King Air C-90

[Ted]

I think you are the only person who has ever asked me the MPG of an airplane.

Yeah, I was just curious for fun.

A lot of my passengers ask me for a MPG number, because it's a term they can understand compared to their car. Keep in mind, my passengers aren't plane people. They're dog people who drive cars, and are on a plane because it's how they're getting to the volunteering efforts they're participating in.

When I'm estimating costs for trips (which is relevant for grants and the like), I figure an average speed of the plane, the cost per hour, and the distance. My estimates are typically within about 5%, so I guess I have it down reasonably well.

 

[Everskyward]

Yeah, I was just curious for fun.

That's what I figured.

A lot of my passengers ask me for a MPG number, because it's a term they can understand compared to their car. Keep in mind, my passengers aren't plane people. They're dog people who drive cars, and are on a plane because it's how they're getting to the volunteering efforts they're participating in.

I think the other option for my passengers is the airlines. I don't think you would find them in their cars unless it's for a drive up to WWW or whatever Clark calls it.

 

[wabower]

Do you further refine the calculation to cage-miles/gal or mutt-miles/gal?

Yeah, I was just curious for fun.

A lot of my passengers ask me for a MPG number, because it's a term they can understand compared to their car. Keep in mind, my passengers aren't plane people. They're dog people who drive cars, and are on a plane because it's how they're getting to the volunteering efforts they're participating in.

When I'm estimating costs for trips (which is relevant for grants and the like), I figure an average speed of the plane, the cost per hour, and the distance. My estimates are typically within about 5%, so I guess I have it down reasonably well.

 

[Ted]

That's what I figured.

Some things one does simply for fun.

I think the other option for my passengers is the airlines. I don't think you would find them in their cars unless it's for a drive up to WWW or whatever Clark calls it.

For the places I'm going with people, typically airplane is the only way to go. Or alternately one can drive, but it's extremely difficult and takes several days instead of several hours. So flying is really the best option. My passengers are typically curious and I encourage that they ask questions, so I try to provide them answers in terms they understand.

Do you further refine the calculation to cage-miles/gal or mutt-miles/gal?

I do come up with average costs of transporting each dog. Again, important for grants, who want to get an idea of how effective the money they're giving us goes.

 

[Dave Siciliano]

I think if one looks at something like miles per gallon it's pretty misleading: one plane can get 5 mpg and one can get 10, but one may hold six or eight people; the other four. So, it may also be interesting to look at seat miles per gallon. The KA sweet spot is really to carry about six comfortably for a medium range trip. Shorter fields also set it apart a bit. On longer trips, other planes may be much faster, but the KA is roomier than many jets.

So, there are a lot of factors to weigh. Look at Flight aware for N700CP to see the ground speeds of the trip out. About 3.4 or 3.5 hours from Dallas to the Tampa area. Average fuel burn of 60 gallons per hour for the trip. You can divide that to see miles per gallon for the plane, but passenger seat miles would be another valid comparison. I'll be about 40 knots slower going back from what I can reasonably see now. Temps aloft and winds sure can influence that.

Best,

Dave

 

[dell30rb]

I like figuring out the value mostly for fun.

The 152 is plenty fun, but after 75 cross country hours logged in it this year i'm pretty burned out on the whole 95 kts thing!

 

[Henning]

I think if one looks at something like miles per gallon it's pretty misleading: one plane can get 5 mpg and one can get 10, but one may hold six or eight people; the other four. So, it may also be interesting to look at seat miles per gallon. The KA sweet spot is really to carry about six comfortably for a medium range trip. Shorter fields also set it apart a bit. On longer trips, other planes may be much faster, but the KA is roomier than many jets.

So, there are a lot of factors to weigh. Look at Flight aware for N700CP to see the ground speeds of the trip out. About 3.4 or 3.5 hours from Dallas to the Tampa area. Average fuel burn of 60 gallons per hour for the trip. You can divide that to see miles per gallon for the plane, but passenger seat miles would be another valid comparison. I'll be about 40 knots slower going back from what I can reasonably see now. Temps aloft and winds sure can influence that.

Best,

Dave

My question was simple, MPG at 180 and 210. Later modifications for seat mile per gallon can be done, but just the simple basic burn number solo in the plane with a full range mission as well as total useful load & fuel numbers, and I can work out all the answers I'm looking for.

