Why are left pedal turns often considered safer?

More power is required for left pedal turns.  If a left turn can be completed, there is enough power available to safely control the helicopter in the current flight conditions.

When wind is from the right, it is similar to having more induced flow, which decreases the angle of attack on the tail rotor.  With the decrease in the tail rotor blades angle of attack, more left pedal is needed to provide adequate anti-torque thrust, which uses more power.  As such, there may not be enough anti-torque thrust available to turn the aircraft to the left.  If this is the case, the flight should be aborted.  If a right pedal turn is conducted under the same conditions, the turn will likely not be able to be stopped.  A right pedal turn uses the torque from the main rotor so is can often be considered a turn with less application of anti-torque thrust.  As such, the right turn could easily become uncontrollable.  The problem would become worse as the right turn reached the conditions where LTE is more likely (tail wind or left crosswind).

Reference(s):

FAA-H-8083-21A – Helicopter Flying Handbook pg. 9-4
Principles of Helicopter Flight, 2nd Edition, pg. 68

Other Helicopter Flight Conditions

What is a ground reconnaissance?

A ground reconnaissance is performed before an off-airport landing.  The reconnaissance is intended to ensure that the aircraft can land safely at the designated location.

The reconnaissance is generally conducted in two phases, a high reconnaissance and a low reconnaissance.  The high reconnaissance is conducted from approximately 500 feet AGL.  At this altitude, the pilot performs a preliminary review of the suitability of the landing site.  The following mnemonic is useful in remembering to review several key items. The Five Ws.

Wind: What is the direction and intensity? Use indicators such as smoke, flags, etc. Is there expected mechanical turbulence, such as from buildings or terrain?

Wires: Are there any obstacles such as highline wire, fences, etc.?

Way In: Is there an obstacle free approach into the area?

Way Out: Is there an exit strategy if the approach needs to be aborted? Also, this phase includes identifying how the departure will be conducted after takeoff.

What If: Are there any other issues, such as moving vehicles, animals, etc.?

Once the high reconnaissance is conducted, a low reconnaissance is conducted while on final approach.  While on final approach, the pilot continues to monitor the landing site for items that might not have been visible during the high reconnaissance.  The pilot is also looking for items that might have changed, such as animals, vehicles, people, etc.  As this is an off-airport landing, be vigilant for the unexpected.

During the high-reconnaissance, the pilot should not lose sight of the landing spot.  Keeping the spot insight, such as out the pilot-side window, minimizes the likelihood of mistaking a similar location as the one the high reconnaissance was just conducted.

Reference(s):

FAA-H-8083-21A – Helicopter Flying Handbook pg. 10-2

Other Helicopter Flight Conditions

An abnormal vibration is felt while inflight, what may be the cause?

Vibrations are caused by out-of-balance forces.  The source of the out-of-balance condition may be unequal rotor mass distribution, inadequate blade tracking, and or unbalanced drive train components.

Low frequency vibrations are generally related to the main rotor and are often due to an out-of-track bade.  This results in a one-per-rev vertical vibration.  Medium frequency vibrations are generally related to the engine and transmission.  High-frequency vibrations are related to components that rotate at high RPMs.  For most helicopters, this relates to tail rotor and its components.  Vibrations originating from the tail rotor are usually felt through the pedals.  Any abnormal vibration should be investigated, as the vibrations can cause significant damage to the aircraft.

Reference(s):

FAA-H-8083-21A – Helicopter Flying Handbook pg. 11-21
Principles of Helicopter Flight, 2nd Edition, pg. 181

Other Helicopter Flight Conditions

How does the pilot handle low rotor RPM?

Lower the collective to reduce drag and increase throttle for more power, if available.  If in forward flight, gently apply aft cyclic.

Low rotor RPM is a significant concern for pilots.  The slower blade speed reduces the amount of lift as velocity is a key factor in lift production.  If the pilot tries to retain the same altitude, additional lift will be needed.  Should the pilot attempt to raise the collective for more lift, the increased drag will further reduce the rotor speed.  As the rotor RPM decays, the centrifugal force reduces and results in increased conning of the blades.  The increased coning compounds the problem as the rotor thrust is directed inward, reducing its vertical lift capacity.  In addition, the size of the overall disc becomes smaller, further increasing the needed for lift is the altitude is to remain the same.

