rebel
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 posted on 16/9/02 at 10:21 AM |
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Chassis question
is there a need for the chassis member R which runs from Q and joins up to T. i think it is there to stiffen up the pedal box area.
but is it really needed 
Are you sure that goes there?
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semi42
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| posted on 16/9/02 at 09:07 PM |
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Its there to stiffen the engine bay area ,and reduce twisting of the chassis due to the torque of the engine, note the torque stiffener on the
opposite sie at the rear (z).I'd recommend you install them.
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cymtriks
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| posted on 16/9/02 at 09:09 PM |
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Yes, it is needed. Tube R is the only diagonal across the top of the engine bay and accounts for, I would estimate, about 10 to 20% of the chassis
stiffness. If possible you would do well to double up tube R by having one on each side of the frame (check engine clearance first). You might be
interested in reading one of my earlier postings regarding advice on chassis design where I state how to double the chassis stifness while reducing
the weight and number of tubes. This is based on an analysis using the same software that mass manufacturers use but you will need to check that
clearances between the chassis and other parts are still OK for your build if you use some of my mods.
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jcduroc
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| posted on 17/9/02 at 10:50 AM |
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Which software is it by the way?
Joćo
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cymtriks
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| posted on 18/9/02 at 08:49 PM |
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I'm using NASTRAN. For the lowcost model I typed in the node and element pattern using the VI editor as it is relatively simple and is composed of
plain shell and beam elements. My work involves a large ammount of manual, as opposed to automesh, construction of FE problems so this approach is
perfectly normal for me. I'm applying the torsional load by using two vertical loads, one at each front spring mount while the constraints are simple
single point constraints at the rear spring mounts, rear tunnel centre and front centre. My results are very similar to a colleagues analysis of a
Westfield which was done entirely independently of my model. I've also had a look at some other kit cars and have found that my results generally
agree well with the few quoted figures that I've found. One surprising thing is that a lot of spaceframes are worse for their weight than a basic
ladder frame and that the same design mistakes are repeated again and again. The most common mistakes are inadequate triangulation or welded paneling
of the front suspension region and of the engine bay. This applies equally well to midengined cars.
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Simon
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| posted on 18/9/02 at 09:10 PM |
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Chaps
When I visited Luego, they suggested (as my eventual power supply will be RV8) that R be replaced with two "R's" - one on each side, obviously not
running from the front, but at very approx 45 deg from respective tunnel tubes to outer rails.
cymtriks - just as a matter of interest, Rover quote something like 27000 nm for the torsional strength of the Rover 75. I take it that's quite good
(forgive phraseology - I'm not an engineer by trade, just think it would have been a more interesting path for me to take!!)
ATB
Simon
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cymtriks
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| posted on 19/9/02 at 08:05 PM |
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27000Nm, about 20000ftlbs, is high even for a modern large saloon like the 75. A good rule of thumb is that the torsional stiffness in ftlbs per
degree should match the cars on the road weight in lbs for a road car with adequate abilities. That weight includes the driver, petrol, etc. For a
sports car or racing car the stiffness figure should be twice or thrice the weight of the car. The 75 easily exceeds these guidelines which helps to
explain why it gets good marks for its chassis in road tests and why MG are considering putting a 4.6 V8 in it.
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