In a message dated 3/21/2006 1:23:05 P.M. Central Standard Time,
jschredl@web.de writes:
Are you using bayonet type probes? Spark Plug Washer type CHT
sensors can yield a reading 50F higher than actual.
Johannes: The probes I
use came with the Vision Micro EPI800 system and are screwed into the
cylinder.
OK, probe style has been eliminated.
Scott, when looking
to your values I noticed an error in my values while
converting fuel consumption (used Imperial Galons ;-(( my right
fuel consumption is: 8,7 US-gal/h
Ahh, that helps. I wish I carried 43 Imperial Gallons instead of 43
US Gallons. I suppose you are using metric measurements except for
Knots.
I also see your EGT is
much lower than mine: my EGT peak at 4500ft is about 1510°F! I lean always to
the rich side at least -100°F as reccomended in the lycoming manual. Is this
correct? My probes are all 3" down from the tube
flange:
Interesting, my probes are 4" down and I am sure some of our difference is
because of that. Electronic Ignitions also reduce EGTs
somewhat.
a. Do you really mean 185 MPH or 185 Knots? The
difference would be significant in gph and cooling differential
pressures. Johannes:I
mean 185 MPH = 161 knots (IAS) and 8,7
gal/h
Ah, now the numbers make sense.
b. Is your oil cooler a Stewart-Warner (other brands are less efficient)?
How many vanes? Johannes: Stewart-Warner 6 vanes
OK, then the high oil temperatures are probably not due to poor cooling
because of the cooler brand.
c. Is your Vernatherm correctly set to send all the oil to the cooler
when the temp exceeds 180F? Oil accounts for at least 1/3rd of the engine
cooling. The vernatherm can be tested in hot water to see if it fully
shrinks (opens) at 180F. Johannes: I´m not shure. But on a hot summer day cruising at
75% oil temp does not exceed 205°F. I think is o.k. Is
it?
I think this is not OK. Even on a hot day I see 180F at cruise
speeds although I have a separate NACA inlet for oil cooler air. There are
several possibilities:
1. The cooler passages are clogged and the cooler should be flushed.
2. There is not enough air going thru the cooler vanes. Maybe you
could measure the upper and lower cooler air pressure?
3. The Vernatherm is faulty and should be replaced. Test in hot water
first. (I did have one fail on my engine)
e. Are you running at peak or lean of peak EGT? (I tend to see lower EGTs
because of the electronic ignition, but not that much lower.) Johannes: rich
side -100°F
OK, then the CHTs are too high.
I thought the
"air speed" gives me an idea about the pressure
situation...
Airspeed is not comparable, pressure is.
In Knots, 135=11.9" H2O, 65=2.8", difference = 9.1" H2O certainly enough
for cooling.
Johannes: The unit
indicated in the graph is Knots (IAS)
OK, it is better when we are talking about the same thing. While I
think the calculation above is correct, it would be best to actually measure
airspeed with the pitot in the upper cowl and the static port in the
lower. Remember to use something like a picolo tube at the open ends
to eliminate false pressures and eliminate the readings jumping up and
down. Try to find a quiet place for the pickups.
I found it interesting that your very nice cowling nose gear door
made no difference as I was just considering one to improve cooling efficiency
and thus reduce cooling drag.
Johannes: To be
honest: I did only a short flight under "bad weather conditions" and did not
notice a huge drop of EGT (as expected ;-). As soon I´ve time I will repeat
this tests using a static port and get more precisely
data!
It would be more interesting to see pressure changes (and CHT changes) with
and without the door.
The short and sharp ending of the Lancair cooling air inlets tend to have
a turbulence which makes the opening appear smaller to the air flow than it
actually is.
Johannes: I totally
agree with you! But until now I refused to touch this cowling part
because of paint design...;-)
Ahhh.... well, each lower expanding diffuser inlet is held on by
2 flat head machine screws into nutplates on the collar. the upper
one could be fastened the same way. Thus there would only be countersunk
screw heads showing.
It´s time to start flying
season!
Great.
Scott Krueger
AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL
(KARR)