Fuel efficient freight planes

[Jonas Heisenberg]

Hi all.

Looked around a bit for fuel efficient (big, commercial) airplanes.
The best ones I found were the Tupolev TU-330 and the Antonov AN-70.
They had cruising speeds/fuel consumption of 780-850 km/h and 118-125
g/t-km. Now my question: would lowering the cruising speed to e.g.
300-400 km/h make them more efficient?

Thanks, Jonas

[Larry Fransson]

On 2003-11-13 18:25:46 -0800, (Jonas Heisenberg) said:

> They had cruising speeds/fuel consumption of 780-850 km/h and 118-125
> g/t-km. Now my question: would lowering the cruising speed to e.g.
> 300-400 km/h make them more efficient?

Most aircraft have a "long range" cruise speed that is less than their maximum cruise speed. But it is more on the order of around 90% of maximum cruise. At the speeds you suggested, they would likely burn even more fuel, and it might even be slower than their minimum controllable airspeed.

--
Larry Fransson
Seattle, WA

[Steve McCroskey]

Jonas,

At some point you'll reach a point of diminishing returns. As
speed decreases induced drag increases and you need to increase power
to maintain altitude/speed. Most jet aircraft have a maximum cruise
power, long range cruise power and intermediate cruise power setting.
Intermediate gives the best time to burn ratio, but if your prime
concern is fuel savings and extended range, then you could fly at the
LRC setting, which, in some aircraft, could yield up to a 15% increase
in range. The expense, though, is flight time.

P.

(Jonas Heisenberg) wrote in message >...
> Hi all.
>
> Looked around a bit for fuel efficient (big, commercial) airplanes.
> The best ones I found were the Tupolev TU-330 and the Antonov AN-70.
> They had cruising speeds/fuel consumption of 780-850 km/h and 118-125
> g/t-km. Now my question: would lowering the cruising speed to e.g.
> 300-400 km/h make them more efficient?
>
> Thanks, Jonas

[Jonas Heisenberg]

Thanks for your replies.

So as I understand it, these planes are constructed to operate most
economically at ca. 80-90% of their maximum speeds. Has it ever been
tried to build planes that are built specifically for lower speeds and
higher efficiencies (recent - no WWII)?

Jonas
> At some point you'll reach a point of diminishing returns. As
> speed decreases induced drag increases and you need to increase power
> to maintain altitude/speed. Most jet aircraft have a maximum cruise
> power, long range cruise power and intermediate cruise power setting.
> Intermediate gives the best time to burn ratio, but if your prime
> concern is fuel savings and extended range, then you could fly at the
> LRC setting, which, in some aircraft, could yield up to a 15% increase
> in range. The expense, though, is flight time.

[Pat Barry]

Yes- look at a Twin Otter.



Jonas Heisenberg wrote:

> Thanks for your replies.
>
> So as I understand it, these planes are constructed to operate most
> economically at ca. 80-90% of their maximum speeds. Has it ever been
> tried to build planes that are built specifically for lower speeds and
> higher efficiencies (recent - no WWII)?
>
> Jonas
> > At some point you'll reach a point of diminishing returns. As
> > speed decreases induced drag increases and you need to increase power
> > to maintain altitude/speed. Most jet aircraft have a maximum cruise
> > power, long range cruise power and intermediate cruise power setting.
> > Intermediate gives the best time to burn ratio, but if your prime
> > concern is fuel savings and extended range, then you could fly at the
> > LRC setting, which, in some aircraft, could yield up to a 15% increase
> > in range. The expense, though, is flight time.

[Larry Fransson]

On 2003-11-15 17:21:08 -0800, (Jonas Heisenberg) said

> So as I understand it, these planes are constructed to operate mos
> economically at ca. 80-90% of their maximum speeds.

I don't know that they are designed and built that way. That's just the way it works out

> Has it ever bee
> tried to build planes that are built specifically for lower speeds an
> higher efficiencies (recent - no WWII)

http://www.nasm.edu/nasm/aero/aircraft/rutanvoy.ht

[Jonas Heisenberg]

The Twin Otter seems to be slower, though less fuel efficient than the
planes mentioned above. Probably the Air-Ships of the 30 were? Saw a
documentary about someone who went 1200km with a glider in the Andes.
Maybe Motor-gliders would be most efficient?

> Yes- look at a Twin Otter.
>
>
>
> Jonas Heisenberg wrote:
>
> > Thanks for your replies.
> >
> > So as I understand it, these planes are constructed to operate most
> > economically at ca. 80-90% of their maximum speeds. Has it ever been
> > tried to build planes that are built specifically for lower speeds and
> > higher efficiencies (recent - no WWII)?
> >
> > Jonas
> > > At some point you'll reach a point of diminishing returns. As
> > > speed decreases induced drag increases and you need to increase power
> > > to maintain altitude/speed. Most jet aircraft have a maximum cruise
> > > power, long range cruise power and intermediate cruise power setting.
> > > Intermediate gives the best time to burn ratio, but if your prime
> > > concern is fuel savings and extended range, then you could fly at the
> > > LRC setting, which, in some aircraft, could yield up to a 15% increase
> > > in range. The expense, though, is flight time.