SL Helicopter Flying Handbook/Aerodynamics - Revision history

Kelly: /* Autorotation */

2021-08-16T04:11:37Z

‎Autorotation

Kelly: /* Autorotation */

2021-08-16T03:59:28Z

‎Autorotation

Kelly: /* Autorotation */

2021-08-16T03:33:51Z

‎Autorotation

Kelly: /* Translational Lift */

2021-08-16T03:32:06Z

‎Translational Lift

Kelly: /* Translational Lift */

2021-08-16T03:31:50Z

‎Translational Lift

Kelly: /* Translational Lift */

2021-08-16T03:30:50Z

‎Translational Lift

Kelly: /* Translational Lift */

2021-08-16T03:08:17Z

‎Translational Lift

Kelly: /* Translational Lift */

2021-08-16T03:07:59Z

‎Translational Lift

Kelly: /* Translational Lift */

2021-08-16T03:01:46Z

‎Translational Lift

Kelly at 02:46, 16 August 2021

2021-08-16T02:46:37Z

← Older revision		Revision as of 04:11, 16 August 2021
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	]]		]]

−	In autorotation, the blades of the helicopter are kept turning by airflow moving up through the rotor system, rather than by engine power.	+	In autorotation, the blades of the helicopter are kept turning by airflow moving up through the rotor system, rather than by engine power. Autorotation allows a helicopter to land safely in the event of an engine failure. A freewheeling unit, or sprag clutch, allows the main rotor blades to continue turning without power from the engine. This is similar to the way a bicycle can coast without constantly turning the pedals.
		+
		+	Aerodynamically, the rotor disk can be divided into three regions during an autorotation as shown in <xr id='fig:autorotation'/>. The three regions are:
		+	*Driving Region – Airflow accelerates rotors and greatest lift produced.
		+	*Driven Region – Drag works to slow rotors. Some lift produced here.
		+	*Stall Region – Blade is stalled with no lift and only drag produced.
		+
		+	An autorotation is normally entered by fully lowering the collective. In the event of an engine failure, the pilot must be ready to react by quickly lowering the collective before the rotor RPM decays too much. If the reaction is too late and the RPM is allowed to decay, it may not be possible to recover.
		+
		+	Most autorotations are performed with forward speed. The pilot maintains this forward speed, typically around 60 knots, then conducts a flare just before touchdown, followed by lifting the collective to cushion the landing.

← Older revision		Revision as of 03:59, 16 August 2021
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	=== Autorotation ===		=== Autorotation ===
		+
		+	[[File:Autorotation.png\|right\|thumb\|
		+	<figure id="fig:Autorotation"><caption>Blade Regions During Autorotation</caption></figure>
		+	]]

	In autorotation, the blades of the helicopter are kept turning by airflow moving up through the rotor system, rather than by engine power.		In autorotation, the blades of the helicopter are kept turning by airflow moving up through the rotor system, rather than by engine power.

← Older revision		Revision as of 03:33, 16 August 2021
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	=== Autorotation ===		=== Autorotation ===
		+
		+	In autorotation, the blades of the helicopter are kept turning by airflow moving up through the rotor system, rather than by engine power.

@@ Line 161: / Line 161: @@
 {| style="float: right"
+|
-[[File:below-etl.png|thumb|right|
+[[File:below-etl.png|200px|thumb|right|
 <figure id="fig:below-etl"><caption>Flight Below ETL</caption></figure>]]
+|
-[[File:above-etl.png|thumb|right|
+[[File:above-etl.png|200px|thumb|right|
 <figure id="fig:above-etl"><caption>Flight Above ETL</caption></figure>]]
 |}

@@ Line 158: / Line 158: @@
 ==== Translational Lift ====
 [[File:below-etl.png|thumb|right|
 <figure id="fig:below-etl"><caption>Flight Below ETL</caption></figure>]]
 When a helicopter is in a hover or at a low speed, airflow through the disk is at a right angle to the rotor plane, and the rotors must provide all induced airflow through the rotors. Additionally, some of the flow recirculates through the rotor system as show in <xr id='fig:below-etl'/>.  As a helicopter accelerates, it moves out of this downward moving/recirculating air and experiences a significant increase in performance.
 ===== Effective Translational Lift (ETL) =====
 At approximately 15-20 knots, the helicopter completely overtakes the recirculating air and moves into clean air (<xr id='fig:above-etl'/>).  This is referred to as Effective Translational Lift (ETL).  As a helicopter passes through ETL, it requires significantly less power to maintain altitude, and more power is available for climbs. This is also the reason that less power is required in cruise flight than for hovering. It is also part of the reason that a normal takeoff involves a short ground run to accelerate past ETL before climbing out.
 === Autorotation ===

← Older revision		Revision as of 03:01, 16 August 2021
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	==== Translational Lift ====		==== Translational Lift ====
		+
		+
		+	<div style="clear: both" ></div>
		+	{\| style="float: right"
		+	\|
		+	[[File:above-etl.png\|200px\|thumb\|right\|
		+	<figure id="fig:above-etl"><caption>
		+	Flight Above ETL
		+	</caption></figure>]]
		+	\|
		+	[[File:below-etl.png\|200px\|thumb\|right\|
		+	<figure id="fig:above-etl"><caption>Flight Below ETL</caption></figure>]]
		+	\|}

	When a helicopter is in a hover or at a low speed, airflow through the disk is at a right angle to the rotor plane, and the rotors must provide all induced airflow through the rotors. As airspeed is increased, some of the induced flow through the rotors begins to be provided by the forward speed of the helicopter. The net result of this is increased lift at no additional cost in power. The largest increase occurs at around 10 to 20 mph and is referred to as ETL (Effective Translational Lift). As an helicopter passes through ETL, it requires significantly less power to maintain altitude, and more power is available for climbs. This is also the reason that less power is required in cruise flight than for hovering. It is also part of the reason that a normal takeoff involves a short ground run to accelerate past ETL before climbing out.		When a helicopter is in a hover or at a low speed, airflow through the disk is at a right angle to the rotor plane, and the rotors must provide all induced airflow through the rotors. As airspeed is increased, some of the induced flow through the rotors begins to be provided by the forward speed of the helicopter. The net result of this is increased lift at no additional cost in power. The largest increase occurs at around 10 to 20 mph and is referred to as ETL (Effective Translational Lift). As an helicopter passes through ETL, it requires significantly less power to maintain altitude, and more power is available for climbs. This is also the reason that less power is required in cruise flight than for hovering. It is also part of the reason that a normal takeoff involves a short ground run to accelerate past ETL before climbing out.

← Older revision		Revision as of 02:46, 16 August 2021
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−	= Aerodynamics =	+	<span class=sa-section>SECTION 2. Aerodynamics </span>

	[[File:Four-forces.png\|left\|thumb\|		[[File:Four-forces.png\|left\|thumb\|