Whats the deal with Soviet Wing design?

[Wurger]

Here is a couple of images of the the rear interior I found via the net. Not of too good quality but it can be noticed that there were two stringers at least. These two running back can be seen at the top of the compartment. According to the diagram there these run up to the tail whiil section. The diagram dosn't show it clearly but there were two more running at the floor level, also the floor there was the reinforcement of the section too. All of the stringers were becoming thinner going farther back what is a correct way of getting tappered stringers for the proper structural strength. The side "longerons" were a kind of stringers in fact that made the structural strength of the tail section with a couple of additional stiffeners and longerons. So it seems that the diagram posted by Koopernic is a little bit inaccurate with the riveting layout.

 

[Juha]

Very interesting photos, thanks a lot, Wurger!
I'd say that there are the normal 4 longerons that formed the box girder to assure longitural stiffness of the fuselage by taking at least part of the bending loads. The basic structure that had been used since the first planes, of course in semi-monocoque the other part of the strength comes from the external skin. But practically no stringers as Koopernic said, so the fuselage skin seems to took greater part of the loads than usual at that time.

 

[Wurger]

And here a couple of diagrams I found via the net additionally.

The Pe-2 ...

The Pe-3...

 

[FLYBOYJ]

Thanks for the pics Wurger...

Juha started to mention the one thing that everyone is missing here...

With all this talk about lack of stringers vs. longerons, has anyone considered the thickness of skin, and the thickness and construction of the longerons? To really determine if this design was "weak' one would have to determine the alloys used in construction, and a stress analysis to determine how strong this really is.

 

[Elmas]

Stringers are needed to prevent buckling: with a thicker aluminium sheet less stringers are needed, and viceversa.

The same in a wing D-box, were stresses are due not only to bending but also to torsion, less important in a fuselage.

Exact calculation, before computers, was not an easy task, as all the theories about bending and stretching of plates were in those days quite recent, as they went out about 1920. Not that today, even with computers, calculation can be a kid's play.

Modellers probably will find this site interesting:

Antrvm Ratvs - Reproducing stressed skin effect in aircraft models

 

[FLYBOYJ]

Stringers are needed to prevent buckling: with a thicker aluminium sheet less stringers are needed, and viceversa.View attachment 303474

The same in a wing D-box, were stresses are due not only to bending but also to torsion, less important in a fuselage. Exact calculation, before computers, was not an easy task, as all the theories about bending and stretching of plates were in those days quite recent, as they went out about 1920.
Not that today, even with computers, calculation can be a kid's play....

That's only part of it. You have to consider the alloying of the components which will determine strength and what kinds of loads they could actually take. You could have a thick skinned structure made from 2024-T3 skins held in place with 6 or 7 7075-T6 longerons and it may have the same structural properties as a thinner skinned structure with thinner longerons and a series of stringers made from 2024 T-6. Mind you this is only an examples that there are dozens of considerations that could effect this.

 

[Elmas]

That's only part of it. You have to consider the alloying of the components which will determine strength and what kinds of loads they could actually take. You could have a thick skinned structure made from 2024-T3 skins held in place with 6 or 7 7075-T6 longerons and it may have the same structural properties as a thinner skinned structure with thinner longerons and a series of stringers made from 2024 T-6. Mind you this is only an examples that there are dozens of considerations that could effect this.

Certainly. But, if the plates are "thin", buckling can arise well before yeld strenght is reached, so using a material with a superior yeld strenght, if the structure is not very carefully studied and tested, is irrelevant.
It is the "mix" of plate thickness, number and size of stringers and yeld strenght of materials that make a rigid and light structure or not,
and this is why some airplanes are "hawks" and some others "turkeys"..... to design an airplane structure must be considered a sort of an "art".

 

[FLYBOYJ]

Certainly. But, if the plates are "thin", buckling arises well before yeld strenght is reached, so using a material with a superior yeld strenght, if the structure is not very carefully studied and tested, is irrelevant.
It is the "mix" of plate thickness, number and size of stringers and yeld strenght of materials that make a rigid and light structure or not,
and this is why some airplanes are "hawks" and some others "turkeys"..... to design an airplane structure must be considered a sort of an "art".

Exactly!

- so it's silly to try to determine the strength or durability of an aircraft just by visually observing how many rivet rows it has!

 

[GrauGeist]

Exactly!

- so it's silly to try to determine the strength or durability of an aircraft just by visually observing how many rivet rows it has!

Also considering that there's virtually no mention of structural failure under severe flight conditions and the Pe-2's max. T/O weight was rated well over 18,000 pounds (amplified by less than desirable airfields), it would seem the tail's construction was sturdy enough.

 

[Wurger]

I haven't found the exactly thickness of the covering plates so far. But russian sources say that it was a little bit more than the standard one used for a such structure. And it was enough fully to keep the tail's construction very sturdy.

 

[Koopernic]

in regards to the use of stretch presses in Spitfire Production at Clastle Bromwhich.
https://www.flightglobal.com/FlightPDFArchive/1941/1941 - 0847.PDF

Lord Nuffield, (William Morris), the genius that set up this factory to run using automotive style mass production deserves credit rather than the shoddy treatment he received at the hand of Beaverbrook. Setting up mass production is a difficult matter.

