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slalombuggy
Samba Member
Joined: July 17, 2010
Posts: 9145
Location: Canada
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 Posted: Sat Jan 18, 2020 5:59 pm Post subject: Re: Beetle Aerodynamic Flow |
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12714
Location: Western Canada
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| Posted: Sat Jan 18, 2020 6:44 pm Post subject: Re: Beetle Aerodynamic Flow |
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| mukluk wrote: |
Found this picture online of what appears to be a '66 European market Beetle in a wind tunnel. Pretty easy to see the airflow separation near the top of the rear window here.
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Yes that looks like I would have expected! |
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12714
Location: Western Canada
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| Posted: Sat Jan 18, 2020 6:49 pm Post subject: Re: Beetle Aerodynamic Flow |
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| Got some bad news for you slalombuggy! You have the wrong car for your speed runs at Bonneville, dump the Buggy and get a Bus. You are going to be way faster! |
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slalombuggy
Samba Member
Joined: July 17, 2010
Posts: 9145
Location: Canada
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| Posted: Sat Jan 18, 2020 9:41 pm Post subject: Re: Beetle Aerodynamic Flow |
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| oprn wrote: |
| Got some bad news for you slalombuggy! You have the wrong car for your speed runs at Bonneville, dump the Buggy and get a Bus. You are going to be way faster! |
Never. I went faster in my street buggy in a mile with a mild 2332 than the current bus record with a full race 2.7L type 4 that had 3 miles to wind it up.
Like I said before Cd is one thing, trying to push the flat face of a bus with 42 sq/ft of frontal area is another.
And as speed increases in a linear fashion, the hp required to increase the speed of the same vehicle increases exponentially. You would probably be looking at needing >650hp to get a bus to do 150mph. I should be able to do it in the buggy with around 220. |
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modok
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Joined: October 30, 2009
Posts: 26785
Location: Colorado Springs
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| Posted: Sat Jan 18, 2020 11:19 pm Post subject: Re: Beetle Aerodynamic Flow |
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I once hauled a 440 chrysler back into town in my bus.
Just need to mount it in there and hook it up..... |
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12714
Location: Western Canada
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| Posted: Sun Jan 19, 2020 5:37 am Post subject: Re: Beetle Aerodynamic Flow |
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Story time!
About 25 years ago we were driving the old '69 Bus into the city and passed an officer of the law who had an old VW Bus pulled over. We were bucking a head wind and struggling to maintain 60 mph so I made the comment to the Missus that at one thing for sure was he wasn't giving out a speeding ticket!
About 20 minutes later who should pull up beside us but the same Bus. When the light turned green there was the unmistakable V8 rumble and as he pulled away I glimpsed an engine mounted midship through the side window! You just never know... |
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rayjay
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Joined: March 26, 2008
Posts: 1506
Location: Buford GA
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nextgen
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Joined: August 19, 2004
Posts: 6025
Location: CONGERS, N.Y.
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12714
Location: Western Canada
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| Posted: Sun Jan 19, 2020 9:23 pm Post subject: Re: Beetle Aerodynamic Flow |
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You might not be wrong. Use that formula to calculate the drag coefficient of a barn. It might just surprise you!
The thing is, it can have the best drag coefficient in the world but if it's huge it's draggy. It can have the worst drag coefficient in the world but if it's tiny it will have next to no drag. Drag coefficient is about the shape not the size. A Bus is a big draggy turd not because of it's shape and drag coefficient but because of it's SIZE!
