Fuel burn from first Phase II flight.

[McFly]

I put 3.5 hobbs hours on my plane during my first Phase II flight/adventure Sunday. Ironically, this flight will be my benchmark for fuel burn rates. During this flight I made four TO and landings and had extended ground ops at two of the airports (15-20 minutes?). My numbers during cruise were 2250 RPM, 18.5? MP at 5500?, indicating 134 knots using very conservative ROP leaning (3 blade Catto climb prop on a TMX O-360). My bud said I flew at idle the entire time.

When I gassed up last night, the plane took 18.9 gallons, which comes to 5.4 gallons an hour for the flight or 28.5 MPG. I was very careful in that I stopped at the bottom of the filler neck at each fillup. I am very happy with these numbers but I have to admit, I would be skeptical of them if I wasn?t the poster.

 

[cjensen]

Hugh, do you remember what your OAT was at 5500'? Just curious what your TAS was.

Great numbers!

 

[McFly]

Just curious what your TAS was

Sorry, I don't have that info (no guage). It was hot though

 

[gasman]

MPG?

I put 3.5 hobbs hours on my plane, this flight will be my benchmark for fuel burn rates. During this flight I made four TO and landings and had extended ground ops at two of the airports (15-20 minutes?). My numbers during cruise were 2250 RPM, 18.5? MP at 5500?, indicating 134 knots using very conservative ROP leaning (3 blade Catto climb prop on a TMX O-360). My bud said I flew at idle the entire time.

When I gassed up last night, the plane took 18.9 gallons, which comes to 5.4 gallons an hour for the flight or 28.5 MPG.

You were running a little over 50% power, that would explain the mid 5s for fuel burn... But miles per gallon needs to be figured when YOU ARE GOING miles per hour 15-20 minutes running on the ground did not get you 51 miles away, did it?
Try this........ Top off each tank, take off on left and get into cruse, then switch to right tank. Start the stopwatch and fly for 30 minutes (or an hour) then switch back to the left tank. Go back and land and fuel up same as last time. Now you know for sure, without any fuzzy math....

 

[McFly]

You're right

But miles per gallon needs to be figured when YOU ARE GOING miles per hour 15-20 minutes running on the ground did not get you 51 miles away, did it?

You are right, thanks for keeping me honest Gasman. Good idea on the tank switching to.

Let me try more fuzzy math for a ballpark MPG. Let?s say my ground ops totaled half an hour and amazingly I burned no gas during ground ops. So 18.9 gal / 3 hrs = 6.3 gph. 154.1 mph/ 6.3 gph = 24.5 mpg. I'll just call it 25 MPG though

 

[gasman]

So would that be 3.67 gallons from CIC to Lake California and back?

Or almost back!!!

 

[David-aviator]

You are right, thanks for keeping me honest Gasman. Good idea on the tank switching to.

Let me try more fuzzy math for a ballpark MPG. Let?s say my ground ops totaled half an hour and amazingly I burned no gas during ground ops. So 18.9 gal / 3 hrs = 6.3 gph. 154.1 mph/ 6.3 gph = 24.5 mpg. I'll just call it 25 MPG though

It's easier to figure mpg if TAS is known. I use Dynon with OAT input and TAS output.

This assumes Dynon is reasonably accurate. It's IAS is about 3 knots slower than Van's indicator, so it probably is in the ball park. Subby also is in the mpg ball park with your Lycoming, at least at this speed.

> RPM 1900/3420
> BURN = 6.6
> TAS = 135kt (156mph)
> MPG = 23.63
>
> RPM 1800/3210
> BURN = 6.0
> TAS = 131kt (151mph)
> MPG = 25.16

 

[gasman]

TRY THIS IDEA...

It's easier to figure mpg if TAS is known.

Is it true that GROUND SPEED is the ONLY speed that you can use for MPG figures? And that is why we use gallons per hour and always allow for extra. In a jet stream your mpg could be 50 mpg and your gallon per hour would not change.

 

[McFly]

MPG: Not for flight planning

Is it true that GROUND SPEED is the ONLY speed that you can use for MPG figures? And that is why we use gallons per hour and always allow for extra. In a jet stream your mpg could be 50 mpg and your gallon per hour would not change.

I agree with you that MPG useless for flight planning. However, MPG is useful for comparing efficiency among machines. Maybe I should have stated "in theoretical still" air or called it AMPG (air miles per gallon)

 

[gasman]

I also agree....

I agree with you that MPG useless for flight planning. However, MPG is useful for comparing efficiency among machines. Maybe I should have stated "in theoretical still" air or called it AMPG (air miles per gallon)

I commute between Petaluma and Lake California. My PA28 151 would use 21 gallons round trip. My 6A will do the loop on 14 gallons and about 30 minutes faster. AAAAaand a lot more fun!!!