EcoModder Forum Think Flight: Using Simple Aerodynamics to Beat High Gas Prices

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 10-28-2022, 10:40 AM #31 (permalink) Master EcoModder     Join Date: Jan 2008 Location: Sanger,Texas,U.S.A. Posts: 15,304 Thanks: 23,414 Thanked 6,920 Times in 4,415 Posts 'Think Flight' V2 noodling I ran an energy balance for all the Subaru configurations. The conditions were: 65-mph ( 95.333 feet/second ) estimated Af= 23.8153 sq-ft OEM, estimated 24.4394 sq-ft with airdam rho = approx. 0.0023256823 Cd 0.29 ( CarsDirect.com ) tires- 205mm width REGULAR Unleaded, reformulated gasoline @ 111,836-Btu/gallon 6.138-pounds/ gallon CVT transmission of 87.71% mechanical efficiency 40% thermal efficiency for engine 2546 Btu/ brake-horsepower 2.2% engine accessory losses Rolling resistance power absorption is carried as a constant Brake Specific Fuel Consumption ( BSFC) is carried as a constant -------------------------------------------------------------------------------------- configuration-1: Cd 0.29, CdA= 6.9064 sq-ft, 35.644-mpg configuration-2: Cd 0.214, CdA= 5.0981 sq-ft, 40.528-mpg configuration-3: Cd 0.2671, CdA= 6.5289 sq-ft, 36.5637-mpg configuration-4: Cd 0.1764, CdA= 4.3114 sq-ft, 43.0971-mpg configuration-5: Cd 0.2291, CdA= 5.5467 sq-ft, 39.4562-mpg configuration-'6'* Cd 0.1721, CdA= 4.2060 sq-ft, 46.5376-mpg ------------------------------------------------------------------------------------- '6' represents a 17.3% radiator blockage to compensate for a now, 'oversized' radiator area. ------------------------------------------------------------------------------------- The 'source' flow for the underbody and diffuser originates at approx. 16.11-inches above ground level before displacement. The separation edge for the slanted diffuser should not be any higher than 16.11-inches, as, at this elevation, the displacement kinetic energy nulls, and constitutes the 'reversal point.' ------------------------------------------------------------------------------------ Additional 'fruit' which lay outside the scope of the Impreza project, if added, could easily bring the Subaru into Cd 0.145 range __________________ Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/ Last edited by aerohead; 11-01-2022 at 01:56 PM.. Reason: add data
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 10-28-2022, 01:45 PM #32 (permalink) Master EcoModder     Join Date: Mar 2022 Location: oregon Posts: 767 Black Bullet - '19 Hyundai Ioniq Hybrid Blue Thanks: 0 Thanked 397 Times in 325 Posts I wish he could build my Ioniq a rear boat tail like that. Wonder how stable it is at 100 mph with “ duct tape” though lol
 10-28-2022, 02:07 PM #33 (permalink) EcoModding Apprentice     Join Date: May 2008 Location: N. Saskatchewan, CA Posts: 1,755 Appliance White - '93 Geo Metro 4-Dr. Auto Last 3: 42.35 mpg (US) Stealth RV - '91 Chevy Sprint Base Thanks: 90 Thanked 434 Times in 308 Posts Aircraft mechanics often refer to "hundred mile per hour tape," but it even gets used on jets. A case of tape was used to temporarily replace much of the fabric on the fuselage and tail of a bush plane that smelled of fish in bear country. Workmanship matters. When sealing a glider canopy for a record run along a windy ridge, someone didn't press hard and consistently, and a small section turned into a screaming reed for over ten hours. __________________ There is no excuse for a land vehicle to weigh more than its average payload.
 The Following User Says Thank You to Bicycle Bob For This Useful Post: aerohead (10-28-2022)
 10-29-2022, 10:24 AM #34 (permalink) Somewhat crazed     Join Date: Sep 2013 Location: 1826 miles WSW of Normal Posts: 3,448 Thanks: 401 Thanked 993 Times in 873 Posts Tape for aircraft comes in flavors, 100, 300, 500 mph mostly dependent on who you are talking to and the construction materials... safe to say 500 is really structural, not used much and super expensive. Doesn't come off either. __________________ casual notes from the underground:There are some "experts" out there that in reality don't have a clue as to what they are doing.
 10-29-2022, 12:49 PM #35 (permalink) EcoModding Apprentice     Join Date: May 2008 Location: N. Saskatchewan, CA Posts: 1,755 Appliance White - '93 Geo Metro 4-Dr. Auto Last 3: 42.35 mpg (US) Stealth RV - '91 Chevy Sprint Base Thanks: 90 Thanked 434 Times in 308 Posts Not a duct tape, but 3M has a double-sided tape that is popular for replacing lines of rivets on box-truck bodies. I have a sample, and I'm a firm believer. __________________ There is no excuse for a land vehicle to weigh more than its average payload.
 The Following User Says Thank You to Bicycle Bob For This Useful Post: aerohead (11-01-2022)
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Quote:
 Originally Posted by Bicycle Bob Not a duct tape, but 3M has a double-sided tape that is popular for replacing lines of rivets on box-truck bodies. I have a sample, and I'm a firm believer.
I was thinking of using 3m double sided tape to attach my extended box cavity versus a full boat tail versus drilling the box cavity in and hurting the value of my car more

 10-29-2022, 05:02 PM #37 (permalink) Master EcoModder     Join Date: Aug 2012 Location: northwest of normal Posts: 25,254 Thanks: 7,131 Thanked 8,017 Times in 6,571 Posts Best would be a tape that can be removed with some solvent that doesn't affect the paint. __________________ . . Without freedom of speech we wouldn't know who all the idiots are. -- anonymous poster ____________________ "If you don't read the newspaper, you are uninformed; if you do read the newspaper, you are misinformed. " someone who was not Mark Twain ____________________
 11-01-2022, 11:41 AM #38 (permalink) Master EcoModder     Join Date: Jan 2008 Location: Sanger,Texas,U.S.A. Posts: 15,304 Thanks: 23,414 Thanked 6,920 Times in 4,415 Posts some Think Flight geometry vs performance With the original modifications, the upper contour of the boat tail best matched the W.A.Mair, and FKFS (Kamm) 1/2-body silhouettes. Maximum down-slope angle is 19-degrees. Diffuser upsweep is 20.5-degrees. The 'highest' streamline filament traveling under the Impreza begins about 16.1-inches above ground level. Along with the other mods, the tail gets the car to approximately Cd 0.214. -------------------------------------------------------------------------------------- For the second-generation, #4 configuration modifications, the upper contour of the boat tail is almost an exact match to W.A.Mair's and Buchheim et al.'s 1981 VW Flow-body tails. Maximum down-slope angle reaches 23-degrees. The diffuser angle is 5-degrees upsweep. All mods contribute to an approximate Cd 0.1764, and achieves an almost 21% improvement in mpg. -------------------------------------------------------------------------------------- Averaging for all configurations, the delta-drag/delta-mpg relationship works out at: delta-10% drag = delta-5.15% mpg ( assuming constant BSFC ) __________________ Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/