Lowering the collective reduces the blade angle, which reduces the angle of attack.  With a reduced angle of attack, the induced drag will be less, and the rotor RPM should increase, assuming the same power requirements.  In addition, aft cyclic will tilt the rotor disc aft which in turn lowers the inflow angle on the rotor, which reduces the angle of attack, and reduces the induced drag.  Due to the aft cyclic application, some of the airflow is now coming from underneath the disc, which reduces the induced flow, which in turn reduces the angle of attack, induced drag, etc.  In addition, the coning angle will increase with aft cyclic.  The increased coning angle reduces the size of the disc, and because of the Coriolis effect, the disc will increase rotation.  Should the rotor RPM be allowed to decay beyond the lower limits, the lack of adequate centrifugal force may allow the blades to collapse.  Remember, lower the collective and increase power to maintain rotor RPM within limits.  Do not let RPM decay.

Reference(s):

FAA-H-8083-21A – Helicopter Flying Handbook pg. 2-15, 11-15
Principles of Helicopter Flight, 2nd Edition, pg. 171

Other Helicopter Flight Conditions

What are the three primary regions of the disc in an autorotation?

The three primary regions of the disc in an autorotation are the stalled, driving, and driven.diagram of the three primary regions of the disc in an autorotation

The stalled area of the disc is the area closest to the hub.  Because the rotation of the disc is slow at this area, the angle of attack of the blade is beyond its critical angle.  As a result, it is stalled and not producing any lift.  The middle section of the blade is the driving region.  The thrust or lift from this section of the blade is slightly forward in the direction of rotation.  As a result, this lift provides the thrust needed to rotate the blades.  The driven area is the outside portion of the disc.  This area is producing a lot of drag.  As a result, its net contribution is not assisting in lift production and is being “driven” by the middle section of the disc.

Unless descending vertically in a no-wind condition, the stalled, driving, and driven regions will be a different size on the advancing and retreating side of the disc.  During autorotation, the pilot changes the size of these regions to control the speed of the rotor disc.  For example, raising the collective decreases the size of the driving region and increases the stalled and driven region.  As a result of the decreased driving region, the rotor RPM decreases.

Reference(s):

FAA-H-8083-21A – Helicopter Flying Handbook pg. 2-25
Principles of Helicopter Flight, 2nd Edition, pg. 144

Other Helicopter Flight Conditions

What is the purpose of the flare at the end of an autorotation?

The flare at the end of an autorotation is to arrest the decent.

When in an autorotation, the decent rate is significant, upwards of 1,500 feet per minute.  This rate of decent must be reduced before attempting a landing.  The flare reduces the decent rate.  As a side benefit, the flare also increases the rotor RPM and reduces forward speed.

Reference(s):

FAA-H-8083-21A – Helicopter Flying Handbook pg. 11-4

Other Helicopter Flight Conditions

Why does turning left require more power during forward flight?

Turning left requires more power to overcome the increased induced drag caused by the increase in angle of attack on the rear of the rotor disc.

To turn left, the AOA must increase at the rear of the disc. Due to precession, this change is felt on the right side of the disc and turns the helicopter left.  In forward flight, the front of the disc receives airflow more horizontally, while the rear of the disc has more induced flow.  As a result, the AOA changes to turn left requires a significant increase in the AOA.  This increase caused more induced drag on the rotor disc.   To maintain the same rotor speed, more power is required to overcome the increased drag.  The opposite is true when turning right.  A right turn changes the AOA on the front of the disc, which is operating with less induced flow.  Also, the reduction in the AOA on the rear of the disc reduces induced drag and less power is required.

The impact of this change is more significant at higher speeds and higher gross weight.  In high performance turbine helicopters, abrupt changes from right to left can place significant stress on the aircraft systems.

Like most items in a helicopter, there are many different forces working with and/or against each other.  In a turn, the increased g forces from the turn also speed up the disc as there is more weight.

Reference(s):

Fundamentals of Flight pg. 1-141

Other Helicopter Flight Conditions