Trans RINA, Vol 156, Part B2, Intl J Small Craft Tech, Jul-Dec 2014
propellers. The 10-inch-pitch 2-blade propeller, with a ~8% decrease in the projected area, results in a decrease in drag of ~15% relative to the 2-blade, 6-inch-pitch propeller. These results are all consistent and to be expected.
The drag results are also presented in Figure 4 in terms of drag coefficients for the locked conditions, and Figure 5 for the freewheeling conditions, with the drag coefficient defined as:
CD VA . 2
FD 0.5 p Here, V is the speed, A p is the propeller blade projected
area to the oncoming flow, and DF is the drag. For the locked conditions, the drag coefficients fall between 1.1 and 1.35. In particular, the drag coefficients for the two 3-blade propellers are nearly constant with values of ~1.33. The two 2-blade propellers also have nearly constant drag coefficients with values near 1.2. The 10- inch-pitch propeller drag coefficient is nearly constant at ~1.1.
(1)
Figure 2. Propeller drag as a function of velocity for locked configurations.
In a similar manner drag levels for the freewheeling condition are shown in Figure 3. In this case we see significant differences between the Sailer and B-Series propellers.
In particular, the Sailer 2 and Sailer 3
propellers show significantly higher drag than the two 6- inch-pitch B-Series propellers. The primary reason for this involves the design of the leading edge. In particular, the leading and trailing edges of the Sailer propellers are 1/8 inch thick with a flat face. The benefit of this treatment is increased longevity for the propeller as it permits many re-conditioning operations. At all speeds, for a given propeller, the freewheeling configurations showed decreased drag relative to the locked configurations. However, the magnitude of the decrease was minimal for the Sailer series propellers.
Figure 4. Drag coefficients for locked configurations as a function of velocity.
Figure 3. Propeller drag as a function of velocity for freewheeling configurations.
©2014: The Royal Institution of Naval Architects
Figure 5. Drag coefficients for freewheeling configurations as a function of velocity.
B-83
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88