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,
My 108 hp O-235C2C LE cruises at 150 kts, about 172 mph, at 75%, which
works out to about 81 hp. I usually burn in the low 6.X range (gph) depending
on altitude, say 6.2 at 7500 MSL. If he is only going 160 mph, he should
require 80% the hp of my Lyc, [(160^3)/(172^3)] since the Cozy is basically a
Long EZ. So, .8 * 81 hp = 65 hp, pretty close to the number with a reasonable
BSFC of 0.40. No magic here, just a low HP motor, just like Burt recommended,
except even lower HP. I burn auto fuel nearly all the time, planning 7 gph for
conservatism. My calc shows my BSFC to be about 0.46, typical for a
carburated Lyc. Of course he thinks that the motor puts out what the
auto rating was, blythely unaware of the prop load curve.
How long can the Subaru put out 65 hp? Since the car load is more like
25 hp, seems like shortened life at least, with unreliablity as a destinct
possibility.
What sort of PSRU? Crank side loads?
Bill Freeman
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