De Havilland Mosquito (Wood vs. Metal)

[Crimea_River]

Picked up the Dec 2022 edition of Aeroplane this am which has an article titled "Mosquito plywood problem solved" highlighting some of the difficulties encountered restoring Mosquito B.35 RS700 in Canada. (Crimea_River - Is this the Mossie that you are working on?). This bit is worth quoting:-

"All British and Canadian built Mosquitos used Baltic birch plywood made to 6V3 [a British Standard]. Part of what that means is that every sheet, regardless of its finished thickness, is comprised of just three layers or veneers. The plywood on the Mosquito varies in thickness from 1.5mm to 6mm. That means the veneers are custom-cut for thickness on each sheet. Where it gets even more complicated is that the grain direction is also specified by de Havilland for every sheet used on the aeroplane. In some places it's 'normal' meaning the grain of the two outer layers runs the length of the sheet; some runs crosswise on the sheet and some runs at a 45 degree angle. The grain direction was decided based on the structural stresses on each section of the airframe."

Yep that's the bird I'm working on. The arrival of the remaining wood that we needed was a huge relief. Despite being a non-flyer, our Mosquito will proudly sport the correct spec wood on its airframe.

The 45 degree grain is used where twisting forces are present. The tail planes, main wing tips, and rear fuselage all have the grain running at 45 degrees to the air flow

 

[BarnOwlLover]

Sorry to necropost, but the repair methods you're using for the Mosquito are sort of similar to what I saw in a video of an AT-21 trainer for holed skins (though probably easier on the AT-21 due to construction differences between the Mosquito and AT-21).

 

[SaparotRob]

I never knew there was a word for it.

 

[MiTasol]

I thought one of the many reasons we came to this forum was to be edjamicated

 

[special ed]

The things one larns here. Somebody used to tell me that.

 

[GregP]

Does this home built Spit (gorgeous) have a serial number/builders plate?

Never mind.

 

[BarnOwlLover]

Was the problems with wood shrinkage/expansion that could happen on the Mosquito effect the fuselage, wings/tail unit, or both? I'm asking because this didn't seem to be a significant issue on the Vampire or Venom, which operated in various climates and used the Mosquito/Hornet type ply/balsa/ply sandwich material used in those aircraft fuselages in the Vampire and Venom's front fuselage (ahead of the engine mount/fuselage fuel tank area).

 

[FLYBOYJ]

Was the problems with wood shrinkage/expansion that could happen on the Mosquito effect the fuselage, wings/tail unit, or both? I'm asking because this didn't seem to be a significant issue on the Vampire or Venom, which operated in various climates and used the Mosquito/Hornet type ply/balsa/ply sandwich material used in those aircraft fuselages in the Vampire and Venom's front fuselage (ahead of the engine mount/fuselage fuel tank area).

I think what you had was most of the load carrying structure (aft of the nose) was made of aluminum and the interior of the wood shell was reinforced with some aluminum structure.

 

[BarnOwlLover]

What I'm wondering is if the fuselage construction of the Mosquito, Hornet, and Vampire and Venom pilot nacelle, as far as how it's built and bonding/treatments used, could maybe help with prolonging the durability of the material. Also as you mentioned, the pilot nacelle on the Vampire and Venom didn't beat most of the forces that the wings and tail fed into the structure--that was the rear fuselage, which was an aluminum monocoque, and also where the engine was mounted.

Also, most of the issues I've heard of structural issues on Mosquitos and Hornets concerned the wings--I've read and heard of few fuselage issues, at least compared to the wings.

One odd quality of the wooden structure was that it did do better than metal at retaining heat, which I think that the Swedes and Swiss who operated Vampires and Venoms probably looked upon favorably in the winter conditions in those two countries.

And also, there's the Tego film adhesive/treatment, which did inhibit moisture and such. That, of course, it why wooden aircraft production was largely screwed after the main factory that made it was bombed twice by the RAF in early 1943. That doesn't directly apply to the Mosquito or Hornet, and most likely the Vampire and Venom, as they mostly used Aerolite (Mosquito) and Redux (Hornet, probably Vampire and Venom). There was Redux made as a film like Tego film, but that came after the development of the Mosqutio, Vampire, and Hornet, and was mostly first used on the all-metal DH Comet airliner (in areas where riveting was difficult or impractical).

But I do think what you brought up (among other things) is why it took until recent years for programs to restore/rebuild Mosquitos to get much momentum, the program to rebuild a Sea Hornet to get going, while there's quite a few Vampires and Venoms of different types preserved and flying--most of which I do believe were Swiss as far as the single seaters go.

