Impregnated plywood

[tallguy]

Anyone know any sources discussing "shpon" the Soviet impregnated plywood and American Duraloid and Duramold?

 

[fortrena]

You may wish to consider looking at https://www.springer.com/gp/book/9780792360377

More specifically the chapter entitled
Wooden Airplanes in World War II: National Comparisons and Symbolic Culture

Pages 183-205

Schatzberg, Eric

 

[riggerrob]

We have been discussing Duramold over on www.homebuiltairplanes.com. "What was the first use of composites in general aviation?
Timm, Fairchild, etc. flew Duramold airplanes during the 1930s.
A few World War 2 airplanes used Duramold, most notably the deHavilland Mosquito. A thousand Avro Anson Mark V - with Vidal/Weldwood fuselages - were built in Canada during WW2.
Postwar, Duramold continued to be used on the DH Vampire jet fighter and Hughes Spruce Goose.

 

[fortrena]

If I may, the Mosquito and Vampire seemingly used de Havilland’s tried and tested plywood-balsa-plywood sandwich for their fuselage, an approach tested on the 1930s Albatross airliner, rather than Duramold per se.

The following may also be of interest... https://www.secretprojects.co.uk/th...ild-f-46-duramold-aircraft.17000/#post-387470

 

[sienar]

The delta technique was similar to duramold and the like but used a different class of resins. It required curing under high temp and pressure - I have the exact numbers somewhere. There were also issues with workers getting sick until they developed better handling procedures. As far as strength goes it was very comparable to the aluminum alloys that the soviets could mass produce in the 30s, but inferior to dural.

 

[Apophenia]

We have been discussing Duramold over on www.homebuiltairplanes.com. "What was the first use of composites in general aviation?
Timm, Fairchild, etc. flew Duramold airplanes during the 1930s.
A few World War 2 airplanes used Duramold, most notably the deHavilland Mosquito. A thousand Avro Anson Mark V - with Duramold fuselages - were built in Canada during WW2.
Postwar, Duramold continued to be used on the DH Vampire jet fighter and Hughes Spruce Goose.

As noted before, the Duramold process was more-or-less specific to Fairchild. Duramold's inventor, Virginius E Clark, went to Hughes where he tweaked the Duramold techniques for the Hughes H-4 Hercules. The Duramold process used heat-activated phenol formaldehyde (PF) resin to bond veneers (birch or spruce) with pressure moulds to do the shaping.

Timm used its own Aeromold process. Unlike Duromold, the Aeromold process used a cold-setting PF resin on die-stamped spruce veneer parts.

The Avro Anson V and VI used the unrelated Vidal-Weldwood Process - hence the prototype conversion being referred to as the 'Vidal Anson'. (The latter was a Mk.I conversion (RCAF 6013, ex-N9943) with a moulded fuselage provided by Gene Vidal's Aircraft Research Corp.) Like Duramold, the Vidal-Weldwood Process used heat-activated PF resins but differed in moulding both skins and stiffeners in one process.

The de Havilland process involved a rather different plywood-balsa-plywood sandwich moulded by strapping flexible steel bands over the male mould to created the final shape.

 

[fortrena]

Delta wood is a composite material obtained by “plasticizing” wood veneer (usually birch) by impregnating it with phenol- or cresol-formaldehyde resin, followed by molding under high temperature and pressure.

Although significantly heavier than ordinary wood, delta wood has more twice the tensile strength of that material. Allegedly stronger than some aluminum alloys, it was not as strong as heat treated and artificially aged duralumin. In addition, delta wood is practically non-flammable, all but impervious to fungal attack and long lasting even in unfavorable conditions.

By the second half of the 1930s, wood was seen to have little future as a material for high performance aircraft. High-strength aluminum-based alloys were the preferred materials.

