,,natural ,,stability      ,,and        
,,the ,,parachute ,,principle      ,,in 
,,aeroplanes        ,,by        ,w4     
,,lemaitre          ,hon4 ,sec41        
,aeroplane ,building and ,flying        
,society        ,,with #cd              
,,illustrations            ,,london     
,e4  ,f4 ,n4 ,,spon1 ,,ltd41 #eg        
,,haymarket        ,new ,york           
,,spon  ,,chamberlain1 #abc ,,liberty   
,,street        #aiaa                   
,,contents                              
,,page        ,,frontispiece            
iv        ,,preface                     
ix        ,,chapter          ,i4 ,,the  
,,importance ,,of ,,stability           
#aa         ,,ii4 ,,speed ,,as ,a       
,,means ,,of ,,stability                
#ad        ,,iii4 ,,the ,,low ,,centre  
,,of ,,gravity                       #ag
         ,,iv4 ,,short ,,span ,,and     
,,area                             #bh  
,v4 ,,variable ,,speed ,,and ,,the      
,,parachute ,,principle      #cf        
,,vi4 ,,the ,,design ,,which ,,fulfils  

,,the ,,conditions         #ci          
,,preface      ,since there is nothing  
new under the sun1 it is useless to     
pretend  that there is anything new in  
the design here advocated or the        
theories advanced4 ,both are rather the 
result of a commonsense  consideration  
of the different points of all flying   
machines1 natural  and artificial1 and  
an endeavour to select from the great   
number of  good points those which seem 
most likely to blend together into a    
practical machine4 ,the conclusions     
reached are the result of a quite       
independent investigation1 carried on   
over three years by means of  numberless
 experiments1 and the writer has        
endeavoured to make no  single statement
 which he cannot by some experiment     
amply prove4          ,,natural         
,,stability ,,in ,,aeroplanes           
,,chapter ,i4    ,,the ,,importance ,,of
 ,,stability4      ,in considering the  
whole question of aviation1 it becomes  
evident that  the one point to strive   

for at the present juncture is          
stability4 ,if  we are ever to have a   
practical flying machine1 that is1 a    
machine  which we can use as we do a    
yacht1 a motor car1 or a bicycle1 it    
must  be one that we can trust to keep  
its balance by reason of the natural    
forces embodied in it1 and without any  
effort of control on the part  of the   
pilot4 ,it may be objected that a       
bicycle does not do this1 and  this is  
true1 but1 on the other hand1 the       
upsetting of a bicycle is a  very small 
matter1 whereas the tilting of an       
aeroplane mostly means  sudden death to 
its occupant1 and it is probable that if
 the same  consequences followed the    
tilting of a bicycle1 bicycles would    
soon  have been made with four wheels4  
,at present aeroplanes are the most     
unstable of all things4 ,the least      
gust1 the least shifting of weight1 the 
slightest difference in the  density of 
the strata of the supporting air1 and   
the machine sways1  and if not instantly

 corrected by the pilot the sway becomes
 a tilt1  the tilt a dive1 and the rest 
is silence4 ,the first aeroplanes1 the  
,wrights' for instance1 were so unstable
 that twenty minutes in one of  them was
 as much as the most iron-nerved man    
could stand1 the  continual strain being
 too exhausting to keep up for any      
length of  time4 ,by throwing out       
extensions and outriggers in all        
directions we  have altered that to a   
certain extent1 but only to an          
extent--we have  not yet got rid of it4 
,the monoplane is probably the most     
unstable1 as  might be expected from its
 smaller surface1 but the bi-plane runs 
it  pretty closely4    ,and the         
difficulty seems to arise chiefly from  
the fact that the  machines are built   
round the propeller4 ,in the case of a  
yacht or a  car1 the machine is built   
first and the propelling means is fitted
 on  as an auxiliary4 ,the consequence  
is that an aeroplane which is safe      
enough while the propeller is exerting a

 tractive force of some #bej  lbs41     
becomes1 the moment this power is for   
any reason stopped1 merely  a shapeless 
construction at the mercy of the wind   
and the force of  gravitation4 ,it is   
true that most machines may be made to  
glide if the  pilot is clever enough and
 quick enough to steer them into the    
proper  gliding angle1 but the machine  
that will naturally and by reason of    
its design assume its proper gliding    
angle when the propelling force  is     
withdrawn1 has not yet been built4      
,such a machine would have 8,natural    
,stability40    ,it will be recognized  
that this natural stability1 which      
depends on  the design of the machine1  
is something entirely different from    
8automatic stability0 of which there are
 many systems1 all having this  one     
defect2 that1 depending upon working    
devices1 movable planes1  gyroscopes1   
compensating balancers1 pendulums1 etc41
 they are all  liable to go wrong and   
refuse to act the moment a sudden strain

