Farnborough Airshow kicked off with the usual impressive aerial acrobatics in the southern town of England, but national budgets are a cause of concern for the exhibitors. While defence companies can recreate realistic flying situations, they cannot simulate good business conditions, and these are worrying times for some of the world's biggest weapons makers. Sikorsky make the famous Black Hawk helicopters relied on by the US military. Yet the company executives are trying no to rely on them too much in return. Russia is facing even greater challenges. The state arms exporter, Rosoboronexport, has a big presence in Farborough. It's presence is considered vital for its business, as recent geopolitical events have closed off some of its most reliable markets. Rich Middle Eastern and Asian countries are taking up some of the slack left by dwindling US and European defence budgets, but the fight for international business will only intensify over the coming years. Al Jazeera's Rory Challands reports from Farnborough, southern England.