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Old 07-12-2008, 04:02 PM   #1 (permalink)
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Morelli Shape

I see mention of the Morelli shape and am trying to find a detailed description of his work in 1983. The pictures I have found look very much like the Aptera, except with integrated wheels.

This is an important topic since the Morelli shape could represent a major breakthrough in automotive aerodynamics. But I would not be sure of this until I saw the details. Curiously this result came out in 1983 but has largely been ignored as far as I can see.

Does anyone have real data on this?

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Old 07-24-2008, 04:53 PM   #2 (permalink)
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Morrelli Shape

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Originally Posted by Jim Bullis View Post
I see mention of the Morelli shape and am trying to find a detailed description of his work in 1983. The pictures I have found look very much like the Aptera, except with integrated wheels.

This is an important topic since the Morelli shape could represent a major breakthrough in automotive aerodynamics. But I would not be sure of this until I saw the details. Curiously this result came out in 1983 but has largely been ignored as far as I can see.

Does anyone have real data on this?
What your looking for is in Hucho's book.It's shown at the bottom of a table of aero forms.And it is virtually the Aptera form.Thing is though,the numbers are for free-stream flow,up out of ground-effect.I've not kept abreast of the most recent developments and personally do not no if Dr.Morelli's shape was ever tested with wheels attached and on the ground plane.The lowest drag form that I know of,occurs in the same table as the Morelli shape.It's a body of revolution,like the 2.5:1 teardrop,has a Cd0.04,has a Cd 0.8 in ground effect,and Cd 0.13 with wheels,same as Paul Jaray's "pumpkin seed" of 1922.Don't expect any "Miracle-Shape" to emerge from any wind tunnels,including MITor Pininfarina.All the fundamental research was done long ago.
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Old 07-24-2008, 05:53 PM   #3 (permalink)
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OOOOOOOOOOOOOOOOOps!!!!!!!!!!!!!!!!

I made a mistake! The Morelli shape is in my phil knox aerodynamic photo album.The image is in the third book down the page in book illustrations.It has Cd 0.5 in ground effect,not 0.08.Adding wheels typically would raise the Cd to 0.10,not 0.13.This would match HONDA Dream-2
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Old 09-02-2010, 01:57 PM   #4 (permalink)
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Is this the best/only image that we have of the Morelli shape?



BTW -- hi, Jim! I realize now that we have been hanging out in some of the same places.

Also, the Morelli shape is premised on the ground plane -- does anybody know what the "H min" dimension is?
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Old 09-02-2010, 03:21 PM   #5 (permalink)
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Eyeballing, it looks like 0.08m.
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Old 09-02-2010, 03:27 PM   #6 (permalink)
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That would be just over 3 inches -- doesn't sound quite right?
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Old 09-02-2010, 04:39 PM   #7 (permalink)
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Morelli Shape

Neil,

Since these posts I managed to track down the 1983 paper by Morelli.

And by the way aerohead, this shape is given short shrift in the very comprehensive Hucho book, which represents the mainstream thinking (not much innovation) of the auto industry.

The book on solar vehicles by Eric Thacher discusses this much better than anywhere but the Morrelli paper itself, which Thacher helped me find.

I am not at home now so I can not give the full reference, but it was a 1982 paper published in a book that was a symposium proceedings.

But as to the value of H, as I recall the Hmin shown got down to about 6 inches, but H was a variable for the testing and started at about half the maximum width.
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Old 09-02-2010, 04:49 PM   #8 (permalink)
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aerohead,

No, the Morelli shape is not a miracle shape, but the discussion of aerodynamics backed up with test data is quite excellent in the actual 1982 paper by Morelli.

But in that paper, Morelli does not proclaim this shape to be a great answer in the real world, though it gets a Cd of .047 for the low to the road position. He goes on to discuss the essential changes that would be needed, including wheels, and this pushed Cd up to .19, again, as I recall, for wind tunnel tests of that form.

My appraisal is that the Morelli shape is quite inefficient from the volume perspective, even though Cd defined on frontal area is very low.

It might be of interest that Cd for airships in the old test data is defined on a volume basis, specifically, the cube root of volume squared to get area like dimensions.
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Old 09-02-2010, 04:52 PM   #9 (permalink)
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...correct me if I'm wrong, but isn't the back end of the "dolphin-like" Morrelli shape purpose to keep the aerodynamics from (a) creating positive lift (ie, a "wing") and trying to fly, as well as, (b) creating negative lift (ie, a "brake") and trying to create too much downward force?

...thus, to most efficiently have the separated upper and lower air streams re-converge as seamlessly and smoothly back together with absolute minimum drag creation?
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Old 09-02-2010, 04:53 PM   #10 (permalink)
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By the way, the current shape that I show is for the USS Akron, but slightly modified with what I call the Morelli rules which are discussed in that paper.

I still rely on a significant ground clearance to preserve the Cd of the airship, but added a slight camber to make a better view for the driver as well as to give a slight tuning out of the ground effect.

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