Aerodynamic Streamlining Template: Part-C

[NeilBlanchard]

Originally Posted by sendler

There is some contradictory information between some of these charts. How is the round shape shown as the same cd as the airfoil at .09. You have posted other charts with the cd of a round rod much higher.

I think it may be off by a decimal point? The Cd of a sphere is 0.47, according to Wikipedia.

[aerohead]

Originally Posted by freebeard

I like that he uses the VW Beetle as a benchmark. It's relevant to my interest.

1.75/2.5=0.7. Assuming a 12' length, increasing the Beetle's fineness ratio to 2.5 would require a 5.14ft boattail. What is the included angle at the tip of the optimal body? I used 45°, as close enough to 2*22° in my experiment with redwood lath, and got a boattail length of 3ft.

For ground reflection in elevation Mair suggests 44-degrees,Buchheim 46-degrees.
For plan-view,technically it would be the same.
I'm favoring the tail contour of the 3.92:1 airfoil section for plan-view.
I can't defend it scientifically.It allows a wider rear wheel track.

[aerohead]

Originally Posted by sendler

There is some contradictory information between some of these charts. How is the round shape shown as the same cd as the airfoil at .09. You have posted other charts with the cd of a round rod much higher.

These coefficients are in aeronautical terms,more like K-values based upon wetted area.The absolute numbers aren't really as important as their relation to one another.
The 2.5:1 streamline body of revolution produces a frontal area-based coefficient of drag of Cd 0.04.

[freebeard]

It allows a wider rear wheel track.

My VLVW Concept has the fenders removed, and fully enclosed cycle fenders like that bus you posted in the other thread. Except instead of being sunk into the side of the body, they're half exposed.

The front fenders have a ducktail outward, so the wheels can turn. The rears are freestanding scoops that pressurize the diffuser. They taper inward to the rear.

The maximum body width moves inward 3in and forward 2ft on each side. That's what allows the 3ft boattail instead of 5 feet. IMHO, of course.

[aerohead]

Originally Posted by freebeard

My VLVW Concept has the fenders removed, and fully enclosed cycle fenders like that bus you posted in the other thread. Except instead of being sunk into the side of the body, they're half exposed.

The front fenders have a ducktail outward, so the wheels can turn. The rears are freestanding scoops that pressurize the diffuser. They taper inward to the rear.

The maximum body width moves inward 3in and forward 2ft on each side. That's what allows the 3ft boattail instead of 5 feet. IMHO, of course.

If we had unlimited resources we could build out the VLVW in all the permutations that you've shared and test them all for inclusion in a master data archive.
The Beetle remains such an endearing form for so many and I think other Bug owners would want to know what they were capable of when taken to the limit.
I thought that by now,your renderings would have lit a fire under others,and we'd see 'em fleshed out 'n goin' down the road.

[freebeard]

You'd think it would light a fire under me.

I have a friend that has a whole boneyard full of Beetles and I'm trying to talk him into building a rat. It would have the whole windshield and top of the dash cut away and the hood moved back 6" to replace the top of the dash. Flip-up racing windscreens and hairpin roll bars. There would be two 12' long pieces of timber bamboo that would be half-rounds on the doortops and curve to a boatail making a 17' long car. 3rd passenger rumble seat in the wooden or bamboo rear deck.

It's hard to get people to do all the work so I don't have to do it all myself.

[wyatt]

Originally Posted by aerohead

With the Cobra Daytona Coupe,they've angled the truncation which allows a torque moment to be produced from the low base pressure riding under and forward of the rear spoiler location,enhancing downforce at the sake of drag.
http://www.conceptcarz.com/images/Sh...-12-AI-a09.jpg

I read an article about the Cobra Daytona. There were restrictions on what they could do as far as modifying a stock car went. They could either alter the drivetrain, or alter the body. Altering the drivetrain was out, since a more powerful engine would have meant needing a more beefy frame. They took a chance on a guy who said he could make it fast enough to keep up with the Ferraris (which were the big competition of the day). They lowered the driver, and gave it a fastback. All of the metal work was done at the go-to metal working shop, where the sheet metal was pounded into shape. The original Daytona did not have a spoiler (though they had wanted to install a driver-adjustable spoiler they just didn't have time). The first real test was once they got a completed car to the test track. They didn't have a working speedometer, but they knew the gear ratio, so using the RPMs they back-calculated the top speed on a straight away. They blew away the stock Cobra's top speed on the first lap. I don't remember speed numbers, or Cd numbers offhand, but Cd was dropped dramatically. The only complaint from the driver was that the back end was a bit squirrelly in the corners. They slapped a spoiler on (non adjustable), the driver took it for a lap, blew away the previous laps top RPM (speed), and returned saying it handled perfectly, and to not touch the spoiler. I'll have to see if I can find that article, so I can properly quote from it. Definitely a worthwhile read.

[aerohead]

It's been awhile since I've revisited this thread and wanted to share some info for those who've followed it.
I've constructed a 1/3rd-scale facsimile of the 'template',with concessions to allow for tail lights and license plate.


If I can make it back to DARKO I'll have a chance to capture some numbers for it finally.
I have a half-day reserved for the afternoon of September 15,2017,at DARKO Technologies' wind tunnel in Ogden,Utah,USA.
The model has a provision which will allow me to drop the tail and measure a separate drag coefficient as a truncated half-body.
My truck has had many issues and I'm hoping she'll hold up long enough to get me up there.
Thanks for your interest in the project.I'll try and post data as soon as I can.And hope to capture smoke-flow video to share as well.

[gone-ot]

Overall 'shape' sorta looks like a 'smooth' Horseshoe Crab without the stinger...on 4 wheels.

[aerohead]

Originally Posted by Old Tele man

Overall 'shape' sorta looks like a 'smooth' Horseshoe Crab without the stinger...on 4 wheels.

That's a great comparison! Amazing animal! PBS just did a program which spent some time with the Horseshoe.They said that it wasn't actually a crab,but more related to spiders and scorpions! They have blue blood and are harvested for it,for use in pharmaceuticals.