Whats the deal with Soviet Wing design?

[GregP]

About the Central Louisiana Electric Company ... I was referring to the always reliable Wikipeida: https://en.wikipedia.org/wiki/CLECO fiasco.

Don't tell me they are WRONG? What? Again?

Oh the humanity of it ... it's like watching the Hindenberg crash all over again ... only it keeps happening over and over and ... you get the idea. What's a poor criminal supposed to do with information this good?

About the stretcher, that's VERY interesting to hear. I have several references that talk about Spitfire manufacturing in general, but ... and here's the catch ... they never mention Castle Bromwich specifically when discussing manufacturing, only that Spitifires were built at the various locations, of which Castle Bromwhich was one. So I knew Castle Bromwich made Spitfires, but not that they had and used a stretcher, especially on Spitfire wings.

It would make forming the leading edge a lot easier, to be sure. I'm not so sure it would make fabrication any easier since you still have to rivet everything, either on a jig or predrilled ... and they didn't have any CNC mill-drills. So, I am again assuming the wings were jigged and had a very specific fabrication sequence.

 

[FLYBOYJ]

So, I am again assuming the wings were jigged and had a very specific fabrication sequence.

Exactly!

 

[gumbyk]

Exactly!

Which is why it takes so much longer to build on now - a lot of that sequencing has been lost.

150 tonne press - possibly used to put the bend in the main spar upper and lower caps. I know that it is a pretty precise piece of work to do, and requires some pretty heavy machinery to do.

 

[GregP]

Hi Joe,

We're in the middle of restoring a North American O-47 wing right now and must replace some skins. The problems is ... the assembly sequence has been lost and we're having a very difficult time deciding how to sequence the work so we can get solid rivets in all the holes. It wouldn't be so bad is we were completely disassembling the wings, but we need to replace a skin roughly in the center of the wing ... and no matter which way you go ... you lose access at some point unless ALL the skins are removed. It's gonna' be interesting to see how it finally works out. I think complete disasembly is the only practical solution, but ... I'll wait for some of Steve Hinton's guys to weigh in with their thoughts before diving in without a wing jig. A few Cherry Maxes are better than a crooked wing ... maybe ... depends on how many would be required.

They built jigs for the F-86 right and left wings and slats ... I doubt they're too interested in building 2 more ...

 

[Koopernic]

Stretch forming was not unknown in the industry at the beginning of WW2. The 150 ton stretch press at Castle Browmwich is surely for sheet stock. The 20 or so cylindrical sized caps I believe are the hydraulic cylinder heads, probably for the clamping jaws to hold the sheet but possibly to raise the forming die.


The Me 109:
EzineArticles Submission - Submit Your Best Quality Original Articles For Massive Exposure, Ezine Publishers Get 25 Free Article Reprints

"The rear section of the fuselage (the section immediately behind the pilot' seat and extending to the front of the tail) was also unique. To explain, first visualise a stack of cups. The rear section or in German, the "Rumpf" is made up of parts that nestle together like a stack of cups. Each section including what would normally be the former or main structural part forming the shape is made of a single sheet of aluminium. Each section was formed on a stretch press with the former being created out of some clever folds to provide strength. To be precise every second section was formed on a stretch press. So, to visualise, keep every second cup and replace every alternate one with a sheet wrapped around the bottom of each cup - that is what the back end of the Bf 109 is like. It was innovative, strong and it greatly simplified production by removing a lot of fiddly framework."

Martin B-26 Marauder:
LiTOT: The Martin Marauder B-26

"The general production setup called for extensive use of spotwelding in secondary structure to eliminate, where possible, the more costly and time-consuming process of riveting. The stretch press, used by the automobile industry at the time of World War I to form fenders, was reintroduced to shape convex-curved pieces of aluminum skin, four times the average size in other aircraft. These large sheets of skin were employed in the fuselage and cowling to eliminate the multiplicity of stringers, rivets and other small detail parts normally associated with a fuselage of this size and length. Hundreds of castings, forgings and plastic parts were used to simplify mass production methods and eliminate the use of critical materials. Thus, the B-26 uses more castings, forgings and other miscellaneous parts adapted to intensive production methods, fewer rivets and detail parts, than any comparable airplane. Some of the new design elements in the Marauder follow:

