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Glad to hear your
incident did nothing more than re-arrange your seat cushion. I have never
had a situation of impending vapor lock (such as caviation of the EFI pumps)
that turning on the boost pump did not resolve. I do however, have my fuel
pumps and header tank shielded with a fiberglass box covered with aluminum
foil. I also have an NACA duct funneling outside air to the box. So
I think your plans would certainly help the situation. Plus, you may have
a bit more heat under you cowl what with the turbocharger. Other than my
header pipe which do a 90 deg bend and out from the cowl - nothing much of
a heat producer, also I do have louvers on both sides as well as a rather large
opening on the bottom.
Hi
Ed;
Fortunately our airport is very
ideal for flight testing, with 3 separate, long runways and a relatively low
amount of traffic. I try to do my flights when there is little traffic and I
always maintain gliding distance to a runway. One of the benefits of the
turbocharger and the constant speed IVO prop is that I can reach circuit height
before I reach the end of the runway, allowing me to maintain gliding distance
to at least one of the 6 runways at all times and I've practiced this as well.
I'm aware of the "oh shit, this can't really be happening to me" time lag that
happens before pilots take action, but I feel I was ready as I run these
scenarios through my mind, before every flight, so it was an automatic
reaction to quickly assess my options and take the best one. While I'm pleased
with the way I handled it, I'm very angry with myself for not recognizing the
vapour press situation developing sooner.
As you may recall, we discussed your
fuel system off-line way back when I was still developing mine and I felt that a
larger header tank located aft of the firewall would reduce or eliminate the
vapour issues while adding the benefit of a useable reserve. As I've just
demonstrated, this is not the case. I wasn't aware that your system is shielded,
so this reaffirms my decision to do this as well. The turbo certainly adds to
the heat creating problems, which is ironic in that it also allows me to quickly
climb to a safe altitude in case of problems, which it is adding to... hmmmnn...
it's a vicious circle.
I had earlier considered adding
louvers to the side as you have, but a post from someone indicating that louvers
are considered to be very high in drag, held off my decision to proceed, but I'm
again considering this. Does anybody know of a source for an off-the-shelf
louver?
I had
considered a fuel line cooler (which they do make), but unless you are funneling
cool outside air to it (and no inside hot air) then it could make the problem
worst by picking up more heat from the hotter under the cowl air. In any
case, I have not tried a fuel line cooler, but would think that provided with
cooling air, its couldn't hurt.
I think that by ducting cool air through a fuel cooler
at the inlet to the shroud around the fuel components, it should adequately cool
the fuel without significantly heating the cooling air allowing plenty of
cooling for the pumps and filters. I just have to find a small enough cooler to
do the job. I also use a gascolator on one of my fuel lines, which I'm
considering removing. I have water drains on each tank and a sump with a drain
on my header tank, so I've never seen a single drop of water when draining my
gascolator.
How large is your cooling duct to your shroud over the fuel
pumps? Where do you have your inlet for this cooling air? I originally
considered ducting from the rad inlets, but I don't want to be stealing any of
this cooling air, so am considering a small NACA duct on the
side.
Leon has sent me an off-line reply with a few additional
suggestions as well. I'm considering replumbing the header tank vent line (which
is normally closed), back to one of the wing tanks, instead of to the vent line
header. This would allow the boost pump to continually recirc cool fuel to the
header tank rather than just pressurizing it. This would also allow me to close
this vent/recirc line when I do want to pressurize the header
tank.
The reason that I originally opted to use a header tank was
it seemed at first to be the simplest way to manage 6 fuel tanks without the
hassle of returning to a single tank and transferring fuel as others have done.
I've now found that it requires much more management than anticipated and is
becoming much more complicated. If I was starting over again, I would
certainly reconsider this idea.
Thanks
for any & all input.
S. Todd Bartrim
Turbo 13B RV-9Endurance
C-FSTB
http://www3.telus.net/haywire/RV-9/C-FSTB.htm
"Whatever you vividly imagine, Ardently desire, Sincerely believe in,
Enthusiastically act upon, Must inevitably come to pass".
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