# Aircraft Design and Weight Estimation Nomenclature Jahnavi ? & Avinash ? Abstract-Weight components of airplane explained as follows: a) Crew weight ( c W ) The crew comprises the people necessary to operate the airplane in flight. e.g., Pilot, Co-pilot, Airhostess etc. This is weight of everything else-the structure engines (with all accessory equipment), electronic equipment landing gear, fixed equipment and anything else that is not crew, payload or fuel. e) Gross weight ( 0 # W ) The sum of these weights is the total weight of the airplane. Gross weight or total weight varies through the flight because fuel is being consumed. The design take off gross weight is the weight of the airplane at the instant it begins its mission. It includes the weight of the fuel. e f p c W W W W W + + + = 0 W W W W W W W W W e f p c 0 0 0 0 + + + = ? ? ? ? ? ? ? ? ? ? + = 0 0 0 1 ) ( W W W W W W W e f p c (1) Author ? ?: Shaili Gardenia, Hyderabad, Telangana. e-mails: Mjahnavi216@gmail.com, Avi.aero29@gmail.com # ) The aircrafts fuel supply is available for performing the mission. The other fuel includes reserve fuel, trapped fuel (which is the fuel which cannot be pumped out of the tanks). Fuel fraction ( 0 W W f ) is approximately independently of aircraft weight. Fuel fraction will be estimated based on the mission to be flown. # I. # Introduction a) Mission profiles Typical mission profiles for various types of aircraft are shown in Fig1. The simple cruise mission is used for many transport and general aviation designs, including home built. Following are the briefly explained the terms that are used in mission profiles: ? Warm Up and Take-Off Warm Up is the engine start up for the airplane kept idling for some time to warm up. Take Off is the point where aircraft is made lift off from ground. It is the motion after warm up i.e., moving of airplane after starting and till it lifts off from the ground. # ? Climb It is between take-off (TO) and cruise (stead level flight with constant speed) Increase in height until airplane achieves steady level flight. # Cruise It is the steady level flight to cover the mission distance. The mission distance is called Range. # ? Loiter Represent the airplane spending in air for some fixed number of minutes near airport before getting the clearance from airport signal or simple spending some time to collect data of some mission (Terrain data). ? Dash It is the mission that must be flown at just a few hundred numbers of feet of the ground for low level strike. # ? Landing It is the aircraft landing on the runway till stopping of engine. # b) Estimation of mission segment weight fractions The various mission segments (legs) are numbered starting from zero denoting, the start of the mission. Mission leg one is usually engine warm up and take-off. The remaining legs are sequentially numbered. For example in the simple cruise mission the legs could be numbered as (0) warm-up and take-off, (1) climb ( 2) cruise (3) loiter and (4) landing. Similarly, the aircraft weight at end of each mission is denoted by i W . Denoting "i"-th segment as mission segment weight 0 W =Beginning airplane weight ("Take -off gross weight") 1 W =Weight of the airplane at end of warm-up and take-off. ... W W W W W W W W W W W W W W x = = So in general it can be written as 1 3 4 2 3 1 2 0 1 0 0 ... ? = = i i i x W W W W W W W W W W W W W W Warm-up/take-off, climb and landing weight fractions: The warm-up, take-off and landing weight fractions can be estimated historically from Table 2. For any mission segment "i" the mission segment weight fraction is expressed as 1 ? i i W W . x W (Assuming "x" segments are present for total mission profile) is the aircraft weight at end of the mission. W ) 0 W W e is function of 0 W , 0 W W f is also a function of 0 W . 0 W is calculated from equation(1) through process of iteration. 0 W is taken a guess value and, then RHS value of equation( 1) is calculated which should match the value of assumed, if it doesn't, increment the assume by some value and iterate it. This process is continued till the absolute difference of RHS value and assumed value is the least and that iteration step will be your nearest solution. II. # Aircraft Conceptual Sketch and Its Gross Weight Estimation Algorithm Aim Write the request for proposal for the particular aircraft, draw the conceptual sketch of the aircraft for given type of aircraft, draw the mission profile and write generic algorithm for gross take-off weight estimation # Sizing The conceptual sketch is used to estimate aerodynamics and weight fractions by comparisons to previous designs. These estimates are used to make a first estimate of the required total weight and fuel weight to perform the design mission. First order sizing provides the information to needed to develop an initial design layout in three view format. This three view drawing is completed with the internal arrangement in detail. The initial layout is analyzed to determine if it will perform the mission as indicated by the first-order sizing. # IV. Algorithm for Gross Take-off Weight Estimation Following steps are involved in gross take-off weight estimation: ? Study the design objectives. ? Sizing mission starts here. ? Aspect ratio selection is done here. ? Sketch the layout in three views. ? Select L/D ratio and engine specific fuel consumption. ? Estimate fuel weight fraction. ? Select empty weight fraction (Historical trends). ? Guess initial gross weight. ? Calculate gross weight from equation. ? Iterate for gross weight by going to step8, until guess and calculated are matched. The following flow chart explains the same algorithm as explained previous It should be in the form of parameters and requirements for the aircraft. ? Draw the conceptual sketch of the aircraft as explained in theory. ? Draw the mission profile for the aircraft. ? What do you understand by flight vehicle design? Explain it with various examples. ? What do you understand by weight estimation and write the algorithm for gross take-off weight estimation. VI. # Result The take-off weight can be estimated by doing the iterations, until we get, W 0 guess = W 0 Calculated ![what the airplane is mentioned to transport passengers, baggage, freight etc. (Military use the payload includes bombs, rockets and other disposable ordnance) . c) Fuel weight ( f W ) This is the weight of the fuel in the fuel tanks. Since fuel is consumed during the course of flight. is a variable, decreasing with time during the flight. d) Empty weight ( e W )](image-2.png "") ![based on ? Historical data and tables ? Refined sizing data and tables ii. Estimation of fuel fraction (](image-3.png "") 1![Fig.1 : Typeical mission profiles for sizing](image-4.png "Fig. 1 :") ![=Weight of the airplane at end of climb.](image-5.png "2W") ![=Weight of the airplane at end of cruise.](image-6.png "3W") ![=Weight of the airplane at end of loiter.5W =Weight of the airplane at end of landing.](image-7.png "4W") ![Specific fuel consumption (C)It is the rate of fuel consumption divided by the resulting thrust. Typical values are depicted in Table3 and Table4 for jet and propeller aircrafts respectively. If the aircraft is propeller, then C should be replaced by , L/D = lift to drag ratio The most efficient cruise is velocity for propeller aircraft occurs at velocity yielding max L/D, where as for the most efficient cruise for a jet aircraft occurs at slightly at a higher velocity yielding an L/D of 86.6% of the maximum](image-8.png "") © 2014 Global Journals Inc. (US)