This thread has helped me see the difference! |
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tzepesh
Samba Member
Joined: May 28, 2003
Posts: 731
Location: Romania
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| Posted: Mon Jan 20, 2020 2:21 am Post subject: Re: Beetle Aerodynamic Flow |
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Did you see Gerrelt's aerodynamic improvements? He details the development of a roof spoiler among others, with flow analysis and tuft testing.
https://www.gerrelt.nl/section-aerodynamics
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Rome
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Joined: June 02, 2004
Posts: 9641
Location: Pearl River, NY
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| Posted: Mon Jan 20, 2020 8:50 am Post subject: Re: Beetle Aerodynamic Flow |
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Floating: thank you for clearly documenting your observations and thoughts.
rayjay-
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| I also want to do some 'coast down' testing. I have several long steep hills nearby and would like to do experiments with aero mods and then see if there is a measurable gain or loss. |
Aero mods such as a "Herrod Helper" rear spoiler, and Foxcraft-style full rear wheelwell skirts?
Another interesting anecdote on this topic. 40 yrs ago I worked at VW's Research & Development Center in Wolfsburg, Germany (FE, Forschung und Entwicklung). I was naturally curious about many aspects of vehicle development, and would walk around the many halls and buildings during lunch break or at an early end of work day. On one trip I went over to the wind tunnel complex. Around one side in the workshops, a new/upcoming vehicle (probably Golf II) was getting its frontal area measured. The car was parked indoors with nose facing out towards a large overhead garage door, leveled to design specs per ride height, tire size and inflation pressure, etc. A large screen was positioned perfectly perpendicular about 3' behind the car. The screen was more like a huge sheet of tracing paper, pulled taut onto the metal perimeter frame. The room had reduced lighting.
Outside about 100' away was a very strong spotlight, aimed in towards the car. It was most likely positioned halfway up the vehicle's height and centered left to right. The shadow of the car's silhouette shone clearly against the rear screen. A technician carefully traced the silhouette sharp edges onto the paper screen from behind the screen so as not to get in the way of the light source. This gave an accurate portrayal of the "face to the wind". The area within the edge lines could easily be determined by running a small distance roller. Effective method before widespread computer use, or to use as a reality check for computations.
In my senior year of college for Mechanical Engineering in NY, I wrote a paper for one of the classes on the effect of aerodynamics for improving fuel economy. My main resource was a technical report from the Aerodynamics team at VW from the late 1970's. One of the 2 authors' names was Hucho. The paper showed the improvements of drag coefficient by painstaking detail work on the VW Dasher (Passat in Germany) facelift for the '78 model year. The report was available via SAE (Society of Automotive Engineers), and Hucho went on to write a reference book on the subject. http://www.yanfabu.com/resources/editupload/files/2013112216461820.pdf |
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slalombuggy
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Joined: July 17, 2010
Posts: 9145
Location: Canada
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| Posted: Mon Jan 20, 2020 9:31 am Post subject: Re: Beetle Aerodynamic Flow |
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Jack Costella, fames landspeed race car designer and builder once said "If you can't go through the air, go under it" Many of his designs are barely knee high. Do a goggle search for images of Nebulous Theorem which is the name his cars bore. I was lucky enough to have NT III parked 2 stalls down from me on pit lane in 2018. Amazing attention to detail.
brad |
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rayjay
Samba Member
Joined: March 26, 2008
Posts: 1506
Location: Buford GA
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| Posted: Mon Jan 20, 2020 10:40 am Post subject: Re: Beetle Aerodynamic Flow |
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[quote="Rome"]] Aero mods such as a "Herrod Helper" rear spoiler, and Foxcraft-style full rear wheelwell skirts? [quote]
I definitely want to do some quick and dirty fender skirts. I just now thought of taking the fenders off and doing the coast down. Actually, I think I may need a less steep hill. Hmm, just have to try it and see. Hmm, the steep hills will equal more mph therefore more drag..... Learning new things is the goal.
