Welcome back to The Daily Aviation for a feature on the most technologically advanced heavy lift aircraft in the US Air Force, the C-17 Globemaster III, which is capable of delivering more than 170,000 pounds of cargo to the four corners of the globe.
That's a vortex, and it's a common occurrence on all turbofans. As others pointed out, it has nothing to do with forward or reverse thrust, since the air is still being ingested from the front of the intake. Former Turbofan Test Engineer for Rolls-Royce at Stennis Space Center from 2007-2012.
The Tornado has nothing to do with Reverse Thrust, those tornados are formed when there isn't enough wind blowing into the engine when it takes power, which would be the case when the aircraft is moving backwards or when wind is blowing from behind the aircraft into the exhaust. When running Gas Turbine engines while standing still you always want the aircraft facing the wind to prevent this type of thing happening. I'd also like to add that almost all airplanes this size including commercial airliners have thrust reversers and it isn't anything special...
The engines are 40,000 HP vacuum cleaners. This is why they do FOD checks on carriers, as anything that gets loose is picked up. The only aircraft that don't get this are those with rear intake over-wing inlets, and they can suck ice from the main wing.