WING ARRANGEMENT — It was decided to depart from the usual procedure of keeping wings integral from nacelle to nacelle by breaking the wing panels at the sides of the fuselage. This entailed the eventual design of the "dumbbell" lower spar chord forging to eliminate the use of heavy and costly fittings. Manufacture of this forging, the largest aluminum type ever made, required five sets of dies, each weighing more than two tons. Thus the wing and its engine and nacelle is an entire assembly. The center section was eliminated. Each wing is attached to the dural forgings at the wing roots, which serve as anchors for the attaching bolts. This arrangement facilitates assembly and replacement.

FUSELAGE — Its construction around a very strong keel made for almost perfect streamlining, and extra strength in crash landings. B-26 crews nearly, always walk away from a forced landing. This same keel was also excellent as an anchor for the external torpedo rack. There are no stringers, just skin and forming frames — five compartments in three major sections."

The Pe-2 also had this kind of structure but was regarded as a little weak.

The below is from "Martin B-26 Marauder" by Martyn Chorlton (Osprey Publishing)

The Marauder was designed and built from the outset to be a mass-
produced aircraft. Martin engineers confidently pre-empted a large order
being received from the USAAF as the world situation continued to
deteriorate. Martin also accurately predicted that the workforce required
to build the bomber would have no, or very little, experience of building
aircraft.

To help achieve the task of building a complex flying machine, the
B-26 was put together from approximately 650 minor sub-assemblies,
which were then joined to create 32 major sub-assemblies, and the final
aircraft. All of the Marauder's frames and stringers were pre-drilled in
their jigs and, once these components were delivered to the shop floor,
the task of riveting was made all the easier.

The Marauder's fuselage was covered in 63 pieces of metal skin, each
with its own compound curvature. Each piece of skin was produced on a
stretch press with a high degree of accuracy and consistency that made
the job of producing the B-26's streamlined fuselage quicker than be-
spoke panel beating.

Wing parts were also produced with the same degree of accuracy and
consistency thanks to Martin working closely with a milling machine
manufacturer to develop a machine with a travelling head and a 30ft bed.
Every part of the wing was produced to be foolproof, basically meaning
that the parts could only be fitted in one way — the correct one!

 

[GregP]

The Pe-2 was weak? Really?

The Petlyakov Pe-2 (Russian: Петляков Пе-2) was regarded as one of the best ground attack aircraft of the war and it was extremely successful in the roles of heavy fighter, reconnaissance and night fighter. It was one of the most important aircraft of World War II, similar in many respects to the British de Havilland Mosquito. Pe-2s were manufactured in greater numbers (11,427 built) during the war than any other twin-engined combat aircraft except for the German Junkers Ju 88 and British Vickers Wellington. The Pe-2 was fast, maneuverable and durable. Several Communist nations flew the type after the war, known by the NATO reporting name Buck. Six captured Pe-2s were also transferred from the Germans to the Finnish Air Force during the Continuation War, with the serial code PE- and the unofficial nickname Pekka-Eemeli.

 

[Juha]

Pe-2 wasn't so good as a ground attack version, the fighter version, Pe-3 was even worse and suffered heavy losses when forced to ground attack work in late 41. And IMHO it wasn't a great success as a heavy fighter. But Pe-2 series did good work as light bomber and recon machine. But as a bomber suffered from light bomb load.

 

[FLYBOYJ]

Hi Joe,

We're in the middle of restoring a North American O-47 wing right now and must replace some skins. The problems is ... the assembly sequence has been lost and we're having a very difficult time deciding how to sequence the work so we cna get solid rivets in all the holes. It wouldn't be so bad is we were completely disassembling teh wings, but we need to replace a skin roughly in the ecenter of the wing ... and no matter which way you go ... you lose access at some point unless ALL the skins are removed. It's gonna' be interesting to see how iot finally works out. I think complete disasembly is the only practical solution, but ... I'll wait for some of Steve Hinton's guys to weigh in with their thoughts before diving in without a wing jig. A few Cherry Maxes are better than a crooked wing ... maybe ... depends on how many would be required.

