Hawker Hurricane and de Havilland Mosquito both used a lot of wood, but would assume they were built differently?

[MIflyer]

The Mosquito used a lot of casin glue, based on milk. It did OKay in Northern Europe but not in tropical climates such as India, Burma, and the Pacific. One engineer from the UK went to India, looked at their Mossies and told them they were unserviceable because of the way the local bugs were eating the glue. When no one paid attention to his concerns, he took a saw and cut the wings off them.

The other glue in use at that time was Resorcinal. It is a thin very volitile glue that required absolutely flat and smooth mating surfaces, followed by careful clamping that had to make the joints tight but not starved of glue. .

Today, when we think of gluing wood we imagine using two part epoxies, polyurehtanes, and so forth. One of the problems of restoring older aircraft is that while the modern glues are definitely superior, the FAA says that was not the glue the airplane was certified with, so you can't use it.

 

[MikeMeech]

The Mosquito used a lot of casin glue, based on milk. It did OKay in Northern Europe but not in tropical climates such as India, Burma, and the Pacific. One engineer from the UK went to India, looked at their Mossies and told them they were unserviceable because of the way the local bugs were eating the glue. When no one paid attention to his concerns, he took a saw and cut the wings off them.

The other glue in use at that time was Resorcinal. It is a thin very volitile glue that required absolutely flat and smooth mating surfaces, followed by careful clamping that had to make the joints tight but not starved of glue. .

Today, when we think of gluing wood we imagine using two part epoxies, polyurehtanes, and so forth. One of the problems of restoring older aircraft is that while the modern glues are definitely superior, the FAA says that was not the glue the airplane was certified with, so you can't use it.

Hi

Jeff Jefford had an article on 'The Mosquito and its Structural Problems in the Far East' in the recent 'RAF Historical Society Journal' No. 74. The conclusion states the following:

"... , while stories of the glue 'breaking down' circulated widely both during the war and after, and there was some factual basis for these, this was not the root cause of the Mosquito's problem. It is true that there were some early manufacturing deficiencies and joints did tend to come apart, but the real problem lay in the swelling and/or shrinkage of the wooden structure, rather than simply inadequate adhesion - although the end result was the same. Despite the remedial action that was implemented, silver-painted, late series Mosquitos, complete with Mod 638, were still grounded for 'defective glued joints' in Singapore as late as 1954, eg VT628 of No 45 Sqn. But was it really defective glue, or a defective joint, or a well-glued well-made joint which had pulled apart through wood shrinkage? It seems self evident that, regardless of the type of glue employed, the colour of the paintwork and the incorporation of Mod 638, the Mosquito was simply unable to stand up to prolonged exposure to the high ambient temperature and humidity of the tropics."

Mike

 

[fastmongrel]

Does anyone know the number of fuselages that were produced every day for each individual mold?

I imagine that at least two or three hours of curing were necessary to allow the glue to be catalyzed and, considering at least another two or three hours to place plywood and balsa on the mold, I do not think that with single mold they could build more than four raw fuselages per day.

But these are only assumptions, some additional information would be very welcome.

Don't know how long it took for the fuselage half to set hard but some factories used concrete moulds with hot water pipes in them to heat the mould.

 

[Elmas]

The Mosquito used a lot of casin glue, based on milk. It did OKay in Northern Europe but not in tropical climates such as India, Burma, and the Pacific. One engineer from the UK went to India, looked at their Mossies and told them they were unserviceable because of the way the local bugs were eating the glue. When no one paid attention to his concerns, he took a saw and cut the wings off them.

The other glue in use at that time was Resorcinal. It is a thin very volitile glue that required absolutely flat and smooth mating surfaces, followed by careful clamping that had to make the joints tight but not starved of glue. .

Today, when we think of gluing wood we imagine using two part epoxies, polyurehtanes, and so forth. One of the problems of restoring older aircraft is that while the modern glues are definitely superior, the FAA says that was not the glue the airplane was certified with, so you can't use it.

I thought he glue used for the Mosquito was a resorcinol based resin.

 

[Admiral Beez]

I thought he glue used for the Mosquito was a resorcinol based resin.

I wonder if the glue varied from plant to plant. Were Canadian mosquitos glued with the same stuff as British ones?

