airplane structural terms
boeing707
I've come across a few terms relating to the fuselage and wing
structure of airplanes that I dont understand. Can somebody please
define the following terms:
1. Mean Aerodynamic chord (relating to wing structure)
2. Percent of mean aerodynamic chord (%MAC) (i think this relates to
wing loading)
3. Wing incidence
I've also seen some blueprints for the 707 (the greatest airplane ever
made :) ) and saw two abbreviations that i did not understand:
1. STA (relating to fuselage) and how are the STA numbers determined?
2. WPL (relating to wing) and how are the WPL numbers determined?
I appreciate any help you may give me.
Ken Smith
ramp agent - USAirways (FLL)
email to Boei...@bellsouth.net
"Nice goin', sweetheart," George Kennedy as mechanic Joe Patroni,
talking to a bomb damaged 707 which returned all passengers and crew
safely, in the movie 'Airport'.
Scott Jacobson
measurement in inches (for Boeings anyway, might be metric for Airbus)
from a zero point (usually near the nose). Commonly used to detemine
weight & balance for an aircraft, or to tell a loader where to place a
given piece of cargo, etc.
MAC: Mean Aerodynamic Chord. As you know, for an ordinary aircraft to fly
the center of balance must be between the leading
and trailing edges, otherwise the plane will be out of balance and fall on
it's nose or tail. Easy enough to measure on a straight wing where the
leading & trailing edges are parallel. But on a swept wing airplane it's a
different story!! So MAC weight & balance formulas are developed for each
type of aircraft and give you a balance point as a percentage of the mean
chord of the wing.
Scott
Ken Ishiguro
1. Chord is an imaginary straight line drawn through the wing from the
leading edge to the trailing edge. Since the wing tapers, the mean
chord is an average length and position. The aerodynamic chord is a
rather complicated calculation (as opposed to the geometric chord).
2. %MAC refers to where the center of gravity falls along the chord
when the aircraft is loaded. There is a forward MAC and aft MAC limit,
and the CG must fall between these points.
3. Wing incidence is the angle (viewed from the side) that the wing is
attached to the fuselage. In other words, if the leading edge were held
in one place and the trailing edge were moved up or down, the angle of
incidence would be changing. Obviously, most wings are securely bolted
to the fuselage, and the AI is fixed (except for the Boeing Tiltrotor).
An "all flying" horizontal tail would be an example where angle of
incidence is variable.
BTW, angle of attack is the angle the wing is meeting the airflow. If
you were to suddenly pull the aircraft nose-up, angle of attack would
increase, while angle of incidence would stay the same (unless the
pull-up tore the wings off) :-)
4. STA is "station", also can be FS for "fuselage station". This is
the coordinate system used to locate items or points on the aircraft.
FS0 is usually at the nose, or just ahead of the nose. It the goes in
inches back to the tail. Inside an aircraft structure, you will often
find ribs, beams, etc. marked with the station number. One complication
is on "stretch" aircraft. In order to keep station numbers consistent
between models (a certain gizmo is always at FS1200 regardless of
model), some manufacturers come up with screwball station number systems
to accomodate the stretch.
5. WPL- I think you mean WBL, which is Wing Butt Line (no, a butt line
is not the Rockettes)! BL0 is the centerline of the fuselage. Boeing
uses LBL and RBL for left and right of centerline in inches, but WBL's
on the wing. Douglas uses negative numbers to the left and positive to
the right, with no Wing BL's.
Vertical coordinates are the Water Line (WL). On a 747, WL200 is the
top of the cabin floor, which places WL0 slighly below the tires. IIRC,
Douglas places WL0 at the window line, and uses positive or negative
coordinates.
Like lots of other aircraft stuff, FS, BL, and WL is from the nautical /
shipbuilding industry.
Ken Ishiguro
David Lednicer
This is actually an aerodynamic term. It refers to a special spanwise
defined as:
(b/2)
/
MAC = 1/wing area * / c^2 dy
/
(-b/2)
where b is the wingspan and c is the local chord. The MAC is used as a
datum length for calculating pitching moments and is also a datum to
which the aerodynamic center of the wing is referred.
> 2. Percent of mean aerodynamic chord (%MAC) (i think this relates to
> wing loading)
No, this is actually a way of referring to the aircraft's center of
gravity location.
