ggower_99(at)yahoo.com
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 Posted: Wed Mar 15, 2006 10:17 pm Post subject: fuel filters and such (Experienced members in the list) |
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Hello Matt and all the new member/builders of the list.
I will try to make this mail short but with good advise.
The list archives is a Trassure for all of us that build a ZAC (or any other) airplane. I have been in this list for a while, and have learn a lot, also have shared some of my experience over my aviation and homebuilt life.
Here we can find advice from some real Experienced members (Some dont like to be named Experts:) this can make our building experience more easy and in some times could save our life.
In the area of fuel pumps, Frank really knows what he is talking about, Pay atention of what he says.
Thanks a lot to all the Experienced builders in this list(s). and enjoy this great (flame free  list and brotherhood.
Saludos
Gary Gower
701 912S Flying from Chapala, Mexico
Building a 601 XL.
"Hinde, Frank George (Corvallis)" <frank.hinde(at)hp.com> wrote:
I think more importantly you need to understand the principles of vapour
lock, then decide how much risk you want to take.
As vapour lock can stop your engine dead on take off on a hot day, my
system is designed so that VL is an almost impossibility. Note that
mogas will boil more easily than 100LL.
The problem with this system is that it means your fuel pumps will be as
close to the tanks as possible (assuming you have wing tanks only). This
is the reason all cars these days have the pump back there.
This system however means that each pump will suck from each tank which
means the reserve really has to be held in each tank. The upside is that
it is a delightfully simple system in that to switch tanks you simple
turn the other pump on and this one off...if you see what I mean.
You don't mention whether you have a mechanical pump or not...Personally
I hate mechanical pumps (or electric pumps on the engine side of the
firewall) because they both suck on the fuel and are in the hottest
place on the airplane. Both prime reasons to cause VL. This is why
"Proper" FI airplanes have the electric boost pump in the cabin down low
to pressurise the inlet to the mech pump.
So now you know that a pump that sucks on warm fuel is the big danger
now you have to decide what you want to do knowing that "suck" and "hot"
are bad.
Now you do have some dihedral...You can put both electric pumps
(assuming no mechanical pump) in the middle of the cabin and have a
selector valve feeding the inlet from each tank. I strongly recommend
you keep the lines feeding from the tanks to the inlet to the pump at
3/8's and preferably aluminium. (less pressure drop)...No other
restrictions on the inlet side to the pumps if you can possibly avoid
them. Tank strainers are OK but no other filters, not that they will
cause you problems but they certainly could.
I would personally avoid having the gascolator upstream of the
pumps...if it devlops a leak it will likely such air into the pump and
air lock it...which is almost as bad as VL.
Gascolators work just fine on the discharge side of the facet fuel
pumps.
Do an archive search on this issue, thee is MUCH discussion on this one
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