Mythbusters question

[R'as al Ghul]

I just saw the Tv program Mythbusters (a few minutes of it).
They tried to bust the myth that the jet produced by the engines of a commercial airliner is able
to blow a car of the street and turn it over.
They took two jet engines of a much smaller size than those of 747's and propped them up on two trucks.
They then aimed the engines' jet at the car and turned them to full throttle. They couldn't blow the car over in their experiment but a few weeks later it happened in Argentina and it was captured on video.

What I don't understand is the buildup of the test.
Why do the jet engines on full throttle don't push the trucks forward?
Do the trucks just brake to prevent moving? Can the brakes hold the enormous power of a jet engine's thrust?
Or are there any blades/ disks in the engine itself that can turn the thrust on and off, thereby making it possible to have the engines run on full power but not giving any thrust?
I do imagine that when done right, you could strongly accelerate a truck with the help of a jet engine, no?
Has anybody seen this and/ or can explain?
Don Corleone, perhaps? I saw that you're a fan.

[matteus the inbred]

somewhere on the Darwin Awards website (worth a visit anyway!) is the urban myth about some guy who strapped a jet engine (or some kind of jet booster pack) to his car and used it to conclusively break the speed limit. so the story goes, his car then took off and understandably failed to negotiate a corner, leaving its charred remains rather widely spread over a rock face...

jet booster packs were used in attempts to set land speed records as well.
they definitely didn't chain or strap the trucks to the floor then? like you, i'd have thought all you'd have got would be a pair of trucks disappearing into the distance...

[R'as al Ghul]

they definitely didn't chain or strap the trucks to the floor then? like you, i'd have thought all you'd have got would be a pair of trucks disappearing into the distance...

I haven't seen any wedges or chains or anything.
The busters didn't mention anything regarding this.

[matteus the inbred]

sorry, i got the wrong episode...they tested the jet-propelled Chevy myth in another one didn't they...?

it could be that the thrust generated by the engines wasn't greater than the weight of the trucks and the engines combined, in which they wouldn't move. i presume they had the brakes on as well, maybe they had weights in the trucks too.

[English assassin]

its a shame the producers of Mythbusters don't watch BBC's "Top Gear" motoring programme, because they put a car behind a 747 recently and it was blown over and over and over.

I can't remember why they did this but it was mildly amusing, although not as good as trying to see if they could get missile lock on a lotus elise with an apache gunship (no) or whether a range rover sport was better cross country than a Challenger tank (also no not surprisingly)

[matteus the inbred]

that Richard bloke from Top Gear's got his own show has he not? where they crash caravans off cliffs or something...

i liked the one about whether Clarkson, driving a fancy car, could beat a pro speed climber to the top of the mountain (no) and whether he could beat him back down as well (also no, the guy was a base jumper as well!)

[Adrian II]

It's a shame the producers of Mythbusters don't watch BBC's "Top Gear" motoring programme, because they put a car behind a 747 recently and it was blown over and over and over.

Excellent programme, Top Gear.



My favourite was the one in which they horrifically abused a Toyota pick-up (throwing it off a cliff, dousing it in petrol and setting it alight, putting it on top of a nine-story building about to be demolished with dynamite, leaving it in the surf on some merciless Cornish coastline for twelve hours) and it survived each successive onslaught to the point where it could still start and drive around the studio without a mechanic's assistance. Clearly the most robust car ever made.

Exhibit A


Anyway they proved the point about the 747 jet engine beyond a doubt.

Jet booster packs were used in attempts to set land speed records as well.

I am a huge fan of Adam and Jamie and their exploits in the Mojave Desert. It's their Jackass aspect that I love most, doings the things your mother warns you against when you are sixteen.

In fact the jet-assisted Chevy was featured in one of their pilots in late 2004. The original story went like this. The Arizona Highway Patrol once stumbled onto a blackened crater in the side of a mountain at the end of a long stretch of desert road. After an investigation, they learned that an Air Force sergeant from a nearby military base had attached a jet-assisted take off (JATO) unit to the roof of a 1967 Chevy Impala. He got up to about 80 mph, and then fired the things off. Within seconds the car was traveling at 350 mph. The crater was found in the mountainside 100 feet off the ground. The skid marks ran for 1.5 miles...

First off, the Arizona Department of Public Safety has already discarded the story because there is no such crater and there has been no such Air Force sergeant.

