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?

Morrelli Shape
 

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.

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

Is this the best/only image that we have of the Morelli shape?

http://img.photobucket.com/albums/v7...2at15322PM.png

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?

Eyeballing, it looks like 0.08m.

That would be just over 3 inches -- doesn't sound quite right?

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.

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.

...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?

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.

Oops,

I am talking about the shape at Miastrada Motors - Side view, large model High vantage point for driverFortified enclosure for safety200-300 "MPGe" for plug-in operation 120MPG diesel operation long trips(At 80 MPH) .

Morelli Shape
 

Old Tele man

The tail evolves from the ideal teardrop but is widened to the tail which is then angled to minimize pitch torque which comes about from the camber.

The main thing is the camber for countering ground effect which is discussed in the context of wingtip vortices. This camber allows the front of the body to be close to the ground but pays for it by providing high ground clearance rearward. Thus, there is high velocity and low pressure forward, but lower velocity and higher pressure rearward. This means that air is first sucked under and then pushed out from under the body, so that the final velocities above and below the tail are equal.

What I call the Morelli rules are the way he uses ellipses to reshape the body of revolution acircular cross sections, yet retains the cross sectional area plan of the original tear drop shape. As I interpret this, the ellipses avoid drag generation as air moves in an S shape along the body length, for the pressure variation reasons I described.

Though I describe this process as Morelli rules, there is still quite a lot of art in how this is actually done since the ellipses can be more or less extreme according to designer choice.

Thanks for the discussion,
Jim Bullis

Right Patrick, that MIT vehicle and the Aptera, too. Maybe Jim can post the page(s) from the Morelli paper?

6" is about where the Schlörwagen was optimized, if I recall the Hucho book correctly. (I have the 4th edition around here someplace...)

Jim, you should start a thread on your vehicle design, so we can discuss it w/o changing the topic here?

I have a copy of Morelli's 1976 paper, but it's copyrighted by SAE so I don't think I can post it here.

I wouldn't mind if Jim also elaborated on the correct shape for the Aerohead Streamlining Template as well.

Or at least a good source for a high quality rendering.

Thanks, Jim.

Patrick, Neil, 3-Wheeler,

I refer to the paper written in 1982 and published 1983 by Morelli. But I have the same concern about copyright as you others do.

I would be glad to look at the Aerohead Template if I can find it. I really am not familiar with this ecomodder site, and tend to get lost. (That is not a criticism since I think I have not given it a fair try.) I will give it a try after writing this.

Neil, I am not sure we have to change topics since the Morelli shape is entirely directed to the issue of running an aerodynamic shape near the ground, and the Miastrada concept is directly related to this issue. I just use a different starting vehicle which is the USS Akron, ZRS4 shape from 1934 tests in NACA wind tunnel reported by Freeman. That paper we can look at since it is public and available both at the Miastrada site and the NASA reports server. (I would try to be more helpful but I am away from home now.) Then I use the Morelli rules to make slight adjustments given that the H value I use is on the upper end of the range tested by him at Pinnafarina (spelling?).

The degree to which the undercarriage impacts the performance of this Morelli modified, Akron shape is an important issue, and it is similar to the issues relating to support of models in wind tunnels. That is for the strut issues. The wheel train arrangement is intended to be a very small profile, single aerodynamic entity on both sides, with almost completely enclosed wheel wells, but the wheel enclosures are themselves pods that form nearly complete closures with the overall wheel train body for straight line travel.

I will try to find a few stray pages from the 1982 Morelli paper that would be fair use of that work.

Jim Bullis, Miastrada Company

Does lifting the main body out of ground effect create such enormous avantages that you can get away with
struts (adding drag and weight);
a 6 wheel drive train (Aptera deleted the 4th wheel to reduce drag) that also needs to articulate to take a corner (complex, more weight);
a retractable canopy and floor (yet more weight);
a rather high CoG (always higher than if the pod was lowered);

and still come out with a high FE ?

Jim and I have started a conversation about his Miastrada design, and my concerns are almost identical to the above post; with the additional one that the aerodynamics of the wheels/batteries/motor(s) in the lower carriages reintroduce the exact issues that raising the passenger pod up high, is supposed to avoid. The driver's sight lines to the ground directly in front of the Miastrada seem quite problematic.

The lower portion will have plenty of aerodynamic interaction with the ground. And, the lower portion will also have an aerodynamic interaction with the passenger pod above it.

