Would it be feasible to build a jet fighter plane based on a wooden construction?

Question

I read about the de Havilland Mosquito recently and that it was a quite successful British bomber in WW2 due its lightweight wooden construction. As far as I understand it, usual planes at that time were built mainly with metal parts already, thus heavier than the Mosquito and hence uncatchable for them. Furthermore it was too fast for getting hit by heavy anti air, namely the German 88mm cannon.

With this traits of a wooden construction, I wonder if it is feasible to build jets mainly of wood and give them a boost in speed. I have doubts however that the wooden construction is stable enough for resisting the hefty g-force mid-air while flying in mach 3 speed.

Answer 1

The wings and a few parts of the body of the Heinkel He 162 jet fighter were made of plywood. https://de.wikipedia.org/wiki/Heinkel_He_162#Konstruktion_und_Ausr.C3.BCstung

The Bachem Ba 349 'Natter', a rocket-powered interceptor, was built almost entirely of wood. https://en.wikipedia.org/wiki/Bachem_Ba_349

Answer 2

Yes it would be possible to build a fighter plane from wood, not one that can fly at Mach 3 however. There are some olden days examples of fighter planes using wood construction, here is another one from 1938: the Fokker G.1. with a wooden wing. These planes don't look like F16s, but were subject to fully aerobatic g-forces.

This document of 1941 provides an overview of knowledge of aeronautical wood construction. Wood is a light construction material, and one of the largest aircraft ever built, the Spruce Goose, was made entirely of wood. Wood also has asymmetrical strength properties: it is much stronger in line with the grain than perpendicular to it, one of the main advantages cited for composites. We could follow the same construction method as for composites: shave off thin layers of wood and embed them in resin, line up the majority of the grain in the direction of greatest stress, and use some alternate grain directions like in plywood to create sufficient strength and stiffness in all directions.

If we consider the properties of aeroplane construction materials:

1. Strength.

   Wood has a specific strength that is slightly lower than that of aluminium: spruce has a compression strength of 27.5 N/mm$^2$ = 27.5 MPa, and a density of 418 kg/m$^3$. Compare this with untempered 7075 aluminium alloy: a tensile strength of 280 MPa and a density of 2,810 kg/m$^3$. Aircraft aluminium alloy is 10.2 times as strong and 6.7 times as heavy as spruce, so its specific strength is 10.2/6.7 = 1.52 that of spruce. But half of the wing is compression loaded, and a thicker skin made of a lighter material buckles less easily. So for wings with a high aspect ratio, part of aluminium's weight advantage is traded in: compressed skin is dimensioned on skin thickness, not on yield strength.

2. Heat resistance/flammability

   Aircraft aluminium alloys yield strength reduces as a function of temperature, as indicated in the graph below (source). The red line is for 2024 aluminium: at 250 °C, the tensile strength (= compression strength) is halved.

   

   Compare this with the compression strength of spruce: halved at around 150 °C (Source: fig 5-14 of the Wood Handbook). There are two graph regions for different moisture contents, and that brings us to the main disadvantage of wood: the variability of a natural material, next under point 3.

   

   But of course the main point of attention would be using a jet engine in a wooden frame. Even the G.1 had an aluminium front engine construction.

3. Consistency and weather resistance

   From AIRCRAFT WOODS: Their Properties, Selection, and Characteristics

   ...the principal factors tending to restrict the use of wood are a not unlimited supply of the most desirable species; a hygroscopicity that results in shrinking and swelling and changes in strength; and a wide difference in properties with different directions of the grain.

   These disadvantages can be partially undone by using plywood, however this has an additional weight penalty.

Wood has not been used for several decades for constructing airliners or fighters, and for a good reason. Fokker successfully built wooden monoplane aircraft in the 1920/1930s, until a high visibility crash of an F.X brought this construction method under scrutiny. Not long after, the Boeing 247 and the DC-2 pioneered aluminium smooth skin aeroplane construction, and the industry has never looked back.

So yes, a fighter can be built out of wood and would be strong enough. However it would be heavier, prone to weather influences, and cause of major headaches for integrating a jet engine into its flammable construction. It cannot fly at Mach 3: the SR-71 needed to be built out of titanium, not aluminium, due to the heat resistance required. Spruce would not stand a chance and go up in flames.

There are no good reasons to not build a fighter jet from metal or nowadays composits.

Answer 3

The Mosquito was not too fast to be hit by AA fire from 8,8 Flak (no aircraft is), but flew too high when operating near its maximum operational ceiling. The larger caliber 10,5 and 12,8 guns would reach higher but were not as widespread. With its maximum ceiling of 14.8 km, the 12,8 could easily shoot down a Mosquito.

