Willy Messerschmitt

© Copyright (as translator) For the entire text below, rests with Calum E. Douglas, no part of this may be reproduced by any means without my permission.

Professor Messerschmitt was called to give a lecture at TU München in 1943 to celebrate the 75th anniversary of the University, sadly only the text was recorded in the file, so the content of the images (figures) Messerschmitt clearly had prepared as slides, are unknown. Despite this it makes interesting reading, and in many cases the contents of the images can be inferred from the descriptions. The aircraft mentioned can be found online without difficulty. I have included two images of the aircraft he mentions. Obviously the favourable comments made regarding the Nazi leadership are purely to be taken as a historically faithful translation of the lecture.

Where Messerschmitt refers to “shell” construction methods, this can be taken to more easily translate as “stressed skin”, however this is not strictly speaking how he chose to refer to it.

Despite the lack of the actual slides, three photographs were taken of the event and dinner itself. One of which I provide below.

Experience in the design of metal aeroplanes.

As simple as a modern aeroplane may look from the outside, it is a piece of equipment that is much more comparable to an armoured cruiser in its technical design than to an automobile. If we look at an aeroplane from 1918 (Fig. 1) and compare it with an aeroplane from today (Fig. 2), the clear, simple lines of the modern aeroplane make a pleasant impression. But it looks quite different when we look inside the aircraft. Even at the end of the <CD: First World> war, the aircraft was still quite basic in its use of equipment. A few devices for operating the engine, a simple compass, an altimeter and an airspeed indicator and a small number of mechanically operated weapons represented almost all the armament.

The development towards better dynamic flight performance, higher speeds and higher altitude required modern, more complicated engines with cooling fans and variable pitch propellers, which became necessary to achieve sufficient efficiency for high speeds and take-off, the demand for good communication with the home-base, the necessity of flying in bad weather, blind flying and even landing at night and in fog required an equipment of radio equipment, long and shortwave transmitters and receivers, direction finders and more. In addition, modern aeroplanes, insofar as they are warplanes, must have considerably more powerful armament than at the end of the world war.

Whereas in the past the defence armament consisted only of machine guns, today the defence cannon has become indispensable alongside the machine gun. Even the offensive weapon, the bomb, has been developed considerably further with all the associated equipment. Mechanical operation of all these devices was no longer possible in the long term, e.g. the variable pitch propeller even had to be automated to relieve the load on the pilot. This development direction necessitated the use of auxiliary powered systems. A modern aeroplane is no longer conceivable without a large-scale electrical system, without a hydraulic system and without a compressed air system.

However, it is not the task of a lecture to inform you about the development of all parts of the aeroplane. I will therefore limit myself primarily to the development of the fuselage construction of the airframe, i.e. the aeroplane without equipment and without engine. If I have told you something about the large number of items of equipment, I have done so to make you realise how important it was to develop the airframe in such a way that the necessary static structure of the aircraft was placed as far as possible into the outer skin and close to it, in order to gain the necessary space for the large number of additional items of equipment already mentioned, without enlarging the aircraft for this respective purpose alone.

(Fig. 3) shows you an old-style aeroplane fuselage. You can see a weak lattice fuselage. However, the parts in the picture are only the supporting skeleton. The moulded outer surface is still attached by strips, so that the real usable space is only a fraction of the space represented by considering the size of the whole outside fuselage form. These structural parts take up a large part of the overall moulded space. The need to create space as cheaply as possible forced the development of the shell construction method <CD: “Stressed skin”>. But the shell construction method also had structural advantages over the frame construction method <CD: Tubes covered by some sort of fabric or perhaps moulded plywood etc.>.

The load-bearing parts of the construction – which are bodies that are subject to bending and twisting – should be placed in the outer skin for static and rigidity reasons, whereby the outer skin, which is necessary for aerodynamic reasons, was appropriately incorporated into the load-bearing structure. Better utilisation of space, better use of materials and greater rigidity are the main features of the shell construction method compared to the old fabric-covered frame construction method. The shell construction method does not necessarily require pure metal construction. Shell parts for aeroplanes can also be made from tempered wood, plywood.

Wood is a very good building material; it is easy to process and can be securely joined by gluing. Wood, despite being suitable for mass production is not as uniform in its strength as metal.

I would now like to move on to my experience in the development of metal aeroplanes. About 14 years ago I received an order for the development of a small commercial aeroplane from the then head of Nordbayerische Verkehrsflug G.m.b.H.. The experience gained with the small two-seater M17, which had been developed directly from the glider and had won a number of competitions, was to be utilised for larger aircraft. I had proposed the new design in plywood construction, as I knew it from the earlier glider.