The first step of Mythbusters is to acquire a JATO unit, which produces 1,000 pounds of thrust for 15 seconds -- but Air Force won't give their permission. Adam and Jamie enlist Erik and Dirk Gates, who have over 20 years of experience in model rocketry. They decide to use three model rocket engines with 1,500 pounds of thrust for 4 seconds each. To get the same effect they must be fired successively.

Jamie and Adam buy a 1966 Chevy Impala with hydraulics kit on the cheap. They make it remote-controlled, use the hydraulic kit to keep the nose down for aerodynamic purposes, mount the three model rockets on the (reinforced) roof and take it to a dry lake bed. After a failed trial run and some repairs, the car 'takes off' and reaches 130 mph, it stays on the ground and everything works out perfectly.

So, myth busted, but this one could have been.

Exhibit B


Heroes

[matteus the inbred]

that's great, thanks AdrianII! the JATO unit was what i was thinking of.

can't find which land speed record attempt used ramjets or rocket boosters, it was on TV a while ago though. it didn't work very well anyway.

[R'as al Ghul]

That's what I expected the truck drivers to look like after they
turned the jets on.
Any idea why they didn't move?

[Sartaq]

Go Mythbusters! Love that show. Top Gear is good too.

Some of my favorite things they ever did was cutting through iron prison bars with a radio and salsa. Also when they threw various electric appliances in the bath and measured their lethality. The one about the supposed ancient Chinese warning system for sappers was interesting too.

[discovery1]

I just saw the Tv program Mythbusters (a few minutes of it).
They tried to bust the myth that the jet produced by the engines of a commercial airliner is able
to blow a car of the street and turn it over.
They took two jet engines of a much smaller size than those of 747's and propped them up on two trucks.
They then aimed the engines' jet at the car and turned them to full throttle. They couldn't blow the car over in their experiment but a few weeks later it happened in Argentina and it was captured on video.

What I don't understand is the buildup of the test.
Why do the jet engines on full throttle don't push the trucks forward?
Do the trucks just brake to prevent moving? Can the brakes hold the enormous power of a jet engine's thrust?
Or are there any blades/ disks in the engine itself that can turn the thrust on and off, thereby making it possible to have the engines run on full power but not giving any thrust?
I do imagine that when done right, you could strongly accelerate a truck with the help of a jet engine, no?
Has anybody seen this and/ or can explain?
Don Corleone, perhaps? I saw that you're a fan.

What kind of trucks and what kind of engines(maker and model)? And you are sure that they were 'full throttle'?

[Don Corleone]

I haven't seen that one yet.

I was utterly flabbergasted to learn that the old Hollywood trick of diving under the water to avoid bullets works under the following conditions:

-The shooter forms an acute angle with the surface of the water (not exactly 90 degrees)

-You're at least 2 feet deep (not really all that much)

-The bullet is fairly high velocity. The only bullet that would have reached a person under water, at a 23-degree angle, was a musket ball. Look out for the 11th Alabama, ya damn yankees! That cr'ck won't help ya none!

[Sartaq]

I haven't seen that one yet.

I was utterly flabbergasted to learn that the old Hollywood trick of diving under the water to avoid bullets works under the following conditions:

-The shooter forms an acute angle with the surface of the water (not exactly 90 degrees)

-You're at least 2 feet deep (not really all that much)

-The bullet is fairly high velocity. The only bullet that would have reached a person under water, at a 23-degree angle, was a musket ball. Look out for the 11th Alabama, ya damn yankees! That cr'ck won't help ya none!

That one was great!
Regarding the cement truck: Is that not the most high explosive they have ever used on the show to date?

[Adrian II]

Regarding the cement truck: Is that not the most high explosive they have ever used on the show to date?

Nope - the most explosive thing on the show is Kari Byron. :drool:

[English assassin]

Top Gear is a great show also.....my favourite moment is the Lotus Exige test, they went and got an Apache Helicopter and put the car´s manoverability against the chopper.....

I think that was probably the apogee of television as a media form. Let's face it, long, serious discussions of the history of western art are best left to books, and complex and subtle studies in character development belong in novels or on film. Put things like that on television is like watching a cart horse tap dancing.

But 2 and a half minutes of a sports car trying to evade missile lock from a helicopter gunship with Hellfire missiles, to the sound of "Ace of Spades", this is the pure spirit of television. It's ephemeral, it's stupid, and it's fun.

And it can be downloaded here:

http://www.bbc.co.uk/topgear/downloads/

(Blowing up cement trucks is also good, though.)

