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Makes sense for strength I guess, but the skin of an aircraft does not generally contribute to the structural strength of an airframe, its just that, the spars and frame. So I have to think the disadvantage would outweigh any minor structural gain. But I am not an engineer. Just always puzzled me. And German engineers have a deservedly great reputation as engineers or excellence so I am left having to assume it did add strength where they wanted it to.You'll notice they didn't do it on any of their even moderately fast aircraft. Because a lot more area is exposed for higher surface drag.
But a corrugated piece of metal is a great deal stronger than just a flat piece of metal of the same gauge.
I have noticed on some of the German Bombers, and transports, they apparently used a corrugated metal skin, even on lifting surfaces of the wings. My question is why? On first appearance it would appear to play havoc with generating significantly more drag> Just wondered if perhaps there really was some benefit?
You are exactly correct based on what I have been reading since I posted. It turned out once I figured out how to get Google to show what I meant as opposed to what I asked, there was a lot of information on the why of it. Basically it was a strengthening measure and Junkers had originally intended a smooth layer on the outside however weight became a consideration and they removed it.Keep in mind, the Ju52 design was on the drawing boards in the late 1920's, a mere 10 years after WW1, during a time of rapid innovations in aviation. The corrugated skin was adopted from the success of earlier Junkers designs. It would be unfair to apply hindsight based on knowledge that's clear to us now but that was still being learned at the time.
Very nice and informative, it jives with what I have since found out as well. When you think in the context of the time, it was during the transition from fabric to metals and of course their were issues to overcome. Seems plain to understand in hindsight it just sort of caught me off guard when I was first looking at it. One of those things I had always wondered about but never put the effort in to figure it out until returning to modelling.The use of corrugated metal was fundamentally an engineering calculation problem and as the theory didn't exist they used corrugated metal to prevent skin buckling.
The Germans invented the stressed skin all metal aircraft, Junkers flew an experimental corrugated skin canard in 1912 and made a series of fighters and ground attack aircraft in WW1. Shortly after WW1, as early as 1919, flat stressed skin aircraft by companies such as Dornier (flying boats) and Rohrbach started to appear.
The reason given in "Aeronautical Research In Germany" is that when they started trying to build stressed skin aircraft (where the skin takes load not just provides covering) there was no theory or method to calculate the stresses and loads. They had two choices:
1 Use Flat Sheet and use diagonal bracing rods to stop buckling
2 Use corrugated sheet metal.
From 1929, probably earlier they had 'wagner web theory' described in patent 547624 and going back to 1921 something called Bredt Torsion Tube theory which seems to have only been used on gliders with composite wings.
When you look at the Ju 52 the corrugations clearly avoided the need for many stringers or ribs in the aircraft. This actually kept the inside of the wink quite 'clean' and fuel tanks fitted nicely.
Notice also that many modern aircraft use a corrugated skin and merely place a sheet skin over it.
When Erhardt Milch took over the running of the Luftwaffe and its procurement he desperately needed a lot of aircraft that would be quick to produce (to train crews, get numbers up) so the Ju 52 was converted into a crude bomber. (Rather than wait for Ju 86 and He 111) It was already out of date but it could be produced relatively quickly because it didn't require a lot of tooling. This ensured truly massive production of the aircraft.
This is why the Ju 52 ended up being the main transport of the Luftwaffe.
Junkers tried to replace the Ju 52 with the Ju 252 which was initially a smooth skin pressurised trimotor about the same size as the ju 52. Lufthansa then wanted it increased in size and then the Luftwaffe wanted a trappoklappe loading ramp. These delays meant few of the excellent aircraft were produced since the resource to tool up went elsewhere.
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I also read the Ford Trimotor was also corrugated and a quick pic look confirmed it.The Dc3 center wing section has a corrugated skin. It's even mounted in compression. Would like to have seen a factory jig used for perfoming such a feat
Makes sense for strength I guess, but the skin of an aircraft does not generally contribute to the structural strength of an airframe, its just that, the spars and frame.
Well that let my ignorance show! Oh well live and learn. Never really understood that but I do now. Thanks for the info, also did some more reading and turns out even the Wright brothers used fabric as a portion of the stiffening of their wing. So apparently the skin of an aircraft has almost always contributed, at least a little, to the strength of an airframe.Absolutely 100% wrong.
Monocoque (also known as Stressed Skin) construction (the most basic concept behind all metal aircraft and some wooden aircraft) is all about using the skin as a primary structural member.
For a good basic intro on the subject read TM 1-410 Airplane Structures which is readily available on the net and probably even on this forum. If you cannot find it let me know and I will post it.
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Most modern aircraft go one stage further and incorporate integral fuel tanks.
In those the fuel tanks are nothing more than the skin and ribs with a small amount of sealing and the minimum necessary inspection panels.
Happy reading
Mi