Reciprocating engines, Superchargers,Propellers

Reciprocating engines, Superchargers,Propellers

Reciprocating engines, Superchargers,Propellers Lecture 9 Chapter 4 Reciprocating Engines Internal combustion recip. (piston) engine Four stroke cycle engine credited German

Nickolaus Otto in 1876. Steam was not successful. Why? Figure 4-13 p. 94 Wright Brothers engine How did it work? Reciprocating Engines 1st reciprocating engines were liquid cooled. 1st airplanes were so slow that air cooled was not

practical The rotary engine was cooled by air. The crankshaft of a rotary is mounted to the airframe & cylinders revolve around it. The cylinders are air cooled even at low speeds. Air Cooled Engines Pro: Cylinders placed radially around the

crankshaft for equal cooling for many cylinders Con: This arrangement allows for high drag with the large frontal area. Horizontally opposed configuration worked well with 2/4 cylinders Horizontally opposed recip. engines with as many as 8 cylinders producing up to 450 horsepower.

Reciprocating Engine Performance Horsepower- English unit One Horsepower = 550 foot-pounds It would take one horsepower to move something requiring a force of 550 lbs over a distance of one foot every second

Mean Effective Pressure- average pressure throughout a stroke {force on the piston} Power Power is the time rate at which work is done The number of power strokes per minute is times the rpm because there is a power stroke every other revolution

The power in one cylinder is proportional to average cylinder pressure times the length of the stroke times piston area times rpm. Terms Brake horsepower- horsepower delivered at the shaft Pony Brake- classical method of

measuring power output. Shaft horsepower- power delivered to the propeller. Thrust horsepower- amount of power that actually gets converted into thrust. Terms Rated brake horsepower- the power output

at a rpm at standard sea level density. Figure 4-15 p. 98 typical variation of brake horsepower with altitude Economy cruise- 55% power Performance cruise- 75% power Good compromise- 65% power Superchargers

Superchargers utilize a small compressor in the intake manifold that compresses the air received from the atmosphere to a higher pressure. Turbosuperchargers are more efficient because they use exhaust gas pressure. Turbosuperchargers

The exhaust drives the turbine, which is connected to the compressor in the intake (like the compressor & turbine function in a turbojet) The effect of supercharging/turbocharging is that sea level, or rated, power can be maintained up to a certain altitude.

Figure 4-16 p. 100 This shows the effect of supercharging The dotted line represents the power available at a constant rpm with turbocharger. The solid line represents the original unsupercharged engine.

Propellers Propeller (airscrew) is essentially a small wing rotated in a plane perpendicular to the path of flight & developing thrust in the same way that a wing develops lift. Figures 4-18 4-25 Propeller Efficiency

The efficiency of the propeller is really how much brake horsepower it converts into thrust power-dependent on the ratio to forward speed to rotational speed. Figures 4-26- 4-28 What are the different types of props? Pros/Cons? Figures 4-29 & 4-30

Turboprop & Turbojet Performance Figure 4-31 Quiz on Lecture 9 Chapter 4 Please take out a sheet of paper

Include todays date & your name Quiz on Lecture 9 Chapter 4 Compare and contrast superchargers and turbosuperchargers.

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