Production of aluminum and aluminum alloys in the USSR was not keeping up with the rapidly growing needs of aviation, however, which meant that many if not most military aircraft still had an all-wood or mixed wood-metal structure. The need to modernize and beef up Soviet military aviation only made things worse. Indeed, as the volume of production increased, problems began even with the supply of high-quality timber, for wing spars for example. The USSR may have been forced to import increasing quantities of this high quality wood. In any event, had supplies of aluminum been found, most aircraft factories had little if any experience with all-metal structures. Topping that off, the machine tools required to mass produce these all-metal aircraft were lacking and would need to be imported, an uncertain prospect in a world where every major power was rearming as best it could.

The difficulties confronting the Soviet aircraft industry spurred experimental work on the use of various types of refined or improved wood which, while significantly superior to ordinary wood, could be put to use using the equipment and tooling available.

Delta wood was seemingly developed around 1935 by a Soviet aeronautical engineer named Leonty Iovich Ryzhkov, when he was working at the Kuntsevo propeller factory, near Moscow. By 1940, it had been studied in detail at the All-Union Institute of Aviation Materials. Production techniques were subsequently improved by specialists at the Karbolit plant of Leningrad.

The Lavochkin LaGG-3, La-5 and La-7 included a large amount of delta wood. Although deficient in performance, the LaGg-3 was one tough machine.

During the Soviet era, some delta wood was used in the aerospace industry, to make the tiny fins of the R-7 ballistic missiles and spacecraft launchers and the tail rotors of some Mil helicopters for example. Delta wood was also used to make the insulators mounted on Soviet era trolleybuses, insulators which proved both reliable and long lasting.

Nowadays, some sort of delta wood is apparently used in Russia to make furniture.

 

[fortrena]

Vidal-wise, the following may be of interest.

Intrigued by the possibility of replacing the fabric-covered steel tube fuselage of the Anson by another, made of molded wood, the Canadian Department of Munitions and Supply asked, in September 1940, a small American company, Aircraft Research, later known as Vidal, to manufacture two test fuselages. The small Canadian company which had made the introductions, Vancouver Sales & Appraisals, was quickly squeezed out of the deal.

A modified Anson flew around July 1941. As the new fuselage had a lot to offer (aerodynamics, comfort, etc.), the Department of Munitions and Supply ordered a hundred additional fuselages from the United States. In 1942, Federal Aircraft, a crown corporation, formed to supervise Canada's Anson production program, prepared the plans for two improved versions of the Anson, one intended for the training of navigators and ordered in 2,300 examples, and the other intended for the training of gunners and ordered in 500 examples. An Anson modified to reproduce the first version flew in January 1943. The prototype of the second version followed in September.

The weapons system of this latter aircraft leaving to be desired, the Canadian government canceled its order but signed other contracts with the affected companies, namely Canadian Car & Foundry (CCF), MacDonald Brothers Aircraft, a subsidiary of MacDonald Brothers Sheet Metal & Roofing, and Cockshutt Molded Aircraft, the Canadian manufacturer of fuselages and a subsidiary of Cockshutt Plow Company, a major manufacturer of agricultural equipment. This respite was short-lived. As Allied successes multiplied on all fronts, the Canadian government reduced the scale of its aircrew training effort as early as 1944. The Royal Canadian Air Force ultimately received only 1,050 or so of the 2,800 aircraft ordered, i.e. 300 or so delivered by CCF and 750 or so by MacDonald Brothers Aircraft

 

[riggerrob]

A major advantage of DeHavilland's molded wood airframes was less parasitic drag compared with 1940-vintage aluminum construction methods. Yes, jet-era aluminum airframes had butt-joints and flush rivets, buts such methods were more labor-intensive and tool-intensive.

To this day, composites laid up in female molds (e.g. Cirrus and Katana) still have weight and drag advantages over sheet metal.

 

[sferrin]

To this day, composites laid up in female molds (e.g. Cirrus and Katana) still have weight and drag advantages over sheet metal.

You still have to use flush fasteners though.

 

[riggerrob]

To this day, composites laid up in female molds (e.g. Cirrus and Katana) still have weight and drag advantages over sheet metal.

You still have to use flush fasteners though.

