Newsgroups: sci.aeronautics.airliners
From: drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Subject: Re: altitude questions
Date: 03 Nov 93 23:30:15 PST

In article <airliners.1993.687@ohare.chicago.com>,
 <campbjw@wkuvx1.bitnet> wrote:
>In the Nashville, TN area where I live, Air Traffic Control usually
>assigns commercial flights to altitude levels of 28000 to 33000 feet -
>what is the highest common flight level used and what is the maximum
>flight level the average commercial plane can attain?

I can't answer that one.

>       Related to
>that, what are the limiting factors in altitude attainment for
>commercial planes?

Two major factors spring to mind immediately.  One is the cabin pressure
differential.  Typically around 8 psi.  This limits most airliners to about
40,000 ft (DC-10s were designed for a higher cabin pressure differential -
about 10 psi if memory serves).  The other limit is the aircraft's
certification altitude.  The 757 for instance is certified to 42,000 ft
last I heard, but there is nothing physically preventing the airplane from
climbing higher (other than the cabin pressure consideration).

The technical performance limitations are mostly wing area and engine
thrust available.  These can be broken down into aspect ratio, span,
induced drag, or other factors/combination of factors depending on how one
wishes to approach the problem, what variables are ground-ruled as fixed,
etc.

>       Are these altitudes typical for trans-oceanic
>flights?  What are typical altitudes for European flights - I assume
>somewhat less since distances travelled are often less than in
>North America?  Does direction make much difference in altitude
>assignments?

Actually, European flights (as defined by flights originating in and
terminating in Europe) are very short compared to the average US flight
length.  We, Boeing, have had carriers who are strictly intra-European ask
for airplanes with much less range than our airplanes are capable of right
out of the box.  For instance, SAS I believe showed average flight lengths
somewhere near 300 miles.  American has average flight lengths somewhere
near double that.  Interestingly, I think Southwest has a relatively short
average flight length.  Karl probably has all the great data and could give
us real hard numbers.  :-)

Typical intra-European flight levels are around 27,000 ft, if the results
of one study I worked on can be generalized to this extent.


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

Newsgroups: sci.aeronautics.airliners
From: drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Subject: Re: What does the 737-X do for Southwest?
Date: 07 Dec 93 11:39:18 PST

In article <airliners.1993.780@ohare.chicago.com>,
 <Watson_John/MEPTEC_dalhp002@dal.mobil.com> wrote:

[Some stuff deleted]

>The new 737-X aircraft have larger engines and a bigger more efficient
>wing.  However, the downside of these increases is a reported 10,000
>pound increase in empty weight.  From what I have read, the airplane
>should not have extra range and can cruise at 41,000 feet for best
>efficiency.

I don't work on the 737-X, so take this with a small grain of salt, but
that 10,000 increase is probably overstated.  Every PD program goes
through a phase where the airplane is too heavy.  We do the basic design,
and then everyone adds features until the airplane is way too heavy.  From
there we subtract stuff until the airplane is at its target weight, which
is determined primarily by aero performance issues and structural
requirements.  Its the same as with a car design, or anything else.
Computer programmers call it 'creeping featurism'.

I have seen their payload-range curves and the airplanes do indeed have
substantially more range than any of the previous models.  The decision to
cruise at 41,000 ft is probably driven by the faster wing.  That is, no
matter how fast the airplane is capable of flying, unless you can get above
the mass of traffic around 35,000 ft it just won't matter - you'll fly the
same speed as everyone else (not always true, just a rule of thumb).  This
can be very important on crowded routes like Boston to Chicago.  Airline on
time performance is judged by block time, not cruise efficiency.

>It would seem to me that for Southwest, they will not be able to take
>advantage of the longer range and higher cruising altitude offered by
>this option.  It would seem that at lower altitudes and shorter route
>segments, that the higher weight would be more of a penalty than a
>benefit.  One might say that Southwest is planning on making longer
>stages or even cross county routes where this would make sense.  If
>so, Southwest would loose one of their advantages in not having to
>have full galleys with ovens, etc.  {I don't think they can get by
>with three hour flights with just penuts.}

I can't speak for Herb Kelleher, but I would not be surprised to see that
extra range used for reducing turn times and operating costs by tankering
fuel.  Or that extra Max Zero Fuel Weight to start hauling more cargo.  The
737-X offers more capability, not just added range.  The galley problem can
be handled with sandwiches and drinks.  Hot meals are not neccessary.