I'm just trying to figure out the rough numeric for the turbine for a given capability. I use 180kts because it is the minimum cruise I find acceptable, and my aerodynamics (as yours) support this as an economic speed. I do well enough for my mission in a 310 that I get 930NM fuel (full), me and my kit (200lbs total) and I have 500lbs to go to gross. I get 8.5nmpg early in the trip, 9.2,mpg later as I burn off fuel. That's pretty good for 3 miles a minute, no car can do that that economically. The King Air buys you pressurization load, I know approximately what I can get that for in a 421 at 180kts. You happen to be the first person I heard looking at giving up KA speed for fuel efficiency so I was looking for real numbers if you had them.

Where turbines earn their keep to me is dispatch reliability in high importance missions. Just so long as the gagging stench doesn't intrude in the cockpit and I don't have to hot fuel in the exhaust stream, I'm Ok with them; I just hate their fuel bill and wish we had a 985 Diesel 450hp TA.

 

[Dave Siciliano]

As Wayne has said, it's difficult to do what you're asking. The power settings I run for engine longivity don't call for those TAS unless I go higher than I normally would fly (would have higher cabin altitude than I would want on a trip). To slow to those speeds, I wouldn't be running hot enough ITTs at the altitudes where the cabin would be reasonable (up to FL210) At FL200, the cabin is 70 on this plane but I run faster TAS than you are requesting to keep ITTs reasonably hot. I'd have to run fairly cool ITTs for the TAS you want or run at a much higher altitude. I could do that to get you the numbers you are requesting, but that's not where you'd want to run these engines. That's why I suggested you look at my flight out here and maybe average it with the flight back to get a feel for that.

The analog fuel flow gauges on this plane aren't very accurate. The show I'm burning more than it turns out I am when I fill the tanks to the top and check.

As a point of reference, I ran at 180 on 4/9 at -14C with 159IAS FF showed 190 on the left and 210 on the right. Does that help at all?

Best,

Dave

 

[Ted]

Asking for a MPG at a particular speed I think is rather silly, for the reasons that Dave pointed out. When I figure it, I take the power setting that the plane is run at (for whatever purpose - engine longevity, speed, economy, etc.) and figure it out at that speed. You wouldn't fly a 310 at 172 speeds.

Unlike cars, planes don't have a reference speed that you can use. Highway MPG for cars is a pretty reasonable comparison - most cars are going to drive at roughly the same speed on the highway.

As I said, the main reason is for fun. But the numbers do end up providing me something reasonably useful for my purposes.

 

[Henning]

Really, Block MPG would be fine, just tell me best altitude and speed and the block MPG, really, I'm looking for basic info.

 

[dell30rb]

Asking for a MPG at a particular speed I think is rather silly, for the reasons that Dave pointed out. When I figure it, I take the power setting that the plane is run at (for whatever purpose - engine longevity, speed, economy, etc.) and figure it out at that speed. You wouldn't fly a 310 at 172 speeds.

Unlike cars, planes don't have a reference speed that you can use. Highway MPG for cars is a pretty reasonable comparison - most cars are going to drive at roughly the same speed on the highway.

As I said, the main reason is for fun. But the numbers do end up providing me something reasonably useful for my purposes.

My 152 poh gives NMPG at various altitudes and airspeeds. It actually is better than my v-8 jeep's highway fuel economy

 

[wabower]

Asking for a MPG at a particular speed I think is rather silly, for the reasons that Dave pointed out.

And even sillier for the purported use and underlying hypothetical scenario. If you ask a hundred King Air pilots for first and second hour fuel burn, they will all give you the correct answer without thinking, e. e. "600# first hour, 400# thereafter."

If you want to know gallons rather than pounds, it's your job to do the arithmetic. If you ask them for MPG, the answer would be "Huh? Uuhhhh, lessee. 'Bout 210 cruise on 'bout 70 gals is what, about 3? Maybe a skosh more if we go high and pull it back?"

If you want to ask amphib King Air pilots about off-the-wall theories about hauling parts to the boat, that will take a little longer.

 

[Henning]

And even sillier for the purported use and underlying hypothetical scenario. If you ask a hundred King Air pilots for first and second hour fuel burn, they will all give you the correct answer without thinking, e. e. "600# first hour, 400# thereafter."

If you want to know gallons rather than pounds, it's your job to do the arithmetic. If you ask them for MPG, the answer would be "Huh? Uuhhhh, lessee. 'Bout 210 cruise on 'bout 70 gals is what, about 3? Maybe a skosh more if we go high and pull it back?"

