The Tree That Shaped Early Aviation

Today on the blog, we have a special guest post from author Ruth Tittensor! Her book, Shades of Green, focuses on the history of the Sitka spruce and its role on two continents, going back 10,000 years. Here, she explains this particular tree’s incredible significance during the First World War and Second World War. Read on to find out why the Sitka spruce was so important to early aviators! 

I am often puzzled by accounts of early airplanes, because they usually contain detailed specifications for the engines but little information on other components. Now, I am an ecologist and not an aircraft designer, but I understand that an engine cannot fly on its own. During the first half of the twentieth century, wood was the main component of a plane’s structure, providing its basic body and wing design,  providing seating for the pilots, attachments for weapons – and – the plane could fly!

1. Avro 504K,UK
The AVRO 504K was an important First World War training plane; 8,340 were built in Manchester and Southampton, England of imported Sitka spruce. Photo: courtesy Tangmere Military Aviation Museum, Sussex, England.

Some descriptions of early aircraft do not mention the ‘wood’ or ‘timber’ at all. Others mention ‘wood’ but not which species of tree – say, ash, birch or walnut – was used for a particular aircraft and its components. I research the ecology and history of forests, plus the past and present uses of trees, so the words ‘wood’ or ‘timber’ alone are not very helpful to me.

Tall Sitka spruce in old-growth forest, Tongass Forest. Alaska. Photo: Andy Tittensor.

The First World War thrust one North American tree species directly into the limelight: forests were left without it, but  memories, histories, and photographs of it were left in abundance in libraries, archives, and family histories.

The history of early aviation is the recent history of this one, globally-rare conifer tree which grows naturally only along the Pacific coast of Canada and the USA: Sitka spruce (Picea sitchensis).

In the later nineteenth and early twentieth century, large-scale logging was clearing the seemingly-limitless coastal rain forests of Washington and Oregon. Sitka spruce was not the most abundant tree in these forests and  was regarded as a ‘weed’  because Europeans had few uses for it at that time – though it had been integral to the lives of indigenous Americans for 10,000 years!

A Mosquito aircraft in the process of restoration. Photo: Andy Tittensor, courtesy Mosquito Aircraft Museum, St. Albans, UK.

However, a few people – aircraft designers – knew its value. For instance, the Wright Flyer in 1903, the Curtiss ‘Pusher’ in 1911 and the Boeing B&W in 1915 were constructed of Sitka spruce. The British, too, knew that this tree was just right for plane construction, even though Britain has no native spruce species: they constructed their early war planes from it, for instance the Airco DH.3 in 1916 – Geoffrey de Havilland designed this and about one third of the Allies’ First World War planes.

In 1917, the Allies asked the USA for 100 million board feet of Sitka spruce so they could build thousands of  war planes and training aircraft. They were picky: they didn’t want any old Sitka spruce, they asked for high-quality, aircraft-grade lumber: straight-grained and defect-free. To produce aircraft lumber, trees had to be 200 ft tall and over 5 ft basal diameter. The Allies were also in  a hurry; they wanted the full amount of Sitka spruce timber by 1918!

The fuselage of a crashed Mosquito aircraft showing longitudinal bands of Sitka spruce enveloped by Balsa wood. Photo: Andy Tittensor, courtesy Mosquito Aircraft Museum, St. Albans, UK.

To  fulfill this request, the US army set up a ‘Spruce Production Division’ in Portland and employed nearly 29,000 soldiers and civilians to work in 60 militarized logging camps and mills spread over 300 miles from Oregon to the Canadian border. Over 2000 soldiers worked in a Spruce Production Mill at Vancouver Barracks near Portland, sawing behemoth Sitka spruce trunks into usable planks. Thousands more soldiers built a railway network into the forests so that desired trees could be reached, felled and transported away for milling. Alaska, Haida Gwaii, and the British Columbia coast were also tapped for Sitka spruce at that time.

The flap of a Mosquito aircraft undergoing re-construction with Sitka spruce ribs. Photo: Andy Tittensor, courtesy Mosquito Aircraft Museum, St. Albans, UK.

