6 Types of Flaps

Flaps are very useful for giving an airplane good handling characteristics at low speed. They are vitally important for giving fast planes the ability to go slow for takeoff and landing.

There are 6 types of flaps

  1. Plain Flaps
  2. Split Flaps
  3. Slotted Flaps
  4. Fowler Flaps
  5. Slots
  6. Slats

Plain Flaps

A simple hinge at the rear of the wing is used to make plain flaps. They are easy to design but they can’t provide much lift before the drag increases very significantly.

Since increasing drag is one of the purposes of a flap the performance is not too bad for landing. When taking off though, drag is not desired.

The reason this flap has so much drag is because the air from above the wing tends to separate and become turbulent when it has to flow downwards at such a steep angle. Think of it like a car on the highway having to make a sharp turn to stay on the road. This airflow separation is like that car spinning out because it can’t make the turn.

Turbulent airflow separation above the wing reduces lift.

Split Flaps

The split flap surface is actually below the wing and pushes down out of the bottom. It does provide some lift but it creates a lot of drag and is almost like a speed brake under the wing.

Slotted Flaps

This is the most common type of flap because it is relatively simple to design and build but provides a huge benefit over the plain flap. The slot created when the flap extends allows air to flow from under the wing.

This airflow provides a cushion for the air from on top of the wing to keep it from separating. It also flows along the top of the flap surface. These two benefits combine to create a lot of extra lift.

Fowler Flaps

Fowler flaps are complex but provide a lot of benefit. They act like slotted flaps opening up a channel for air, but they also slide outwards as depicted below. By sliding out from the wing they greatly increase wing area.

Put simply, they make the wing bigger. A bigger wing means lots of lift!

Most modern airliners use double or triple slotted fowler flaps. These have several flap surfaces that extend out from each other as the flaps are lowered creating a much larger wing with several slots for air to pass through.

Slots

This modification to the leading edge of the wing provides a channel of air that is pushed up over the wing and channeled towards the upper surface. At low speeds, this simple fixed device can increase the critical angle of attack (the angle at which the wing stalls). This means that the plane can fly much slower without stalling.

Slats

Slats are another type of leading edge flap. They slide down at low speeds and provide a large increase in lift like the fixed slot. The benefit of the slat is that it is retractable and won’t create extra drag at high speeds because it slides up into the wing surface.

Wind Pushes and Pulls

We commonly think about how the wind pushes the airplane, but did you know that the wind pulls as well?

Cruising with a tailwind pushes us forward while headwind pushes us back. If we are flying with a crab angle we can look at the ground and get the feeling that we are flying sideways. In these cases, the wind is pushing us from whichever direction it is coming from.

Sometimes the wind pulls us

Continue reading “Wind Pushes and Pulls”

Traffic Patterns Part 3: Departure

You might think that departing from the pattern at a non-towered airport is simple, and it usually is. However, there is a standard way to do it that is safer than the alternatives.

First, if you aren’t sure about how the traffic pattern works, please read Traffic Pattern Basics and Traffic Pattern Entry first.

See this diagram from the Aeronautical Information Manual.

For our purposes, we are only interested in #6. Notice the only two ways out of the pattern are straight ahead, or a 45 degree turn to the left. This is what the AIM says about it:

From AIM 4-3-3
If departing the traffic pattern, continue straight out, or
exit with a 45 degree turn (to the left when in a left−hand
traffic pattern; to the right when in a right−hand traffic
pattern) beyond the departure end of the runway, after
reaching pattern altitude.

It’s pretty clear from this that there is only one real way out of the pattern.

When can you turn?

The AIM recommends a straight out departure, but you will need to turn at some point unless you happen to be going where the runway points.

Continue on your straight out or 45 degree departure until you are outside of the normal traffic pattern (2 miles from the airport).

Make a plan that helps you to maintain clearance from the traffic pattern if you need to pass back over the airport. This means being at least 500 feet above pattern altitude before passing over any part of the pattern, including the inbound 45 degree leg.

Why not depart from downwind?

Have you ever heard the story of the high wing airplane flying just under the low wing airplane, and neither can see the other. This kind of thing can really happen, and downwind is where it would occur. If you are climbing through the pattern while others are maintaining altitude in the pattern you are inviting this type of setup.

Conversely, it is hard to imagine this occurring on a straight out departure leg. Keeping traffic separated based on activity makes the pattern safer by making it easier to anticipate where planes are and what they are doing.