Regarding this comment;
You guys are too well educated with all your
calculations. You are confusing yourselves and each other. Look at
other aircraft in the hangar, they all work well some have 3/8" and
some 1/4".
Stop your intellectual
aerobatics and get on withthe job.
The Boeing 747 racked up a lot of hours before a center fuel
tank on one blew up. Did those hours prove that the fuel system was risk free?
No.
The Concord only
had one accident, but the Concord accident
RATE, accidents per billion miles, was much worse than for the 747. Did the
accident free hours prove that the Concord
could survive a tire failure? No.
Lancairs have a much higher accident rate than the Concord.
Do those accidents prove that all engineering risk factors have been identified
and eliminated? No.
In the course of blogging for a rational energy policy I
have received countless disparaging remarks over the years. I understand that
they are a reflection on their author. Many Lancair builders are thoughtful intelligent
people with good ideas, but some are more sensitive and choose not to
participate to avoid deprecating responses.
The problem is that their missing input makes my life and
your life more dangerous than they need to be. So if you find yourself writing
a flaming comment, save yourself some embarrassment and do us all a favor by
not clicking the send button.
We have not talked much about fuel tank vent systems, but
our lives depend on them. They deserve a full analysis that includes all
possible conditions, not just straight and level.
In a worst case emergency like fire in the cockpit, I would
lower the gear and descend at near red line speed. I expect a sink rate in the
range of 6,000 10,000 fpm. If a wing tank is empty I would expect to see it
being crushed in the lower altitudes. No good choices there.
How many Lancairs have made an emergency maximum rate
descent from high altitude to sea level with an empty wing tank, any
volunteers?
I
was thinking about putting 3/8 vent line in my header tank (under construction)
but the opposite question is --- would it over pressure the tank?
Under steady state conditions the pressure depends largely
on the angle of the vent opening with respect to the wind as explained by Chris Zavatson.
The vent can act much like a pitot tube and easily
capture most if not all of the available ram pressure. Our wings show
visible deformation, even under just one psi. Lung pressure is enough to
see it.
. In flight I could see the ribs as my skins were bulging under
pressure. Attaching an airspeed indicator to the vent line indicated
almost full ram pressure. I began filing the underside until pressure
drop to just a few tenths of a psi.
Like Chris, I reduced the angle on my vents to about 10 deg to avoid excessive tank
pressure.
At 300 mph CAS, the dynamic pressure is 60.9 inches of
water, 30 psi, 4,305 pounds per square foot. We do not want that kind of
pressure trying to blow the skins off our wings. I do not know how efficient
the NACA vents on LIV wing tip vents are at converting airspeed to pressure. It
is probably highly dependent on the exact location and orientation of the vent.
I would like to see some data on that.
Any hole in your airplane should be as small as possible in
order to get it's job done.
Not true. The smallest possible hole is no hole at all. Each
hole has an optimum size based on its function and environment.