Aero474 Design Example

Aero474Aircraft Design

Aircraft DesignAero474

Dr. Mohammad TawfikE-mail: [email protected]


Design Example


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


Data Collection● Data of 30 different aircraft was collected● Some relations were plotted and

regression relations were calculated


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)


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


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)


JPAT Data


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


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


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


First Sketch


Undercarriage Placement


Longitudinal Position


Lateral Position


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


Mass Distribution Table


Aerodynamic Performance Estimation


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!


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.


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


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


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


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


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!!!


Flight Dynamics and Stability


Flight Dynamics and Stability● Now that we have all the aerodynamic

coefficients, we may approach the problem of dynamics of the aircraft


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


Pitching Angle Response


The reason for instability!


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%!!!


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


Performance Analysis


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

)


Drag-Thrust vs Mach Number


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)


Vertical Speed vs Mach No.


Climb Speed vs Altitude


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)


Other Parameters● Range● Endurance● Flight in a horizontal circle● Take-off runway● Stall speed● Time to reach 5000 m


Wing Loads


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


Aircraft Skeleton


Wing Section


Cost Estimates● Engineering hours● Tooling hours● Manufacturing hours● Quality control hours● Development Support● Flight test cost● Material cost● Avionics● Engine


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 Design Example

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