The Brontanax drone was unveiled at the Farnborough International Airshow on July 22 - Andrew Matthews/PAAn "all-British" autonomous fighter jet will use an American engine following a clash between defence giants BAE Systems and Rolls-Royce over costs, The Telegraph can reveal. The Brontanax drone, which was unveiled last week, is being pitched as the sole domestic candidate for the RAF's "loyal wingman" drone programme. A demonstrator is being developed by BAE with support from a consortium of more than 70 British firms. However, Rolls – long a stalwart of domestic fighter jet programmes – has not been included following a dispute between the companies over pricing, it is understood. But in talks about the Brontanax demonstrator, Rolls was seen to not "lean in" fully to the project and its engine was deemed too expensive by BAE, according to a person briefed on the situation.