Lower Propeller Research Articles

Distance and Rotational Speed Analysis of Coaxial Rotors for UTHM C-Drone

The prototype of UTHM C-Drone use a coaxial hexacopter concept for its propulsion system. A coaxial rotor consists of two motor and two propellers mounted above each other and aligned in relation to their axis of rotation. The propellers are based on the T-Motor U15XXL KV29 model used in UTHM C-Drone. The distance between the two propellers is usually relative to the radius of the propeller or can be lesser. The objectives for this study are to investigate the effect of distance between upper and lower propeller in a coaxial rotors system and the effect of rotational speed. This study is important to ensure the C-Drone power efficient and capable to lift 180 kg payload. The CAD model of the propeller and coaxial rotors system were designed based on the specification from T-Motor company by Solidworks software and the flow simulations were conducted using Solidworks Flow Simulation module. The total of six CAD models; one for a single propeller and five for coaxial rotors with five difference of distance cases were constructed. For each model, the total thrust was tested from 50% throttle power up to the 90% throttle power. It was found that the coaxial rotors system can generate more thrust than a single propeller but less than double. It was also found that if the lower propeller rotates faster than the upper propeller, the increment of total thrust is very small. However, if the upper propeller rotates faster than the lower propeller, the total thrust increase significantly. For the case of faster upper propeller, as the higher the throttle applied, the thrust increment ratio will decrease, and the efficiency of the thrust produced will be affected. In addition, for same rotation speed, the thrust generated was lesser when both propellers rotate in a same direction compared to when each propeller rotates in the opposite directions of each other.

Computerized Fluid Dynamic Study of Parameter Effects on the Performance of Coaxial Propellers

The computerized fluid dynamic (CFD) analysis was performed for 1.8 m diameter coaxial propellers to be applied to the multi-copter type Personal Air Vehicle (PAV) having conceptually 600 kg of Maximum Take-Off Weight (MTOW). Methods/Statistical analysis: Using the commercial CFD program STAR-CCM+ (13.03.11), the coaxial propellers were analyzed at the same RPM under the steady state condition. The three-dimensional Compressible Reynolds Mean Navier-Stokes equation was applied and the Moving Reference Frame (MRF) technique was used. With the optimum single pitch angle of upper propeller, the lower propeller’s pitch was changed for the varying propeller spacing to identify the performance variation and the interference effect. The lower propeller has to be different pitch setting other than the upper propeller’s optimum pitch angle because of the interfered flow effect between propellers. The propeller spacing is not so sensitive to efficiency if the spacing is more than 0.25 of propeller diameter. Study shows that the identified pitches and spacing of coaxial propellers are essential for designing the configuration and control of multi-copter type PAV which uses variable pitch propellers for safety and efficiency.

Analysis of the causes and the countermeasures for the serious complications after perforating pedicle flap of lower leg

Objective To analysis causes of the serious complications after the operation of the lower leg perforator pedicle screw flap, and to explore the corresponding countermeasures. Methods From June, 2012 to August, 2016, 60 cases of soft tissue defect of ankle and foot were repaired with propeller flaps pedicled with perforator of lower legs. with the area were soft tissue defect ranged from 3.0 cm×2.0 cm to 19.0 cm×9.0 cm, and all with bone exposure. Two cases of traumatic tissue defect, 7 cases were chronic osteomyelitis of the distal tibia, 13 cases were incision infection and necrosis after the operation of ankle joint fracture and Pilon fracture, 10 cases were simple incision necrosis after calcaneal fracture, 18 cases were calcaneal osteomyelitis, 1 case were soft tissue defect after the ankle tumor operation, 6 cases were soft tissue necrosis after the Achilles tendon rupture, and 3 cases were soft tissue defect of the dorsum with infection. The posterior tibial artery perforator pedicled propeller flap was used in 18 cases. The pedicle of the vascular pedicle was 6.0-18.0 cm from the medial malleolus, the flap rotation was 135°-180°. There were 42 cases of the perforator pedicle propeller flap of the peroneal artery, 5.0-18.0 cm from the pedicle of the vascular pedicle and 120°-180° rotation in the flap. The area of the flap was 9.0 cm×3.0 cm-34.0 cm×18.0 cm. There were 32 cases of direct suture in the donor site and 28 cases of free skin grafting. Results The color, swelling, elasticity, capillary reaction and healing of donor site were observed after operation. There was no flap ischemia occurred in 60 patients. Fourteen cases had venous reflux obstruction, all of which had swelling above II degree, 8 cases had swelling above III degree with obvious purple blood stasis, resulting in partial flap necrosis in 4 cases, all necrosis in 1 case, including 4 cases of free skin grafting, 1 case of flap transplantation and repair. There were 3 cases of necrosis after skin grafting in the flap area, all of which were partial necrosis. There was case of necrosis of the wound surface after direct suture of the donor site and 1 case of skin disintegration after disassembly, and all wounds healed after the replacement of the wound and the external use of the dried blood powder. All the 60 patients were followed-up for 12 to 30 (mean, 24.5)months. The flaps survived and the donor site scars healed well. The range of motion of the ankle was from -10°to 10°(mean, 5.6 °) and the flexion of the plantar was from 20 °to 50 °(mean, 37.8 °). Fourteen patients with venous reflux disorder were followed up for 15 to 28(mean, 22.3)months. The flap and skin graft survived well. Ankle dorsiflexion ranged from -10° to 10 °(mean, 2.4 °) and plantar flexion from 20° to 45 °(mean, 35.6 °). There was no obvious limp in walking. Conclusion Although the overall effect of the lower leg perforator pedicle propeller flap to repair the soft tissue defect of the foot and ankle is satis-factory, there are still various serious complications, which are mainly due to iatrogenic. Doctors should strictly follow the basic principles of skin flap surgery from preoperative to postoperative, and during operation and postoperative man-agement, so as to reduce the incidence of complications. Key words: Lower leg; Perforator vessel; Propeller flap, perforator flap; Ankle and foot; Complication

Modulating the propeller-like shape of a tripodal C(CH 2PPh 2) 3 fragment by the size of the substituent at the pivotal carbon atom in macrobicyclic tri-λ 5-phosphazenes

The chiral macrobicyclic tri-λ 5-phosphazenes formed by tripod–tripod coupling of tris(3-azidobenzyl)amines and 1,1,1-tris[(diphenylphosphino)methyl]methanes present helical topologies as a result of combining two propeller-shaped tripodal fragments with the same sense of twist. The introduction of a series of R piv substituents of increasing size at the pivotal carbon of the lower tert-butane fragment R piv–C(CH 2PPh 2) 3 causes a gradual decrease of the helicity in the lower propeller. This phenomenon is revealed in their CDCl 3 solution NMR spectra, and the activation energies for the racemization process of the tri-λ 5-phosphazenes were calculated by coalescence VT-NMR experiments.