Listen up Grasshopper,
1. If the engine is carbureted, you may be out of luck as
there is no way to control the F/A ratio in each cylinder. However, you
can try step 3 for informational purposes if you have the equipment listed in
step 2.
2. You must have an engine monitor and sensors that display (or record) EGT
for each Cyl and the fuel flow.
3. Injected engines must perform the GAMI lean test before a "next
step." At 75% power (that means at or above 6500 MSL, 7500 if using ram
air and KIAS is less than 190, or higher), WOT (necessary to control air
distribution when running LOP) .
a. Starting sufficiently ROP, lean in small steps
(less than .3 gph) and record the EGT for each step for Cyl 1. Continue
past peak EGT for that Cyl for about 50F degrees LOP or until ugly
roughness.
b. repeat "a" for each cylinder.
c. Check the gph for each cyl peak EGT. If
the spread in .3 gph or less, you are done and you should be able to run LOP
20F, 30F, 40F depending on the spread).
4. If the spread is GT .3 gph, you must fix the A/F
ratio. A cheap way to start is to provide equal air pressure to each
injector - a wee plenum distribution to each shrouded injector) and repeat the
Lean Test.
5. if the lean test shows the proper spread, go fly LOP (less than
75% power)...................
6. If the lean test fails (GT .3 gph spread), consider different sized
injector nozzles (either GAMI or others) for the rich/lean cyls.
Grayhawk can fly a 320 at 8500 MSL, ROP, 9.5 gph and see 195 KTAS
or LOP, 7.5 gph and 186 KTAS (all things being equal) thus eliminating a fuel
stop at 3.5 hours cause he could go another hour. 195 x 3.5 = 683, 186 x 4.5 =
837, 837/195 = 4.3 + 1 (re-fuel stop time) = 5.3 Duh!
Grayhawk
In a message dated 8/24/2009 2:40:57 P.M. Central Daylight Time,
Tim@5000feet.com writes:
Hey
guys, I am remembering a long time ago reading about
how the air pressure
surrounding the injector can affect how
well the injector works. If
I'm not mistaken, turbocharged
engines even use some pressure manifold
around the injector
to accommodate for the increased Manifold
Pressure.
What gets me curious is that I'm having a discussion with
some
folks right now who are all having problems running Lean of
Peak
and their engines stumble before they get to peak EGT. Between
the
group, there are a variety of ignitions such as 2 mags
or 1 lightspeed and
one mag, and varieties such as 8.5:1,
9:1, and 10:1 compression ratios, but
the one constant is that
they all have what is purported to be a more
effective cowl...
the Sam James cowl with a plenum. So I'm wondering
if the
knowledge base some of you have would provide any insight
to the
issue. I originally was worried that the 10:1 pistons
might make LOP
operation harder to accomplish, but perhaps
there is just too much air
pressure on the outside of the
injector? The cowl is known to often
have too little exit
area, so it could be that the pressure differential
is
even too high between the top and bottom half of the
cowl.
Any
insight you can give?
Thanks,
Tim
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