I have a funny 'aero' story  . I bought an SCCA HP Fiat 850 and put a 1300cc Abarth engine conversion in it for Solo 1 use. I moved the radiator up front and built a nice aero duct that exited out the top. I had to redo the airdam and lowered it a bit with some thick reinforced rubber strapping. The first event I ran was at an abandoned WWII training field in Bainbridge GA. The surface might have been called macadam. It was some kind of binder with pea gravel as the filler. Lots of loose pea gravel on the 45+ year old surface. At the first hard braking point my new airdam came into hard contact with the surface which threw a lot of pea gravel out front and up into the air which I then hit at a good speed. Lots of pea gravel dinking off my face shield and into the cockpit with me !! Now I saw why the original airdam was as high as it was !! When I got home and put the car on stands I could see that every forward facing vertical surface on the underside had all the paint blasted off it. |
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slalombuggy
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Joined: July 17, 2010
Posts: 9145
Location: Canada
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| Posted: Mon Jan 20, 2020 12:23 pm Post subject: Re: Beetle Aerodynamic Flow |
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Dean Lowery did a white knuckled 111mph in a stock bodied beetle in the late 60's early 70's. He went back to the pits took the Herod's Helper off one of the road cars in the pits, put it on the race car and did a solid 132mph
I went through the traps on my first ever run on the salt at 115mph. I had been sitting in an open car baking in the sun in a 3 layer one piece fire suit for close to half an hour due to delays (we took an umbrella next time) before the run. I cooled off considerably due to the wind through my fire suit but by this time my helmet and head sock were soaked and I had sweat running in my eyes. I coasted for a bit and then flipped my visor open to get some fresh air. My head was slammed back in the seat and pulled up. I slapped my visor shut and looked down at the gps.......I was still coasting at over 90mph and my visor made a hell of a wing.
brad |
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Floating VW
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Joined: April 28, 2015
Posts: 1596
Location: The South Zone
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| Posted: Mon Jan 20, 2020 2:51 pm Post subject: Re: Beetle Aerodynamic Flow |
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Nice!
Too bad something like that is not practical on a street car. I used to have one of those Kamei air dams, and even that thing kept getting ripped off every time I went over a speed bump or a particularly large and juicy bit of roadkill. After a while, I got tired of patching it back up and just took it off the car. I kind of miss it now, though. I wish I still had it.
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Floating VW
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Joined: April 28, 2015
Posts: 1596
Location: The South Zone
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| Posted: Mon Jan 20, 2020 3:34 pm Post subject: Re: Beetle Aerodynamic Flow |
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| oprn wrote: |
| The thing is, it can have the best drag coefficient in the world but if it's huge it's draggy. It can have the worst drag coefficient in the world but if it's tiny it will have next to no drag. Drag coefficient is about the shape not the size. A Bus is a big draggy turd not because of it's shape and drag coefficient but because of it's SIZE! |
Exactly this!
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"It's time you started treating people as individuals, rather than mathematically predictable members of an aggregate set, regardless of how well that works." |
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Floating VW
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Joined: April 28, 2015
Posts: 1596
Location: The South Zone
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| Posted: Mon Jan 20, 2020 3:45 pm Post subject: Re: Beetle Aerodynamic Flow |
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| Rome wrote: |
| Floating: thank you for clearly documenting your observations and thoughts. |
Think nothing of it. I'm just happy someone out there is actually willing to read it!
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"It's time you started treating people as individuals, rather than mathematically predictable members of an aggregate set, regardless of how well that works." |
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rayjay
Samba Member
Joined: March 26, 2008
Posts: 1506
Location: Buford GA
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| Posted: Wed Jan 22, 2020 7:45 am Post subject: Re: Beetle Aerodynamic Flow |
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Another aero thought. DD baja bugs must have terrible aero. More or less the same frontal area but I guess the CD is real bad ????
Is even talking about CD in reference to cars a waste of time ? |
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rayjay
Samba Member
Joined: March 26, 2008
Posts: 1506
Location: Buford GA
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| Posted: Wed Jan 22, 2020 7:49 am Post subject: Re: Beetle Aerodynamic Flow |
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I wonder how much drag is created by the rear half of the wheel openings ? |
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terryly
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Joined: September 21, 2012
Posts: 309
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| Posted: Wed Jan 22, 2020 2:00 pm Post subject: Re: Beetle Aerodynamic Flow |
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Ya tell me about wind drag haha
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