Do heavy planes really consume more fuel?

[Ecky]

I know little about planes, but as it applies to cars, driving faster burns more fuel, not less. A linear increase in speed does not equal a linear increase in drag, and so the faster you go, the worse your economy.

If you need to lift more weight, you are going to create more turbulence by displacing more air, and that takes energy, which ultimately comes from the fuel.

[freebeard]

Weigth and thrust are just arbitrary [although related] numbers. It's all down to the airframe. Primarily the aspect ratio of the wing.

Although there is some interesting work with the Prantl-D wing. It uses washout on the wingtips to deflate wingtip vortexes.


http://www.nasa.gov/centers/armstrong/news/FactSheets/FS-106-AFRC.html

Something something span-wise loads something.

[jamesqf]

Humm... Piper Cherokee 180, weight 1230 lbs empty, 2400 max, fuel consumption 8-10 gph. Boeing 747, weigh 128,700 lbs empty, 255,000 max, fuel consumption ~3600 gph (or about the weight of 10 Cherokees).

So yes, I think it's fair to say that heavier aircraft burn more fuel :-)

[redpoint5]

Originally Posted by jamesqf

Humm... Piper Cherokee 180, weight 1230 lbs empty, 2400 max, fuel consumption 8-10 gph. Boeing 747, weigh 128,700 lbs empty, 255,000 max, fuel consumption ~3600 gph (or about the weight of 10 Cherokees).

So yes, I think it's fair to say that heavier aircraft burn more fuel :-)

The Cherokee cruises at 124 kts compared to the 740 at 573 kts. We haven't held enough variables constant to make a comparison.

... and the 747 is ~100x heavier, not 10x.

Economies of scale generally favor larger machines. It would take more fuel to carry the same payload as the 747 using a fleet of Cherokees.

[3-Wheeler]

Originally Posted by redpoint5

....Economies of scale generally favor larger machines. It would take more fuel to carry the same payload as the 747 using a fleet of Cherokees.

Similar to a comparison between a single Grey Hound bus and a enough cars to carry the same number of people.

Jim.

[RedDevil]

Originally Posted by redpoint5

The Cherokee cruises at 124 kts compared to the 740 at 573 kts. We haven't held enough variables constant to make a comparison.

... and the 747 is ~100x heavier, not 10x.

Economies of scale generally favor larger machines. It would take more fuel to carry the same payload as the 747 using a fleet of Cherokees.

He meant just the fuel a 747 burns in an hour weighs as much as 10 complete Piper Cherokees
Quite impressive.

But it is just 8 gallon per passenger per hour, or thereabouts. Say 70 mpg per passenger.
About the same as the Cherokee, I guess.

A loaded Greyhound bus beats anything smaller with an ICE on mpgpp.
Trains might do better though.

[redpoint5]

Originally Posted by RedDevil

But it is just 8 gallon per passenger per hour, or thereabouts. Say 70 mpg per passenger.

... and the 747 would arrive at the destination much sooner than the Cherokee, reducing the number of hours that it has to massively consume fuel.

The fuel consumption is quite astonishing. 1 gallon per second.

I think I once calculated that a fully loaded 747 (or other jumbo jet) gets 100 mpg per person, which is somewhat close to what you said above. 70 mpg per passenger is not too shabby. We don't need to shame people for flying considering they probably wouldn't save any fuel by driving unless they had 3 or more passengers in their vehicle.

Generally, I choose to fly when traveling solo. With 2 people, it's a toss up on if I fly or drive, depending on current fuel prices, airfare, and how valuable my time is. 3 or more and I make every effort to drive.

[RedDevil]

It depends on the fuel load too.
My nephew is a pilot flying 747s for KLM. I thought he said it uses 8 kilos of fuel per kilometer, which would be around 2500 gallon per hour.
But that could be with the tanks near empty; if full the plane can be over 50% heavier.
I bet anything in the range from 70 to 100 mpgpp is about right.

Ships are terrible for mpgpp, especially the fast ones.
I once took a ferry from Lübeck, Germany to Helsinki, Finland. 1100 km in 23 hours at a speed of 56 km/hour. Enough to break the ice up to 200 meters away by the wake alone. The ferry doubles as an ice breaker.
(not that that was necessary in the record heat wave at the time)
It used 30 metric tonnes of diesel fuel per hour. 700,000 liters for the trip. Over 300 liters (80 gallons) per passenger. 9 mpgpp...

In the weekends it did not use its turbine jet engines but conventional piston engines, taking almost twice as long for the trip but using only 4 tonnes of diesel per hour.
Weekend trips are favorite with the Fins as they get 2 whole days on board to enjoy the view of the Baltic sea and the tax free liquor shop.

[redpoint5]

Interesting about ships. I'd like to read a little more, but I found this graph interesting and the accompanying explanation.



https://people.hofstra.edu/geotrans/...inerships.html

[Natalya]

The plane must use fuel to overcome gravity.

The more massive plane has more acceleration towards the ground because of gravity acting on the increased mass.

Therefore the more massive plane must expend more fuel to overcome that acceleration.