Ground Effect, Conning

7/23/2019 Ground Effect, Conning

http://slidepdf.com/reader/full/ground-effect-conning 1/11

BLADE CONNING ANDBLADE CONNING AND

GROUND EFFECTGROUND EFFECT



Blade ConingBlade Coning

In vertical takeoff two major forces i.eIn vertical takeoff two major forces i.e

centrifugal force and lift are in action.centrifugal force and lift are in action.

As a result the blades assume a conical As a result the blades assume a conicalpath instead of remaining in the planepath instead of remaining in the plane

perpendicular to the mast.perpendicular to the mast.




Centrifugal force balances the upwardCentrifugal force balances the upward

movement of rotor blades.movement of rotor blades.

In a semirigid and rigid rotor system,In a semirigid and rigid rotor system,coning results in blade bending.coning results in blade bending.

In an articulated rotor system, the bladesIn an articulated rotor system, the blades

assume an upward angle throughassume an upward angle through

movement about the flapping hingesmovement about the flapping hinges




Coning Angle :Coning Angle :

Angle between the tip path Angle between the tip pathplane and spanwise length of blade.plane and spanwise length of blade.

The coning angle will vary with combinations ofThe coning angle will vary with combinations ofrotor thrust and rrotor thrust and r




!actors effecting conning angle:!actors effecting conning angle: "otor thrust:#"otor thrust:# If increased and r remainsIf increased and r remains

constant, the blades cone up.constant, the blades cone up.

r is reduced:#r is reduced:# Centrifugal force decreasesCentrifugal force decreases

and if rotor thrust remains constant, theand if rotor thrust remains constant, the

blades again cone up.blades again cone up.

$eight of the blade:#$eight of the blade:# It will also have someIt will also have someeffect but for any given helicopter this will beeffect but for any given helicopter this will be

constant.constant.



Limits of Rotor RPMLimits of Rotor RPM

The area of the rotor disc reduces as theThe area of the rotor disc reduces as the

coning angle increases.coning angle increases.

Centrifugal force gives a measure ofCentrifugal force gives a measure ofcontrol of the coning angle through r.control of the coning angle through r.

The r is kept above a laid downThe r is kept above a laid down

minimum, the coning angle will always beminimum, the coning angle will always be

within safe operating limits.within safe operating limits.



Ground EffetGround Effet

$hen hovering near the ground, a$hen hovering near the ground, a

phenomenon known as ground effectphenomenon known as ground effect

takes place. This effect usually occurs lesstakes place. This effect usually occurs less

than one rotor diameter above the surface.than one rotor diameter above the surface.

%over height close to the ground%over height close to the ground The downwash meets the groundThe downwash meets the ground

Is opposedIs opposed

&scapes hori'ontally&scapes hori'ontally




(ressure of the air beneath the helicopter (ressure of the air beneath the helicopter IncreasedIncreased

)pposes I!)pposes I!

"educes I!"educes I!

*o that angle of attack and hence T"T are

increased for a given pitch setting.




"estricts the generation of blade tip vortices."estricts the generation of blade tip vortices.

+ue to the downward and outward airflow+ue to the downward and outward airflow

making a larger portion of the blade produce lift.making a larger portion of the blade produce lift.

$hen the helicopter gains altitude vertically, with$hen the helicopter gains altitude vertically, with

no forward airspeed, I! is no longer restricted.no forward airspeed, I! is no longer restricted.

The blade tip vortices increase with theThe blade tip vortices increase with the

decrease in outward airflow.decrease in outward airflow. +rag increases which means a higher pitch+rag increases which means a higher pitch

angle.angle.



Fators affeting Ground Effet

%eight%eight I! is reduced greatlyI! is reduced greatly

round effect reducesround effect reduces

egligible above -/ rotor diameter egligible above -/ rotor diameter

*lope*lope Air flows downhill Air flows downhill

Absence of a divergent duct Absence of a divergent duct

"educed ground effect"educed ground effect



Fators affeting Ground Effet

ature of the roundature of the round *moother the surface creates stronger ground*moother the surface creates stronger ground

effecteffect

+isruption of air flow+isruption of air flow Tall grass, rough terrain, revetments, andTall grass, rough terrain, revetments, and

water surfaces alter the airflow patternwater surfaces alter the airflow pattern

$ind$ind +ownwind reduces ground effect+ownwind reduces ground effect $ind speed increases I! is reduced$ind speed increases I! is reduced

Ground Effect, Conning

Documents

Transcript of Ground Effect, Conning