My old chevy plow truck has a 454, weighs 7000 #'s, and burns 6 gallons an hour running 4500 rpm's at times. My skylane burns twice as much with the same displacement turning half as fast and half as heavy.

Well it is partly that cruising around steady state your actually putting out more horsepower to stay aloft than your Chevy is to keep rolling along. Top ends of aircraft engines are also somewhat fuel cooled, leading to a bit of inefficiency. Transfer of power output through a propeller is not as good percentage wise as through a set of wheels. Your truck does not need to overcome gravity & drag to maintain speed.

Kinda like Bowling
Just see how much energy it takes to throw that bowling ball all the way to the pins!!
GT

M6RV6 wrote:Kinda like Bowling
Just see how much energy it takes to throw that bowling ball all the way to the pins!!
GT

Yeah, but chuck one outta your airplane and it hauls ass pretty good!

Gump

Because mags with no advance and carbs or mechanical injection are horrible, look at the fuel burn difference between the modern Rotax and a comparable lycoming
3.75 vs 5gph.....
Sent from my EVO using Tapatalk 2

GumpAir wrote:

M6RV6 wrote:Kinda like Bowling
Just see how much energy it takes to throw that bowling ball all the way to the pins!!
GT

Yeah, but chuck one outta your airplane and it hauls ass pretty good!

Gump

Yep!!
I guess if you pointed the bowling ball, truck, and airplane straight down with no power they all wood get the same MPG!!
Damn bowling ball probably still win the race though!!
GT

Well, I guess I should be thankful I don't have to make the ol plow truck fly. Never thought I'd own something that makes a big block seem economical. An old man told me when I bought it to always buckle up so I didn't get sucked into the carburator.

Mongo wrote:Because mags with no advance and carbs or mechanical injection are horrible, look at the fuel burn difference between the modern Rotax and a comparable lycoming
3.75 vs 5gph.....
Sent from my EVO using Tapatalk 2

I'd have to disagree with the carbs being horrible. I can set up a 383 stroker to gwtbjust as good, if not better fuel mileage and power then a new 6.0. You'd think Chevy would've figured out to get better then 12mpg out of a 3/4 ton pickup by now...
David

where there is confusion there is money to be made.

A1Skinner wrote:

Mongo wrote:Because mags with no advance and carbs or mechanical injection are horrible, look at the fuel burn difference between the modern Rotax and a comparable lycoming
3.75 vs 5gph.....
Sent from my EVO using Tapatalk 2

I'd have to disagree with the carbs being horrible. I can set up a 383 stroker to gwtbjust as good, if not better fuel mileage and power then a new 6.0. You'd think Chevy would've figured out to get better then 12mpg out of a 3/4 ton pickup by now...
David

where there is confusion there is money to be made.

Not to play devils advocate, but a buddy was talking about how much better his fuel economy in his old truck got vs mine. 1997 vs 2008 f250s. He claimed that with all the modern advances mine should do significantly better.

We dug into it a little bit. His curb weight was ~4500lbs. Mine is ~8800lbs. Apples to oranges.

Remember your airplane at a low power setting is still producing 60% power or more. Your plow truck is probably averaging 20% or less output, even while plowing.


The new motors are also trading fuel burn for emissions control, too.

(yeah, I can't make sense of that one either)

I guess if you pointed the bowling ball, truck, and airplane straight down with no power they all wood get the same MPG!!
Damn bowling ball probably still win the race though!!

Airplane *should* win because of less drag. Bowling ball is very draggy.

It's because airplane engines are about as technologically advanced as a Harley Davidson engine.
Actually, they are less advanced than a Harley.
If the feds would allow a little "New Tech" into certified engines, the whole "Low Lead" issue might not even be an issue.

I'll check out some garage sales for bowling balls (and pins).... sounds like more fun than "Flour drops"

Austin NV next year for some aviation bowling..... I think we're onto something here

Nosedragger wrote:My old chevy plow truck has a 454, weighs 7000 #'s, and burns 6 gallons an hour running 4500 rpm's at times. My skylane burns twice as much with the same displacement turning half as fast and half as heavy.

My 182 gets between 13 - 15 miles per gallon at cruise depending on my power settings, at about 140 mph.

I haven't driven my 1/2 ton truck at 140 mph, but I'm sure that the mileage would be the same or worse as my 182 because at 75 mph my truck gets about 16-17 miles per gallon.

Don't get me wrong, I wish I burned half as much in my 182 as I do.

If you consider the physics, general aviation airplanes aren't unreasonably efficient. Kinetic energy quadruples when the velocity doubles. Your 182 gets around 11 mpg at twice the speed of the truck. That's not a horrible trade off.

It takes a lot of energy to drag a 175 square foot wing through the air at 140 mph. Attach a Cub wing to your truck and drive 140 mph and I'll bet you will be burning quite a bit more fuel than you would be in the 182.

