|The Sweetest Ride|
As I come in the door late for supper, everyone is here and #2 grandson Hudson sternly asks why I’m late. I guess he thinks four year olds are in charge of that stuff. He finally grins big. I answer that I have just been on the sweetest ride in my plane, ever.
They wooow and ooooh and ask questions and my thirty second explanation, which makes no sense to them and surely seems like an hour, starts with mention of the takeoff temp of 105 degrees with 120 degrees on the runway, and a straight 140 mph climb to ten thousand feet. Oh yes, and with good temps. I have mercy on them and leave it at that, not mentioning that this flight demonstrated the success or failure of all the induction rework, saving them from death by the lean-of-peak.
The hot afternoon flight would confirm cylinder and oil cooling in extreme heat, but the real goal was to finally get to 10 thousand feet for the lean of peak drill. No better way to know the results of the induction work than to get up there and do it.
Before pushing out, buoyed by recent temp successes, I do a minor adjust and tweak to the throttle micro switch, adding the final finesse to the warning system, and crossing off the last item on “the list”.
From 700 feet msl the 120 degree takeoff and initial CHTs are all around 395 F, gradually cooling to an average of 330 after the climb to 10K. I’m amazed how close the CHTs are in the climb, the aft two cylinders being just a little cooler. Interesting.
The oil temp is off the peg after a short taxi approaching the runway. After takeoff it climbs quickly to 212 degrees, levels back at 208 and holds for the climb. Then it gradually decreases with higher speeds. Were all those oil cooling flights really real? I am a happy guy. All the good temps are pretty well expected. That isn’t the sweetest part.
Why the longer intake run?
This is not about inlets and expansion chambers and slowing the outside air before it goes into a carb or cylinder fins or oil cooler. That’s a whole nother deal. This is about the length between the carb and where the induction splits to go to the cylinders. This is about how evenly the fuel is mixed and distributed to the cylinders. Or not.
Pictures of the induction setup can be seen here on ez.org on the Featured Canards link. Every once in a while a guy gets to stick his neck out on a limb without fear getting it cut off. Here, besides a few ounces of blood smudged around over time, only my ego and is at risk. While this is of major significance to me, most folks enjoy a modicum of happiness in life even though totally unaware of cruising lean of peak. Not us. It’s so bad, thanks to Jimmy Buffet on the radio earlier, I am now into an hour into an unfortunate musical lyric cycle with “cruising away in lean-a-peak-a-ville” being snuffed and then sneaking back in, with no end in sight. Don’t let it start…
Specifically, the ingredients in mind here include
and today now to be determined -
During the self-imposed 25 hour restricted period I expected to do the normal break-in and soon be trying things out at 12K. A leaking intake valve guide (occasional oil-fouled plugs) was resolved. Twice. They did the wrong valve the first time. This resulted in several months of chasing occasional slightly erratic engine operation. Nothing that significant, just an unexplained distracting mosquito buzzing around.
Naturally, after the leaking valve was fixed the first time (not), when the plugs fouled a few flights later and erratic runup RPMs showed up again, you had to look sideways at the long intake. I did. After collecting numbers on the long intake, the carb was temporarily installed on a short induction tube, and then back on the longer question-mark shaped intake. This confirmed the effect of the longer versus shorter lengths on starting, takeoff or cruise. No difference. On this aircraft.
A couple of things were learned in that long vs short experiment, like the benefit of having at least some straight tube at the carb attachment, maybe an inch, before curving over the crankshaft.
In the whole lean of peak spectrum, this
note is an éclair, not
sirloin. Most of you probably know more about this than me. And if you
are less experienced, good for you.
Lean of peak cruise
I could have stayed with the carb mounted on the 0-290 oil sump. It did fine. Until the RACES. That’s where I heard about this particular culprit, the oil pan induction spider. It became more undesirable as time went on and I heard more about it. They seemed to be saying that on the normal Lycoming oil pan induction setup, after the air/fuel mixture travels up from the carb, it has only a three or four inch run before splitting off in the spider. That short mixing distance, combined with the jet squirting to one side, results in lopsided air/fuel mixing. This is OK normally. Most of us never have cause to even notice it. And most of us are so enamored with the way our crude Cessna engine now works magic in a sleek speedster that we don’t even consider looking for a higher nirvana.
The problem is exacerbated some when you try to leave the throttle wide open and reduce the RPM with the mixture lever. Evidently the stock setup runs rough enough there to discourage the extreme lean of peak stuff. The natural response would be, if it hurts to hit your finger, don’t hit your finger. But nooooo. You gotta to do it.
Listening around, I agree with the simple image of the engine as a long air pump, scrunched up. So it makes sense that the open throttle plate allows free-er flow. Hearing positive comments on automotive installations with long or crossover induction components seemed to indicate that the longer run can be used in spite of its initially common sense suspect characteristics.
At Jackpot and Kanab and Oshkosh and such, the way I saw it unfold, several folks were serious enough about obtaining the smooth lean of peak cruise capability (advantage) that they modified their intake elements to extend the mixture run. With their obvious beneficial results. To say the least, their design is probably superior. I compensated using things like gentle turns into the spider and splitting the spider off in firing order into the four equal length intake tubes.
