Message text written by INTERNET:JohnJMoran@aol.com
>I considered your suggested approach and then didn't follow through due to
two possible problems: water ingress and noise. The water problem has been
confirmed since by comments on the net. Perhaps the noise problem doesn't
exist or is not a problem when wearing a headset, but hundred mile per hour
air rushing past a hole 2 feet from one's ears caused me to avoid this
approach. Of course, the intake NACA's make a major noise contribution
too.<
A rearward facing cowl should prevent water ingress (in the air due to
airflow and on the ground due to the downward sloping rear fuselage). Noise
should be proportional to airflow which is controllable via the input
vents. Once in the cruise it should be possible to close these down to a
minimum setting.
Two other thoughts:
>A NACA extractor vent(s) farther back, connected by a skeet tube to a
hole(s)
in the baggage bulkhead. Water probably couldn't make the trip into the
cabin due to the slope involved; a small drain in the bottom of the tube
could let water out into the aft section without damage.<
Sounds good but as my fuselage has been painted I don't want to make
another NACA vent.
>NACA extractor vents under the seats. Although this is a bit higher
pressure
area, they should work and would also provide drains in the event of a
leak
---From the fuel filters under the seats. No possibility of water intake.
Noise
should be muted by the cushion, etc. Air flow would be somewhat restricted
by cushions but it should be an improvement over the current situation.
These vents can be added later since any surgery will not be obvious.<
I suspect that the extraction power of the NACA duct will not overcome the
positive pressure in that area. Input NACA ducts do not work on the roof
panel with the negative pressure there.
>One other thought in an allied area. I included 1/4 inch soundproofing
foam
in the footwells under the carpet. This seems to help considerably in
reducing heat transfer through the firewall. Didn't cover the top of the
footwell since it isn't visible -- will probably end up re-thinking that
decision now that I've seen how hot the top surface gets.<
I used 1/4" foam for the whole of the footwells and firewall except the
footwell floors. To provide both heat and noise insulation for the footwell
floor I drilled a pair of holes in the rearward facing step (one at each
end) and injected expanding foam in one hole until it emerged from the
other one.
>Just some musings on the subject. Cabin airflow in the US may be more
problematic than in the UK due to the extreme temperatures often
encountered
when visiting our southwest.
<
I am sure you are right. On the ground and during initial climb in high
summer it can get pretty hot even in the UK.
Many thanks for your inputs.
Regards
Nigel Charles
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