STRUCTURES MMTB Flashcards
The basic questions of
configuration, arrangement,
size and weight, and
performance are answered
Conceptual Design
Begins when the major changes are over
Preliminary Design
Begins in which the actual
pieces to be fabricated are designed.
Detail Design
Mathematical modeling of the outside
skin of the aircraft with sufficient
accuracy to ensure proper fit between its
different parts designed by different designers.
Lofting
Structural Weight is between 30 to 35%
of the total weight
PRELIMINARY WEIGHT ESTIMATE
Total Weight of the aircraft as it begins the mission for which it was designed.
Design Take-off Gross Weight
ππΆπππ€ + ππππ¦ππππ + πππ’ππ + πππππ‘
π0/ total weight
Part of the fuel supply that is available for
performing the mission
Mission Fuel
Fuel which cannot be pumped out of the
tanks
Trapped Fuel
The firing of gun and missiles, and is often
left out of the sizing analysis
Weapon Drop
Rate of fuel consumption divided by the
thrust
Specific Fuel Consumption
A measure of the designβs overall aerodynamic efficiency
Lift-to-Drag Ratio
Curvature characteristics of most airfoil
Camber
Line equidistant from the upper and lower surfaces
Mean Camber Line
Maximum thickness of the airfoil divided by its chord
Airfoil Thickness Ratio
π‘/c
Thickness Ratio
Point about which the pitching moment
remains constant for any angle of attack
Aerodynamic Center
Ratio between the dynamic and the
viscous forces in a liquid
Reynoldβs Number
οLift coefficient at which the airfoil has the
best πΏβπ·
οPoint in the airfoil drag polar that is tangent to a line from origin and closest
to the vertical axis
DESIGN LIFT COEFFICIENT
οStall from the trailing edge
οTurbulent boundary layer increases with
angle of attack
Fat Airfoils (πβπ > ππ%)
οFlow Separates near the nose at a very small angle of attack but reattaches itself so that little effect is felt.
οAt higher angle of attacks the flow fails to
attach, which almost immediately stalls
the entire airfoil
Moderate Thick Airfoils (6-14%)
οThe flow separates from the nose at a
small angle and reattaches almost
immediately
Very Thin Airfoils (πβπ < π%)
Cause the wing to stall first at the root.
Twisting/Washout
οDrag increases with increasing thickness
due to separation
AIRFOIL THICKNESS RATIO
For a wing of fairly high aspect ratio and
moderate sweep, a larger nose radius
provides higher stall angle and greater
maximum lift coefficient
AIRFOIL THICKNESS RATIO
Wing structural weight varies approximately inversely with the square
root of the thickness ratio
AIRFOIL THICKNESS RATIO
οAngle of concern in supersonic flight
οIt is common to sweep the leading edge behind the Mach cone to reduce drag.
Leading Edge Sweep
Sweep most related to subsonic flight.
Quarter-Chord Line Sweep
Aerodynamic Center for SUBSONIC
0.25c
Aerodynamic Center for SUPERSONIC
0.4c
Has tips farther apart making them less affected by the tip vortex and the tip vortex strength is reduced
High aspect ratio wings
Wing weight increasing with___
increasing aspect ratio
will stall at a
higher angle of attack than higher aspect ratio wings
Lower aspect ratio wings
If the Aspect ratio is High, the Induced Drag is _______
Low
If the Aspect ratio is High, the Lift-Curve Slope is _______
High
If the Aspect ratio is High, the Pitch Attitude is _______
Low
If the Aspect ratio is High, the Ride in Turbulence is _______
Poor
If the Aspect ratio is High, the Wing Weight is _______
High
If the Aspect ratio is High, the Wing Span is _______
Large
If the Aspect ratio is Low, the Induced Drag is _______
High
If the Aspect ratio is Low, the Lift-Curve Slope is _______
Low
If the Aspect ratio is High, the Pitch Attitude is _______
High
If the Aspect ratio is Low, the Ride in Turbulence is _______
Good
If the Aspect ratio is Low, the Wing Weight is _______
Low
If the Aspect ratio is Low, the Wing Span is _______
Small
Primarily used to reduce the adverse
effects of transonic and supersonic flow
WING SWEEP
are wings with one wing
swept aft and the other swept forward.
