_Fig。　15。　Utilizing　Momentum。_
  CUTTING　OFF　THE　POWER。This　curve；　A；　may
  reach　that　point　where　momentum　has　ceased　as
  a　forwardly…propelling　factor；　and　the　machine
  now　begins　to　travel　rearwardly。　（Fig。　16。）　It
  has　still　the　entire　supporting　surfaces　of　the
  planes。　It　cannot　loop…the…loop；　as　in　the　instance
  where　the　planes　are　fixed　immovably　to　the　body。
  Carefully　study　the　foregoing　arrangement；　and
  it　will　be　seen　that　it　is　more　nearly　in　accord　with
  the　true　flying　principle　as　given　by　nature　than
  the　vaunted　theories　and　practices　now　indulged
  in　and　so　persistently　adhered　to。
  The　body　of　a　flying　machine　should　not　be　oscillated
  like　a　lever。　The　support　of　the　aeroplane
  should　never　be　taken　from　it。　While　it　may　be
  impossible　to　prevent　a　machine　from　coming
  down；　it　can　be　prevented　from　overturning；　and
  this　can　be　done　without　in　the　least　detracting
  from　it　structurally。
  _Fig。　16。　Reversing　Motion。_
  The　plan　suggested　has　one　great　fault；　however。
  It　will　be　impossible　with　such　a　structure
  to　cause　it　to　fly　upside　down。　It　does　not　present
  any　means　whereby　dare…devil　stunts　can　be　performed
  to　edify　the　grandstand。　In　this　respect
  it　is　not　in　the　same　class　with　the　present　types。
  THE　STARTING　MOVEMENT。Examine　this　plan
  from　the　position　of　starting；　and　see　the　advantages
  it　possesses。　In　these　illustrations　we
  have　used；　for　convenience　only；　the　monoplane
  type；　and　it　is　obvious　that　the　same　remarks　apply
  to　the　bi…plane。
  Fig。　17　shows　the　starting　position　of　the　stock
  monoplane；　in　position　1；　while　it　is　being　initially
  run　over　the　ground；　preparatory　to　launching。
  Position　2　represents　the　negative　angle　at　which
  the　tail　is　thrown；　which　movement　depresses　the
  rear　end　of　the　frame　and　thus　gives　the　supporting
  planes　the　proper　angle　to　raise　the　machine；
  through　a　positive　angle　of　incidence；　of　the　plane。
  _Fig。　17。　Showing　changing　angle　of　body。_
  THE　SUGGESTED　TYPE。In　Fig。　18　the　suggested
  type　is　shown　with　the　body　normally　in　a　horizontal
  position；　and　the　planes　in　a　neutral　position；
  as　represented　in　position　1。　When　sufficient
  speed　had　been　attained　both　planes　are
  turned　to　the　same　angle；　as　in　position　2；　and
  flight　is　initiated　without　the　abnormal　oscillating
  motion　of　the　body。
  But　now　let　us　see　what　takes　place　the　moment
  the　present　type　is　launched。　If；　by　any　error　on
  the　part　of　the　aviator；　he　should　fail　to　readjust
  the　tail　to　a　neutral　or　to　a　proper　angle　of　incidence；
  after　leaving　the　ground；　the　machine　would
  try　to　perform　an　over…head　loop。
  The　suggested　plan　does　not　require　this　caution。
  The　machine　may　rise　too　rapidly；　or　its
  planes　may　be　at　too　great　an　angle　for　the　power
  or　the　speed；　or　the　planes　may　be　at　too　small　an
  angle；　but　in　either　case；　neglect　would　not　turn
  the　machine　to　a　dangerous　position。
  These　suggestions　are　offered　to　the　novice；　because
  they　go　to　the　very　foundation　of　a　correct
  understanding　of　the　principles　involved　in　the
  building　and　in　the　manipulation　of　flying　machines
  and　while　they　are　counter　to　the　beliefs　of
  aviators；　as　is　shown　by　the　persistency　in　adhering
  to　the　old　methods；　are　believed　to　be　mechanically
  correct；　and　worthy　of　consideration。
  THE　LOW　CENTER　OF　GRAVITY。But　we　have　still
  to　examine　another　feature　which　shows　the　wrong
  principle　in　the　fixed　planes。　The　question　is
  often　asked；　why　do　the　builders　of　aeroplanes
  place　most　of　the　weight　up　close　to　the　planes？
  It　must　be　obvious　to　the　novice　that　the　lower
  the　weight　the　less　liability　of　overturning。
  FORE　AND　AFT　OSCILLATIONS。The　answer　is；
  that　when　the　weight　is　placed　below　the　planes　it
  acts　like　a　pendulum。　When　the　machine　is　traveling
  forward；　and　the　propeller　ceases　its　motion；
  as　it　usually　does　instantaneously；　the　weight；　being
  below；　and　having　a　certain　momentum；　continues
  to　move　on；　and　the　plane　surface　meeting
  the　resistance　just　the　same；　and　having　no　means
  to　push　it　forward；　a　greater　angle　of　resistance　is
  formed。
  In　Fig。　19　this　action　of　the　two　forces　is　illustrated。　The
  plane　at　the　speed　of　30　miles　is　at
  an　angle　of　15　degrees；　the　body　B　of　the　machine
  being　horizontal；　and　the　weight　C　suspended　directly
  below　the　supporting　surfaces。
  The　moment　the　power　ceases　the　weight　continues
  moving　forwardly；　and　it　swings　the　forward
