Daylight Flight Research Articles

Extremely low daylight sea-crossing flights of a nocturnal migrant.

Understanding the trade-off between energy expenditure of carrying large fuel loads and the risk of fuel depletion is imperative to understand the evolution of flight strategies during long-distance animal migration. Global flyways regularly involve sea crossings that may impose flight prolongations on migrating land-birds and thereby reduce their energy reserves and survival prospects. We studied route choice, flight behavior, and fuel store dynamics of nocturnally migrating European nightjars (Caprimulgus europaeus) crossing water barriers. We show that barrier size and groundspeed of the birds influence the prospects of extended daylight flights, but also that waters possible to cross within a night regularly result in diurnal flight events. The nightjars systematically responded to daylight flights by descending to about a wingspan's altitude above the sea surface while switching to an energy-efficient flap-glide flight style. By operating within the surface-air boundary layer, the nightjars could fly in ground effect, exploit local updraft and pressure variations, and thereby substantially reduce flight costs as indicated by their increased proportion of cheap glides. We propose that surface-skimming flights, as illustrated in the nightjar, provide an energy-efficient transport mode and that this novel finding asks for a reconsideration of our understanding of flight strategies when land-birds migrate across seas.

Ojukwu’s Biafra: Relief Corridor, Arms Smuggling, and Broken Diplomacy in the Nigerian Civil War

This article examines the rationale behind, or motivation, for the Biafran head of government, General Chukwuemeka Odumegwu Ojukwu’s sustained objection both to proposed mercy corridor and daylight relief flights into Biafra by the International Committee of Red Cross (ICRC) despite the prevalent starvation in Biafra during the Nigerian Civil War. Ojukwu’s public justification for his objection to the proposals was that there was a possibility that the Nigerian forces could poison the food and medicine destined to Biafra. He also argued that agreement to daylight flights could expose Biafra to bombardment by Nigerian forces. Surprisingly, some scholars have either ignored this aspect of the conflict or accepted Ojukwu’s claims in their analysis of the relief debates. Using mainly archival sources and interviews, this paper argues that while it may be possible for Biafra’s infrastructure to be attacked by federal forces, Ojukwu’s main reason of objection to the proposals was to keep open the lines through which Biafra was receiving its arms and ammunition from external sources.

Flight trajectory optimization of sun-tracking solar aircraft under the constraint of mission region

The optimal yawing angle of sun-tracking solar aircraft is tightly related to the solar azimuth angle, which results in a large arc flight path to dynamically track the sun position. However, the limited detection range of payload usually requires solar aircraft to loiter over areas of interest for persistent surveillance missions. The large arc sun-tracking flight may cause the target area on the ground to be outside the maximum coverage area of payload. The present study therefore develops an optimal flight control approach for planning the flight path of sun-tracking solar aircraft within a mission region. The proposed method enables sun-tracking solar aircraft to maintain the optimal yawing angle most of the time during daylight flight, except when the aircraft reverses its direction by turning flight. For a circular region with a mission radius of 50 km, the optimal flight trajectory and controls of an example Λ-shaped sun-tracking solar aircraft are investigated theoretically. Results demonstrate the effectiveness of the proposed approach to optimize the flight path of the sun-tracking aircraft under the given circular region while maximizing the battery input power. Furthermore, the effects of varying the mission radius on energy performance are explored numerically. It has been proved that both net energy and energy balance remain nearly constant as the radius constraint varies, which enables the solar aircraft to achieve perpetual flight at almost the same latitude as the large arc flight. The method and results presented in this paper can provide reference for the persistent operation of sun-tracking solar aircraft within specific mission areas.

Diurnal Flying Activity of a Neotropical Bat (Saccopteryx leptura): Effect of Light Intensity, Temperature, and Canopy Cover

Nocturnal behavior is a critical life-history trait associated with the evolutionary success of bats. Avian predation, competition with birds, and hyperthermia may explain the origin of this behavior, but it is difficult to assess the validity of these hypotheses due to the rarity of diurnal activity in bats. In Gorgona National Natural Park, Colombia, the population of the lesser sac-winged bat (Emballonuridae: Saccopteryx leptura) has an unusual daylight flight activity, which provides an opportunity to learn about the origin of nocturnality in bats. We described the daylight activity of S. leptura in Gorgona Island and explored the influence of environmental factors at different spatiotemporal scales, potentially involved in this particular behavior. We registered the variation of light intensity and temperature across days, months, and different vegetation canopy covers and assessed their effects on the number of daylight flights. We found that the daytime activity of this insular population increases with vegetation cover, decreases with light intensity and temperature, and varies seasonally. These responses of flying activity to environmental temperature and light intensity seem to be related to avoiding the risk of overheating. Furthermore, bats were also active at night, and daytime flights included echolocation and feeding, which suggest that daytime activity complements but does not replace night-time activity. Consequently, our results provide empirical support for the notion that the nocturnality in bats can reflect the actions of avoiding overheating during the day.

