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16 hours ago, JoeSchmuckatelli said:

Speaking of Volcanoes: Floating Stones in the South Pacific:

Volcano F is the origin of 'floating stones' (phys.org)

 

Pumice can cause serious issues. After an eruption of an underwater volcano in Japan in August of last year, pumice clogged ports across the archipelago, resulting in fishermen being unable to depart to do their work.

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120px-Pit_maneuver.svg.png

In a typical scenario of PIT maneuver during police chase, the pursuing police vehicle rams the target vehicle's sides rear from the rear (cars are typically heavier on the front, while the rear is lighter), hopefully to make the target spin out of the control by using it's heavier front as a rotation point. Now, if we take this occurence in an ideal scenario, taking the physics into account, what would happen to the target vehicle and the police vehicle if:

1. The target's rear is as heavy as the front (no lighter or heavier side)

2. The target's overall weight is much heavier than the front of police vehicle

3. The target has a rear mounted engine (meaning the rear that's getting rammed is the heavier side while the front is the lighter side)

Edited by ARS
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6 hours ago, ARS said:

1. The target's rear is as heavy as the front (no lighter or heavier side)

2. The target's overall weight is much heavier than the front of police vehicle

3. The target has a rear mounted engine (meaning the rear that's getting rammed is the heavier side while the front is the lighter side)

1. 50/50 weight distribution is somewhat common in mid to high range cars. they handle much better than front heavy vehicles. Add in advanced traction/dynamic control and you have a car that could drive out of such a maneuver if the traffic/road conditions were right.

2. The PIT maneuver is more about overloading the lateral traction of the rear axles' tires than overall weight. If a heavy vehicle had worn tires(or a poor choice of tires) on it a PIT could be even more effective.

3. Rear and/or mid engine cars usually have a 50/50 distribution.  I once owned a Pontiac Fiero it was a 45/55 distribution. The second the rear tires lost traction it would flip directions. A PIT on that car would be super effective.

 

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12 minutes ago, AngrybobH said:

1. 50/50 weight distribution is somewhat common in mid to high range cars. they handle much better than front heavy vehicles. Add in advanced traction/dynamic control and you have a car that could drive out of such a maneuver if the traffic/road conditions were right.

2. The PIT maneuver is more about overloading the lateral traction of the rear axles' tires than overall weight. If a heavy vehicle had worn tires(or a poor choice of tires) on it a PIT could be even more effective.

3. Rear and/or mid engine cars usually have a 50/50 distribution.  I once owned a Pontiac Fiero it was a 45/55 distribution. The second the rear tires lost traction it would flip directions. A PIT on that car would be super effective.

 

I wonder how a Tesla on autopilot would behave driving out of it…? Oh right, it would detect the lights and pull over! (unless that feature is still in beta)

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40 minutes ago, StrandedonEarth said:

I wonder how a Tesla on autopilot would behave driving out of it…? Oh right, it would detect the lights and pull over! (unless that feature is still in beta)

Pull over :) no it will try to run away. 
Its an rumor that Tesla uses an heavy modded GTA 5 as part of their AI training and we know some stuff carry over. 

The PIT would be extremely effective on old real wheel driven cars before traction control, more so it the target was flooring it who is likely in an car chase. 
Old rear wheel drive cars tended to flip around a lot then you get ice on the road, ran into it a lot but once on an straight road driving at 80 km/h. 

But the Tesla would be an hard car to do this on, its heavy and is very smart.  I assume the traction control would brake rear wheels if this happens to increase drag on the real wheels, increase power to the front wheels would help, not something an standard traction control would o as it could get you into more problems but could easy see an Tesla AI doing that. 
 

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21 hours ago, ARS said:

 

1. The target's rear is as heavy as the front (no lighter or heavier side)

2. The target's overall weight is much heavier than the front of police vehicle

3. The target has a rear mounted engine (meaning the rear that's getting rammed is the heavier side while the front is the lighter side)

Now it’s been 20+ Years since I took my offensive driving course, but IIRC It didn’t matter in the field.   If we needed to spin them we did.  