  end　of　the　frame　upwardly；　Fig。　20；　and　we　now
  have；　as　in　the　second　figure；　a　new　angle　of　incidence；
  which　is　30　degrees；　instead　of　12。　It　will
  be　understood　that　in　order　to　effect　a　change　in
  the　position　of　the　machine；　the　forward　end　ascends；
  as　shown　by　the　dotted　line　A。
  _Fig。　20。　Action　when　Propeller　ceases　to　pull。_
  The　weight　a　having　now　ascended　as　far　as
  possible　forward　in　its　swing；　and　its　motion
  checked　by　the　banking　action　of　the　plan　it　will
  again　swing　back；　and　again　carry　with　it　the
  frame；　thus　setting　up　an　oscillation；　which　is　extremely
  dangerous。
  The　tail　E；　with　its　unchanged　angle；　does　not；
  in　any　degree；　aid　in　maintaining　the　frame　on
  an　even　keel。　Being　nearly　horizontal　while　in
  flight；　if　not　at　a　negative　angle；　it　actually　assists
  the　forward　end　of　the　frame　to　ascend。
  APPLICATION　OF　THE　NEW　PRINCIPLE。Extending
  the　application　of　the　suggested　form；　let　us　see
  wherein　it　will　prevent　this　pendulous　motion　at
  the　moment　the　power　ceases　to　exert　a　forwardly…
  propelling　force。
  _Fig。　21。　Synchronously　moving　Planes。_
  In　Fig。　21　the　body　A　is　shown　to　be　equipped
  with　the　supporting　plane　B　and　the　tail　a；　so
  they　are　adjustable　simultaneously　at　the　same
  angle；　and　the　weight　D　is　placed　below；　similar　to
  the　other　structure。
  At　every　moment　during　the　forward　movement
  of　this　type　of　structure；　the　rear　end　of
  the　machine　has　a　tendency　to　move　upwardly；
  the　same　as　the　forward　end；　hence；　when　the
  weight　seeks；　in　this　case　to　go　on；　it　acts　on　the
  rear　plane；　or　tail；　and　causes　that　end　to　raise；
  and　thus　by　mutual　action；　prevents　any　pendulous
  swing。
  LOW　WEIGHT　NOT　NECESSARY　WITH　SYNCHRONOUSLY…MOVING　WINGS。
  A　little　reflection　will　convince
  any　one　that　if　the　two　wings　move　in　harmony；
  the　weight　does　not　have　to　be　placed　low；
  and　thus　still　further　aid　in　making　a　compact
  machine。　By　increasing　the　area　of　the　tail；　and
  making　that　a　true　supporting　surface；　instead　of
  a　mere　idler；　the　weight　can　be　moved　further
  back；　the　distance　transversely　across　the　planes
  may　be　shortened；　and　in　that　way　still　further
  increase　the　lateral　stability。
  CHAPTER　V
  DIFFERENT　MACHINE　TYPES　AND　THEIR　CHARACTERISTICS
  THERE　are　three　distinct　types　of　heavier…than…
  air　machines；　which　are　widely　separated　in　all
  their　characteristics；　so　that　there　is　scarcely　a
  single　feature　in　common。
  Two　of　them；　the　aeroplane；　and　the　orthopter；
  have　prototypes　in　nature；　and　are　distinguished
  by　their　respective　similarities　to　the　soaring
  birds；　and　those　with　flapping　wings。
  The　Helicopter；　on　the　other　hand；　has　no　antecedent
  type；　but　is　dependent　for　its　raising
  powers　on　the　pull　of　a　propeller；　or　a　plurality
  of　them；　constructed；　as　will　be　pointed　out　hereinafter。
  AEROPLANES。The　only　form　which　has　met
  with　any　success　is　the　aeroplane；　which；　in
  practice；　is　made　in　two　distinct　forms；　one　with
  a　single　set　of　supporting　planes；　in　imitation　of
  birds；　and　called　a　monoplane；　and　the　other　having
  two　wings；　one　above　the　other；　and　called
  the　bi…plane；　or　two…planes。
  All　machines　now　on　the　market　which　do　not
  depend　on　wing　oscillations　come　under　those
  types。
  THE　MONOPLANE。The　single　plane　type　has
  some　strong　claims　for　support。　First　of　these
  is　the　comparatively　small　head　resistance；　due
  to　the　entire　absence　of　vertical　supporting　posts；
  which　latter　are　necessary　with　the　biplane　type。
  The　bracing　supports　which　hold　the　outer　ends
  of　the　planes　are　composed　of　wires；　which　offer
  but　little　resistance；　comparatively；　in　flight。
  ITS　ADVANTAGES。Then　the　vertical　height　of
  the　machine　is　much　less　than　in　the　biplane。　As
  a　result　the　weight；　which　is　farther　below　the
  supporting　surface　than　in　the　biplane；　aids　in
  maintaining　the　lateral　stability；　particularly
  since　the　supporting　frame　is　higher。
  Usually；　for　the　same　wing　spread；　the　monoplane
  is　narrower；　laterally；　which　is　a　further
  aid　to　prevent　tilting。
  ITS　DISADVANTAGES。But　it　also　has　disadvantages
  which　must　be　apparent　from　its　structure。
  As　all　the　supporting　surface　is　concentrated
  in　half　the　number　of　planes；　they　must
  be　made　of　greater　width　fore　and　aft；　and　this；
  as　we　shall　see；　later　on；　proves　to　be　a　disadvantage。
  It　is　also　doubted　whether　the　monoplane　can
  be　made　as　strong　st