106 Through Exam 3 Flashcards
(56 cards)
What is feathering
increasing or decreasing the angle of attack
What is an aerodynamic downside of rotors
there is an imbalance of lift along the span of the blades
tip produces more lift as it is going the fastest
highest forward speed comes from the ____ blade
advancing
What is washout
a design where the blade has the lowest angle of incidence between the blade root and blade tip
In forward flight, the sped of air over the blades is _____ on the advancing and reatreating blade and in hover the speed is _____
different, the same
Where is there greater force on the helicopter (right or left)
right side
What is gyroscopic precession in relation to helicopters
a helicopter pitches up rather than rolling over
What do flapping hinges do
equalizes lift on each side of the helicopter
Hinge up where there is more lift and down with less lift
how does flapping equalize lift
changes relative wind approaching blades - changes AoA and therefore CL
What happens to the CG of a helicopter when a blade flaps up
CG shifts more toward center - results in bad rotor vibration and pitching up tendency
what was the purpose of lead/lag hinges
to reduce the vibration caused by the advancing blade wanting to go faster and retreating blade wanting to go slower - ended up creating worse vibrations
How does a semi-rigid rotor work
uses central pivot to allow rotor to teeter at the center
allows advancing blade to rise and retreating to fall
relative wind change produces desired AoA on each side
How does the semi rigid rotor system get affected by Coriolis
CG of blades appear to move towards the center at the same time, so Coriolis doesn’t need to be messed with ~as much~
What is a fully articulated rotor head
has flapping hinges
has lead lag hinges
has lead lag dampeners
(common in helicopters with +2 rotors)
How are semi rigid rotors designed in regards to the pivot point
rotors hang below pivot point so CG does not shift in/out board as like a fully articulated rotor
Explain CG and semi rigid rotors
instead of flapping up: underslung, see-saw type pivot moves whole blade outboard as the system tilts, keeping the CG in the same place laterally
instead of flapping down: underslung, see-saw type pivot moves whole blade inboard as the system tilts, keeping the CG in the same place laterally
Advantages of rigid rotor elastomeric bearings
improved control response
substantial improvements in vibration control
no risk of ground-resonance as with fully articulated
(very expensive though)
Advantages of the star flex system
centrifugal force is contained by flexible arms so “star” arm can be connected by polymer fitting
allows whole blade and plate to flex so blade can lead and lag
no hinges that require lubrication: no additional lead lag dampener, no hydraulic fluid, easily exposed parts for inspection
To move forward, which blade moves up? (If 12 o’clock is forward)
9:00 blade increases in pitch causing disk to rise to highest point at 6
to move backward, what happens with the blades (back is 6)
blades at 3:00 increase in pitch, making spinning disk rise to highest point at 12
What are aluminum alloys for compared to straight aluminum
they add strength
may be as much as 15% of alloy by weight
iron, silicon, copper, magnesium, manganese, zinc
a metal’s strength is directly related to its ___
grain size, orientation, and heat treatment (temper)
what is a composite material
material that is produced from two or more materials
What is AC 43.13 1B
methods/techniques “acceptable” for repairing aircraft when there are no manufacturer repair or maintenance instructions
