SAWE Report - Cal Poly San Luis Obispo

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9 Weight & Balance Weight and balance is one area often overlooked in aircraft design. The weights engineer develops a buildup that heavily influences aircraft performance engineer in terms of wing sizing, propulsion system selection, and in predicting aircraft performance. The stability and control engineer must rely on the weights engineer in order to size control surfaces, to develop flight control systems, and to develop stability derivatives. The configurator must work carefully with the weights engineer in order to develop a feasible inboard layout. In all aspects, the weights engineer plays a major role coordinating the design of any aircraft. After having sized the aircraft using the weight fractions technique, and after having developed an initial configuration, the next step is to develop a more accurate, class II weight buildup of the aircraft. The class II method used in the design of the Vendetta was developed from those methods found in the Nicolai, Raymer, and Roskam texts in order to obtain a collaborative and unbiased perspective. These methods involved defining several physical and geometric parameters of the aircraft. These parameters were inputs into a series of equations developed from historical weight trends. The weight estimations for various components as well as the level of agreement between authors are shown below in Table 9.I. Table 9.I - Initial Component Weight Buildup Roskam Nicolai Raymer Average Roskam Nicolai Raymer Component Weight (lbs) Weight (lbs) Weight (lbs) Weight (lbs) Accuracy (%) Accuracy (%) Accuracy (%) Structures Wing Group 9,687 11,466 7,870 9,674 0% -31% 26% Horizontal Tail 1,135 1,694 958 1,262 14% -62% 32% Vertical Tail 801 1,538 1,497 1,279 47% -34% -28% Fuselage 10,681 16,031 10,398 12,370 19% -52% 22% Main Landing Gear 2,742 2,969 1,156 2,289 -33% -52% 60% Nose Landing Gear 387 405 408 400 5% -2% -3% Propulsions 10,636 10,878 11,199 11,209 4% 0% -4% Systems 18,649 14,506 14,350 20,574 -29% 12% 13% Payload 9,500 9,500 9,500 9,500 0% 0% 0% Fuel 58,974 58,974 58,974 58,974 0% 0% 0% TOGW 123,653 128,435 128,435 127,531 4% -2% -2% The detailed weight buildup of the structures, control surfaces, systems, payload, and fuel groups has been compacted in order to save space and can be viewed in its entirety in Foldout 1. The table indicates that all three authors tend to disagree to some extent in their weight estimates of certain components, and for other components, one author may have no way of estimating that components weight at all. The most accurate way to develop the most detailed component weight buildup was to consider all three methods and take the average shared between them. An author’s estimation was discarded if it did not agree to within ±30% of the average of the other authors’ estimations. Once the estimations were in agreement to within ±30%, they were averaged in order to develop a weight buildup for the entire aircraft. The class II weight buildup for the Vendetta after the downgrading process is shown below in Table 9.II. 55
Table 9.II - Final Component Weight Buildup Roskam Nicolai Raymer Average Component Weight (lbs) Weight (lbs) Weight (lbs) Weight (lbs) Structures Wing Group 9,687 XXXXXX 7,870 8,779 Horizontal Tail 1,135 1,694 958 1,262 Vertical Tail 801 1,538 1,497 1,279 Fuselage 10,681 XXXXXX 10,398 10,540 Main Landing Gear 2,742 2,969 1,156 2,289 Nose Landing Gear 387 405 408 400 Propulsions 10,636 10,878 11,199 11,209 Systems 18,649 14,506 14,350 20,574 Payload 9,500 9,500 9,500 9,500 Fuel 58,974 58,974 58,974 58,974 TOGW 124,800 Inertias were calculated using guidelines outlined by the Society of Allied Weight Engineers (SAWE). Each components mass and location in reference to the aircraft center of gravity was used to calculate that components inertia. The sums of these inertias were then used in calculating the total moments of inertia about the Vendetta’s principal axes shown in Figure 9.1. In order to determine whether or not these values were accurate, the moments of inertia were transformed into non-dimensional radii of gyration coefficients. These coefficients were then compared to typical values for a jet bomber provided by SAWE. These comparisons are shown below in Table 9.III. Table 9.III - Inertia Estimation Figure 9.1- Principle Axes Inertias (slug*ft 2 ) Ix Iy Iz Vendetta 35,248 807,819 838,575 Nondimensional Radii of Gyration Rx Ry Rz Vendetta 0.11 0.29 0.38 SAWE 0.31 0.33 0.47 Accuracy 63% 13% 18% The table indicates that the inertias are well within the typical values for a jet bomber except about the roll axis. This is because the Vendetta is similar to a typical jet bomber in length; however, it has a much shorter wingspan. This would constitute a smaller moment of inertia about the roll axis. After having developed an initial configuration and a more detailed class II weight buildup, the next step was to balance the aircraft. This was done for two types of payload, the first being fixed equipment and the second being variable payload. The variable payload aboard the Vendetta consists of both fuel and weapons because the weight and center of gravity of these 56
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SAWE Paper No. 3232 Category No. 10
Page 3 and 4:
Table of Contents Abstract_________
Page 5 and 6:
List of Figures Figure 1.1 - Design
Page 7 and 8:
Figure 13.4 - Rectilinear Vision Pl
Page 9 and 10:
Nomenclature AIAA American Institut
Page 11 and 12:
α Angle of Attack, degrees, rad.
