A question for you engineer types...

"BaconSandwich is tasty." (baconsandwich) 02/09/2019 at 18:43 • Filed to: None

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I’ve been wondering about gull-wing doors lately. In particular, I’v e b een wondering how they affect the structural rigidity of a vehicle. Let’s look at a few examples to see what I mean.

(Image shamelessly ripped from Wikipedia)

In the case of the Mercedes Benz 300 SL, it seems to have a very thick door sill to compensate for the lack of support in the roof. Let’s look at another example:

(Image again shamelessly ripped from Wikipedia)

The Delorean DMC-12 doesn’t seem to have the same door sill. So how is the Delorean’s chassis not floppy as a piece of room-temperature, week-old celery?

How is it possible to have both gull-wing doors, and a stiff chassis without having a huge door sill? Also, how does the missing chunk of the roof affect rigidity along the A-pillar?

I would think that you would want a continuous line from the A pillar up, across the roof, and back down the B pillar to give some strength, in particular in the event of an impact on the top of the A pillar.

Arch Duke Maxyenko, Shit Talk Extraordinaire > BaconSandwich is tasty. 02/09/2019 at 18:58

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That chunk of the roof really doesn’t do much. That’s also how T-Tops are able to function.

My X-type is too a real Jaguar > BaconSandwich is tasty. 02/09/2019 at 19:03

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The Delorean had an X Frame and a Fiberglass Chassis under the Stainless Steel Body Panels. The doors really didn’t even need to be there

nermal > BaconSandwich is tasty. 02/09/2019 at 19:03

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Same concept as a full convertible. Just add reinforcements underneath until it’s stiff enough. 

jimz > BaconSandwich is tasty. 02/09/2019 at 19:04

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the DeLorean was body-on-frame, so almost all of its stiffness would have been determined by that. 

BaconSandwich is tasty. > My X-type is too a real Jaguar 02/09/2019 at 19:04

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Huh, neat.  I’ve never seen that before, and that does make a lot more sense.  I always thought it was more unibody than anything.

and 100 more > BaconSandwich is tasty. 02/09/2019 at 19:08

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The Delorean has sort of a structural backbone down the middle of the car; what would be the transmission tunnel is a rigid structure, and the rest of the body attaches to it.

With t he 300SL, the frame itself is a perimeter structure, widening out behind the front wheels, and narrowing down again to clear the rear wheels, forming a hoop that the interior sits inside of.

sony1492 > My X-type is too a real Jaguar 02/09/2019 at 19:19

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Its practically a lotus

arl > BaconSandwich is tasty. 02/09/2019 at 19:20

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Pulled up behind a parked Tesla X with it’s rear gullwing doors open. It was cool.

Spanfeller is a twat > BaconSandwich is tasty. 02/09/2019 at 19:44

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Note that I say this as a student who hasn’t had material’s resistance... This is just what I suppose that happens;

In the two cases you describe it doesn’t really matter, as both cars are practically body on frame. The body atop it serves little structural purpose.

As for more modern cars, lets look at a Volvo XC40 and a C7;

The red represents the strongest bits of steel, but as you can tell, those are centered around the passenger compartment for safety, wherease even the suspension towers have medium streght metal.

What that means is that the strongest sections of the unibody are for safety, and not structural rigidity; For that the floor sections in orange suffice.

As for a sporty car, lets look at a C7, since wierd doors predominate on sporty cars, this might be more representative;

Even though the C7 doesn’t have roof rails, the car is pretty stiff, because of the floor.

Now, if you added a set of gulwing doors it would add a lot more weight to the roof, and make it wobble a lot more, but with little chasis modification you could avoid a wobbly feeling.

gogmorgo - rowing gears in a Grand Cherokee > BaconSandwich is tasty. 02/10/2019 at 02:34

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Can’t be  any less rigid than a convertible body.

Distraxi's idea of perfection is a Jagroen > Spanfeller is a twat 02/10/2019 at 03:24

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FWIW, strength of steel has no impact on stiffness when you’re in the normal operating (ie below yield) range . Young’s Modulus is the same for all steels, it’s just yield and ultimate stresses that change.