They built jigs for the F-86 right and left wings and slats ... I doubt they're too interested in building 2 more ...

I dealt with Westpac Aviation a few years ago - they moved here from SoCal when Rialto airport closed. they are in the final throws of restoring a P-38F (White 33) I believe flown by several aces. They had the same issue and had to make bucking bars to fit inside the wing corrugations. Westpac Restoration - P-38 White 33

 

[FLYBOYJ]

Stretch forming was not unknown in the industry at the beginning of WW2. The 150 ton stretch press at Castle Browmwich is surely for sheet stock. The 20 or so cylindrical sized caps I believe are the hydraulic cylinder heads, probably for the clamping jaws to hold the sheet but possibly to raise the forming die.

The Pe 2 also didn't have stringers in the fuselage and was regarded as rather week, possibly because it was made differently to Magruder's Marauder.

The Pe-2 was weak? Really?

The Petlyakov Pe-2 (Russian: Петляков Пе-2) was regarded as one of the best ground attack aircraft of the war and it was extremely successful in the roles of heavy fighter, reconnaissance and night fighter. It was one of the most important aircraft of World War II, similar in many respects to the British de Havilland Mosquito. Pe-2s were manufactured in greater numbers (11,427 built) during the war than any other twin-engined combat aircraft except for the German Junkers Ju 88 and British Vickers Wellington. The Pe-2 was fast, maneuverable and durable. Several Communist nations flew the type after the war, known by the NATO reporting name Buck. Six captured Pe-2s were also transferred from the Germans to the Finnish Air Force during the Continuation War, with the serial code PE- and the unofficial nickname Pekka-Eemeli.

Koopernic - why do you keep guessing?!?!?

 

[Juha]

To the original question. Not knowing but my guess is that it was a result of TsAGI research.

 

[Juha]

Hello Koopernic
thanks for the Spitfiresite link, many interesting photos there.

Juha

 

[Wurger]

The Pe 2 also didn't have stringers in the fuselage and was regarded as rather week, possibly because it was made differently to Magruder's Marauder.

So.. what kind of structure was the Pe-2 fuselage ?

 

[Juha]

Pe-2 was used also as dive-bomber, so it should not be too fragile.

 

[GregP]

Sure LOOKS like it has stringers:

Look at all the little stringer-type-thingies in the fuselage around the tailwheel area.

 

[Elmas]

What does it mean "fragile" by a techical point of view?
A6M was certainly not fragile structurally, but was extramely fragile in a combat environment, were it is possible to receive a shower of bullets...

 

[drgondog]

FUSELAGE — Its construction around a very strong keel made for almost perfect streamlining, and extra strength in crash landings. B-26 crews nearly, always walk away from a forced landing. This same keel was also excellent as an anchor for the external torpedo rack. There are no stringers, just skin and forming frames — five compartments in three major sections.[/I]"

The Pe 2 also didn't have stringers in the fuselage and was regarded as rather week, possibly because it was made differently to Magruder's Marauder.

I immediately wonder how applied loads to the empennage in all three axes were taken to withstand bending - A 'shell' without fore and aft longerons, to intersect with bulkheads and connect all with shear panels will not work - except in case of Mosquito type construction where the 'shell' acts a cylindrical Plate with inherent bending load absorption capability.

Stringers are nothing more or less than smaller (than Longerons) beams upon which thin sheet metal shear panels are riveted fore and aft, and vertically at the bulkheads.

 

[Juha]

What does it mean "fragile" by a techical point of view?
A6M was certainly not fragile structurally, but was extramely fragile in a combat environment, were it is possible to receive a shower of bullets...

I meant from structural viewpoint, the optimal pull-up for Pe-2 was 3G and there was a warning system if the pilot pulled over 4G. Not much for a fighter but not bad for a bomber which pe-2 was. It wasn't a Zero, it had some armour and inert gas could be pumped into the fuel cells. But sometimes they blew up when hit by MG 151/20 shells.

