Aircraft Powerplants GLENCOE PDF

Preview

Summary

Lihrary of Congres-s Cataloging-in-Publication Data Kroes, Michael .T. /\ircraft powcrplants I Michael J. K roes. Thomas W. Wilcl.- 7th cd. p. c m.-(Aviation technology series) Rl.:\', cd. of: Aircraft powerplams I Michael J. Kroes ... let al.]. 6th ed. © 1990. Includes index. lSB. 0-02-801874-...

Description

Lihrary of Congres-s Cataloging-in-Publication Data Kroes, Michael .T. /\ircraft powcrplants I Michael J. K roes. Thomas W. Wilcl.- 7th cd. p. c m.-(Aviation technology series) Rl.:\', cd. of: Aircraft powerplams I Michael J. Kroes ... let al.]. 6th ed. © 1990. Includes index.

lSB. 0-02-801874-5 J. Airplanes- Motors. po\\'erplants.

111. Title.

I. \Vild , Thomas W. TV. Sl.:rics.

11. Aircraft

TL70l.A4 1995 629. 13-J. '35-clc20 9~- 3-J...J.-1.5

CTP Aircmft Pmre17Jlants. Sevemh Fdilion

Copyright © 1995 by Glencoe/McGraw-Hill. All rights reserved. Copyright© 1990 by the Glencoe Division of Macmillan/McGraw-Hill School Publishing and McGraw-Hill, Inc. All rights reserved. Copyright© 1985, 1978 by James L. McKinley. All rights reserved. Copyright© 1965 as Powerplants for Aerospace Vehicles by James L. McKinley. All rights reserved. Copyright 1955, 1948 as Aircraft Power Plants by James L. McKinley. All rights reserved. Except as permitted under the United States Copyright Act, no part of this publication may be reproducec or distributed in any form or by any means, or stored in a database or retrieval system, witho..n prior written permission from the publisher.

Send all inquiries to: Glencoe/McGraw-Hill 8787 Orion Place Columbus, OH 43240 ISBN 978-0·02-801874-4 MHID 0-02-801874-5 Printed in the United States of America. 12 13 14 15 DOWiDOW 0 9 8

Preface ilircrajf Po werplams, Seventh Edition. is designed to provide aviatio n students with both the theoretical and practical know ledge they nr.:ed in order to quaLify fo r ccni Ci cation as FAA powe.rplant technicians in accordance w ith the Federal Aviation Regulations iFAR). This edition is a revision designed to reflect not onl y the latest changes in FAR Part 147 but also the current and changing needs of the aircral't industry . Tlu·oughout the tex t, FAR Part 147 has been used for reference to ensure that FAA requircrncnrs have been met. The FAA Written Test Guide, Advi;;ory Circular 65-22, has· been revir.:wed carefully to ensure that all technical clara studen ts will need in order to prepare for FAA written and oral examinations arc included. This edition of Aircrqf'r Pmre17Jlants features expanded coverage of turbine-engine theory and nomenclature. Additio na l current models of turbofan, turboprop. and turboshaft engines have been included. lnformation on turbine-engine fuel , oil. and ignition systems has been expanded and is now divided into separate chapters. New material has also been added ro the chapters on propellers, including infom1ation on composite propellers, dynamic propeller balancing. and auxiliary propeller systems such as aurofeathering. synchrophasing. and deicing systems. Review questions at the end of each chapter enable students to check their knowledge of the information presented. ThroughoUt the text. a special emphas is has been placed on the integration of information on how individual components and systems operate together. This tex t will provide maximum benefit when used in conjunction with the other books in the Glencoe A viation Techno logy series (Aircraft Basic Science. Aircraft i\1/aimencmce and Repair, and Aircrafr 1-.Jecrriciry and Elecmmics). which as a group encompass information on all phases of airfra me and aircrai'L powerplant technology. This book is designed to be used lades in a Prop-fan permits it to be smaller in diameter ~an conventional propellers. Conventional wrboprop air.::-aft have been Iimit.ed in tl1e maximum speed thar they can .::.::ain because of the onset of propeller shock waves due :;:imarily to the large diameter of the propeller. The smai i:::--Diameter Prop-Fan coupled w it h an impro ved aerody=.;;.mic design has greatly reduced the onset and effects or ,_:ock waves, which has greatly increased the speed range :::· :he Prop-Fan. :\ Prop-Fan can save significant amounts of fuel com~ed to a turbofan engine in the range of 450 to 550 mph - : - .05 to 884.95 km/hl because it develops a higher level -~- ?:Upulsion elTicicncy (sec Fig. 1-20). The Prop-Fan is particu larly suited l'or 80- to HiO-pas..=.: ~er planes that fly s hort ho ps in the 300- to 500-rni --~: . - - to 804.5-krnl range, during which most of the time , £?en! climbing and descending.

