Aicraft Reciprocant Engines Weeks 5 -6

Eng. JAIRO ANDRÉS GUTIÉRREZ S

2

Cylinders

Place were combustion takes place

• Strong to withstand pressure forces

• Lightweight metal construction

• Good heat conduction properties

• Easy – inexpensive to manufacture / inspect / maintain

3

Cylinders

• Cylinder consists of cylinder head and the cylinder barrel

• Cylinder Head constructed from aluminum alloy

• Barrel usualy built from steel

4

Cylinder Head

• Provides a place for the combustion to happen

• Provides heat conductivity for cooling

• Provides a mounting point for valves, spark plugs and their assemblies.

• In air cooled engines, cylinder heads must have cooling fins

5

Cylinder Barrel

• Usually built from a high strenght material

• Steel alloy forging with inner surface hardening

• Hardening by exposing steel to ammonia / cyanide gas (cianuro / ammoniaco) -> nitriding

• If barrels have got wear they can be overhauled to proper dimensions

Cylinder - Numbering

Source: FAA AMT Powerplant Vol 1

Valves

Source: FAA AMT Powerplant Vol 1

8

Valves

• Intake / Exhaust Valves

• Mushroom and Tulip Types (Hongo / Tulipán)

• Subjected to high temperatures, stresses , etc.

• Intake valves operate at lower temperatures (usually built from nickel chromiun steel)

• Exhaust valves operate at higher temperatures: Cobalt chromiun steel or other temperature resistant alloys

Aviation Reciprocant Engine Valves

Source: FAA AMT Powerplant Vol 1

Mechanical Arrangement

The Exhaust Valve

needs to be open,

to allow the

burnt gases out

The Inlet Valve

needs to be open,

to allow the

fuel/air mixture in

Inlet Valve Exhaust Valve

Valve Operating Mechanism (Opposed Engines)

Source: FAA AMT Powerplant Vol 1

Mecanismo del eje de levas en motores opuestos – sistema hidráulico

Source: FAA AMT Powerplant Vol 1

Valve Operation Push Rod Mechanism

Mechanical Arrangement

Rocker

Rocker Shaft

Return Spring

Valve Seat

Push Rod

Cam Shaft

Valve Lift

Inlet Valve Closed

Valve opening motion:

1) Starts at rotating camshaft

2) Camshaft moves a pushrod and

lift the rocking lever

3) Through a rocker shaft the valve

opens

4) Spring helps the valve returning

to its place

Valve Operation

Mechanical Arrangement

Overhead Cam No Rocker

Overhead Cam and Rocker

Cam Shaft

Return Spring

Valve

Rocker Arm The less parts there are,

the more accurate the work with

opening and closing times,

and the more efficient

the engine.

Some engines feature a

hydraulic system for valve opening

(closing via a return spring),

but driven by a cam.

Some manufacturers now fit

VARIABLE valve timing;

to ensure that the valves

operate at the optimum point

at all rpm values

to gain maximum efficiency

from a piston engine.

Valve Operation The Cam Drive

Mechanical Arrangement

Modern Engines

use a toothed

rubber belt to drive

the cam shafts

Cam Drive Mechanism

Pistons and Crank Shaft

Twin Cam System

Chain Tensioners

Valve Operating Mechanism (Opposed Engines)

Source: FAA AMT Powerplant Vol 1

Mecanismo del eje de levas en motores opuestos

Source: FAA AMT Powerplant Vol 1

Mecanismo del eje de levas en motores opuestos – sistema hidráulico

Source: FAA AMT Powerplant Vol 1

Rodamientos

Source: FAA AMT Powerplant Vol 1

Reduction Gears

Source: FAA AMT Powerplant Vol 1

Source: FAA AMT Powerplant Vol 1

Aircraft Reciprocant Engine Definitions

• DISPLACEMENT (CILINDRAJE) • CYLINDER BORE • PISTON STROKE • TOP DEAD CENTER / BOTTOM DEAD CENTER (TPC Y BDC) - • COMPRESSION RATIO (RELACIÓN DE COMPRESIÓN • VOLUMETRIC EFFICIENCY| • BRAKE HORSEPOWER

DISPLACEMENT

DISPLACEMENENT (CILINDRAJE O DESPLAZAMIENT) REFERS TO THE TOTAL VOLUME DISPLACED BY THE ENGINE IN A THERMODINAMIC CYCLE. IT MAY ALSO REFER TO THE DISPLACEMENT OF A SINGLE CYLINDER DISPLACEMENT= CYLINDER DISPLACEMENT (Cd) * # of Cylinders

ENGINE BORE AND STROKE

REQUIRED TO MEASURE ENGINE SIZE “Engine size is determined by the cylinder diameter (BORE), the amount of piston travel (STROKE) and the number of cylinders”

ENGINE BORE AND STROKE

ENGINE BORE

Diameter of the engine cylinder

Measured across the cylinder, parallel with the top of the block

Cylinder bores vary in size, but typically range from 3–4" (75–100 mm)