 

[FLYBOYJ]

in regards to the use of stretch presses in Spitfire Production at Clastle Bromwhich.


Lord Nuffield, (William Morris), the genius that set up this factory to run using automotive style mas production deserves credit rather than the shoddy treatment he received at the hand of Beaverbrook.
Setting up mass production is a difficult matter.

What is being shown there are presses that more form than stretch, although there is stretching involved. That's usually done with annealed aluminum (2024-0 or back in ww2 24-0). The forming and stretching would work harden the component depending on the "amount of forming and stretching". There many be post forming heat treating involved depending on the component and what type of loads it may face. This is a fabrication process of individual components and not reflective in the ease or difficulty of the actual assembly of a major sub structure such as a wing.

 

[Balljoint]

Thanks for the pics Wurger...

Juha started to mention the one thing that everyone is missing here...

With all this talk about lack of stringers vs. longerons, has anyone considered the thickness of skin, and the thickness and construction of the longerons? To really determine if this design was "weak' one would have to determine the alloys used in construction, and a stress analysis to determine how strong this really is.

I've thought of stringers as working in tension and not much in compression, while longerons have enough "depth" to provide compression (bending) strength. Similarly, a thin stressed skin is primarily a tension member while a thicker skin has significant compressive strength.

 

[FLYBOYJ]

I've thought of stringers as working in tension and not much in compression, while longerons have enough "depth" to provide compression (bending) strength. Similarly, a thin stressed skin is primarily a tension member while a thicker skin has significant compressive strength.

Again this will be dependent on what the material you're working with as well. 7075 aluminum is strong but not flexible, it could probably take shear loads good but not bending. 2024 T-3 will take bending but depending on application could eventually work harden and fatigue. In a high heat area one could use stainless steel but now you're looking at a weight factor as well as possible dissimilar metal issues (corrosion). It's all a balancing act.

 

[pbehn]

Certainly. But, if the plates are "thin", buckling can arise well before yeld strenght is reached, so using a material with a superior yeld strenght, if the structure is not very carefully studied and tested, is irrelevant.
It is the "mix" of plate thickness, number and size of stringers and yeld strenght of materials that make a rigid and light structure or not,
and this is why some airplanes are "hawks" and some others "turkeys"..... to design an airplane structure must be considered a sort of an "art".

Guys, be careful when comparing properties, the top of a wing buckles when under compression. Compressive yield is similar to tensile yield but not exactly the same. Resistance to torsional loads is related to yield strength but is not exactly the same.

 

[Balljoint]

Again this will be dependent on what the material you're working with as well. 7075 aluminum is strong but not flexible, it could probably take shear loads good but not bending. 2024 T-3 will take bending but depending on application could eventually work harden and fatigue. In a high heat area one could use stainless steel but now you're looking at a weight factor as well as possible dissimilar metal issues (corrosion). It's all a balancing act.

Maybe beam loading would be a better term than bending since the material doesn't have to bend to take such loading. If it's in tension on the outer loading and tension at the inner loadingit's loaded "in bending" even though the material is tough rather than compliant,

 

[FLYBOYJ]

Maybe beam loading would be a better term than bending since the material doesn't have to bend to take such loading. If it's in tension on the outer loading and tension at the inner loadingit's loaded "in bending" even though the material is tough rather than compliant,

Again you're going to have to be specific on where you're talking about. I'm not a structural engineer but have done structural repairs based on data developed by an engineer. In laymen's term I've always dealt with engineers dealing with bending, twisting, shear and compression loads.

 

[parsifal]

Interesting discussion guys. Id really like to know about the Zeke wing. ive read it was exceptionally lightly constructed, with about half the fasteners of a spitfire, made of a new alloy material, with something called a single spar construction (whatever the hell that is) that made its fabrication difficult. the Zeke was generally regarded as a difficult aircraft to construct. I was hoping someone like greg might illuminate me........

 

[tyrodtom]

I'm certainly not Greg, but i'll attempt to tackle it.

I've seen it called a one piece wing spar, but that doesn't mean it's a one spar wing. There's plenty of cutaways online showing two distinct wings spars front and rear, even the rivet pattern on the wing points them out.
But the wing spar going under the fuselage is continuous, and integrates with the fuselage so completely, that once constructed by the factory could not easily be taken apart without almost completely disassembling the whole central structure of the aircraft. The fuselage came apart behind and in front of the cockpit, and the wings appear to have a joint about half span. No wing strong points bolted to fuselage strong points, it was all one riveted piece, and lighter because of that.

It's construction caused problems when the Zero damaged in the Dutch Harbor attack was found at Attu island. The crew sent to recover it couldn't disassemble it the way most aircraft they were probably used to.

 

[GregP]

Hi Parsifal,

Our Zero is intact and complete ... but undergoing overhaul. If you are interested I can get some pics, but there is no access to the wing interior.

Perhaps the attachment might help you out.

- Greg