Aeronautics and astronautics – Aircraft sustentation – Sustaining airfoils
Patent
1985-01-29
1987-02-17
Blix, Trygve M.
Aeronautics and astronautics
Aircraft sustentation
Sustaining airfoils
244130, 244200, B64C 2304
Patent
active
046433767
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to correcting undesirable flight characteristics of an aircraft. More particularly, this invention relates to an aerodynamic device used to remedy a nonlinear, unstable high Mach number stall characteristic of a swept-wing jet transport commonly called "pitch up".
As known to those skilled in the art, air flowing over the upper surface of an airplane wing separates from the wing surface when the wing reaches a given angle of attack at sufficiently high airspeed, resulting in a loss of lift or a condition known as stall. Moreover, with a swept-wing airplane operating at high Mach numbers, e.g., above approximately 0.6, as the angle of attack of the wing is increased, air flowing over the upper surface of the outboard wing separates from the wing before air flowing over the upper surface of the inboard separates; thus, the outboard section of the wing effectively stalls at a lower angle of attack than the inboard section.
Two factors contribute to the earlier separation of airflow over the outboard wing. The first factor is spanwise airflow over the wing due to the sweep of the wing. The spanwise airflow augments the adverse pressure gradient experienced by air flowing over the outboard wing's upper surface, thereby contributing to earlier separation of airflow from the outboard wing's upper surface. A second factor causing earlier separation of airflow over the outboard wing is shock-induced separation. As air flowing over the outboard wing's upper surface reaches supersonic velocity, a shock is formed, and it is formed at lower airspeeds than on the inboard wing. The shock takes energy out of the airflow behind it, causing the airflow to tend to seperate from the wing's surface. Thus, as the angle of attack of a swept wing is increased when the airplane is operating at high Mach numbers, the outboard wing loses lift before the inboard wing.
On present-day swept-wing jet transports, the pitch axis of the airplane extends laterally through the center of gravity of the airplane and is generally located at approximately 25% of the mean aerodynamic chord of the wing. The centers of lift of the inboard and outboard wings are generally located rearward of the pitch axis; thus, the lifting forces generated by the inboard and outboard wings create a pitching moment that tends to force the nose of the airplane downwardly. In a stable flight condition, the pitching moment created by the lift of the wings is counteracted by a downward force exerted by the airplane's horizontal stabilizer. When the angle of attack of the wing is increased to the point where separation occurs on the outboard wing causing a decrease in the lift component, a resultant tendency toward pitch up occurs since the lift component of the inboard wing is still linearly increasing with increasing angle of attack and the downward force of the horizontal stabilizer increases proportionally with increasing inboard wing lift. The unstable character of this phenomenon is undesirable and is further aggrevated by unpredictable factors such as local atmospheric conditions including local ambient wind patterns, e.g., gust upsets. Because of the abruptness of the effect at certain Mach numbers and the element of unpredictability, combined with the associated increase in load factor and the increase in buffet load at high Mach numbers and high angles of attack, various aerodynamic solutions to the problem have been proposed that are not dependent upon pilot response.
Two basic approaches have been used attempting to solve the high speed pitch up problem. In one approach, devices have been employed to enhance the outboard wing lifting capability. These include fences on the outboard wing or midwing, wing twist, profile camber changes, leading edge contour changes, wing planform changes (saw-tooth, gloves, etc.) and vortex generators located at the midspan of a wing. However, none of these have completely eliminated the pitch up problem. Most have increased the coefficient of outboard wing lift as a function
REFERENCES:
patent: 2739770 (1956-03-01), Fanti et al.
patent: 2800291 (1957-07-01), Stephens
patent: 2885161 (1959-05-01), Kerker et al.
patent: 2967030 (1961-01-01), Whitcomb
patent: 2990142 (1961-06-01), Ferri
patent: 2997256 (1961-08-01), Walker
patent: 3199813 (1965-08-01), Roper
patent: 3270990 (1966-09-01), Webb
patent: 3288399 (1966-11-01), Gaster
patent: 3327965 (1967-06-01), Bockrath
patent: 3370810 (1968-02-01), Shevell et al.
patent: 3471107 (1969-10-01), Ornberg
patent: 3744745 (1973-07-01), Kerker et al.
patent: 3806067 (1974-04-01), Kutney
patent: 3960345 (1976-06-01), Lippert, Jr.
patent: 4243188 (1981-01-01), DeBlois
patent: 4272043 (1981-06-01), Spillman
patent: 4311681 (1982-01-01), Finch
patent: 4314681 (1982-02-01), Kutney
patent: 4334658 (1982-06-01), Mackenzie
patent: 4354648 (1982-10-01), Schenk et al.
Blix Trygve M.
Corl Rodney
Donahue B. A.
Hamley James P.
The Boeing Company
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