As designed, should Semis be allowed on the same roads as cars?

[Porsche-O-Phile]

Originally Posted by Shaun 84 Targa

We need more capitalism to fix the failures of government regulation.

Fixed that for ya'.

[Shaun @ Tru6]

Originally Posted by Porsche-O-Phile

Fixed that for ya'.

doooooooood, I was just restating Sniper's case, you know, for clarification.

I would have liked to have gone off on tearful tirade about what a bad man you are for changing my post, but I hear that's been done.

[m21sniper]

I have no problems with some government regulation, it just depends on what they're regulating...and how much.

[Porsche-O-Phile]

I'm just messin' around with ya. Got to stir the pot a bit every now and again ya' know...

[island911]

Originally Posted by m21sniper

.... I'm pretty sure we can get better performance from disc brakes.
.

Don't be. You generally have to go to multi disk to get the same pad pressures.

That "easy button" that Jeff has on his desk; you can tell if it's working because it immediately releases massive cash from the sky.

That is, 'performance' costs you MONEY!

[m21sniper]

You know i'm just not so sure about this whole "Drum brakes are better for one time panic stops" business.

I had a 68 LeMans with 4 wheel drums. It SUCKED in panic stops. Seriously- it was horrific. The guy that bought it off of me swapped in Wilwood front discs. I got to drive it a few months later, the transformation in braking performance was immense.

Night and day.

[fingpilot]

The poblem is not the trucks.

It's the felony truckers.

[island911]

fwiw, many drums have a camming action --which helps them grab faster, but are then slower to ungrab. The camming is not a necessary feature. Just guessing that any with ABS do not have the camming action.

[island911]

Hey singpilot, what the minimum stopping for one of those heavies? ...and what do they weigh on landing?

[fingpilot]

My usual last ride weighed typically 440,000 pounds at landing. Being nice to the pax meant 7 to 8 thousand feet of runway roll. An full-on emergency stop would be 4K feet.

Takeoff reject was another matter. Gross takeoff weight was just over 910,000 pounds. Sea level standard day (65F, 20% humidity) and no taxi to runway with a fairly new set of tires and brakes and being prepped to stop at worst possible moment? (This never turns out this way cuz of a guy named Murphy). 8900 feet dry, 11,200 feet wet. Will also entail a 45 minute park with the brakes released to cool, and will probably mean a couple of popped tires with fire standing by.

My Cathay friends are already flying the latest Airbus. It makes my ERF blush when it comes to weights, burns and slosh.

I am pretty sure I got out just right.

[island911]

Thx. How fast could you be going, to still stop 910,000 pounds in 8900ft?

[Amail]

I can't believe this has gotten to 6 pages.

What am I missing?
Do truck brakes not have the ability to lock up all their wheels at will? If so, for sure they need to improve the brakes.
Do trucks not have the ability to modulate their braking pressure for threshold braking? If so, for sure the need to improve the brakes.

If trucks can do the above, then the problem is NOT their brakes! I always get a kick out of reading "My Porsche has such good brakes, it can stop faster than anything out there!".

BS.

Porsche brakes are good because they are easy to modulate and don't fade. Beyond that, it's a function of the TIRE. Remember jet-fockin' black? There's a prime example of a car not stopping well because of the condition of the tire. Not brakes.

I agree - trucks could be made to stop better, but if their brakes can consistently keep the truck at threshold braking, then they need better tires.


All this is out the window when discussing trucks running down long grades and overheating their brakes. Yeah, that could stand improvement.

[fingpilot]

Originally Posted by island911

Thx. How fast could you be going, to still stop 910,000 pounds in 8900ft?

150-ish MPH.

[Jeff Higgins]

Originally Posted by fingpilot

150-ish MPH.

Is this with or without thrust reversers?

[island911]

So let's see how much energy that is...

E=1/2mv² m=910000_lb & v=150mph

E=928,009,504_J

and for an 80,000_lb truck at 70mph ...

E= 17,767,020_J

...So, the plane has 52.2 time more energy.

or, 1996.3 Joules per ft (based on the 8900' stopping distance)


So, who has o-70 stopping distance for a typical 80k_lb truck? ...is it more or less than 170_feet? (8900/52.2)

Considering that 170 feet is what pickups use to stop from 60mph, I'm guessing it's higher for the big rigs. (but really don't know - need numbers)

[TimT]

Do truck brakes not have the ability to lock up all their wheels at will?

They do have that ability... believe me I have locked up the wheels on our transporter on more than one occasion...

Regarding modulating the braking... Si

Up until ABS comes into play... on our transporter the tractor has air brakes with ABS... the trailer has hydraulics which are electrically actuated...

The few times I've had to panic stop it....the trailer wheels lock, and the tractor wheels judder from the ABS..

Stops in a straight line... lot of tire smoke from the rear...

There is really a lot of tech in the modern Semis... the old one like the Mack R600 are still on the road, they were never a long haul horse but they are out there..

Big rigs routinely plow into stopped traffic

I travel a lot and don't see this...

What usually happens is when there is an accident with a big rig.....Its usually a big..

[Porsche-O-Phile]

I bet far more people get plowed into by drunk idiots driving SUVs in Vegas than in all of the rest of the USA by big rig drivers.

Just sayin'

[island911]

Originally Posted by Jeff Higgins

Is this with or without thrust reversers?

I would expect it's with.

But how much forward trust do those give? ...they seem to usually just redirect 90° - mostly just pinching off the rear thrust.

You're the airplane engineer, so you tell me.

[Jeff Higgins]

Originally Posted by island911

I would expect it's with.

But how much forward trust do those give? ...they seem to usually just redirect 90° - mostly just pinching off the rear thrust.

You're the airplane engineer, so you tell me.

You are right - the thrust is really not "reversed" or directed forward at all; it is sent out at about 90 degrees to the direction of travel, and at greatly reduced flow as opposed to going straight through the engine and out the back (exhaust) side. What this does is effectively "back up" all that air going through the fan (on a bypass type engine), creating very high pressure turbulence behind it. Essentially, the air going through the fan has nowhere to go, turning that big fan into the brake. Think of it as a high-tech "jake brake".

[1967 R50/2]

Originally Posted by pete3799

So roads would last forever if we keep trucks off of them?

Practically speaking, yes, they would last much, much longer.

In many climates though, it is not practical to keep all trucks off the roads. Snowplows are indeed heavy trucks and of course are exerting much more stress on the tarmac than even a regular truck as a result of the plow.