De Havilland Mosquito (Wood vs. Metal)

BarnOwlLover said:

But then, there was also production, too. From that standpoint back then, wood was probably cheaper and easier to work with, depending on the company

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A lot of your wood workers would be better employed building office or barracks furniture. Or upgraded ones help build MTBs/power launches.
There were not that many high quality cabinet makers around and most (all?) of them were used to working with different woods than what aircraft used.
Nobody was having bespoke Spruce 20 seat dining tables or giant armoires built.
Through in the different glues and such and it is not that big a deal to train a lot of your workers from scratch.

This is what tripped up some European makers.
The aircraft makers were moving away from "wooden" construction as used in WW I and into more high tech stuff using new glues and techniques.

The fancy wood plane shown earlier required baking in an autoclave for a period of hours to set the glue and help impregnate the glue into the wood structure.
you may be able to build hundreds of tiger moths per year (or a few thousand J-3 cubs) but trying to build thousands of fighters a year may exceed supply.

Crimea_River said:

The back part of the nacelles were wood. Had a pic but lost it.

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Interesting - I do not remember that on KB976 and I worked on it for over 18 months. As I posted on "a new book in my library" last week I now have a Lanc I & III vol 1 and Illustrations manual so I will need to check them out when I get home.

In comparing Britain and the USA with wood v metal construction decisions one has to bear in mind that the two economies were very different.

Britain had 1/5 the population of the USA and vastly less land whose flat bits were vital for agriculture, other industries or towns. By the beginning of 1942 Britain had been at war three years and evolved probably the most war driven economy reaching the envelope in most resources. It was very much an either/ or economy. To make 'X' required one not to make 'Y'. Most materials were imported across oceans subject to weather, delay and naughty submarines making unscheduled holes in the hulls.Not to mention naughty airmen dropping tons of bombs across the densest industrial bits of the country and a rail system clogged to capacity to the extent that coastal convoys had to be used to transport materials around the country including along the Channel within 15 miles of artillery fire never mind air attack. Labour was subject to direction so wooden aeroplanes could draw upon marginal unskilled and semi skilled workers in remote sub contractors. Often in large sheds or garages and house tenements. Whilst a core of skilled wood workers were necessary for training and the most complex items the marginal (teenagers, old men and women) that could not be suitably for directed factory labour or conscripted into the mines. By late 1944 the sheer shortage of men for infantry was limiting the capacity of the army and assorted non infantry troops including aircrew in training were shifted into the infantry and consideration was being made to import USA coal to release miners into the army.

By contrast the USA had no domestic threat, plentiful suitable land, a large labour force and domestic material resources. It had a far larger population to draw upon so a far larger number of skilled workers. Locally there would be military manpower shortages but strategically it had no shortage of young men for the forces. Whole divisions of equipment in Europe were scheduled to be manned by US troops but they were saved from this by the renewed French army manning them. So the USA had no need to actually seek to turn to marginal labour or materials so, whilst wooden aeroplanes were looked at, they filled no actual need.

Looking elsewhere we can see the Soviet Union making use of wooden aeroplanes to use marginal resources but later turning to metal by preference as the marginal needs reduced and supplies of materials and skilled labour increased. Germany made negligible use of wooden aeroplanes at first but, as they had to turn to marginal resources, wooden designs were investigated and wooden alternative parts incorporated into later versions of previously metal aeroplanes. Japan displayed the same behaviour.

Overall, wooden production of aeroplanes could compare with metal in performance when purpose designed but metal proved the preferred choice when circumstances allowed for a variety of reasons. The drive towards wood instead of metal was a need to exploit marginal resources in materials and labour. The forum period was one of rapid changes in glue and resin technologies and formed the basis of modern glues and resins which allowed the mass production of 'plastic' aeroplanes today.

In short, metal aeroplanes were a better choice in WW2 but wooden ones could compete and were the alternative when one had to turn to marginal resources. Less an engineering matter than an economic one.

MiTasol said:

Interesting - I do not remember that on KB976 and I worked on it for over 18 months. As I posted on "a new book in my library" last week I now have a Lanc I & III vol 1 and Illustrations manual so I will need to check them out when I get home.

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Well the manual has no section on structure so that is no help and the parts illustrations are next to useless.
I did learn that the Lanc had wood in some areas though.

The first one looks like a seat back


The second is in the top turret support structure

The third is the cover for when the top turret is removed


and the last shown is the rear floor that I am positive was metal on KB976. Maybe the later marks had metal or maybe it was one of the Arctic Research modifications

yulzari said:

Overall, wooden production of aeroplanes could compare with metal in performance when purpose designed but metal proved the preferred choice when circumstances allowed for a variety of reasons. The drive towards wood instead of metal was a need to exploit marginal resources in materials and labour. The forum period was one of rapid changes in glue and resin technologies and formed the basis of modern glues and resins which allowed the mass production of 'plastic' aeroplanes today.

In short, metal aeroplanes were a better choice in WW2 but wooden ones could compete and were the alternative when one had to turn to marginal resources. Less an engineering matter than an economic one.

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Wood is labour intensive but MOST can be done with fairly simple tooling.

For mass production metal needs lots of costly machinery but far fewer manhours. Much of the riveting was done on the work bench using heavy machinery so riveting that takes hours on a restoration may have only take minutes on the production line.




Using a simple wing rib as an example the wood rib can be made using very basic cutting tools, basic jigs, a steamer, glue and nails. Every part is made individually then assembled in the jig. Each process is time consuming and the rib must stay in the jig until the glue has cured so for every team many jigs are required for mass production

A properly designed metal rib needs:

• a pantagraph router or similar device to cut the metal - but that can cut out multiple rib blanks at one time. In thin ribs up to 50 at a time
• heavy machinery to shape the metal such as
  • a form block, often cast, that is designed to create the finished shape of the finished rib, along with a hydroform press to press the blank around the form block. Many hydroform presses in ww2 had input/output tables on all four sides and some could make more than one pressing a minute. Many ribs had the brackets that the stringers were attached to built in thus eliminating hours of work per aircraft. OR
  • a drop press, with dies to shape the metal.
• heat treat facilities if the rib has tight angles.

