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Congratulations…Welcome to UTHM PARIT RAJA….A Place To Be..
DR. ZAMRI BIN OMAR Department of Aeronautical Engineering Faculty of Mechanical & Manufacturing Eng. Phone : /7711 Room: C & A4, 2nd Floor
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~(5) A Better Weight Estimation
In step 1, weight is estimated based on historical data. Now we have the aircraft layout: size & shape are known. weight is so important special task for ‘Weight Engineers’ We’ll do crude weight buildup BUT more detail than in Step 2 So the layout will let us re-calculate the weight buildup. Guidelines from Raymer for GA aircraft, Units ! Area : ft2 weight : lb
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~(5) A Better Weight Estimation
Consider wing weight, Exposed planform area: area seen in Fig (projected area not included) Sw=176 ft2: projected area included. From fig. 8.19, for one wing, the area is 176/2 = 88 ft2.
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~(5) A Better Weight Estimation
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~(5) A Better Weight Estimation
Based on previous 3 figures, Calculation for wing;
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~(5) A Better Weight Estimation
Estimate of wetted area of FL. What is wetted area ?? FL is composed of 3 parts as shown Total wetted area;
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~(5) A Better Weight Estimation : Fuselage wetted area.
Elliptical area = pi x ( a/2) x (b/2) Conical area = pi x r x sqrt(r2+h2)
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~(5) A Better Weight Estimation :
Now solve the following equations, got to deal with iterations ! = 2.5 x 148 ft2 = 370 lb = 2.0 x 35.3 ft2 = 70.6 lb = 2.0 x 14.4 ft2 = 28.8 lb = 1.4 x ft2 = lb = x 5,158 lb = 294 lb = 1.4 x 547 lb = lb = 0.1 x 5,158 lb = lb *TOTAL EMPTY WEIGHT = 2,474 lb *In 1st estimation, We/W=0.62, We = 3,198 lb (WW) (WHT) (WVT) (WF) (WLG) (WIE) (WEE)
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~(5) A Better Weight Estimation :
TOTAL EMPTY WEIGHT = 2,474 lb Gross Take-off Weight With this Wo, we recalculate WLG & WEE (eqn. 8.83e & 8.83g), and recalculate We, Landing gear weight = x 4,434 lb = lb All else empty = 0.1 x 4,434 lb = lb With new WLG & WEE , give us new We & Wf ; We = 2,360 lb, Wf = x 4,434 lb = 705 lb Yet, another value of Wo is obtained, Wo = ,360 = 4,205 lb Repeat this process (recalculate We, Wf & Wo), until we obtain convergence.
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~(5) A Better Weight Estimation :
Summary of iteration process; Now compare these weight buildups with their old values in step 1 We = 3,198 lb, Wf = 820 lb, Wo = 5,158 lb Better airplane’s weight is estimated ! Step 5 just completed.
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