A comparison of theory and experiment for aeroelastic stability of a hingeless rotor model in hover

Theoretical predictions of aeroelastic stability are compared with experimental, isolated, hingeless-rotor data. The six cases selected represent a torsionally soft rotor having either a stiff or soft pitch-control system in combination with zero precone and droop, 5 degree precone, or -5 degree droop. Analyses from Bell Helicopter Textron, Boeing Vertol, Hughes Helicopters, Sikorsky Aircraft, the National Aeronautics and Space Administration, and the U.S. Army Aeromechanics Laboratory were compared with the experimental data. The correlation ranged from poor to fair

An experimental investigation of the flap-lag-torsion aeroelastic stability of a small-scale hingeless helicopter rotor in hover

A small scale, 1.92 m diam, torsionally soft, hingeless helicopter rotor was investigated in hover to determine isolated rotor stability characteristics. The two-bladed, untwisted rotor was tested on a rigid test stand at tip speeds up to 101 m/sec. The rotor mode of interest is the lightly damped lead-lag mode. The dimensionless lead-lag frequency of the mode is approximately 1.5 at the highest tip speed. The hub was designed to allow variation in precone, blade droop, pitch control stiffness, and blade pitch angle. Measurements of modal frequency and damping were obtained for several combinations of these hub parameters at several values of rotor speed. Steady blade bending moments were also measured. The lead-lag damping measurements were found to agree well with theoretical predictions for low values of blade pitch angle. The test data confirmed the predicted effects of precone, droop, and pitch control stiffness parameters on lead-lag damping. The correlation between theory and experiment was found to be poor for the mid-to-high range of pitch angles where the theory substantially overpredicted the experimental lead-lag damping. The poor correlation in the mid-to-high blade pitch angle range is attributed to low Reynolds number nonlinear aerodynamics effects not included in the theory. The experimental results also revealed an asymmetry in lead-lag damping between positive and negative thrust conditions

Interim Guidelines for Design of Highway Pavements

The adequacy of a pavement design is directly related to the accuracy of traffic data, axle load information and materials data. It is assumed that appropriate construction procedures will be employed and that the pavements will be maintained periodically during the course of their service lives. It is assumed that the subgrade will be constructed at or near the optimum moisture content and to the maximum dry density as specified in appropriate standard specifications. It is also assumed that the base course materials meet design requirements, that the aggregates will meet soundness and durability requirements and that the aggregate base will be compacted to specified densities. Pavement layers should meet mixture design requirements and be compacted to specified densities. The construction process should be structured to provide as homogenous a pavement layer as practical within the limits of existing construction practices. In the event it is not possible to construct pavements to meet design assumptions, pavement designs should be modified to reflect actual construction conditions. Most pavement thickness design procedures (including. the Kentucky procedures) are founded on the assumptions that quality materials will be used to construct the pavement, that appropriate construction conditions exist, and that appropriate construction procedures will be used. It is possible to develop pavement thickness designs for less than ideal conditions or for marginal materials. Examples of pavement designs involving marginal materials include those pavement designs wherein by-product (waste) materials have been used in one or more layers of the pavement structure. The level of pavement performance associated with a given thickness design also presumes some level of routine pavement maintenance. Designs may be modified to reflect other levels of maintenance such as the zero maintenance concept. This interim design guide addresses only pavement designs presuming adequate subgrade construction conditions, appropriate construction techniques for aggregate and pavement layers, accurate information concerning the strengths and quality of materials used in the pavement, and accurate information concerning the magnitude and quantity of loads for which the pavement is designed to accommodate. Alternate design strategies should be used in the event these assumptions are violated

Rutting and Longitudinal Cracking and Temperature Cracking: A Case Study (US 23, Greenup County, MP 6.0 to 28.8)

US 23, Greenup County, Ashland-South Shore, developed rutting and transverse and longitudinal cracking. The pavement was about 14 years old and had served heavy trucks. Road Rater tests, crack surveys, and various inspections had been made prior to the fall of 1985. Inspection and a report by KTRP led to further evaluation, examination internally by trenching, and additional tests and surveys. This report combines pertinent facts and records. It includes recommendations for overlayment