Also maybe of interests (though some construction methods are different), there's a program in France to build a possibly airworthy replica of an Arsenal VG-33 that's made significant headway in the post-Covid period.

 

[Shortround6]

Something to consider as far as shrinkage/expansion goes is over what distance?
if a given material changes at 0.X millimeters per meter then problems over 3 meters are going to be a lot less than problems over 12 meters as an example.

 

[FLYBOYJ]

BarnOwlLover You bring up some good questions, but have to ask yourself - even before fiberglass and composites became commonplace in modern combat aircraft construction, why did wood go away?

 

[BarnOwlLover]

Probably because of bad press mostly wooden aircraft got after the plane crash Knute Rockne died in along with other fatalities in the same incident. As well as that metal aircraft were more durable and cost effective in a peace time market. Wood came back for combat aircraft in World War II's SHTF situations when there was worries about aluminum shortages. Also, while an airliner was expected/hoped to have a long service life, combat planes may or may not come back from their missions, and hence are sort of throwaway aircraft that may end up having a short life. In that situation, aircraft like the Mosquito and Hornet do make sense.

However, my question is why did the Vampire and Venom persist with using wood in their structure, even though it wasn't as major a structural element as what the wings/tail/engine were joined to, which was aluminum instead of wood. I know that the Air Ministry suggested the use of wood on the Vampire for what wasn't really needed to be metal. But Ronald Bishop (who designed most DH aircraft from 1937-the 1950s) wanted the original Vampire (DH99) to be all metal, but the DH100 was the mixed aluminum and ply/balsa/ply construction that made it to production. Bishop seemed to believe (rightfully so) that metal was the future, but with the Vampire, the Air Ministry were maybe still in SHTF mode with the Vampire, and, maybe, a little blinded by the Mosquito's success.

 

[Shortround6]

This may fit in here

 

[FLYBOYJ]

Probably because of bad press mostly wooden aircraft got after the plane crash Knute Rockne died in along with other fatalities in the same incident.

The only "bad press" that came out of the Rockne incident were the limitations of wood aircraft in commercial airlines operations.

As well as that metal aircraft were more durable and cost effective in a peace time market. Wood came back for combat aircraft in World War II's SHTF situations when there was worries about aluminum shortages. Also, while an airliner was expected/hoped to have a long service life, combat planes may or may not come back from their missions, and hence are sort of throwaway aircraft that may end up having a short life. In that situation, aircraft like the Mosquito and Hornet do make sense.

OK

However, my question is why did the Vampire and Venom persist with using wood in their structure, even though it wasn't as major a structural element as what the wings/tail/engine were joined to, which was aluminum instead of wood. I know that the Air Ministry suggested the use of wood on the Vampire for what wasn't really needed to be metal. But Ronald Bishop (who designed most DH aircraft from 1937-the 1950s) wanted the original Vampire (DH99) to be all metal, but the DH100 was the mixed aluminum and ply/balsa/ply construction that made it to production. Bishop seemed to believe (rightfully so) that metal was the future, but with the Vampire, the Air Ministry were maybe still in SHTF mode with the Vampire, and, maybe, a little blinded by the Mosquito's success.

That lies with some thinking in the Air Ministry. Sometimes you have some individuals who want to be conservative in their approach to an engineering solution, my guess is they were looking at producibility and cost.

 

[swampyankee]

BarnOwlLover You bring up some good questions, but have to ask yourself - even before fiberglass and composites became commonplace in modern combat aircraft construction, why did wood go away?

Possibly because aircraft-quality wood is a fairly scarce resource, but also because wooden construction may be more labor-intensive and more sensitive to environmental conditions during construction. From a design perspective, a metal (or composite) aircraft will have less internal volume taken up by structure.

 

[Shortround6]

Bishop seemed to believe (rightfully so) that metal was the future, but with the Vampire, the Air Ministry were maybe still in SHTF mode with the Vampire, and, maybe, a little blinded by the Mosquito's success.

It is hard to say.
The Air ministry had banned (pretty much) wooden frames several years before the Knute Rockne crash (March 31, 1931) even though they used fabric covering well into the 30s.
I man not sure if the cost of fabrication had anything to do with it. Just a guess.
Somewhere there is a drawing showing all the wooden "stuff" in a British WW II four engine bomber, I thought it was a Lancaster but I can't find it. Crew seats, radio shelves, equipment shelves, storage, some hatches, a few fuselage panels. Basically stuff that was not dealing with stress.
Sometimes contracts included thoughts about keeping certain industries in operation in case of future need. A lot easier to scale up production from an existing small company than to restart a company that had been defunct for for several years.

