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A method is reported for calculating the shapes of ionic comet tails that use the magnetic field along the tail to channel the tail plasma. The local momentum field in the solar wind determines magnetic field line locations along the tail. Thus, the magnetic field acts as a transparent wind sock in trapping field lines in the cometary plasma around the nucleus long enough to be effectively fastened to the comet's head.
On the basis of photographic observations made at the Cerro Tololo Inter-American Observatory, the radial and transverse brightness profiles and time variations in the surface brightness of the anti-tail of Comet Kohoutek were examined. In the process of photometric reduction one-dimensional radial tracings passing through the comet's nucleus and covering the entire anti-tail were used in the place of the standard two-dimensional scans. Each radial scan was defined by the position angle, and 'noise' variations were interpolated from the known field brightness outside the anti-tail. An analysis of the results provides quantitative support for a previously proposed model (Sekanina, 1974) suggesting that the dust particles in the anti-tail suffered a significant loss in radius due to evaporation near the perihelion passage. Preliminary calculations indicate that only particles initially larger than 100-150 micrometers in diameter survived. The emission rate of dust may be comparable to those derived for Comets Arend-Roland (1957 III) and Bennett (1970 II).
An experimental wind tunnel investigation has been made to determine the longitudinal and lateral aerodynamic stability and control characteristics of two tail fin arrangements of a monowing missile model. Both a conventional cruciform and a low profile tail arrangement were tested. The results indicate that the tail surfaces of both configurations were effective in producing pitch control. It was also concluded that both are effective in producing roll and yaw control that is accompanied by proverse yaw and roll, respectively. The conventional cruciform tail produces the most roll and yaw control.
The effects of tail design on spin and recovery were investigated in a spin tunnel. A 1/11-scale model of a research airplane which represents a typical low-wing, single engine, light general aviation airplane was used. A tail design criterion for satisfactory spin recovery for light airplanes was evaluated. The effects of other geometric design features on the spin and recovery characteristics were also determined. Results indicate that the existing tail design criterion for light airplanes, which uses the tail damping power factor as a parameter, cannot be used to predict spin-recovery characteristics.
A wind tunnel investigation was made at free stream Mach numbers from 1.70 to 2.86 to determine the effects of fixed and free rolling tail fin afterbodies on the static longitudinal and lateral aerodynamic characteristics of a cruciform canard controlled missile model. The effect of small canard roll and yaw control deflections was also examined. The results indicate that the fixed and free rolling tail configurations have about the same lift curve slope and longitudinal stability level at low angles of attack. For the free rolling tail configuration, the canards provide conventional roll control with no roll control reversal at low angles of attack. The free rolling tail configuration reduced induced roll due to model roll angle and canard yaw control.
Attention is focused on a form of cometary activity which has been known for some time but is poorly understood: the discarding of a plasma tail by a comet. A link is found between plasma-tail rejections and conditions in the solar wind. A model is presented in which a disconnected tail is the end result of magnetic-field-line reconnection in the cometary ionosphere caused by the traversal of a magnetic sector boundary. Observations of plasma tails appear to be the best and only method at present of mapping the interplanetary sector structure out of the ecliptic plane.
Classical drag equations in a modern version were used to calculate the influence of tail modifications on the drag of a standard class sailplane. The profile drag which depends on the Reynolds number is included in the calculations. Minimum drag is compared with real drag for two lift coefficients. Some results have no clear tendency but low tail area and relatively low tail aspect ratio give some advantages. Optimum and real lift ratios between wing and tail plane are compared for the original sailplane.
Pressure coefficients were obtained in the Langley Unitary Plan wind tunnel for a wingless missile with a clipped delta tail. The angle of attack was varied from -4 deg to 20 deg, model roll angle was varied from 0 deg to 90 deg in 22.5 deg increments, and tail deflections were 0 deg to - 15 deg. The pressures were measured on two adjacent tail surfaces using 91 pressure orifices per tail surface. Results are presented in plotted and tabular form.
An investigation was made of the forces and moments on the cruciform aft-tail control surfaces of a wingless missile model to determine the variation of panel load and center of pressure with angle of attack, tail deflection, model roll angle, and Mach number. Also, a limited force-moment and surface-pressure investigation was made on a noncircular aft end. These investigations were made in a unitary plan wind tunnel at Mach numbers of 1.60, 2.36, and 3.70 and at a Reynolds number per meter of 6,600,000. The cruciform aft-tail results indicate very little variation in the center of pressure for the highly loaded windward tail. The noncircular aft-end test results indicate no significant effect of the fin unporting on the fin loads.
A NASTRAN model of a UH-1B tail boom that had been designed for another project was used to investigate the effect on structural integrity of simulated projectile damage. Elements representing skin, and sections of stringers, longerons and bulkheads were systematically deleted to represent projectile damage. The structure was loaded in a manner to represent the flight loads that would be imposed on the tail boom at a 130 knot cruise. The deflection of four points on the rear of the tail boom relative to the position of these points for the unloaded, undamaged condition of the tail boom was used as a measure of the loss of structural rigidity. The same procedure was then used with the material properties of the aluminum alloys replaced with the material properties of T300/5208 high strength graphite/epoxy fibrous composite material, (0, + or - 45, 90)s for the skin and (0, + or - 45)s for the longerons, stringers, and bulk heads.