So Jim, I am very doubtful that your intended benefit of ultra-low aerodynamic drag is possible with this design. I think it might be possible to get the benefit of the ultra-low drag Morelli concept with highly streamlined wheel pods like these:

http://img.photobucket.com/albums/v7...d/DSC04229.jpg
http://www.cgadvertising.com/media/C...atar-06-lg.jpg
http://www.thesupercars.org/wp-conte...peed-Tilt-.jpg

In fact the Audi Avatar is pretty much exactly a Morelli shape with really sleek wheels on the ground. It would still be a complex structural and controls and entry and exit issues, but it avoids many of the snags that the Miastrada design has.

3
 

Neil,the Ford Probe IV,with front spoiler deployed and air suspension dropped to it's minimum came in at 3.5-inches ground clearance,so maybe 3-inches is realistic.
Modern low profile tires would allow 'rim' height criteria for minimum ride height to be respected.

If it is 3"+, then Jim doesn't have to do proverbial back handsprings to raise his car high off of the ground?!

Morelli's Cds
 

Jim,does Morelli go into any of his wind tunnel protocols?
Back in the late 70s the CNR model car created quite a stir with Cd 0.161.
In later articles about the full-scale development car,it was reported that this form achieved this low drag and then "when wheels were added and the car lowered onto the ground the drag jumped to Cd 0.34.
With additional work,and with a cooling system and cabin ventilation they believed that the car might achieve in the range of Cd 0.201-.23.
This is the reason I've had guarded enthusiasm for the new form.
No one else has ever achieved a 3-D technical system which scored lower than Cd 0.04 in free stream,above critical Reynolds Number,and that would translate to Cd 0.08 in ground image reflection,after Jaray/Prandtl.
Morelli's shape is a 3-D variation on the Von Mises wing profile with reflexed-camber tail.
According to boundary layer theory it should be impossible for the flow to remain attached under the tail.It violates everything ever investigated for diffusers on cars with excellent onset flow from ahead and with perfectly smooth bellies.Unlike the wing in 'flight' condition,there is no free stream below the body to pump momentum into the boundary layer.The wing is operating at zero separation and is governed by skin friction,Morelli's form would be governed by pressure drag should separation occur.
The 'banana' car had pontoons blended into the body which acted in part to communicate base pressure forward under the car to cancel lift and also had a ducted rear bumper to also expose underbody flow to the wake's low base pressure.
The Morelli shape as depicted possesses none of these features.
I don't know how it would work.Western Washington State University's Viking series of cars used a milder version of this form and never achieved remarkable Cds.

source
 

Jim,the 'Template' is based on a 2.5:1 streamline body of revolution.I generated my image as a photo-enlargement from Hucho's drag table.
I concentrated on the aft-body,as Hucho and all the other PhDs say the fore-body is of lesser importance in light of today's auto bodies.

Cds
 

Jim,if you can snag a copy of Sighard Hoerner's book,Aerodynamic Drag,he's got formulas to convert Cds from surface area,volume,and frontal area.
He also does a minor drag breakdown on airship 'Los Angeles' ( LZ 126 ) designed by Paul Jaray,perhaps similar to the Akron.

Google found this elsewhere on this site: Morelli's design all tweaked for the road. Road & Track did a feature on it.
1978 CNR - Pininfarina - ??????????? - ????? 100000 ?????????? ???????????

Neil,

Audi thing shown does not follow what I call Morelli rules as far as the elliptical cross section requirement. Thus, air moving toward the low pressure region under the vehicle will traverse a most un-aerodynamic ridge, and again when it flows upward toward the rear the same issue comes about.

However, the Avatar pretty much meets my definition of struts holding the body apart from the wheels. Somehow it looks more like a fashion design effort pretending to be aerodynamic, but maybe not.

bicycle bob,

It might be that this is a Morelli design, but it bares scant resemblance to the Morelli shape that accomplished such good aerodynamic performance.

We have to get the Morelli paper of 1982 somehow, in order to see the difference. Again, Prof. Thacher's book on solar cars discusses the important points. But that also is under copyright.

aerohead,

Hoerner's book is also informative but not all that free of the conventional automobile straight-jacket.

I think the Los Angeles is another airship along the lines of the 1906 Fuhrman (Prandtl's student) airship. They really seem about the same, and the only reason I specifically use the USS Akron zrs4 is that the testing reported by Freeman 1934 is by far the most complete and the best explained. It also was done at a scale where the actual test body was about the size of a car, so no real scaling is even needed. That report is free and very well detailed.

Neil from 3:34 pm.

