 meters long, and is finished in a typical late-war camo scheme. The builder was Christian Hoffmann.
The Initial Image
I made a number of screen grabs of this FF model, and I decided to make an in-flight image based on this grab.
Like all grabs from videos, this one is very soft, which makes selection of the structural and décor elements tricky, as I know from previous experience; I once presented an image of a Hanriot HD.1 made from a grab like this.
Another aspect of this kind of image is that the rendition of colour is sometimes misleading. For example, the Geschwader emblem aft of the canopy shows the black areas as red!
Treatment of the Image
A lot of work was needed to sharpen the image and improve the rendering of colour, but the biggest challenge was the re-modelling of the engine pod on top of the fuselage. I calculated that the intake cowling should be reduced to 70% of that on the model; that is the scaling effect in practice! The outcome is that the engine pod is a lot more hump-backed than the one on the model, as it is on the 3-view drawing in Wagner's book. Some trial and error was needed to get the pod looking about right.
In choosing a background image, I was mindful of the original purpose of the new Stuka aircraft commissioned by the RLM. It was to be used for precision bombing of enemy ships in the event of an attempt to make amphibious landings on the North Sea coast. None of the artworks I've seen of the Hs 132 suggest that.
I would have liked to be able to consult Chrisian Hoffmann about my intentions, but drew a blank on all my efforts to get in touch with him.
Regarding the background image, I at long last found an application for my photo of the island of
Wangerooge, which is one of a long chain of small islands that stretches from the mouth of the Ijsselmeer, along the German, and then up the Danish coast as far as Blavandshuk. Any seaborne invasion of any part of that coast would have to contend with the defences on these islands.