I decided against using the prefabricated NACA vents for three reasons.
Firstly as indicated by the recent emails the quality is poor.
Secondly the access for adjustment is poor.
Thirdly there is no facility for adjusting direction of flow hence the
problem of cold knees.
Although a fixed vent produces a small amount of extra drag when not in
use
it is easier to attach a car type flow and direction controller on the
inside. Having looked over a car scrapyard I chose ventilator outlets from
a
Volvo 340 as these give both flow and direction control whilst not being
too
large. If the fixed NACA vent flap is inset by the right amount it will
match up perfectly with the flow control flap when it is fully open. If
the
NACA vent is cut as far forward as practical, the face of the vent outlet
is
flush with the panel.
On new build it is easy to make a fixed NACA vent by cutting the shape out
---From the skin except the forward end, flexing inwards and glassing in top
and bottom
side faces.
Although these vents work well my main ventilation control is via an
overhead ventilator with a pair of eyeball vents. This ensures a flow of
cool air to the face.
Nigel Charles
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