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Table 1.II - Summary of Design Requ
Page 15 and 16: Figure 1.3 - F-15 Strike Eagle F-11
Page 17 and 18: Table 1.III - Comparison of the F-1
Page 19 and 20: Many of the equations buried in the
Page 21 and 22: 3 Configuration The current configu
Page 23 and 24: Another problem arises from the 20
Page 25 and 26: • Span = 54.7 ft • m.a.c. = 32
Page 27 and 28: 4 Stealth Considerations As mention
Page 29 and 30: Table 4.I - Common Ground Radars Ra
Page 31 and 32: 30 20 10 0 -10 -20 -30 -40 -50 1 GH
Page 33 and 34: 5 Aerodynamics The major aerodynami
Page 35 and 36: 1 GHz. 40º LE Sweep 10 GHz. 40º L
Page 37 and 38: 5.3 Wing Thickness The effect of wi
Page 39 and 40: 5.4 Airfoil The NACA 65A-003 airfoi
Page 41 and 42: 1 Section Lift Coefficient 0.9 0.8
Page 43 and 44: 90 80 Wing Cross Sectional Area (ft
Page 45 and 46: 6 Propulsion In developing the prop
Page 47 and 48: Table 6.II - RFP Dimensions Compare
Page 49 and 50: 38 Figure 6.1 - VAATE Goals
Page 51 and 52: TSFC 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.
Page 53 and 54: Deflection Angle Analysis for Mach
Page 55 and 56: Figure 6.8 - Cost Association with
Page 57 and 58: The inlet has a boundary layer dive
Page 59 and 60: 7 Materials and Structure The overa
Page 61 and 62: Vertical Attachment Points Horizont
Page 63 and 64: 8 Landing Gear Landing Gear design
Page 65: steel. This means that more braking
Page 69 and 70: throughout the 5-hour mission. Usin
Page 71 and 72: 10 Stability and Control To initial
Page 73 and 74: difference in neutral point and cen
Page 75 and 76: 40 30 20 10 0 -10 -20 -30 -40 -50 2
Page 77 and 78: The Vendetta configuration utilizes
Page 79 and 80: -0.6 -0.4 UNSTABLE NEUTRAL -0.2 Lif
Page 81 and 82: Validation of an aircraft design su
Page 83 and 84: consumption. The main aspects of th
Page 85 and 86: In addition to the performance requ
Page 87 and 88: 70,000 Altitude (ft) 60,000 50,000
Page 89 and 90: 11.4 Mission Requirements By comple
Page 91 and 92: Table 11.VIII - Landing Flight Prof
Page 93 and 94: 11.7 Alternate Missions In addition
Page 95 and 96: 12 Payload Weapon internal layout d
Page 97 and 98: 13 Cockpit Cockpit Design began wit
Page 99 and 100: that could be used in landing and t
Page 101 and 102: 14 Systems The systems of the Vende
Page 103 and 104: 14.3 Fuel System Initial fuel syste
Page 105 and 106: 15 Manufacturing Several manufactur
Page 107 and 108: 16 Cost Analysis The final and perh
Page 109 and 110: Appendix Threats Chart Common Surfa
Page 111 and 112: Wing Break Point Fuel Aft Fuselage
Page 113 and 114: The Vendetta Design Team Chris Atki
Page 115 and 116: References 1. “Ejection Systems,
Page 117:
35. www.dfrc.nasa.gov/PAO/PAIS/HTML
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