Energy optimization and investigation for Z-shaped sun-tracking morphing-wing solar-powered UAV

To achieve perpetual flight, solar-powered UAVs (SPUAVs) need to convert sufficient solar energy into electricity during daylight flight. However, perpetual flight at middle and high latitude regions in winter days still poses great challenges for gaining enough solar energy due to the low sun elevation angle and short daylight duration. Among measures for flight endurance enhancement, tracking the sun through changing geometry of wing and orienting flight direction may be an effective design scheme for gaining more solar energy. In this paper, the energy optimization method for Z-shaped sun-tracking morphing-wing SPUAV is developed and used to investigate the advantages on energy performance of the optimal Z-shaped wing over the conventional planar wing. Energy optimization for a whole year's flight shows that the optimal Z-shaped wing is capable of achieving longer flight endurance, improving perpetual flight latitude and extending perpetual flight date efficiently compared with the planar wing, especially for the middle and high latitude regions during winter days. The investigation on implications of conversion efficiency of solar cells indicates that, with higher conversion efficiency of solar cells, the optimal Z-shaped wing is more effective to collect more net energy, retain more energy margin and achieve perpetual flight at higher latitude. The Z-shaped sun-tracking morphing-wing design combined with the energy optimization method proposed is helpful to increase flight endurance and improve perpetual flight latitude for SPUAVs.

Effect of Trap Size, Trap Height and Age of Lure on SamplingXyleborus glabratus(Coleoptera: Curculionidae: Scolytinae), and its Flight Periodicity and Seasonality

Xyleborus glabratus (Coleoptera: Curculionidae: Scolytinae) is a non-native pest that transmits the causal pathogen of laurel wilt disease to plants belonging to the Lauraceae. To improve the current monitoring and survey techniques of X. glabratus, various trapping and flight behavior studies were conducted in natural areas with host species in Alachua County, Florida. Daylight flight rhythm studied at Austin Cary Memorial Forest twice in Sep 2010 using sticky traps baited with manuka lures showed that X. glabratus flies mostly between 1600 and 1800 h daylight saving time. Flight height of the beetle was determined in a trapping study using ladder-like traps. The largest number of beetles was trapped at heights of 35–100 cm above the ground. Seasonality of X. glabratus was studied in Florida from Mar 2010–Dec 2011. Three peaks of trap catches occurred during Apr 2010, Oct 2010 and Mar 2011. To find the optimal Lindgren funnel trap design for X. glabratus, a study was conducted using 4, 8, 12 and 16 funnels per trap. Funnel traps with 8, 12, 16 funnels per trap captured similar numbers of X. glabratus, but significantly more than with 4 funnels per trap. The effect of aging of manuka lures was studied at 2 different sites in Alachua County, Florida. New manuka lures trapped significantly more X. glabratus than lures aged 2, 4 and 6 wk. Trap color, whether black, white, blue, yellow, red or transparent, had no significant influence on the number of X. glabratus trapped.

Trapped in the darkness of the night: thermal and energetic constraints of daylight flight in bats

Bats are one of the most successful mammalian groups, even though their foraging activities are restricted to the hours of twilight and night-time. Some studies suggested that bats became nocturnal because of overheating when flying in daylight. This is because—in contrast to feathered wings of birds—dark and naked wing membranes of bats efficiently absorb short-wave solar radiation. We hypothesized that bats face elevated flight costs during daylight flights, since we expected them to alter wing-beat kinematics to reduce heat load by solar radiation. To test this assumption, we measured metabolic rate and body temperature during short flights in the tropical short-tailed fruit bat Carollia perspicillata at night and during the day. Core body temperature of flying bats differed by no more than 2°C between night and daytime flights, whereas mass-specific CO2 production rates were higher by 15 per cent during daytime. We conclude that increased flight costs only render diurnal bat flights profitable when the relative energy gain during daytime is high and risk of predation is low. Ancestral bats possibly have evolved dark-skinned wing membranes to reduce nocturnal predation, but a low degree of reflectance of wing membranes made them also prone to overheating and elevated energy costs during daylight flights. In consequence, bats may have become trapped in the darkness of the night once dark-skinned wing membranes had evolved.

Out of the dark: Diurnal activity in the bat Hipposideros ruber on São Tomé island (West Africa)

Geographical areas historically characterized by a lower risk of diurnal avian predation should in theory allow bats to be active in daytime too, especially to forage. Oceanic islands are ideal for studying temporal niche shifts in bats since they often feature depauperate avian assemblages with fewer birds of prey. We report on the second case of diurnal activity known for an insular insectivorous bat, Hipposideros ruber on the island of São Tomé (Gulf of Guinea). We present observations of daylight flights made at several sites on the island in six months (from July to November and in January). We also carried out daytime (09h00–16h00) emergence counts at three roosts. In this time interval, bats were continuously active, although activity rates changed: bats tended to return to roosts in early afternoon and, at two sites, to decrease emergence rate under intense light probably to reduce the risk of hyperthermia. At one roost, we observed that heavy rain caused abrupt daytime returns of large numbers of bats. In daytime bats did forage and kept echolocating. Social interactions (chases) were also frequently observed. In daytime adult males were significantly more frequent than females, while the opposite was noticed at night, an intersexual segregation possibly leading to temporal niche partitioning.

