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
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.
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.
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 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.
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 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.
Airplane instruments and systems are usually as simple as possible. This is because simple systems will break less often. The magnetic compass is one of the simplest instruments there is.
How the magnetic compass works
A compass is made up of a housing with a lens on the front and a vertical line (called a lubber line) inside the glass representing the current heading. Inside of the housing, there is a liquid with the compass “float” suspended on a pivot. The float itself has the sensing magnet inside and markings for every heading. As the aircraft turns the float spins and indicates the planes heading along the lubber line.
There is also a second adjustable magnet in the bottom of the unit to correct for errors.
Finally, most magnetic compasses will have a light mounted above the lens so it can be viewed at night.
Magnetic Compass Errors
The construction of the compass causes a few problems when reading it during turns and changes in speed. There are 3 basic types of errors.
This is the simplest type of error. In turbulence, the indicator may bounce around because it is floating. If the compass is moving around continuously don’t expect to get a precise heading from it.
To determine your heading during turbulence, look for the midpoint or average of the oscillations.
Dip Errors – Turning
When banking the compass will turn to follow the vertical component of the earth’s lines of magnetic flux. In other words, the compass is drawn down towards the earth.
So if you are heading North and you start a turn the compass will try to point down towards the low wing. As the magnet is drawn down it will turn the indicated magnetic heading indicating a turn in the wrong direction.
Conversely, if you begin a turn while heading South the compass will indicate a turn in the right direction but it will turn more than your actual heading.
During turns, the compass lags when you are heading North and leads when you are heading South.
Remember OSUN or UNOS.
Dip Errors – Accelerating
When the aircraft accelerates the inertia of the heavy magnet causes the compass to rotate. It pulls towards the Northerly heading. Conversely, when slowing down the magnet pulls the card towards a southerly heading as it is moved forwards. This effect is most prominent when heading East or West and doesn’t have any effect when heading North or South.
An aircraft is full of magnetic parts and flowing electrical currents that can interrupt the magnetic compasses ability to sense magnetic North. The adjustable compensator is set by a technician to account for these errors.
However, the compensator can’t fix this completely so a compass card is included with deviations corrections. When flying a magnetic heading read the heading you want under “For” and then turn to the indicated heading under “Steer”. Don’t forget about this when setting your directional gyro to match your compass.
The giveaway for March is over. I emailed the winner directly and I will announce the name on Facebook if I get permission.
For those of you that did not win, take heart! The next giveaway is coming soon.
On April 30th 2018 I will be giving away another 172 Reality Expansion Pack along with a scenery pack that offers one of the most difficult landings in the world.
April 30th Giveaway – Simulated Dream Vacation in X-Plane 11
Simcoders Cessna 172 Reality Expansion Pack
Saint Barthélemy Airport by Nimbus
To enter the drawing: Use the form below to join my mailing list and a subscriber will be chosen at random on April 30th. This will also automatically enter you in all future drawings!
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