Jim (that is me) has to do handsprings because he is not using a Morelli shape; the USS Akron is the basic shape with only some tweaks according to Morelli's guiding principles.

The Aptera does not have to do handsprings because it is almost exactly a Morelli shape,except for the rear wheel which is on centerline so it might not cause too much of a problem. However, the Aptera is plenty long, but still has no rear seat, since the Morelli shape requires the underside curve that cuts into where the floor would need to be.

Right, the Morelli shape, and the Aptera are specifically meant to provide side-by-side seating. And the earlier Aptera prototype "Zen" had a Cd of just 0.11 -- I think that will be hard to beat.

The only other car with actual wheels on the ground that has an even lower Cd is the Mercedes Bionic model, which has a Cd of 0.095:

http://img.photobucket.com/albums/v7...ar-Body-lg.jpg

This is the basis for my CarBŒN Concept EV Open Source Project.

The basic boxfish model had a Cd of 0.06:

http://www.ae-plus.com/Car%20compani...05C2545_45.jpg

It has a nearly square cross section and so the interior volume is very usable.

Neil,

I might be mis-remembering but the boxfish work I read about said that the Cd of .095 was for just moving the ideal shape close to the ground. Wheels made the Cd come up quite a lot more.

Neil,

I want to also say that this seems like a very good way to approach the problem, even though we might differ a little on the numbers.

Hi Jim,

I'm pretty sure that the free space number on the boxfish shape was 0.06 and the 0.095 number applies to the blue model with wheels. There is a later blue model with open wheels (no mention of it's Cd) and the final "real" Bionic car with diesel engine and open wheels (partial rear skirts only) with a Cd of 0.19.

The 0.095 is the lowest number I have ever seen for a wheeled car -- I have confirmed that I am remembering it correctly. Since it already has wheels, that issue is removed... Unfortunately, that is the only image of the model I have ever found, so extrapolating all the key bits is not easy.

And as I said, since the section is basically square-ish, the volume inside is very practical and usable.

OT - here's a video on the Bionic Car: http://www.youtube.com/watch?v=qXEJHCuWliU

...cute illustration.

Patrick, you are a scholar and a gentleman! That video had an all too brief glimpse of the earliest Bionic/Boxfish clay model, and I've done a series of screen captures (low rez but much better than nothing!), and posted them here:

http://ecomodder.com/forum/showthrea...tml#post192455

You can't compare the Cd of full-size cars against clay models. In the translation from model to reality, M-B added 0.10 to the Cd. Some of that was from altering the basic body shape for more usable interior space, but they also added panel gaps and dozens of necessary features like door handles and brakes.

Anyway, you've seen lower drag shapes: the Goldenrod salt flats car, most EcoMarathon cars, some early 80's concepts from Detroit, and probably even the AeroCivic and Dolphin.

Hi Matt,

Mercedes may have accounted for the scale difference/Reynolds Number by increasing the velocity; we don't know? I tend to think that they know enough to have the right number. The final Bionic is a real car with a Cd of 0.19, and the progression up from the fish, fish model, car model, to the built car, all fit.

The Goldenrod has a Cd of 0.11-0.12. You could be right about the Dolphin, but the AeroCivic is ~0.17.

Neil and all,

I like to think it is possible to get beyond the limits of the standard car. It will never be possible to actualy achieve .04, but that should be the target.

Daimler Benz started out with the boxfish, but then reality set in, which means the bankers took control. And of course MB is not willing to break out of the 4 wheeled box that has been set as the standard for motor vehicles.

If a car could actually have an overall Cd of .07 and a frontal area half that of the conventional car with double wide seating, we might see energy needed for cars cut by 75% or so. That would start to change things.

It can be fun to put different moldings on production cars, and some stuff can be learned, but for real innovation we need to really think about getting free of the ground effect and conventional wheel arrangements.

Jim,

I truly think that 0.1 is the lower limit for a street going car; no matter how many seats it might have. Even the 0.095 car had no cooling or circulation intakes. The best Aptera did was 0.11.

I just don't think you can take a Cd 0.04-0.06 "ideal shape" and put wheels on it, and put the wheels on the ground, and do it without hitting 0.1 or so. It just can't be physically done.

The fact that the 0.095 car has wheels and is that low Cd is amazing enough. The wheel skirts are unrealistically low clearance -- change that just a smidge, and you're up over 0.1.

I think it is pretty cool that nature and evolution has fine tuned things so well. Also, check out the structural "innovation" of the boxfish; with it's hex structure within the skin.