By 1918, almost enough Sitka spruce had been produced for the Allies. It was exported via rail to ports and then via ship to Europe. At the end of the War, the Allies had added about 8,000 war planes to their preexisting 300!

After the war, there was a surfeit of wooden planes in the world. Research and development started producing aircraft made of metals, although de Havilland continued with wooden planes, for instance the DH.88 ‘Comet’ and DH.91 ‘Albatross’ in the 1930s.

6.SilverDartReplica,Canada 1959.JPG
The Silver Dart biplane, designed by a group including Alexander Graham Bell, was flown in 1909 from the ice of Bras D’Or Lake, Nova Scotia. The wooden parts, except the propeller, were of Sitka spruce. This was the first fixed-wing powered flight in Canada. This b/w photograph of a replica was taken by the RCAF photographer in the same location in 1959. Photo: courtesy Atlantic Canada Aviation Museum.

The actual species of tree used for aircraft structure is important. There are seven species of spruce tree native to North and Central America. But Sitka spruce has the ideal combination of anatomical features: it is very lightweight but very strong; it has long wood fibers, which amongst other features, do not tear when bullets strike; and it grows sufficiently tall and large at maturity that very long lengths of straight-grained planks can be produced by efficient milling.

In 1943, the American Curtiss-Wright C-76 ‘Caravan’ plane was built of plywood mahogany which was found to be an unsatisfactory timber: only a few production models were built. However, the British DH.98 ‘Mosquito’ aircraft, designed in 1940, was mainly laminated Sitka spruce and birch, making it light and strong. Its speed and ease of repair meant that 7,850 were built in England,  Canada, and Australia during the Second World War. Its contribution to the war effort was enormous, despite being wooden!

7. SilverDartReplicaCanada.jpg
Silver Dart replica displayed in the Baddeck Museum at the Alexander Graham Bell National Historic Site, Cape breton, 2008. Photo courtesy Atlantic Canada Aviation Museum, Halifax, NS.

Although wooden planes are now rarely produced, the properties of Sitka spruce timber ensure that it has many other important uses in modern society. Timber from slow-grown Alaskan trees, ensure it is the best wood to make soundboards for stringed instruments. Thousands of modern guitars and pianos have Sitka spruce soundboards. Pulp for the greedy paper-users of North America and Europe comes mainly from Sitka spruce. Roof trusses, joinery, and model aircraft are a few of its other uses.

8. HarvestingSSinUK
Harvesting closely-planted, quick-grown Sitka spruce in a UK plantation: unsuitable for aircraft, but just right for paper-pulp, pallets, and chips. Photo: Andy Tittensor.

With nearly a century and a half of heavy logging, Sitka spruce has become an infrequent tree species in its natural range, apart from Alaska. However, since being introduced into Britain in 1827 by David Douglas, it has found a  perfect new home in Atlantic Europe. The high rainfall and maritime climate of the western coasts of Ireland, Norway, and Britain suit it so well that it grows three feet in height a year! Such quick-grown timber is soft and not suited to aircraft construction. However, Sitka spruce plantations in Scotland are harvested at about 30 years old and made into many other useful and desirable domestic, commercial and recreational items: biomass chips, construction timber, kitchen-units, pallets, paper pulp, particle-boards, pit props, tonewood. And regarding flight, the British still use imported Sitka spruce to repair historic aircraft, and to build gliders and model airplanes.

9. SSLoch Ossian, UK
Commercial plantation of Sitka spruce at 1319 ft (402 m) adjoining Loch Ossian, Scottish Highlands, UK. Photo: Andy Tittensor.

9781909686779Ruth Tittensor‘s well-illustrated book Shades of Green: An Environmental and Cultural History of Sitka Spruce is available from Casemate Academic for $49.95.

She weaves together the social, ecological, and economic strands of Sitka spruce’s history and current status on two continents, with color illustrations and maps to match the variety of subject in the text. It is a story of interactions between trees and humans going back 10,000 years.

Ruth is an experienced researcher, lecturer, and writer in environmental history and lives in Scotland.

Purchase your copy of Shades of Green here>>>

To learn more about Great War aviation, visit our website here>>>

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