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Q: Basic Flight (Airplane) Physics ( Answered 5 out of 5 stars,   2 Comments )
Subject: Basic Flight (Airplane) Physics
Category: Science > Physics
Asked by: rabbt-ga
List Price: $5.00
Posted: 16 Jun 2006 20:02 PDT
Expires: 16 Jul 2006 20:02 PDT
Question ID: 738854
My fiance gets nervous about flying, and one way that he expresses
this is to complain about the plane banking during takeoff. He insists
that if the plane had simply started out "going the right direction",
then there would be no need for banking.

I'm fairly terrible at physics, but I am convinced that planes bank
during takeoff for reasons related to gaining altitude in the aircraft
safely, or perhaps to the coordination with the flight control towers.
I have been looking for information on this on various flight
mechanics websites, but haven't found anything useful so far. So, why
do planes bank at takeoff? And, if the plane "started out going the
right direction" wouldn't they still need to?
Subject: Re: Basic Flight (Airplane) Physics
Answered By: byrd-ga on 17 Jun 2006 08:16 PDT
Rated:5 out of 5 stars
Hi rabbt-ga,

Actually, airplanes don?t really bank during takeoff itself, but keep
their wings level until reaching a safe height (altitude) above the
ground, after which they then may turn (bank) for one of a number of
reasons, none of which really have anything to do with flight physics,
or aerodynamics. Your speculation about control towers is much closer
to the truth. Here?s how the whole thing works.

First of all, unlike some smaller or more specialized aircraft, a
large jet airliner must take off from a runway. It is designed to need
that long, level, paved surface in order to gain enough speed to lift
off safely.

And then, in addition to enough speed, all aircraft must generally
take off INto the wind in order to maximize lift and get best engine
performance. Exceptions would be if the wind is calm or very light, or
blows across the runway (as long as it?s not blowing too hard). What
that means in practice is that, for an airport with one runway (or two
or more parallel runways), an aircraft has only two choices of takeoff
direction, depending on which way the wind is blowing. If there is one
(or more) intersecting runway(s), there may be four choices. At some
very large airports, there may be as many as six or eight choices of
takeoff direction, but which direction is used at any given time is
directly related to the direction of the wind. Watch the traffic at an
airport sometime, and you?ll see that all the airplanes are both
taking off and landing in the same direction. Listen to the weather
before traveling and see which direction the wind is from. That?s the
direction you?ll be taking off.

Ok then, suppose for instance that the runway is lined up north and
south, and the wind is blowing from the south. An aircraft will then
have to take off to the south in order to follow the rule of taking
off into the wind. But then suppose the destination of that flight is
to the north. You see that, for reasons of safety and performance, the
airplane simply could NOT take off ?going in the right direction.? And
then, unless there is some other reason for the airplane to fly a long
distance out of its way, it just makes sense for it to turn to the
?right direction,? in this example north, as soon as possible. And as
long as it is at a safe altitude, it?s most practical for it to begin
turning as soon as possible, even while still climbing.

In this scenario, the plane would still have to turn after takeoff if
it were heading east or west or any direction other than south. On the
other hand, if the plane?s destination were due south, it could simply
fly straight after takeoff with no need to turn (bank).

BUT -- there are a few other reasons why a plane turns after takeoff
that might still result in that plane turning even if it was
ultimately going the same direction as the runway it took off from.

The main reason airplanes turn after takeoff, or before landing, is
for safety in operating close to an airport, where there might be a
lot of other airplanes in the air. The job of the Air Traffic
Controller in the airport Control Tower is to keep all these airplanes
out of each other?s way. So controllers instruct pilots which way to
turn, and pilots comply with these instructions. These instructions
are given and received via radio, and pilots of airliners are in
constant radio contact with air traffic controllers, who are in both
the control towers at airports, and in control centers at various
locations across the country and the world.

In addition, just as a driver on the ground may use a map to plan his
trip, airliners use maps too (called charts) and follow flight plans
to get where they are going. And just like a car following roads on
the ground, airliners follow invisible ?roads? in the air. Sometimes,
just like in a car, they have to go briefly in one direction or
another just to get or stay on the road, and that may not always be
exactly ?as the crow flies.? So you see, even if the airplane takes
off ?going the right direction? in general, it may still need to turn
to in order get established on the right road.

