Rotary Wing - Week 5

distance from blade root to tip

span

distance from trailing edge to leading edge

chord

angle between relative wind and chord

angle of attack

angle between chord and reference plane

pitch angle

all blade tips follow same path

in track

blade tip paths are different

out of track

blades that are out of track cause

vibrations

in a hover what forces are working together

lift & thrust and weight & drag

occurs when blades are at rest

blade droop

limits the amount of blade droop

droop restraints

outward force when the blades are rotating

centrifugal force

factors that affect centrifugal force

blade weight and blade speed

blades bending up under load in flight

coning

in forward flight relative wind the advancing blade produces more lift than the retreating blade

dissymmetry of lift

helps equalize lift over the entire blade span

blade twisting

helps to combat dissymmetry of lift

blade flapping

flapping blades bring mass closer to center of gravity which makes blades speed up

coriolis effect

combats the effects of the coriolis effect

lead/lag hinge

lead/lag is also called

hunting

used to smooth out hunting

hydraulic or elastomeric dampers

semi-rigid main rotor heads allow for

pitch change and flapping through teeter totter motion (one blade up one blade down)

fully articulated main rotor head allows for

pitch change, flapping, leading/lagging

rigid main rotor head allows for

pitch change, blade flapping and lead/lag done through blade flexibility and not hinges

example of a helicopter that uses rigid main rotor head

mbb 105

bell 47 main rotor head

semi-rigid with stabilizer bar

main components of bell 47 main rotor head

yoke, blade grips, thrust bearings, drag brace, counter weight, pitch horns, gimbal ring, trunnion

bell 206 main rotor head

semi-rigid without stabilizer bar

secures the blade grip to the yoke

tension torsion straps

tt straps cannot bend more than

90 degrees

blade pitch changes are done through

pitch horns

purpose of flap restraint kit on the bell 206

to limit flapping or teetering of main rotor system

sikorsky 2-58t main rotor head

fully articulated

s-58t hub is

two pieced, splined to the mast, and does not tilt

s-58t has this installed at each blade

droop restraint

hughes 500 main rotor head

fully articulated

replaces the need for flapping and feathering hinges on the hughes 500

strap pack

sikorsky s-76 main rotor head

fully articulated

how does the s-76 eliminate the need for lead/lag hinges

elastomers

as350/as355 main rotor head

fully articulated

as350/as355 main rotor heads use this instead of metal construction

composites and elastomeric bearings

provides flapping to the as350/as355 main rotor head

starflex assembly

bell 407/412 main rotor head

fully articulated

provide pitch, flap, lead/lag in the bell 407/412 main rotor head

flexible beams and elastomers

the bell 407/412 main rotor head is known as

soft in plane due to elastomers

purpose of rotor brake

slow the rotor down quickly during shut-down or prevent the rotor from turning due to winds when the helicopter is parked

how does the rotor brake work

rotational energy absorbed by friction of brake linings on a disc

the friction of the rotor brake transforms

kinetic energy into heat