> 3. Wing incidence
This is the angle of pitch that the wing is attached to the fuselage
at.
> 1. STA (relating to fuselage) and how are the STA numbers determined?
Stations (STA) are measurements in the axial direction from some given
reference location. These measurements, on Boeing aircraft, are made in
inches. In a true interpertation, fuselage station (FS) 732 is 732
inches aft of the reference. The nose on the basic 707 is at station
130. However, the 707 came in various body lengths. When Boeing
stretched the fuselage to these lengths, they introduced a region of the
fuselage that is all identified by the same station number. For
example, on the 707-120, the nose moved forward 80 inches (the wing box
stays at the same FS location). Hence, the nose is really at FS 50
(130-80), but in the Boeing system, the nose is still at station 130,
and from station 620, for the next 80 inches, locations are 620A, 620B,
etc.
There are also wing, horizontal tail, etc. stations, which are measured
in some local axis system. Wing stations on the 707 are measured along
the forward spar in the wing chord plane (as near as I can determine).
> 2. WPL (relating to wing) and how are the WPL numbers determined?
> I appreciate any help you may give me.
Are you sure you're not looking at WBL, not WPL? WBL is the wing
buttline, measured spanwise in the wing chord plane system. WBL 0 is at
fuselage BL 6.65 on the 707-120.
-------------------------------------------------------------------
David Lednicer | "Applied Computational Fluid Dynamics"
Analytical Methods, Inc. | email: da...@amiwest.com
2133 152nd Ave NE | tel: (206) 643-9090
Redmond, WA 98052 USA | fax: (206) 746-1299
Don Stauffer
boeing707 wrote:
> Hi everybody.
> I've come across a few terms relating to the fuselage and wing
> structure of airplanes that I dont understand. Can somebody please
> define the following terms:
> 1. Mean Aerodynamic chord (relating to wing structure)
This is for a wing which has a planform which is NOT a rectangle. The
chord is the distance from the leading (front edge) of the wing at any
distance from the fuselage measured parallel to the centerline of the
aircraft, to the trailing edge.
A rectangular wing would have its chord equal everywhere along the wing.
One could compute an average geometrical chord with simple geometry on a
non-rectangular wing. The mean aerodynamic chord would be very similar to
this geometrical average chord for all practical purposes.
> 2. Percent of mean aerodynamic chord (%MAC) (i think this relates to
> wing loading)
This is the location of the center of gravity. Rather than refer to
station, to be defined below, it is referred to a percentage of chord
because this number has a great deal to do with the stability of the
aircraft. Lets say an aircraft has a chord of five feet. Lets say the
center of gravity for longitudinal (fore/aft) balance is at a point one
foot back from the leading edge. The CG is then at 20% of chord. The
aircraft will go unstable if a different weight distribution moves the CG
back beyond a certain critical percentage of the chord, depending on the
airfoil, the tail, and other design features of the aircraft.
> 3. Wing incidence
We mentioned above that the chord is the line from the forward most
extension of the leading edge to the very trailing edge. Not only is the
distance important, but the angle between this line and the centerline of
the aircraft is important. The airfoil must be at a certain angle to the
oncoming air at a given condition of flight. If the wng has no incidence,
the fuselage now points upward at various "angles of attack". We can keep
the fuselage level during flight by making the wing have the proper angle
to the air by adding the necessary "wing incidence."
> I've also seen some blueprints for the 707 (the greatest airplane ever
> made :) ) and saw two abbreviations that i did not understand:
> 1. STA (relating to fuselage) and how are the STA numbers determined?
This is an old shipbuilding convention. A ship or an aircraft has three
reference axes. The planes perpendicular to the longitudinal axis are
are called 'stations'. These are just reference planes when we talk about
drawings, etc.
While no one FORCES the designers and draftsman to do this (and there have
been aircraft that do NOT use this convention), the convention even from
the earliest days of building ships by lofting (drawings) has been that
the stations are measured from the very nose of the ship or plane. So
STAtion 100 means the station is located 100 inches from the extreme
nose. Aircraft designers usually use inches for measurement, shipbuilders
(I think) still use feet.
> 2. WPL (relating to wing) and how are the WPL numbers determined?
> I appreciate any help you may give me.
