Famous Case #1: gluing together the world’s largest airplane (in 1947)
The Spruce Goose was an aircraft built by the aircraft designer Howard Hughes, a very successful engineer, aircraft pilot and businessman, under a 1942 contract with the US War Department. A need had been identified at that time to transport war materiel and personnel from the United States to Great Britain when supply ships were running the risk of being sunk by German submarines.
Because of the shortage of aluminium, Hughes decided to build the aircraft mainly from wood. Wood composites were already used for their lightness and strength in smaller aircrafts and boats. Despite the name, the chosen wood was birch.
The aircraft was huge for the time, with a length of 66.65m, a wingspan of 97.54m and a height of 24.18m. It weighed 114 tons empty and 180 tons fully loaded (60 tons of cargo). It was propelled by eight radial engines. It was designed as a “flying boat” taking off and landing on water, reaching a speed of 408 km/h and a range of 4,800 km. By comparison, the first Boeing 747-100B “Jumbo Jet” measured 70.6m from tip to tail and had a wingspan of 59.6m. It weighed 162 tons empty and 333 tons loaded, thanks to its four more powerful jet engines.
The Hughes H-4 Hercules prototype aircraft was completed after the war ended so it was never made operational. Hughes personally flew it for the first time in November 1947 over a short distance at a speed of 217 km/h and an altitude of 21m off the Californian coast water. It was then retired and is now kept on display at the Evergreen Aviation Museum in McMinnville, Oregon, close to Portland.
The glue holding the wood composite together was a thermosetting urea and/or phenol-based resin capable of resisting moisture, heat, cold, bacteria and fungi and providing high structural stability. It was supplied by the Plaskon division of the Libbey-Owens-Ford Glass Company in Ohio.
The composite was made using the Duramold process. Birch piles are impregnated with resin and laminated together in a mould under heat and pressure. Weight-for-weight, the composite is stronger than aluminium.
Plaskon resin was also used to make assault boats during the Second World War.
Today 70% of urea-formaldehyde resins are used by forest industry products: particleboards, fiber boards, hardwood plywood and laminating adhesive (source: Wikipedia).