Rivets Technique PART 1

RIVETS TECHNIQUE Part 1.  Stressed Skin Effectfor model aircraft

In the old kits of kits there were many problems in the line that were not engraved, but embossed. Over the years, modeling companies have found a way to improve their layouts and portray them quite correctly in their kits.

  But the demonic mind of some, more experienced model, from the need for perfection in detail, created new tools and techniques.

One of them is the technique of "stressed skin" or in Greek "crumpled sheet metal" - without the exact translation.
All aircraft have a structural frame, on which the outer coating is coated with aluminum sheets, which is fixed with special rivets, in panels. It is worth mentioning how the structure is, so that it is understandable, how the forces are exerted on the frame of the aircraft and how, we will be able to transfer it properly to a model.

You probably already have the opportunity to see models that show the application of the "stressed skin" technique. It is a very interesting effect that adds a lot of realism to your model, as this phenomenon is to some extent present in any aircraft. There are two or three variations of the methods for simulating stressed skin, but before I get into the subject, let me start by saying that there is something wrong with the look of all the kits on the market!

The phenomenon of crumpled sheet metal is much more intense in old planes and mainly in large transports and bombers.
The newer planes present it to a much lesser extent.

Improving the structural design and better quality of the metal alloys they have, has extended the life of modern aircraft. That is why we do not easily find the crumbling in aircraft built after the 80's until today.

 To understand what stressed skin is, let's start by talking about some details in structural design. As you know, any aircraft structure is essentially a frame covered by an outer covering (almost like the balsa wood models). The parts of the skeleton are generally rods, ribs and strings. These structural elements provide strength against bending and tangent loads, but almost no resistance to puncture. If one were to use only rods and ribs and still aim for piercing forces, the weight that would result in the design would be prohibitive. There, the panels come into play, lightening the overall weight of the planes

  Τα πάνελ  δεν είναι μόνο ένα λεπτό μεταλλικό φύλλο που τοποθετείται κατά μήκος των πλευρών και των χορδών. Πρέπει να είναι προτεταμένο - ή τουλάχιστον να είναι καλά στερεωμένο στη θέση του-, πράγμα που σημαίνει ότι οι τρύπες των πριτσινιών  υπολογίζονται να ανοίγονται  κατά μήκος γραμμών ελαφρώς μικρότερων από τις αντίστοιχες κατά μήκος των χορδών και των νευρώσεων. Ως αποτέλεσμα, τα πάνελ πρέπει να είναι τεντωμένα για να ταιριάζουν στην  θέση τους.

At these points you will see that the panels of a wing or a fuselage are stretched, just like a guitar string. The result is a much stronger construction than we would have if the panels were not well stretched.

The distortion, then, is visible at these points, in the middle of almost every panel placed. Let's say here that the phenomenon of distortion is not found in all panels, or on the entire surface of the aircraft. You will notice that, for example, the wings of the wings do not show this deformation, but only the large surfaces at the points of overlap of the skeleton.

It is easier to understand the points where the forces and the distortions are exercised. That is exactly where our attention should be focused, in order to have a realistic result. Observe the wings of the B-17 in the photo.

At this point it is important to understand that the wing (or any other structural section) supports the forces (During takeoff, or during landings) You cause the wings to bend, it is an example of forces acting on the structure of the wing.

Lifting loads tend to bend the wing upwards. This causes compression of the upper wings of the wing and traction in the lower frames. Since the compressive strength of the aluminum cover (panel) is minimal, it can bend outwards, making a bubble in the area within each line (And again, this does not necessarily fit all planes)

    Another point of observation is the fuselage in the old fighters. For example, those operated by aircraft carriers. Because of the violent approaches and the bounces.

The fuselage tended to work like a vertical spring. As a result, we could see a distortion.

There are cases where the phenomenon is as intense as in the F6F of the image


.Because there is a different structure in each frame, from plane to plane, we see that the lighter aircraft (eg Kawasaki Ki61) due to a smaller and lighter frame, strongly present the phenomenon of distortion. For a different reason, very heavy planes have a much more severe deformation

 Although the B-25 is almost new in photography, it has visible distortion along the fuselage due to its weight. But look and compare with the B-17 which has a different structure in the design of its frame and different forks for the joints, than the B-25.

  As I mentioned at the beginning. The alleged distortion of the panel is the result of the forces exerted on the entire skeleton. Both in the old and in the modern flying means.

As we can see the Sikorsky UH-60A Black Hawk along its entire length.

As in the F-4E Phantom II. It is less intense but there is
A) What I would suggest is to have a variety of photos of the plane you want to make.

B) A plan of the skeleton, so that you have a good picture of its structure.

C) A three-sided plan with forks to be exact. You will benefit from good quality aircraft designs.

These designs will help you find out where the lines of the rivets are, beyond the lines of the panels. There are several options (Kagero, Koku-fan, Model Art, Design exactly like the F6F-) and you can search for them on the internet.