Lawnmowerman
Go to
http://www.geocities.com/profemery/aviation.html
Down the page - in the ACN chart section - is a chart of the 737-800 jet blast at TAKEOFF THRUST, not breakaway thrust.
Typical rules are:
maximum wind velocities which people, objects and buildings in the vicinity of an aeroplane may be subjected to must not be more than:
(a) passengers and main public areas, where passengers have to walk and people are expected to congregate . 60kph;
(b) minor public areas, where people are not expected to congregate . 80 kph;
(c) public roads . 50kph where the vehicular speed may be 80 kph or more, and . 60kph where the vehicular speed is expected to be below 80 kph.
(d) personnel working near an aeroplane . 80kph;
(e) apron equipment . generally not in excess of 80kph;
I got to tell you – even 50 kph feels like a lot more. Saw some tests recently using a hand-held anemometer from Bureau of Meteorology. Here is what was written: "Pilot was requested to use maximum power takeoff consistent with safety for the purpose of measurement. 737-300 aircraft. Maximum measured jet blast was 45 kph with instantaneous gust to 50 kph. Note that there was significant dust/sand blast, and without the benefit of the anemometer it would have felt to be a higher blast velocity than actually measured."
In normal speak – it really feels like you're being blasted even at these modest blast speeds. This test wasn't unsafe at all – just [forgive me for this] a real blast.
Boeing jet blast data for the 737-300 (and –400 series) (D6-58325-2; July 1990) shows 56 kph blast contour to go out to 155m for breakaway thrust. The 56 kph takeoff power contour goes to 579m (geez - same as what DDG was quoting - nice to find two technical documents agreeing). Back to the tests "The breakaway thrust contour is consistent with the measured maximum blast velocity, and supports the use of breakaway thrust for blast design".
So 200m would seem to be pretty reasonable. There are airports which have got public areas which are closer. Some of them stick up blast walls, some don't. Some do, and the photographers got annoyed because they can't see the aircraft. Some don't and no-one complains about the blast.
Just looked at the movie that ROB-x38 linked to. Great clip.
The van looks to be about 20m behind the tail - maybe a little less. From the 737-800 blast graph, and assuming that the United had engines wound up to takeoff thrust for the demonstration, that works out to be 300-325 km/hr jet blast. Up close like that, jet bast is a killer.
That blast speed is faster than then the winds in a bad cyclone. Explains why the van got trashed. Wonder if the van was a rental.