TMann Posted October 13, 2007 Share Posted October 13, 2007 I see a lot about the NACA type scoop vs. the P-51 style scoop. What is the bottom line when it comes to performance and drag trade-offs. I know that Waiter swapped out his NACA style on his rebuild but that was based on a Lycoming power plant. My plane will be using a mazda rotary with the radiator in the area below the engine so the armpit/downdraft solution is out of scope here. Quote T Mann - Loooong-EZ/20B Infinity R/G Chpts 18 Velocity/RG N951TM Mann's Airplane Factory We add rocket's to everything! 4, 5, 6, 7, 8. 9, 10, 14, 19, 20 Done Link to comment Share on other sites More sharing options...
rsrguy3 Posted October 16, 2007 Share Posted October 16, 2007 This is a question that I want to know as well for my upcomming prodject. I have heard that the NACA is very sensative and must be totaly dialed in to work properly. Is it all that much more aerodynamic than a scoop? -Guy Quote Link to comment Share on other sites More sharing options...
--D-- Posted October 16, 2007 Share Posted October 16, 2007 A proper NACA *should* give you less drag, all other issues aside. However, the "other issues" (like shoving air through a radiator) can't be tossed aside. There's a good reason the P-51 doesn't have a NACA on the belly... Keith Spreuer recently replaced his NACA with a "P-51" male scoop due to inadequate dP across his radiator (Subaru). He posted this to the Cozy list... "My conclusion is that the P-51 style scoop with 3:1 expansion and less than 11 deg expansion rate is key. The P-51 scoop is much more compatible with a radiator installation. This is because the fine fin arrangement of a radiator requires a higher delta P than the wide fin spacing of an air cooled engine. The P-51 scoop does a much better job of delivering that pressure." Pics and graphs and such are here (look under "P-51 Scoop" and get a cup of coffee because it takes an eternity to download anything): http://briefcase.yahoo.com/kspreuer The graph shows twice the dP, 73%+ dT, and he reported no noticeable loss in performance (increase in drag). Plus, his plane looks more like a P-51 now. D Quote Link to comment Share on other sites More sharing options...
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