The design drafts had made good progress when Croneiss, the head of the aforementioned company, came to give a lecture to make it clear to us that a wooden fuselage would be unsustainable for a passenger aircraft in the event of any accidents due to the risk of splinters. The suggestion was made to weld the structure in the usual framework construction of steel tubes. However, as I had very little experience in welded construction, and a sheet metal construction made of a high-strength aluminium alloy (Dural) seemed easier to me, therefore we agreed to build the fuselage of the aircraft from sheet metal. The wings and tail unit were still to be made of wood. It was only during the construction phase that I decided, initially against the wishes of the client, to also build the other parts of the aeroplane from sheet metal. Apart from a considerable delay in production, this attempt went well and I was able to gain valuable experience for the future.

The aircraft, the M18, was a complete success.

I had no experience whatsoever in metal construction in these early times and first had to get an idea of the strength properties of sheet metal construction through a huge number of different physical tests. These times during the development of this aircraft type was later decisive for the development of my metal aeroplanes in general. I took great care to ensure that sufficient strength was achieved with the least amount of material. The design task was therefore very suitable for this economic aim. With only 120 hp, 5 men with luggage were to be transported at a cruising speed of around 140 km/h, as was usual at the time, in order to make the operation as economical as possible. I also succeeded in making the skin of the aeroplane as strong as possible. Even then, as with all my aeroplanes today, the wings consisted of only one spar.

The construction was carried out in a similar way to shipbuilding. A series of frames were connected by longitudinal stiffeners, and the sheet metal panelling was pulled over this relatively light frame and fastened to the frame with many rivets. I didn’t have much confidence in the riveting process for my first aeroplane, as the thin sheet metal was usually only 0.4 to 0.6 mm thick – rivets with an average thickness of 3 mm. During construction, I therefore had another rivet added. That was my good fortune, because due to a lack of experience I had forgotten that the rivets supplied by the supplier have to be tempered before they are hammered. When the aircraft was inspected by the testing centre, it was determined that the untempered rivets would not be sufficient.

At the time, I was asked to drill out the thousands of rivets and replace them with hardened and tempered ones. However, experience showed that sufficient safety was achieved by sealing the rivets. In my subsequent designs, I then went back to larger rivet spacing using properly tempered rivets. Extensive tests, which were carried out continuously with all fuselage components, served to introduce a system into the entire design. <CD: By “system” he probably means that a specific detail design of how to join the panels in various areas of the airframe was arrived at, and applied consistently to the different “sub-family” of these areas of the fuselage. Probably the complexity of the design meant that different techniques were needed for say, a tail brace, as opposed to an aileron, but that these techniques were probably condensed down into a few “set” systems which would apply to any aircraft.>

Of the aircraft models developed in the following period that were related to the M 18, I will only show you one commercial aircraft for 12 passengers, which was the fastest aeroplane in the world in 1928 with a speed of 210 km/h. The following main difficulties arose with this series of aircraft models, which were all similar in design:

1) The relatively poor accessibility of riveted hollow bodies in general. It was sometimes very difficult to drive the last rivet, as it was often difficult to hold the rear face of rivet, this applied in the wing and tail unit parts in particular.

2) In individual prototype production, this type of construction was more expensive than timber construction as expensive jigs and fixtures had to be avoided for reasons of economy. The ribs (picture), braces and stiffeners had to be hammered out by hand using primitive hardwood moulds and beading irons. Where sheets that could not be rolled were necessary for reasons of shape <CD: I.e shapes with compound curvature, curves in more than one axis at once>, these had to be painstakingly driven by hand over moulded timbers. Given the large number of moulded parts, this was an expensive process.

3) Unsatisfactory smoothness of the upper surface, as the sheet metal edges and the round rivet heads protrude and cause increased air drag resistance (up to 40%). The question often arose as to whether it would not be expedient to return to the old wood or wood-steel tube construction with fabric covering. However, the advantages of metal construction had become so obvious, and the possibilities of the future were so great, that I refused to take this step backwards despite the economic hardship of the aircraft industry at the time. The great upheaval of 1933 removed this hardship at a stroke; I was able to develop aeroplanes that were built in large numbers. Using the experience I had gained and employing new manufacturing processes that were only economical for large quantities, I was now able to successfully develop metal aeroplane construction further.

