RE: Multi-holes drilled air brake : any good ? I just spoke to my flying buddy, Carl "Flaps" Laffert, 84, who flew both the SBD Dauntless during WW II with the Marine Corps from Mindanao. He also flew the Curtiss SB2C Helldiver. He told me the perforations create more drag. They were first used in the US on the Northrop (a Douglas division at the time) A-17, built for the Army. It had 3-section flaps, one under each wing and one in the center. These were on the bottom only, not split as on the Dauntless. The Army didn't like dive bombers so Douglas built the Dauntless for the Navy with the split dive flaps/brakes.
He said the first version on the Helldiver had "smooth" flaps (as he called them) and the dive speed was 315 knots. On a later version they perforated then like on the Dauntless and at the same dive angle, the dive speed was 285 kts. Story by Ed Moorman, Shalimar Fl, 553, Former R/C Report Fun Aerobatics Columnist. 76 and up to my old tricks! Also found this; Abstract Measurements are described of the drag coefficient of porous circular cylinders (60% open-area ratio) fixed between solid hemispherical end caps, for five values of aspect ratio between 7.92 and 2.67. The Reynolds number varies between 104 and 2.6 ? 105. It is found that the drag coefficient increases with aspect ratio much as a solid cylinder's but its drag coefficient is about 20% higher (varying between 0.88 to 0.96 as the aspect ratio is increased). Flow-visualization experiments have also been conducted, and show how fluid passes through the cylinders and how the vortex shedding is weaker than for solid cylinders. Although based on a cylinder and not flat plate. Joe On Dec 25, 2014 9:54 PM, "bjoenunley" <bjoenunley at gmail.com> wrote: > I'm going with a solid belly board. I'm no aerodynamic engineer, but I > can't image more deflection than with a solid piece. > > Joe > > > Sent from my Verizon Wireless 4G LTE smartphone > > > -------- Original message -------- > From: Dan via KRnet > Date:12/25/2014 7:23 PM (GMT-06:00) > To: 'KRnet' > Subject: KR> Belly Board > > Can't get into the archives so here's my question. Holes or no Holes? I'm > getting ready to install the belly board and before I do I would like to > get > some feedback. > > > > Thanks > > > > Dan Prichard > > Portland, Or. > > _______________________________________________ > Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. > To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org > please see other KRnet info at http://www.krnet.org/info.html > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > options >
