Airplanes are cool, especially when you consider the amount of thought that goes into their engineering and design.

Here are seven little known features on a plane, as compiled by Reader's Digest:

1. Extra room

The aisle seat is not only convenient when it comes to toilet access. You can actually enjoy more leg room if you sit next to the aisle by turning up the armrest. Just push the button under the armrest closest to the aisle. The button should be located near the hinge.

2. Hidden handrail

Navigating your way along the aisle can be awkward indeed. If you are reluctant to hold on to other people's seats, just hold onto the bottom of the overhead compartment as this can help you maintain balance while moving around on an airplane.

3. Secret sleeping pod

The pilots and flight attendants needs sleep too, especially on long-haul flights. Some planes, such as the Boeing 777 and 787 Dreamliner, have a secret sleeping pod for the staff that is usually located near the front of the aircraft.

4. Not-so-smooth wings

The glistening white surface of the wings is not as smooth as you think. On an Airbus plane's wing there are yellow bumps with holes. The holes function as hooks for the rope that is used to help passengers move in case of an emergency water landing.

Read also: What flight attendants say you should do when traveling

5. The helpful black triangle

Riding through the air can be bumpy. If you easily get motion sickness when traveling, the best place to sit is between the wings as it is the center of a plane's gravity. The windows next to the wings are usually marked with a black triangle as an indicator for flight attendants who might need to check the airplane's slats or flaps — the things you see moving on the wings.

6. The hole in the window

An airplane's window has three panes, and the middle one has a hole in the bottom. The hole is said to help balance the pressure gap between the outermost pane and the inner one, especially during takeoff and landing.

7. Hidden handcuffs

Flight attendants have the right to use handcuffs to restrain unruly passengers. While in the United States, metal cuffs are typically used, most airlines will use zip ties as an alternative. (dev/kes)