N 8 8-1663 0 Comprehensive Rotorcraff Analysis Methods
The paper describes the development and application of comprehensive rotorcraft analysis methods in the field of rotorcraft technology. These large scale analyses and the resulting computer programs are intended to treat the complex a_'.romechanicM phenomena that describe the behavior of rotorcraft. They may be used to predict rotor aerodynamics, acoustics, performance, stability and control, handling qualities, loads and vibrations, structures, dynamics, and aeroelutic stability characteristics for a variety of applications including research, preliminary and detail design, and evaluation and treatment of field problems. The principal comprehensive methods developed or under development in recent year1 and generally available to the rotorcraft community because of US Army Aviation Research and Technology Activity (ARTA) sponsorship of all or part of the software systems are the Rotorcraft Flight Simulation (C81), Dynamic System Coupler (DYSCO), Coupled Rotor/Airframe Vibration Analysis Program (SIMVIB), Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics (CAMRAD), General Rotorcraft Aeromechanical Stability Program {GRASP}, and Second Generation Comprehensive Helicopter Analysis System (2GCHAS). 312 https://ntrs.nasa.gov/search.jsp?R=19880007247 2018-04-23T06:50:56+00:00Z
Coupled Rotor/Airframe Vibration Analysis.
A coupled rotor/airframe vibration analysis developed as a design tool for predicting helicopter vibrations and a research tool to quantify the effects of structural properties, aerodynamic interactions, and vibration reduction devices on vehicle vibration levels is described. The analysis consists of a base program utilizing an impedance matching technique to represent the coupled rotor/airframe dynamics of the system supported by inputs from several external programs supplying sophisticated rotor and airframe aerodynamic and structural dynamic representation. The theoretical background, computer program capabilities and limited correlation results are presented in this report. Correlation results using scale model wind tunnel results show that the analysis can adequately predict trends of vibration variations with airspeed and higher harmonic control effects. Predictions of absolute values of vibration levels were found to be very sensitive to modal characteristics and results were not representative of measured values.
Irish-Potato Farming in Plateau State, Nigeria: A Profitability Analysis
: Notable efforts are on-going to improve Irish potato production in Plateau State, the major producer of the crop in Nigeria. However, little attention has been given to the profitability of the enterprise while the determinants of profitability level are scanty in the literature. Thus, paper analyses the profitability of Irish-potato farming using primary data from 252 Irish potato farmers in Plateau State, Nigeria. Cost structure and profitability level of Irish potato farming were investigated using farm budgeting technique while probit regression model was used to examine the determinants of profitability level of Irish potato farms. Irish potato farming was found to be profitable with most (53.97%) farmers at high profitability level. The net farm income was ₦604, 245.81 per hectare with returns per naira spent of ₦1.70. The cost structure showed that costs of seeds, labour and fertilizer made up the largest share of the total cost of production per hectare. The probability that a farm will be at high profitability level was determined by agrochemicals, sex, farm size and labour at 1% level, respectively. It was concluded that increasing agrochemicals, reducing farm size and labour and being a male farmer will improve profitability level of Irish potato farms. This study recommended that increased use of agrochemicals and more efficient use of labour and farm land be encouraged among potato farmers increase their profitability level.