April Propwash 2018 web.pub

So far I’ve avoided a technical discussion of cavitation. Feel free to skip this part and concentrate on the practical aspects of our hydrofoils explained above. You may have noted the number on the right side of the cavitation pictures. That’s called the cavitation number. It’s approximately the ratio of atmospheric pressure to the dynamic pressure caused by flow over the hydrofoil. The lower this number, the more cavitation is expected. At a cavitation number of 0.5 you would expect the beginning of cavitation around 45 mph. A cavtation number of 0.2 indicates the beginning of cavitation around 70 mph. A symmetrical strut would need to be 10% thick or thinner to avoid cavitation at a cavitation number of 0.2. All our boats run fast enough and the hydrofoils are shallow enough that ventilation will always occur on struts, rudders, and turn fins. In fact, that’s probably happening rather than cavitation. It doesn’t really matter since the effect on flow is the same. NAMBA Nationals Records 2017 By Mark Grim NAMBA Records Chairman I would Like to congratulate all of the contestants that set new records at the NAMBA Nationals at Sunset Park in Las Vegas, Nevada. The Huntsville Model Boat Club will be hosting it’s first NAMBA Time Trials event April 2nd and 3rd of 2018. There will be Straight-Line and 2 Lap. All NAMBA classes will be offered. Set this date aside on your calendar and come out for the event. Monos also use turn fins. These are set at the transom unlike hydro turn fins that are set near the center of gravity. The fins are set at right angles to the hull bottom. In the turn the fin will be vertical as the hull rolls onto the bottom. Both straight and curved turn fins have been used. The curved fins help hold the transom down in the turns while the straight fins only provide side force. PROPWASH April 2018 Page 11 Crackerbox with Curved Turn Fin Crackerbox with Straight Turn Fin Eagle Turn Fin Showing Relaxed Twist Fast Electric: Ray Presnall Nitro: Chris Wittrig Chris Bopp Brad Tuttle Gas Dave Pillado Steve Lopez Richard Romero Sean Boundy Jesse Alvitre Class P Limited Mono A Hydro B Hydro Sport 20 GX-2 Mono GX-2 Catamaran Jersey Skiff GX-2 Sport Hydro GX-2 Sport Hydro Time 101.13 seconds 86.85 seconds 85.47 seconds 108.87 seconds 78.06 seconds 86.68 seconds 101.29 seconds 76.7 seconds 75.6 Seconds Check this out: http://otc.podbean.com/