Rombac111 From Uruguay, joined Jul 1999, 49 posts, RR: 0 Posted (14 years 8 months 2 weeks 4 days 14 hours ago) and read 1003 times:
Hi all !
Hey... yesterday i was at a known of mine, that is located under the final approach route for our RWY 06 at Carrasco Intl. in Uruguay.
Fortunately i could see two B-737-200 on arrival and it called my attention the following (hope to explain it clear in english for you): from the wingtips, something like steam/vapour was coming out... i know they land at more than 200 km/h, but the sky was clear, clouds were quite higher than the aircraft height... no clouds there... and i do not think they have any exhaust pipes near the wingtips... could somebody tell me what was that ? Both 732s did the same, and it was for about 150-200 mts no more...
As you can see from these photos, this is a common occurence when the amount of moisture in the air is high enough. You'll note that the aircraft in these photos linked below (757, DC10, DC11, 737) all share a common trait--the vapor starts where the outboard edge of the extended trailing edge flap(s) is next to the trailing edge of the wing.
I'm not an aerodynamic engineer, so I can't provide the textbook description, but my own understanding is that as the airflow above *and* below the wing come back together at the trailing edge, but that with flaps *extended* the trailing edges are now in two different places. It appears that the boundry between these two regions creates enough low pressure to the point where the moisture is visible in high humidity conditions, much like the visible vapor one sometimes sees on the *tops* of the wings in similar conditions during takeoffs.
if you want to know why condensation takes place, please study the "Ranke-Hiltsch Effect". You'll find it on good search engines.
Ranke and Hiltsch had discovered that a swirl separates in cold (center) and warm (circumference) air.
good luck in trying to understand