Chassis torsional stiffness 1965 and today
Chassis torsional stiffness 1965 and today
(OP)
http://www.sportscars.tv/Newfiles/Chaparral2.html
About 1/3 way down the page.
"The Chaparral Frame
The basic frame of the Chaparral 2 is a most interesting and unusual piece of engineering. It was conceived jointly by Hall and Andy Green of PlasTrend, Fort Worth. The design requirements laid down by Hall called for a maximum frame weight of 150 Ib, combined with an axle-to-axle torsional rigidity of at least 3000 lb-ft deg."
3000 lb-ft/degree ~ 4040 Nm/degree
Are all modern cars so much stiffer than an early Chaparral?
http://youwheel.com/home/2016/06/20/car-body-torsi...
Please say it isn't so !!
About 1/3 way down the page.
"The Chaparral Frame
The basic frame of the Chaparral 2 is a most interesting and unusual piece of engineering. It was conceived jointly by Hall and Andy Green of PlasTrend, Fort Worth. The design requirements laid down by Hall called for a maximum frame weight of 150 Ib, combined with an axle-to-axle torsional rigidity of at least 3000 lb-ft deg."
3000 lb-ft/degree ~ 4040 Nm/degree
Are all modern cars so much stiffer than an early Chaparral?
http://youwheel.com/home/2016/06/20/car-body-torsi...
Please say it isn't so !!





RE: Chassis torsional stiffness 1965 and today
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Chassis torsional stiffness 1965 and today
je suis charlie
RE: Chassis torsional stiffness 1965 and today
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Chassis torsional stiffness 1965 and today
http://www.forgottenfiberglass.com/fiberglass-car-...
RE: Chassis torsional stiffness 1965 and today
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: Chassis torsional stiffness 1965 and today
I think a lot of those early cars (Chapparal included) have a lot more in common with, say, a modern shifter kart, than they do with an LMP car or the like.
This bit of data is interesting, in that it shows the effect of a highly engineered car having it's roof cut off:
Bugatti Veyron 60,000
Bugatti Veyron Grand Sport 22,000
RE: Chassis torsional stiffness 1965 and today
RE: Chassis torsional stiffness 1965 and today
In the Chaparral's day, the unibody Chevrolet Corvair (2,400 lb vehicle) had about 6,000 lbft/deg and the unibody Lincoln Continental (5,500 lb vehicle) had about 10,000 lbft/deg.
Body-on-frame construction was very willowy. If you see crash tests of cars from the '50s and older, a common event in an accident was the popping open of doors and ejection of non-seat belted dummies. In fact, with the common door latch designs (like house doors) combined with vehicle flex, a door could pop open when the car hit a pothole or made a violent maneuver. See the Jack Nicholson movie "The Postman Always Rings Twice".
RE: Chassis torsional stiffness 1965 and today
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Chassis torsional stiffness 1965 and today
American auto door latches went through several design iterations between the '50s and '70s. They improved the lateral latching with ratcheting in case of incomplete door closure. But, GM did not make a longitudinal interlocking latch until late in the period. It is hard to imagine why, but they may have been reluctant to make a pry bar proof latch for the sake of extraction of passengers???
RE: Chassis torsional stiffness 1965 and today
As 140Airpower alluded to, it would be more instructive to know stiffness when normalized to mass, i.e. torsional frequency.
Speaking of which, does anyone know what restraints are used when specifying frequency?
RE: Chassis torsional stiffness 1965 and today
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Chassis torsional stiffness 1965 and today
But BIW doesn't tell the whole story, i.e. what's the all-up mass the chassis has to deal with.
Are any other frequency or deflection measurements done on the rolling vehicle, other than subjective road test impressions?
RE: Chassis torsional stiffness 1965 and today
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Chassis torsional stiffness 1965 and today
RE: Chassis torsional stiffness 1965 and today
Excellent; can you share what some typical whole-vehicle chassis torsional frequencies are?
RE: Chassis torsional stiffness 1965 and today
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Chassis torsional stiffness 1965 and today
RE: Chassis torsional stiffness 1965 and today
RE: Chassis torsional stiffness 1965 and today
http://www.dailymotion.com/video/x2afw2u_watch-the...
I wonder what the torsional stiffness is for a 737.
RE: Chassis torsional stiffness 1965 and today
I believe the torsional stiffness of my truck frame is probably very nonlinear, rising steeply past the one degree measurement I took (but certainly orders of magnitude below figures in this thread). What amount of twist is typically used to rate chassis torsional stiffness?
RE: Chassis torsional stiffness 1965 and today
If the frame is just sitting on jack stands, it will take very little torque to lift one corner. I suspect the difference you saw in your test was due more to inconsistent setup (not a slight against you- test of this kind would need fractions-of-a-millimeter precision to be repeatable, which is not possible with a tape measure) and the increased weight of the frame after modification.