PISTON STROKE

Distance the piston moves from top dead center (TDC) to bottom dead center (BDC)

Crankshaft journal offset (throw) controls the piston stroke

MAIN CALCULATIONS

This is the main formula to be used with the given numbers

But also: Crankshaft Offset*2 = stroke

Bore/Stroke Ratio

Bore – to –Stroke Ratio

COMPRESSION RATIO Compares the cylinder volume with the piston at TDC to the cylinder volume with the piston at

BDC

Ratio of swept volume V1 divided by combustion chamber volume V2

Clearance volume = combustion chamber volume

Compression Ratio

Source: FAA AMT Powerplant Vol 1

Compression Ratio

Compression Ratio – Gasoline Engine

Compression Ratio – Diesel Engine

Volumetric Efficiency

• Simply put, it is the ability of the engine to breath in on the Intake Stroke

Formula:

Volumetric Efficiency =

actual volume of air taken into each cylinder

volume of the cylinder

Ratio of air drawn into the cylinder and the maximum amount of air that could enter the cylinder

Volumetric Efficiency

Engines are capable of only 80–90% volumetric efficiency. Restrictions in the ports and around the valves limit airflow. Can you name some of the factors that would impede air flow into and engine?

Brake Horsepower Example

Exercises Examples

If one piston displaces 25 cu. in. and the engine has four cylinders, what is the engine displacement?

25 cu. in. 4 = 100 cu. in.

If one piston displaces 500 cc and the engine has six cylinders, what is the engine displacement?

500 cc 6 = 3000 cc = 3.0 L

Exercises

A continental IO engine has got 6 cylinder, a bore of 5.25in, a stroke 4in. Determine

a) Cylinder Displacement

b) Engine Displacement & Bore – Stroke ratio

c) Compression ratio if volume in combustion chamber(clearance volume) is 11.5in3

Workshop Draw and calculate an engine with the following parameters:

1) Cylinder displacement must be between 50 to 100 in3 per cylinder

2) Compression ratio must be at least 7:1 or more. Maximum compression ratio is 10:1

3) Cylinder number must be 4 or 6

4) Calculate crankshaft distance to crankpin

5) Bore to Stroke ratio from 1:1 to 3:1

Workshop Calculate:

1) Bore size, Stroke Size

2) Crearance volume, connecting rod size, crankpin to crankshaft center distance

3) Draw at scale

4) Find real displacement with a volumetric efficiency of 90%.

5) Find the piston average speed if RPM´s are 2700

6) Use the following website to understand connecting size to stroke (also 2 times crankpin to cranshaft distance) http://www.torqsoft.net/piston-position.html . Compare both your drawing with the website calculations

Assignment 1 – Exposition (35%)

Explain a specific aircraft piston engine system The following options are available: • Aircraft engine Fuel System • Aircraft engine Induction/Exhaust System • Engine Starting, Ignition & Electrical • Aircraft engine Lubrication System • Aircraft engine Cooling System (liquid and air

cooling) • Aircraft engine Propeller System (fixed and

variable pitch)

Assignment 1 – Exposition (35%)

What I want? Groups 3 People – INDIVIDUAL GRADES At least 50 min long presentation • Why is the system important? Main functions • Description and function of system components • A complete exposition of the system (types, parts, system

diagram, work scheme, videos, etc) • Use images from bibliography, AMM, IPC, etc • System Diagrams • Indicating Instruments in Aircraft Cockpit (can use Flight

Simulator) • Maintenance Practices (basic)

Assignment 1 – Exposition (35%)

Nota:

La nota se asignará de acuerdo a:

• Claridad en la exposición.

• Profundidad en la explicación del sistema.

• Ayudas audiovisuales

• Profesionalismo (ejemplos: bajará nota textos largos leidos, letra pequeña, colores que dificulten lectura, etc.)

• Resolución de preguntas

Assignment 1 – Exposition (35%)

REFERENCES: • FAA-H-8083-32-AMT-Powerplant-Vol-1 y Vol-2

(gratis) • FAA Pilot Handbook- Chapter 06 (gratis)

(http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2006.pdf)

• Antonio Esteban Oñate, Conocimientos del Avión (biblioteca)

• Aircraft powerplants, Michael J. Kroes Thomas W Wild (biblioteca)

• AMM´s, IPC, etc (already given to students)

Assignment 2 (15%)

Search for FAA accident records on Reciprocating engines. Find technical documentation on the type (manuals, views, drawings, TC), and explain to class what happened.

http://www.ntsb.gov/aviationquery/

Assignment 2 (15%)

1) Explain what happened, and the possible causes, type of aircraft, etc. 2) Use technical documentation to detaily explain the parts involved. Give P/N, location, system components

3) If it involves a system, explain how it works

4) Give conclusions and maintenance recommendations so it wont happen again

Piston Engine Types - Layouts

Firing Order: -

1 – 4 – 3 – 2

Horizontally Opposed (Or flat) 4 Vee 8

1 – 8 – 4 – 3 – 6 – 5 – 7 – 2