572

FLIGHT.

J U N E  g 1938.

WESTLAND LYSANDER MARK

(890

  b.p. Bristol Mercury XII

DIMENSIONS

AREAS

Length o.a. ... —

Wing span  ... ... .... _  «• •••

Height o.a ... ... ... ... 1*

Wheel track

Chord at root  .. ,.. ...

Tailpiane

 span

  ... ... ... -•• •

„ chord

 at

 roo t ,;-. .

  ...

Airscrew diameter / _ . . . / -  ...

Wing (incl. ailerons)

„

  elear

 of

 fuselage

Ailerons

Fi n

  '.

Rudder

Tailplane

Elevators

Flaps

sq.H.

260.0

250.0

18.5

17.5

8

35.0

  3 S

29.0

When these considerations  axe  taken into account,  the

adopt ion o   thin type of  undercarriage, which would other-

wise  be  rather puzzling, becomes quite logical.

From  the  aerodynamic point  of  view,  the  Westland de-

signers deserve  the  very greatest credit  for  having pro-

duced a  fully slotted and  flapped wing in which all opera-

tion is  entirely automatic.  The Han dley Page leading-edge

slots extend over  the  entire span  of the  wings,  the  inner

portion being  a  lift slot, while  the  outer portion  is a

normal  tip  slot.  The  inner slot  is  connected  by  levers

and linkages  to the  trailing-edge flaps.  By  very careful

design  the  arrangement  has  been  so  adjusted tha t  by a

suitable choice of  take-off attitude  the pilot  can cause the

lift flaps  to  come down the  desired number  of  degrees.

If  he  lifts  the  tail more during  the take-off,  the  machine

will run along w ithout  the slots opening or the flaps coming

down, whereas  if the  tail  is  kept lower than desired  the

slots and  flaps will open fully,  and the drag will be greater

than desirable,  so  that probably  the  take-off  run  will be

increased. Similarly,  on  landing:  by  dropping  the  tail

sufficiently  the  leading-edge slot automatically brings  the

flap down  to its  full ext en t, wh ich results  in the  steepest

approach  and  shortest landing  run.

No  Snag

It might have been thought that  as the  leading-edge

slot  is, so to  speak, incidence-operated,  it  might  be pos-,

sible,  in  pulling  the  machine  out of a  steep dive,  for

example,  to cause the slot and  flap to open at  high speed.

This, however,  has not  been found  to be the  case, pre-

sumably because  in a  pull-out from  a  dive,  the  machine

does  not  reach  an  angle  of  incidence sufficiently great  to

cause  the  slot  to  open.

Older readers of  light  will doubtless recollect  the  little

Widgeon monoplane built for one of the Lympne light plane

competitions  and  afterwards bough t  by Dr.  Reid. Th at

little machine was also a  strut-braced monoplane, and its

plan form was very m uch like that of the modern Lysander

monoplane. This is not, of  course, any mere coincidence,

bu t  is due to the  fact th at on the one hand it is not desired

to have a wide chord at the fuselage,  and on the other tha t

the maximum wing strength  is desired at the  point where

the lift struts  are  attached. Consequently,  in  plan form

the chord  is  greatest along  the  line joining  the  lift str ut

a t tachments  to the  wing,  and the  wing tapers outward

and inward from this line.

The fuselage  of the  Lysander has the  usual girder type

of construction,  but the  external shape  is  made rounded

by  the  addition  of a  light fairing  of  wood construction

clipped  to the  me tal fuselage prim ary struct ure . Gener-

ally speaking,  the  fuselage  is of  good shape from  a  drag

point  of  view, although  the  fact that  it was  desired  to

place  the  pilot high above  the  fuselage  in  order  to  give

him a good view has somew hat interfered with w hat would

otherwise be a  very nearly perfect streamline shape. That

the drag cannot  be  excessive  is  proved  by the  fact that

the Lysander Mk. I,  when fitted with a Mercury XII engine

of  890 h.p., has a top  speed  of  abou t  230 m.p.h .  The

landing speed  is 52  m.p.h. ,  the  wide speed range being

attained very largely by a  combination  of high-wing load-

ing and the use of slots and  flaps.

From  a  structural point  of  view, also,  the Lysander is

rather unorthodox.  To sum it up  quite briefly  it  might

perhaps  be  said that  the  outstanding feature  in its con-

struction  is the  very extensive use of  extruded sections of

light alloy. There  has  been very close co-operation be-

tween  the  Lysander 's designers  and two  specialist firms,

High Duty Alloys,  of  Slough,  and the  Reynolds Tube

Co., Ltd.

Accessibility  and ease of maintenance and servicing were

the guiding principles  in  deciding upon  the  general type

of construction . Th at solved  the  problem, girder or

monocoque?  There still remained  the  deta ils. Ulti-

mately  it was  decided  to use in the  front portion  of the

fuselage  the  type  of  construction  of  which  the  Westland

firm had such long and  successful experience in the Wapiti

and Wallace biplanes: duralumin tubes  of  square section

joined  by  bolts  and  flat plates.  For the  rear portion,

Straight and sloping forked lugs are cut from special channel-

section extrusions.