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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1961

Atmosphere Entries with Vehicle Lift-Drag Ratio Modulated to Limit Deceleration and Rate of Deceleration: Vehicles with Maximum Lift-Drag Ratio of 0.5

An analysis has been made of atmosphere entries for which the vehicle lift-drag ratio was modulated to maintain specified maximum decelerations and/or maximum deceleration rates. The part of the vehicle drag polar used during modulation was from maximum lift coefficient to minimum drag coefficient. The entries were at parabolic velocity and the vehicle maximum lift-drag ratio was 0.5. Two-dimensional trajectory calculations were made for a nonrotating, spherical earth with an exponential atmosphere. The results of the analysis indicate that for a given initial flight-path angle, modulation generally resulted in a reduction of the maximum deceleration to 60 percent of the unmodulated value or a reduction of maximum deceleration rate to less than 50 percent of the unmodulated rate. These results were equivalent, for a maximum deceleration of 10 g, to lowering the undershoot boundary 24 miles with a resulting decrease in total convective heating to the stagnation point of 22 percent. However, the maximum convective heating rate was increased 18 percent; the maximum radiative heating rate and total radiative heating were each increased about 10 percent.

Katzen, Elliott D.↗
NASA NTRS1959

The Problem of Obtaining High Lift-Drag Ratios at Supersonic Speeds

The importance of the lift to drag ratio is well known to all aircraft designers since it gives, to a great extent, the aerodynamic efficiency of the airplane. Aerodynamic efficiency, however, is only one component of the grand compromise that a completed airplane represents. At subsonic speeds, lift-drag ratios of well over 200 have been measured in wind tunnels on airfoil sections; but few powered aircraft have attained (L/D) value of 20. It is invariably true that the requirements of stability and control, structure, and flight operation all contribute to reducing the design (L/D) (sub max)) considerably below those exotic values which can be predicted from unrestricted aerodynamic theory. If, however, a certain range or operating efficiency is required, there is most certainly a minimum (L/D) (sub max)) value for which the goals are just attainable. If we examine the range equation we see that range is proportional to the lift-drag ratio, the thermopropulsive efficiency, and the logarithm of the initial to final weight ratio. The appearance of the lift-drag ratio as a linear factor in the range equation indicates that every attempt should be made to increase (L/D) (sub max)); however, the search for higher (L/D)max may lead to strange and unorthodox configurations. Most frequently, such configurations are ruled out by the adverse effects of their geometry on the weight ratios. In the present paper, we will deal with the maximum lift-drag ratio problem for conventional configurations having a wing and a body in close proximity to each other. No attempt will be made to select a particular configuration as being the best. However, the promising direction to go from the aerodynamic view will be stressed with the understanding that the other factors may outweight the aerodynamics

Brown, Clinton E.↗
NASA NTRS1959

Lift-Drag Ratios for an Arrow Wing With Bodies at Mach Number 3

Force and moment characteristics, including lift-drag ratios, have been measured for bodies of circular and elliptic cross section alone and combined with a warped arrow wing. The test Mach number was 2.94, and the Reynolds number was 3.5 x 10(exp 6) (based on wing mean aerodynamic chord). The experimental results show that for equal volume the use of an elliptical body can result in a noticeably higher maximum lift-drag ratio than that obtained through use of a circular body. Methods for estimating the aerodynamic characteristics have been assessed by comparing computed with experimental results. Because of good agreement of the predictions with experiment, maximum lift-drag ratios have been computed for the arrow wing in combination with bodies of various sizes. These calculations have shown that, for an efficient wing-body combination, little loss in maximum lift-drag ratio results from considerable extension of afterbody length. For example, for a wing-body configuration having a maximum lift-drag ratio of about 7.1, a loss in maximum lift-drag ratio of less than 0.2 results from a 40-percent increase in body volume by extension of afterbody length. It also appears that with body length fixed, maximum lift-drag ratio decreases almost linearly with increase in body diameter. For a wing- body combination employing a body of circular cross section, a decrease in maximum lift-drag ratio from about 9.1 for zero body diameter to about 4.6 for a body diameter of 13.5 percent of the body length was computed.

Jorgensen, Leland H.↗
NASA NTRS1959

Approach and Landing Investigation at Lift-Drag Ratios of 2 to 4 Utilizing a Straight-Wing Fighter Airplane

A series of landings was performed with a straight-wing airplane to evaluate the effect of low lift-drag ratios on approach and landing characteristics. Landings with a peak lift-drag ratio as low as 3 were performed by altering the airplane configuration (extending speed brakes, flaps, and gear and reducing throttle setting). As lift-drag ratio was reduced, it was necessary either to make the landing pattern tighter or to increase initial altitude, or both. At the lowest lift-drag ratio the pilots believed a 270 deg overhead pattern was advisable because of the greater ease afforded in visually positioning the airplane. The values of the pertinent flare parameters increased with the reduction of lift-drag ratio. These parameters included time required for final flare; speed change during final flare; and altitude, glide slope, indicated airspeed, and vertical velocity at initiation of final flare. The pilots believed that the tolerable limit was reached with this airplane in the present configuration, and that if, because of a further reduction in lift-drag ratio, more severe approaches than those experienced in this program were attempted, additional aids would be required to determine the flare-initiation point.

Matranga, Gene J.↗
NASA NTRS1976

Estimated lift-drag ratios at supersonic speed

Recent developments in supersonic flow theory are applied to obtain estimates of the lift-drag ratios that may be achieved by aircraft employing sweptback wings. Lift-drag ratios greater than 10 to 1 can be maintained up to a Mach number of 1.4by the use of large angles of sweep and high aspect ratios. As the speed increases in the supersonic range the attainable lift-drag ratios decrease and the gain due to sweepback also appears to diminish. An efficient configuration for M = 1.4 would require about 60 deg sweepback, an aspect ratio of 4 and a wing loading of one third the atmospheric pressure. For a wing loading of 50 pounds per square foot the cruising altitude would be 60,000 feet and the indicated airspeed 290 miles per hour.

Jones, R. T.↗
NASA NTRS1959

The Effect of Lift-Drag Ratio and Speed on the Ability to Position a Gliding Aircraft for a Landing on a 5,000-Foot Runway

Flight tests were made to determine the capability of positioning a gliding airplane for a landing on a 5,000-foot runway with special reference to the gliding flight of a satellite vehicle of fixed configuration upon reentry into the earth's atmosphere. The lift-drag ratio and speed of the airplane in the glides were varied through as large a range as possible. The results showed a marked tendency to undershoot the runway when the lift-drag ratios were below certain values, depending upon the speed in the glide. A straight line dividing the successful approaches from the undershoots could be drawn through a lift-drag ratio of about 3 at 100 knots and through a lift-drag ratio of about 7 at 185 knots. Provision of a drag device would be very beneficial, particularly in reducing the tendency toward undershooting at the higher speeds.

Reeder, John P.↗
NASA NTRS1960

A Supersonic Area Rule and an Application to the Design of a Wing-Body Combination with High Lift-Drag Ratios

A concept for interrelating the wave drags of wing-body combinations at supersonic speeds with axial developments of cross-sectional area is presented. A swept-wing-indented-body combination designed on the basis of this concept to have significantly improved maximum lift-drag ratios over a range of transonic and moderate supersonic speeds is described. Experimental results have been obtained for this configuration at Mach numbers from 0.80 to 2.01. Maximum lift-drag ratios of approximately 14 and 9 were measured at Mach numbers of 1.15 and 1.41, respectively.

Whitcomb, Richard T.↗