The variety of car types don’t really matter.   Even if they don’t end spinning out in classic fashion, they will be redirected and slowed down at the very least, allowing for other vehicles a better chance to block the target vehicle.  
 

PITs aren’t supposed to be done in isolation, it’s a team based play.   

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3 hours ago, Gargamel said:

offensive driving course

And yes, I've been waiting those 20+ years to bring this up in conversation without sounding pretentious.    Not easy to do. 

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7 hours ago, Gargamel said:

And yes, I've been waiting those 20+ years to bring this up in conversation without sounding pretentious.    Not easy to do. 

It isn't so much that you sound pretentious, as much as it sounds like you're the guy we're going to start tagging when the weird driving questions come up. ;)

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Is there a consensus on what would happen to high rise buildings in a nuclear detonation? I recall seeing a claim many years ago that it was possible that skyscrapers might absorb part of the blast and spare outlying structures to a certain extent, but other sources say otherwise.

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2 hours ago, SunlitZelkova said:

Is there a consensus on what would happen to high rise buildings in a nuclear detonation? I recall seeing a claim many years ago that it was possible that skyscrapers might absorb part of the blast and spare outlying structures to a certain extent, but other sources say otherwise.

It all depends on proximity.  

 

FM 8-9 Part I/Chptr 3 Effects of Nuclear Explosions (fas.org)

jcssp.2012.1520.1530.pdf (thescipub.com)

NAE Website - A Nuclear Explosion in a City or an Attack on a Nuclear Reactor

 

Edited by JoeSchmuckatelli
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2 hours ago, JoeSchmuckatelli said:

Asking for a 'friend'

 

On 1/20/2022 at 6:44 AM, SunlitZelkova said:

Is there a consensus on what would happen to high rise buildings in a nuclear detonation? I recall seeing a claim many years ago that it was possible that skyscrapers might absorb part of the blast and spare outlying structures to a certain extent, but other sources say otherwise.

Also asking for a friend? :joy:

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On 1/21/2022 at 8:23 AM, JoeSchmuckatelli said:

Advice time again:  Anyone have experience with 'Robotics Kits'? 

6th Grade Science Fair is coming up.

 

...

 

 

Asking for a 'friend'

:D

Last century there was a thing called "The Armatron".   I wore it out mixing drinks one new Years Eve.

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Okay, here's a question for the petrochem experts.

I know that the majority (if not all) of tire rubber is made from "oil" i.e. petroleum. Am I correct in assuming that it's the heavier fractions that are used, i.e. bitumen?

I ask because naturally Alberta screams blue murder at any suggestion of curtailing the tar sands mining operations. Would it be a sensible suggestion to become a tire manufacturing hub, although there are already established factories elsewhere around North America? This would include tread for re-tread plants, which may be all that's left to manufacture if Michelin's new product gains traction.

https://interestingengineering.com/michelin-airless-tires-hit-public-streets-for-first-time

Tweel

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1 hour ago, StrandedonEarth said:

I know that the majority (if not all) of tire rubber is made from "oil" i.e. petroleum. Am I correct in assuming that it's the heavier fractions that are used, i.e. bitumen?

Unfortunately it doesn't look that way. Instead, industrial polymers are made from the various short-chain aromatics harvested from naphthas.

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Does a forward swept canard makes sense for high-speed fighter jet? (While the wing are trapezoidal like F-35). Also, what's the impact of the size area of rear horizontal stabilizer when compared with the wing size area? (Aka, the effect of surface area ratio between wing and stabilizer (stabilizer surface area is up to half the wing area))

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On 1/21/2022 at 11:14 AM, StrandedonEarth said:

 

Also asking for a friend? :joy:

 i really want to know where the 'friend' lives now.... might break forum rules though.