Training on many of these tools took a relatively short time and some machines could produce dozens, if not hundreds, of parts per hour. Just think of how many pressed ribs there are in each B-24 wing - they built over 18,000 of each one, plus spares for field repairs.

Once sanded down the final three-ply birch outer skin was glued onto the half fuselage and clamped until fully boded. The overall thickness of the birch and balsa sandwich skin was a surprising 11 mm. This sandwich skin was so stiff that no internal reinforcement was necessary from the wing's rear spar to the tail bearing bulkhead.
From

Season to taste.

Basically, a model airplane. A very large flying model.

yep - a 1:1 model

special ed said:

Basically, a model airplane. A very large flying model.

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I just had a flashback of "Flight of the Phoenix".

Tea Brewer said:

..... The overall thickness of the birch and balsa sandwich skin was a surprising 11 mm. This sandwich skin was so stiff that no internal reinforcement was necessary from the wing's rear spar to the tail bearing bulkhead.

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Actually, the thickness of the balsa filler alone was 7/16 inches or 11mm. To that you add the inner birch ply skin of 1.5 to 2mm plus the outer skin which was 2 or 3mm depending on location and you get an overall thickness of approx. 15 or 16mm.

Aft of the the wing rear spar which is at Bulkhead #3, you will find 2 intermediate internal structural bulkheads (#4 and #5) before reaching the two aft bulkheads that support the vertical stab so it's not just the skin between the wing spar and tail.

Crimea_River said:

Actually, the thickness of the balsa filler alone was 7/16 inches or 11mm. To that you add the inner birch ply skin of 1.5 to 2mm plus the outer skin which was 2 or 3mm depending on location and you get an overall thickness of approx. 15 or 16mm.

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That thickness was 5/8 of an inch. Have you not heard of the Imperial system of measurement?

Truth of the matter is, there is a huge difference between building aircraft in England where they are constantly on a war footing, whereas in the USA I do not recall any attacks on any US factory. Yes, the US was attacked but very limited to Pearl Harbor, The Aleutian Islands, these being several years after the war started. The Us arriving at committal late again.

ww2restorer said:

Truth of the matter is, there is a huge difference between building aircraft in England where they are constantly on a war footing, whereas in the USA I do not recall any attacks on any US factory. Yes, the US was attacked but very limited to Pearl Harbor, The Aleutian Islands, these being several years after the war started. The Us arriving at committal late again.

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There were a few incidents in the first half of 1942 where Japanese submarines shelled the west coast and triggered invasion scares. And in Sept 1942 a couple of air raids.

But they were enough to cause aircraft factories to be camouflaged.

And also the balloon bomb campaign of 1944/45

But none of these achieved very much.

The covered factory camouflage system used in the US was brilliant.

Howard Gibson said:

That thickness was 5/8 of an inch. Have you not heard of the Imperial system of measurement?

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Yes I've heard of it. However, look at this excerpt from an original DH drawing:

ww2restorer said:

The Us arriving at committal late again.

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And your point is?!?!

Crimea_River said:

Yes I've heard of it. However, look at this excerpt from an original DH drawing:

View attachment 700241

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dH used a lot of metric measurements in their engines as well, presumably because it is far more precise than inFerial measurements are. Other Brit manufacturers also used meteric so dH were not alone on that. There is only one dimension called a mm but there are multiple inches and other inferial measurements and you need to know exactly which of the many measurements with the same name they are using

For example many inferial users talk about n gauge material. Here are just a few of the gauges in use in ww2. For a good example of how confusing these can be note the lines that say



This manual alone has another two and a half pages of different gauges in common use in 1945.

MiTasol said:

dH used a lot of metric measurements in their engines as well, presumably because it is far more precise than inFerial measurements are. Other Brit manufacturers also used meteric so dH were not alone on that. There is only one dimension called a mm but there are multiple inches and other inferial measurements and you need to know exactly which of the many measurements with the same name they are using

For example many inferial users talk about n gauge material. Here are just a few of the gauges in use in ww2. For a good example of how confusing these can be note the lines that say

Birmingham Gauge for Sheets and Hoops. (See Birmingham Gauge).
Birmingham Gauge. Abbreviation: B.G.
Not to be confused with the Birmingham Wire Gauge.​

View attachment 700273

This manual alone has another two and a half pages of different gauges in common use in 1945.

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To be read by everyone who suggests country A just licence makes a foreign design. I am sure every sheet metal supplier in Poland had all of these on the shelves……..

To me the biggest stupidity that both the US and Aus engaged in during ww2 was the total redrawing of imported designs. Packard wasted untold manhours redrawing all the Merlin blueprints to US standard when it would have been far simpler to train the production staff to read and use the RR drawings. These were all new hire staff and had to be trained in reading the US blueprints so sticking with the UK prints would have been easier and faster and have no chance of the inevitable conversion errors that arise when converting mm to US inches etc. Likewise training their draftsman to work with the RR drawing standards would have taken a minute fraction of the time taken to redraw every blueprint.

In Aus they wasted time the same way, for example dH Australia converting dH Gypsy drawings from mm to inches.

In both cases 8mm studs and bolts with a 1mm pitch became the weird 0.315" diameter with a thread pitch of 0.0393".

That has no practical benefit.

CAC on the other hand stuck purely to NAA standards for all their Wirraway and other technical drawings and trained all their new hire staff to those standards