Slow Flight

The slower an aircraft flies, the greater the angle of attack is required and the slower an aircraft flies, the more induced drag increases.

The faster an aircraft flies, the more parasitic drag increases.

The total drag is the combination of induced drag and parasitic drag.

Induced Drag

The induced drag is created from the production of lift, decreases as airspeed increases and increases with higher angles of attack.

Parasitic Drag

Parasitic drag increases as airspeed increases. Parasitic drag is a combination of the following:

Form Drag is created as a result of the body of the aircraft going through the air and affected by the size and shape of the aircraft along with any object’s on its surfaces.

Interference Drag is created as a result of the vortices that form where two surfaces of the airplane join together at a sharp angle such as where the wings meet the fuselage.

Skin Friction Drag is created as a result of the friction between the air and the surface of the airplane.

Drag Curve

The bottom of the drag curve is the speed that has the least drag (requiring the least power & provides maximum endurance) as well as provides the best glide angle.

The area to the bottom left of the drag curve is know as the “region of reverse command” and also called the “back side of the power required curve”.

When operating in the “region of reverse command” range, it takes more and more power to fly slower and slower. This is reverse of normal which is why this area is called the “region of reverse command”.

Also, speed is unstable in this “region of reverse command”e  – if the aircraft gets a little slow, it will continue to get slower and slower. – if the aircraft gets a little fast, it will continue to get faster and faster.

Operating in the range above is considered to be in “Slow Flight”

Slow Flight

When in flow flight, less air flows over the control surfaces which make them less effective.

You can tell when you are in slow flight due to the feel of the controls at slow speeds and the sound of the air flowing over the aircraft.

Learning how to control the aircraft in these speeds prepares for landing.

When flying in slow flight, you can used a combination of Pitch and power to control the airplane while thinking that pitch controls airspeed – forward pressure to increase speed and back pressure on the control wheel to reduce speed.

For slow flight, power controls altitude whereas increased power increases altitude and decreasing power reduces altitude.

Also for slow flight right rudder will need to be used due to slow speeds and higher power. Trim is used to relieve pressure.

Slow Flight = Low Airspeed -+ High Angle of Attack + High Power Setting -= Maintain Altitude

 

Learning Slow Flight will help to practice approaches and landing at lower airspeeds.

Slow flight helps build on the skills for straight and level flight, climbs, turns and descents.

To start slow flight,

  • perform the pre-maneuver checklist,
  • pick a visual reference point,
  • note the current heading and altitude then
  • reduce power to approximately 1500 RPM,
  • add a little back pressure on the control wheel to hold altitude
  • add in trim to help relieve control pressure
  • add power when slightly above your target airspeed of approx. 50-60 knots
  • increase the power to approximately 1700-21 RPM (as appropriate to maintain altitude)
  • use right rudder
  • ensure power setting and trim are set to hold altitude

When in slow flight, demonstrating the four fundamentals of flight will be shown by

  • Straight and Level
    • use pitch to control airspeed
    • Use power to control altitude
  • Turns
    • a 90 degree turn to the left using no more than 15 degrees of bank(note a landmark and initial heading & if needed, set bug)
    • a 90 degree turn to the right (adding power, more right rudder pressure and back pressure in turns)
  • Climbs
    • Note a heading reference
    • apply full power and right rudder
    • pitch to maintain around 55 knots
    • climb approximately 200 feet
    • reduce power to momentarily level off
  • Descents
    • reduce power to 1500 RPM or idle as desired
    • reduce right rudder pressure
    • pitch to maintain around 55 knots
    • descent approximately 200 feet
    • add power to the original setting required to maintain straight and level flight
    • increase right ridder pressure
    • momentarily level off

Once demonstrated, recover from the maneuver by

  • adding full power
  • increasing right ridder pressure
  • maintain altitude
  • gain airspeed
  • reduce the flap settings

Once at normal cruise speed

  • reduce power back to the normal cruise power setting
  • reduce right rudder pressure

Wow. that’s a lot of information.

Minimum Controllable Airspeed

The “minimum controllable airspeed” is the speed at which a stall will result if there is any additional increase in the angle of attack or reduction of power.

When performing slow flight, the stall warning horn may sound if you are flying at the slowest airspeed possible also known as the “minimum controllable air speed”. This stall warning will sound when at 5-10 knots above stall in all flight conditions.

Load Factor While Turning in Slow Flight

If practicing slow flight and add bank, the wings will have an increased load factor. In order to prevent a stall or loss of altitude, a small amount of power  and back pressure on the control wheel will need to be added to compensate. Sicne power will be added, right rudder pressure will need to increase.

When bank is increased in a level turn, the stall speed increases and the safety margin between stall speed and the actual speed is less when bank is increased.

Then turning in slow flight it is best to use shallow turns of around 15 degrees usually to avoid an accidental stall.

A good rule of thumb is to avoid more than 30 degrees of bank when within 1000 of the ground when in the traffic pattern.