Ed Swearingen once remarked that, regardless of what material you use, a design would turn about equal in weight. This is certainly true for GA aircraft if you compare wood, aluminium and composites. For a military aircraft, wood would have the biggest disadvantage because it is sensitive to water and will rot if it is not kept dry. If you can live with that, a subsonic wooden jet is easy to design.

In 1944 the wings of the Messerschmitt 109 were re-designed for wooden construction and the result turned out to be equivalent to the aluminium original, but a little heavier. Their main disadvantage, however, was that the wooden wings needed more working hours to complete. That the wooden rudder used in later variants was heavier than the aluminium rudder it replaced was mainly due to the enlarged size which improved directional stability at high speed.

Oh, and there are plans (and a few flying samples) of an all-wooden Me-109.

However, a pure wooden structure would be very hard if not impossible: Structural parts with high point loads (like the landing gear attachment or the engine mounts) could not be made of wood, but will need metal reinforcement. Like the engine, the landing gear itself would need to be made from steel. But the fuselage skin and wing surfaces could easily be wooden.

In fact, there was already a wooden jet fighter. The Horten IX (or Gotha 229) had wooden wings and a steel tubing frame in the mid wing with wooden skin. The skin would use a special type of plywood, called "Formholz", the layers of which were glued together in a mold so they came together with the right shape and curvature. Wood was chosen both to make the plane less visible to radar and as a non-strategic material.

I expect, however, that the designers would have selected a full metal construction had those limitations not existed.

If you want your jet to reach supersonic speed, I would definitely prefer to build large parts of it, like the wing's leading edge or the region around the afterburner, from metal. Wood could best be used if it is heavily filled with epoxy resin and not really pure wood anymore.

Answer 4

Wood is definitely lighter than metals, but it is not as strong. One important figure of merit here is the strength to weight ratio, i.e. the tensile strength divided by the density. Wikipedia lists strength to weigh ratios of various materials. Let's compare just oak and 7075 aluminum. Aluminum weighs about 4 times as much as oak, but is about 5 times as strong. So to take a given load, you need less aluminum (by mass) than you do oak. That is why wood is not used in any aerospace construction. Also note on this table how much higher carbon fiber composite is than aluminum. That's a big driver behind why aerospace companies are moving to that material (e.g. the Boeing 787).

Answer 5

The Vampire - De Havilland again, and not long after the Mosquito (though too late for active service in WW2) - was partly of wooden construction. Like the Mosquito, being developed under wartime conditions (first flight in 1943) was no doubt one reason why.

Unlike the Heinkel 162 its development wasn't an act of desperation but a serious fighter that remained in service for 20 years with the RAF, and apparently until the 1990s as a jet trainer in Switzerland.

So, definitely possible, at least in the subsonic era, though the latter page says it was the last time wood/metal composite construction was used in high performance military aircraft (presumably counting the derivative Venom and Sea Venom as part of the same basic design)

Photos here quite clearly show the woodwork.

Answer 6

The answer is contained in your question and further implied although sometimes rather obliquely in some of the comments and answers.

The wooden de Havilland Mosquito used two Rolls Royce "Merlin" engines, with the exhaust stacks angled backwards because about the time of the development of that order of engine with that amount of power, it had been discovered that angling the exhaust stacks rearward gave a speed advantage in the low tens of miles per hour over the top speed of a 300mph-plus aircraft compared to when it did not have the stacks angled rearward. ie. there was something of a "jet" component already in the Mosquito with large quantites of hot air from powerful engines blasting backwards at full throttle.

EDITED: REFERENCE ADDED:

The below references about the "jet" effect I mention above, are not the two historical references I first discovered in 2010, which first led me to respond to the question. I have mislaid those references in house moves and computer changes. I have not read the below references but it is all I could find now, probably given that jet effects from piston engine exhausts are rather irrelevant, and doubtless gradually becoming of even less interest, in modern aviation whether in war or peace time.

https://en.wikipedia.org/wiki/Rolls-Royce_Merlin

Scroll down to "Ejector Exhausts". Note citations no.35 & 36.

cit.35: Price 1982. p. 51 (Bib: Price, Alfred. The Spitfire Story. London: Jane's Publishing Company Ltd., 1982. ISBN 0-86720-624-1).

cit.36: Tanner 1981, A.P.1565E, Vol.1, Section II (Bib:Tanner, John. The Spitfire V Manual (AP1565E reprint). London: Arms and Armour Press, 1981. ISBN 0-85368-420-0).

(end of the references edit)

Therefore I can't see much difference with pulling the Merlins out of a standard Mosquito and replacing them with gas turbines. And there is my answer to the first part of your question.

Obviously the presence of scorching hot exhaust gases from two piston engines providing that "extra" thrust didn't bother the wooden Mosquito.

