Contribution to the aerodynamics of rotating-wing aircraft

The chief defect of the investigations up to now was the assumption of a more or less arbitrary "mean" drag coefficient for a section of the blade. This defect is remedied through replacement of the constant coefficient by a function of higher order which corresponds to the polar curve of the employed profile. In that way it is possible to extend the theory to include the entire range from "autogyro" without power input to the driven "helicopter" with forward-tilted rotor axis. The treatment includes the twisted rectangular blade and a non-twisted tapered blade. Proceeding from the air flow and stresses on a section of the blade, the formulas for torque, axial and normal thrust of a linearly twisted rectangular blade, and a non-twisted tapered blade, are derived

Characteristics of hingeless rotors with hub moment feedback controls including experimental rotor frequency response, Volume 1

Wind tunnel tests to determine the dynamic characteristics of hingeless rotors with hub moment feedback controls and to acquire experimental hingeless rotor transfer functions are discussed. Rotor transfer functions were calculated from data acquired during open loop frequency response tests. The transfer functions are linear and present the rotor longitudinal and lateral frequency responses to collective pitch, longitudinal cyclic pitch, and lateral cyclic pitch. The theoretical analysis was based on the rigid blade flapping model coupled with appropriate control system and cyclic pitch actuator equations of motion

Research program to determine rotor response characteristics at high advance ratios Final report

Stability and response characteristics of directly controlled rigid rotors at high advance ratios and correlation of mathematical model with wind tunnel test dat

Hingeless rotor theory and experiment on vibration reduction by periodic variation of conventional controls

The reduction of the n per rev. pitch-, roll- and vertical vibrations of an n-bladed rotor by n per rev. sinusoidal variations of the collective and cyclic controls is investigated. The numerical results presented refer to a four-bladed, 7.5-foot model and are based on frequency response tests conducted under an Army-sponsored research program. The following subjects are treated: extraction of the rotor transfer functions (.073R hub flapping and model thrust versus servo valve command, amplitude and phase), calculation of servo commands (volts) required to compensate .073R hub flapping (3P and 5P) and model thrust (4P), evaluation of the effect of the vibratory control inputs on blade loads, and theoretical prediction of the root flapbending moments generated by 0 to 5P perturbations of the feathering angle and rotor angle of attack. Five operating conditions are investigated covering advance ratios from approximately 0.2 to 0.85. The feasibility of vibration reduction by periodic variation on conventional controls is evaluated

Contribution to the aerodynamics of rotating-wing aircraft. Part II

The interrelations established in an earlier report (NACA-TM-921) are used to study the best assumptions for hovering and horizontal flight. The effect of the twisted and tapered blade on the rotor efficiency is analyzed and the gliding coefficient at different stages (from autogyro to helicopter) of horizontal flight compared. To the extent that model or full-scale test data are available, they are included in the comparison

Therapeutic anticoagulation for splanchnic vein thrombosis in acute pancreatitis:A national survey and case-vignette study

BACKGROUND: Splanchnic vein thrombosis (SVT) is a major complication of moderate and severe acute pancreatitis. There is no consensus on whether therapeutic anticoagulation should be started in patients with acute pancreatitis and SVT. AIM: To gain insight into current opinions and clinical decision making of pancreatologists regarding SVT in acute pancreatitis. METHODS: A total of 139 pancreatologists of the Dutch Pancreatitis Study Group and Dutch Pancreatic Cancer Group were approached to complete an online survey and case vignette survey. The threshold to assume group agreement was set at 75%. RESULTS: The response rate was 67% (n = 93). Seventy-one pancreatologists (77%) regularly prescribed therapeutic anticoagulation in case of SVT, and 12 pancreatologists (13%) for narrowing of splanchnic vein lumen. The most common reason to treat SVT was to avoid complications (87%). Acute thrombosis was the most important factor to prescribe therapeutic anticoagulation (90%). Portal vein thrombosis was chosen as the most preferred location to initiate therapeutic anticoagulation (76%) and splenic vein thrombosis as the least preferred location (86%). The preferred initial agent was low molecular weight heparin (LMWH; 87%). In the case vignettes, therapeutic anticoagulation was prescribed for acute portal vein thrombosis, with or without suspected infected necrosis (82% and 90%), and thrombus progression (88%). Agreement was lacking regarding the selection and duration of long-term anticoagulation, the indication for thrombophilia testing and upper endoscopy, and about whether risk of bleeding is a major barrier for therapeutic anticoagulation. CONCLUSION: In this national survey, the pancreatologists seemed to agree on the use of therapeutic anticoagulation, using LMWH in the acute phase, for acute portal thrombosis and in the case of thrombus progression, irrespective of the presence of infected necrosis.</p

Structured alcohol cessation support program versus current practice in acute alcoholic pancreatitis (PANDA):Study protocol for a multicentre cluster randomised controlled trial

Background/objectives: The most important risk factor for recurrent pancreatitis after an episode of acute alcoholic pancreatitis is continuation of alcohol use. Current guidelines do not recommend any specific treatment strategy regarding alcohol cessation. The PANDA trial investigates whether implementation of a structured alcohol cessation support program prevents pancreatitis recurrence after a first episode of acute alcoholic pancreatitis. Methods: PANDA is a nationwide cluster randomised superiority trial. Participating hospitals are randomised for the investigational management, consisting of a structured alcohol cessation support program, or current practice. Patients with a first episode of acute pancreatitis caused by harmful drinking (AUDIT score &gt;7 and &lt; 16 for men and &gt;6 and &lt; 14 for women) will be included. The primary endpoint is recurrence of acute pancreatitis. Secondary endpoints include cessation or reduction of alcohol use, other alcohol-related diseases, mortality, quality of life, quality-adjusted life years (QALYs) and costs. The follow-up period comprises one year after inclusion. Discussion: This is the first multicentre trial with a cluster randomised trial design to investigate whether a structured alcohol cessation support program reduces recurrent acute pancreatitis in patients after a first episode of acute alcoholic pancreatitis, as compared with current practice. Trial registration: Netherlands Trial Registry (NL8852). Prospectively registered.</p

Splanchnic vein thrombosis in necrotizing pancreatitis:a post-hoc analysis of a nationwide prospective cohort

Background: Treatment guidelines for splanchnic vein thrombosis in necrotizing pancreatitis are lacking due to insufficient data on the full clinical spectrum. Methods: We performed a post-hoc analysis of a nationwide prospective necrotizing pancreatitis cohort. Multivariable analyses were used to identify risk factors and compare the clinical course of patients with and without SVT. Results: SVT was detected in 97 of the 432 included patients (22%) (median onset: 4 days). Risk factors were left, central, or subtotal necrosis (OR 28.52; 95% CI 20.11–40.45), right or diffuse necrosis (OR 5.76; 95% CI 3.89–8.51), and younger age (OR 0.94; 95% CI 0.90–0.97). Patients with SVT had higher rates of bleeding (n = 10,11%) and bowel ischemia (n = 4,4%) compared to patients without SVT (n = 14,4% and n = 2,0.6%; OR 3.24; 95% CI 1.27–8.23 and OR 7.29; 95% CI 1.31–40.4, respectively), and were independently associated with ICU admission (adjusted OR 2.53; 95% CI 1.37–4.68). Spontaneous recanalization occurred in 62% of patients (n = 40/71). Radiological and clinical outcomes did not differ between patients treated with and without anticoagulants. Discussion: SVT is a common and early complication of necrotizing pancreatitis, associated with parenchymal necrosis and younger age. SVT is associated with increased complications and a worse clinical course, whereas anticoagulant use does not appear to affect outcomes.</p