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MPG

blaplante

Well Known Member
Given current fuel prices (and a retirement income), I did some more experimentation with LOP operation on my cross country flying (MN to CA). Yesterday flew from KRTN via KLVS, OTO, to KSJN. Flew 10,500', under 60% power, LOP, running about 6.1 gph in cruise. Calculated 26 (statute) mpg in cruise (160 mph TAS).

For confirmation - flight aware shows flight was 2 hours 9 minutes, and the distance is 297.8 NM. Fill up was 14.3 gallons, so 23.9 (statue) mpg. Not surprising that the leg mpg was less as that includes the start, taxi, climb. Winds aloft weren't much of a factor - a bit of tailwind at first, and then a bit of headwind for most of the flight.

Yes, it goes slower, but definitely can do longer hops (if the body will take it).

RV6A, (I)O-320-H2AD, Lightspeed & 1 mag. 980RV
Catto Prop (fixed pitch)
 
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Slowing down too

I had the same idea and am running my -10 in the mid teen altitudes. I am doing 155 TAS on just under 9 gph. I am not injected so not very lean of peak. The next 5 knots cost over 10% (1 gph) more.
 
IO-360 with balanced injectors, EFII Ignition on a -7, fixed pitch 3 blade.

11.5 - 12.5K at 8.5 - 8.7 gph will produce 163 - 167 ktas. That equates to about 21-22 mpg according to Dynon and GPS data. The FF range mostly depends on gross weight.

Back it off to about 8.1 - 8.3 and drop another 5 kts or so, but the plane feels like it's on the back side of the curve, kinda mushing along. Don't care for that much. That might be a function of my fixed pitch prop.

I'm sure you could squeeze more mpg's out of it going slow, but I just can't justify the extra air frame/engine time, not to mention my bladder starts to protest!!!

LOP is the way to go, lots of info here and elsewhere to educate your mind ...

Cheers
 
IO-360 with balanced injectors, EFII Ignition on a -7, fixed pitch 3 blade.

...

I'm sure you could squeeze more mpg's out of it going slow, but I just can't justify the extra air frame/engine time, not to mention my bladder starts to protest!!!

...

Cheers

I think engine time is tach time, which is based on RPM, so running less RPM on your fixed pitch won't actually cause more engine hours for a given flight. At least that's my understanding.
 
I think engine time is tach time, which is based on RPM, so running less RPM on your fixed pitch won't actually cause more engine hours for a given flight. At least that's my understanding.

From the JPI website, for example. I suspect other EIS units are similar, but I’m unsure about a mechanical gauge.

Tach Time is calculated based on the average cruise RPM for your aircraft. Tach Time is accumulated once per second, using the following calculation:
Tach Time = Tach Time + (Current RPM / Average Cruise RPM).
Tach Time is true (counting at 1:1 with HOBBS), when your current RPM is at the Average Cruise RPM setting in the EDM.
When your RPM is less than Average Cruise RPM (when taxiing, decent, etc), Tach Time will count slower than HOBBS Time.
When your RPM is higher than Average Cruise RPM (during takeoff, climbing, etc), Tach Time will count faster than HOBBS Time.
Calibrating Tach Time
 
I have fond memories of N19EA My Piper PA23-160 (Apache Twin Engine). This was early 90's and fuel was cheaper but I was also building multi time (and having fun). It had two O-320's 160HP each side. I cruised around at 22/22 square, 6.5 gal/hr, 13 gal/hr total, while doing +160MPH true. With 118 total gallons in 4 tanks I had some legs (8 hrs with 1 hr reserve). I recall the longest flight was 7 or 7.5 hours, Seattle to Phoenix direct. So yes throttle back can save fuel. The BEST way to operate at low percentage power is climb to higher altitudes and be WOT (wide open throttle), if winds are favorable. Flying with partial throttle makes the engine less efficient. It is called PUMPING LOSS, as you restrict the intake. Best to be flying at max altitude and if no O2 below 12500' or 11,500' East Bound. Using O2 and going up into the teen's can be beneficial both in reducing fuel burn, and especially if there a nice tailwind higher up. Winds tend to be stronger as you climb which can be a good thing or bad, depending on tailwind or headwind. Sometimes I would fly very low and higher power. You fly slower with tailwind (to take advantage of it longer) and faster in a headwind (to minimize exposure to headwind).
 
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Flew 10,500', under 60% power, LOP, running about 6.1 gph in cruise. Calculated 26 (statute) mpg in cruise (160 mph TAS).

Thats direct too, I wonder how it would compare to "road MPG". By that I mean following roads that zigzag the countryside and don't go direct like an airplane.

I bet airplanes become even more efficient when compared against the route a car must take.
 
Google Maps says Raton to St. Johns is 421 miles (or 484 NM), so distance covered is substantially shorter. Most of the route is interstate: I-25 and I-40. The one bit that is unfair is that St. Johns AZ is not on the interstate, and so involves a 28 mile deviation. If driving, there wouldn't be a need to go to St. Johns.

Nonetheless - good point made - figuring in flying straight vs. the mountain terrain of the route makes the plane look even better.
 
Thats direct too, I wonder how it would compare to "road MPG". By that I mean following roads that zigzag the countryside and don't go direct like an airplane.

I bet airplanes become even more efficient when compared against the route a car must take.

I had read an article somewhere that said, in general, straight line flying vs driving the curves in a road equals about 15%, so a drive that is 1k miles would be about 850 miles straight line. I have found this to be generally true over longer trips.

I know that on a trip from TX to MN, or back, I can find cheaper fuel by angling a couple more degrees on the heading left or right, adding a total of a few minutes to my overall route, that would be HOURS drive difference.

And I visit some people that don't live that far away, but there is no direct road there, but they live 4 minutes from their local airport (that they didn't know existed :) ), so the time not spent driving into the major city, to pick up the major highway going their direction, is huge.
 
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