More effective induction? What could go wrong.
Here we go. Level at 10K, throttle wide open, mixture coming back. I’m ready to be hopefully only mildly disappointed. But even starting out, the plane is strong and smooth as glass. Hertzler’s prop is great.
The mixture was left slightly rich during climb. Coming back now an eighth-inch at a time, the EGTs and CHTs gently climb. As the air/fuel ratio improves, the RPM is climbing 2460, 2520, 2580, 2600. Throttle still wide open, a little more leaning and it lowers to 2580. Things are happening a little faster and gooder and the four CHTs are amazingly even. They have come back a little, around 320. Things are good all the way back to 2400 RPM. After a moment I choose the high-end for now and richen it slightly to 2580.
Hertzler listed speeds and such with his prop on my plane. Good numbers. I was doubtful. But now this is right at the RPM I told Hertzler I was hoping for at this point, without wheelpants. When the pants are installed the RPM and speed increase should put the top end right in there where he predicted. Of course top end is not the focus. Rather, solving the fuel crisis using efficient full open throttle cruise with smooth engine operation is the goal. I have absolutely no interest in speeds.
What fun it’s going to be refining all this. I can only aim toward Hertzler’s magic 2200 RPM and 2.5 gph, hoping to luck out and find my own sweet spot.
Lined out on the third leg at 13,280 DA the plane is extraordinarily smooth and I am buzzing, unable to tell, and not really caring, if the rush is actually the airspeed or me. I had expected to be pretty excited, and am. But I don’t quite explode. Instead, am just sitting here acting like I know what I’m doing, thinking, OK, this is what you should have been doing all along. Aimed at me and the plane. But I’ll take it. I’ll take it!
As things hold together and settle down some, the speed and temp pieces are still coming together. It’s magically intriguing. While scanning one bit of good news, another creeps in, and then another, and then another. After the months of sabotaged conditioning by the leaking intake valve guide, I’m not prepared for this much good blending of speeds and rpms and temps. Initially hoping wildly for only a minor catastrophe, the unexpectedly encouraging strong rhythms leave me sitting here enthralled with nothing to do but hang on and fly. Ha!
Along the way the lower plenums have been scrutinized with the intent of hopefully deducing that they were of neutral value, and then going back to the original 0-235 short stacks exiting out under the cylinders. That was a great setup and provided augmentation. Hangar buddy Dancin Dave does fine with that setup. However, even though I started from a weight and complexity prejudiced position, with their fairly simple operation and the even more excellent CHTs that are showing in the extreme heat now, the lower plenums are earning their keep and I can’t justify removing them.
The late afternoon takeoff was timed hoping to be descending into the sunset right about now. The horizon up here starts turquoise and goes deep through all the right pastel hues, to a reddish golden contrast over the darkening world down there. Spectacular. Everything.
Leveling off at 3K and throttling up again with only a humming hint of vibration I’m immersed in the rush of everything melding together with the whole greater than the sum of the parts (this is a great time for finally getting to use that phrase), getting only stronger and smoother. I won’t even mention the low CHT numbers even in this heat. At only 25 hours into the 100 they told me to expect for chrome cylinders, there’s some legitimacy in sensings of improving operation.
After the previous stunted breakin schedule, this is indeed sweet. Approaching Spinks, the tower is closed and the pattern is clear and a call is made for entering from an overhead break. Only one thing would be more fun than watching from this the ground and hearing just seconds between the call for break, downwind, base, final, clear of the runway … and that would be to be up here doing it.
Benefit of balanced mixture distribution
Along these lines, some criticisms and comments on the intake suggested that takeoff performance would suffer a little in trade for the high cruise benefit. That has not been my observation. Using the 0-235 takeoff and cruise numbers from testing my original Batprop against a friend’s brand name 0-235 VariEze prop, shows about the same takeoff acceleration and ground roll now with about half throttle. Yes, that includes awareness that full action is actually at ¾ throttle throw. Standing back here Monday-morning quarterbacking things under the shadetree and safely of the ground, with the benefit of known results, it only seems right that better fuel distribution and more even power would mean better prop efficiency and who knows what else all benefiting takeoff as well.
Bottom line, the basic engine operation is observed to be transparent at 700 feet msl, it functions smoothly at extreme lean of peak at altitude as hoped for, and seems to provide more even power all around. Sweet enough.
For months, any encroaching thoughts of the good old days in front of the carefree, spartan 0-235 installation have been diverted away. Non-stop 1400 mile jaunts. Atlanta round-robins. Mindless sunset therapy. But now those rosy thoughts of yesteryear are allowed to sidle up and mingle with recently hurdled challenges, looking toward repeats.
Last month, one evening was spent perched as a self-proclaimed oil cooling expert king for a day. Today I luxuriate in the glow of surviving and coming out on this deal OK. Tomorrow, who knows. In any case, back to the salt mines.
Bill James, Lean-a-peak-a-ville VariEze