Stroke Plane Research Articles

Neuromuscular activity and wing movements at the start of flight ofPeriplaneta americana andSchistocerca gregaria

1. The electrical activity of the fast flight muscles is recorded extracellularly using copper wires and conventional methods of amplification and display. Some features of the neuromuscular activity at the start of flight are illustrated and discussed (Fig. 1). 2. A method is described for taking photographs of tethered, flying insects at up to 140 frames per sec, and correlating the wing movements with the electrical activity of the flight muscles. 3. Abnormal “wingbeats”, in which the wings are only partially opened, are often observed before normal flight movement begin. They appear to be caused by incomplete activation of the flight muscles, or by the muscular force being applied to the wing at the wrong phase of its movement (Figs. 2–5). 4. The elevator muscles raise the wing from its closed position to the position which it normally occupies at the top of each wingbeat in steady flight. From this position, the depressor muscles lower the wing in the stroke plane, if they are activated at the appropriate phase relative to the movement of the wing (Fig. 6). 5. Thus wing opening depends upon the action of the muscles which raise and lower the wing in normal flight. It is suggested that the onset of normal flight movements depends upon improved internal co-ordination of the flight system, and not upon sensory feedback. 6. It is concluded that the neuromuscular events and wing movements at the start of flight are a product of the neural mechanism which generate the rhythm of the wingbeats of steady flight.

Flight in Drosophila. II. Variations in stroke parameters and wing contour.

ABSTRACT In tethered flight in a wind tunnel fruit-flies adjust lift and thrust by shifting the horizontal component of the lower extreme wing position. The upper extreme wing position is nearly constant. Stroke angle and stroke plane are fully interdependent parameters. Angle of attack varies along the length of the wing; no length-wise twisting occurs. Angle of attack varies with flying speed ; pitch is unchanged as speed is increased. These characteristics suggest that the flight machinery of fruit-flies is considerably simpler than that of larger flying animals.

The supply of oxygen to the active flight muscles of some large beetles.

ABSTRACT Measurements of the wing-beat frequency, wing-stroke amplitude and stroke plane and of abdominal ventilation have been made during the tethered flight of twenty-six species of beetles belonging to five families, mainly in Uganda. Abdominal ventilation is weak or absent in all species of Cerambycidae, Elateridae and Anthribidae examined in flight. The tracheal system in these families is characterized by the complete absence of air sacs, and in larger species by the presence of four giant trunks running through the metathorax between spiracles 2 and 3 and forming the primary supply to the flight muscles. Abdominal ventilation is strong during the flight of all species over o·6 g. in weight of the Scarabaeidae and Buprestidae which were examined. Their tracheal systems contain an abundance of air sacs while giant trunks are absent. Measurements of the thoracic volume changes which accompany each wing beat show that the amount of air which can be pumped in this way increases in larger Cerambycidae per second per gram as compared with small species. Large Cerambycidae pump more per gram than Scarabaeidae of comparable size. During the flight of the cerambycid Petrognatha the thoracic pump exchanges 540 μ1. air/sec./g. Its action is mainly on the compressible secondary tracheae. In a wind speed of 5 m./sec. 1050 μ1. air/sec./g. are driven through the four giant trunks, entering through spiracle 2 and leaving from spiracle 3. The trunks are stout-walled and probably unaffected by the thoracic pump.

Biology and Physics of locust flight II. Flight performance of the desert locust ( Schistocerca gregaria )