Propeller efficiencies are generally very high. You will lose a lot more energy using universal joints, bevel gears, and deforming tire rubber than you do pushing a little atmosphere around with your direct drive propeller.

I have thought about the airplane bowling thing out in the desert. That would be a real good time!

Weight doesn't have so much to do with it as we think. A locomotive gets over a 100 mpg considering similar weight ratio per pound of useful load using diesel electric. Expanding that theory, a diesel electric bowling ball could be awesome.

http://gas2.org/2010/05/25/freight-trai ... ince-1980/

Scolopax wrote:Propeller efficiencies are generally very high. You will lose a lot more energy using universal joints, bevel gears, and deforming tire rubber than you do pushing a little atmosphere around with your direct drive propeller.

I think a lot of efficiency is lost to compressibility of air in the propeller vs rubber-on-road argument.

I think there are many factors that contribute to the greater burn rate:

1. Air vs solid medium for propulsion. Like swimming vs walking. Which uses more energy?

2. A glance at the four forces diagram tells you that you're using your fuel to contribute to accelerating against gravity in the vertical axis, in addition to drag in the horizontal axis. You get a little of that in driving your truck up a slope, but nothing like climbing through the atmosphere.

3. Lack of auto-responsive fuel mixture and fuel injection controlled by a computer. Modern auto engines use O2 sensors to constantly monitor mixture for optimal performance. Without that, even with GAMIs and a fancy engine monitor, it's still up to the nut in the left seat to stay on top of it. Constant power settings and altitude definitely make that easier though. Most pilots run too rich anyway. According to Mike Busch, you can lean to peak EGT at 75% power or less.

4. Fixed timing, like Mongo said.

5. Can't really point to the transmission analogy... we have constant speed props that let us optimize for cruise.

6. Poor cylinder cooling due to uneven and inefficient air cooling requires a sloppier bore/piston tolerance for expansion. Not winning any efficiency points there.

Many things combined contribute to burning more fuel than a modern auto engine. Take a look at the challenges involved in converting an auto engine to an aircraft though and suddenly the simplicity of a good old Lycoming or Continental seems...okay.

dirtstrip wrote:Weight doesn't have so much to do with it as we think. A locomotive gets over a 100 mpg considering similar weight ratio per pound of useful load using diesel electric. Expanding that theory, a diesel electric bowling ball could be awesome.

http://gas2.org/2010/05/25/freight-trai ... ince-1980/

The article states "It would be equivalent to a Mazda Miata (which weighs about one ton) getting 480 miles per gallon. Imagine that! In the real world, a fully loaded train (depending on the kind of train) a gallon of fuel per mile."

I don't see 100 mpg here. I see 1 gallon / mile

CSX freight states that they can move 1 ton of freight nearly 500 miles (480 miles) on a gallon of fuel. However, they weigh 5000 tons on average so that's 5000 gallons /480miles or 10.4 Gallons /mile which is really good, but it's not 100mpg its .096 miles per gallon.

The article mentions the miata getting 480 miles per gallon, but you have to move 5000 of them at once to cash in on the savings. A train can handle 5000, but as the number declines, so do the savings. Economy of scales.

I guess I'm not the only one pondering the question. STOL could have solved the riddle by telling us how much his snow plow truck engine burns dragging his airplane around.

I look at it like this. I travel cross country all the time. 356 road miles. My truck will NOT make that on a tank of gas (24Gal). But its real close. takes 6M hrs, 5 if I'm in a hurry, and dont run into troopers. My 7ECA did the trip in 3 hours, and used around 21 gals. But I upgraded to a scout now, so 2.5 hours, at lets say 10gal/hr, so 25 gals. half the time, for the same fuel. Even compared to the girlfriends jetta, which can do the trip with 12 gals, the extra $70 is well worth half the time travel.

1. Typical prop efficiencies hover around 68%-72% on a good day. A middle-of-the-road manual tranny does better than 90% on a bad day. If it didn't, it would cook itself.

2. Drag goes up as the square of the speed increase. If you drove fast enough to keep up with a 182, the Ford would be subject to the same pesky laws of physics.

3. Timing. Many car engines (not all) use knock sensors to advance to the onset of preignition. On a 4.6l I had, for example, the advance was around 3 degrees retarded from the onset of roughness. That isn't a luxury we have with our Model T technology on our planes. Optimal timing plays a moderate role in specific fuel consumption.

4. You use 50%-70% power for cruise in a plane. In a car,perhaps 15% to 20% (maybe 25% in a small car). While you usually burn more fuel per HP at lower power settings in general, it is offset by the lower HP...

5. I get ~13-14 mpg in the 182. The distance on average to a distant destination airport is 15% less than the road difference, and often as much as 30%. So it is like getting perhaps the equivalent of 15-16 mpg, while going over twice as fast. Not bad.