1、- Edited by: Jan Roskam 0s 0, c 0 N76-13957 (KASA-C3-145tL7) P5UCEEI:IhGS OF THE KkSA, REI3iICTICIi WOrKSHOP (Kansas Univ.) 454 F HC N76- 11023 63/01 39440 3 IN cu SI rtrim, interference, tail, and cooling drag. The various topics to be covered in the next three days are shown on F igure 2. Note tha
2、t although cooling drag can be a large percentage of total drag (as high as 25%), it has previously been covered in a NASb (2) induced flow or vortex flow primarily a function of wing aspect ratio; and 3) pressure effects associated with the profile or form of various parts of the aircraft. wetted a
3、rea with Reynolds number for fully turbulent and laminar flow conditions. Note that at large Re numbers typical of flight cruise conditions, the drag associated wiih turbulent flow is ten times higher than for laminar flow. In another example of the effect of flow conditions, Figure pres the equival
4、ent drag of a laminar flow airfoil and a circular wire. If nothing else, this is an incentive to avoid using exposed landing wires. Shown on Figure 5 is the variation of flat plate drag coefficient based on Drag Prediction Techniques Moving along to the first topic of our workshop, the various drag
5、prediction techniques in use toduy are noted in Figure 7. The empirical approach takes udvmtage of semi-analytical methods in which wind-tunnel and flight-test results of similar type aircraft are factored in to establish a data base. Wind tunnel measurements of drag for a new design are usually mad
6、e, particularly for high-performance aircraft. Extrapolation of smafl-scale (low Re no.) data to flight conditions can be difficult when including power effects and the accuracy of how well the small-scale model represents the actual aircraft. Finally, theoretical estimates, although used extensivel
7、y in the past, hwe become more popular because of the availability of large capacity digital computers. Solutions of 3-dimensional viscous flow effects appear to remain a challenge even with very large (and expensive) digital computers such as the ILLIAC IV based at the NASA Ames Research Center. 12
8、 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-n example of results from drag prediction methods developed ut ASA-Ames dynam ics su brout ine ca culates a series of factors which are used to establish drag values. Form factors are used for each com
9、ponent to represent drag increases above that of a flat plate to account for 3-0 effects, interference, roughness, and excrescences. These calculations were made for the Learjet , Citation, Cessna 340, Piper Arrow, and Cessna 1.50. Note first , not unexpectedly, that the wing and Fuselage are respon
10、sible for the largesf source of drag. Of interest in the last column is the amount to be added to match flight values of drag. This item varies greatly, gbing from less than 2 percent for the Learjet to 37 percent for the Cessna 150. improvements are needed to more accurately account for such factor
11、s as 3-0 effects, cooling drag, landing gear, slipstream drag, etc. Factors Influencing Fuselage Drag In the next item of our workshop agenda, Figure 9 gives several factors which affect fuselage drag. The surface conditions are very important because of the large wetted area. Windshield shape can s
12、ignifikantly affect total drag at the higher Mach numbers. Fuselage shape in terms of fineness ratio, nose shape and rear-end shape must be carefully considered. Shown in Figure 10 is the effect of afterbody contraction ratio on drag. The contraction ratio must be greater than 2.0 to avoid a drag in
13、crease. A similar Consideration must be given in the vertical plane,. Factors Influencing Wing Drag Figure 11 lists several factors which are considered in selecting a wing for a new aircraft design. A large background of data is available from NACA research on airfoil sections and newer types such
14、as the GAW-I airfoil to challenge the designer in selecting the correct airfoil section for his aircraft. The NASA has underway a program on airfoil development aimed primarily at optimizing airfoils for specific operating conditions. Thickness rat io effects are generally well-documented. Planform
15、and aspect ratio effects are also important as influenced by structural considerations. Wing-tip effects on induced drag will be covered specifically in a Langley Research Center paper describing the trade-offs on using “Winglets. I Another reminder of the importance of surface conditions and thickn
16、ess ratio on drag is given in Figure 12. These NACA data tend to exaggerate the effect of roughness because the lower curve represents a mirror-finish surface condition. The 13 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-ance jets is to use icker
17、 airfoil sect ions for e considerat ions. Factors Influencing Trim Drag Of the various factors shown in Figure 13 which affect trim drag, tail location and static stability have recently been given increased attention. A tail location out of the slipstream (“TI tail designs) offer some drag decrease
