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Old 04-12-2012, 06:21 PM   #301 (permalink)
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long

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Originally Posted by drmiller100 View Post
Real world is sometimes different then wind tunnels.

Real world says too short is pretty bad.

Too long is almost exactly the same as "perfect."

Form drag is orders of magnitude worse then skin drag.
If you have to choose,go long.The friction increase is nothing compared to pressure drag if you lose the boundary layer.

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Old 04-12-2012, 06:38 PM   #302 (permalink)
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plan taper

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Originally Posted by NeilBlanchard View Post
Wow, plan taper adds as much as 0.09 -- or maybe ~42.5%. That is huge.

If the ideal taper in the side profile is maximum of 22 degrees, then what is the ideal plan taper? This will greatly shorten the length of the back of the body.
The plan contour would mimic the contour in elevation.Everything depends on where the max roof camber point is with respect to the point of max body width,as this is the zero-point for beginning the plan taper.And the pan-taper would never exceed 22-degrees as well.
On the 'Template',technically,the zero points are at the same location,as we're working with a body of revolution.
In the real world though,the body needs to be more narrow,so we have to morph the top and side contours together best we can.
As Frank Lee has mentioned a number of times,if the body is 'tall' let width be the dominant factor for the taper.
If the car is wider,use the height.
If they're the same,do each equally.
-------------------------------------------------------------------------
If you want to see some minimums,GOOGLE:
Fairchild C-82 Packet
Fairchild C-119 Flying Boxcar
Fairchild C-119J Beaver tail
Bristol 170 Wayfarer
Gotha Go 345
Armstrong Whitworth Argossy
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Old 04-12-2012, 07:59 PM   #303 (permalink)
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Here is the plan view of the C-82 and C-119


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Old 04-12-2012, 08:15 PM   #304 (permalink)
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Surely that thing lost attached flow at the rear . The angles are so steep !
If there is still indeed attached flow all the way back, is this do to the combination of the plan taper and side taper working together ?
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Old 04-12-2012, 10:41 PM   #305 (permalink)
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I highly doubt they'd design a fuselage that doesn't have good flow all the way back, especially with the empennage right there behind it, which requires good clean flow to work.
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Old 04-13-2012, 01:14 AM   #306 (permalink)
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Any one knows where to get the aerodynamic streamlining for the Aptera car?
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Old 04-13-2012, 01:19 PM   #307 (permalink)
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Google "morelli body".

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Old 04-13-2012, 05:00 PM   #308 (permalink)
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flow

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Originally Posted by Cd View Post
Surely that thing lost attached flow at the rear . The angles are so steep !
If there is still indeed attached flow all the way back, is this do to the combination of the plan taper and side taper working together ?
According to Mair,the flow would be separating as soon as the angle exceeds 22-degrees.
One of the sites at the GOOGLE C-119 is by a pilot who flew the 119.The plane was incapable of in-flight load drops,so if they did drops they simply removed the doors.He claimed that airspeed suffered without the tail ( no numbers reported ) so even as a mediocre boat tail,it was preforming a drag reducing function.
The C-119 J was produced at the end of production and you can see how the tail was extended.
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Old 04-13-2012, 05:05 PM   #309 (permalink)
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clean flow

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Originally Posted by Frank Lee View Post
I highly doubt they'd design a fuselage that doesn't have good flow all the way back, especially with the empennage right there behind it, which requires good clean flow to work.
Frank,I would just have to presume that there was some of that 'phantom' tail phenomena going on,with a small burble of turbulence just aft of the tail,and the outer flow just skipping off it as Kamm and Korff and Morelli and others have reported.Don't know.
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Old 04-13-2012, 05:15 PM   #310 (permalink)
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side wind

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Originally Posted by drmiller100 View Post
for the sides, the real number is 22 degrees minus side winds.

I don't think 22 degree sides is realistic in the real world IMO.

The top of the car is not affected by side winds.
If an auto maker wants to brag they'll quote the zero-degree drag coefficient.Some companies test for yaw and report a crosswind-averaged Cd.
In 1987,the Arivett Brothers designed a streamlined Top Fuel dragster which had Cd 0.20 at zero-degrees and Cd 0.18 at 12-degrees of yaw.The best funny cars of the day were measuring at around Cd 0.60.
I'll be posting some 'streamlined' cars of the past,soon I hope,and you'll see that some were designed for plan-view,with fineness ratios which would mimic a streamlined section,rather than a streamlined body of revolution.
A section of 3.92:1 has the lowest drag,so the boat tail angles are more generous.

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