 makes  their perfect action most       
important4    ,considering that the     
propeller is the only means the         
aeroplane has of  keeping in the air at 
all1 the question arises3 ,is it        
possible to  design a machine that will 
be stable to the extent of descending   
safely when the propeller stops1 and    
that will yet be a good and  speedy     
flyer8    ,that is the problem we have  
to solve4          ,,chapter ,,ii4      
,,speed ,,as ,a ,,means ,,of            
,,stability4      ,it is recognized on  
all hands that speed is a great factor  
in the  problem of stability4 ,to begin 
with1 a machine going at high speed     
would be practically untouched by gusts 
of wind1 different densities  of air    
strata1 holes in the air1 etc4 ,also its
 greater momentum would  tend to keep it
 in a straight line1 not only relative  
to its course  but also relative to     
itself4 ,that is to say1 its wings being
 started  in a horizontal plane1 would  
tend to keep in the same plane and would

  not easily tilt or sway out of it4    
,both these effects of natural law  show
 that a high speed machine must be more 
stable than a low speed  machine4 ,how  
then are we to design a high speed      
machine8    ,leaving aside the question 
of higher power1 the first point that   
suggests itself is to lessen the head   
resistance4 ,all fast things1  boats1   
birds1 arrows1 even motor-cars1 are made
 long and narrow4 ,it  will be objected 
that a bird with its wings outspread is 
not long and  narrow1 but in the sense  
in which this illustration is meant1 the
  bird's wings1 being merely its        
propelling apparatus1 do not count1 and 
when the bird is at its fastest1 as in  
the swoop of a hawk or an  eagle1 the   
wings are shut tightly to the body so as
 to offer no  resistance to its         
lightning passage through the air4 ,if  
we are to  follow previous experience in
 ,nature's laws1 our aeroplanes must be 
considerably reduced in span4 ,to drive 
through the air at a high speed  with a 

machine of #dj foot span is a practical 
impossibility1 both  because of the     
tremendous power it would require and   
also by reason of  the great strength   
the plane must have to withstand the    
resistance of  the air4    ,in reducing 
the span1 however1 we reduce the lifting
 surface of the  machine4 ,but on the   
other hand it must be remembered that   
the lifting  efficiency is increased by 
increasing the speed4 ,lift is the      
product  of supporting surface and      
speed4 ,a small plane driven at a high  
speed  will give as great a lift as a   
large plane driven at a low speed4      
,speed1 again1 is the difference between
 the propelling power and the  head     
resistance1 and we can increase the     
speed by decreasing the  resistance4 ,it
 follows1 then1 that we need not        
necessarily give up  lifting power by   
reducing the span of the wings1 since   
the shorter  span gives greater speed1  
and the increase of efficiency by reason
 of  the greater speed would go to make 

up for the loss of span4    ,it is1     
then1 quite possible to design a short  
span machine which shall  be as         
efficient for lift as a long span       
machine1 and which will have  the       
advantage of possessing1 by reason of   
its speed1 much greater  stability4     
,but the span is not the only factor in 
the speed problem4 ,in the low  speed   
machines at present in use we have found
 it necessary to curve  the planes to   
get greater efficiency4 ,this efficiency
 is also gained  at the expense of head 
resistance1 and it is already recognized
 that  the higher the speed the less is 
the need of camber4 ,this is the same   
problem over again4 ,a high speed flat  
plane will give as much lift as  a low  
speed cambered plane1 and we gain in    
stability with every  additional mile   
per hour4    ,the third point to be     
considered in the problem of speed is   
the  resistance caused by the multitude 
of struts and wires1 the body of  the   
pilot1 the tanks1 engine1 and all the   

other impedimenta projecting  in all    
directions from the body of the         
aeroplane4 ,it has occurred to  our     
builders that if the whole of these     
things could be collected  together and 
enclosed in a light covered-in car of a 
proper shape1 the  skin friction of such
 a car would be much less than the total
 head  resistance offered by the        
different obstructions so covered4 ,and 
there  is another advantage to be gained
 here1 for if1 at #dj miles per hour1   
the force of the wind is very seriously 
uncomfortable for the pilot1  the       
position at such speeds as #gj or #ajj  
miles per hour would be quite           
impossible4          ,,chapter ,,iii4   
,,the ,,low ,,centre ,,of ,,gravity4    
,the first thing that occurs to the     
investigator on the subject of          
stability is that nature offers us a    
sure means of keeping our  machines     
upright by adopting the simple method of
 placing all the  heavier parts at the  
bottom4 ,in all other constructions we  