 

[Crimea_River]

Don't know how long it took for the fuselage half to set hard but some factories used concrete moulds with hot water pipes in them to heat the mould.

I hadn't heard that but heat lamps were also used.

The time taken to produce one half was not only affected by glue setting time but also by the fact that the skins were produced in stages, each of which required clamping. The inner skins were first glued and screwed to the bulkheads and other protruding internal stiffening members and then clamped to the mould using steel straps. After a sufficient cure, the straps were removed and inter-skin components, primarily spruce stiffening members and balsa filler strips, were glued in place. The balsa strips had to be dry-fitted and custom cut/adjusted before gluing to the inner skin. The inter-skin layer was then strapped again and allowed to cure. Once cured, the straps were again removed and the balsa strips were shaped to a smooth contour to receive the outer plywood skin. The outer skin was then glued to the balsa and the spruce structural members and strapped again for curing.

I have yet to come across the time taken between the start of this sequence and the point at which the final straps were removed. In our restoration work using modern epoxies, the recommended setting time under clamps is 8 to 10 hours at room temperature and we followed those recommendations with successful results. In wartime aircraft, the casein glues initially used are known today to cure in about 4 hours. The glue used later (not sure when the switch was made) was a urea-formaldehyde glue and modern versions recommend a clamp time of 6 hours. That said, I still don't know what actual clamp times were used in production with added heat sources.

 

[Elmas]

I hadn't heard that but heat lamps were also used.

The time taken to produce one half was not only affected by glue setting time but also by the fact that the skins were produced in stages, each of which required clamping. The inner skins were first glued and screwed to the bulkheads and other protruding internal stiffening members and then clamped to the mould using steel straps. After a sufficient cure, the straps were removed and inter-skin components, primarily spruce stiffening members and balsa filler strips, were glued in place. The balsa strips had to be dry-fitted and custom cut/adjusted before gluing to the inner skin. The inter-skin layer was then strapped again and allowed to cure. Once cured, the straps were again removed and the balsa strips were shaped to a smooth contour to receive the outer plywood skin. The outer skin was then glued to the balsa and the spruce structural members and strapped again for curing.

I have yet to come across the time taken between the start of this sequence and the point at which the final straps were removed. In our restoration work using modern epoxies, the recommended setting time under clamps is 8 to 10 hours at room temperature and we followed those recommendations with successful results. In wartime aircraft, the casein glues initially used are known today to cure in about 4 hours. The glue used later (not sure when the switch was made) was a urea-formaldehyde glue and modern versions recommend a clamp time of 6 hours. That said, I still don't know what actual clamp times were used in production with added heat sources.

A very successful, but quite not a straightforward method of construction, considering also that probably a major repair on the field of such a structure (say, changing a wing...) would have been difficult, I dare say.

 

[Crimea_River]

A very successful, but quite not a straightforward method of construction, considering also that probably a major repair on the field of such a structure (say, changing a wing...) would have been difficult, I dare say.

Not as bad as you would think. Depending on where they were on the aircraft, large holes could be repaired by simply patching new plywood and doped fabric over them. Below is an example of an allowable repair taken from the RAAF repair manual:

Removal of the tailplane and fin was easy as they were single piece assemblies bolted to steel eyes on the fuselage. The hardest part of removing the wing was disconnecting all of the electrics, pneumatics, hydraulics, and flight controls which ran along the bomb bay walls as the latter had to be removed to enable the wing to drop out. This would not have been done at the squadron level but rather at repair units.

 

[MIflyer]

I believe it is in the book "Druid's Circle" where a squadron commander in the ETO noted that the Mossie he was assigned had a tendency to vibrate in a dive, but it did not happen every time he flew. The engineering officer took it up and dove it, determined to figure out what was going on. The airplane crashed, killing the pilot. They later concluded that the rudder or fin had a flaw in the bonding that was sensitive to moisture; sometimes it caused vibration and other times it did not. It vibrated so badly in that dive on that day that it broke up.

 

[tyrodtom]

I doubt there was very much wooden furniture being made during the war and I assume that meant they had some excellent craftsmen available. And besides, it greatly annoyed the Germans, who did have a serious shortage of aircraft materials. Goring raged about the British being able to build a very fast aircraft out of wood when it was the Germans that were short of aluminum.