You're correct in that a conventional ladder frame from a truck is not going to be very rigid, compared to a unibody car.
A modern box-section truck frame, depending on the specifics of construction, could be expected to deliver 3,000-3,500 ft. lb. per degree.
I would expect an older c-channel frame, as long as the connections are in good condition, to deliver something like one half to one third of that number, in the realm of 1,000 ft-lb per degree.
RE: Chassis torsional stiffness 1965 and today
Not sure about that.
If the jackstands are 3' apart and each support 1000 lb (assume they're at the front where most of the weight is), it would take 3000 lb-ft.
RE: Chassis torsional stiffness 1965 and today
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Chassis torsional stiffness 1965 and today
-----------------------------------------------------------------------------------------------------------------------------------------
The frame was not lifting from the rear supports; I had thought it might, until I began testing.
Yes, my torsional testing certainly did deal with "... fractions of a millimeter..."; As an engineer and machinist, I routinely calculate/measure/machine to fractions of .001" (.001" is roughly 1/40th of millimeter). In fact, I milled a scrap piece to .209" thick to space up one end of my 24" level (tangent of 0.5 degrees times 24" = .2094").
"... quite difficult to get an accurate number..." was said, along with "... inconsistent setup...". I don't agree. My measurements were very accurate and repeatable.
"... an old C-channel frame to be in the realm of 1,000 ft.lb. per degree..." is not what I would expect. My frame had no damage and only a little surface rust.
----------------------------------------------------------------------------------------------------------------------------------------
Now, having said all that... I must remind you that my test was limited to a one-half-degree twist. I imagine that this limit is responsible for my low torque values. Without specifying the displacement, torsional stiffness is not very meaningful since it definitely won't be constant throughout the twist range.
RE: Chassis torsional stiffness 1965 and today
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Chassis torsional stiffness 1965 and today
Can you share any details of why you were evaluating an out-of-production ( I infer/assume from your comments ) T-bird?
The best I come up with is a university prof or boss wanted to beef up HIS bird .
regards,
Dan T
RE: Chassis torsional stiffness 1965 and today
Yes, but with items much stiffer and much smaller than a truck chassis.
RE: Chassis torsional stiffness 1965 and today
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Chassis torsional stiffness 1965 and today
RE: Chassis torsional stiffness 1965 and today
RE: Chassis torsional stiffness 1965 and today
Stiffness values are quoted as lb-ft or Nm/deg because over the realistic range of chassis displacements that don't involve accidents, the behavior is linear, or at least near enough to linear that it isn't worth listing an equation instead of an easy to understand scalar.
RE: Chassis torsional stiffness 1965 and today
jgKRI- How did you conclude that torsional resistance of a [typical] chassis is "near linear"?
RE: Chassis torsional stiffness 1965 and today
Nonlinearities in the chassis torsional stiffness vs amount of twist imply that nonlinear structural elements are present somewhere in the load path(s), such as the bushings in bodywork resiliently mounted over a separate frame.
Norm
RE: Chassis torsional stiffness 1965 and today
Why put quotes on something I didn't exactly say?
I said why, but to elaborate, metals have a very linear stress-strain curve until yield is approached.
Do you think twisting your frame a few degrees is anywhere near yield?
Just remembered something though - older vehicles may have bolted and/or riveted joints, which if not sound could behave nonlinearly even for small deflections.
Norm, suspension roll resistances are not in the load path (or shouldn't be) when measuring chassis stiffness.
RE: Chassis torsional stiffness 1965 and today
http://forums.pelicanparts.com/porsche-911-technic...
In a proper lab we'd run several repeats.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Chassis torsional stiffness 1965 and today
Through my own experience, limited as it is, and because when people with a lot more experience tell me so I tend to believe them.
If you approach it from a first principles standpoint, it's easy to deduce that the behavior should be linear or close to it.
Once enough load is applied to the system to take up any irregularities between the chassis, fixture, and load application scheme, the chassis is basically a big spring that isn't flexed anywhere near yield. The amount of local strain present anywhere in a modern chassis that is twisted a degree or two is very very small.
RE: Chassis torsional stiffness 1965 and today
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Chassis torsional stiffness 1965 and today
I realize that, but chassis torsional stiffness isn't a property that exists in its own vacuum. Mostly I was trying to justify the notion that using a degree or less of chassis twist for torque measurement wasn't out of the ballpark when the amount of cornering roll envisioned is maybe 5° or less. As an occasional track day participant, perhaps I see a greater value in being able to adjust my car's handling behavior via roll stiffness tuning and damper adjustments than the average driver who rarely exceeds 0.3g in any direction by direct intention. IOW, a downstream consideration from the chassis stiffness itself.
Might be a different story if you were into Jeeps and rockcrawling.
Norm
RE: Chassis torsional stiffness 1965 and today
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?