have  adopted this plan with perfect    
success4 ,in boats1 yachts1 cars1       
balloons1 everything man uses in fact1  
the simplest1 best and most  obvious    
method of keeping a thing upright is to 
utilize the force of  gravity1 place the
 lighter or supporting parts above and  
the weight  below1 and the thing is     
done4    ,this simple method of         
obtaining stability did not escape the  
aeroplane  designers1 and we have had   
several machines which embodied this    
principle1 more or less4 ,unfortunately1
 however1 they all proved  failures4 ,a 
machine would be designed1 and1 with the
 weight high1  would fly well1 though it
 was unstable4 ,put the weight low and  
you got  rid of the instability1 and at 
the same time the machine became        
unmanageable4 ,it looked as if flying   
and instability were  interchangeable   
terms4 ,so1 as it was a machine that    
would fly the  designers were after1 the
 weight was kept up and the stability   
was  left to the pilot4 ,the machines   

were made 8sensitive0 as it is called1  
that is to say1 sensitive to a touch of 
the rudder or the balancers4  ,they are 
also1 it is true1 equally sensitive to a
 gust of wind or a  slight shifting of  
weight or pressure1 and this has caused 
the  smashing of a good many machines   
and some pilots2 but after all this  is 
the fortune of war1 and no one is       
compelled to go up in an  aeroplane4    
,the curious thing about it is that it  
does not seem to have occurred  to our  
designers that if their pet design would
 not fly with the  weight low1 perhaps  
it might be possible to alter the design
 instead  of altering the position of   
the centre of gravity1 and so obtain    
what  we are all looking for1 a         
naturally stable machine that is yet    
sensitive to control4    ,there are two 
chief difficulties in the way of the low
 centre of  gravity machine4 ,one is    
that the heaviest portion of the machine
 being  some distance below its support1
 it is apt to give rise to a pendulum   

or swaying motion4 ,the other is that of
 tilting1 or banking up1 in  turning a  
corner4 ,these are really two           
developments of the same  difficulty1   
i4e4 pendulum motion4    ,if we take a  
strip of stiff paper to represent a     
plane and put a small  weight in the    
centre of the plane1 the model on being 
glided to earth  does not tend to sway  
7,fig4 #a74 ,if we put our weight on a  
tiny piece  of wire an inch or so below 
the plane 7,fig4 #b7 and set the model  
free1  it will probably acquire a       
swinging motion as it descends4 ,that is
  the whole trouble4 ,the trouble is    
real enough1 but the fallacy is in      
supposing it to be all the fault of the 
low centre of gravity4 ,all  ships that 
were ever designed have a low centre of 
gravity1 yet some  roll dreadfully and  
others do not1 which1 in itself1 should 
be proof  sufficient that it is the     
design of the machine and not the       
position  of the ballast that is at     
fault4    ,illustration3 ,,fig4 #a41    

,,fig4 #b4 ,,and ,,fig4 #c4    ,let us  
now try some experiments4 ,it will be   
noticed that in the  machines which have
 employed the low centre of gravity the 
span of the  wings has usually been #cj 
feet or more1 and the centre of gravity 
about #f feet below the centre4 ,here is
 a paper model of the present  aeroplane
 7,fig4 #a74 ,here is the same machine  
with a low centre of  gravity 7,fig4    
#b74 ,now bend the paper upwards as in  
,fig4 #c and you get  rid of the        
swaying4 ,also1 of course1 you get rid  
of the supporting  surface4 ,but there  
is probably some point of greatest      
efficiency where  you may compromise4   
,if you take model #b and bend it       
slightly 7,fig4 #d7  it will sway1 but  
not much1 not so much as ,fig4 #b4 ,now 
with a pair of  scissors clip the wings 
a bit at a time1 and you will find that 
as the  span gets shorter the swaying   
decreases1 and that when you have the   
three points formed by the ends of the  
two wings and the weight  equidistant   