You got me on WPL
--
Don Stauffer in Minneapolis
home web site- http://home1.gte.net/stauffer/
home email- stau...@gte.net
work email- stau...@htc.honeywell.com
Keith Barr
> Can somebody please define the following terms:
> 1. Mean Aerodynamic chord (relating to wing structure)
> 2. Percent of mean aerodynamic chord (%MAC) (i think this relates to
> wing loading)
>From ASA's "Flight Engineer Test Prep 99":
The MEAN AERODYNAMIC CHORD (MAC) is the average distance from
the leading edge to the trailing edge of the wing. The MAC
is specified for an aircraft by determining the average chord
of an imaginary wing which has the same aerodynamic
characteristics as the actual wing.
LEMAC stands for LEADING EDGE of MEAN AERODYNAMIC CHORD. Its
position is expressed in inches aft of the datum.
CG of Gravity (CG) of swept wing aircraft is normally calculated as a
percent of MAC. For example, if MAC is 141.5" and the CG is at 22.5%, the
CG is at 31.84" aft of LEMAC.
> 3. Wing incidence
This is the angle the wing is mounted at on the fuselage.
> 1. STA (relating to fuselage) and how are the STA numbers determined?
STA is the station number, normally in inches aft of the datum used for
weight and balance determination.
--
Keith Barr AeroSys Engineering, Inc. & New England Airlines
mailto:ba...@aerosys-eng.com Broomfield, CO & Block Island, RI
http://www.aerosys-eng.com/barr BN-2, PA-32, PA-28
David Fielding
at any section, from the leading edge to the trailing edge. The mean chord
is an average of this line over the span of the wing. It is useful for
determining the angle of the wing in relationship to the rest of the plane,
and the air moving past it.
The percent of MAC refers to a distance from the leading edge of the wing;
often used to locate the center of gravity, or center of lift of a wing.
For instance, the lifting force of a given wing might center a third of the
way back from the leading edge, or 33% of Mean Aerodynamic Chord.
Wing incidence is the angle of the wing MAC in relation to the centerline
of the aircraft; it is a fixed figure, rivetted into the structure of the
plane (although a few planes were made with variable-incidence wings). A
separate matter is angle of attack, which is the angle between the MAC and
the relative wind, or air moving past the wing. Angle of attack is a
changing figure, based on speed, weight, control input, and other factors.
Hope this helps.
David Fielding
dfi...@epix.net
Wish me luck on the Instrument written...
P. Wezeman
> 3. Wing incidence is the angle (viewed from the side) that the wing is
> attached to the fuselage. In other words, if the leading edge were held
> in one place and the trailing edge were moved up or down, the angle of
> incidence would be changing. Obviously, most wings are securely bolted
> to the fuselage, and the AI is fixed (except for the Boeing Tiltrotor).
> An "all flying" horizontal tail would be an example where angle of
> incidence is variable.
On the Boeing Tiltrotor the wing incidence is fixed and the
engines with their rotors tilt. There were earlier designs, some
American, some Canadian, and perhaps one Japanese, where the entire
wing tilted. The Vought Crusader carrier based fighter, still used
with the French Navy until the naval version of the Rafale is
operational, has a variable incidence wing. This allows it
to increase wing incidence for landing and take-off while keeping
the fuselage horizontal for good pilot visibility over the nose.
The incidence changing mechanism was lighter than the longer landing
gear needed without it to accommodate landing with nose up. The
Martin XB-51 also had variable incidence. There is a homebuilt
aircraft design, called I believe the FreeWing, that uses wings
with variable incidence differentially for roll control, and collectively
for lift control (you can't really say that the wings control pitch
since the fuselage stays aligned with the relative wind).
Peter Wezeman, anti-social Darwinist
"Carpe Cyprinidae"
Hugh Dickson
do use a jack screw to move the horizontal stab. The "diesel eight" had
a similar system but you had to move the "suitcase handles" on the
pedestal.
There was an "AD" on the Boeing system that called for a paper towell
to be inserted in the braking mechanism of the jack screw to remove
grease and moisture. A real "hi-tech" fix.
Regards, Hugh
djd...@banet.net
STA numbers are measured in inches from an imaginary reference line
called the datum line. This line can be anywhere on the aircraft and is
often actually somewhere in front of the aircraft( reason being to make
weight an ballance calculations easier.
The measurements left and right on the wings are measured from the
center line of the aircraft.
Hope this helps you out
Dave