A wind-tunnel missile model with either a lower vertical tail fin with a pair of horizontal fins having 0 deg, 22.5 deg, or 30 deg dihedral or an upper vertical tail fin with horizontal fins having 0 deg, -22.5 deg, or -30 deg dihedral was investigated. The results indicated that those configurations with horizontal fins at or below the horizontal plane had nearly linear pitching-moment characteristics, while those with the horizontal fins above the horizontal plane experienced pitch-up which increased with increasing horizontal-fin-dihedral angle. At zero angle of attack, the configurations were directionally stable at most test Mach numbers. Generally, those configurations with the upper vertical fin had positive effective dihedral at zero angle of attack, while those with he lower vertical fin had negative effective dihedral. For roll control, three deflected tail fins produced more total roll control than two horizontal fins. For yaw control, three tail fins deflected equally or differentially produced more total yaw control than the single vertical fin.
The feasibility of using static wind tunnel tests to obtain information about spin damping characteristics of an isolated general aviation aircraft tail was investigated. A representative tail section was oriented to the tunnel free streamline at angles simulating an equilibrium spin. A full range of normally encountered spin conditions was employed. Results of parametric studies performed to determine the effect of spin damping on several tail design parameters show satisfactory agreement with NASA rotary balance tests. Wing and body interference effects are present in the NASA studies at steep spin attitudes, but agreement improves with increasing pitch angle and spin rate, suggesting that rotational flow effects are minimal. Vertical position of the horizontal stabilizer is found to be a primary parameter affecting yaw damping, and horizontal tail chordwise position induces a substantial effect on pitching moment.
Longitudinal aerodynamic characteristics of a configuration consisting of an elliptical body with an in plane horizontal tail were investigated. The tests were conducted at Mach numbers of 2.3, 2.96, 4.0, and 4.63. In some cases, the configuration with negative tail deflections yielded higher values of maximum lift drag ratio than did the configuration with an undeflected tail. This was due to body upwash acting on the tail and producing an additional lift increment with essentially no drag penalty. Linear theory methods used to estimate some of the longitudinal aerodynamic characteristics of the model yielded results which compared well with experimental data for all Mach numbers in this investigation and for both small angles of attack and larger angles of attack where nonlinear (vortex) flow phenomena were present.
It is shown that the folding phenomenon of the comet tail rays is compatible with the Ferraro isorotation law if the comet tail magnetic field has no azimuthal component, that is, B sub phi (the polar angle) equals zero. Considering electric drift due to convectional electric fields, a formula is obtained for the angular rate of a ray closure which reduces to that of Ness and Donn (1966) if the velocity profile across the tail is linear. The magnetic field B of approximately 20-40 gammas in the coma and less than about 10 gammas in the distant tail is estimated under typical solar wind conditions at 1 AU.
A satisfactory orbital solution for Comet Howard-Koomen-Michels 1979 XI is found on the assumption that the comet's line of apsides coincided with that of the Kreutz sungrazing comet group. The derived perihelion distance then shows that this is the first known case of a comet falling into the sun. A dust tail that survived the comet is studied as a particle flow phenomenon controlled by no force other than solar gravity and solar radiation pressure. The tail's outline is interpreted in terms of an onset of dust production, a peak repulsive force on the particles, and a circumsolar dustfree zone due to particle sublimation. It is shown that the surviving debris consisted mostly of absorbing, submicron size particles in hyperbolic trajectories convex to the sun and curving toward the earth. The tail width may be a product of the interaction of charged dust in the tail with a complicated structure of the coronal magnetic field.
In connection with the findings of the Voyager 1 mission, it appears that the tail lobe of Saturn is very different from that of earth and Jupiter, in that the latter are devoid of energetic particles, and magnetic field lines in this region are thought to be open and interconnecting with the interplanetary magnetic field at large distances in the antisolar direction. The present investigation is concerned with a possible explanation of these observations, taking into account a model of Saturn's magnetosphere. It is shown that the Voyager 1 spacecraft remained in the closed region of the magnetotail during its entire tail traversal and did not have an opportunity to penetrate into the high latitude lobe. It is concluded that Saturn probably has a tail lobe just like earth and Jupiter. However, this tail lobe was not traversed by Voyager.
The first descriptions of combined tail measurements from the Pioneer Venus plasma analyzer, magnetometer, and plasma wave detector are presented. The analysis concentrates on those orbits which are representative of the first tail passage. Summary plasma analyzer parameters are used to show that waves occurring at the boundary of the magnetotail can be identified as Doppler-shifted ion acoustic oscillations. High-density plasma distributions in the magnetotail region usually appear to be non-Maxwellian at the highest time resolution. These distorted distribution functions are generally accompanied by enhanced plasma wave signals and magnetic field reversals indicative of electric currents. A different time for the spacecraft entrance into the magnetotail from that previously defined is identified. It is shown that the wave activity in the Venus tail appears similar to the broadband noise identified in the earth's tail, except that at Venus the levels are usually higher.
A model scale hover test was conducted in the Sikorsky Aircraft Model rotor hover Facility to identify and quantify the impact of the tail rotor on the demonstrated advantages of advanced geometry tip configurations. The test was conducted using the Basic Model Test Rig and two scaled main rotor systems, one representing a 1/5.727 scale UH-60A BLACK HAWK and the others a 1/4.71 scale S-76. Eight alternate rotor tip configurations were tested, 3 on the BLACK HAWK rotor and 6 on the S-76 rotor. Four of these tips were then selected for testing in close proximity to an operating tail rotor (operating in both tractor and pusher modes) to determine if the performance advantages that could be obtained from the use of advanced geometry tips in a main rotor only environment would still exist in the more complex flow field involving a tail rotor. The test showed that overall the tail rotor effects on the advanced tip configurations tested are not substantially different from the effects on conventional tips.