Morelli Shape

[Jim Bullis]

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) .

[Jim Bullis]

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

[Patrick]

Originally Posted by NeilBlanchard

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

DC 2010: EVA/DC converted electric vehicles -- Autoblog Green

[NeilBlanchard]

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?

[Patrick]

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.

[3-Wheeler]

Originally Posted by NeilBlanchard

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

[Jim Bullis]

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

[euromodder]

Originally Posted by Jim Bullis

The degree to which the undercarriage impacts the performance of this Morelli modified, Akron shape is an important issue, (...)

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.

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 ?

[NeilBlanchard]

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:





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.

[aerohead]

Originally Posted by NeilBlanchard

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

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.