FIG. 1-21 Unducted fan.

(fVA SAj

or

One such type of Prop-Fan engine is the unductcd fan developed by General ~lectric and illustrated in Fig. 1-2 1. This engine incorporates counterrotating turbines \hat drive tw o pusher unduc ted fa ns. The counterrotating fans inc rease the Prop-Fan 's ability to convert energy to thrust. The Prop-Fun blades are constructed from compo;;,ite material , al low ing conto urs for optimum aerod ynamic and acoustic efficiency .

1. List the advantages of the in-line engine. 2. Describe t he d ifference between upright-V-type and inverted-V-type engines. 3. \11/hat type of reciprocating engine design provides the best power-to-vveight ratio? 4. List the advantages of the opposed-type engine design . 5. Co nven t io nal p isto n en g i nes are class" tc according to vvhat characteristics 7

Concepts and Designs in Aircraf t Pow erp lants

11

6. Name four common engi ne classif ications by cylinder arrangement. 7. The letter "0" in an engine designation is used to denote w hat? 8. The greatest single advance in aircraft propulsion w as the development of what type of engine?

12

9. What does the power lever on the Po rsche engine operate? 10. What are the advantages of the Prop-Fan over a turboprop or turbofan engine?

Chapter 1 Aircraft Powerplant Classification and Progress

Reciprocating-Engine Construction and Nomenclature Opposed-Engine Crankcase

Famil iarity with an engine' s components and construction is bas ic to understanding irs operating principles and maincatecl next to the main. or power, secti on. This section P lain bear in gs are illu stra~e d in Fig . 2-4. T hese bearings :.o uses the diffuser vanes and supports the internal blower are usually designed to take radial loads; however. plain _:rtpeller when the engine is equipped with an internal ~be.arings with t1anges are often used as thrus t bearings in i Bearings

15

FIG. 2-4 Pain bearings.

opposed aircraft engi nes. Plain bearings arc used for connecting rods. c rankshafts. nncl camshaft~ of low-power aircraft engines. The metal used for plain bearings may be silver. lead. an alloy (sLa:h as bronze or babbitt.), or a combination or met

r.n

(/)

EXHAUST VALVE OPENS

w

0: Cl.

The takeoff power rating of an engine is determined by the maximum rp m and manifold pressure at which the ai rp lane engine may be operated during the process or taking off. The takeoff power may be g ive n a time limitatio n, s uch as a period of 1 to 5 min. Manifol d p ressure is the pressure or the fuel-air mixture in the intake manifold between the carburetor or inlcrnal supercharger and the intake valve. T he pressure is give n in inches of me rcury (in Hg) lkilopascals (kJ>a)J above absolute zero pressure. Since sea-level pressure is 29.92 inHg [101.34 kilopascals (kPa) J, t he. reading on the ma nifold pressure gage may be either above or below this figure. As the m anifo ld pressure increases, the power output of the engine increases, pro vided that the rpm remains constant. Likew ise. the power increases as rpm inc reases, provided that the manifold pressure remains constant. The takeoff power of an engine may be abo ut I 0 perce nt above the maximum continuous power-ompu t allowance. This is the usual increase of power output perrnilled in the United States, but in British av iation the increase abo ve maxim um cruising power may be as much as 15 percent. lt is sometirnes referred to as the overspeed condition. The maximum continuous power is also called the maximum except takeoff liVIETO) po wer. During takeoff condi tio ns with the engine operating at maximum takeoff power. the vol ume of air flowing around the c yli nders is restricted because of the low speed of the airplane during takeoff. and the initial carbure tor air temperature may be very high i n hot weathe r. For these reasons the pi lot must exercise. great care, especially in hot weathe r. to avoid overheati ng the en!!ine and darmu~ing the valves. pistons, and piston ~ings. Th~e overheating ~1ay cause detonation or preignition, with a resultant loss of powe r in additio n to engine damage. The rated power, also called the standard engine rating, is t he maxim um horsepower output which can be obtained from a n engine when it is operated a t speci fied rpm and ma nifo ld pressure conditions established as s afe for continuous operation. This is the power guaranteed by the manufacturer of the engine under the specified conditions and is the same as the METO po wer. J\'laximum JlOwer is the greatest po wer output. that the engine can develop a t a ny lime under an y condition.

l Critical Altitude

AM BIENT PR ESSURE

TOP CENTER

VOLUM E --~

FIG. 3-13 Cylinder pressure indicator diagram.