One other reason why aircraft frequently make a turn immediately after
takeoff is for noise abatement. It?s no secret that large jet
airliners make a lot of noise, and there are many airports located in
congested areas where there are a lot of homes and businesses. In
order to minimize the impact of the noise on these areas, aircraft are
instructed to climb to a higher altitude as soon as possible, and
often also to turn to a direction away from any congested areas until
reaching an altitude where the noise is no longer a factor, after
which they then may turn to the desired direction of travel.

So to sum up, the direction of takeoff for any aircraft is determined
by the direction of the wind. The aircraft will take off into the
wind, which action IS determined by flight physics, or aerodynamics.

After takeoff, the aircraft may turn (bank), on instructions from the
air traffic controller, for one or more of several reasons, including

  - aircraft separation
  - noise abatement 
  - getting established on the planned route

The turning itself is not dictated by flight physics, but by
considerations of safety and navigation.


Here are a few resources for you, that explain a bit more about all this:
Check out Chapter 8 on ?Air Traffic Control? from the Air Transport
Association (ATA) ?Airline Handbook.? Scroll down to the section on ?A
Typical Flight,? which says,
?The tower assumes full control of the aircraft as soon as it reaches
the end of the runway it will use for takeoff. When the runway is
clear, the tower grants permission for takeoff. It also instructs the
crew on the heading, or direction, it should follow immediately after

Here?s a document from Bristol International airport in England that
addresses many of these same points. It?s specific to Bristol in some
ways, but also a good general explanation. 

  *Note: this is a .pdf document, which will require you to have Adobe Acrobat  
  Reader in order to view. If you don?t already have that, you can download a 
  free copy, here:

This document from the FAA is kind of technical, but it?s great at
explaining some of the factors that air traffic controllers must take
into account when separating departing and arriving traffic. They also
give examples of the kinds of instructions controllers give to pilots
when clearing them for takeoff, including telling them which direction
to fly and when/if to turn and where: 

If you?d like to pursue this a little further, here?s the main index page:

Here?s a simple but excellent explanation of how the overall air
traffic control system works:


If you and/or your fiance would like to explore basic flight physics a
little further, one of the best resources is NASA?s ?Beginner?s Guide
to Aerodynamics.?  Find it here:

For a good illustration of banking in particular, how it works and the
forces involved, check out this page: 

?How Stuff Works? also has a good primer on how airplanes fly:


Finally, for anyone (like your fiance, for instance) who?s nervous
about or afraid of flying, here are a few things you might like to
look into.

Here?s a free online self-help course:
List of other resources related to the fear of flying: 

Consider giving your fiance (and yourself!) a flight lesson at your
local airport. Look in the yellow pages under ?Aircraft? for ?Flight
Training Schools? and make some calls. When you do, be sure to ask if
they have a program or instructor who specializes in helping people
with a fear of flying.

A couple of other sources for finding local flight instructors are: 

AOPA (Aircraft Owners and Pilots Association) Flight Training website,
which answers many questions about flight training and can help you
locate a local instructor:

(Note: if the page doesn?t load right, scroll way down to the bottom,
under the heading ?Flight,? click on the link for ?Flight-Schls.?


I hope this information answers your question about why airplanes bank
after takeoff. If anything isn?t clear, please use the ?Request for
Clarification? feature to ask before rating and closing your question.
I want to be sure you?re satisfied with the information provided.

Best wishes,

Search strategy:

I answered the question mainly from my own knowledge and experience as
an Instrument Rated Commercial Pilot. In addition, I then used a
combination of my own bookmarks and search to locate supporting
information. Search terms used included:

[aircraft ATC takeoff]
[airlines takeoff direction]
["flight physics" OR aerodynamics]
["fear of flying" OR "afraid of flying"]
rabbt-ga rated this answer:5 out of 5 stars
Thanks so much for the in-depth response -- and the great references
for future research!

Subject: Re: Basic Flight (Airplane) Physics
From: stanmartin1952-ga on 17 Jun 2006 13:29 PDT
As far as I know, planes have to take off into the wind and then bank
to change direction to where they want to go.
Subject: Re: Basic Flight (Airplane) Physics
From: byrd-ga on 25 Jul 2006 05:31 PDT
Hi rabbt-ga,

You're very welcome. I'm glad you found the information helpful, and
do hope you'll follow up on some of those resources. Thank *you* for
the kind words and five stars. Best of luck to you - and your fiance.


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