Quote:
Originally Posted by JamesH
For goodness sake, that's twice in a week I find myself agreeing with wnut.
Even basic car windscreen are safety devices (amongst other things), otherwise they wouldn't be expensive laminated objects. Why else do you need to carry around a hardended pointed hammer to break them if you fall in to a river (Well, I do - lots of long roads next to rivers where I live)
And yes, an F16 screen can withstand impacts at mach 2 - so not really comparable to f1's rather palty 200mph.
And to be honest, they don't need to withstand penetration as such, just need to deflect enough energy go give better protection that a visor alone.
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Again, the primary function of glass in automobiles (windshields, side windows, etc.) is for convenience purposes. Yes windshields/windscreens do provide some safety. They are good at deflecting small stones, etc. However their primary function is not as a safety device. Air bags, crushable structures, crush resistant structures, harnesses/belts, helmets, fire resistant material, ABS brakes, etc. are all examples of safety devices. If anyone knows of specific regulations regarding prevention of intrusion into the passenger area of an automobile via glass covered areas, I would love to hear about them. They may exist, but I don’t know of any.
Regarding laminated “Safety” and tempered glass that is used in modern automobiles, the special features of these types of glass is not to protect you from other things. It is used to “protect you from the glass itself when it breaks”. Laminated windshields are to prevent damage to you from injury from either you impacting the windshield or having large sections of windshield glass impacting you. The lamination holds the large pieces together. Tempered side windows are not laminated, but due to internal stress are designed to break into very small pieces to again prevent injury to you from flying glass.
Regarding the thickness of a fighter jet canopy, clearly the FIA thought that there was some merit to using one as part of their recent tests. It may well have been that this was the easiest to obtain example of a small protective cockpit covering that used a clear material. I have no idea what the requirements are for a jet fighter canopy. I suspect that the primary concern is bird strikes. So I did the math for kinetic energy of a worst case scenario for an F1 car and then compared that to a bird strike on an airplane canopy. What speed would a goose have to be traveling to equal the kinetic energy of an F1 car at speed impacting a solid object such as a barrier?
Maybe I am doing my math wrong. Someone point my errors out.
Using Energy = (1/2) * Mass * Velocity squared
F1 weight = 640 kg
F1 speed = 180 MPH = 80.5 m/s
.5 * 640 * 80.5^2 = 2,073,690 J
Reverse the equation to determine velocity needed for the Goose to get equivalent energy
Velocity = Square root of ( 2 * Energy / Mass)
Goose weight = 35 lbs = 15.9 kg
Energy = 2,073,690 J
That results in a velocity for the Goose of 510.7 m/s or 1140 mph or about 1.48 Mach at sea level. Even that speed surprised me.
So, yes that is an extreme example with respect to the F1 car impact. The deceleration forces would probably kill the driver regardless of protection from cockpit intrusion. I also suspect that the one inch thick jet canopies are in fact not designed to handle such a large bird at those speeds.
But my point is that everyone should not be so quick to say “Oh, it will never be that thick”. The forces they might need to protect against on an F1 car may be larger than you think and the resulting canopy surprisingly thicker than most people’s “gut” estimates.
Clearly it all depends upon what they (FIA) might try to protect against. The scenario above may be overly extreme and overly simplified (or not). But protection against suspension assemblies, wheels and smaller debris might be something that can be reasonably protected against.
And this is all a minor hypothetical point and I apologize for being pedantic and overly verbose. For those that don’t agree with me, we will just have to agree to disagree.
Richard