Newsgroups: sci.aeronautics.airliners
From: drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Subject: Re: Efficiency of commercial planes
Date: 06 Oct 93 03:50:49 PDT

In article <airliners.1993.613@ohare.chicago.com>,
Andy Ruina  <ruina@cornell.edu> wrote:

>How efficient are planes?
>
>The number I would like to know is the total passenger miles
>of the airline industry divided by the total number of gallons
>of fuel used. That is, how many passenger miles per gallon to
>planes actually get on average.

I don't have the data to do this one.

>But other breakdowns would be interesting, say by length of
>flight.  How good are the best planes running optimal distances
>with full passenger load? etc.

This one is a bit easier.  :-)
A good long range airplane will take you 5 or 6 thousand miles for about
50 miles per passenger per gallon.  And that isn't at no measly 60 MPH
either.  A 757 cruises at Mach 0.80, a 747 cruises at Mach 0.85+.  Do
*that* in your VW Rabbit.  :-)

>Also, how small a fraction of the average fuel cost per passenger
>is  the incremental fuel cost of adding a passenger?

It will vary pretty widely depending on the airplane, the engines, the
condition of the engines, the range the airplane is intending to fly, and
the weather (hotter is always worse).  All that to say a precise answer is
very difficult and will wobble a great deal.  A good tire kicking number is
to figure about half the weight of the passenger and bags.  That is, if a
180 lb passenger+bags is added at the last minute, you can probably figure
that on the average flight on the average airplane somewhere near 90 lb of
fuel (more for longer ranges, older aircraft, etc).  That is about 15
gallons.

>I was told by a reasonably credible person that planes get
>about 15 passenger miles per gallon (worldwide average) but
>that Lufthansa gets about 25 passenger miles per gallon. I
>find this interesting because it meanse that flying, on average,
>is as fuel intensive as driving a fuel-hog car alone. But is this
>true?

Kind of depends on what all you are including in the worldwide average of
planes.  I don't think I've seen a passenger/MPG number under 30 for the
latest airliners.  The general aviation types bring the average down, as do
the military types.

I'd also like to reemphasize that this is done at speeds and energy levels
much higher than your 'fuel-hog' car.  Consider that doubling the speed
requires eight times the power and that the average airliner cruises at
speeds about ten times faster than your car and those numbers become much
more impressive.

Good luck!  Fly lots!  We could use the business...

--
Terry
drinkard@bcstec.boeing.com
"Anyone who thinks they can hold the company responsible for what I say has
more lawyers than sense."