EcoModder Forum Aerodynamics Seminar #3 - by Phil Knox

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The picture showing "formula for aerodynamic horsepower" was lost when this got moved to a new thread.
Here's one from Wikipedia.

Horsepower required to overcome aerodynamic drag -

Quote:
 is the force of drag, is the density of the fluid (Note that for the Earth's atmosphere, the density can be found using the barometric formula. It is 1.293 kg/m3 at 0 °C and 1 atmosphere.), is the speed of the object relative to the fluid, is the reference area, is the drag coefficient (a dimensionless parameter, e.g. 0.25 to 0.45 for a car), and is the unit vector indicating the direction of the velocity (the negative sign indicating the drag is opposite to that of velocity).

 02-14-2009, 08:47 PM #3 (permalink) Master EcoModder   Join Date: Jan 2009 Location: Maui, Hawaii Posts: 813 Thanks: 5 Thanked 34 Times in 26 Posts Don't you end up using 4x as much fuel at 2x the speed, because one of those 2x is cancelled out by getting to your destination in 1/2x the time?
 02-15-2009, 01:55 AM #4 (permalink) Master EcoModder   Join Date: Aug 2008 Location: South Dakota Posts: 460 WonderWagon - '94 Ford Escort LX Last 3: 51.52 mpg (US) DaBluOne - '99 Ford Escort SE 90 day: 48.97 mpg (US) DaRedOne - '99 Ford Escort ZX2 Hot Thanks: 0 Thanked 15 Times in 4 Posts Remember he's talking about how much additional HP is required to overcome drag - not average fuel economy. Less time burning fuel applies but, drag is only one factor. Parasitic losses in the engine, drive train and suspension go up as well - just not as fast as drag losses. So 2x speed (in same gear) means MORE than 4x fuel consumed.
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in 1/2x the time

Quote:
 Originally Posted by winkosmosis Don't you end up using 4x as much fuel at 2x the speed, because one of those 2x is cancelled out by getting to your destination in 1/2x the time?
We have to consider each vehicle on a case-specific basis, along with it's BSFC map under all operating regimes and changes to rolling resistance and any effects of road conditions,grades,temps,wind,etc.-------------------- For the aero portion only,doubling the velocity increases the road load power requirement by a factor of eight.The rolling resistance will not vary the same way.So you've got to calculate the total road load for any given speed.------------------- Using my truck for an example,at say 40 MPH you'd see low 40s mpg,and then pushing it to a steady 80 mph she falls off to around 30mpg.----------------- At the low speed the truck is mainly battling rolling resistance with only marginal air drag.At 80 mph,about 80% of available engine power is being absorbed by aero drag.--------------------- Every individual has to way out the implications of the higher velocity.

 03-01-2021, 10:02 AM #6 (permalink) Master EcoModder   Join Date: Dec 2014 Location: Radium Springs, NM Posts: 465 Ford XLT Naked - '14 Ford F-150 XLT 90 day: 15.04 mpg (US) Ford G-4 with Stinger - '14 Ford F-150 4X4 Super Crew XLT 90 day: 19.8 mpg (US) Ford Stealth G-4 - '14 Ford F-150 4X4 Super Crew XLT 90 day: 18.88 mpg (US) XLT Towing Keystone 5th wheel trailer - '14 Ford Keystone 5th Wheel XLT 90 day: 9.58 mpg (US) Trip 2015 C Max Energi - '15 Ford C Max Energi SWP 90 day: 38.2 mpg (US) Local 120 volt 2015 C-Max Energi - '15 Ford C-Max Energy SEL 90 day: 55.65 mpg (US) Local 240 volt 2015 C-Max Energi - '15 Ford C Max Energi SLE 90 day: 57.63 mpg (US) Energi Combined - '15 C Max Energi Leather 90 day: 51.2 mpg (US) MoonDust for Travel - '19 Chevrolet Bolt LT 90 day: 123.11 mpg (US) MoonDust 3 with 90% CE - '19 Chevy Bolt LT 90 day: 127.57 mpg (US) Ecopia IV - '19 Chevy Bolt Lt 90 day: 126.39 mpg (US) Ecopia IV Trip Log - '19 Chevy Bolt LT 90 day: 116.15 mpg (US) Rate Rider Chevy Bolt - '19 Chevrolet Bolt LT-2 90 day: 124.83 mpg (US) Thanks: 2 Thanked 528 Times in 278 Posts For Phil Knox, a video by Bjorn showing watt hours per kilometer with a regular cargo box and then he tested one that was designed to mount backwards and it showed a 9% drop in energy consumption. P.S. it was also quieter. This is what I told him was better some years ago but he just only now got around to testing it. Apparently it is illegal to mount them backwards unless they are specifically manufactured to do so with the mounting hardware. https://youtu.be/Z0P6i1YsgII __________________
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 03-03-2021, 11:06 AM #7 (permalink) Master EcoModder     Join Date: Jan 2008 Location: Sanger,Texas,U.S.A. Posts: 15,296 Thanks: 23,411 Thanked 6,919 Times in 4,414 Posts backwards So we're finally catching up to WW-II technology. Anyone with Hoerner's book, ' Aerodynamic Drag,' will already be familiar with the canopies and blisters which are the 'proper' application of the streamlined form. Some aircraft which demonstrate the technology are: * Grumman AF-2W submarine hunter * Douglas EA-1 Skyraider AEW * Boeing PB-1W * Fairey ( Westland ) Gannet AEW Mk 3 * Tupolev Tu-16 ' Badger-C ' * Tupolev Tu-142 'Bear/ AEW * Myasishchev M-4 ' Bison ' * British Aerospace Nimrod * Sikorsky S-70/ SH-60 B Seahawk * Grumman E-1 ( WF-2 'Willy Fudd' ) Tracer * Scaled Composites Proteus/ Angel Technologies HALO * Boeing 737 800 dorsal WIFI fairing * Carlisle ARINC 791 SATCOM fairing ------------------------------------------------------------------------------------ * General Motors Proving Grounds towed-dynamometers Don't let the past pass you by! __________________ Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
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Quote:
 Originally Posted by MetroMPG A NASCAR race car can travel 50-mph with 15 horsepower. At race speeds,to go from 195 mph to 196 mph will take an additional horsepower just for a 1 mph increase in speed.
You lost me.

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lost me

Quote:
 Originally Posted by j-c-c You lost me.
If you take the aerodynamic drag and rolling-resistance road-load horsepower requirement at 50-mph, add the powertrain loss, and engine accessory losses, you find that 15-brake-horsepower will be adequate to maintain the 50-mph velocity.
On a long, NASCAR superspeedway, like Daytona, Florida, the rolling-resistance drag power requirements will increase arithmetically with speed, while aerodynamic drag-related power requirements increase geometrically, as the cube of the velocity.
Passing, without a draft can easily require an additional horsepower / mph at the velocities they run at.
The 2021 Hennessey Venom 5 is allowing 1,850-horsepower for the 311- mph rated top speed.
At the Indianapolis 500, Dalara race cars have only 55-miles range per tank of fuel. Real range anxiety!

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