Episode 22: Boom-Lift Catapult, AC vs. Windows down

Air Date: November 10, 2004

A boom-lift can potentially catapult its operator 200 feet (60 meters).

busted

When a car engine was dropped from the boom lift it barely even wobbled, much less catapulted Buster. In an attempt to duplicate the myth result, the boom lift was converted into a trebuchet, mounted on several shipping containers to give it clearance to rotate. On its first throw, it threw Buster at a steep angle towards the ground, and then collapsed between the containers, destroying it.

Running a car with air conditioning on is more fuel efficient than running with the windows down.

partly confirmed*

Tests were performed under varying conditions (55 mph versus 45 mph). The 55 mph test used a computer to estimate fuel efficiency based on air intake, not actual fuel consumption, and showed A/C was more efficient. The 45 mph test consisted of running the tank until it was empty, and showed open windows were more efficient.

*Because the original tests were inconclusive, this "urban puzzle" was revisited in episode 38: It is more fuel efficient to use air conditioning when the car is traveling approximately 50mph or more. Otherwise, windows are more fuel efficient.

20 Comments

  1. Mike B says:

    Umm is it something in the air the USA that causes people not to notice little things like your tachometer indicating significantly more revs per minute (hence using more fuel)with the aircon turned on and less with it turned off for the same speed. Maybe you don’t have them fitted to your cars. Could this be because all our cars come standard with a manual gearbox and tacho and an automatic gear box costs more as it is an optional extra?

    Why don’t the myth busters come down to Australia and do a show or two.

    We have plenty of myths down here you can try.
    Water going down the plug hole the wrong way?
    Do we really have drop bears?
    Does speeding over a real corregated dirt road at higher speeds in a car with decent suspension smooth out the ride?
    Do we really have the longest straight stretch of road in the world?
    Are kangaroos endangered?
    Are kangaroos harmless cute and cuddley critters?
    Will a koala piss on you if it is upset?
    Can you escape from a crocodile by running in a zig zag?

    Can you see the curvature of the earth on the Nullabour Plain?

    Sometimes I just have to thank God i’m an Australian.

    • Robert-Alan says:

      They tested a couple of these in later episodes.

    • Chris S says:

      I’m Australian, and I know that a higher tachometer reading = higher revolutions per minute = increased road speed. AC just uses more fuel to maintain the same RPM. Finally, it’s corrugated, cuddly, and Nullarbor (Null = none, Arbor = Tree).

      Sometimes I just have to thank the Australian education system.

  2. Umpa Lumpa says:

    I’m thanking him too.

  3. Matt Gags says:

    Mike B. you’re an idiot. Your engine will not run at a higher rpm because of the ac being on, it will require more throttle to stay at that same rpm though.

    You Australians are quite scholarly huh?

  4. Zane says:

    It really depends on you’re engine computer. My ’00 Ford Zx2 will idle higher with the A/C on versus my ’02 F150 that doesn’t. Then again, thats a L4 vs. a v8.

  5. Ryan says:

    Air conditioning work by compressing a gas which creates a cooling effect that is then blown into the car. At Idle yes most cars have an idle up feature simply because the compressor creates drag directly on the engine via serpentine belt and most engines would drop idle significantly if the idle was not increased, but at higher speeds the engine does not spin any faster than with the ac off, just there is more drag on the engine. That would explain the difference between the 4cyl zx2 and the V8 F150, because the F150 has enough power at idle the drag from the compressor does not effect the engine as much as the Zx2

  6. Josh says:

    you made one big time flow on the boom lift myth when the boom lift spun around you made it keep swinging not letting the dummy leave till hit hit ground if the boom woulg have been trieng to pick something up and lifted of the ground and tipped backwords then have the chain cut or snap the boom would swing just like a catupolt then come to an abrupt stop causing the dummy to shoot out

    just like a swing when some stops it or grabs on to hit you fly out

  7. neil says:

    On your Boomlift,you have been making the whole machine move,where it is the boom that makes it catuplot. so to do this bolt the body of the boom lift down and then fully extend boom and set at 40-45deg or higher. then whinch basket down,with Quick release. You may find myth comfirmed

  8. Steve says:

    Thanks for revisiting this. Wind resistance increases with the square of speed, so it makes a huge difference whether you drive at city or highway speeds (the original test really simulated city speeds). On the opposite side, the air conditioner is going to cycle at more or less the same rate no matter what your speed so if you are going slower you increase the number of cycles.

  9. Eric says:

    I think Zane makes a very good point and I wish this had been addressed by the mythbusters. I believe the vehicles they were using were fairly large both in physical size and engine. The AC unit in a car and SUV would be roughly the same size but the SUV has much more power. Therefore it would effect a small car much more then a vehicle with a larger engine. Also I don’t remember but were the windows all the way down? I don’t think many people drive 55 mph with all the windows wide open.

  10. Danielle says:

    Appreciate the info guys, thanks

  11. The Vyrys says:

    I think the A/C conclusion is that if you got an a/c and want to use it, by all means don’t let the fuel efficiency difference scare you.
    You paid for it, and the difference is pretty much negligible over the long term.

    Paul Harvey had a story of a preacher who refused A/C on a car stating it was a waste of money at $300.
    On the drive home in his new car, he was warm, so he rolled the windows down, a truck passed stirring up dust, causing him to sneeze and shoot his new dentures out the window. Another truck ran over them costing him $700.

    G’day mates!

    • TeeDee says:

      Thanks for the laugh, I needed it :D

  12. Brent says:

    Why didn’t they install an external fuel cell so that they knew exactly how much fuel was in the vehicle? Instead they just pumped out the fuel and then added fuel back to a tank in which there wasn’t any way to determine how much fuel was left when they stopped pumping. try it again with different type vehicles and try it with exact amounts of fuel.

  13. Robert says:

    Power is proportional to the cube of wind velocity. At 25% more speed the power almost doubles. Hence the 50 per hour transition point for their model of vehical.

  14. Ken says:

    the boom lift catapauly needed somethign to make it stop in mid swing for teh final experiment to get the desired results

  15. smith brown says:

    Good Day..This is SMITH BROWN,I want to order for Electric Boom Lifts store. We provide Electric Boom Lifts . that you have in your shop.I want you to get back to me with the price including taxes and I want to know do you accept Credit cards as your payment.Hope to hear from you soon.

    Thanks for your Co-operation.

    SMITH

  16. Michael Horton says:

    To set up a boom lift catapult situation, the machine needs to be in motion, generally towards the counterweight on the superstructure. Drop the leading tires 10: or more, such as when going over railroad tracks or over a curb. The energy is transferred up the boom to the basket occupants leading to a possible ejection. A similar result can be had by driving the boomlift downhill with the counterweight leading and then bringing the machine to a quick stop.

  17. frank says:

    I remember that episode. The vehicle was a full size SUV. Driven around an oval track at 50 mph with the cruise on. Windows down vs a/c on. a/c on won by 3/8 of a mpg. What was disturbing to me was with those perfect conditions the mpg for that vehicle was only 13.3 mpg. What would the mpg be if it was stop and go? Mileage of a helicopter!

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