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Yep Ed!
Sure does.
The one concern of Tracy's very simple direct
system, was the transfer system - I suppose you could have a hand pump
back-up.
At this point in time, I'm thinking ( for a low
wing design) a small exterior sump tank (under the pilot), Gravity fed (
maintaining equal fuel distribution from both tanks - like a water level) with
duel pumps inside the sump tank, which is vented to one or both wing
tanks.
Being exterior it's easier to get at for maintenace
and repair, no probs with fuel in the cockpit or fumes and kept
cool.
George (down under)
George, its actually a siphon pump for a two tank
system. They use the fuel being released by the fuel pressure regulator
in one tank and run it through a restriction ( a Ventura) and it flows
through the Ventura (returning back into the main tank) it develops a low
pressure, this low pressure region of the jet is plumbed to the second
tank. The "suction" action pulls fuel from the second tank into the main
tank where the EFI pump, "Jet pump" and fuel pressure regulator are all
located. This is used as a "transfer" pump but does not require another
"electric" pump such as a facet pump that many of us use as either a boost
pump or fuel transfer pump. Interesting concept for sure - but if for some
reason something would break the "siphon" effect (say trash in the Ventura)
then NO fuel transfer from the second tank. But, then a transfer pump can
fail as well - sigh nothing never breaks {:>)
Hope this explains it well enough.
Ed A
----- Original Message -----
Sent: Monday, February 14, 2005 9:01
PM
Subject: [FlyRotary] Re: Fuel System
Design - Jet Pump
Mark/Ed,
What's a Jet pump?
George ( down under)
Good Idea, Mark
I think that people get pretty hung up and
adamant about certain things - even though they may indeed
work. While all fuel systems clearly require careful design and
construction attention, some appear to require even more scrutiny.
What I think sometimes gets folks in trouble is they "copy" a design they
have seen/hear works. However, they seldom ever copy the design
faithfully either due to space/configuration constraints - or they have an
"improvement" to it. The bottom line is the system has changed,
"Yes, Virginia, it may really matter as to whether the pickup is at the
top vs the bottom, etc. ".
Even Tracy's system can byte you if you are
not careful. You must pay attention to fuel transfer or you can
end up with the return fuel pushing out the vent of the return
tank. So while I do believe his design eliminates (or certainly
diminishes the chance of vapor lock) - you now must carefully
monitor how much fuel is in the return tank. I
believe Tracy uses a facet pump to move fuel from one tank to the
other - which even though unlikely, could fail leaving fuel
unavailable. I would have to agree though that scenario certainly
would leave you a bit more time to consider your options - than a
faltering engine on take off.
But, yes, it would appear that the "jet
pump" might indeed be a replacement for the facet pump. Interesting
concept.
Ed A
----- Original Message -----
Sent: Monday, February 14, 2005
4:40 PM
Subject: [FlyRotary] Fuel System
Design - Jet Pump
Ed,
Thanks for that excellent
article on fuel system design. In reading through it, on page 5, I
came to the description of the jet pump and had a thought (that alone is
a scary thing). I was thinking that this could be used to
eliminate the need for the facet pump in a design such as Tracy’s which
would simplify things even more than Tracy’s system already does.
Of course, as in Tracy’s design, this would eliminate
the need for the fuel selector valve too. As it was designed to
do, the Jet Pump would be powered by excess fuel from the main fuel pump
located in the left tank. Fuel from the other (right) wing tank
would be drawn into the main (left) tank by the Jet Pump. To
prevent overfilling the main tank, transfer could be controlled by a
small solenoid valve. Since you would be drawing fuel from the
right tank pretty much all the time, it may be possible to route the
return fuel to the right tank. I guess this idea could also be
used with a sump tank. Time for a sanity check.
Mark S.
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