The Murphy Builders Site

Ben, what is that underneath Ken's Rebel...looks like some sort of air
induction scoop. It's a great photo. cw

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
bransom@dcsol.com
Sent: Tuesday, January 29, 2008 9:50 AM
To: rebel-builders@dcsol.com
Subject: [rebel-builders] Contact! magazine, Ken Lehman cover article

I was thrilled to see a pretty yellow Rebel on the cover of Contact!
magazine #91 in the mail yesterday. It features Ken's EJ-22 Subaru Rebel
and is great to see some of the detail and the article gives a clue to how
much Ken has accomplished. (Contact is maybe my favorite aviation
magazine, and obviously Rebel's are #1, so how can you go wrong?) Thanks a
lot Ken.
http://www.contactmagazine.com

There is also a brief article on alternatives to the 912/914 power output
range -- looks like Ram Engines (Sub EA-81) and Raven (Suziki) being the
current active suppliers. Definitely not everyone's cup of tea, but ...

Ken, I'm wondering what if any consideration you've given to an in-flight
adjustable prop? That could get you the best of cruise, climb, smooth
running, and the fuel economy you mention at the top of the article.

-Ben



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Radiator for the liquid cooling :)
Ken

Craig Walls wrote:

Ben, what is that underneath Ken's Rebel...looks like some sort of air
induction scoop. It's a great photo. cw

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Thanks Ben. I haven't seen the edited version of the article yet but
that's cool that we got a Rebel on the cover.

While I left a spot on the panel for a variable pitch control, I am of
the opinion that there is little to be gained for me unless perhaps I
also increased the psru ratio substantially. I'm after reliability
rather than max performance though. Chuck Kondas found that with his
turbo he needed a coarse pitch to absorb the takeoff power and -that
coarse pitch was pretty close to ideal for cruising at 100 mph or so. I
figure I'm in a similar situation as I normally cruise at much less than
takeoff power and certainly less than the 75% that many Lyc's cruise at.
I'm still planning to use a bit of nitrous (instead of a turbo) on
floats so again I should still be in a similar situation as Chuck. It
would certainly drop the cruise burn a bit to run lower rpm and higher
manifold pressure so I am curious whether Warp will ever bring an
in-flight adjustable to market but don't really think it is worth the
complication for me. Non certified in-flight adjustables have had their
share of problems.

I also have reason to believe that I can pick up about 10% more power
just by putting an intake scoop on the upper cowl door to drop the
combustion air intake by 25 or so degrees C. I hate to butcher the door
though and I don't really need any more power on wheels ...

Ken

bransom@dcsol.com wrote:

I was thrilled to see a pretty yellow Rebel on the cover of Contact!
magazine #91 in the mail yesterday. It features Ken's EJ-22 Subaru Rebel
and is great to see some of the detail and the article gives a clue to how
much Ken has accomplished. (Contact is maybe my favorite aviation
magazine, and obviously Rebel's are #1, so how can you go wrong?) Thanks a
lot Ken.
http://www.contactmagazine.com

There is also a brief article on alternatives to the 912/914 power output
range -- looks like Ram Engines (Sub EA-81) and Raven (Suziki) being the
current active suppliers. Definitely not everyone's cup of tea, but ...

Ken, I'm wondering what if any consideration you've given to an in-flight
adjustable prop? That could get you the best of cruise, climb, smooth
running, and the fuel economy you mention at the top of the article.

-Ben



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<clip>

turbo he needed a coarse pitch to absorb the takeoff power and -that
coarse pitch was pretty close to ideal for cruising at 100 mph or so. I
figure I'm in a similar situation as I normally cruise at much less than
takeoff power and certainly less than the 75% that many Lyc's cruise at.

I take it you mean you also cruise slower than you could, i.e. higher
throttle and power is available? What is your typical cruise speed and rpm
for that 4.5 gph?
-Ben



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Yes exactly. I generally loaf along at about 85 knots/100 mph at
4.5gph. That is about 4200 engine rpm and 21 inches MAP when heavy.
(Probably only about 60 hp.) Solo it was going that fast at 3900rpm this
week with one notch of reflex.

She's quite happy to go 100 knots at about 4400 rpm and occasionally I
wind it up to about 110 for spacing in the circuit which is maybe 4700
rpm. I usually only see about 4400 to 4500 during takeoff and climb
which corresponds to peak torque and an estimated 120 hp. Peak power is
about 140 hp. at around 5400rpm but I choose not to go there although
many guys do with this ej22 engine.

In theory cruising at full throttle and controlling rpm with a variable
pitch prop reduces pumping losses and increases efficiency but the gains
may be offset due to an enriched mixture and other complications.

Ken

bransom@dcsol.com wrote:

<clip>

turbo he needed a coarse pitch to absorb the takeoff power and -that
coarse pitch was pretty close to ideal for cruising at 100 mph or so. I
figure I'm in a similar situation as I normally cruise at much less than
takeoff power and certainly less than the 75% that many Lyc's cruise at.

