Calculation and Construction of the Polar ALS

7/28/2019 Calculation and Construction of the Polar ALS

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Calculation and construction of the polar ALS

The coefficient of drag

To construct a polar necessary to know the dependence of the coefficientsof lift and drag Su aircraft angle of attack . The drag coefficient is thesum of the coefficients of the aircraft profile and induced drag with acoefficient of drag at zero lift; = - coefficient of induced drag, resulting fromthe creation of lift . The drag coefficient C plane x0 belongs to the wing areaS and is given by where C xkr , C xgo , C xvo , C xf , C xmg , C XIII -resistancecoefficients in Cy = 0 isolated wing, horizontal and vertical tail, fuselage ,engine nacelles and landing gear and the second in-the relative areas ofthe horizontal and vertical tail surfaces; S m F , S m. M , S m. W -midsection ofthe fuselage, engine nacelles and landing gear, respectively. The dragcoefficient of a wing at C in = 0 is given by where C xr -profile dragcoefficient; K AB -interaction coefficient of aerodynamic wings and fuselage;S pF -wing area occupied by the fuselage; - sum of the coefficients toaccount for the additional resistance of surface cleanliness wing cracks in itand add-ins. profile drag coefficient can be determined by theformula where is the coefficient of friction of a flat plate; - coefficient takinginto account the transition from a flat plate to the chosen profile of thewing. The coefficient is shown in the graph (Fig. 2.10, a) as a function ofReynolds number, calculated by the formula where V-speed flight; b sah -

mean aerodynamic chord of the wing - the kinematic viscosity of air. Itsvalue as a function of altitude is shown in the graph in Fig. 2. 10b.


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Figure 2.10 Calculation of aerodynamic drag of the wing

Coefficient depends on the position of the transition point boundarylayer to turbulent. Its position, in turn, depends on several factors, mostimportant of which are a form of the profile and the purity of its surface, theuniformity of the basic flow. Even with a sufficiently smooth surface of the

wing coordinate of a point does not exceed the percentage of the chordprofile, located in front of its maximum relative thickness. For most profiles


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(except laminarizirovannye)


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Figure 2.11 Determination of the drag coefficient of fuselage

Washed by the fuselage surface S st is calculated by drawing a generalform of ALS.The exact value of the coefficient can be obtained only bypurging. When designing an ultralight its approximate value can be taken

from Table. 2. 2.

Table 2.2: Values of the coefficients C x *

Unfortunately, in the Table. 2. 2 does not include the values of the

coefficients for frequently used for ALS bluff fuselages. This isbecause of the large number of possible configurations of the coefficientsof resistance vary widely. And even to determine their approximate values

are needed purge in wind tunnels. The values of the coefficient of thebackground can be taken as follows: lantern with a short


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gargrotom______________0, 040 Lantern Longgargrotom_______________0, 010Lantern Long fairings, passing in the tailsection fyuzelyazha_0, 005 nacelle drag coefficient C x mg is definedsimilarly to the coefficient of drag of the fuselage.resistance factor chassis

can be determined by the formula where C x ca and C x nkcoefficients ofresistance of the ground and the front (rear) wheels; C oc x and C x ps - themain drag coefficients (back) landing gear; S m.ok , S m.pk , S m.os and S m.ps -square sections midoley main wheels, the front (rear) wheels, and the mainfront (back) legs. The values of the drag wheel chassis, depending on theshape of their transversal cross-section can be taken as follows: 0.25___________________________ rectangular with roundedugolkami___0, 35 rectangular (such as carting )___________ 0.50 Byusing the drag wheel fairings can be reduced to 2 ... Factor of 3. Thevalues of the drag struts, springs and other design elements that are in the

incoming flow can be determined using the data in Table. 2. 3.

Table 2.3 Coefficients of aerodynamic resistance of structuralelements


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Induced drag coefficient is given by where is a coefficient that takes intoaccount the lengthening and narrowing of the wing; ef-effective aspectratio. The coefficient b can be removed from the graph in Fig. 2. 12.


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Figure 2.12 Determination of reactance ALS

To determine the effective wing aspect ratio of ALS can use theapproximate formulawhere -aspect ratio; S zan -wing area occupied by thefuselage and pods (if engines are located on the wing). In the calculationseasy to use formula (2. 22), written in the following form: whereexpression is called the blade polars.


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The coefficient of lift aircraft

For the normal scheme of ALS can be assumed that the lifting force iscreated only by the airplane's wing. If the characteristics of the original wing

profile are known, the calculation of the lift coefficient is reduced to theplane plotting . For ALS, having a wing with aspect ratio of morethan five, we can assume that the values to angles of attack equal to14 ... 16 , increase in proportion (Fig. 2. 13) and correspond to the originalprofile. The maximum lift coefficient is given by where Cumahkr - maximum liftcoefficient of the wing profile; - sweep angle profile of the chord.Themaximum lift coefficient nestrelovidnogo wing can be taken as 92% of themaximum value of the initial profile. After determining with the minds of its valuewill be plotted (Fig. 2. 13) in a horizontal line. From the point of intersection

of two straight four postponed distance = 1 , and points 2 and 3 areconnected lekalnoy curve.


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Figure 2.13 Calculation of the coefficient of Lift force of ALS

The construction of the polar plane

The polar plane is a curve describing the dependence of drag coefficientC x of the lift coefficient C y , on the curve plotted as the angle of attack. To construct the polar of the aircraft must have the values of thecoefficients C x and C y , depending on the angle of attack . Theircalculation is convenient to the table prepared in accordance with thesample table. 2. 4

Table 2.4 Calculation of the aerodynamic coefficients


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defining the pre-values of the coefficients C x0 and A. Filling in the table,

you can begin drawing the polars of Fig. 2. 14.

Figure 2.14 The polar plane

To do this in a coordinate system with y , with x plotted points correspondingto the selected angle of attack , and joined a smooth curve. The polarplane quickly and easily identify several important aerodynamiccharacteristics used in the calculation of his aircraft performance data. Avery important characteristic that evaluates the aerodynamic perfection of

the aircraft is its aerodynamic efficiency. Its increase is one of the maintasks of aerodynamic design of aircraft. aerodynamic quality of the aircraft,


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at any selected angle of attack can be defined by the formulas: Maximumglide plane is at an angle of attack corresponding to the point of tangencyof the straight line passing through the origin drawn tangent to thepolar. The angle of attack corresponding to the highest quality aircraft

aerodynamics, is most advantageous. The curve changes aerodynamicaircraft constructed in accordance with the polar Fig. 2.14 is shown inFig. 2.15.

Figure 2.15 Changing the aerodynamic qualities of ALS as a functionof wing angle of attack

Materials: PI Chumak, VF Krivokrysenko "Calculation and design of ALS"

Calculation and Construction of the Polar ALS

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