The main purpose is to analyze how a number of wing-stroke parameters are related to the lift (average vertical force) and thrust (average horizontal force) produced by the insect under well defined aerodynamic conditions. The locust was suspended from a complicated balance and flew against a uniform horizontal wind from an open-jet wind tunnel. The wind speed was automatically adjusted to the preferred flying speed (air speed), i.e. the speed at which the thrust equals the extra-to-wing drag . The lift was measured as the apparent reduction in weight; it is given as a percentage of the weight which the individual would have if it had flown for about one hour, was full-grown and well fed but, if a female, with undeveloped eggs ( = basic weight). This figure is the relative lift, and it is used because the actual weight changes much with age, feeding, sexual development, etc., while the dimensions of the flight motor remain constant. The angle between the wind and the long body axis is the body angle and was chosen by the observer or by the insect itself. Most experiments took place at 30° C (constant temperature room), but series were run at the upper and lower limits for flight, including experiments with small flocks of locusts suspended from a roundabout. The rate of evaporation of water from the thorax was kept constant. In a large number of individuals sustained steady-state flight was studied; at regular intervals a set of simultaneous readings were taken consisting of the lift, the speed, the body angle, the stroke frequency, the extreme angular positions of the wings, and of the inclination to the vertical of the stroke planes. In addition, the angular movements of the entire wings relative to the body were estimated from slow-motion films. The results are seen in §§4 to 7. The frequency distribution of the relative lift has its maximum about 100 %, showing that, in this respect, the flight comes near to free flight. It varied from 35 to 175 %, i.e. about five times. During continuous horizontal flight the flying speed was 3•5+ 0•1 m/s and may increase to 4•2 m/s in free flight. At larger lifts (climbing) the steady-state speed could reach 4•5 m/s. During the first minutes the speed was often 4•5 to 5•0 m/s, the maximum observed being 5•5 m/s. No locust lifted its own weight at speeds less than 2•5 m/s. The power necessary to overcome the extra-to-wing drag only corresponds to 1 to 3 % of the total metabolic rate. The effect of altering the body angle is fundamentally different from that of altering the pitch of an aircraft; the lift is controlled and kept constant by the locust and proved to be independent of alterations in the body angle amounting to as much as 20°. This is the basis for the technique and for the treatment of the results. In spite of the large variations in lift, the following stroke parameters varied little or not at all: the stroke angles , the stroke-plane angles , the middle position of the wings , and the time course of the angular movement of the entire wing, y = y(t). The latter function deviates considerably from a simple harmonic oscillation. According to figure II, 20, the average points are determined with an accuracy of better than + 1 %, permitting graphical differentiation. The stroke frequency was rather constant but increased with the reflexly controlled lift, contrary to Chadwick’s experiments on Drosophila , and decreased with increasing size, according to Sotavalta’s findings in other insects. The maximal changes were small, however, amounting to 8 % (lift) and 15 % (size) respectively. The flight performance and the stroke parameters were independent of changes in air temperature (no radiant heat) within 25 to 35° G, although the pterothorax is subjected to similar changes. Sustained flight does not take place below 25° C and above 35° G, but short performances were observed between 22 and 24° C as well as above 37° C. The great variation in lift could not be explained by changes in the measured stroke parameters, and by analogy with a variable-pitch propeller, it must be caused by differences in wing twisting 0(r,t). It was also found that lift and thrust varied in a more intricate way than in a simple actuator disk. The regularity of the stroke and its independence of temperature makes it possible to define a standard stroke , making it easy to compare a given performance with the normal.

Experiments with positive rays

Wing kinematics in forward-flying fruit-flies was measured using high-speed cameras and flows of the flapping wing were calculated numerically. The large lift and thrust coefficients produced by the wing were explained. The wing flaps along a forward-tilting stroke plane. In the starting portion of a half-stroke (an upstroke or downstroke), the wing pitches down to a small pitch angle; during the mid portion (the wing has built up its speed), it first fast pitches up to a large pitch angle and then maintains the pitch angle; in the ending portion, the wing pitches up further. A large aerodynamic force (normal to the wing surface) is produced during the mid portion of a half-stroke. The large force is produced by the fast-pitching-up rotation and delayed-stall mechanisms. As a result of the orientation of wing, the thrust that propels the insect is produced by the upstroke and the major part of the vertical force that supports the weight is produced by the downstroke. In producing the thrust the upstroke leaves a “vortex ring” that is almost vertical, and in producing the vertical force the downstroke leaves a “vortex ring” that is almost horizontal.