I take it you mean you also cruise slower than you could, i.e. higher
throttle and power is available? What is your typical cruise speed and rpm
for that 4.5 gph?
-Ben

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On 1/30/2008 7:03 PM, klehman@albedo.net wrote to rebel-builders:
<...clip>

In theory cruising at full throttle and controlling rpm with a variable
pitch prop reduces pumping losses and increases efficiency but the gains
may be offset due to an enriched mixture and other complications.
Ken

I heard somewhere else that stock Subaru ECUs go to full rich at full
throttle. Is this why you say ' ..may be offset due to an enriched
mixture...' ?
-Ben



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Yes stock ecu's (computers) target 14.7:1 stoichmetric air:fuel ratio to
keep the CAT converter happy at road cruising power levels and that is
historically the purpose of the Oxygen sensor. However it usually only
takes a little more throttle to make them richen up for better power and
driveability. I see the EGT drop at least 20 C. as I approach full
throttle. Many ecu's richen even sooner.

Some guys have tried reducing fuel pressure to lean while cruising at
full throttle but then you really should restore normal pressure for
takeoff and max power situations. Without a CAT, there is no good reason
to even cruise at stoich though, so small gains are possible by leaning
further even if you are not cruising at full throttle. (That would
correspond to running a balanced Lycoming Lean of Peak.) Some of the
newer ecu's actually use "wide band" oxygen sensors and improved CAT's
to target variable fuel/air ratios. Anyway now we are starting to
justify an aftermarket programmable ecu. However many aftermarket ecu's
do not have the fail safe abilities of stock units. Unfortunately
modern stock ecu's do so many other "car" and emission things that they
are getting very difficult to use anyway. Bottom line is that there is
little performance or economic gain for me to justify the additional
complication of an in-fight adjustable prop.

Other complications include the gearbox. Running full throttle near
torque peak rpm) maximizes power pulses and stresses. Most psru's will
last longer at higher rpm and less stress. Especially for 4 cylinder 4
stroke engines that have a negative torque pulse between each power stroke.

Ken

bransom@dcsol.com wrote:

On 1/30/2008 7:03 PM, klehman@albedo.net wrote to rebel-builders:
<...clip>

In theory cruising at full throttle and controlling rpm with a variable
pitch prop reduces pumping losses and increases efficiency but the gains
may be offset due to an enriched mixture and other complications.
Ken

I heard somewhere else that stock Subaru ECUs go to full rich at full
throttle. Is this why you say ' ..may be offset due to an enriched
mixture...' ?
-Ben



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Ken, thanks for fleshing this out. With so many after market ECUs, both
for car/motorcycle enthusiasts as well as turn-key airplane auto
conversions, it seems like not necessarily the weak link in the auto
conversion consideration. Not just that they are common, but from all the
reading I've done I can't recall much along the lines of ECU's being the
cause of engine trouble or failure. That said, I'd feel even further out
on the edge to go non-stock ECU if I were doing my own conversion.
-Ben

On 1/31/2008 5:14 AM, klehman@albedo.net wrote to rebel-builders:

Yes stock ecu's (computers) target 14.7:1 stoichmetric air:fuel ratio to
keep the CAT converter happy at road cruising power levels and that is
historically the purpose of the Oxygen sensor. However it usually only
takes a little more throttle to make them richen up for better power and
driveability. I see the EGT drop at least 20 C. as I approach full
throttle. Many ecu's richen even sooner.

Some guys have tried reducing fuel pressure to lean while cruising at
full throttle but then you really should restore normal pressure for
takeoff and max power situations. Without a CAT, there is no good reason
to even cruise at stoich though, so small gains are possible by leaning
further even if you are not cruising at full throttle. (That would
correspond to running a balanced Lycoming Lean of Peak.) Some of the
newer ecu's actually use "wide band" oxygen sensors and improved CAT's
to target variable fuel/air ratios. Anyway now we are starting to
justify an aftermarket programmable ecu. However many aftermarket ecu's
do not have the fail safe abilities of stock units. Unfortunately
modern stock ecu's do so many other "car" and emission things that they
are getting very difficult to use anyway. Bottom line is that there is
little performance or economic gain for me to justify the additional
complication of an in-fight adjustable prop.

Other complications include the gearbox. Running full throttle near
torque peak rpm) maximizes power pulses and stresses. Most psru's will
last longer at higher rpm and less stress. Especially for 4 cylinder 4
stroke engines that have a negative torque pulse between each power stroke.

Ken

bransom@dcsol.com wrote:

On 1/30/2008 7:03 PM, klehman@albedo.net wrote to rebel-builders:
<...clip>

In theory cruising at full throttle and controlling rpm with a variable
pitch prop reduces pumping losses and increases efficiency but the gains
may be offset due to an enriched mixture and other complications.
Ken

I heard somewhere else that stock Subaru ECUs go to full rich at full
throttle. Is this why you say ' ..may be offset due to an enriched
mixture...' ?
-Ben



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