The wrong stuff

Modern simulation techniques have revealed that one of Man’s greatest achievements very nearly failed to get off the ground. Jon Excell reports.

On 17 December 1903, Wilbur and Orville Wright successfully flew their aircraft, The Wright Flyer, at KittyHawk, North Carolina, ushering in the era of powered flight.

However, a study by software company Fluent has revealed that despite their undoubted engineering expertise, the Wright brothers’ achievement maynot have happened but for a sizeable slice of luck.

The study, carried out by software engineer Dr. Christophe Heimcke, was commissioned by the American Institute of Aeronautics and Astronautics – one of a number of teams that recently launched replica Wright Flyers to commemorate the centenary of powered flight.

The AIAA, which based its replica on blueprints from Washington’s Smithsonian Institute, asked Fluent if it could help with the safety analysis of the plane by modelling the airflow around its propellers.

The laminated spruce propellers used for the 1903 flight were hand carved by Wilbur during the winter of 1902/3, while Orville worked on the engine.

Hiemcke’s simulations showed that the blades performed very well for a wide range of operating speeds. However, although his studies confirmed the efficiency of the propeller they also indicated that the brothers were flying exceptionally close to stall conditions.

‘The combined propeller performance and motor performance at that time were just enough to allow the plane to fly a few miles an hour above stall speed,’ he said.

The Wright Flyer was actually 75lbs heavier than Wilbur and Orville had anticipated, which meant that thepredicted propeller performance would not have been sufficient to enable them to fly.

According to Heimcke it was only thanks to a combination of favourable wind conditions and the fact that the brothers had underestimated the performance of the propeller that they were successful at all.

Another often overlooked factor was the skill of the pilots, and Heimcke said that keeping the Wright Flyer airborne would have been something of a balancing act.

‘If you had a wind loss down you went; if you went into a bank and the bank got too steep then you would stall. That stall danger in conjunction with the difficulty of control made for pretty difficult flying. If you watch the now-famous film of the flight you see the pilot’s hand continually going up and down with the elevator control.’

Heimcke explained that the AIAA engineers used the results of his simulations to reduce the stall risk. He said the main thing they wanted to know was whether the propeller would be able to cope with being spun faster.

‘We provided aerodynamic pressures and aerodynamic shear stresses so that they could conduct FEA to see whether the propeller would hold up.’

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