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Aero474 Aircraft Design
Design Example
Aero474 Aircraft Design
Problem definition
• A military training aircraft
• Load factors +6 & -3G
• Two pilots, 105 Kg each
• Baggage 22.5 Kg
• Takeoff distance of 1500 m
• Climb to 5000 m
• Cruise 15 min at a speed of no less than 87 m/s
• Manoeuvre at 103 m/3 for 60 min
• Return to base
• Taxi and parking
Aero474 Aircraft Design
Data Collection
● Data of 30 different aircraft was collected
● Some relations were plotted and
regression relations were calculated
Aero474 Aircraft Design
Thrust History
1955 1960 1965 1970 1975 1980 1985 1990 1995
0
0.2
0.4
0.6
0.8
1
1.2
Year
T/T
max(2
5.9
8 K
N)
Aero474 Aircraft Design
Empty to Take-off weight
1000 2000 3000 4000 5000 6000 7000 8000 9000
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0.8
Wo (Kg)
Wo
/We
Aero474 Aircraft Design
Wing loading vs aspect ratio
4 4.5 5 5.5 6 6.5 7
100
150
200
250
300
350
400
450
500
550
AR
L (
Kg
/m^
2)
Aero474 Aircraft Design
Preliminary Sizing
● Using the relations obtained from the data,
equations could be obtained to fill in the
equation
● You obtain a quadratic equation in the
take-off weight which can be solved readily
● The number was 3220 Kg
Aero474 Aircraft Design
Preliminary Sizing
● Similarly, the wing loading could be found
to be: 290 Kg/m2
● From which you get the wing area to be 11
m2
● Which yields and Aspect ratio of 5 and
span of 7.5 m
Aero474 Aircraft Design
Geometric Considerations
● From the data collected, the taper ratio of
0.5 was used
● The distance between the tail and the is,
similarly, taken to be 3 times the mean
wing chord
● For the area of the stabilizers, the volume
ratio was the determinant as per a
reference and taken as 0.7
Aero474 Aircraft Design
First Sketch
Aero474 Aircraft Design
First Sketch
Aero474 Aircraft Design
Undercarriage Placement
Aero474 Aircraft Design
Longitudinal Position
Aero474 Aircraft Design
Lateral Position
Aero474 Aircraft Design
Components Weight
● Formulae are given in different references
to estimate the weight of different
components
● What is really important is the weight
distribution
● The distribution of the masses of the
aircraft will be assumed to be regular as
per the external size
Aero474 Aircraft Design
Aerodynamic Performance Estimation
Aero474 Aircraft Design
Aerodynamic Performance
Estimation ● The Aerodynamic coefficients may be
evaluated using different methods
● There are simple formulae to determine
them
● You may use some Lattice methods to
estimate the coefficients
● You may solve the full Navier Stokes
equations!
Aero474 Aircraft Design
For the Example
● Selection of the aerofoil was NACA4212
for the wing and NACA0009 for the tail.
● Using Prandtl lifting line theory, the wing
and tail lift coefficients were calculated
● The induced drag coefficient was also
evaluated using the same theory
● Finally, the maximum lift coefficient was
calculated using emperical relations.
Aero474 Aircraft Design
Total Coefficients
● Finally, the total lift, drag, and moment
coefficients were calculated
● BUT … Flight stability literature indicated
that the moment and lift coefficients were
not adequate!
● First modification was to change the tail
incidence angle
Aero474 Aircraft Design
Total Lift
-4 -2 0 2 4 6 8 10 12 14 16 18 20
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
Alpha
CL tota
l
Aero474 Aircraft Design
Lift-Drag ratio variation with CL
0 0.2 0.4 0.6 0.8 1 1.2
0
2
4
6
8
10
12
CL
CL/C
D
Aero474 Aircraft Design
CL-M curves for different
altitudes
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
M
CL
CL SL
CL 5000
CL 10000
Aero474 Aircraft Design
CRITICAL!!!
● Reviewing those results, it was found that
the lift coefficient at cruise conditions is so
much near the maximum!
● To remedy this problem, the wing loading
was reduced!
● Increasing the area of the wing, changed
EVERYTHING!!!
Aero474 Aircraft Design
Flight Dynamics and Stability
Aero474 Aircraft Design
Flight Dynamics and Stability
● Now that we have all the aerodynamic
coefficients, we may approach the problem
of dynamics of the aircraft
Aero474 Aircraft Design
Longitudinal Dynamics &
Stability ● The Response for an impulse elevator
input could be plotted using the Runge-
Kutta method
● The two main modes of motion of the
aircraft in longitudinal direction are:
● Phugoid
● Short period
Aero474 Aircraft Design
Pitching Angle Response
Aero474 Aircraft Design
The reason for instability!
Aero474 Aircraft Design
Third iteration!
● Now, the aircraft need to be modified again!
● However, before doing all that effort again, let's
examine the weight requirements of the fuel
● When recalculating the fuel requirements using
detailed relations for each step of the mission,
the weight was reduced
● That lead to the stability of the aircraft!
● Fuel weight was reduced by more than 50%!!!
Aero474 Aircraft Design
Aerodynamic Refinement
● A VLM code was developed for the
aerodynamic analysis of aircraft
components
● The results obtained for the combined
wing-tail problem gave better estimates for
the aerodynamic characteristics
Aero474 Aircraft Design
Performance Analysis
Aero474 Aircraft Design
Engine Performance
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0
2000
4000
6000
8000
10000
12000
14000
M
T (
N)
0
3300
5000
6600
10000
13000
16000
Aero474 Aircraft Design
Drag-Thrust vs Mach Number
Aero474 Aircraft Design
Max M vs Altitude
0.65 0.67 0.69 0.71 0.73 0.75 0.77 0.79 0.81
0
2000
4000
6000
8000
10000
12000
14000
M max
Altitude (
m)
Aero474 Aircraft Design
Vertical Speed vs Mach No.
Aero474 Aircraft Design
Climb Speed vs Altitude
Aero474 Aircraft Design
Time to reach Altitude
0 2000 4000 6000 8000 10000 12000 14000 16000
0
50
100
150
200
250
300
350
400
450
500
Altitude
Tim
e (
Sec)
Aero474 Aircraft Design
Other Parameters
● Range
● Endurance
● Flight in a horizontal circle
● Take-off runway
● Stall speed
● Time to reach 5000 m
Aero474 Aircraft Design
Wing Loads
Aero474 Aircraft Design
Forces and Moments
0 1 2 3 4 5
0
2000
4000
6000
8000
10000
12000
14000
Y
Vz
0 1 2 3 4 5
0
500
1000
1500
2000
2500
3000
3500
4000
Y
My
0 1 2 3 4 5
0
5000
10000
15000
20000
25000
30000
Y
Mx
Aero474 Aircraft Design
Aircraft Skeleton
Aero474 Aircraft Design
Wing Section
Aero474 Aircraft Design
Cost Estimates
● Engineering hours
● Tooling hours
● Manufacturing hours
● Quality control hours
● Development Support
● Flight test cost
● Material cost
● Avionics
● Engine
Aero474 Aircraft Design
Homework #1
● Form teams
● Collect data
● Create correlation graphs
● Prepare a report
● Prepare a presentation!
