Bleed air taken from the engines and "blown" over the underside of the wing and trailing edge flaps, therefore increasing airflow over the flaps and creating more lift. I'm sure someone can elaborate more, as I'm not an expert on exactly how they work.
Most of the blown flap mechanisms that I have read about actually blow air across the top of the wing surface and flaps. The Coanda effect causes the air to "stick" to the upper contours of the wing and flap. When the air is blown across a deflected flap, it will be vectored downwards. This makes additional lift.
I might be wrong, but I thought "blown flaps", at least as seen on the C-17, were simply flaps that are extended down behind the engines - into the exhaust stream. They thereby exert a downward force on the jet exhaust, and create more lift.
David L From United Kingdom, joined May 1999, 9577 posts, RR: 42
Reply 13, posted (8 years 1 month 1 week 1 day 6 hours ago) and read 3528 times:
Quoting 474218 (Reply 12): why do you think its landing? The flaps appear to be only about a third to half way extended, which would suggest takeoff.
I was hoping someone else would ask that! Two clues I can think of are the flap position and the attitude but I don't see those as necessarily indicating a landing. But, if it's landing, why are the trails in question extending down and back, even some way behind the aircraft?
MidEx216 From United States of America, joined Jun 2005, 655 posts, RR: 4
Reply 18, posted (8 years 1 month 1 week 1 day 1 hour ago) and read 3403 times:
Quoting Airfoilsguy (Reply 14): Otherwise the photographer took a pic of it landing then waited for everyone to deplane, fuel up, new passenger boarding, and push back in order take a pic of push back.
Those two pictures, though taken of the same airplane at the same airport on the same day, were not taken by the same person. So, chances are one person took a picture of it it's arrival, and then the other took a picture of it about an hour later pushing back for departure..
One is internally blown flaps, where the bleed air is channelled through the wing and then vented out the back. I have a feeling that this was really only common on fighters, with a centrally-mounted engine like the F-104.
The other is externally blown flaps, which Vik was describing. Interestingly, the A380 uses this concept.
By the way - check out the stall speed on this thing;