I had a lucky break one evening when I headed up to Paine Field for one thing, only to discover that the 777-9 development airframe was undergoing taxi tests.  I got there to see it on the Boeing ramp with cooling fans running to cools the brakes.  I was worried that I may have missed all of the action but this was not the case.  They had two more taxi trials that they ran before wrapping up.  Each time they would have a brake cooling session with the fans.

The engines are a problem at the moment so they don’t have a flight clearance.  That means that the taxi trials will not get too fast.  High speed taxi trials require a flight clearance to be available should the aircraft get airborne by accident.  These were not going to do anything like that so no lifting the nose wheel.  Just accelerate down the runway, gather data points and apply the brakes.  I wrote a piece for GAR which is here that covered the trial and there is some video below which includes a head on view of the folding wingtips being lowered into the flight position.