[Sartaq]

Nope - the most explosive thing on the show is Kari Byron. :drool:

No argument there

[Ronin]

I´m fairly sure that when a comercial airliner with 4 engines is about to take off they take the engines to full throtle, but the plane doesn´t move while the brakes are one...

as to why this happens?....I´d guess that the combination of friction between the tires and the ground and the inertial of the airplane are "stronger" than the jet engines.
I saw the tv show and I think they had 2 trucks, one with one engine each, I guess the same principle as the plane takes place, I remember that the trucks didn´t look to be tied down or anything.

Mythbusters is great....my favorites are allways anything that envolves explosions....which in that show tends to be a lot of the experiments


Top Gear is a great show also.....my favourite moment is the Lotus Exige test, they went and got an Apache Helicopter and put the car´s manoverability against the chopper.....very cool the guy from the show looked like he was really having a blast driving the thing.

[discovery1]

I´m fairly sure that when a comercial airliner with 4 engines is about to take off they take the engines to full throtle, but the plane doesn´t move while the brakes are one...

Wrong. They don't start rolling with the engines at full throttle. Note the next time you fly how you feel the acceleration down the runway. It should be a gradual acceleration, not all at once, whihc is what it should be if it starts at full throttle.

[Ronin]

Wrong. They don't start rolling with the engines at full throttle. Note the next time you fly how you feel the acceleration down the runway. It should be a gradual acceleration, not all at once, whihc is what it should be if it starts at full throttle.

I didn´t mean that they start rolling at full throttle...but I think it´s a normal security procedure to put the engines at full throttle before take-off when the brakes are still on, that way you have a better chance to detect if there is some problem with the engines.

[Adrian II]

Mythbusters is great....my favorites are allways anything that envolves explosions....

You are gonna love this one.

[Gregoshi]

Ah, the cement truck. That was one of my favourite segments. As I recall they shutdown a nearby highway for safety reasons and the crew was a mile away from the truck. Of course when they started, they were only supposed to use enough explosives to remove to break up the dried cement inside the drum...

The other one Sartaq mentioned about the ancient Chinese sapper warning system was fascinating too. That a device a thousand or two years old can detect something modern listening devices can't is just amazing.

[Adrian II]

I´m fairly sure that when a comercial airliner with 4 engines is about to take off they take the engines to full throtle, but the plane doesn´t move while the brakes are one...

Found it! Gentlemen, meet Top Gear's '747 Crosswind' segment.

At full throttle the engines developed 58,000 pounds of thrust. Each experiment had to be restricted to twenty seconds lest the engines' backwash tore up the runway...

Oh, the 2CV... Jezus H. Christ...

[R'as al Ghul]

What kind of trucks and what kind of engines(maker and model)? And you are sure that they were 'full throttle'?

I´m fairly sure that when a comercial airliner with 4 engines is about to take off they take the engines to full throtle, but the plane doesn´t move while the brakes are one...
as to why this happens?....I´d guess that the combination of friction between the tires and the ground and the inertial of the airplane are "stronger" than the jet engines.I saw the tv show and I think they had 2 trucks, one with one engine each, I guess the same principle as the plane takes place, I remember that the trucks didn´t look to be tied down or anything.

Wrong. They don't start rolling with the engines at full throttle. Note the next time you fly how you feel the acceleration down the runway. It should be a gradual acceleration, not all at once, whihc is what it should be if it starts at full throttle.

I didn´t mean that they start rolling at full throttle...but I think it´s a normal security procedure to put the engines at full throttle before take-off when the brakes are still on, that way you have a better chance to detect if there is some problem with the engines.

I agree with all of the above observations. discovery1, I didn't observe anything else than Ronin.
The question I have could be rephrased to:
Why doesn't an Airliner move that has its engines on full throttle? (let's say the engines are being tested)
If Ronin is right, the friction and the brakes are sufficient to negate the thrust produced by the jets. I can imagine that it's true but it sounds somewhat unlikely. Can someone confirm this?

[Adrian II]

If Ronin is right, the friction and the brakes are sufficient to negate the thrust produced by the jets. I can imagine that it's true but it sounds somewhat unlikely. Can someone confirm this?

A 747 weighs approx. 350 metric tons. With 4 Rolls Royce engines the combined thrust is 232,000 pounds. Someone else do the math, please?

[Ronin]

A 747 weighs approx. 350 metric tons. With 4 Rolls Royce engines the combined thrust is 232,000 pounds. Someone else do the math, please?

yeah....somebody is gonna have to calculate the inertia value of the aircraft, and somehow try to calculate the resistance value between the tyres and the ground surface with the brakes on.


don´t look at me.......my last physics class was a good 3 years ago