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Aero474Aircraft 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
Aero474Aircraft Design
Data Collection● Data of 30 different aircraft was collected● Some relations were plotted and
regression relations were calculated
Aero474Aircraft Design
Thrust History
1955 1960 1965 1970 1975 1980 1985 1990 19950
0.2
0.4
0.6
0.8
1
1.2
Year
T/T
max
(25.
98 K
N)
Aero474Aircraft Design
Empty to Take-off weight
1000 2000 3000 4000 5000 6000 7000 8000 90000.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0.8
Wo (Kg)
Wo/
We
Aero474Aircraft Design
Wing loading vs aspect ratio
4 4.5 5 5.5 6 6.5 7100
150
200
250
300
350
400
450
500
550
AR
L (K
g/m
^2)
Aero474Aircraft 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
W o=W eW fW pW c
Aero474Aircraft 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
Aero474Aircraft 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
Aero474Aircraft 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
Aero474Aircraft 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!
Aero474Aircraft 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.
Aero474Aircraft 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
Aero474Aircraft 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
1.4
Alpha
CL to
tal
Aero474Aircraft Design
Lift-Drag ratio variation with CL
0 0.2 0.4 0.6 0.8 1 1.20
2
4
6
8
10
12
CL
CL/C
D
Aero474Aircraft 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 10
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
CL SLCL 5000CL 10000
M
CL
Aero474Aircraft 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!!!
Aero474Aircraft Design
Flight Dynamics and Stability● Now that we have all the aerodynamic
coefficients, we may approach the problem of dynamics of the aircraft
Aero474Aircraft 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
Aero474Aircraft 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%!!!
Aero474Aircraft 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
Aero474Aircraft Design
Engine Performance
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
2000
4000
6000
8000
10000
12000
14000
0330050006600100001300016000
M
T (N
)
Aero474Aircraft Design
Max M vs Altitude
0.65 0.67 0.69 0.71 0.73 0.75 0.77 0.79 0.810
2000
4000
6000
8000
10000
12000
14000
M max
Altit
ude
(m)
Aero474Aircraft Design
Time to reach Altitude
0 2000 4000 6000 8000 10000 12000 14000 160000
50
100
150
200
250
300
350
400
450
500
Altitude
Tim
e (S
ec)
Aero474Aircraft Design
Other Parameters● Range● Endurance● Flight in a horizontal circle● Take-off runway● Stall speed● Time to reach 5000 m
Aero474Aircraft Design
Forces and Moments
0 1 2 3 4 50
2000400060008000
100001200014000
Y
Vz
0 1 2 3 4 50
1000
2000
3000
4000
Y
My
0 1 2 3 4 50
5000
10000
15000
20000
25000
30000
Y
Mx
Aero474Aircraft Design
Cost Estimates● Engineering hours● Tooling hours● Manufacturing hours● Quality control hours● Development Support● Flight test cost● Material cost● Avionics● Engine