18、, and canard horizontal tail locations have appeared on experimental aircraft. In consideration of the small percentage of the tail surfaces to total drag indicated previously, one must be careful not to compromise stability and control in looking for performance imporvements . In this connection th
19、e control configured-vehicle (CCV) and relaxed static stabif ity have received attention recently. An illustration of the effect of reducing static margin on the horizontal tail area required is shown in Figure 14. These curves indicate the variation of tail size with static margin to trim out the w
20、ing-fuselage pitching moment and the tail area needed for maneuvering. To achieve the minimum tail area and therefore the least amount of drag, the static margin must be slightly aft of the neutral point (dsdk = 0) but ahead of the maneuver point (dFJd,ti, = 0). Obviously, some for of stability augm
21、entation must be provided to meet the FAR if minimum tail size is desired. At this point one would logically question the merits of reducing static margin for moot General Aviation aircraft. L Considerations for Drag of Complete Aircraft In the final analysis, drag of the complete configuration is t
22、he most difficult to rationalize. As noted in Figure 15, cost is a factor that must be considered in each aspect of aerodynamic drag reduction. Cost aspects will be discussed in a paper later in the workshop. In this regard use of composites may offer promise in that extremely smooth surfaces with a
23、ttendant low drag can be achieved without high-cost manufacturing techniques. The second point, aerodynamic drag of the complete configuration, must take into account items such as wing nacelle and tail location, fuselage camber, wing and nacelle incidence, wing loading, cruise I ift coefficient, et
24、c. This area will be covered also on the last day of the workshop. The next item, propulsion system integration, is an important area, particularly for higher performance aircraft. Nacelle size and location can significantly affect high subsonic Mach number performance, as will be discussed by NASA
25、Lewis Research Center. Fabrication details, the next item, must be considered in the I ight of cost and aircraft appearance. A 14 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-t only has the potential for higher erfmce, mprtat point to know is the
26、relative magnitude of the various sources o tion. This leads to the next point of discussion. ause of the many trade-offs in aerodynamic drag reduc- In Figure 16 the relative drag values are compared for a high performance aircraft. Leading the list is the friction drag, with induced drag a close se
27、cond. Cross flow or 3-D effects can cuuse drag problems and are unfortunately the most difficult to predict. Induced drag primarily a function of wing aspect ratio can be reduced by wing-tip modifications, as will be covered by Langley Research Center. Historical Survey of Drag Figure 17 presents th
28、e variation of drag based on wetted area as a function of time. Starting with the Wright Brothers design as the highest drag vehicle-not too surprising if you recall how large a drag penalty wires can create. The lowest drag values correspond to fighter aircraft such as the Douglas A-4 and LTV F-8.
29、There is no question that improvements have been made with time, but how well are we doing in realizing the goals of drag previously noted. Shown in Figure 18 is a comparison of flight drag data with fiat plate skin fraction curves for turbulent and laminar flow conditions. The data which are for ty
30、pical general aviation aircraft fall short of even achieving the turbulent flow drag values. The lowest drag value quoted is for the black buzzard (coragyps atratvs) which in some 150 million years of evolution has no doubt managed to achieve reasonably good flow conditions without having to contend
31、 with cooling drag and propef ler sf ipstream effects. There are indications that these idealized goals can be approached by aircraft with good surface finishes, such as the point for the Learjet at 30 million Re. Concluding Remarks In conclusion, three main points should be kept in mind during the
32、next three days (see Figure 19). We need to more accurately clarify the sources of drag for general aviation-type aircraft so that new designs can benefit from more accurate prediction techniques. Next, by knowing more about the sources of drag it will be possible to bring out the greatest potential
33、 for drag reduction. Finally, we must use our expertise to identify gaps in knowledge and point out areas which should receive high priority R and D efforts. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-A drag nformaion, 2 10 mph I rreet ing a cha
34、nge in equivalent flatplate area from 16.1 to 7.2 square feet. 16 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-t E 2 8 e P t! P 8 B rc- 0 .- z c 17 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-n
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36、by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1 1 I B 0 ti 2 s a U ? D 20 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-. m C .- & S e, L .- 3 21 Provided by IHSNot for ResaleNo reproduction or networking
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