But Koopernic might well be right that there was no stringers, only the longerons. Difficult to say anything definite, I have only a handbook drawning of the front part of the fuselage and some photos of the cockpit and of the area front of the cockpit.

 

[Koopernic]

Sure LOOKS like it has stringers:

Look at all the little stringer-type-thingies in the fuselage around the tailwheel area.

The following link:
Pe-2 family by V.M.Petlyakov, A.M.Izakson, A.I.Putilov, V.M.Myasichev

"Fuselage (designed by A.I.Putilov) was close to monocoque of circular cross-section. Sparsely placed ribs (each 0.5m) supported thick (1.5 to 2.0mm) aluminum alloy skin without stringers, only windows, cockpit and turret openings had enforcing frame."

While I am very much inclined to believe your drawing (one can trust a draftsman more than an author) I have read of the claim that the Pe-2 lacked stringers several times and these drawings are after all often reconstructions for a magazine and not manufacturing general assembly drawings. Of course through the wonders of Google one can always verify incorrect information by putting in the search string to get what one wants.

Looking at some of the detail images in the above link I do notice a distinct lack of rivet lines over where there could be stringers on the mid rear section of fuselage. In other words there were stringers up to the trailing edge area, then most of thr stringers cut off, then near the tail section they restarted. This tends to conform the stringer free statement, A picture of the fuselage inside would clear things up here.

I admit the Pe-2 didn't have a weak structure, that comes from the Germans sources as they regarded it as vulnerable to canon fire as the structure could collapse during attack, as Elmass suggested. I would not regard this as a serious criticism given the immense destructive power of 4 canon armament that was showing up in the Fw 190A (and Typhoon/Tempest/Mosquito/Beuafighter) under which German aircraft or any aircraft would not survive long.

The Pe-2 rather conforms to the original abandoned German Zerstoerer concept which envisaged a 3 man crew. Petlokov along with Tupolev were both sent to a Soviet concentration camp (Gulag) for allegedly forming counter revolutionary groups. It took 4 days to break the men down to the point they signed confessions of all sorts. Petlokov was supposed to have sold the Pe-2 to the Germans who turned it into the Me 110, supposedly. Petlokov did have German contacts, he learned the art of aluminium aircraft construction at Junkers in the 1920's. He was the Soviet expert in this field.

 

[drgondog]

I'm inclined to agree - no stringers aft - all bending/torsion taken out by longerons, bulkheads and shear panels just aft of trailing edge of wing.

 

[Koopernic]

I immediately wonder how applied loads to the empennage in all three axes were taken to withstand bending - A 'shell' without fore and aft longerons, to intersect with bulkheads and connect all with shear panels will not work - except in case of Mosquito type construction where the 'shell' acts a cylindrical Plate with inherent bending load absorption capability.

Stringers are nothing more or less than smaller (than Longerons) beams upon which thin sheet metal shear panels are riveted fore and aft, and vertically at the bulkheads.

There is a subtle difference between the longeron and stringer which may have escaped some authors. The following is from Wikipedia, it does cite an engineering textbook.

"Sometimes the terms "longeron" and "stringer" are used interchangeably. Historically, though, there is a subtle difference between the two terms. If the longitudinal members in a fuselage are few in number and run all along the fuselage length (usually 4 to 8.), then they are called "longerons". The longeron system also requires that the fuselage frames be closely spaced (about every 4 to 6 in or 10 to 15 cm). If the longitudinal members are numerous (usually 50 to 100) and are placed just between two formers/frames, then they are called "stringers". In the stringer system the longitudinal members are smaller and the frames are spaced farther apart (about 15 to 20 in or 38 to 51 cm). Generally, longerons are of larger cross-section when compared to stringers. On large modern aircraft the stringer system is more common because it is more weight-efficient, despite being more complex to construct and analyze. Some aircraft use a combination of both stringers and longerons.[2]"

My previous post #45 added the fact that all of the B-26 63 fuselage panels were stretch pressed. The design was stringer free but it supposedly had a "keel" from which the torpedo could be hung. I'm sure it had longerons though the source says there were forming frames. The B-26 was known for strength.