FLIGHT OF THE HONEY-BEE .6. ENERGETICS OF WIND-TUNNEL EXHAUSTION FLIGHTS AT DEFINED FUEL CONTENT, SPEED ADAPTATION AND AERODYNAMICS

To gain information on extended flight energetics, quasi-natural fligh t conditions imitating steady horizontal flight were set by combining the tethered-flight wind-tunnel method with the exhaustion-flight meth od. The bees were suspended from a two-component aerodynamic balance a t different, near optimum body angle of attack alpha and were allowed to choose their own speed; their body mass and body weight was determi ned before and after a flight; their speed, lift, wingbeat frequency a nd total flight time were measured throughout a flight. These values w ere used to determine thrust, resultant aerodynamic force (magnitude a nd tilting angle), Reynolds number, total flight distance and total fl ight impulse. Flights in which lift was greater than or equal to body weight were mostly obtained. Bees, flown to complete exhaustion, were refed with 5, 10, 15 or 20 mu l of a 1.28-mol . l(-1) glucose solution (energy content w = 18.5, 37.0, 55.5 or 74.0 J) and again flown to co mplete exhaustion at an ambient temperature of 25 +/- 1.5 degrees C by a flight of known duration such that the calculation of absolute and relative metabolic power was possible. Mean body mass after exhaustion was 76.49 +/- 3.52 mg. During long term flights of 7.47-31.30 min sim ilar changes in flight velocity, lift, thrust, aerodynamic force, wing beat frequency and tilting angle took place, independent of the volume of feeding solution. After increasing rapidly within 15 s a more or l ess steady phase of 60-80% of total flight time, showing only a slight decrease, was followed by a steeper, more irregular decrease, finally reaching 0 within 20-30 s. In steady phases lift was nearly equal to resultant aerodynamic force; tilting angle was 79.8 +/- 4.0 degrees, t hrust to lift ratio did not vary, thrust was 18.0 +/- 7.4% of lift, li ft was somewhat higher/equal/lower than body mass in 61.3%, 16.1%, 22. 6% of all totally analysable flights (n = 31). The following parameter s were varied as functions of volume of feeding solution (5-20 mu l in steps of 5 mu l) and energy content. (18.5-74.0 J in steps of 18.5 J) : total flight time, velocity, total flight distance, mean lift, thrus t, mean resultant aerodynamic force, tilting angle, total flight impul se, wingbeat frequency, metabolic power and metabolic power related to body mass, the latter related to ''empty'', ''full'' and ''mean''( = 100 mg) body mass. The following positive correlations were found: L = 1.069 . 10(-9) f(2.538); R = 1.629 . 10(-9) f(2.464); P-m = 7.079 . 1 0(-8) f(2.456); P-m = 0.008 nu + 0.008; P-m = 18.996L + 0.022; P-m = 1 9.782R + 0.021; P-m = 82.143T + 0.028; P-m = 1.245 . bm(f)(1.424); P-m rele = 6.471 . bm(f)(1.040); beta = 83.248 + 0.385 alpha. The followin g negative correlations were found: V = 3.939 - 0.032 alpha; T = 1.324 .10(-4) - 0.038 . 10(-4)alpha. Statistically significant correlations were not found in T (f), L(alpha), R(alpha), f(alpha), P-m(bm(e)), P-m rele(bm(e)), P-mrelf(bm(e)), P-mrelf(bm(f)).