Gidday,
Recent certification flying of the Europa in Australia requiring carbon
monoxide testing, led to unusual findings. The aircraft in question was
fitted with modified NACA similar vents just forward of the pilots outboard
knee, and passengers. In the rear cabin bulkhead were 2x3" diameter fixed
vents. These vents proved inefficient without the addition of a small
trailing edge scoop taped externally to funnel air into the vent. No doubt
the location is not suitable for this type of vent, being in a low pressure
area When the aircraft launched for the CO2 testing the levels were only
acceptable with the NACA vents OPEN!
When they were closed the CO2 levels went "way above the required level".
Why is the obvious question? If the CO2 is entering through the NACAs it
will only come in when they are open. The exhaust pipe fitted is a standard
Europa supplied version, which it has been noted does not appear to be the
one fitted to EURO, or another Co. a/c. in recent newsletter photos. It
appears that the airflow around the mainwheel is such that the cabin will
suck exhaust fumes through the actuating lever, even though the lever was
shrouded with the "hairy nylon" sealing "stuff". This is because of the
existence of the "non-standard/approved?" rear cabin vents, or I am
presupposing that this is the case. In the message below a query was made as
to how much the rear fuselage breathes. I am a long way from this stage,
however it appears that it breathes "just fine". In fact it probably
"sucks"! The builder in question was reticent to seal the rear vents at my
suggestion on the day of testing because the CAA loaned CO2 tester had a
barometric funtion and a storage function, and he didn't want to compromise
his last run which gave marginally acceptable results.
It turns out a few days later after I wrote the above text, that the rear
vents were definitely the problem. By reaching over and covering the vents
the CO2 levels dropped to perfectly acceptable levels.
Does anyone have a venting system in place that works effectively?, or is it
a necessity to using the currently located NACA/or similar, to open your
rear vents. This of course would require the installation of closeable vents.
Any Tips??
Regards
Tony Renshaw
Builder No.236
>I don't understand how the ventilation system is intended to work on the
>Europa. That is, I note that most are fitted with NACA inlets on the sides
>for fresh air inlet but I haven't seen any standard way for air to exit the
>cabin once it gets in. Elsa had two 3" vents added to the baggage bulkhead
>but this seems minimal for good cooling in hot weather. It seems as if
>efforts are concentrated on getting air into the cabin rather than
>considering the complete path. While it is true that increasing the inlet
>area will likely increase the pressure and thus the flow, it seems that flow
>could also be increased by adding additional outlet area. Is leakage around
>the retraction and brake levers into or out of the cabin, i.e. is this the
>intended exit point?
>
>Is the location of the NACA inlets critical? Kim Prout's vents didn't satisfy
>him initially and he eventually added little extensions which protrude into
>the airstream to increase the flow -- this increases drag above that of a
>normal NACA vent of course. NACA inlets are supposed to be located at a
>relative high pressure point; where is this on the Europa?
>
>Further, once air is passed through the baggage bulkhead where does it go
>from there? I don't see any outlets specified on the plans. My understanding
>is that allowing air to escape perpendicular to the airstream through
>existing holes e.g. around flap hinges, tailwheel shaft, and servo tab drive
>would cause increased drag. Air passing out through the opening between the
>fin and rudder probably causes little drag but the openings through the rear
>bulkhead are so small that probably only a small fraction finds this path.
> Per the recent articles in "Kitplanes" I would guess than a NACA type
>extractor vent located on the fuselage top slightly aft of the wing trailing
>edge (relatively low pressure here?) might be appropriate. Has anyone tried
>this?
>
>Is the seal at the wing fairing sufficient to prevent leakage there via the
>spar openings?
>
>What about sealing of the tunnel bulkhead around the flap drive; how is this
>done? Is it necessary? Are accordion type seals as used on axel shafts of
>front wheel drive cars appropriate?
>
>Any thoughts by those who have trod this path before would be appreciated.
>
>Regards, John
>
>
|