Stability assessment of trees is considered important in urban areas to detect possible occurrence of tree failures that often result in disastrous damages. Tree-pulling test is a low-cost, well-known method that has been practiced by researchers and practitioners alike from several decades ago. From the method, a number of parameters related to the physical characteristics of the tree can be further derived. However, the tree-pulling test has only been widely practiced mostly for tree species in subtropical region, such as pines, spruces, and birches. In this paper, a tree-pulling test on sengon (Paraserianthes falcataria), a tree native to Indonesia is reported. Such a study is imperative as sengon is among the most commonly planted tree species in the urban areas of Indonesia and there have been alarming reports of falling sengon trees. Two kinds of tree-pulling test are conducted. i.e. destructive and non-destructive. From these experiments, the critical force that results in a breakage as well as the fl exibility of sengonare obtained. Numerical simulations are also carried out. The results arecompared and they show a good fi t to the experimental data, justifying the assumed linearly elastic behavior.

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Drones nowadays have become an important part of people’s lives. Drones for transporting people or goods are considered to develop into reality. To be effective and efficient, the drone should be light but have big propulsion for big lift and thrust forces. This paper presents a way to improve the performances by designing usage of only 2 propulsion motors with ducted and special fan blades. The special designed fan blades theoretically will produce more thrust with smaller propeller size and lower RPM since combine the lift blade and momentum thrust effects. The required propulsion force to fly the drone with its payload is analyzed and detemined. Then the torque, rpm, airfoil type, Thrust Coefficient, and blade twist angles can be determined based on that propulsion force. Afterward, an evaluation is performed with fluid dynamics simulation tools to predict the forces acting on the propeller.

Spontaneous combustion of coal has been well-known as a problem faced by coal industries, especially in storing and trans-shipping processes. The negative impacts of this phenomenon have led to several hazardous incidents and degrading product quality. Several methods have been researched to minimize the impacts; one of the proposed ways is immersing heat exchangers inside the coal stockpile. An experiment was conducted to analyze the cooling effect of an immersed simple heat exchanger made of a copper coil. By varying the number of windings, the experiment showed a significant decrease in pile temperature due to the immersed heat exchanger. This work continues exploring the possibility of applying the method by observing and analyzing the simulation model. COMSOL Multiphysics was used to model the physics phenomena that occur within the coal reactor. The effect of the heat exchanger surface area was studied from the model to observe the heat propagation within the coal reactor. The vast reach of heat propagation from the heat exchanger through the coal pile on the simulation was promisingly showing that this method was useful to limit the occurrence of spontaneous fire in coal piles.

An aircraft must have durability, whether for normal flight condition and for a critical flight condition. One of the critical flight conditions of a twin-engines aircraft is the failure of one engine while the aircraft is cruising. The aircraft with only one live engine on will still have enough power to generate thrust. However, the aircraft will experience a moment couple due to the thrust on the remaining engine that makes the aircraft to yaw. This yaw effect must be compensated by the flight control in order to maintain a stable flight condition. The rudder as one of the flight control systems manages the aircraft yaw motion. So, therefore the rudder deflection angle must be set properly as a treatment to overcome the moment force of the live engine. Study to determine best approximated optimum rudder deflection angle setting were conducted to get the figures of how the counter side forces generated on the rudder can maintain a stable flight. The result of the study can be applied as important guidance for a pilot to control the aircraft in a critical flight condition due to one engine fails. Considerations on the strength and integrity of the rudder structure especially at the hinge pivot points between the dynamic and the static parts are taken account as well.