from the centre where they meet1 the    
plane is stable 7,fig4  #e74 ,the reason
 is that it is not the pendulum with the
 weight at the  bottom that swings so   
much1 but the long wings that see-saw4  
,by  shortening the wings you have      
reduced the length of the see-saw1 which
  is the same as reducing the length of 
the pendulum1 and consequently1  by     
pendulum law1 the oscillations must be  
much quicker and shorter and  will at   
once damp out4 ,it is curious that this 
point seems to have  escaped the        
designers4 ,it is well known that all   
pendulum motion tends  to damp out1 and 
the shorter the pendulum the quicker it 
comes to  rest4 ,hitherto the idea has  
been to shorten it vertically1 but the  
same effect exactly is obtained by      
shortening it horizontally1 and the  low
 centre of gravity remains to give      
stability4 ,it was stated by some       
sapient objector to the low centre of   
gravity1 that the pendulum  motion once 
set up1 increased till it turned the    

machine over4 ,a  pendulum which        
increased its swing at every stroke     
would be something  new in the          
scientific world4    ,illustration3     
,,fig4 #d4    ,illustration3 ,,fig4 #e4 
,another development of the pendulum    
difficulty is the probable fore  and aft
 sway1 but this may be overcome by      
increasing the supporting  surface of   
the tail4 ,many machines do not lift    
with the tail at all1  and those that do
 employ lifting tails1 have them with   
very small  surface4 ,consequently1 the 
centre of gravity comes nearly under the
  centre of the main plane1 and the     
whole machine1 turning on its centre  of
 gravity in all directions as on a      
pivot1 is liable to swing fore  and aft4
 ,if the supporting surface of the tail 
be increased and the  centre of gravity 
carried further aft1 this pendulum      
motion is also  rendered impossible1 and
 the machine is stable both ways4    ,a 
few illustrations may serve to make the 
advantages of the low centre  of gravity

 more clear1 and to avoid complications 
we will suppose the  planes to be still 
and in still air4 ,let ,fig4 #f         
represent an ordinary  flat plane having
 its centre of gravity coincident with  
its centre of  pressure1 the centre of  
pressure of each half or wing being at  
,a ,a4  ,the plane is in equilibrium4   
,now allow it to tilt 7,fig4 #g71 and it
  will be seen that it is still in      
equilibrium1 since the weight is in  the
 centre and the wing tips equidistant   
from it4 ,let it tilt still  more till  
it is vertical 7,fig4 #h71 and the      
balance is still the same4  ,it is      
evident1 therefore1 that such a plane   
would travel equally well  in any of the
 positions shown1 and that it can only  
be kept in  position 7,fig4 #f7 by the  
skilful manipulation of the pilot4      
,illustration3 ,,fig4 #f41 ,,fig4 #g41  
,,and ,,fig4 #h4    ,in the same way1   
the machine having no lifting tail is   
longitudinally  unstable1 for1 being    
balanced on its centre of pressure which

 would be  coincident with its centre of
 gravity and probably about #b feet from
  the trailing edge of the plane--it may
 assume any position 7,figs4 #i1  #aj1  
#aa and #ab71 and still be in           
equilibrium1 when it is evident that    
the proper position 7,fig4 #i7 is only  
maintained by the constant  control of  
the tail elevator4    ,illustration3    
,,fig4 #i41 ,,fig4 #aj41 ,,fig4 #aa41   
,,fig4 #ab41 ,,and ,,fig4 #ac4    ,now  
take the case of a machine having a low 
centre of gravity4 ,its  natural        
position is shown at ,fig4 #ac1 and it  
is at once evident that  any other      
position such as ,figs4 #ad and #ae     
could not be maintained for  a moment1  
since the weight being at an angle1 must
 inevitably drag the  machine back to   
its natural position 7,fig4 #ac74 ,in   
the same way with  regard to            
longitudinal balance1 a machine with two
 lifting surfaces  such as ,fig4 #ac1 is
 in its natural position with the centre
 of gravity  perpendicularly under the  

centre of pressure1 any other position1 
such  as ,fig4 #ag1 ,a1 is impossible1  
as the gravity pull must drag the       
machine along the dotted line till it   
resumes its proper and natural  position
 7,b74    ,illustration3 ,,fig4 #ad41   
,,fig4 #ae41 ,,and ,,fig4 #af4    ,the  
next difficulty is in the banking or    
tilting caused by the turning  of the   
machine in going round a curve4 ,in a   
very interesting  discussion carried on 
in the 8,aero10 it was stated that a low
 centre  of gravity machine could not   
bank up1 as the pull of gravity acting  
on  the low weight would prevent it4 ,it
 was also stated by another writer  that
 the machine would bank up too much and 
slide down sideways1  because the       
greatest weight having the greatest     
momentum would swing  out too much4     
,there is evidently some confusion here4
 ,let us consider  the question4    ,in 
turning there are three forces to take  
into consideration3    7#a7 ,the        
centrifugal force1 which tends to make  

