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  • KTH

    Department of Aeronautics 25 October 2002

    Technical Report of Phyxius

  • Table of Contents 1 Introduction ............................................................................................................3 2 Design.....................................................................................................................4 3 The Human Power..................................................................................................5 4 Hull Design ............................................................................................................6 5 Propulsion...............................................................................................................6

    5:1 Air propeller ....................................................................................................7 5:2 Water propeller................................................................................................7 5:3 Surface piercing propeller ..............................................................................8 5:4 Pelton turbine wheel........................................................................................8

    6 Transmission ..........................................................................................................8 7 Performance ...........................................................................................................9 8 Stability and Steering ...........................................................................................11 9 Hydrofoil Design..................................................................................................12 10 Conclusion..........................................................................................................13

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  • Technical Report of Phyxius

    1 Introduction 16 students in their last year of a Master of Science degree at KTH (the Royal Institute of Technology, Stockholm, Sweden), have formed a team with the purpose of building a waterbike. The faculty is not involved other than by advising in special matters. The work is part of a project course and the team consists of five people studying aeronautics and aerospace engineering, and the others are conducting their studies in lightweight construction. No member of the team is studying marine technology and this could have as a result that questions are raised in the report which might be easy to answer for someone with good knowledge in that subject.

    The project was launched in mid August and the waterbike, called Phyxius from Latin which means ready to lift, is planned to be finished in late spring 2003. The economical budget for the project is $4000 and the time budget is 12 weeks of full time work per team member. The goal of this project is to combine the knowledge of those studying aviation, whose main task is to build the hydrofoil and the propulsion system, with the skills of those who have the task of building the watebike light and rigid. The ambition is to use the theoretical knowledge gathered during three years at school and to transform it into the practical building of a water-based vehicle. Our ambition is to learn as much as possible in ship constructing without a specific knowledge in marine technology.

    The specification is fairly simple: obtain maximum velocity on water using human power only.

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  • 2 Design

    Figure 1: Phyxius with a front mounted airpropeller

    To minimize the resistance while the vessel is still in displacing mode the best solution is to have just one hull and eventually two supportive pylons are needed to stabilize in roll. To stabilize in both roll and pitch in flying mode the vessel is equipped with two stabilizers in front. To prevent drag from the propeller, it is not to be in the water. In this example it is placed in front of the mast to get free air stream. To get the hull out of the water there are two wings: one big to get enough initial lift and one small to get the highest speed while flying. The big wing will leave the water when the speed is high enough.

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  • Figure 2: Phyxius with a front mounted surfacepiercing propeller

    In this example the waterbike is equipped with a surface-piercing propeller. The propeller is placed in the very forward because of the raise of the aft. This option is now being studied considered to forces and efficiency. In other aspects this vessel is equal to the one above. The placement of the small pylons is still to be decided. Because those contribute to dead weight in flying mode they are to be dropped in this mode (see section Stability and Steering). A third propulsion system based on Pelton wheels (see section Propulsion) is under investigation and close to be abandoned since there is doubt about the efficiency of this propulsion system can achieve a velocity of 11m/s and therefore a sketch do not yet exist. The Pelton wheel is only treated in the Propulsion section.

    3 The Human Power The task has been to estimate the available human power. Tests were done on a training bicycle and data from the tests were used to evaluate the time (somewhere below a minute) it would take to reach 11m/s. Tests during 30 s and 1 min have been performed for both normal position and the more laid-back one. Statistics were used to compare the results and those gave a hint of the results. A first class athlete is able to deliver 730 W during 30 s and 600 W during a minute. Tests results showed that the laid-back position was more effective than the normal bicycle position, although not by much. Since laid-back position lowers the center of gravity and gives stability

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  • and as well minimizes the area in the air, the upright position was abandoned. The test which was done in the laid back position resulted in the following:

    t = 30 s t = 60 s n = 130 rpm n = 90 rpmP = 620 W P = 500 W

    Table 1: Test result from cycling in laid back position

    These results gave a hint of the available power.

    4 Hull Design Data about the hull that was decided early in the project:

    Max length of the hull; 6 m, LOA (Length Over All) due to practical reasons. Displacement about 0,090 m3

    The hull will be optimized to achieve a low drag and highest possible speed, however since the vessel will be constructed with only one hull, the stability must be addressed. The drag in lower parts of the velocity region will be dominated by the skin friction. It is important to reduce the skin friction because the hull is entering the first flight-regime at an early stage. Reducing the wetted surface is one way to achieve a lower skin friction level. Increasing the speed, introduces another phenomena, wave drag. Analysis of the total drag clearly indicates that increasing the length of the hull will especially lower the wave drag. A flat or slightly curved hull bottom will allow a higher speed, and a rather large longitudinal curvature lowers the center of gravity and increases the stability. The freeboard has to be slightly inclined to keep the stability even when the hull is heavily loaded. To satisfy all these aforementioned shape-points an already existing hull such a K1-kayak will be a good choice.

    5 Propulsion The power output available has been decided by trials to be approximately 550 W during 45 seconds keeping an rpm of about 110. These numbers has been the starting point for choosing propulsion unit. Four different propulsion solutions have been investigated: an air propeller, water propeller, surface-piercing propeller and a Pelton turbine wheel. Initially an air propeller and water propeller was compared, showing equal efficiency. The water propeller has the distinct disadvantage of having a submerged drive shaft and propeller axle, creating a significant amount of drag. The air propeller was considered to be the best solution regarding efficiency and drag though it has the disadvantage (or maybe advantage?) of being sensitive to wind. It was found that a diameter of 3.2 meters and a geometric pitch of 3.9 meters was the most efficient solution for a speed of 11 m/s.

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  • 5:1 Air propeller When designing the air propeller the following data has been used; n = 110 rpm Pavailable = 550 W (for approx. 45 s) Vnecessary = 11 m/s CL, = 2 (thin airfoil theory) These numbers has been derived from trials on an ergonometer in a gym and from the current world record holder. A combination of blade element and momentum theory was used to calculate the optimum propeller blade layout. Momentum theory says that it is more efficient to accelerate a large volume of air a little than accelerating a small volume much.

    0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 3.6

    3.7 3.8

    3.9 4

    4.1

    4.2

    4.3 4.4

    4.5

    4.6

    0.8

    0.82

    0.84

    0.86

    0.88

    0.9

    0.92

    0.94

    0.94

    Figure 3: Geometric pitch (m) on the y-axis, radius (m) on the x-axis and efficiency as contours.

    That, together with the foremost successful example, Decavitator, gave that a propeller diameter of 3 m was chosen initially. By changing different parameters such as geometric pitch, chord distribution and diameter the following conclusions were made regarding the efficiency over the blade radius (fig. 1). Hence a geometric pitch of 3.9 m, mean chord of 0.08 m and a diameter of 3.2 m shows to be the most efficient solution. The total efficiency obtained through the calculations is probably a bit too high due to simplifications made but still show the best layout. 5:2 Water propeller The same methods used for the air propeller was used in evaluating the water propeller design. It was concluded that the same efficiency coul