Cold-Weather Flight Tests of an OH-58 Helicopter Equipped with an Elastomeric-Bearing Main Rotor

1973 ◽  
Author(s):  
C. H. Fagan
Keyword(s):  
Cold Weather ◽  
Main Rotor ◽  
Flight Tests ◽  
Elastomeric Bearing

scholarly journals Variable-speed tail rotors for helicopters with variable-speed main rotors

2017 ◽  
Vol 121 (1238) ◽  
pp. 433-448 ◽  
Author(s):  
D. Han ◽  
G. N. Barakos
Keyword(s):  
Present Method ◽  
High Speed ◽  
Flight Test ◽  
Power Reduction ◽  
Main Rotor ◽  
Variable Speed ◽  
Rotor Speed ◽  
Flight Tests ◽  
Yaw Control ◽  
Good Agreement

ABSTRACTVariable tail rotor speed is investigated as a method for reducing tail rotor power, and improving helicopter performance. A helicopter model able to predict the main rotor and tail rotor powers is presented, and the flight test data of the UH-60A helicopter is used for validation. The predictions of the main and tail rotor powers are generally in good agreement with flight tests, which justifies the use of the present method in analysing main and tail rotors. Reducing the main rotor speed can result in lower main rotor power at certain flight conditions. However, it increases the main rotor torque and the corresponding required tail rotor thrust to trim, which then decreases the yaw control margin of the tail rotor. In hover, the tail rotor may not be able to provide enough thrust to counter the main rotor torque, if it is slowed to follow the main rotor speed. The main rotor speed corresponding to the minimum main rotor power increases, if the change of tail rotor power in hover is considered. As a helicopter translates to cruise, the induced power decreases, and the profile power increases, with the profile power dominating the tail rotor. Reducing the tail rotor speed in cruise reduces the profile power to give a 37% reduction in total tail rotor power and a 1.4% reduction to total helicopter power. In high-speed flight, varying the tail rotor speed is ineffective for power reduction. The power reduction obtained by the variable tail rotor speed is reduced for increased helicopter weight.

An unmanned helicopter control with partial small body force compensation: Experimental results

Robotica ◽  
2018 ◽  
Vol 36 (10) ◽  
pp. 1436-1453 ◽  
Author(s):  
Bryan Godbolt ◽  
Alan F. Lynch
Keyword(s):  
Body Force ◽  
Small Body ◽  
Tracking Error ◽  
Unmanned Helicopter ◽  
Stabilization Problem ◽  
Main Rotor ◽  
Flight Tests ◽  
Helicopter Control ◽  
Error Dynamics ◽  
Force Compensation

SUMMARYA generally accepted helicopter model used for control includes the effect of Small Body Forces (SBF) which couple the vehicle's rotational subsystem inputs to its translational dynamics. SBF result from tail rotor thrust and lateral forces due to main rotor flapping. It is well-known that SBF lead to a theoretically challenging stabilization problem for the tracking error dynamics. Hence, much of the existing work has neglected SBF in order to simplify control design. We design a controller that directly compensates the influence of the tail rotor component of the SBF. The design is validated in simulation and flight tests.

Validation of a rotorcraft mathematical model in autorotation by use of gyroplane flight tests

2004 ◽  
Vol 108 (1079) ◽  
pp. 51-58 ◽  
Author(s):  
V. M. Spathopoulos
Keyword(s):  
Mathematical Model ◽  
Steady State ◽  
Research Work ◽  
Main Rotor ◽  
Rotor Speed ◽  
Flight Tests ◽  
Handling Qualities ◽  
Alternative Approach ◽  
Mode Of Operation ◽  
Engine Failure

Aircraft handling qualities in autorotation are critical in determining the level of safety of rotorcraft. For helicopters suffering from an engine failure, transcending from powered to autorotative flight occurs rapidly and requires immediate and accurate pilot reaction. Although it is important for the handling qualities in this flight state to be predicted correctly, obvious difficulties will exist in using flight tests as a means of validation when autorotation constitutes an abnormal mode of operation. In the research work presented in this paper an alternative approach is applied, of configuring a generic rotorcraft model as a gyroplane, a type of vehicle for which its main rotor is constantly in autorotation. Flight tests are used for the validation purposes both for steady state and dynamic response cases. Results are produced to complement those already existing for a dissimilar gyroplane type thus increasing the level of confidence obtained. It is concluded that important handling qualities indicators such as the steady state trends are correctly predicted although limitations are imposed due to rotor speed discrepancy.

Cold Weather Integrity Dig on a Scenic River, Northern Michigan

2015 ◽  
Author(s):  
Jay B. Bergman ◽  
Robert J. Schoneberger ◽  
Matthew A. Fournier
Keyword(s):  
Cold Weather ◽  
Northern Michigan

99. Characterization of Cold Weather Plumes from Jet Engine Start-UPS

2000 ◽  
Author(s):  
A. Armendariz ◽  
D. Leith ◽  
M. Boundy ◽  
R. Goodman ◽  
L. Smith
Keyword(s):  
Cold Weather ◽  
Jet Engine ◽  
Start Ups ◽  
Engine Start

Vulnerability of sweet cherry cultivars to continuous periods of spring frosts in Plovdiv, Bulgaria

2020 ◽  
Vol 12 (4) ◽  
pp. 348-352
Author(s):  
S. Malchev ◽  
S. Savchovska
Keyword(s):  
Sweet Cherry ◽  
Weather Conditions ◽  
Frost Damage ◽  
Cold Weather ◽  
Bud Burst ◽  
Intermediate Group ◽  
Air Temperatures ◽  
Wide Range ◽  
Group Form ◽  
Sweet Cherry Cultivars

Abstract. The periods with continuous freezing air temperatures reported during the spring of 2020 (13 incidents) affected a wide range of local and introduced sweet cherry cultivars in the region of Plovdiv. They vary from -0.6°C on March 02 to -4.9°C on March 16-17. The duration of influence of the lowest temperatures is 6 and 12 hours between March 16 and 17. The inspection of fruit buds and flowers was conducted twice (on March 26 and April 08) at different phenological stages after continuous waves of cold weather conditions alternated with high temperatures. During the phenological phase ‘bud burst’ (tight cluster or BBCH 55) some of the flowers in the buds did not develop further making the damage hardly detectable. The most damaged are hybrid El.28-21 (95.00%), ‘Van’ (91.89%) and ‘Bing’ (89.41%) and from the next group ‘Lapins’ (85.98%) and ‘Rosita’ (83.33%). A larger intermediate group form ‘Kossara’ (81.67%), ‘Rozalina’ (76.00%), ‘Sunburst’ (75.00%), ‘Bigarreau Burlat’ (69.11%) and ‘Kuklenska belitza’ (66.67%). Candidate-cultivar El.17-90 ‘Asparuh’ has the lowest frost damage values of 55.00% and El.17-37 ‘Tzvetina’ with damage of 50.60%.

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