Interestingly enough, in WWI the Germans introduced the steel tube fuselage because they were out of suitable wood.

View attachment 590566View attachment 590567

The WW1 German use of steel tube fuselages had nothing to do with a shortage of wood.
Welded steel tube fuselages were a design method of Fokker aircraft even before WW1, and only Fokker.
Almost every other German aircraft producer stuck with wood.
Fokker Aircraft was still designing welded steel tube fuselage aircraft going into WW2. The Fokker Eindecker right through the Fokker XXI of the late 30's were all steel tube fuselages, with wooden wings.

 

[MIflyer]

The Smithsonian says says they went to steel tube due to wood shortages.

 

[tyrodtom]

What German aircraft builder that had steel tube fuselages other than Fokker ?
And Fokker always had been welded steel tube from before the war.
There might have been a shortage of some woods, but no German aircraft builder changed their fuselage production methods .
Can you name any that did?

 

[nuuumannn]

Fokker's designer Reinhold Platz was a very innovative designer, but Fokker's use of a welded steel tube frame had nothing to do with a shortage of wood. It was primarily adopted owing to its rigidity and inherent strength. The principal structural element of the wings of Platz's aircraft was wood; he designed a wooden box spar comprising two wooden spars joined by sheets of ply, around which the frames fit, and the leading edge of these frames was wooden sheeting. Although not the first Fokker aircraft with steel tube fuselages, even the famous Eindekker had a metal framework, this method of construction was used in Platz's subsequent fighters, the Dr I, D VII and D VIII (E V).

0407 Science Museum Eindekker

Platz's first wholly indigenous design with Fokker was the V I prototype of 1916, which incorporated a circular welded steel tube fuselage, cantilever wings, with his box spar structural element and all moving horizontal and vertical stabilisers, with the lower sesquiplane wing all moving as well, to enable the adjustment of its incidence.

Fokker V.1 - Wikipedia

Let's also not forget that Hugo Junkers was developing all-metal aircraft in 1915, with the original J I, but with wooden forming elements. His choice of metal construction came from his realisation of the inadequacies of wood as a structural material, being subject to greater change in rigidity owing to fluctuations in temperature and humidity. The J IV, militarily known as the J I, which confuses things since Junkers' first all-metal aircraft was called the J I, was an all metal armoured ground attack biplane that did incorporate wooden formers in the fuselage.

Junkers J IV (J I) fuselage.

Junkers J I

 

[MikeMeech]

Let's also not forget that Hugo Junkers was developing all-metal aircraft in 1915, with the original J I, but with wooden forming elements. His choice of metal construction came from his realisation of the inadequacies of wood as a structural material, being subject to greater change in rigidity owing to fluctuations in temperature and humidity. The J IV, militarily known as the J I, which confuses things since Junkers' first all-metal aircraft was called the J I, was an all metal armoured ground attack biplane that did incorporate wooden formers in the fuselage.

Junkers J IV (J I) fuselage.

View attachment 590949Junkers J I

Hi

The Junkers J.I was not a 'ground-attack' aeroplane it was a n 'Infantry' aeroplane to conduct 'Contact Patrols' to locate 'friendly infantry' and get that information back to commanders. They could also give other information on the battlefront (details are laid down in the German documents of the period). Its offensive capability was the observers machine gun, it was not equipped with forward firing machine guns in service (trials were made with downward firing machine guns and the Becker 20 mm cannon), its lack of manoeuvrability ruled it out for ground attack missions really. It was issued in ones and twos to units to undertake its particular task. The ground attack aircraft used by the Schutzstaffel/Schlactstaffel tended to have no or lighter armour protection, the J.I could call these in by wireless or use the same means to call in artillery fire (British Contact machines did the same), it was not a WW1 'Shturmovik', it had its own important task to undertake.

Mike

 

[nuuumannn]

The Junkers J I was not a 'ground-attack' aeroplane it was an 'Infantry' aeroplane to conduct 'Contact Patrols' to locate 'friendly infantry' and get that information back to commanders.

Indeed it was, my mistake. The J I was indeed an infantry support aircraft.

 

[Koopernic]

I thought he glue used for the Mosquito was a resorcinol based resin.

From 1943 or 1944 the glue was changed to a formaldehyde based glue from the Aerolite company.