WELCOME TO AT 262 BASIC AIRCRAFT POWERPLANT SCIENCE

WELCOME TO AT 262 ! BASIC AIRCRAFT POWERPLANT SCIENCE Introduction: Professor Michael Leasure Handout Syllabus and review Review class and lab schedule Sign-in sheet explanation (Lab and Lecture) Outline of lab project content Lab tour

O-290 Lycoming

Lab#1 ……………. . . …Engine Familiarization Lab#2…………………. . . ……Engine Parts Familiarization Lab#3…………Horsepower Computations and Dyno Run Lab#4……………. . . Test Cell Dynamometer Run Lab#5………………. . 100 Hour Inspection Lab#6………………. . . …. Ignition Lead Repair Lab#7………………. . Valve Adjustment Lab#8………………. Troubleshooting Runs Lab#9………………. …Turbocharging Run

262 Unit #1

Reciprocating Engine Description • Intermittent combustion • Piston travels up and down in cylinder (reciprocates) • Ignition of fuel/air is timed to piston position • Burning fuel/air increases pressure in the cylinder and drives the piston downward, performing work

Reciprocating Engine Operating Principles • Internal combustion • The ignition of the fuel/air occurs inside a cylinder or combustion chamber • An example of external combustion would be a steam engine • All internal combustion engines have the following sequence of events in common:

Reciprocating Engine Operating Principles • Intake - fuel and air are taken into the combustion chamber • Compression - fuel and air are compressed • Ignition - mixture is ignited • Power - gases burn and expand • Exhaust - burnt gases are expelled to clear combustion chamber

Reciprocating Engine Operation • Otto Cycle, Single Cylinder, Animation

Two Stroke Reciprocating Engines • All events must occur in one revolution of the crankshaft (2 strokes) • Most commonly used in ultralight, experimental, and development aircraft engines • The crankcase is used as a manifold for the fuel/air mixture • Intake and exhaust valves are not used. Ports in the cylinder opening and closing perform the valve function • 2 strokes are less efficient and more difficult to lubricate, however, they are simpler and often lighter than 4 stroke engines

Two Stroke Reciprocating Engines A. Crankcase intake/ Cylinder Compression B. Ignition/ Power/ Crankcase pressure C. Cylinder Intake/ Cylinder Exhaust

Two Stroke Reciprocating Engines

4 Stroke Reciprocating Engine • Otto cycle is the term used to describe events • Two revolutions of the crankshaft are required to complete one cycle (4 strokes) • Intake and exhaust valves are used to control the fuel/air mixture • Ignition is timed to piston position by number of degrees before top center on the compression stroke • Valve overlap is defined as the number of degrees that both valves open

4 Stroke Reciprocating Engine INTAKE COMPRESSION POWER EXHAUST

4 Stroke Reciprocating Engine • Terms: • TDC - Top Dead Center (top of piston travel) • BDC - Bottom Dead Center • BTC - Before Top Center • ATC - After Top Center • BBC - Before Bottom Center • ABC - After Bottom Center • IO - Intake Opens • IC - Intake Closes • EO - Exhaust Opens • EC - Exhaust Closes

Valve Timing Diagram

Formulas and Calculations for Engines • Cubic Inch Displacement • CID = 3. 14 x radius of cylinder squared x stroke • Answer x number of cylinders is total CID • Example: bore = 5” stroke = 6” number of cylinders = 4 total CID = 471 cubic inches • More cubic inches creates more power • A “square” engine (bore=stroke) is considered to be the most efficient

Formulas and Calculations for Engines

Formulas and Calculations for Engines • Compression Ratio • Volume in the cylinder at the bottom of its travel as compared to the top • Expressed as a ratio 10: 1, 7: 1, etc……. . • Higher compression ratios produce more power • Compression ratio is limited by fuel octane and engine strength • The higher the compression ratio, the more apt the engine is to detonate or “knock”

Formulas and Calculations for Engines BDC TDC

Compression Ratio

Horsepower • Work accomplished over time

Horsepower • Brake horsepower is used to compare aircraft engines and is the power measured at the propellor shaft using a dynamometer (Prony brake)

Horsepower Dynamometer in Test Cell (Purdue)

Horsepower Dynamometer at G&N Engines Inc.

Small Engine Dynamometer

Horsepower • • • BHP = F x L x 2 x 3. 14 x RPM 33, 000 F = force produced by the lever arm L = length of lever arm RPM = speed of engine measured at the crankshaft • Indicated horsepower is the total power produced in the cylinders and it includes both brake horsepower and friction horsepower

Volumetric Efficiency • VE is the ratio of the amount of air the engine takes into the cylinder to the total displacement of the cylinder • The ratio will always be less than 100% in engines that are not supercharged due to bends and restrictions in the induction system • VE = volume of fuel/air charge • piston displacement • The fewer bends and restrictions in the induction system, the higher the VE

Volumetric Efficiency

Factors Affecting Engine Performance • Detonation The explosion of the fuel/air mixture instead of a steady burning at approximately 35 ft/sec • This explosion causes an abrupt rise in cylinder temperatures and pressures that may cause engine damage (knock) • Detonation may be caused by several factors: low octane fuel high cylinder temperatures high prop load (cylinder pressure) lean mixture high compression ratios etc………. .

Factors Affecting Engine Performance • Preignition The ignition of the fuel/air mixture before the properly timed spark occurs (ping) • Preignition may be caused by several factors: hot spots on the cylinder wall improper spark plug heat range carbon glowing hot in the combustion area • Preignition causes the temperature and pressure in the combustion chamber to rise and may lead quickly to detonation

Factors Affecting Engine Performance • Prevention of detonation and preignition – – use fuel with the proper octane rating use correct spark plug operate engine according to pilot’s operating handbook do not lean the mixture during high power operations

Engine Descriptions and Classifications • Cylinder arrangement is one method of identifying engines • Typical arrangements include: inline (upright and inverted) “V” (upright and inverted) Opposed Radial (including multiple rows of cylinders) • Prefix letters (GTSIO - 520) L - left hand rotation V - vertical crankshaft helicopter H - horizontal crankshaft helicopter A - aerobatic

Engine Descriptions and Classifications • Prefix letters T - turbocharged I - fuel injected G - gear reduced prop drive S - supercharged O - opposed R - radial • The numbers are the cubic inch displacement • Colors are Lycoming gray/blue or Continental gold • Suffix letters vary by manufacturer and model and must be deciphered by reference to the service manual

Engine Descriptions and Classifications INLINE INVERTED

Engine Descriptions and Classifications RADIAL

Engine Descriptions and Classifications OPPOSED

Engine Descriptions and Classifications “V”

Engine Operation • A checklist from the pilot’s operating handbook should be used for start, run, and shutdown procedures • The checklist will contain any precautions or procedures that are specific to the engine • Controls are required by regulation to be legibly marked as to type and direction of action, such as: MIXTURE PULL LEAN CARB HEAT PULL HOT

Engine Operation • Typical checklist for starting • • • Inspect engine exterior Check oil level Drain fuel filter Fuel valve “ON” Mixture “RICH” Throttle open 1/4” Magneto switch to “BOTH” Carburetor heat “COLD” Engage starter Check oil pressure Run at 1000 RPM to warm