Jim Brewer wrote:
This was posted to the Cozy list by Al Wick. A report of his work with a
Subaru. Consider it another data point for liquid cooled engines.
Jim Brewer
Prior to installing the 2.5 liter(165hp) Subaru engine into my cozy, I
regarded the install as an increased risk. I made sure I made no airframe
mods that might prevent a lycoming install if it didn't pan out. I was
unable to locate anyone who had installed a 1995 or newer engine. These
newer engines have special firmware mandated by the Feds(ODBII). I was
unable to find any accurate info on how to defeat this firmware.
I have now flown with the engine for about a year. I no longer consider
this type of installation as higher risk than a Lycoming. Of course, it
would take many such installs operated for many years to know the true
risk, but preliminary info is very very promising. This engine has
performed flawlessly the entire time. These new engines constantly check
the status of the various sensors and systems. If the crank sensor fails,
it reports it and then uses the cam sensor as an alternate. This is part
of the reason the new autos are so reliable. Further, since I have a
completely stock installation, I reap the reliability benefit of all
individual components. Unfortunately, I have no hard facts to prove my
point. So........what are the facts?
Fuel consumption:
I burned avg 4.5 gph at 130 mph with my first prop. The prop was clearly
under pitched (66x66). I now have 64 diam x 86 pitch prop. Huge change. I
get 4.8 gph at 160 mph cruise at 5k ft. Prop #2 is clearly over pitched,
but I love the 33 mpg! Auto fuel. $5.40 per hour.
Performance:
I reported one outstanding unexpected performance benefit earlier. When
I pull back to idle position, it would drop like a rock. For first time
canard pilots this was fantastic. Landings were so easy, always on the
numbers. The rate of descent was similar to Cessna 150 at 30 degree flap!
Well guess what? This characteristic completely disappeared for a number
of months. When I was going ground testing I deliberately overheated the
engine many times. You'd have to be familiar with DOE testing to
understand why I flew for months with the resulting compression leak.
Anyway, this compression leak was enough to require me to make the
typical long approaches of a canard. Months later I replaced the head
gaskets, but did not achieve all of that original descent rate since I
now have much courser pitch prop. It still is very favorable however.
Prop #1 achieved 1000 fpm climb. Prop #2 is 900 fpm climb.
Negatives:
The engine is prone to trapping air in coolant. I consider this a design
defect. This model engine is particularly sensitive, as it's prone to
head warp and compression leak when overheated. The effect of all this is
fairly benign. Slow increase in coolant temp under high load conditions.
Very simple solution too. I just added a vent line from the top of engine
to the coolant resevoir.
When I finally get my prop pitch correct I'm supposed to be able to get
200 mph cruise. I don't think it's going to happen. I expect I'll achieve
190/195 mph or so. We'll see.
Would I install this engine if I had to do it over? In a heartbeat.
-al wick
Artificial intelligence in cockpit, Cozy IV powered by stock Subaru 2.5
N9032U 120+ hours on engine/airframe
It always amazes me when I hear these numbers. 4.5 gallons an hour
165 HP, 27.45 pounds per hour fuel burn. Let me give him the biggest
benefit of the doubt I can think of.... a BSFC of .40!!! 27.45 pounds
per hour divided by .40 = 68 HP. What happened to the 165 HP??
Lets say the Subaru by some miracle is as good as any diesel engine
ever invented and it has a BSFC of a wondrous 0.375. 27.45 pounds per
hour divided by .375 is 73 HP. What happened to the 165 HP?????
There is something seriously wrong here. Who is Al Wick and what does he
do for a living? I suspect he is somehow connected with selling Soob engines
for airplanes.
Paul Lamar
Paul, he's not saying 165 HP at that fuel burn. Nor is Tracy saying he's getting
190 HP at 170 mph @ 6 gph (or so).
That kind of fuel burn has little to do with the engine and a lot to do with the
airframe.
Finn
Yes but how many people cruise at 40% power? The fuel burn has a lot to do with the
HP the engine is actually generating.
Things just don't add up. We just went through all this
with Herb's airplane. It is the 165 HP claim I question mostly. The Subaru
makes a pretty good 100 HP engine. After all 2.5 liters is only
152 cubic inches. To get 165 HP out of this piston engine he is going to
have to really scream the piston engine at around the red line of say
6500 RPM with a 2.8:1 or better PSRU. Ask him what RPM he runs on
takeoff and cruise.
Here is what I think it should do with an Equivalent Flat Plate Area
of 1.8 and a real 165 HP.
Paul Lamar
OK here is new information. According to second hand information
Al Wick is running a Ross 1.85:1 gear box. I have heard about these
but they are rare. In that case Jim Wick well never see 165 HP
out of his Subaru with that PSRU ratio. Say his prop tips start to
run into the speed of sound barrier at 2800 RPM. The max RPM he will then
see on his Subaru engine will be about 5150 which is probably well below
the 165 HP level. Say he cuts the prop down a bit in diameter. At a prop speed
of 3000 it would be about 5550. Still too low for max HP out of a 152
cubic inch engine. I suspect most people are just afraid to zing
a piston engine to 6500 RPM for take off and climb out.
Paul Lamar
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