Aerodynamic Streamlining Template: Part-C

[Sven7]

Tes-

Thanks for the comments. I recall him saying the template stuff months ago

Yes, the telescoping would need some soft portion but I was thinking the shells would be hard- ABS or fiberglass. You could actuate them any number of ways, one of which could be to pull it out by hand before you drive on the highway or push it in after you park. Some latches would keep it in place and rubber flanges/gap fillers would keep the wind out.

I think the side wind issue is that you get more "frontal" area on the sides. Since that area is behind the rear axle it tends to use your entire car as a lever... and the wind has the mechanical advantage! I noticed this with the Anal Probe (40"/1m boattail). It tended to want to turn itself slightly when hit by a strong crosswind.

If you want to run a trailer you may have a hard time making up for the extra rolling resistance, weight, etc. but it has been done. Aerohead did it on his T-100 and there's surely a very detailed thread about it somewhere

Otherwise, just cut the end off wherever you please- just like a loaf of bread. That's how you design a "partial" boat tail!

Hotrodfeguy, there are a few threads floating around regarding DIY wind tunnels and the consensus is that you can't really build one unless you have a lot of money and a lot of space. Like, monstrous amounts of space. When you scale the car down you have to double the wind speed to get usable results. 1/1=20mph, 1/2=40mph, 1/4=80mph, 1/8=160mph, etc. Plus, the size of the vehicle's frontal area (IIRC) has to be 5% of the cross section of the wind tunnel to make sure the walls don't affect your results.

I'd also like to know if my Patrol blueprint thingy is correct in plan view.

Ha, Macs. If I had to buy a computer right now it'd be a Mac to avoid Windows 8 (aka Windows greaaaat...)

[Sven7]

Jaray's combination form patent.


Jaray patent 1 by kitchener.lord, on Flickr

Gorgeous drawing of the gorgeous Jawa 700 Coupe by Jaray which demonstrates the combi form (also see Ley T6, Tatra 77, 78, etc)

Jawa 700 Coupe Jaray by kitchener.lord, on Flickr

[aerohead]

[QUOTE=Sven7;353004]Tried that on my laptop here (where the numpad is over letter keys) and it opened a History tab and a "save as" window. They say my generation is good at computers but sometimes I just don't know...



Exactly. That's why the width dominates my illustration. I know you weren't trying to cut it short, either

Tropfenwagen, top. Too bad for the unfaired wheels and other 1920's accessories that dragged it down.




Is that Mac?



I know we've been over this before, but isn't it important on wagons that the top of the rear portion doesn't "stick out" of the template? Ie, that we have to move it back until it forms a tangent with the trailing edge. Otherwise you have a vertical step before the boat tail starts.

Originally Posted by aerohead

If the 'interference is so great as to be able to closely match top and sides we streamline the main body separately from the greenhouse,creating the 'combination form'.[/aerohead]

What do you mean by interference? Is that another way of saying pressure differential?

"advocated the tail truncation at 50% frontal area wake area to ease driving in traffic and parking issues."

How about you cut the tail in half and the smaller half moves in to nest inside the larger one when you need to park. Kinda like aero Russian nesting dolls.

*If the existing roofline is hyper-'Template',then we'd have to 'adjust' for reality.So maintaining vehicle height,we'd slide the 'Template'contour rearwards until it just grazed the existing contour,building back and down from there.
*Interference would be a conflict in the original body architecture which would prevent a contour from beginning where we'd like.EXAMPLE: You've got a BMW 1600 GT and you'd like the body to taper in like the roofline is tapering down.But to do that you'd have to narrow the rear track,like EV1,or Insight-I,and completely re-engineer the rear suspension.Ain't gonna happen!
So the boat-tailing must be dragged rearwards,beginning where crucial internal elements would allow for it.
*The 'nesting' could be your baby! Imagination capital is the only thing which limits our options for aft-body mods.As long as there was no bulkhead at the 50% Af parting line,the extension should just slide right in so long as the depth were there.Fun!

[freebeard]

Originally Posted by Sven7

You could actuate them any number of ways...

Put the top half of this:


into this:

Ha, Macs. If I had to buy a computer right now it'd be a Mac to avoid Windows 8 (aka Windows greaaaat...)

There's a lot of that lately. Here's my perspective: I bought my first Mac 'in the first hundred days' in 1984. Finder v1.1.

I'm now at 10.6.8 and I'm reluctant to get current (although I probably will for the SMS from the desktop). Every time I launch Seamonkey, the OS says approximately "This is an application you downloaded from the Internet. Are you sure you want to?" I read that as "You are running software you didn't by from our app store, and we know it." This is moving toward the walled gardens of the iPhone/iPad/iTunes Store.

Of course I was upset when the OS started asking "Are you sure?" at Shutdown, just so Windows converts wouldn't freak out.

[aerohead]

Originally Posted by hotrodfeguy

This all makes a ton of sense, and I will give you the wind tunnel it would be money in the bank. All of your data is spot on gentlemen !!! But in real world how much is to much? My point is this, lets say your doing 55 and have a 30MPH side wind. It kinda goes to $hit, the long side, boat tail then becomes a negitive impact on areo. Not trying to be a killjoy. Just that I see some holes in some of this. Why double the side area or even at 25% of the car to gain, front to back areo? cause when you introduce a side wind it then becomes more area for drag. look at the car form angles like a diamond if you will, It should not be areo view from just one angle. wind soes not blow form one direction.