If you want to ask amphib King Air pilots about off-the-wall theories about hauling parts to the boat, that will take a little longer.

Wow, general curiosity is that threatening to you? Simple, I heard him talking about 210 TAS so I figured he had that. I also figured there's a long range number published around 180. Yeah, I like to know basically what the cost/energy delta for various levels of capability are, WTF is so irrational about that?

Oh, and I can see your point where considering operating efficiency is beyond most pilots because 'work performed' is a foreign concept.

 

[Everskyward]

My 152 poh gives NMPG at various altitudes and airspeeds. It actually is better than my v-8 jeep's highway fuel economy

Turbine aircraft use pounds as a unit for fuel rather than gallons. In other words the fuel gauges are in pounds, the fuel flow is measured in pounds per hours, etc. The only time I use gallons is when I give a refueling order to line service. At that time I convert the pounds I need into gallons. My reaction upon being asked about MPG was "Huh? Let met get out my calculator..."

 

[wabower]

I'm deathly afraid of lightning, snakes and side-hill puts, but not threatened by much of anything on the internet.

Cost/energy delta, eh? King Air cruise vs some cockamamie amphib/boat/parts/might-get-to-fly-a-piston-single explanation? Now that you mention it, demented is probably more appropriate than irrational, but knock yourself out.

And yeah, you're smarter than everybody else, and with posts to prove it.

Wow, general curiosity is that threatening to you? Simple, I heard him talking about 210 TAS so I figured he had that. I also figured there's a long range number published around 180. Yeah, I like to know basically what the cost/energy delta for various levels of capability are, WTF is so irrational about that?

Oh, and I can see your point where considering operating efficiency is beyond most pilots.

 

[gismo]

It actually is better than my v-8 jeep's highway fuel economy

Until your flying into a 25 Kt headwind.

 

[Dave Siciliano]

I'm finishing up at SICMOM; heading out to dinner with family tonight and flying back tomorrow; so, I've only been able to get on here once-in-awhile. Another factor in turbines is slowing down for better fuel economy can actually cost more because of running the turbine longer. That is, the life of the turbine is set until TBO and many inspections are at a time period or hours/cycles flown. It is actually less costly to burn a bit more gas and run the turbine for a shorter period. As Ronnie said earlier, you don't buy a turbine to go slow.

I gave you fuel for the trip to Tampa. Just divide miles in to gallons I put in the plane and you'll have block MPG, won't you?

Best,

Dave

 

[Henning]

Turbine aircraft use pounds as a unit for fuel rather than gallons. In other words the fuel gauges are in pounds, the fuel flow is measured in pounds per hours, etc. The only time I use gallons is when I give a refueling order to line service. At that time I convert the pounds I need into gallons. My reaction upon being asked about MPG was "Huh? Let met get out my calculator..."

What ever you got, I'll put the calculator to it.

 

[Henning]

I'm finishing up at SICMOM; heading out to dinner with family tonight and flying back tomorrow; so, I've only been able to get on here once-in-awhile. Another factor in turbines is slowing down for better fuel economy can actually cost more because of running the turbine longer. That is, the life of the turbine is set until TBO and many inspections are at a time period or hours/cycles flown. It is actually less costly to burn a bit more gas and run the turbine for a shorter period. As Ronnie said earlier, you don't buy a turbine to go slow.

I gave you fuel for the trip to Tampa. Just divide miles in to gallons I put in the plane and you'll have block MPG, won't you?

Best,

Dave

Yeah, sorry, missed that post, will look, that will do.

 

[Ted]

Turbine aircraft use pounds as a unit for fuel rather than gallons. In other words the fuel gauges are in pounds, the fuel flow is measured in pounds per hours, etc. The only time I use gallons is when I give a refueling order to line service. At that time I convert the pounds I need into gallons. My reaction upon being asked about MPG was "Huh? Let met get out my calculator..."

As I recall, you gave me your cruise speed at FL410 and your fuel burn, and I did the math for you since I was asking the question.

I'm finishing up at SICMOM; heading out to dinner with family tonight and flying back tomorrow; so, I've only been able to get on here once-in-awhile. Another factor in turbines is slowing down for better fuel economy can actually cost more because of running the turbine longer. That is, the life of the turbine is set until TBO and many inspections are at a time period or hours/cycles flown. It is actually less costly to burn a bit more gas and run the turbine for a shorter period. As Ronnie said earlier, you don't buy a turbine to go slow.