Native Aggregates for Skid Resistance

The objectives of the study were 1) to identify sources of native aggregates with varying histories of skid resistance performance; 2) to evaluate and correlate native aggregate characteristics, processing techniques, and other factors with skid resistance and surface mixture performance; and 3) to provide guidelines for implementation of research findings. Limestone, sandstone, river gravel, and control aggregates (granite, traprock, and slags) were subjected to a battery of tests to determine physical relationships between aggregate type and skid resistance. Laboratory results were analyzed for correlations among themselves and for correlations with skid number data obtained from pavements containing aggregates involved in the study. No significant correlation could be found between any of the laboratory results and field skid numbers. This was particularly disturbing with reference to the KTRP test. It was thought that it could be used to adequately predict field skid performance. However, preliminary findings have shown no such relationship. It is recommended that the KTRP test be amended to provide a more defined weight loss over time to attempt to explain the behavior of an aggregate\u27s skid resistance over time

Evaluation of Asphalt Additive -- Chemkrete

Construction, performance, and cost-effectiveness evaluations of an AC-10 treated with Chemkrete (CTI-101) and an untreated AC-20 are presented. Laboratory tests, and field tests which include marshall stability, density test, repeated load test, road-ratter deflection data, and visual observation are summarized. Because of the apparent failure of Chemkrete to significantly enhance the performance of the pavement, and the additional cost for the use of Chemkrete, it would not be recommended for further use in the state of Kentucky

Rutting, a Case Study (US 23, 1.5 miles north of Louisa)

This case study of rutting in an asphaltic concrete pavement makes recourse to trenching full width and full depth to expose and observe the entire cross section of the structure. Rutting occurred in the vicinity of Station 59+00 on US 23, 1.5 miles north of Louisa, during August and September 1983 when traffic was diverted onto newly constructed northbound lanes (without final surface and shouldering) while excavation into the hillside was completed for the southbound lanes. Earth movers crossed the northbound lanes going to and from a waste area. Coal trucks (Figures 1 and 2) slowed, stopped, and crept where rutting was greatest. Some rutting had occurred throughout

Laboratory Evaluations of Stabilized Flue Gas Desulfurization Sludge (Scrubber Sludge) and Aggregate Mixtures

The Kentucky Transportation Research Program has completed a laboratory study involving the use of flue gas desulfurization sludge (scrubber sludge) for potential application as a highway subbase and/or embankment material. Scrubber sludge is a waste produet formed when fly ash (and other residue) is combined with a lime dust slurry filter cake and stabilized with quicklime (calcium oxide). Samples of stockpiled (field) sludge and dry sludge components were obtained from the Robert Reid Station (Big Rivers Electric Corporation) in Sebree, Kentuclty. Dry sludge components (fly ash, filter cake, and quicklime) were uaed to prepare sludge samples in the laboratory, allowing a higher degree of quality control for compariaon purposes. Mixtures for testing included scrubber sludge, scrubber sludge with pond ash (bottom ash), and scrubber sludge with dense graded limestone aggregate (DGA). One objective of laboratory analyses was the determination of optimum mixture proportions. A mixture of 20-percent scrubber sludge and 80-percent pond ash was determined to be the optimum design mix. That mixture showed significant strength gain with curing and had a static-chord modulus of elasticity approximately 118 times the compressive strength. Strength and modulus tests indicated that mixtures of scrubber sludge and pond ash were superior to mixtures of scrubber sludge and DGA. The scope of the study, however, did not permit complete explanation of these observations. An economic study showed that scrubber sludge with pond ash can be used economically as a highway subbase material, especially on low-fatigue roads, by partially replacing more expensive pavement layers. Triaxial tests and computer simulations indicated that scrubber sludge could be used as an embankment material in some applications. However, this would be economical only if suitable fill material was not available at or near the fill site