holy hydraulics, batman!

Part IV in The World’s Best Mechanical Engineer Explains It All for You series:

Joe-Henry,

Q. How do you move the wings on the end of an airplane up and down?

A. I think you're talking about the ailerons. They are used to control the banking (or leaning) of the aircraft.

Almost all of the moving devices on an airplane are controlled by hydraulic cylinders. Hydraulics is one of my specialties, as much as I have a specialty. A hydraulic cylinder works just like a pneumatic cylinder, except it uses oil instead of air to move the cylinder.

Hydraulics are way more powerful than pneumatics. All the big machinery that you see is hydraulically powered, things like cranes, forklifts, and bulldozers.

Pneumatics operate at around 100 pounds per square inch (about the same as your Mom accidentally stepping on your toe). Hydraulics usually run at around 3000 psi (about the same as a Tyranosaurus Rex stepping on your toe). Because hydraulics are so powerful, you can put a very mighty device in a very small space. That's why they use them on airplane ailerons.

Armed with the power of hydraulics you will now amaze the world by lifting your Mom. Here's how:

Go to the grocery store and buy three things: a roll of duct tape (the good stuff, not some crummy no name brand), a pair of rubber gloves, and that's right... you guessed it.... a two liter bottle of Mountain Dew. But this time the science isn't just an elaborate ploy to get great soda. You actually NEED the Mountain Dew ......bottle. You'll also need a board, like a piece of plywood, big enough to set a chair on.

Then go to a good record store and buy Thomas Dolby's "The Golden Age of the Wireless" CD.

Go home and chug that bottle of Mountain Dew with your Mom. Now squash the two liter bottle flat (but don't put any holes in it). Take the bottle, rubber gloves, a chair, and duct tape out to the garden hose. Dry off the end of the hose, and the top of the bottle.

Put the end of the hose against the end of the bottle.

Now wrap the rubber glove tightly around the connection between the bottle and the hose.

Secure the glove with duct tape. Now wrap the entire joint thoroughly with the duct tape. Overlap a lot of the bottle, and a lot of the hose.

When you think you have enough, put some more on, you'll probably just get one shot at this. Now set the bottle on the ground flat. Set the board on top of it with the hose and bottle neck sticking out, and the chair on top of the board in arms reach of the water spigot.

Put the Thomas Dolby in the CD player and put on "She Blinded Me With Science". Have your mom sit in the chair. Yell, "SCIENCE!" with Thomas Dolby, and turn on the hose just a LITTLE. Hop on your mom's lap, she'll cushion your fall if something goes wrong. The water will lift you and your mom up until the bottle is full or nearly full. If your connection between the hose and bottle leaks, turn up the flow. When the pressure becomes too great, your duct tape will come loose, and the board, chair, Mom and scientist will all drop back to the ground, so keep the fingers and toes out from under that board.

You just lifted your Mom with a few psi[1] of water pressure. Just imagine what you could do with thousands of psi! A cylinder the diameter of a golf ball can lift your Mom's entire car. A few small cylinders could lift your house!

— The World’s Best Mechanical Engineer

[1] pounds per square inch -- a unit of pressure


Also in this series:
• solenoid spectacular
• springs & things
• the world's best mechanical engineer explains it all for you