>Can anyone shed any light on how the "X" upgrade would beneift
>Southwest?  Is the new wing so efficient, that short hauls are made
>more efficient?  Was the price that Boeing offered so competitive to
>get the new version off the ground that it was too good to pass up?

Another reason that Southwest may be interested is that the 737-X should
have lower maintenance costs.  One of Boeings goals in general is to reduce
the cost of keeping the airplane in the air, and I believe the 737-X people
are working that pretty hard.  Another reason is that even with all the
improvements in maintenance, speed, and range, the price of the 737-X is
not likely to be much more than the current family.  This is a real value
to a customer, any customer - not just Southwest.  The Boeing goal is to
continue to reduce the cost of our products without reducing value.

Just a note, I saw that same article in the Seattle Times about the -600
number being held for an airplane less than 100 seats.  I checked, and that
was a journalistic brain fart.  The -600 will be the same size as the
current production -500.  The -700 that Southwest ordered is the same size
as a current production -300.  There is no -900.

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

Newsgroups: sci.aeronautics.airliners
From: drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Subject: Re: 767 Service Ceiling
Date: 05 Aug 94 03:35:28

In article <airliners.1994.1487@ohare.chicago.com>,
Karl Swartz <kls@ohare.Chicago.COM> wrote:
>>  I was wondering if anyone has information on the service ceiling of
>>any of the 767 variants.
>
>According to a chart in a Boeing 757/767 brochure I have, the initial
>cruise altitude of the 757 at low gross weight is 42,000 ft.  The 767
>(both -200 and -300) is 42,000 to 43,000 -- it's a graph, not hard
>numbers, and I can't tell for sure.  Near the maximum TOW, initial
>cruise is about 35,000 ft.

Initial cruise altitude is weight and thrust dependent for any given
airplane type, until you get to the maximum certified altitude, which is
the highest the airplane is legally permitted to fly with passengers aboard
in commercial service.  Maximum certified altitude is the highest alitude
at which the airplane can maintain an 8,000 ft pressure altitude in the
passenger cabin.  This is generally a structural limit of the body skins.
There are obvious economic tradeoffs that determine what maximum
certified altitude to design for - the higher weight of the stronger skins,
which cost more in terms of fuel burn for the enormous percentage of time
that the airplane is not operating at or near its maximum certified
altitude, must be balanced against the increased fuel burn associated with
poor airways routing in heavy traffic.  The short hop guys (Southwest comes
to mind) don't give a rip about high altitude capability because their
routes don't give them time to use that capability; therefore, they are
carrying around, and paying for, capability that they don't use.  The
general public might care because carrying that extra weight makes their
tickets more expensive.  The long haul guys (like some of United's routes)
desparately want the high altitude capability because they can save gobs of
time and fuel by getting above all the short haul traffic and getting
better routing to their destination.  This becomes a knotty problem because
the airplane is generally built with only one kind of body skin, and that
choice must be all things to all operators.  No one really appreciates the
dilemmas that face the airplane designer.  I know this is true because we
never get the hot babes and no one ever buys us a beer.  :-)

>Higher alititude generally means better cruise performance, with the
>limiting factor being cabin pressurization and not aerodynamics or
>engines, so I'd guess the top cruise altitude is close to or equal to
>the service ceiling.  (With oxygen for the pilots, I suspect either
>aircraft is capable of significantly higher altitudes.)

Higher altitudes up to about 36,000 ft mean better cruise performance.
Flying above the tropopause is done to get better airways routing and to
get out of the traffic (one must get out of the traffic to get better
routing is actually how it works).

Interestingly, service ceiling is a light aircraft type of parameter.  It
is fairly meaningless for heavy commercial airplanes.  The cruise altitude
is generally pretty close to optimum cruise altitude at any given stage of
the flight.  This is an economic issue as it is pretty costly to fly off
optimum.  The 500 fpm climb rate line is generally well above the optimum
cruise altitude, and service ceiling is defined as the altitude where the
rate of climb is 100 fpm.  The lowest climb parameter I've seen is 300 fpm,
and that is well above even the 500 fpm line.

The thought I'd like to leave you with is this:  The heavy commercial
jet transport is designed for operation in a given flight envelope.  That
envelope does not include 100 fpm climb rates.  Therefore, a better
indication of altitude capability is certified maximum altitude.

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