projecting　frame。
  _Fig。　53。　Plan　view。_
  The　full　page　view；　Fig。　53；　represents　a　plan
  view；　with　one　of　the　wings　cut　away；　showing　the
  general　arrangement　of　the　frame；　and　the　three
  wheels　required　for　support；　together　with　the
  brace　bars　referred　to。
  The　necessity　of　the　rear　end　elevation　will
  now　be　referred　to。　The　tail　need　not；　necessarily；
  be　located　at　a　point　on　a　horizontal　line
  between　the　planes。　It　may　be　higher；　or　lower
  than　the　planes；　but　it　should　not　be　in　a　position
  to　touch　the　ground　when　the　machine　is　about
  to　ascend。
  _Fig。　54。　Alighting。_
  The　angle　of　ascension　in　the　planes　need　not
  exceed　25　degrees　so　the　frame　does　not　require
  an　angle　of　more　than　17　degrees。　This　is　shown
  in　Fig。　54；　where　the　machine　is　in　a　position
  ready　to　take　the　air　at　that　angle；　leaving　ample
  room　for　the　steering　rudder。
  ACTION　IN　ALIGHTING。Also；　in　alighting；　the
  machine　is　banked；　practically　in　the　same
  position　thus　shown；　so　that　it　alights　on　the　rear
  wheels　O。
  The　motor　U　is　usually　mounted　so　its　shaft　is
  midway　between　the　planes；　the　propeller　V　being
  connected　directly　with　the　shaft；　and　being　behind
  the　planes；　is　on　a　medial　line　with　the
  machine。
  The　control　planes　L；　M；　N；　are　all　connected　up
  by　means　of　flexible　wires　with　the　aviator　at　the
  set　W；　the　attachments　being　of　such　a　character
  that　their　arrangement　will　readily　suggest　themselves
  to　the　novice。
  THE　MONOPLANE。From　a　spectacular　standpoint
  a　monoplane　is　the　ideal　flying　machine。　It
  is　graceful　in　outline；　and　from　the　fact　that　it
  closely　approaches　the　form　of　the　natural　flyer；
  seems　to　be　best　adapted　as　a　type；　compared　with
  the　biplane。
  THE　COMMON　FLY。So　many　birds　have　been
  cited　in　support　of　the　various　flying　theories　that
  the　house　fly；　as　an　example　has　been　disregarded。
  We　are　prone　to　overlook　the　small　insect；　but　it
  is；　nevertheless；　a　sample　which　is　just　as　potent
  to　show　the　efficiency　of　wing　surface　as　the　condor
  or　the　vulture。
  The　fly　has　greater　mobility　than　any　other　flying
  creature。　By　the　combined　action　of　its　legs
  and　wings　it　can　spring　eighteen　inches　in　the
  tenth　of　a　second；　and　when　in　flight　can　change
  its　course　instantaneously。
  If　a　sparrow　had　the　same　dexterity；　proportionally；
  it　could　make　a　flight　of　800　feet　in　the
  same　time。　The　posterior　legs　of　the　fly　are　the
  same　length　as　its　body；　which　enable　it　to　spring
  from　its　perch　with　amazing　facility。
  _Fig。　55。　Common　Fly。　Outstretched　Wings。_
  The　wing　surface；　proportioned　to　its　body　and
  weight；　is　no　less　a　matter　for　wonder　and　consideration。
  In　Fig。　55　is　shown　the　outlines　of　the　fly　with
  outstretched　wings。　Fig。　56　represents　it　with
  the　wing　folded；　and　Fig。　57　is　a　view　of　a　wing
  with　the　relative　size　of　the　top　of　the　body　shown
  in　dotted　lines。
  _Fig。　56。　Common　Fly。　Folded　Wings。_
  The　first　thing　that　must　attract　attention；　after
  a　careful　study　is　the　relative　size　of　the　body
  and　wing　surface。　Each　wing　is　slightly　smaller
  than　the　upper　surface　of　the　body；　and　the　thickness
  of　the　body　is　equal　to　each　wing　spread。
  _Fig。　57。　Relative　size　of　wing　and　body。_
  The　weight；　compared　with　sustaining　surface；
  if　expressed　in　understandable　terms；　would　be
  equal　to　sixty　pounds　for　every　square　foot　of　surface。
  STREAM　LINES。The　next　observation　is；　that
  what　are　called　stream　lines　do　not　exist　in　the　fly。
  Its　head　is　as　large　in　cross　section　as　its　body；
  with　the　slightest　suggestion　only；　of　a　pointed
  end。　Its　wings　are　perfectly　flat；　forming　a　true
  plane；　not　dished；　or　provided　with　a　cambre；　even；
  that　upward　curve；　or　bulge　on　the　top　of　the　aeroplane
  surface；　which　seems　to　possess　such　a　fascination
  for　many　bird　flight　advocates。
  It　will　also　be　observed　that　the　wing　connection
  with　the　body　is　forward　of　the　line　A；　which
  represents　the　point　at　which　the　body　will　balance
  itself；　and　this　line　passes　through　the　wings
  so　that　there　is　an　equal　amount　of　supporting
  surface　fore　and　aft　of　the　line。
  Again；　the　wing　attachment　is　at　the　upper　side
  of　the　body；　and　the　vertical　dimension　of　the
  body；　or　its　thickness；　is　equal　to　four…fifths　of　the
  length　of　he　wing。
  The　wing　socket　permits　a　motion　similar　to　a
  universal　joint；　Fig。　55　showing　how　the　inner
  end　of　the　wing　has　a　downward　bend　where　it
