Paul B. MacCready

STRUCTURE OF ATMOSPHERIC TURBULENCE

Abstract Experimental data on the energy spectra, correlation coefficients and energy isotropy of atmospheric turbulence at low elevations are presented. It is shown that the very simple formulas derived with the aid of Kolmogoroffs Similarity Hypothesis are remarkably consistent with the experimental evidence of this and other research projects. The Similarity Hypothesis, although only directly applicable to turbulent eddies small enough to be isotropic, appears in some instances to be useful in its simplest form for atmospheric problems with scales varying between one cm and a thousand km. Some possible applications are described together with the regions where the Similarity Hypothesis might be expected to hold. Several measurements of vertical turbulent heat flux at various elevations were made with rapid-response equipment. A systematic variation of the heat flux with elevation was noted even at the low elevations involved.

Sun-powered aircraft designs

Two piloted aircraft have been developed and flown powered solely by photovoltaic cells in a program sponsored by the DuPont Company. The 30.8-kg (68-lb), 21.6-m (71-ft) span, Gossamer Penguin was used as a solar test bed, making a 2.6-km (1.6-mile) flight in August 1980. The 88.1-kg (194-lb), 14.3-m (47-ft) span Solar Challenger was developed for long flights in normal turbulence. Stressed to +9 G, it utilizes Kevlar, Nomex honeycomb-graphite sandwich wall tubes, expanded polystyrene foam ribs, and Mylar skin. With a 54.9-kg (121-lb) airframe, 33.1-kg (73-lb) propulsion system, and a 45.4-kg (100-lb) pilot, it flies on 1400 watts. In summer, the projected maximum climb is 1.0 m/s (200 ft/min) at 9,150 m (30,000 ft). Sixty purely solar-powered flights were made during winter 1980-1981. Using thermals, 1,070 m (3,500 ft) was reached with 115-minute duration.

Bistatic acoustic wind monitor system

In a Doppler acoustic radar system, bistatic transmitting and receiving antennas are employed in a manner to significantly improve wind measurement performance, and to simplify equipment deployment.

Atmospheric turbulence measurements and analysis

Abstract Satisfactory measuring techniques have been developed which overcome the four, principal experimental problems arising in the investigation of atmospheric turbulence. 1. The data are made reproducible for statistical analysis by recording them on a portable magnetic tape recorder. 2. and 3. The problems of measuring wind velocity fluctuations over broad ranges (frequencies between 0 and 50 cycles per second, and magnitudes between 0.25 and 20 meters per second) are solved by using hot-wire anemometers together with non-linear amplifiers. 4. Measurements at elevations up to several hundred meters are made feasible by the use of a multi-cable tethering system for a balloon which supports the measuring devices. The techniques permit the measurement of velocity distributions, frequency spectra, autocorrelation coefficients, and heat flux at any elevation. The difficulty of constructing such measuring and analysis equipment is balanced by the relative simplicity with which a complete statistical analy...

An Isolated Cumulus Cloud Modification Project

Abstract A randomized seeding experiment was conducted in Flagstaff, Ariz., in July and August of 1967 wherein the heights, rainfall amounts and rainfall durations of isolated cumuli were measured. Twenty-one clouds were studied, 10 seeded and 11 not seeded, on 11 days. On nine days there were paired seed and no-seed events. The choice of the test clouds and much of the analysis was performed with the aid of a simple numerical model of cumulus dynamics and microphysics. The project aims were to show distinct effects of seeding on cloud-top height, rainfall and duration; to verify and/or improve the model; and to use the model to interpret the importance of the seeding effect. For the 21 test clouds, the average increases in radar tops, precipitation and duration were 5900 ft, 2.00 mm and 10 min, respectively, with students t-test significance values being 96, 92 and 81%, respectively. On the nine days of paired seed and no-seed events, the t-test significance exceeded 98% for the three variables quoted a...

New Technologies of Art — Where Art and Science Meet: Conference Report

The conference presented the work of leading artists, scientists and engineers whose visual experiments are involved to varying degrees with new technology. Addressing questions critical for today’s artists, the participants illustrated some of the ways this new technology could be used to extend one’s work. The program also offered artists an opportunity to examine many new avenues for exploration. Presentations by Paul MacCready and Friedrich St. Florian are included in condensed form as supplements to the general article.

Aerodynamics and Other Efficiencies in Transporting Goods

Recognizing both the pollution effects of fuel use and the likely increases of fuel cost in coming decades puts high priority on alternative energy for trucks, buses and trains. There are still gains available in decreasing aerodynamic drag and rolling friction, using efficient engines, and minimizing fuel waste, but it is appropriate to explore decisions that would be suitable if fossil fuel were deemed unattractive. One then would consider utilizing natural energy (sunlight, wind, wave), getting energy from braking, employing hydrogen, putting different priorities on trucks vs. buses vs. trains, exploring integration with water deliveries and automatic local air transport, etc. Such an investigation might illuminate early alternatives that would at least permit partial improvements.

Art and Nature in the Technology of Flight

Nelson-Atkins Museum of Art, Kansas City, MO, 1979. Through use of projected light and a series of slides, the Cloister was altered almost beyond recognition and then allowed to return slowly to its original appearance. 8. Some of his credits include Close Encounters, Star Trek (Part 1) and The Rising Sun. 9. Friedrich St. Florian is currently Dean of Architecture at the Rhode Island School of Design. 10. Otto Piene is Director of M.I.T.s Center for Advanced Visual Studies. 11. A discussion of Otto Pienes sky art as well as illustrations of these two heliumfilled inflatable sculptures can be found in Leonardo 19, No. 3 (1986).

Doppler Acoustic Sounding: Application to Dispersion Modeling

The use of acoustics to study atmospheric properties is well-established. A review of atmospheric effects on acoustic signals can be found in Thomson (1975) and the history of acoustic sounder development is given by Gaynor (1982). However, the use of Doppler acoustic sounders in air pollution applications, as pointed out by Gaynor (1982), has gained acceptance only very recently. Doppler acoustic sounders with proven reliability have become commercially available only in the past decade and, even now, only a limited number of units are routinely being used to collect wind data.