Lesson 5 Flashcards
(14 cards)
What are the characteristics of a fixed pitch propeller?
Designed for optimum efficiency at cruising speeds
Relaible
Low maimtainance costs
What are the characteristics of VPP/CPP?
Angle of attack can change to give optimum efficiency at all speeds
Increased cost in blade maintenance
Define SR
Number of times the shaft rotates around a fixed point per second
Define BR
Number of times a blade passes a given point per second
What is fundamental frequency?
The base or origin frequency measured in cycles per second and expressed in Hertz
What is Harmonic frequency?
Is an echo or numerous echos of the fundamental frequency throughout the spectrum
How does blade rate, shaft rate and number of blades relate to eachother
Blade rate/shaft rate = number of blades
What are the 2 main types of diesel engines?
2 stroke
4 stroke
What is the difference between the two types of diesel engine?
4 stroke fires every second rotation. So 2CFR =CSR
2 stroke fires every rotation so CFR=CSR
What is CSR?
Crank shaft rate.
Number of rotations of crankshaft in one second
What is CFR?
Number of times a cylinder fires in one second
What is ERPM
Engine revolutions per minute
Number of times crank shaft rotates per min
60CSR
What is reduction ratio?
CSR/SR
Reduction between engine RPM and Shaft RPM through a gearbox
What is the most common blade and shaft fit for military vessels?
Multiple shafts , 4-7 blades