 

[EwenS]

I have an Aeroplane Special publication from 2014 on the Vampire where Martin Chorlton & Tony Buttler describe the Vampire's origins.

The starting point was the DH.99 design, a "High Altitude Fighter with Halford engine" presented to the Air Ministry in June 1941. That was criticised for lacking detail and being optimistic on the weight front. It was all metal and it had all the major features of the DH.100 Vampire layout. Once the go ahead was given in August it was renumbered the DH.100 by November becoming part wood in the process.

The article then goes on

"Developed from the construction of the DH.91 Albatross, this composite technique had several advantages, such as reducing the aircraft's weight, which improved performance and more practically, it helped to keep the cockpit warm. The fuselage was built in two halves just like the Mosquito, placed over interior contour wooden or cement moulds and once glued, were held together by flexible steel bands."

So weight saving seems to be the main driver.

 

[BarnOwlLover]

It's been stated in various threads that wooden construction tended to be heavier than aluminum construction. That, however, seemed to refer to aircraft that were designed to be metal originally, but modified to be partially or all wood due to fears of light alloy shortages. Granted, especially in terms of fuselage, the Mosquito, Hornet, and front of the Vampire and Venom fuselages were built of a sandwich material that was sort of an early form of composite construction that was very light and strong (so much so that Mosquito and Hornet fuselages, at least per cutaways, lacked a lot of the formers and stringers that most metal construction had.

So maybe weight was a consideration for not just the Vampire, but also maybe the Hornet. But one issue could be internal volumes for the Comet, which was a jet powered long range airliner. That thing needed as much fuel as could be safely packed into it, given that jet engines were fuel hungry compared to piston engines, and still keep it's load carrying capacity. Not to mention as a peace time airliner, it was hoped to have long service (issues with pressurization that were unknown at the time in the industry not withstanding).

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. A Spitfire or even the Hurricane to a large degree needed factories that were tooled up for and a work force who knew how to work with light metal. For the Mosquito, de Havilland could contract furniture makers and wood workers to make components as subcontractors very easily. And a lot (not quite all, but most) repairs done to a Mosquito were easily handled by wood workers.

It's like what the late Ian Hogg said about submachine guns during World War II. Often times, high powered rifles, be it bolt action or let alone semi-autos, needed factories and workers tooled up for and skilled in working with stuff like metallurgy and metal treatments and such for high power, high pressure rifle rounds. SMGs, which were simpler to build and used much less powerful pistol ammo, could be made by small machine shops and metal working concerns.

In a total war like World War II, everything and everyone was looked at for contributions, and, especially among the British in 1940 when their back was against the wall, there was no shortage of volunteers who wanted to contribute something. And if nothing else--and even that can be seen as big--the Mosquito and other wooden aircraft of aircraft components did free up workers and materials for things like the Spitfire and other programs. And having Mosquito bombers, PR planes and night fighters and strike aircraft--on top of how well they did their jobs--was a hell of a lot better than no planes at all.

Not to mention this factor, that some things do allow other future items to be possible. In it's own way, the Mosquito did make the Vampire, Venom, Hornet, Comet and Sea Vixen possible, one way or another.

 

[MiTasol]

Somewhere there is a drawing showing all the wooden "stuff" in a British WW II four engine bomber, I thought it was a Lancaster but I can't find it. Crew seats, radio shelves, equipment shelves, storage, some hatches, a few fuselage panels. Basically stuff that was not dealing with stress.

I do not remember any wood in the Lancaster but certainly wood was common in Spitfires and Beauforts for holding access panels on to the structure. It was also used in early Australian Beauforts for the radio crate and on all Beauforts for the bomb doors and main entry door. The Americans used plywood seats in a number of aircraft

Sometimes contracts included thoughts about keeping certain industries in operation in case of future need. A lot easier to scale up production from an existing small company than to restart a company that had been defunct for for several years.

Yes. If the SHTF right now many countries would be in deep sh-one-t because they have contracted too many of their supply needs to China. Australia keeps its 90 days strategic oil reserves in the USA which would be a problem if China was to attack Aus.

 

[Crimea_River]

I do not remember any wood in the Lancaster.......

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