3. 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
4. Data Collection
● Data of 30 different aircraft was collected
● Some relations were plotted and
regression relations were calculated
Aero474
Aircraft Design
5. Thrust History
1.2
1
0.8
T /T ma x(25.98 KN)
0.6
0.4
0.2
0
1955 1960 1965 1970 1975 1980 1985 1990 1995
Ye a r
Aero474
Aircraft Design
6. Empty to Take-off weight
0.8
0.75
0.7
0.65
W o/W e
0.6
0.55
0.5
0.45
0.4
1000 2000 3000 4000 5000 6000 7000 8000 9000
W o (Kg)
Aero474
Aircraft Design
7. Wing loading vs aspect ratio
550
500
450
400
350
L (Kg/ m^2)
300
250
200
150
100
4 4.5 5 5.5 6 6.5 7
AR
Aero474
Aircraft Design
9. Preliminary Sizing
● Using the relations obtained from the data,
equations could be obtained to fill in the
equation
● W o=W e W f W pW c
● You obtain a quadratic equation in the
take-off weight which can be solved readily
● The number was 3220 Kg
Aero474
Aircraft Design
10. Preliminary Sizing
● Similarly, the wing loading could be found
2
to be: 290 Kg/m
● 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
11. 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
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Aircraft Design
17. 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
20. 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
21. 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
22. 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
26. 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
28. Flight Dynamics and Stability
● Now that we have all the aerodynamic
coefficients, we may approach the problem
of dynamics of the aircraft
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Aircraft Design
29. 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
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Aircraft Design
32. 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
33. 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
41. Other Parameters
● Range
● Endurance
● Flight in a horizontal circle
● Take-off runway
● Stall speed
● Time to reach 5000 m
Aero474
Aircraft Design
46. Cost Estimates
● Engineering hours
● Tooling hours
● Manufacturing hours
● Quality control hours
● Development Support
● Flight test cost
● Material cost
● Avionics
● Engine
Aero474
Aircraft Design
47. Homework #5
● Prepare a 30 minutes presentation
● Presentation includes all your work up to
this point
● History, data, project plan, etc...
● Plus preliminary weight estimations and
geometric considerations
Aero474
Aircraft Design
