Windscreen frame query

[mallockat]

Hello everyone, I'm new here having just bought a LWB Roadster (Marina) needing a little TLC, although it has a nice patina. However, I'm not new to Marlins, having owned a SWB roadster in the late 80s/early 90s (SDX 900J).

I've never liked that ugly windsreen frame, even though I know that it serves as a "sort of" rollover bar. I say "sort of" as it's not braced or triangulated in anyway, and in the event of a serious roll would probably collapse. Having hillclimbed and sprinted many kitcars, not to mention a Mallock Mk14, it is my intention to fit a rear mounted rollover bar to RAC MSA spec, and so would like to cut off the windscreen frame and fit aeroscreens. This is just one of the many modifications I have planned for my car. Question is... how much torsional strength does the windscreen frame actually contribute. I would have thought very little due to it's unbraced open design, and also bearing in mind that there is a hefty brace beneath the dash, between the door pillars.

Anyone have any thoughts regarding the removal of the frame from a structural point of view. Thanks for looking.
Cheers Chris.

[jon_cox]

Re: Windscreen frame query

Hi Chris,
Take a look at modern convertibles. A case in point would be say the Audi A4 convertible. This car has a very stong structure, similar to that found on the roadster, beneath the pretty outer skin of the windscreen surround. It has been tested by Audi to withstand a rollover type accident and it protects the occupants well.
You say there is no "bracing". The bracing is provided by the glass. Modern cars all use the glass as part of the structural regidity which is why they are now glued / bonded in place. Paul Moorhouse was ahead of the times when he used this method on the roadster. Paul did some testing on the car in the early days which was shown in a kit car magazine of the day which pictured the results of rolling the car. These pictures may still be available from somewhere.
However, the chassis is made from ludicrously thick box section and I am sure if the frame was removed it would have little effect on the torsional regidity of the car especially if all the alloy panels are bonded to the chassis as well as bolted using silkaflex or silicon sealer.
If anyone has a 3D CAD model of the chassis then I will do some FEA (Finite Element Analysis) to get you some accurate results.

[ggrum]

Re: Windscreen frame query

Hi Chris,

I remember talking to the owner of a purple roadster in Devon who had removed the screen frame and fitted aero screens and he didn't think it had any detrimental effect. It also looked good.

[mallockat]

Re: Windscreen frame query

Thankyou very much for your replies. I think I may go ahead and do it! I'm trying to make it more aesthetically pleasing (subjective I know)and also trying to reduce weight wherever possible. A little here...a little there all adds up.
Cheers Chris.