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Hi Kevin,
Looks like you have found the
restriction.
I have to confess that I've never had problems with
paper element type fuel filters. AS someone else said (Georges I
think), the early EFI filters had banjo fittings each end that took
usually an M12 or M14 banjo bolt with a 8 mm hole. Ideally,
they need to be mounted vertically to avoid an airlock, but should be more
than adequate for your purposes. I also have to confess that I've never
had trouble with the ordinary plastic cased paper fuel filters either, as
long as they are changed regularly. The 3/8" bore ones would be the
GO.
I use SpeedFlow stuff (I'm sure Earl's will have
similar stuff) on the race cars which take a -10 fitting.
See:
The pix show the system that feeds a 340 BHP
bridgeport. No pix of the actual filter unfortunately. There is
a Speedflow filter unit before the pump (out of view), and there is
another large EFI high pressure filter (off a Toyota I think from
memory) up in the engine bay.
Someone also mentioned that he uses a diesel type
fuel filter on his aircraft. I've also used them on both road and race
cars. You can get small ones off a Daihatsu that will fit on a Mazda oil
filter pedestal thread. This can then be mounted on a bracket and supply
clean fuel to the lift pump. I've done this on several RX7 race & road
cars (sorry no pix at the moment).
You will also need some sort of water trap
(gascolator?) in your fuel system that is able to be drained before each
flight. It should be the lowest point in the fuel system, and
preferably before the actual filter. Water is not usually an issue in cars
these days, but is an ever present danger in aircraft. LOTS of
people come to grief each year because of carelessness in checking for water in
the fuel system.
However, apart from the water issue,
the all important thing is to concentrate on FLOW, not pressure.
Once you do the mods, double check your open head flow AT the carby,
and make sure it is 25% more than you need for the power of your engine (as per
BSFC calcs I mentioned in a previous email).
15 (US?) gal per hours doesn't seem quite enough
for 150 - 160 BHP. Let's "run the numbers":
1 US Gallon = 3.79 Litres (approx). Assuming
a fuel density of 0.7, that's 2.63 Kg = * 2.2 = 5.84 Lbs of fuel.
So 15 US gallons / Hr = 5.84 * 15 = 87.55 Lbs per
hour.
Assume 0.55 BSFC (Lbs / Hr / BHP) = 159.2 BHP
approx.
Assume 0.60 (WOT & FULL Rich) = 146.0 BHP
approx.
So your fuel flow is at the VERY BEST just
marginal. You have NO 25% flow margin, so ANY restriction
inside the carb, or the SLIGHTEST clogging of a filter or a
silghtly worse BSFC, or even just running the carb "Full Rich"
etc will cause your engine to run slightly lean at WOT (which is what you
are currently experiencing).
You need a minimum of 15 * 1.25 = around 18.5 US
Gallons /Hr (or preferably more) to have anywhere near some safety margin.
I don't think anyone on the list wants to
hear about you having a gliding experience, or burn your valves or melt
your pistons, or worse, ending up like poor old Paul Conner ... As
Al P Wick just said:
"Please investigate thoroughly and resist
assumptions. Your life depends on it."
Cheers mate,
Leon
(Excess Fuel Flow capacity is always
good, and even more Fuel Flow capacity is always better,
and too much Fuel Flow capacity is almost but probably never just quite
enough)
----- Original Message -----
Sent: Friday, July 29, 2005 2:43 AM
Subject: [FlyRotary] fuel filter
question
I suspect that my engine problems stem
from a design flaw, rather than a blockage. I normally never run my
engine full power, full rich, but have been while breaking in the new
rings. even leaning the engine a few notches prevents my problem, so it
never arose in the past. my auto fuel filters are on the "suck" side,
between the tanks and the selector valve. they are small, glass see-thru
mesh filters. I realize now that all the fuel passes thru a pair of like
1/8" holes from a common 1/4" passage. I also see that the facet pump,
despite pumping 15+ gals / hr with no head pressure, will only produce 1.75
lbs pressure when attached to the carb and bypassing the manual
pump.
my question - I was
told not to use a fuel injection filter on a low pressure system like
mine. I would like to keep the filters where they are rather than moving
them to the engine compartment, since they filter stuff ahead of my flow meter
and pumps. I like how they fit along the wing spar below my knees.
I had problems with the replaceable filters shedding fibers into the carb,
which is why I changed to the mesh filters. does anyone know what
I should be using?
I plan to do more
testing this weekend if my wife will let me drive her car("no, I'm not feeling
sleepy :-)" to get to the airport.
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