Fred and others,
Finding exhaust intrusion into the cockpit is not intuitive. Your very nic
e wing gap seal is the key to many of the exhaust intrusion problems.
>From older posts on the subject:
NACA cockpit vents supplied in the kit placed low on the cockpit side, allo
w a direct inlet of exhaust gas to the pilots side. Placing the vents on o
r near the fuselage glue line helps.
Always seal the wing root area well as the stock exhaust will arc up right
into the leading edge of the wing and come in through the gap, enter the ri
gging hole and into the cockpit through the tunnel.
Mono wheel extension causes a draw behind the gear arm and can suck in exha
ust into the wheel well. Holes in the wheel well around throttle, brake, g
ear handle etc. and a cockpit that has high draw out will exacerbate the pr
oblem.
Exhaust pipes should be long enough to move the exhaust well clear of the c
ockpit inlets. (This is where my nice short exhaust stack out of the 914 l
eaves a easily seen exhaust lead trace on the fuselage, that exhaust trace
showed that during climb, exhaust gas goes from the pipe, and arcs directl
y up and over the wing root during climbs below 100 knots. My NACA cockpit
vent is right in line with the exhaust trace. As you know I have my Ultim
ate Ventilators in my windscreen corners because of it.)
You can=92t get quality air flow in the cockpit unless the cockpit is a low
pressure. The lowest pressure area is on the top of the canopy. If the c
ockpit seals are not tight, this will lower the air pressure in the cockpit
improving the draw of air into the cockpit and through the wheel well to c
ockpit holes.
The rear fuselage is generally a lower pressure area. I put vents or stand
offs the D panel cover to exhaust air out of the cockpit and improve press
ure vent performance. At low speed or high angles of attack the suction of
air at the wing root fillet is quite high.
Jabiru exhaust pipes coming right out of the center cowl will, at high angl
es of attack, inject exhaust into the wheel well with the mono gear down.
Pipes must be angled to clear the mono trailer arm for transport anyway so
move the Jabiru pipes outboard and exhaust intrusion can be reduced also.
Trigear aircraft built with a sealed wheel well, rarely have an exhaust int
rusion problem unless the cockpit vents are in line with the exhaust, or th
e wing gap seals are leaky.
Pay attention to the hole behind the wing root right where the flap and roo
t come together. Looking into the wing root from behind the wing will show
a direct path to the rigging hole and a direct cockpit gas entry. (I=92ve
never had a problem with this hole if the gap all around the wing fillet i
s sealed tightly.)
Mono wheels in the retracted position tend to have a large bubble of air ca
using pressure in the wheel well that makes for a high flow of air through
the gear, brake and throttle slots in the wheel well making for a cold cock
pit at altitude. Keep the gaps around the main wheel as small as possible.
Silicone cowl seal or similar will reduce the gap in these slots and help
keep dirt, grass and cold air out of the cockpit. (Exhaust also I guess.)
Just archive searching.
Regards,
Bud Yerly
Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Window
s 10
From: Fred Klein<mailto:fklein@orcasonline.com>
Sent: Friday, September 15, 2017 3:42 PM
Subject: Re: Europa-List: Re: VENTILATION IN FLIGHT & POSITIVE CABIN PRESSU
RE
On Sep 14, 2017, at 11:38 AM, Brian Davies <brian.davies44@gmail.com<mailto
:brian.davies44@gmail.com>> wrote:
I had a CO problem about a year ago and carried out some investigation. Th
e big clue, found by using a CO meter, was that the CO doubled when the fla
ps were down. I talked to Andy Draper who said the exhaust gases could ent
er via the flap slots and travel forwards through the tunnel and into the c
ockpit via the various control slots. I resisted cleaning my aircraft for
a period and traced exhaust stains along the fuselage that travelled to the
(Trigear) leg/fuse join and up to the flap slot.
These enhanced wing root fairings cover the flap slot=85
Also=85one of the reasons my bird has yet to fly...
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