On my Driver metro I was going to do a kamback with no sides like a naked edged Kamback to get data then put sides on it to see if I have a real issue here with sidewind or not. I know the more improvements I have made(flat hubcaps, mirroe delete passenger side, wheel well covers, grill block, front air dam) the more the car tends to get shoved off the road by cross wind. And at the last few pages thats where this 22* may be affected, In my humble opinion it should be more agressive to cheat or be more universal to cross wind. I know there is a perfect forula for front back, but I am saying maybe in daily winds it should be more general purpose?

Maybe I am all out in left field. I could be totally wrong.

Your concern for crosswind stability is something which has attracted attention since the 1920s.
Depending upon the position of a cars center of gravity,and center of pressure,gusts and crosswinds could destabilize a car at speed.
Professor Kamm was obsessed with stability,and his last project,around 1966,was with a DKW sedan which he modified to a K-form roofline.Kamm added his signature dual,split-fin stabilizers (Egyptian round-hulled sailing ships used these 'steering-rudders' 4,500 years ago) to guarantee crosswind stability.
Ten years after Kamm's DKW,Professor Morelli determined that Jaray's downward sloping nose,rounded fenders,and Von Mises' reflexed-camber tail could easily mitigate any crosswind funny business.
General Motors Research Labs ascertained that in the United States,we experience an annual mean-averaged 7-mph crosswind condition during driving.
On My trip to Bonneville last September,I drove through a storm front in the Texas panhandle which killed a family of five.I maintained 70 mph through 50 mph crosswind unabated until I got into Santa Rosa ,New Mexico that night.Sure,at times it was 'busy',but at no time did I feel endangered.No one else kept up with me.
My opinion is that a boat tail is zero liability.

[sgtlethargic]

Will someone please explain the two front dashed lines? And the rear dashed lines? As I understand it, they're the top view. I don't get why they're longer than the profile view. Another way to say it is why doesn't the 2.5d measurement equal L? Why is there no measurement for the second from the front dashed line? A 3-d model of the template would really help.

[Tesla]

Originally Posted by sgtlethargic

Will someone please explain the two front dashed lines? And the rear dashed lines? As I understand it, they're the top view. I don't get why they're longer than the profile view. Another way to say it is why doesn't the 2.5d measurement equal L? Why is there no measurement for the second from the front dashed line? A 3-d model of the template would really help.

The template is half of a symetrical airfoil, top half represents a vehicle on the ground, because of ground effect the air acts as if the same image is mirrored below ground.

The point of max camber (height) is the 0 point of the template and each line going back represents 10% of distance to tail tip.

2.5 d does = L, remember d is the diameter, that is the top image max camber to the mirrored image max camber below.
and from the 0 point to tip of tail is 1.78d.

So if your vehicle is 48" high then d is 96"

[sgtlethargic]

Originally Posted by Tesla

The template is half of a symetrical airfoil, top half represents a vehicle on the ground, because of ground effect the air acts as if the same image is mirrored below ground.

The point of max camber (height) is the 0 point of the template and each line going back represents 10% of distance to tail tip.

2.5 d does = L, remember d is the diameter, that is the top image max camber to the mirrored image max camber below.
and from the 0 point to tip of tail is 1.78d.

So if your vehicle is 48" high then d is 96"

Thank you. That sheds some light, but there are still questions.

How does 2.5d = L? They are markedly different lengths in the diagram. L is the overall length of the vehicle, and 2.5d is the overall length of the outermost airfoil shape.

What does the outermost airfoil shape represent? What does the other (smaller than the outermost airfoil, larger than the vehicle; not dimensioned) airfoil represent? Are they leading edge air buildup at higher and lower vehicle speeds, respectively? Which are therefore the vehicle's effective airfoils?

[Tesla]

Originally Posted by sgtlethargic

Thank you. That sheds some light, but there are still questions.

How does 2.5d = L? They are markedly different lengths in the diagram. L is the overall length of the vehicle, and 2.5d is the overall length of the outermost airfoil shape.

What does the outermost airfoil shape represent? What does the other (smaller than the outermost airfoil, larger than the vehicle; not dimensioned) airfoil represent? Are they leading edge air buildup at higher and lower vehicle speeds, respectively? Which are therefore the vehicle's effective airfoils?

The outermost shape is the "template", you don't really need to concern yourself with the front, it's from the highest point back that is relevant to this exercise.

I think I should let Aerohead explain this further, I have already started mangling some of the descriptions.

You need to read through the previous discussions below, they will give you a better understanding of the template and it's application.


http://ecomodder.com/forum/showthrea...part-9285.html

http://ecomodder.com/forum/showthrea...rt-b-9286.html

http://ecomodder.com/forum/showthrea...rt-c-9287.html

[sgtlethargic]

Originally Posted by Tesla

The outermost shape is the "template", you don't really need to concern yourself with the front, it's from the highest point back that is relevant to this exercise.

I think I should let Aerohead explain this further, I have already started mangling some of the descriptions.

You need to read through the previous discussions below, they will give you a better understanding of the template and it's application.


http://ecomodder.com/forum/showthrea...part-9285.html

http://ecomodder.com/forum/showthrea...rt-b-9286.html

http://ecomodder.com/forum/showthrea...rt-c-9287.html

This thread is pretty spread out. I might reread it and try to decipher it. I'm craving a concise summary.

Regarding the front end- I'm looking at the template as if I was going to build a car from scratch. I may try to model it using CAD software.

It seems there would've been text instructions to go along with the diagram in the original source.