Of course, one would need to consider exact mounting position for turbine engines on a Mosquito as they spew out a lot more, and hotter, gas than piston engines, but I don't see that as an insurmountable problem.

And how "hot" is hot? Was it the Canberra jet, a metal twin engined aircraft, which had the jet engines on the wings? I never read anything about, for example, the paint on any logos painted on the sides of that aircraft being scorched or melted off by jet exhaust. I suggest therefore, that even with the aviation understanding of the 1940s, that the Mosquito could stand as an example of a wooden jet aircraft that wasn't built, but could have been if the engines had been available.

And no, I am not suggesting the Mosquito would be capable of supersonic speed as a twin-jet. That issue has already been addressed in comments and answers.

VAMPIRE BRIEF EDIT: The WWII-developed de Havilland Vampire was of course part-wood construction. It was used as the Royal New Zealand Air Force's fighter force for perhaps 20 years. The evidence of successful overall design was strong by dint of my personal observation of the aircraft screaming over my house for decades from the Ohakea AFB some 30 miles away. It's a moot point how much the wood contributed to the Vampire's success as a fighter, but it must contribute to part of the body of evidence that wood and jets can work together, even if only partially and at subsonic speeds.

Answer 7

A bomber? Yes, but FYI, the Mosquito was a fighter-bomber and was used extensively as a night-fighter.

Previous answers have pointed out - correctly - that high-performance subsonic aircraft have been constructed using wood.

I say 'using' because even the Mosquito used some steel and aluminium - but the wing spars, the skin, and the structure of the fuselage were wood, and that's a reasonable definition of 'made from wood'.

Wood's a good composite material, when used with care - but it's variable, and both the manufacturer and maintenance team need to use skill and judgement to use it effectively. And that's the point: as aircraft design pushes further at the limits of the materials, the safety margins are reduced - but safety is maintained within those tighter margins by precise stress analysis at the design stage, rigorous quality control in manufacturing, and repeated inspection in service.

You can do this with the consistent materials we manufacture from metal, and (nowadays) from carbon and Kevlar composites - and composites were dogged by the same problems of consistency that bedevil wooden components until the last 10-15 years.

It's not that they, or wood, were weaker at a given cost and weight - in some cases, they are stronger - the issue is that they didn't deliver the performance consistently and therefore couldn't be used without widening the safety margins - extra weight - and an uneconomical excess of effort in quality control and in-service inspection.

Moving to the supersonic flight regime, it's all much more demanding. The wings have to be much thinner - chord ratio less than five percent - so both the spars and the skin have to be thinner and that's pushing the envelope too far to do it safely with wood. Note also, that the friction forces are higher - massively so in some areas - as are the positive and negative pressure loadings on the skin during the transition between sub- and supersonic flight.

This is especially true of the control surfaces.

It is theoretically possible to do it, with some metal in critical areas and serious epoxy injection, but you'd be getting close to making the wing out of solid wood and you wouldn't do it for the tailplane at all. The weight penalty would've been a no-fly for the first-generation supersonic aircraft and, while more powerful engines make that less of an issue today, the cost in range and payload is unacceptable.

Also, it would glide like a sawn log and that's got implications for safe landing speeds as well as safely landing 'deadstick' with an engine failure.

As a final note, the Mosquito was surpassed by the Hornet in 1944/45 - too late for WW2 and a hundred knots slower than the Gloster Meteor. I mention this because the Hornet was, in broad terms, the 'Wooden Wonder' re-engineered in aluminium: similar size, similar planform, same engines. While the Mosquito was good, it's nowhere near Winkle Brown's "The excess of power was such that manoeuvres in the vertical plane can only be described as rocket-like" that he and other pilots experienced in its metal successor.

And that's your answer: you can build high-performance aircraft out of wood, but you'll always be able to build a better aircraft out of aluminium and steel.

Answer 8

Do not forget the material shortage during world war 2 which required intelligent methods of equipment construction with materials which were readily available i.e wood.

I would think that the higher performance of todays aircraft would be a significant factor when it came to maintenance. Wood vs metal alloy in a higher stress environment would require more maintenance.

If you look at airfields today, I have found all wood frame and canvas aircraft sitting in hangers overnight where as spam cans are left outside in all weather.

Answer 9

Yes, a jet fighter made primarily of wood is possible.It has been done! https://en.m.wikipedia.org/wiki/Heinkel_He_162

Answer 10

According to an article by Reimar Horten in the Argentinian National Aeronautics magazine, in 1936, the German company Farben Werke (Color Works) had build an all-plastic, supersonic flying wing prototype, to be powered by a turbine engine. Would the De Havilland Mosquito have flown supersonic with its Balsa Wood parts if adequately shaped and powered? Why not?