Flat or Teardrop?

[mistareno]

If I use the VW floorpan, I could get away with a shape like below and still cover all the hard points with 13inch wheels.

It would use 4 large semi flexible solar panels. The front 2 panels would tilt forwards to allow fairly easy entry and exit and to allow access to the front storage area. The battery pack would be behind the front seats and the motor would sit in the cavity where the VW gearbox would normally reside driving a diff from an E30 BMW or similar in direct drive.

The dimensions would allow sufficient overhang at the sides to allow the front wheels to turn full lock and not foul on the sides. I would run a 'straight ahead' fairings on what was visible of all 4 wheels.

It would be quite large in plan at 1980mm wide and 4900mm long but the frontal area should be pretty small and the 2D nature of the design should make it relatively easy to manufacture. I can further reduce the weight of the donor floor pan by replacing the steel floor with aluminium panels.



These are the solar panels I wish to use.

They are 24V and 300W each.

They weigh 9 Kg each and are 2020 x 990 x 2.5mm.

I could fit additional panels on the sides but their value would be minimal unless the sides could flip out when parked.

[aerohead]

Way fun project!
Consider a couple of guide-ons or camera system for the front corners,as your going to have difficulty discerning where the front of the car is from your seated position.
'don't want to crunch that beauty!

[aerohead]

Here is a cleanup of the drag/power table for the 1996 HONDA Dream WSC winner.
The blue area is Rolling-Resistance
The yellow,aerodynamic
At 99.419 mph,the car requires only 5.862 kW (7.861 hp)
If you give it the powertrain mechanical efficiency of a 1962 pickup truck and the BSFC of a Chevy V-8,your looking at 188 mpg @ 99 mph.
This is the game you're entering into.

[freebeard]

The plan appears logical, except for the 8 solar cells to either side of the passenger compartment. Do they come as small subsets of the four big ones?

You know what it reminds me of? Joseph Ganz's Mayfly:



and that Bugatti Stratos concept:



Here's what the Stratos concept did to deal with the crosswind problems you get with those slab sides


The best way to approximate a compound curve with a rectangle would be to leave the central diamond flat and roll each of the corners down. That would introduce gaps in the middle, front and back, and either side of the doors. But it would help crosswind performance. In the real world it's always a crosswind.

Edit: Think about fineness ratios. The headrest fairings and wheel spats should be 10:1 but the main body can be 2.5-4:1. I estimate yours as about 10:1 and Ganz's as 4:1. Maybe I should be taking twice the height—aerohead may have an opinion.

But consider a stretched version of the Ganz profile. The front panels could roll over the front wheels and drop down to lower the beltline, and then the rear panels roll over the rear wheels to provide a bluff body for the turbulence from the open cockpit to reattach.

What is your measured wheelbase. It looks to be a foot or more long. A 165/50R-15 tire has a 2 3/8" sidewall, and so a 20 1/2" diameter on your 15" rims. Else Rabbit 13" rims might clear the brake parts.

[mistareno]

I'm a little restricted in overall shape by how far the solar panels can curve.

That shape is probably getting close to the curve limit.

I legally need the front to be section to be above 400mm so I can fit the headlights and Number Plate in the front curve. The front will be a tight radius curve of lexan. I can't really fit the headlights anywhere else with the solar panels.

The little solar panels are just to fill in the gap. I'm sure I can find something in a similar size or even just make my own.

I was planning on running 13 inch wheels with a 135/80R13 tyre which is why the wheelbase looks long. It's pretty much to scale with that tyre.

[freebeard]

I'm looking at these with a 4" brass caliper held up to my screen. YMMV The Beetle has a wheelbase measured at 2 1/4" and a cowl height of 3/4" — 9/3. Your drawing measures 4 1/4" and 1" — 17/4. If that's a small-diameter wheel, then it's an even tinier mannequin (blue dot to top of head = wheel diameter suggests 5' figure). I know it's a lower seating position, but still...

If you move the 0° camber point forward, there would be more curvature in the front facia and less needed in the solar panels. Are the windscreens transparent over the solar panels? You could have a legal-height light in the front of each one and the melt-the-roadsign-reflectors lights low on the front or they could pop up out of the headrest fairing.

