Mallard 75 An A4 Pacific Steam Locomotive at 126 . What did it look like

As a personal tribute to a legendary achievement exactly 75 years ago, I thought it appropriate to indulge in this little demonstration. Using the footage I captured a couple of weeks ago and adjusting replay speed over a measured 1 mile to 28.6 seconds, we can re-create the image of 60009 Union of South Africa running at an apparent 126 . As a comparison I have included images of simulated 75 and 90 . to demonstrate just how impressive a speed of . (to be exact) is for a steam locomotive. The removed streamlining of the B.R. form of A4 shows the motion fully exposed and demonstrates that the limiting factors for speed on a conventional steam locomotive are not just that of overcoming drag but (and maybe more importantly) the survival of motion bearings trying to cope with the extreme out-of-balance forces at such high rotational accelerations. In fact, aniseed was mixed in with the bearing lubricating oil on Mallards record run of 3rd July 1938 in order to produce a “nasal“ wa