BOTTOM CENTER

The c.ritic.al altitude i!.i the highest le.vel at which an engine will maintain a given horsepower output. For example, an aircraft en>!ine mav be rated at a certain altitude which iimple and adaptable to a wide range of products. It can be used for both fla:-.h-point and fire-point tests. When a test is made, the amount of oil, rare of heating, siz.e of igniting flame, and time of exposure are all specified and must be cardul ly controllccl to obtain accurate results. In a test of stable lubricating oils. the fire point is usually about 50 to 60"F r28 to 33°Cj higher than the flas h point. I\otc that the determinati on of the fire point does not add much to a test.. bur the !lash point of oil gives a rough indication of its tendency to vaporize or to contain light volatile material.

or

In a comparison of oils, if one has a higher or lower flash or fire point, this docs not necessaril y reflect on the quality of the oil-unless the fire point or flash point i~ exceptionally low in comparison with the fire or flash point~ of similar conventional oils. If oil which has been used in an aircraft engine is tested and found to have a very low t1ash point. this indicates that the oil has been diluted by engine fuel. lf the oil has been diluted only slightly with aviation-grade gasoline, the fire point is not lowered much because the !!asoline in the oil ordinarily evaporates before the lire point is reached. If the oil has been greatly diluted by gasoline, the flre point will be very low. ln testing oil which has been used in an engine, it is possible to obtain more accurate results from the t1ash-poinl and fire-point tests if the sample of oil is obtained from the engine while both the engine and the oil arc still hot.

Viscosity Visc.osity is techn ically defined as the t1uid friction (or thLher factors remain the same, the gain in power output ti'om the engine is proportional to the increase of pressure. However, the other factors do not remain con1>tant, and there are limits beyond which safe operation is not possible. One of these l'adurs is temperature. When air is compressed, its tempe.rature is raised. This reduces the efficiency of the supercharger because heated air expands and increases the amount of power required to compress it and push it into the cylinde.rs. The. increased air temperature. also reduces cngi ne efficiency because any gas engine operates better if the intake mixture of fuel and air is kept cool. 'W hen the fuelair mixture reaches an excessively high temperature, preignition and detonation may take place, resulting in a loss of power and often a complete mechanical fai lure of the pO\vellJlanl. The temperature increase resulting from superc harging is in addition to the heat generated by the compression in the engine cylinders. For this reason, the combined corn-

Relation Between Horsepower and JVIAP. The relation between MAP and the engine power output for a certa in engine at maximum rp m is shown in the chart in Fig.

[820.6 ] 1100 [74611000

E?

II

1

[671.41 900

1-

~

s 3 ~

I 1--·l I

{522.2] 700

a: 1447.6] UJ

15.:..

J

[596.81 800

! 373l

I_ 600 500

:Q !298 41 400 0

[223.8 1 300 [149.2 i 200

36 i nHg

270 inHg

L QW.. INTAKE PR ESSURE

45 inHg

405inHg

HIGH-INTAKE PRESSURE

FIG. 5-11 Effects of ai r pressure entering the cylinde r.

I

17

UJ

I

[7

v

I

20 25 ! 67.741

I

I

30

I 35

I I

I

40

45 50 [ 152.42 ]

MAN I FOLD PRESSU RE- ir1 Hg I kPa [

FIG. 5-12 Relation betvveen MAP and horsepovver. Principles of Supercharging and Turbocharging

89

pression of the supercharger and of the cylinders must be kep t wi thin the correct limi ts determined by the antiknock qualities or octane ratings of the engine fuel. lf a supercharger were designed with enough capacity w raise the press Ltre of a ir at sea level from I 4 . 7 to 20 psi l l0 1.36 to 137.9 kPal. it would he possible to obtain about 40 percent more power than would be generated if there were no supercharging to increase the air pressure. II' this superc harger were ins talled with a I 000-hp f74 5 . 7 -kW] engine, the piston displacement of the 1000-hp [745.7-k\:Vl engine wou ld nor need to be any greater than the piston displacement of a 710- hp 1529.45-k\Vl engine that was not supercharged. However. note that an engine which is to be pro\'icled with a supercharger must be designed to withstand the highe r stresses deve loped by the increased powe r. lt is not s imply a matter or adding a s upercharger to a 71 0-hp 1529.45- kWJ engine to obtain a 1000-hp [745. 7-kW J output. The diffcn:nce betwee n 710 and I 000 hp [5:?.9.45 and 745 .7 kWJ is 290 hp f21 6.25 k \Vl , but it requi res about 70 hp l52.22 kWl to operate the supercharger for this imagiuary engine: the refore, not merely 290 hp f216 .25 kWJ, bur 290 + 70 = 360 hp f268.45 kW] must be de veloped in the e ngine to obtain the 1000-hp 1745.7-kW I o utput. So the supercharger must account for the devclopmem of an additional 360 hp [268.45 k\Vl when added to the 7 10 -hp f529.45-kW l engine in order aclllally to obtain the 1000 hp [745.7 k\Vl des ired. A sea- lc,·el supercharger or turbocharger provides an effective means for inc reasing the pumping capacily of the e ng ine with a minim um inc rease in weigh t. but a powerpl unt equipped with the sea-leve l supe rcharger is uffec ted by changes in altirude in the same manner as an unsupercharged engine. as shown in Fig. 5- 13. E ngines are no longer being manufactured w ith sea-level. superchargers. a ltho ugh many or these " a ltitude" engines are still in operation. Engines currently being manufactured employ turbochargers to turbonormalize the engine. T he turbocharge r provides the intuke air compression that makes it possible to maintain sea-level pressure at high altitudes.