Incidental tourism: British Imperial air travel in the 1930s

Few air travellers along Britain's Empire air routes in the 1930s were intentional holidaymakers. Survey data and passenger profiles culled from other contemporary sources show that most commercial airline passengers flew on work assignment. High fares deterred leisure travel by air, but air passengers flying long-distance on paid business or public service errands incidentally became tourists by virtue of the slow, low altitude, daylight flights that stopped frequently for refuelling: infant aeronautical technology and air travel economics created tourism of sorts along new routes. Sightseeing from the air and on the ground was integral to Empire air journeys. Unpredictability added to the adventure value of flying; the novelty of aerial views added to its scenic value. Airline publicity, documentary films, and passenger accounts and diaries, stressed this in-flight and en-route experience: flying was a new way of seeing and experiencing foreign and historic places and landscapes, and for spotting game. Flying was not just a way of reaching a destination.

Visual Flow Scene Effects on the Somatogravic Illusion in Non-Pilots

The somatogravic illusion (SGI) is easily broken when the pilot looks out the aircraft window during daylight flight, but it has proven difficult to break or even reduce the SGI in non-pilots in simulators using synthetic visual scenes. Could visual-flow scenes that accommodate compensatory head movement reduce the SGI in naive subjects? We investigated the effects of visual cues on the SGI induced by a human centrifuge. The subject was equipped with a head-tracked, head-mounted display (HMD) and was seated in a fixed gondola facing the center of rotation. The angular velocity of the centrifuge increased from near zero until a 0.57-G centripetal acceleration was attained, resulting in a tilt of the gravitoinertial force vector, corresponding to a pitch-up of 30 degrees. The subject indicated perceived horizontal continuously by means of a manual adjustable-plate system. We performed two experiments with within-subjects designs. In Experiment 1, the subjects (N = 13) viewed a darkened HMD and a presentation of simple visual flow beneath a horizon. In Experiment 2, the subjects (N = 12) viewed a darkened HMD, a scene including symbology superimposed on simple visual flow and horizon, and this scene without visual flow (static). In Experiment 1, visual flow reduced the SGI from 12.4 +/- 1.4 degrees (mean +/- SE) to 8.7 +/- 1.5 degrees. In Experiment 2, the SGI was smaller in the visual flow condition (9.3 +/- 1.8 degrees) than with the static scene (13.3 +/- 1.7 degrees) and without HMD presentation (14.5 +/- 2.3 degrees), respectively. It is possible to reduce the SGI in non-pilots by means of a synthetic horizon and simple visual flow conveyed by a head-tracked HMD. This may reflect the power of a more intuitive display for reducing the SGI.

Laser in situ keratomileusis in a combat jet aircraft pilot

Pilots who have had laser in situ keratomileusis (LASIK) surgery are disqualified from flying status in a combat jet aircraft in the United States Navy and Air Force. We report the case of a jet aircraft pilot who had LASIK for myopia. The pilot resumed flights 2 weeks after the procedure and has performed several dozen uneventful daylight flights in a combat jet aircraft. We recommend a clinical study to reevaluate the appropriateness of LASIK in military jet aircraft aviation.

Requirements for Hud Raster Image Modulation in Daylight

Head-up displays (HUDs) represent the leading candidate display technology for inclusion in an enhanced or synthetic vision system (EVS or SVS) for commercial transport aircraft. One common EVS concept assumes the raster display of raw or processed sensor (radar or IR) data. However, experience with the use of raster rather than stroke display modes has been largely limited to the presentation of images captured by IR sensitive and image-intensified cameras during night flying conditions when the luminance of the forward scene over which the image will be superimposed is much lower than in daytime. The objective of this work is to generate a specification for minimum HUD raster image modulation assuming real-world luminance values typically found in low-visibility, daylight flight. Six Honeywell pilots rated the image quality and utility of flight video as presented through a military-style HUD in a transport cockpit mockup. Flight video came from daylight FLIR and daylight CCD cameras. The luminance of the forward scene against which the HUD image was superimposed was varied among nine levels ranging from 5 fL to 10,000 fL. The results indicate that HUD raster luminance must be approximately 50% external scene luminance to promote good pilot awareness of general terrain. To maintain good utility and visibility of standard, high-contrast runway markings, runway center line, and runway edges, HUD raster luminance must be approximately 15% of the forward scene luminance.

Why do Insectivorous Bats in Britain Not Fly in Daylight More Frequently?

Why do Insectivorous Bats in Britain Not Fly in Daylight More Frequently?

Ambient Temperature Measurements from Radiosondes Flown on Constant-Level Balloons

A cause of erroneous temperatures obtained in the earlier phases of a study using standard radiosondes flown on constant-level balloons at White Sands Missile Range is discussed. A simple and inexpensive modification of the radiosondes which produces more accurate ambient temperatures on daylight flights is described.

Daylight Flight to Panama

Daylight Flight to Panama

Daylight Flight to Panama

Daylight Flight to Panama