This, of course, ends up being true in any aircraft. The difference with pistons being that if you run at a power setting that produces a slower speed, you may end up with lower engine maintenance costs. However, one must make certain assumptions in making estimates. To be conservative, I assume the same engine life and operating expenses for power vs. economy cruise, and I set that on the high side to make sure there's more money rather than less.

Fuel is not the only cost.

 

[Everskyward]

What ever you got, I'll put the calculator to it.

My mpg estimate was just a WAG. There are too many variables to come up with a meaningful number.

 

[Everskyward]

As I recall, you gave me your cruise speed at FL410 and your fuel burn, and I did the math for you since I was asking the question.

I definitely remember doing the math myself because it took me a while to figure out what I was supposed to be dividing by what. Maybe you did it too, probably faster than I did. Still that number is pretty meaningless except for curiosity's sake since you would really need to consider the whole trip, not just cruise.

 

[Henning]

As I recall, you gave me your cruise speed at FL410 and your fuel burn, and I did the math for you since I was asking the question.



This, of course, ends up being true in any aircraft. The difference with pistons being that if you run at a power setting that produces a slower speed, you may end up with lower engine maintenance costs. However, one must make certain assumptions in making estimates. To be conservative, I assume the same engine life and operating expenses for power vs. economy cruise, and I set that on the high side to make sure there's more money rather than less.

Fuel is not the only cost.

I will not defend reciprocating gasoline engines. I will defend reciprocating Diesel/Mid Weight Fuel Oil reciprocating engines in the 250-1400hp jobs with common rail. Caterpillar already built a 450hp old tech Diesel R-1820 long ago. With Common Rail injection ignition can be pulsed to manage the pressure by elongating the time the fuel is fed and where in the combustion cycle to add the most fuel. That's what EFI/ HP Common Rail buys; a lighter engine due to controlled pressure front. A lot of fuel efficiency plus algae oil capability as well....

 

[Ted]

I definitely remember doing the math myself because it took me a while to figure out what I was supposed to be dividing by what. Maybe you did it too, probably faster than I did. Still that number is pretty meaningless except for curiosity's sake since you would really need to consider the whole trip, not just cruise.

Yeah, exactly. It's a number that serves no purpose other than curiosity.

 

[ronnieh]

Henning, one thing that I know you know already is most turbine operators run the engine the same on every trip. Even in the -61's I run, I am almost always temp limited. So from 180 and up I am useing max available power, which is 50 deg below peak. On a standard day at FL180 I am looking at 292-294 KTAS BUT, my fuel flow is over 700 pounds. If I am at FL280 on the same day I am down to 286 but my fuel flow is down to 600 pounds or less. MPG for most turbine pilots is a factor of altitude and wind, not power selection. Again, nothing you don't already know but might explain some of the comments about asking about MPG for turbine operators. Just too many variables to have even an average figure.

 

[Dave Siciliano]

Ted: I agree with you on costs to run a plane, but the cost to overhaul a turbine is much more significant than a piston; so, fuel cost becomes a smaller part of the equation. Running at a lower power setting on a turbine puts more time on it per trip and moves up the cost to overhaul. Fuel cost was more significant to me in the 58P and did put more hours on the plane, but the cost per hour to run the engines is much less than for the KA with twin turbines. I guess that was the point I was trying to make. You may spend a bit less for gas, but sulfidation and overhaul costs would outweigh that. So, going higher allows less fuel burn without giving up much TAS while allowing a high power setting. That would be tempered with having a decent cabin altitude. Strong headwinds might influence that if it's an upper air event and they relatively improve lower in light of the loss of TAS lower. A smooth ride comes into play also. Four hours of bumps sure isn't fun.

Best,

Dave

 

[Ted]

Very true, Dave. I understood your point, I just didn't convey it well.

 

[Dave Siciliano]

Looks like 60 knot headwinds tomorrow in the low FLs---oh joy(sarc)!

Best,

Dave

 

[Ted]

The first trip I made in the Cheyenne, the winds at FL220 (our altitude) and the winds at 6000 ft were such that I could have made the trip in the same amount of time in the 310.

Of course, he has since proven to be faster overall. But seeing 140-150 kts GS for 450 pph is painful.