I'm curious about transmission you mentioned. My thought was to get a small enough motor that you could take the gearset and nosecone off the transaxle and stuff it inside the case.

[mistareno]

Originally Posted by freebeard

I'm looking at these with a 4" brass caliper held up to my screen. YMMV The Beetle has a wheelbase measured at 2 1/4" and a cowl height of 3/4" — 9/3. Your drawing measures 4 1/4" and 1" — 17/4. If that's a small-diameter wheel, then it's an even tinier mannequin (blue dot to top of head = wheel diameter suggests 5' figure). I know it's a lower seating position, but still...

If you move the 0° camber point forward, there would be more curvature in the front facia and less needed in the solar panels. Are the windscreens transparent over the solar panels? You could have a legal-height light in the front of each one and the melt-the-roadsign-reflectors lights low on the front or they could pop up out of the headrest fairing.

I'm curious about transmission you mentioned. My thought was to get a small enough motor that you could take the gearset and nosecone off the transaxle and stuff it inside the case.

Thanks for the feedback.

I think cooling of the motor would be a problem if it was enclosed, but it might save weight. I really need a small lightweight alloy diff...maybe a Subaru rear diff or similar.

The pan I'm thinking of using is a Type 3 with trailing arm rear end.

I'm not sure if the wheelbase is different but I got it as close as I could using the rulers on paintshop...

Yeah, the windscreens I'm thinking of are clear plastic off a motorbike.

Yeah, the shape may change a bit depending on seating position and legalities.

I'm just trying to get a plan together so I can talk to the engineer before I start so I don't end up backed into a an expensive corner down the track.

[freebeard]

You have an engineer? Do you know your auto history? Here's the Bugatti 'Tank', the Type 32

Specifications:

Wheelbase: 78.5 in (1994 mm)
Track: 41.4 in (1052 mm)
Power: 90 hp (67 kW)

Notice the plan taper ahead of and behind the axle lines. It wasn't enough to make it a successful design. It came in third in one race. Have you thought about considering other solar panel options? The long narrow strips on that solar racer look more managable. Personally, I'd prefer 4" hexagons that snap together with conductors in the edges.

A Type III pan, eh? The front footwells aren't so cramped, but do you know about the differences in the front suspension? The framehead comes out in four fingers to hold a stamped axle beam.



The best thing about the Type III is the front and rear suspensions are both on rubber isolated subframes, so they ride real nice. And you can adjust the torsion bars front and rear with the stock parts.

What do you plan for between the flooprpan and the solar panels?

[mistareno]

In Australia, modifications have to be approved by a Government Approved Engineer to ensure the car is safe and complies with all the regulations before it can be registered and driven on the road. If you can present a plan before you start, the engineer can look it over and tell you what needs to be changed so you don't end up with an expensive boat anchor at the end.

The 'tank' has much more frontal area than I'm hoping for but I will try and taper the edges to prevent votice formation, but it's a compromise between having maximum solar area and aero. If I can keep the frontal area really small, the slab sides hopefully wont be too much of an issue.

With 13 inch wheels and a small tyre, the suspension beam will be the highest chassis hard point on the car.

There will be a spaceframe chassis between the pan and the panels that will also house the batteries and other associated electronics. I'll probably use a chromoly steel to keep the weight down. I may even get it made from alloy tube and bolt the spaceframe to the pan. I'll calculate the weight difference and go from there.

I want to house all the EV drive stuff behind the front seats to keep cable runs short and to keep the weight balanced and low.

I tried calculating a few other solar panel options but none could provide the same output in the available space. I may end up using some smaller panels or single cells on the sides, but I'm not sure how much benefit they will provide (although the sun is rarely directly overhead)...

[freebeard]

The 'tank' has much more frontal area than I'm hoping for but I will try and taper the edges to prevent votice formation, but it's a compromise between having maximum solar area and aero. If I can keep the frontal area really small, the slab sides hopefully wont be too much of an issue.

If you take the shape of the Bugatti, only above that swage line 10" above the ground, and the diameter of the wheel w/o the tire, it's a pretty close match to your plan—given that the wheelbase is 18" less and the track is 10" less than the VW.

The plan taper is less than what would be helpful; but the real problem is the 90° edge between the top and sides. Theory wants a minimum radius 4% of the gross width. With your 86" panels, that adds 7".