All metal Mosquito ??

[Markus Becker]

WI the Mosquito had been made out of aluminium instead of various types of wood? IIRC duraluminium is lighter/strong than wood, meaning an all-metal Mossi would have been even better, or am I overlooking something?

I do that an aluminium Mosquito wasn´t an option as there was not enough aluminium, so this is a purely theoretical question.

[Graham Boak]

Theoretically, it would have been lighter. Practically, it would have depended upon the design team's experience with aluminium.

I don't think it was an actual shortage of the metal, though one would have been feared, but a willingness to use manufacturing sources outside of the already overstretched aircraft industry. You were better off using trained woodworkers than having to train new metal fitters.

[MarkRS]

Actually the average density of Balsa wood is 170 kg/m3 which is far less than Aluminium at 2700 kg/m3. Even when you take into account that Balsa is far weaker than Aluminium, The strength to weight ratio of Balsa is about 40% better. So an Aluminium Mosquito would have been heavier and slower.

[Graham Boak]

No. Wooden aircraft are heavier than metal aircraft (and the main component of the Mosquito was not balsa but Spruce.) The main reason for this appears to be that the strength of the wood cannot be relied upon, so greater safety factors are required. Directly comparable cases are the wings of Soviet fighters, which changed from wooden spars to metal ones once the supplies of aluminium were sufficient. Attempts to create wooden versions of aircraft designed in metal end up heavier - see the Nakajima Ki.84 for an example.

One other advantage of metal is that it provides more internal space than the thick skins and internal structure of wooden aircraft.

Heavier aircraft are not necessarily slower, as weight has little effect on top speed. The wooden aircraft may be faster, because of a smoother external surface without steps and gaps between the panelling.

[MarkRS]

Sorry to disagree, but Mosquitos were not ordinary aircraft. They were the highest of high tech at the time. They were made from wood on purpose because it made them lighter. And they were pushing the limits on safety factors. Spruce was used where better bending strength was needed, the rest was Balsa and plywood. Spruce is also one of the lighter woods, 450 kg/m3. Its improved strength over Balsa retains the same 40% strength to weight advantage over Aluminium. These aircraft were built using the same principles as modern composite aircraft today. Assuming the same aerodynamics, weight is highly relevant to top speed and acceleration. The Mosquito could fly away from a Spitfire carrying the same payload as a B17.

[MarkRS]

You get a really good description of the construction of the Mosquito in:
De Havilland Mosquito: An Illistrated History By Ian Thirsk.

http://books.google.com/books?id=6nb...page&q&f=false

Page 39 onward.

[Graham Boak]

Sorry, despite not being a structural engineer I will back my experience in the industry. Yes, the Mosquito was cutting-edge technology for the day. So were the Russian types. Metal construction is lighter than wooden. (Plywood is not a type of wood, but a treatment of it).

I was an aerodynamicist specialising in aircraft performance - weight is not "highly relevant" to top speed. Top speed is dominated by the zero-lift proportion of the total drag (mainly profile drag, skinfriction drag and excrescences), whereas weight only features in the lift-induced drag which is only 10-15% of the total at most - differences in weight therefore will be at most 5-10% of that, or 1-2% of total drag.

The Mosquito was not faster than the Spitfire, at least not comparing equivalent versions. Its normal payload was 2000lb of bombs. You are thinking of the overload payload of a single 4000lb - these aircraft were draggier and a ton heavier. The maximum payload of a B-17 was 8000lb.

[MarkRS]

A Mosquito carrying 2000 lb was at least 20 mph faster than a Spitfire. It was designed that way. Its defence against fighters was to fly away from them. I am a structural designer, among other things, and aluminium structures are not lighter than composite wood ones. That is why the Mosquito was made the way it was. The Hornet and the Vampire were of similar construction. I have a lot of experience with modern composites. Homogeneous metals do not even come close to competing with them. As I said, if the aerodynamics are the same, weight is important. They were doing everything they could to find an extra 5 mph. It is also a myth that the Mosquito was built of wood because a shortage or fear of shortage of aluminium. They had to go to Canada for the right woods. The Mosquito was structurally a much higher tech aircraft than any of the metal aircraft. It was so far out there that De Havilland had trouble selling it to RAF, until they started flying them, that is.

[Six Nifty .50s]

Originally Posted by MarkRS

A Mosquito carrying 2000 lb was at least 20 mph faster than a Spitfire. It was designed that way.

Not if we reference RAF performance trials. The maximum speeds in level flight were almost identical, going by test reports of Mosquito MP469 (408mph in January 1943) and Spitfire AB505 (409mph in April 1942). Both test aircraft had Merlin 61 engines.

Originally Posted by MarkRS

Its defence against fighters was to fly away from them. I am a structural designer, among other things, and aluminium structures are not lighter than composite wood ones. That is why the Mosquito was made the way it was. The Hornet and the Vampire were of similar construction. I have a lot of experience with modern composites. Homogeneous metals do not even come close to competing with them. As I said, if the aerodynamics are the same, weight is important. They were doing everything they could to find an extra 5 mph.

I think he meant that you might have oversimplified the correlation between horsepower, weight, and aerodynamic efficiency.

In March 1944, RAF Mustang FZ107 was tested with a U.S. built Merlin 61 (Packard V-1650-3). The loaded weight of Spitfire AB505 was considerably less, but Mustang FZ107 was about 25mph faster at all throttle settings. I don't know if this Mustang had the standard underwing pylons installed, because that would have reduced top speed by at least 10 mph.

[mhuxt]

Better comparison would be against the prototype with 61s, as MP469 had a gun fairing slung underneath the fuselage.

AFDU report said the Mosquito IV was 4-5 mph faster than the Spitfire V, though the Spit was using emergency boost, the Mossie not.