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Is there any structural purpose to the skuttle area? Could there be?

Would it help or hurt anything to make it as part of the frame?

Not being an engineer I can only guess that it doesn't make a huge difference. There seems to be 3 ways to do the scuttle. The first is the book way. Fabricate it as a unit and bolt it on. If I had to guess which style is strongest I'd say it's that style but it's not as light as the other styles. I went this route and found it easier to fabricate it off the car, paint it, and bolt it on. The second route is the fiberglass scuttle, quick and simple. There is still some frame work under for the mounting the steering etc. so there's a bit of strength added that way. The third style is the original Lotus 7 style. Basically a hoop welded to the frame plus some added parts. Look on the Simplesevens site to see photos of original Lotus 7s.

Ron

It is a god thing for some structure in there. If you don't have a roll cage, you should put a double hoop inside a fiberglass scuttle. Then put some sheet metal to fill in the double hoops. It would be nice to have a beam across there but that makes it harder to get in and out. Look for some prints/pictures of the "DSK" model seven for hints.

This is from memory, so maybe I'm off. Anything you can do to provide strength or stiffness across the top of the cockpit is a good thing. I'm not talking about heavy structure though.

At least stiff enough for the screen or Windshield you plan to use...

Hi Carson-
Welcome to the group!

In my design- and I've actually welded up this part!- the shape of the scuttle is defined by the front roll hoop, which extends upwards from the lower frame rails. It is an integral part of the chassis and does add appreciably to the stiffness. I'll have a shot in my build log... Soon as I start one...

Have a good one-
JDK

I never built any really strong structure into my skuttle, mostly since I used the one piece fiberglass one from Kinetic. My steering column support was only as strong as it needed to be to prevent steering load induced flexing. After the fact I regretted not beefing it up some. Beyond stiffening the frame, I think it will make your car safer. Driving my car at night I often wondered what it would feel like to have a 180lb. deer land in my lap at 60 mph. Also consider that a book frame is only 13" tall. Add your ride height to that (a generous 6") and you you get 19" of area that is effectively behind steel structure. Now imagine driving you locost under a parked truck or guard rail that is 20" high. The first thing that hits this object 20" off the ground, after of course your fiberglass nosecone, valve cover, fiberglass scuttle, and steering wheel is going to be your face. A good stiff bar extending up the hieght of your scuttle will add another 8" to that 19" or steel reinforced space, bringing it up to 27".

Look at Hempy and Moti's use of roll bar type reinforcement as excellent examples. (though perhaps bordering on overkill for a street car- since they are both track cars of varying degrees)

How much ground clearance does a deer have anyway?

If you look at the Prince blueprints for the original Sevens, you can see a small tube goes up around the inside of the scuttle. In the DSK version there are also small braces from that tube going forward to the next vertical members. If you put something like that in that will be a help.

Another option if you have the trans set far enough rear for gear shifter clearance, is to run tubes up from the trans tunnel to the scuttle cross tube.
Dave W

I always wondered why more folks dont connect the trans tunnel to the "dash"...

I've always invisioned putting in a "terry hoop" on a Seven type frame. The big downside is it would limit how wide ones legs could be. Here's a link to a pic of the "terry hoop" on a Lotus 23 chassis (the pic is way too big) : http://www.elitefab.com/000_0345.JPG

Also, on some of the later Lotus sports racers (15 & 17's) and the Caterhams, the dash hoop was gussetted at the corners to add some strength.

As for the scuttle itself, mines a Caterham one and is just Aluminium without any reinforcement for the windscreen stantions. Its held up just fine and has seen 100+ mph without any failure.

Cheers,
Rod

You don't need the wide parts on the side to get benefit from that type of dash and under knee reinforcement. I suppose more is better, but that is not a reason to not to make the dash the way that picture above is. The important part of the way the dash is made is the upper and lower tube parts connected by a sheet metal shear web. Since you can't so easily connect it with a direct tube, you build a bridge which is a curved I-beam...

My FF does that for it's dash area, even though the lower part is just 1/2" tube. You also see the cross member under the knees sometimes done that way too. The description of the DSK model Seven specifically mentions the effort that went into strengthening that part of the Seven frame because they felt it was lacking.

I've always thought that not using the scuttle frame as a structural member is a lost opportunity. My car (although it's a middy rather than a traditional Locost) has a fully structural scuttle, using the sort of "portal frame" that cs3tcr referred to above. Here's a shot from when the frame first came off the build table onto the ground (at ride height).


And here's a closer look at the passenger side stiffening web - it's 1mm steel sheet and the lightening holes have been flanged for stiffness (and looks )


Hope this is of interest,

Dominic

Dominic, that looks nice. You also have wide and structural side rails. I think that is a good tradeoff when you don't need the drive tunnel anymore with a mid-engine.

yes, looks very solid

Thanks for the compliment. Quite a bit of thought went into those side rails - they provide (hopefully) lots of strength as well as improving side impact resistance (hopefully that'll never get tested!). Because they're out at the sides they should contribute more to stiffness than a centre tunnel does too for the same reason that a tube is stiffer than the much smaller solid metal rod made from the same amount of metal. The further from the "neutral axis", the greater the contribution to stiffness.

The proof will come when it gets its (mandatory) beaming and torsion strength tests. It has to reach at least 4,000Nm/degree in torsion (I think that's about 3,000 ft-lb/degree). A "Book" Locost chassis will not make 4kNm - I'm hopeful that this chassis will beat it easily. Hopefully it'll get tested sometime in the first half of this year.

Anyway, as I said originally, don't miss the opportunity to make something structural rather than just "cosmetic".

Dominic