 

Ask your friend to just move to another country if he still can... that's the best way out.

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44 minutes ago, ARS said:

Does a forward swept canard makes sense for high-speed fighter jet? (While the wing are trapezoidal like F-35). Also, what's the impact of the size area of rear horizontal stabilizer when compared with the wing size area? (Aka, the effect of surface area ratio between wing and stabilizer (stabilizer surface area is up to half the wing area))

Good choices for canard depend on the speeds it has to operate at. A sweep of any kind of wing is necessary to allow operation in transonic regions. Something that operates bellow Mach 0.6-0.7 is better off with straight wings. Direction of the sweep doesn't matter too much for that, but a forward sweep results in a less stable arrangement. For a fighter jet that might be a benefit, depending on what you're building for. A canard is also inherently reducing stability, so you have to keep that in mind. A rear-swept canard with rear-swept wings might require very little correction from flight computer, or might even be possible to pilot directly. A forward swept canard is almost a guarantee that a computer is flying that aircraft.

For supersonic operation, you want to reduce points that are generating shocks. These generate a lot of heat, requiring heavier materials for construction, and drag, which is just generally bad. A canard should ideally be entirely contained within the shock cone of the nose. In which case, a rear swept or trapezoidal canard might be easier to accommodate. At low supersonic speeds, there might be room for forward swept canard as well, however.

One advantage of the canard over the tail stabilizer is that canard adds to the aircraft lift, while tail stabilizer reduces lift. This is because the CoM is usually located forward of the main wing's CoL, and the canard/stabilizer act as a lever arm against that. A canard lifts the nose, while tail stabilizer pushes on the tail down. Consequently, if you're going with tail stabilizer, it's more efficient to have a smaller tail further out from the aircraft. But again, once you start building for supersonic flight, that becomes a far more important factor, and having larger stabilizer closer to the CoM might be warranted.

In short, there isn't a simple answer here. It all depends on exactly what kind of aircraft you're dealing with and what it is built to accomplish.

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4 hours ago, StrandedonEarth said:

Michelin's new product gains traction.

I always took this project as the fusion reactor of tires. I wouldn't hold my breath about these being put on regular everyday cars anytime soon. I could be wrong, but note the article says there no word on price and since there is almost no margin on tires I would bet, if they get them to work, they will be expensive mostly because they can. Cost will keep the manufacturers and car owners away even if they end up better in every other way.

As for the tire manufacturing process, I was under the assumption that the natural rubber (that is absolutely required) was the only problem resource. I can't imagine Canada having large quantities available.

 

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17 minutes ago, AngrybobH said:

Cost will keep the manufacturers and car owners away even if they end up better in every other way.

Hopefully it’ll be more like the optical drive industry (until it went obsolete): The early adopters pay the freight on the R&D and tooling, and once that’s paid for prices drop through the floor. 

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1 hour ago, K^2 said:

In short, there isn't a simple answer here. It all depends on exactly what kind of aircraft you're dealing with and what it is built to accomplish.

Is there a general rule for when the canard needed in aircraft design? When it's acceptable or just a hindrance when added?

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9 hours ago, ARS said:

Is there a general rule for when the canard needed in aircraft design? When it's acceptable or just a hindrance when added?

The only situations where it's just a bad idea is if you are either trying to build a light aircraft that's controlled directly by the pilot without any stability assist, because such aircraft would be too unstable to fly safely, or if you are building something that's meant to go really, really fast, and you can't fit the canard of adequate size within the innermost hypersonic shock cone.

In all other cases, it's a tradeoff. Canard gives you more lift and sometimes more maneuverability, but it makes the aircraft less stable and can make stall recovery very difficult. These aren't stellar benefits, but not catastrophic drawbacks either. You can build around it either way. I don't think there are any situations where a plane needs a canard, but there are plenty where that's a way to design this type of plane.

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