Factors Considered in Designing Altitude Superchargers Tf t he powe r to run the s upe rc harger is take n from t he engine cranks baft, the net gain in horsepower obtaine d by supercharging is reduced.

T he net gain in ho rsepowe r obta ined from supercharging is not fully ret1ected in the overall ai rplane performance because the supercharging equipment requires additional space and increases the weight of the airplane. The degree of s upercharging mus t be restricted withi n definite limits to avoid preignition and detonation which result from excessive temperatures and pressures. A spec ial cooling apparatus must be used to reduce the temperat ure of the fue l-a ir mix ture because of the excessive heat resu lting from the extra compression requ ired at extreme alti tudes. This apparatus requ ires space. adds to the weight of the airplane. and c o mplicates operation, inspection, and maintenance. The special rad iators used for s uch cooling are called intercoolers or aftercoolers, depending on their location with reference to the carburetor.

Internal and External Superchargers Most s uperc ha rgers use.d o n conve ntio nal a irp lanes are alike in that an impe ller (blower) rotati ng at high speed is used to compress e ither the air before it is rnixed with the fu e l in the carburetor or the fue l-air m ixture whid1 kaves the ca rburetor. It is the refore possible to c lassify any supercharger. accordi ng 10 its location in the induc tion system ot' the airplane. as either an internal or external type. When the supercharger i ~ located between the carburdor a nd the cy linder intake ports, it is an inl.ernal-type supercharger. as shown in Fig. 5-14. Air enters the carbure tor at atmosphcric pressure and is mixed with the fuel. The fuel a ir mix ture leaves the carburetor at. near-atmos phc:ri~ position, the a lever by removing the link pin. Turn the block and adjustment screw until the adjusting wheel is centered and the dis tance between the blocks is the same as previously measured. There is now additional adjustment range. and the reference point is retained . S. Make the final idle-speed adjustment to obtain the desired idling rpm with the throttle dosed. 9. If the setting does not remain s table, check rhe idle linkage for looseness. In all cases. allow for the effect of weather conditions . The prevailing wind can add to or Bendix RSA Fuel Injection System

163

TROUBLESHOOTING CHART Problem

Probable cause

Hard starting.

Techni que. Flooded. Throttle valve opened too far. Insufficient prime (usua lly accompanied by a backfire). Mixture too rich or too lean.

Rough idle.

Plugged nozzle(s) (usually accompanied by high takeo ff fuel-flow readin gs). Slight a ir leak into induc ti on system through mani fold drain check valve. (Usual ly able to adjust initial idle, bu t rough in· 1000 to 1500 rpm range.} Slight air leak into induction system throu gh loose intake pipes or damaged 0 rings. (Usually able to adj ust initial idle, but rough in 1000 to 1500 rpm range.} Large air leak into induction system. Several cases of - in [3.175-mm] pipe plugs dropping out. (U sually unable to throttle engine down below 800 to 900 rpm.) Internal leak in injector. (Usually unable to lean out idle range.) Unable to set and maintain idle. Fuel vapori zing in fuel lines or distributor. (Encountered only under high ambient temperature conditions or following prolonged operation at low idle rpm s.)

i

Low takeo fl fu el flow.

Strainer plugged. Injector out of adjustmen t. Faulty gage. Sticky flow divider valve.

High fuel flow ind ica tor read ing.

Plugged nozzle if high fuel flow is accompanied by loss of power and roughness. Faulty gage. Injector ou t of adjustment.

Remedy Refer to a~rcraft manufacturer' s recommended starting procedure. Clear engine by cranking with :hrottle open and mixture control in ICO. Open throttle to a position at approximately 800 rpm. Increase amount of priming. Confirm with mixture control. A too- rich mixture will be corrected and roughness decreased during lean -out, whi le a too -l ean mixture w ill be aggravated and roughness increased. Ad just id le to give a 25 to 50 rpm rise at 700 rpm. Clean nozzles. Confirm by temporarily plugging drain line. Replace check valves as necessary.

Repair as necessary.

Repair as necessary.

Replace injector. Replace injector. Cool engine as much as possible b...