Origins of Junkers' aircraft corrugated skin?

[Silencer1]

Hello!

I'm trying to figure out, how Junkers company starts to introduce corrugated metal sheets as a skin for their combat aircraft.
I knew, that one of the early aircraft designs, participated by Hugo Junkers was a 'Reissner Ente" with very large sheets of corrugated metal, used for surfaces.
Then, during WW1, Junkers design a and build aircraft with smooth (even a metal) skin. Suddenly, corrugated sheets have been successfully incorporated in the aircraft structure.

I wonder, from where the idea of corrugated sheets come? Only one subject, similar to it is roof plating... Although, it has been definitely "rougher" by "waves" dimensions.

For me the introduction of corrugated skin in aviation is similar to the "big bang". Kindly appreciates all suggestions, based on reliable sources

 

[Abraham Gubler]

Corrugations or ribs were being fitted to classical armour 2,000-3,000 years ago to provide additional strength. Nature has evolved several several examples of corrugation strengthening many millions of years before.

 

[Silencer1]

Thnks Abraham Gubler!

Your answer is a good, but I'm looking for more close (by time) influences on usage a corrugated plating for aircraft' surfaces.
Personally, I think, that Herr Junkers seen something much modern, then warriors' or animals' armor before he decide too experiment with corrugated, rather then smooth skin.

 

[Hood]

Corrugated plating was in use at the time in building construction, for example Major Peter Norman Nissen began experimenting with the Nissen Hut in 1916, and I'm sure the Germans also used it for similar purposes. Junkers had been experimenting with steel and alloys and the strength afforded by corrugation would not have passed them by, in fact it might have been a result of trying to strengthen weak alloy sheets. When the D.1 was designed and built Germany was suffering from grave material shortages so alloy quality may have been affected.

 

[cluttonfred]

Reissner Ente (canard, duck) of 1912 already had corrugated metal wings built by Junkers. A gentleman named Cochrane was producing model and later full-size aircraft propellers with corrugated aluminum blades as early as 1909. This from searching for the word "corrugated" in the Flight Global archives from 1909 to 1912. See https://www.flightglobal.com/pdfarchive/

 

[Silencer1]

Thank you, cluttonfred!

Your tip is great - I read the result of searches on Flightglobal and now more aware on the subjects of interest from 1910s!

Curiously, "corrugated" relates to sheets of metal, used in the structure of the water radiators and buildings.
Perhaps, Junkers, as owner of company, produced water-cooling home devices was new about the corrugated metal sheets in it's production?
I'm also found, that first attempt to incorporate corrugated sheets in the wing structure have been based on the internal usage of them, with a smooth skin as a cover.
How many steps aviation were made!

 

[klaud3]

Hi Silencer -- I know the explanation behind the corrugated skin of PZL constructions (e.g. wings of all Pulawski fighters), I guess this may have sth to do with Junkers.
The point is in these years (1920s) it was impossible to calculate the joint behavior of the frame and the skin of the construction when loaded. So from the engineering point of view, the frame was calculated to take 100% of loads and the first metal covers were precisely covers, it was assumed that they don't take loads, pretty much like fabric (but they did not rot, like fabric). But -- any metal is much less elastic than fabric, so very thin (0.3-0.4 mm) sheets had tendency to broke or buckle in flight. Sołtyk even mentions in one book that a few sheets of dural had to be replaced after each landing of PZL-4! So corrugated skin was introduced to make metal sheets behave pretty much like fabric -- i.e. to deform with the load-carrying truss without damage from shear tensions. True load-carrying skins that emerged later had to be much thicker and they required much more engineering practice to calculate. The above is also the reason why e.g. the common British construction practice in 1920s/1st half of 1930s was metal truss + fabric cover, they didn't play with metal skins until Blenhiem (?).
So it might be that the initial smooth-skin constructions of Junkers were built to optimize drag but were sub-optimal in operations -- and only when more experience was collected post-war, Junkers fully switched to corrugated skin for the next 10-15 years.

 

[Silencer1]

Hi klaud3!

Thank you for suggestions about aircraft structure load calculations, as well for the story of PZL fighters.
I found a very informative page about Hugo Junkers and his activities in the various fields.
www.junkers.de - not surprise

Some of pages already have English version, some requires translation from German, which Google translate with some strange words.
Anyway, looks that Junkers and his colleges made a lot of attempts to incorporate metal (initially - steel, then - duraluminium) structure to the aircraft.
Moreover, looks like J.1 experimental monoplane has been covered by smooth skin over corrugated one!
Some pictures on this site demonstrate something similar to that. Moreover, corrugation waves initially goes transversally to air stream, and only later became a laterally aligned to it.

http://www.junkers.de/junkers-j1-the-worlds-first-all-metal-aircraft

So, if the question, from where the idea to use thin (0.1-0.2 mm) comes is still open. Perhaps, it could be connected to other Junkers businesses of previous time - piston engines and gas heaters?

 

[JohnR]

How did the corrugation effect the aerodynamics of the aircraft, did it increase drag compared to a more conventional smooth skinned aircraft?

Regards.

 

[Silencer1]

Hi JohnR!

In 1910-20s there were a lot of things on aircraft, that produce drag, despite the corrugated skin.
Did Junkers' company knew about the drag decreasing by introduction of smooth skin?
In my humble opinion - yes, although they decided to build their planes, keeping in mind all pros and contras.

In USSR in 1933, 4-engined TB-3 bomber (totally covered by corrugated aluminium) has been tested to figure out the effect of improving aerodynamic:
Step by step most of the common drag-inducing details have been removed or changed: bomb racks removed; then turrets; then holes and hatches covered; main landing gear supplied with fairings; all small details raises from skin have been removed. After all that it's speed and range increases only at 4.5%. Previously it's max. speed was 211 km/h.

Shavrov, soviet aviation historian wrote, that after that experiments it's obvious: for large and relatively slow aircraft benefits of introducing smooth skin instead of corrugated was very small, and most important was smooth covering of wing leading edge and upper surface up to aft spar.

Another Soviet aircraft, long-rang record-setter ANT-25 has been initially build with corrugated skin of wing. Tests shows that range and speed were much lower, then expected. So, wing has been covered by fabric (sewed on the corrugation via small holes) and painted by varnish. With other aerodynamical improvements there measures allow ANT-25 to made two successful flights from Moscow to North America via North Pole.

And SR-71 also has parts of wing with corrugation!

 

[shedofdread]

Chordwise corrugations near the trailing edge can increase CLmax. The mixing of the flows can help invigorate the flow on the suction side of the aerofoil. Sometimes seen in motorsport.

It's possible that in some circumstances, the corrugations could also act against spanwise flow.

One suspects the real reason is to reduce the rib spacing by making the skins stiffer.

 

[Silencer1]

Hi shedofdread!

Could you be so kind to add some illustration, regarding current usage of corrugated skin in motorsport?
Never previously seen them before.

I guess, that idea of using corrugated skin by Junkers was much complex, then just decrease number of ribs. Entire aircraft (like WW1 types or F13 airliners) have been designed with tubular internal structure and covered with corrugated sheets. So, it was integration of several ideas and technologies in one design. With the increasing of cruising speed such type of skin became more and more obsolete: increased resistance, limitations in production, increased loads on all aircraft parts (with the smaller thickness of them).

Anyway, corrugated skin has been important part of aircraft technology after WW1 and allows the to develop effective airliners and airlines.

I'm still interested, if someone of form members could tell me more about the initial topic' subject