Pitching moment

About: Pitching moment is a research topic. Over the lifetime, 3213 publications have been published within this topic receiving 38721 citations.

The Generation of Forces and Moments during Visual-Evoked Steering Maneuvers in Flying Drosophila

Abstract: Sideslip force, longitudinal force, rolling moment, and pitching moment generated by tethered fruit flies, Drosophila melanogaster, were measured during optomotor reactions within an electronic flight simulator. Forces and torques were acquired by optically measuring the angular deflections of the beam to which the flies were tethered using a laser and a photodiode. Our results indicate that fruit flies actively generate both sideslip and roll in response to a lateral focus of expansion (FOE). The polarity of this behavior was such that the animal's aerodynamic response would carry it away from the expanding pattern, suggesting that it constitutes an avoidance reflex or centering response. Sideslip forces and rolling moments were sinusoidal functions of FOE position, whereas longitudinal force was proportional to the absolute value of the sine of FOE position. Pitching moments remained nearly constant irrespective of stimulus position or strength, with a direction indicating a tonic nose-down pitch under tethered conditions. These experiments expand our understanding of the degrees of freedom that a fruit fly can actually control in flight.

Six component wind tunnel balance

Abstract: A six component balance for use in measuring forces and moments on an aircraft model in a wind tunnel or the like. The balance is mounted on a wind tunnel sting by means of a sleeve that surrounds and is spaced from a central core. The central core is connected to a model by support bars passing through slots in the sleeve from the core. Core ends are secured to the sleeve and support the central core through a plurality of webs. A plurality of strain gages are mounted on the webs to detect strain on the webs resulting from forces and moments applied to the model. This system measures six components, i.e., lift force, drag force, side force, pitching moment, yawing moment and rolling moment.

Active Control of Leading-Edge Dynamic Stall

Abstract: The control of dynamic stall by periodic forcing was studied on a NACA 0012 airfoil under incompressible conditions by means of two-dimensional zero mass-flux blowing slots, oriented at 45° and 90° to the chord-line respectively. Time-resolved surface pressure and wake survey measurements were phase-averaged and integrated to yield the aerodynamic loads. Dynamic stall was controlled by "trapping" the bubble upstream of the forcing slot and the momentum imparted by the zero mass-flux device that was required to affect control was proportional to the square of post-stall angle of attack. Deep dynamic stall, where the static stall angle is exceeded by a large margin, was effectively eliminated but relatively large momentum coefficients, greater than 0.04, were required to achieve this. For various reduced frequencies and momentum coefficients, the 45° slot exhibited greater control authority over moment coefficient excursions than the 90° slot. A comparison of NACA 0012 and 0015 airfoils showed that for the ...

On the effect of sweep on separation control

Abstract: The performance of a flapped wing based on a NACA 0012 airfoil section and equipped with a linear array of fluidic oscillators was investigated experimentally to assess the significance of wing sweep and aspect ratio on the efficiency of the actuation. The semi-span wing that was suspended from the wind tunnel ceiling through a six-component balance could be withdrawn partially from the test section and rotated in a plane parallel to the flow thus its sweep could vary from 0° to ±45° and its aspect ratio could change from 2.4 to 7.5. The wing incidence, its flap deflection, and the level and distribution of the actuation were the additional independent parameters investigated. The experiments were carried out at Reynolds numbers varying between 300,000 and 500,000. The boundary layer was tripped in order to fix the location at which transition to turbulence occurs. To overcome separation at high flap deflections in the absence of wing sweep, a minimum momentum coefficient of the order of 1% was required. However, on a swept-back wing a substantially lower input level could improve the lift generated by the wing by some 20% and alter the pitching moment provided the aggregate number of the actuators was small. Under these conditions, the actuators acted as fluidic boundary layer fences that can be switched ON or OFF on demand and change the aerodynamic characteristics of the wing for takeoff and landing purposes. An attempt was made to explain the mechanism that makes the fluidic oscillators so effective.