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Laitone, E. V.

Publications and source records attributed to Laitone, E. V..

5 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Effect of a nonconstant C/m-alpha/ on the stability of rolling aircraft

An analytical study is carried out of the behavior of modern high-speed aircraft of inertially slender configurations in maneuvers involving large rates of roll. Inertia cross-coupling, as well as a linear variation of longitudinal static stability (C/m-alpha/) with angle of attack, are considered. The steady-state solutions of the nonlinear equations of motion, based on principal inertia axes, are studied to obtain useful information on the response behavior of the state variables during roll maneuvers. It is shown that, in addition to the critical values of aileron deflection that have been previously found to limit a steady-state roll with constant longitudinal static stability, there can be two new critical values introduced by a linear decrease of the absolute value of longitudinal static stability with angle of attack. For aileron deflections near these critical values, the response of the aircraft exhibits violent oscillations and dangerous peak loads, due to the cross-coupled motion accompanying a roll maneuver. These critical values define a new range of aileron deflections in which no steady-state roll is possible.

Davari, B.↗
NASA NTRS1974

Effect of thrust on the longitudinal oscillations of missiles

Exact linearized solutions are provided for the longitudinal oscillations of missiles when the trajectory is nearly horizontal and the thrust is either zero, a specified constant value, or increasing with the square of the increasing flight speed. The results indicate that in all cases any increase in the thrust, or any acceleration along the nearly horizontal trajectory, will directly increase the damping of the angle-of-attack oscillations, whose increase in frequency is at first negligible, and then grows very slightly with time.

Laitone, E. V.↗
NASA NTRS1972

Stability criteria for accelerating and decelerating aircraft.

Derivation of the linearized differential equation for the longitudinal oscillations of an aircraft for the general case when the atmospheric density, thrust force, and velocity are varying. Exact solutions and stability criteria are presented for several different conditions. For the zero thrust coasting aircraft that is being decelerated by its drag force, new stability criteria are derived for both ascending and descending flight. A critical altitude is found for ascending aircraft that are attempting to coast out of the atmosphere. Above this critical altitude the oscillations cease, and there is a monotonic increase in the angle of attack. Exact solutions for the oscillations of coasting aircraft are presented in terms of the confluent hypergeometric functions. It is shown that previous attempts to predict a critical altitude for ascending vehicles were in error because they did not include the second type, or logarithmic solution, of the confluent hypergeometric function.

Laitone, E. V.↗
NASA NTRS1972

Longitudinal dynamic stability of a shuttle vehicle.

Analytical study of the longitudinal dynamic stability of a nonrolling, lifting vehicle gliding at hypersonic speeds. The analysis applies to shuttle vehicles designed for operating up to the rim of a planetary atmosphere. A general nondimensional time transformation is introduced to derive a unified second-order linear differential equation for the angle of attack, valid for all types of reentry of a general type of vehicle. The stability of motion is discussed for two fundamental regimes of flight that are based on widely different assumptions. For near ballistic entry along a straight line trajectory, the equation reduces to a confluent hypergeometric equation, the solution of which can be expressed in terms of Whittaker's function. Using a theorem in the theory of stability of differential equations, criteria for damped oscillations are derived. It is shown that the aerodynamic criteria for stability are the same as for the case of ballistic entry. In addition, for each vehicle configuration, and specified planetary atmosphere, there exists an altitude range where the angle of attack frequency is nearly equal to the orbital frequency causing instability in pitch. This resonance instability is due to the ellipticity of the orbit. Criteria for eccentricity instability are derived.

Vinh, N. X.↗