 

[ronnieh]

With everybody's indulgence let me muddy this up some more.
I know Henning was asking for MPG at different power settings. He never got an answer mostly because nobody knows. Dave is the only person I know to run a turbine at less than max available power. Yes I know some very long legs in turbo fans may be run at max endurance cruse setting or at least something below best speed. In the real world with turbo props we mostly wish for cooler air so we can push more kerosene without harming the CT blades. Of course in my case I don't have to pay for fuel, Dave does
Back to Henning, just in case you are interested I just ran some flight plans for an 8:45 PM CDT departure from MSL to MIA tonight. You will have to convert the NM/LB of fuel into MPG. I hope this comes out in a format that is understandable. All numbers are block time and takes into consideration climb and descent and winds are sampled every 3000 feet for calculations.

FL 270 Total fuel 1470 # Time enroute 2:12 burn rate .45 NM/pound

FL 250 TF 1537# Time enroute 2:11 fuel burn .43 NM/pound

FL 230 TF 1587# Time enroute 2:12 fuel burn .41 NM/pound

FL 210 TF 1669# Time enroute 2:12 Fuel burn .39 NM/pound

Fl190 TF 1726# Time enroute 2:15 fuel burn .38NM/pound

And it is worse at 170. Power settings are not even an option on this flight planning software. It is assumed best power.
I do not know if this answers anything for you but, it is real world numbers.
In NA piston airplanes you have a much smaller window of altitudes and the wind at 7000 may not be much different than at 9000.
In the above, weather permitting I would choose FL 270. I will trade one minute for 10 gallons anytime.

 

[wabower]

I was planning to check winds prior to this post, but you beat me to the draw. The most common reduced-power legs in King Airs are into strong winds, hoping to stretch fuel supply and preclude a fuel stop.

One of the best examples is Ft. Myers to Dallas in a B-200 with 6-8 pax. plus baggage. Filling all tanks (3,600#) is out of the question, so mains only (2,500#) is normal. Fuel burn is ~700# first hour and 500# thereafter, and yellow low-fuel arc on fuel gages begins at ~600# total fuel on board.

Accordingly, the crew knows that a 4-hour trip into 40 kt winds (cruise speed of 280-40 knot headwind=240-kt groundspeed for a 960 nm trip) will require approximately 4 hours and 2,200# fuel burn at normal power settings. Since that combination would deplete desired reserves by ~50% (600# desired vs. 300# on board) the crew will be required to pull back the power levers until sufficient reserves are achieved.

Fortunately, the GPS units are ususally wired into the fuel system, so the pilot has only to pull the power levers back until the "Fuel over Destination" screen shows the desired number. There have been days when the trips became tortuously long for both pax and crew.

Looks like 60 knot headwinds tomorrow in the low FLs---oh joy(sarc)!

Best,

Dave

 

[ronnieh]

Wayne, I have no operational experience with the B 200 only a very little with the straight 200. You can get fuel flows down to 500 # on a somewhat normal day at best power setting? On very hot days I have never seen less than 550-560 in the -61's. Of course I may be making more power at FL 280 with the -61's but your speeds dont seem to suggest that. On a +20 day about 286 true second hour speed with a burn of about 560 pounds. Interesting. Not disagreeing, just commenting.

 

[Doggtyred]

Ted: I agree with you on costs to run a plane, but the cost to overhaul a turbine is much more significant than a piston; so, fuel cost becomes a smaller part of the equation. Running at a lower power setting on a turbine puts more time on it per trip and moves up the cost to overhaul. Fuel cost was more significant to me in the 58P and did put more hours on the plane, but the cost per hour to run the engines is much less than for the KA with twin turbines. I guess that was the point I was trying to make. You may spend a bit less for gas, but sulfidation and overhaul costs would outweigh that. So, going higher allows less fuel burn without giving up much TAS while allowing a high power setting. That would be tempered with having a decent cabin altitude. Strong headwinds might influence that if it's an upper air event and they relatively improve lower in light of the loss of TAS lower. A smooth ride comes into play also. Four hours of bumps sure isn't fun.

Best,

Dave

How much of your maintenance cycles are determined by hours and how many by operational cycles (start/shutdown)??

 

[wabower]

Good questions, and the answers might be a bit different for trips in other parts of the country.

Weather in the south/southeast tends to be a bit warmer, with upper air temps of ISA+20/30 not uncommon. I flew to numerous destinations in FL on more than 60 trips over the years in B-200's Citation 650's and G-V's and don't remember a single trip on which temps were close to ISA.