Yes, but composites require far fewer fasteners ... down from thousands of rivets.
They only need a few bolts to attach larger components (e.g wings to fuselage) and many of those joints are better served by bolts connecting spars to bulkheads INSIDE the fuselage.

 

[sferrin]

To this day, composites laid up in female molds (e.g. Cirrus and Katana) still have weight and drag advantages over sheet metal.

You still have to use flush fasteners though.

Yes, but composites require far fewer fasteners ... down from thousands of rivets.
They only need a few bolts to attach larger components (e.g wings to fuselage) and many of those joints are better served by bolt connecting spars to bulkheads INSIDE the fuselage.

No lie there.

 

[Apophenia]

You asked specifically about Duramold and Duraloid. Those two terms get used interchangeably but shouldn't be - they have different origins. A lot of the confusion dates back to widespread use of the original synthetic phenol formaldehyde (PF) - Bakelite. In some cases, attempts were being made to get around Leo Baekland's patents. In other cases, 'bakelite' is being used as a generic for synthetic resins rather than the specific synthetic phenol trademarked by the Bakelite Corporation.

There were heaps of Bakelite-inspired phenolic materials developed in the '20s and '30s - Textolite (cloth-based), Lamacoid (or Lamicoid phenol sheet), Dilecto (paper, fabric, asbestos) Micarta, etc. [1] Most of these never got beyond being used for electrical components, insulated washers, etc.

Both Duramold and Duraloid processes employed pressure moulds and thermo-setting PF resins. In the case of Fairchild's Duramold process, the formula of that resin had been tweaked by VE Clark. The Duraloid process has been described as Bakelite-bonded plywood structure. Developer Robert Nebesar patented his shape-forming process but the resin was Baekland's Bakelite. One difference was that formed Duraloid structures were covered in doped fabric which in turn was puttied with a thin coat of saw dust mixed into Bakelite resin.

Were this a race, it wasa roughly tie - the Duramold Fairchild F-46 flew in May 1937, the Duraloid Bennett BTC-1 in October 1937 (I think?). Were it a competition, Fairchild clearly won. Duramold was used in a number of WW2 trainers. Duraloid ended up being used to make knitting needles ... The Duramold Beechcraft AT-10 would beat out the BTC-1 for a USAAC contract. In a final irony, Bennett's successor firm - Globe - would license-built 600 AT-10 Wichitas in Texas during the war.

Confusion continues. Plenty of online sources insist that Globe's Swift was to be built out of Duramold. In Vintage Airplane Vol 21, No 7, July 1993, page 16, even the Bennett BTC-1 is described as having been "built by the Bennett Aircraft Corp. of Fort Worth, TX, using 'Duramold', a bakelite-bonded plywood developed by Dr. Robert Nebesar". Close but no cigar EAA!

Confusion is increased by an alternative use for Duraloid. In the early 1930s, Duraloid was first used as a coating - often by dipping or brushing on. Rather than bonding moulded parts, Duraloid's original use was as a stiffener for other materials. For example, fragile bamboo ski poles were coated with Duraloid to stop them splintering. Duraloid is still used as protective coating material but, for a moment there, it built airplanes too.

___________________________________

[1] Micarta is another cotton-reinforced PF resin form. It is a sheet form of Novotext which goes by lots of other names - Textolite and Ferrozell (bar), and Tufnol (sheet).

_

 

[riggerrob]

The 1941 Globe Swift prototype had flying surfaces covered in Bakelite plywood. The fuselage was welded steel tubing covered in fabric. Post-war, the Swift was re-engineered to all metal.
As an aside, the pre-war Ercoupe prototype was also made of wood with some fabric covering, but post-war production Ercoupes were all metal with a bit of fabric covering.

 

[fortrena]

A question for maintenance people. What might be easier to repair in the field, an all metal airplane or a composite airplane?

 

[Foo Fighter]

That would depend on where and how much damage would it not? There are images around showing large chunks of mosquito aircraft having chunks of airframe and wing replaced, some on here to but I can't remember where tbh.