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The Italian Job

  1. Mar 11, 2010 #1
    Hi folks,

    I'm new here so I thought I would introduce myself and introduce two subjects that a friend and I disagree on. First, as the title says: The Italian Job.

    I like most people love the film; I'm talking about the earlier one with Michael Caine. However, although it might be great entertainment I don't think the mini going into the bus scene would work. I say that the speed of the minis of say even thirty miles an hour (I think it's actually more in the film) would be too fast even for the first one to stop in time before hitting the front of the bus; the second car would definitely crash into the first and the third would bury itself into the back of the second. This is what I say, my friend thinks they would all stop in time. Even the action of the minis' wheels travelling at thirty miles an hour, coming to a dead stop as it rides up the ramp and then falls back I feel would tear the front tyres off the cars. What do you say about this?

    Second, we disagree on this problem as well. Imagine a jet airliner powering skyward, it becomes almost perpendicular and then starts to stall. Normally it would just fall out of the sky. Now imagine the same scenario, but the aircraft manages to stay perpendicular - let's say some form of a giro system keeps it that way, it doesn't really matter how for the sake of the problem, let's just imagine it does. The question or rather questions are: could the engines keep powering at full thrust? And if so would that thrust help to arrest the falling motion? And if so what difference would that make to the decent? I say it would make a significant difference - my friend disagrees.

    If anybody finds any of these problems interesting and would like to contribute to our knowledge and understanding, my friend and I would be most obliged and we thank you in advance.

    If, on the other hand, it is felt that for a new member I have been a little too over expectant of people's time in asking these questions, or that the questions are in the wrong places in the forum then I apologise profusely and beg your forgiveness as I am new to forums. My friend and I are constantly coming up with problems like these, they fascinate us and we thought that members of this forum would feel the same. In the past we have never had anybody of a like mind to share our interests and then we found this forum and now hope to make new friends.

    Thank you,

    Tony
     
  2. jcsd
  3. Mar 11, 2010 #2

    mgb_phys

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    The mini thing has been done, either mythbusters or the UK equivalent - as long as it's a front wheel drive car it's not too difficult.

    A plane can be made to fly vertically upward largely on engine power. You need some forward direction to have some angle of attack on the wing, but you could have powerful enough engines that the wing wasn't needed - that's all most surface-air missiles are.
    It isn't going to work for an airliner but a bunch of 1950s era interceptor fighters ( British Lightning, US Starfighter) could take off and climb almost vertically pretty much until the air is too thin for the engines.
     
  4. Mar 15, 2010 #3
    Thank you mgb_phys.

    But I was more concerned with the aircraft maintaining a perpendicular position in the air as it falls. I've thought about this since posting and feel I didn't express myself clearly - my fault, I apologise. I will try to be more specific.

    Imagine a jet airliner, say a Boeing 747 at a take off weight of 400 tons (inclusive of 54,000 gallons of fuel). Powering skyward it becomes almost perpendicular and then starts to stall. Now let's say there is a fault in controlling the air surfaces eg: rudders; flaps and ailerons. Normally it would just fall out of the sky and hurtle down to earth and crash at some 200 mph if we accept that an object is drawn to earth by gravity at 9.81 meters per second squared up to a maximum speed regardless of mass.

    Now here is the real puzzle: Let's now imagine the same scenario, but just before the point of stall the pilot dumps thousands of pounds of fuel (retaining one thousand pounds which is enough to keep the engines firing down to the ground) the aircraft manages to stay perpendicular with the engines on full thrust as it falls back to earth tail first and this is because a powerful helicopter/s is attached via the nose of the aircraft and is pulling in the opposite direction - up).

    Now with the aircraft's engines still powering at full thrust 63,300 lbs per engine = 253,000 lbs in total the question or rather questions are:

    (1) Would that thrust help to arrest the aircraft's falling motion?

    (2) If so what difference would that make to the aircraft's decent speed?

    (3) And what would this equate to in terms of weight? For example: with the helicopter holding it so the combined forces pulling and pushing cancel out resulting in zero speed, i.e., with the aircraft's engines slowing the rate of decent and as such reducing the drag on the helicopter, what weight would the helicopter be supporting?
     
  5. Mar 15, 2010 #4

    BobG

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    Divide your thrust by your mass (in slugs) to get the airplane's acceleration in ft/sec^2.

    Add in acceleration due to Earth's gravity (negative) -32 ft/sec^2 since gravity pulls you down.

    You're left with your net acceleration. (positive if up; negative if down)
     
  6. Mar 15, 2010 #5

    BobG

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    You don't explain why you don't think it would work. Because the tires are spinning fast enough to propel the car at 30+ mph when they hit the ramp, and, having an incredibly high coefficient of friction, they immediately grab full traction sending the car up the ramp at 30 mph relative to the ramp, and now the car has to go from 30 to 0 on the ramp? (In other words, is this a car on the conveyor belt question instead of a plane on the conveyor belt question?).

    In reality, the tires probably wouldn't have a high enough coefficient of friction to instantly grab the ramp at that speed. If you kept your foot on the gas, the tires would spin. Mind you, at 1969 prices, each mini must have carrying around 2300 lbs of gold and the mini is a small car with small tires - those tires aren't going to create an instantaneous 30 mph change in speed. (Of course, in making the movie, the cars won't actually be carrying 2300 pounds of gold. They'll be carrying something lighter that happens to be painted gold.)

    The way a good driver would do the trick would be to speed up fast enough that he could push in the clutch and let up on the gas, coasting part way up the ramp, and quickly releasing the clutch and adjusting the gas pedal as soon as the tires were rotating up the ramp. The goal would be a fine enough touch that you'd never spin the tires.

    Enough of a speed differential just before reaching the ramp and you might never have to touch the gas, relying solely on the ramp and the brakes to slow the car down, not from 30 to 0, but from whatever the speed difference is to 0 (i.e. - if the truck is going 30 mph and the cars, 45 mph, the car needs to slow from 15 mph to 0 once on the truck).

    You'd practice on a stationary truck, driving just fast enough so the car would coast up the ramp with just a little to spare so the driver would have to put on the brakes to bring the car to a complete stop. Once you've figured out the necessary speed difference, drive the truck at a set rate with the cars going fast enough to recreate the condition they practiced with the stationary truck.
     
    Last edited: Mar 15, 2010
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