  joins　the　back；　as　at　B。
  THE　MONOPLANE　FORM。For　the　purpose　of
  making　comparisons　the　illustrations　of　the　monoplane
  show　a　machine　of　300　square　feet　of　surface；
  which　necessitates　a　wing　spread　of　forty
  feet　from　tip　to　tip；　so　that　the　general　dimensions
  of　each　should　be　18　1/2　feet　by　8　1/2　feet　at　its
  widest　point。
  First　draw　a　square　forty　feet　each　way；　as　in
  Fig。　58；　and　through　this　make　a　horizontal　line
  1；　and　four　intermediate　vertical　lines　are　then
  drawn；　as　2；　3；　4；　5；　thus　providing　five　divisions；
  each　eight　feet　wide。　In　the　first　division　the
  planes　A；　B；　are　placed；　and　the　tail；　or　elevator
  C；　is　one…half　the　width　of　the　last　division。
  _Fig。　58。　Plan　of　Monoplane。_
  The　frame　is　3　1/2　feet　wide　at　its　forward　end；
  and　tapers　down　to　a　point　at　its　rear　end；　where
  the　vertical　control　plane　D　is　hinged；　and　the
  cross　struts　E；　E；　are　placed　at　the　division　lines
  3；　4；　5。
  The　angles　of　the　planes；　with　relation　to　the
  frame；　are　usually　greater　than　in　the　biplane；
  for　the　reason　that　the　long　tail　plane　requires
  a　greater　angle　to　be　given　to　the　planes　when
  arising；　or；　instead　of　this；　the　planes　A；　B；　are
  mounted　high　enough　to　permit　of　sufficient　angle
  for　initiating　flight　without　injuring　the　tail　D。
  Some　monoplanes　are　built　so　they　have　a　support
  on　wheels　placed　fore　and　aft。　In　others
  the　tail　is　supported　by　curved　skids；　as　shown
  at　A；　Fig。　59；　in　which　case　the　forward
  supporting　wheels　are　located　directly　beneath　the　planes。
  As　the　planes　are　at　about　eighteen　degrees
  angle；　relative　to　the　frame；　and　the　tail　plane
  B　is　at　a　slight　negative　angle　of　incidence；　as
  shown　at　the　time　when　the　engine　is　started；　the
  air　rushing　back　from　the　propeller；　elevates　the
  tail；　and　as　the　machine　moves　forwardly　over
  the　ground；　the　tail　raises　still　higher；　so　as　to
  give　a　less　angle　of　incidence　to　the　planes　while
  skimming　along　the　surface　of　the　ground。
  _Fig。　59。　Side　Elevation；　Monoplane。_
  In　order　to　mount；　the　tail　is　suddenly　turned
  to　assume　a　sharp　negative　angle；　thus　swinging
  the　tail　downwardly；　and　this　increases　the　angle
  of　planes　to　such　an　extent　that　the　machine　leaves
  the　ground；　after　which　the　tail　is　brought　to　the
  proper　angle　to　assure　horizontal　flight。
  The　drawing　shows　a　skid　at　the　forward　end；
  attached　to　the　frame　which　carries　the　wheels。
  The　wheels　are　mounted　beneath　springs　so　that
  when　the　machine　alights　the　springs　yield　sufficiently
  to　permit　the　skids　to　strike　the　ground；
  and　they；　therefore；　act　as　brakes；　to　prevent　the
  machine　from　traveling　too　far。
  CHAPTER　X
  POWER　AND　ITS　APPLICATION
  THIS　is　a　phase　of　the　flying　machine　which　has
  the　greatest　interest　to　the　boy。　He　instinctively
  sees　the　direction　in　which　the　machine　has　its
  life；its　moving　principle。　Planes　have　their
  fascination；　and　propellers　their　mysterious　elements；
  but　power　is　the　great　and　absorbing　question
  with　him。
  We　shall　try　to　make　its　application　plain　in
  the　following　pages。　We　have　nothing　to　do　here
  with　the　construction　and　operation　of　the　motor
  itself；　as；　to　do　that　justice；　would　require　pages。
  FEATURES　IN　POWER　APPLICATION。It　will　be
  more　directly　to　the　point　to　consider　the　following
  features　of　the　power　and　its　application：
  1。　The　amount　of　power　necessary。
  2。　How　to　calculate　the　power　applied。
  3。　Its　mounting。
  WHAT　AMOUNT　OF　POWER　IS　NECESSARY。In　the
  consideration　of　any　power　plant　certain　calculations
  must　be　made　to　determine　what　is　required。
  A　horse　power　means　the　lifting　of　a　certain
  weight；　a　definite　distance；　within　a　specified
  time。
  If　the　weight　of　the　vehicle；　with　its　load；　are
  known；　and　its　resistance；　or　the　character　of　the
  roadway　is　understood；　it　is　a　comparatively　easy
  matter　to　calculate　just　how　much　power　must　be
  exerted　to　overcome　that　resistance；　and　move　the
  vehicle　a　certain　speed。
  In　a　flying　machine　the　same　thing　is　true；　but
  while　these　problems　may　be　known　in　a　general
  way；　the　aviator　has　several　unknown　elements
  ever　present；　which　make　estimates　difficult　to
  solve。
  THE　PULL　OF　THE　PROPELLER。Two　such　factors
  are　ever　present。　The　first　is　the　propeller
  pull。　The　energy　of　a　motor；　when　put　into　a
  propeller；　gives　a　pull　of　less　than　eight　pounds
  for　every　horse　power　exerted。