Vt(Ø) = -.166033 + 4.91844Ø - .888016Ø2 +
.054888Ø3 £ 9.20
where, Vt(Ø) is the terminal velocity of a raindrop with
diamter Ø in still air (m/s).
This shows that normal drops fall at about 5
m/s, but the speed can vary from less than 1m/s to almost 9 m/s.
Hence, if the wind speed is the same as the drop speed, the rain angle will
be 45 degrees and other angles can be calculated. however, the
aerodynamics around buildngs complicate things. Overhangs and sloped roofs
cause the wind to lift up and over buildings, thereby carrying drops over the
wall over depositing rain in front of it.
A 6' overhage for 1 storey house will protect
you from almost all storms (except for weird parts of the world) and a 2' per
storey overhang will make a huge difference. I have measure a peak roofed
one stroey building with an 8" overhang and seem an improvement of almost 50%
over blunt edged flat roofed buildings elsewhere.
So, the question is complicated!
---------------------------------------
John Straube
Civ
Eng Dept and School of Architecture
University of Waterloo
T: 519 888
4015
F: 519 888 6197
-----Original Message-----
From: owner-strawbale@crest.org [mailto:owner-strawbale@crest.org]On
Behalf Of Andrew
McD
Sent: Friday, January 28, 2000 6:44 PM
To:
strawbale@crest.org
Subject: How fast does a raindrop drop ?
Dear
All,
I have a question that has been bugging me. How big do you make the
eaves on a straw
bale house. I know everyone has different opinions, I have
had people tell me that 3'
is fine and other say that 9' is best. Does
anybody have information on the angle
rain falls at? The winds I'm interested
are the SW and NE winds at about 25-30km/hr
(say 20-25mph). Once I know the
angle I can figure the minimum porch depth, as too
bigger porch will darken
(and cool) the house. Ofcourse I may have to use clear
roofing if the porch
needs to be big or use water proofing on the bottom course
of
bales.
Andrew Mc
Springston,
NZ