Our -42 engines redlined at 800C. We used 760C as normal limit and used high 20's as much as possible without RVSM. As a result our ff/hr was in the 500# range, although I tried to use the ~ (approximate) symbol as much as possible in the other post to indicate the numbers were approxmations rather than hard numbers. I think your -61's are a bit more stout than the -42's.

Wayne, I have no operational experience with the B 200 only a very little with the straight 200. You can get fuel flows down to 500 # on a somewhat normal day at best power setting? On very hot days I have never seen less than 550-560 in the -61's. Of course I may be making more power at FL 280 with the -61's but your speeds dont seem to suggest that. On a +20 day about 286 true second hour speed with a burn of about 560 pounds. Interesting. Not disagreeing, just commenting.

 

[ronnieh]

Wayne, I understand the temps. I am based in Alabama. The -61 in my application redline is at 810 and I too use 760. Will the B200 on a +20 day true 280 at FL 280? Did not know they were that much faster than a straight 200. But, like I said I have zero experience in the B model. The IIIA will true 286 at FL 280 at +20, if I departed 500 pounds under gross.

 

[wabower]

Ronnie,

No, neither of the factory airplanes will make those numbers. The Raisbeck-equipped airplanes (all that I flew were so equipped) will get closer, but I don't have the performance charts at hand to obtain a better number. 200 and B-200 performance is identical below FL180. At higher altitudes the B-200's extra 50C available temp provides better performance, as does the Raisbeck conversion. Better performance isn't free, however, as the fuel flow will increase as well.

Wayne, I understand the temps. I am based in Alabama. The -61 in my application redline is at 810 and I too use 760. Will the B200 on a +20 day true 280 at FL 280? Did not know they were that much faster than a straight 200. But, like I said I have zero experience in the B model. The IIIA will true 286 at FL 280 at +20, if I departed 500 pounds under gross.

 

[ronnieh]

That explains it, thanks for satisfying my curiosity. Just like the III and IIIA. Identical performance up to about 15,000 feet or so.

 

[Henning]

FL 270 Total fuel 1470 # Time enroute 2:12 burn rate .45 NM/pound 3NMPG

FL 250 TF 1537# Time enroute 2:11 fuel burn .43 NM/pound

FL 230 TF 1587# Time enroute 2:12 fuel burn .41 NM/pound

FL 210 TF 1669# Time enroute 2:12 Fuel burn .39 NM/pound

Fl190 TF 1726# Time enroute 2:15 fuel burn .38NM/pound 2.5NMPG

And it is worse at 170. Power settings are not even an option on this flight planning software. It is assumed best power.
I do not know if this answers anything for you but, it is real world numbers.
In NA piston airplanes you have a much smaller window of altitudes and the wind at 7000 may not be much different than at 9000.
In the above, weather permitting I would choose FL 270. I will trade one minute for 10 gallons anytime.

Yes, thank you; good enough. I see the speed remained rather constant, so that is between 285 & 290 KTAS in a KA model ??? or what?
What is max range/long range and how much load in the cabin at that range?

So, the power put out for a temp limit equates the same TAS so no altitude/speed advantage once you hit temp?

I'd love to have 350hp compound supercharged Diesels (or multifuel plug engines)

 

[denverpilot]

I definitely remember doing the math myself because it took me a while to figure out what I was supposed to be dividing by what. Maybe you did it too, probably faster than I did. Still that number is pretty meaningless except for curiosity's sake since you would really need to consider the whole trip, not just cruise.

This is true of cars too, but we average it out (well, EPA does) with an agreed-upon set of assumptions, to compare one car/truck to another.

And yeah, I know there's problems with the EPA's assumptions on cars and trucks.

I only point out that it's not completely impossible to come up with a number that applies on a standard day at some altitude for comparison of similar types.

I agree, lots of variables and in the end the numbers won't be accurate. Just like cars.

I can make my Yukon get 9 MPG all day without even trying hard. The other end of the spectrum, I've seen 16 MPG on road trips with no trailer on behind.

But there are EPA numbers (that don't match the real world) out there for comparison against other trucks...

 

[Everskyward]

I only point out that it's not completely impossible to come up with a number that applies on a standard day at some altitude for comparison of similar types.

What use is it to come up with numbers for only one altitude when you are comparing different types of airplanes? The optimum altitude is going to be very different when you compare a piston to a turboprop to a jet. Not only that, there is a large difference in fuel burn with altitude, especially in jets. Also, as others have pointed out, in the real world you don't slow down to save fuel unless you think you are going to be somewhat fuel-limited for that leg.