Oblique wings
tend to have lower wave
drag
Oblique wings
improves stability
Wing sweep
increases the effectiveness of vertical tails at the wing tips
Wing sweep
Better ride through turbulence characteristics
Wing sweep
Increases Critical Mach Number
Wing sweep
Highly undesirable tendency, upon
reaching an AOA near stall, to suddenly
and uncontrollably increase AOA
Pitch up
Solution to constant sweep problems
Variable Sweep
Complex and attendant balance problems
Variable Sweep
If there is an increased wing sweep forward, the Lift-Curve Slope is ___
Low
If there is an increased wing sweep forward, the Pitch Attitude in Low
Speed, Level Flight is ___
High
If there is an increased wing sweep forward, the Ride through Turbulence is ___
Good
If there is an increased wing sweep forward, the Asymmetric Stall is ___
Best
If there is an increased wing sweep forward, the Lateral Control at Stall is ___
Best
If there is an increased wing sweep forward, the Compressibility Drag is ___
Low
If there is an increased wing sweep forward, the Wing Weight is ___
Highest
If there is an increased wing sweep on none, the Lift-Curve Slope is ___
High
If there is an increased wing sweep (none), the Pitch Attitude in Low
Speed, Level Flight is ___
Low
If there is an increased wing sweep (none), the Ride through Turbulence is ___
Poor
If there is an increased wing sweep (none), the Asymmetric Stall is ___
Good
If there is an increased wing sweep (none), the Lateral Control at Stall is ___
Good
If there is an increased wing sweep (none), the Compressibility Drag is ___
High
If there is an increased wing sweep (none), the Wing Weight is ___
Low
If there is an increased wing sweep aft, the Lift-Curve Slope is ___
Low
If there is an increased wing sweep aft, the Pitch Attitude in Low
Speed, Level Flight is ___
High
If there is an increased wing sweep aft, the Ride through Turbulence is ___
Good
If there is an increased wing sweep aft, the Asymmetric Stall is ___
Poor
If there is an increased wing sweep aft, the Lateral Control at Stall is ___
Poor
If there is an increased wing sweep aft, the Compressibility Drag is ___
Low
If there is an increased wing sweep aft, the Wing Weight is ___
High
Ratio between the tip chord and the centerline tip chord
Taper Ratio
Affects the distribution of lift along the span of the wing
Taper Ratio
More taper
lesser the weight
Less taper means
more fuel volume
If there is High Taper Ratio, the Wing Weight is ____
High
If there is High Taper Ratio, the Tip stall is ____
Good
If there is High Taper Ratio, the Wing Fuel Volume is ____
Poor
Used to prevent tip stall and to revise the
lift distribution to approximate an ellipse
TWIST
Actual change in airfoil angle of incidence, usually measured with respect
to the root airfoil
Geometric Twist
Twist angle changes in proportion to the distance from the root airfoil
Linear Twist
Angle between zero-lift angle of an airfoil
and the zero-lift angle of the root airfoil
Aerodynamic Twist
If identical airfoil is used root to tip, aerodynamic twist is_____ as the
geometric twist
the same
If there is a Large Twist Angle the Induced Drag is,
High
If there is a Small Twist Angle the Induced Drag is
Small
If there is a Large Twist Angle the Tip Stall is,
Good
If there is a Small Twist Angle the Tip Stall is
Poor
If there is a Large Twist Angle the Wing Weight is,
Mildly Lower
If there is a Small Twist Angle the Wing Weight is,
Mildly Higher
The pitch angle of the wing with respect
to the fuselage
WING INCIDENCE
Minimizes drag at some operating conditions, usually cruise
WING INCIDENCE
If the WING INCIDENCE IS LARGE, the Cruise Drag is ___
High
If the WING INCIDENCE IS SMALL, the Cruise Drag is ___
Small
If the WING INCIDENCE IS LARGE, the Cockpit
Visibility is ___
Good
If the WING INCIDENCE IS SMALL, the Cockpit
Visibility is ___
Watch out
If the WING INCIDENCE IS LARGE, the Landing
Attitude is ___
Watch out
If the WING INCIDENCE IS SMALL, the Landing
Attitude is ___
No problem
Angle of the wing with respect to the horizontal when seen from the front
DIHEDRAL
Tends to roll an aircraft whenever it is banked
DIHEDRAL
_____of sweep provides about 1Β° of effective dihedral
10Β°
Produced by excessive dihedral effect
Dutch Roll
Repeated side-to-side motion involving yaw and roll
Dutch Roll
To counter the tendency of Dutch Roll, the vertical
area must be _____
increased
If there is a POSITIVE DIHEDRAL, the Spiral Stability is ____
Increased
If there is a POSITIVE DIHEDRAL, the Dutch Roll Stability is ____
Decreased
If there is a POSITIVE DIHEDRAL, the Ground Clearance is ____
Increased
If there is a NEGATIVE DIHEDRAL, the Spiral Stability is ____
Decreased
If there is a NEGATIVE DIHEDRAL, the Dutch Roll Stability is ____
Increased
If there is a NEGATIVE DIHEDRAL, the Ground Clearance is ____
Decreased
Allows placing of the fuselage closer to
the ground
High Wing
Provides sufficient ground clearance without excessive landing gear length
High Wing
Wingtips less likely to strike the ground
High Wing
usually presents less
weight but struts adds to drag
strutted wing
For a ______ aircraft, a high wing provides ground clearance for the large flap necessary for high CL
STOL