The following fundamental improvements were achieved:

1) The accessibility for the riveting could be increased by making it possible to openly rivet the individual hollow bodies in partial shells. <CD: he probably means what we would call “fuselage sections” here> By creating suitable fixtures, sufficient accuracy could be achieved so that the corresponding shell halves could subsequently be joined together with a few rivets or screws.

2) Whereas previously individual ribs had to be partly beaded by hand and partly built from small pieces, now the ribs could be made from one pressed part -or at worst just a few- which only required a few minutes of labour. This also had the advantage of greater precision. I also built the outer skin of the fuselage on so-called sections, i.e. the half-shell to form the fuselage does not consist of longitudinal and transverse bracing with riveted-on sheet metal, but of sheet metal strips to which the cross-braces are directly attached by means of pull tabs. These sections, each with two tightened ribs, are then riveted to a sheet that can be simply formed by rolling. The tightened frames are provided with holes and the longitudinal profiles are inserted through them, which are then riveted to the skin (picture). This picture clearly shows the development of the weft* construction method <CD: *The word used here was “Schussbauart”, I am uncertain about the correct translation of it>. In 1933, frames were still riveted to the sheet metal, with the inserted stiffeners that only extended from frame to frame. In 1934 the tightened frames, i.e. already a small number of parts; still had stiffening profiles which interrupted the frames or pre-bonded together by short inlaid straps. In 1935, holes were instead punched through the tightened frames and the profiles were then able to be pushed through in just one piece.

This resulted in greater strength at the joints. To make the outer skin smooth, the tightened frames were simultaneously pulled in by the thickness of the sheet metal.
An engineer from the fixture construction department came up with the idea of tightening 2 frames in one operation. This reduced the production time of the shots by half and only half of the jigs were needed. I have explained this example of the development of a simple hull design – probably the simplest known today – in such detail because it is a typical example of how simplifications can be achieved through years of development work in the design office and experimental construction without having to add a single gram of weight.

3) I have already explained to you that the smoothness left something to be desired. The mechanical production of the individual parts has made it possible to reduce this unevenness by countersinking the sheet metal joints. In addition, it is now common practice to countersink the rivets in performance aeroplanes. In the case of thin sheet metal, this is done by retracting the sheet metal at the same time as the rivets (Fig.). In the case of thicker sheet metal over 1.5 mm, the outer sheet metal is countersunk.

Our fixture construction department had the task of further developing the tools themselves in parallel with the development of the design. It often turned out that pressing or drawing tools made of steel were too expensive and unnecessarily heavy. In many cases, we therefore switched to drawing tools made of light metal or wood cement.

Pressing tools are often made of plastic. The service life of such tools is generally sufficient. For a long time, sheet metal was still cut to size by hand. The male and female dies, which have to be fitted together very precisely, are very expensive.

We have now learnt to work with only one male die; the female die is replaced by rubber. The process only requires a crisper cutting template, which is ground flat to sharpen the edges. The template is inserted into the press and the sheet metal is placed over it. The rubber is inserted into the upper part of the press, which then bulges out the sheet along the edges of the cutting template (picture). In this presentation I have only talked about my experience in a small area of aircraft construction. As I mentioned at the beginning, the usable aeroplane is influenced by many branches of technology. A modern design office consists of a large number of specialised engineers in addition to the design engineers and draughtsmen. It is just as clear that high-quality aerodynamic engineers are involved in the shaping of the aircraft parts, especially the wing, as is the presence of the weapons specialist, the structural engineer with his special experience in aircraft construction, and the electrical engineer. However, the correct deployment of all these forces will only lead to complete success.

For years, the Versailles Dictate prohibited Germany from building any powered aeroplanes at all. A number of courageous young men were not deterred and thought: if we can’t fly with a motor, then we can fly without one. The aeronautical engineering departments of the technical colleges were the most advanced in the development of aviation after the war. A virtue was made of necessity; without the experience of gliding, it would not have been possible to bring modern aeroplanes to today’s level of development so quickly. I am proud of the fact that I was able to build up my own factory without ever having to work in a foreign aircraft factory and that it can work so successfully.

Until 1933, our work* in aviation was very poor <CD: * “in Germany”>. Many ideas could not be tested; they remained in the heads of a few and in unrealised designs.

This impossibility of realising ideas was more due to the oppressive circumstances imposed than the poor economic conditions which prevailed. No other branch of technology must therefore be as grateful to our Führer Adolf Hitler and our Field Marshal Göring as we aeroplane technicians.

We owe the great rise of aviation in Germany to them. It was only through their planned support that it was possible not only to catch up with foreign countries in just a few years, but also to put Germany at the forefront of all nations in almost all branches of aviation technology.