Redtail led us out of SoCal and we yapped on the radio about economy. After we crossed the hills into the central valley, Redtail ducked down for the aerial reconaissance he came to do. I climbed up to 10,500' and began some experimenting. I was supposed to pick Jen up around 8:30am, but I would have been way early had I just continued cruising at WOT (wide open throttle). Here was my WOT power setting...7.1 gallons per hour doing 167 knots over the ground, getting 27.1 miles per gallon. This was flying into a light quartering headwind. 27.1 mpg ain't bad, but let's see just how much better this puppy can do!
I gradually started pulling the throttle back, and leaned to about 75 LOP. With 17.3" of manifold pressure I was burning 5.3 gallons per hour, still doing 146 knots over the ground (into a headwind, mind you) for an economy of 31.7 miles per gallon. That's a 17% increase in economy for just a 14% decrease in speed.
In case you don't believe me about the groundspeed, here you go.
Throttling back even more to 15.9" of manifold pressure, the economy continued to improve. At 5.0 gallons per hour I was getting 34.1 miles per gallon.
Let's see, at this fuel flow I have more than 7 hours fuel remaining...and this was after I had already flown more than 120 nautical miles at power settings that were less economical than this. Let's see...7 hours at 145 knots, that's 1015 nautical miles or 1167 statute. At that power setting I could probably juuust make it to Guadalajara non-stop! Might have to try that next time (nah).
Still was doing 144 knots over the ground at a Cessna 152 fuel burn.
Checking the winds again...still a light quartering headwind if anything. Wind was almost negligible at this point, so groundspeed was a relatively decent indication of true airspeed.
I had my O2 pumpin' -- or oxymizin' as the case may be. I checked my pulse-ox and it was right where I wanted it at 94%.
Ok, let's see where peak economy lies for these conditions...I throttled back further to 15". 4.8 gallons per hour for 35.4 miles per gallon. That's the highest I've seen it get without a tailwind. The wind had lightened up a knot or two, because my groundspeed went up slightly. At this fuel flow, I could basically fly an 8 hour leg -- and that includes 15 minutes of climbing (it never takes that long) at 15 gallons per hour (it never averages that high in the climb). Of course that's with no reserve... But a 7-hour leg in this configuration is definitely a possibility. Comparing this configuration to my original WOT setting, it's literally a 30% increase in economy for about a 15% decrease in speed. I'd call that a fair trade.
At some point the economy has to plummet if I keep pulling the throttle back, and I wanted to see where that peak in the curve was. Somewhere between 15.0" and 13.8" of manifold pressure the economy started dipping again, predictably. At 13.8" I was burning 4.5 gallons per hour but only getting 33.1 miles per gallon. I didn't reduce power any further since I was already on the "back side of the economy curve."
So to sum all this up...if I ever want to get the most from my avgas dollars, I can run this puppy at about 15" of manifold pressure, burn less than 5 gallons per hour, have more than 7 hours of endurance, and still be doing about 145 knots true. Absolutely friggin' amazing. Talk about being able to squeeze the most out of your fuel investment. Do I have the patience to fly 20-25 knots slower than I normally do? Not all the time, but sometimes -- like today, when I was very early for my "appointment" -- I can definitely sit back and enjoy the scenery and the wonderfully inexpensive flight time. I mean hell...even at $4 a gallon for fuel, I'm only spending $20/hour on fuel. Add the other overhead costs to that for stuff like oil, hangar, insurance, maintenance, and engine reserve, and the cost per hour to fly this plane (at least as often as I do) is less than half what it would cost to rent a friggin' beat-up 40-year-old Cessna. Do I need to bother mentioning this is slightly more fun?
Am I evangelizing? Am I boasting? I don't know. I'm not trying to. I guess I myself am still in awe over the economy of this silly tin can my wife and I built in our garage.