|
I can't wait for the next dinner party where someone
asks a question about Aquaplaning.
----- Original Message -----
Sent: Tuesday, May 09, 2006 8:41 AM
Subject: RE: [Aus-soaring] aquaplaning -
was Cruise Controls and Gliding Ops
The rough rule of thumb for dynamic hydroplaning (i.e.
aquaplaning) is 9 x
SQRT (Tyre pressure). If tyre pressure is in PSI, this
gives the minimum
hydroplaning speed in knots. If the car tyre pressure is
36 psi,
hydroplaning should happen above 54 nm/hr or 100 km/hr which is
roughly
consistent with the figure that Ann quoted. That's why Harvards can
fly in
formation skimming along the water and super-cubs with 18" balloon
tyres can
land on the water in Alaska and roll up to the river bank (See
video in
http://www.alexisparkinn.com/aviation_videos.htm)
The
formula is only an approximation and the tread width and tread length
also
has a bearing on the speed.
The other types of hydroplaning such as
viscous and reverted rubber (as in
wombat's worst-case scenario) happen at
lower speeds. There are many
internet references on the subject if anybody
wishes to find more
information.
Happy landings,
Patrick
Barfield
>
>A car will normally aquaplane when it is
travelling at approximately
>112 kph without cruise control on.
There is nothing you can do
>about it once it starts.
>
>It
happens often on the motorways in the UK.
>
>Ann
There is
an old formula relating aquaplaning speed in MPH to some
factor times
Square root of (tyre pressure in PSI) - but I can't
remember the factor. I
thought there was a 27 there somewhere -
perhaps SQRT of 27 x TP which
roughly fits Ann's numbers. Water depth
must also exceed ability of tread
to clear the water, so worn tyres
increase the risk. Anyone else remember
the formula?
Worst-case scenario is aquaplaning on melted rubber from
locked
wheels, which rapidly wears flats on the tyres. However if
you lock
wheels the water also accumulates more than if the wheels are
turning, and the aquaplaning speed decreases dramatically - this is
the origin of the Dunlop "Maxaret" anti-skid device which is the
precursor of ABS brakes. Both work by releasing brake pressure if one
wheel stops rotating and the others keep on turning.
Wombat
_______________________________________________
Aus-soaring
mailing list
[email protected]
To
check or change subscription details, visit:
http://lists.internode.on.net/mailman/listinfo/aus-soaring
|
_______________________________________________
Aus-soaring mailing list
[email protected]
To check or change subscription details, visit:
http://lists.internode.on.net/mailman/listinfo/aus-soaring
