That link provided by OverRun raises a big question in my mind. I hope this isn't digressing too much.
If the jet blast is coming out the back of the engine at somwhere around 350 km/h (190 kt) at say 98% N1 (typical number for our 800's) how do the engines produce any thrust when the aircraft is flying at or above 190 kt? Surly if the aircraft is passing through the air at say 250 kt or even 300 kt, it would be imposible for the engines to be doing any work on the air. Or another way of looking at it, if the jet blast comes out the back of the engine at 190 kt, and the jet engine has a forward speed of 300 kt, the air passing through the engine, enters the front of the engine with zero velocity, and comes out the back with a FORWARD velocity of 110 kt (300 kt - 190 kt). That doesn't make any sense.
Or another analogy. While a boat is tied to a warf, it's outboard motor can push water out the back at 20 kt. There is no way that boat can reach speeds of 30 kt!!. The closer the boat gets to 20 kts across the water, the closer the propeller gets to achieving zero work on the water (that is, applying force over a distance).
Can anyone enlighten me?
Thanks.