the machine fly off at  a tangent to the
 curve at which it is turning4    7#b7  
,the action of gravitation4    7#c7 ,the
 extra lift given by the wing on the    
outside of the curve1  owing to the fact
 that it travels faster through the air4
    ,illustration3 ,,fig4 #ag4    ,the  
centrifugal force acts strictly in      
proportion to the mass it acts  on1 but1
 at the same time it must be remembered 
that the greater force  acting on the   
greater mass has the greater mass to    
move4 ,that is to  say1 that if the top 
part of the machine was very light and  
the  bottom part very heavy1 the force  
acting on the light part would be       
sufficient to send that part swinging   
out when rounding a curve1 and  the     
greater force acting on the greater mass
 at the bottom would be  sufficient to  
send that out to exactly the same       
degree4 ,consequently1  if only         
centrifugal force is considered1 the    
whole machine would swing  out without  
any tilting at all1 retaining its       

upright position4 ,but  here we must    
take another factor into consideration1 
the resistance of  the air4 ,this       
resistance would be greater on the      
greater surface of  the light top part  
than on the heavy bottom part1 and      
consequently the  bottom part would1    
automatically1 swing out most1 giving   
the banking  effect4 ,this would be     
increased by the extra lift given to the
 outer  wing by reason of its greater   
speed4 ,if we then take the force of    
gravitation into the problem we shall   
see that we have two  factors--unequal  
speed and unequal air                   
resistance--tending to bank up  the     
machine1 and one force--gravity--tending
 to pull it straight  again4 ,at a      
certain angle due to the amount of force
 exerted by each  of these1 the two     
opposing factors would balance1 and the 
machine  would be in equilibrium4    ,it
 would appear that most of the          
difficulties connected with the low     
centre of gravity machine are the result

 of hazy thinking and  slip-shod        
reasoning1 and that they do not exist in
 fact4 ,and let it be  remembered that  
the low centre of gravity machine with  
short span has  not yet been tried      
except by the writer1 who has succeeded 
in making a  paper model on this plan   
turn in its own length without in any   
way  losing its stability1 swaying1     
banking too much1 turning over1 sliding 
sideways1 or doing any of the frightful 
things which some people  declare it    
must do4 ,what it does do is to recover 
its balance though  started from the    
most impossible positions and always    
land on its  feet4          ,,chapter   
,,iv4    ,,short ,,span ,,and ,,area4   
,both on account of speed1 and also on  
account of stability1 with a low  centre
 of gravity1 we are forced in the       
direction of the short span  machine4   
,how are we to construct a machine with 
a span short enough to  damp out swaying
 and yet with sufficient lifting surface
 to raise the  machine and its load8    

,the position is somewhat simplified1 as
 already pointed out1 by the  fact that 
though the lift is decreased by the     
decrease in span1 it is  to a great     
extent compensated by the increase in   
speed4 ,also another  compensation is   
offered by the fact that fore and aft   
stability  requires a lifting tail4     
,lift is largely in proportion to the   
length of the entering edge of  the     
plane1 but it does not always follow    
that this entering edge must  be at     
right angles to the direction of flight4
 ,the ,dunne machine  obtains its lift  
with an entering edge that is entirely  
at an angle of  some #de degrees1 and   
its shape is an exact replica of the    
arrow head  of prehistoric man and the  
paper darts of our schooldays1 a design1
 by  the way1 that was patented in      
#ahfj4    ,at first sight it would seem 
that the lift on a plane shaped thus    
7,fig4 #ah71 would only be equal to the 
lift given by a plane with an  edge as  
long as the distance between ,a and ,c1 

thus 7,fig4 #ai71 but this  is not so4  
,although the lift is not so great as it
 would be if the  edge was straight in  
one line 7,fig4 #bj71 it is very much   
greater than  it would be on ,fig4 #ai4 
,the probability is that it is about    
half-way  between 7#ai7 and 7#bj71 but  
probably nearer to 7#bj7 than 7#ai74    
,there  are no exact data to go on1 but 
the efficiency of the ,dunne machine    
would seem to show this4                
,illustration3 ,,fig4 #ah4              
,illustration3 ,,fig4 #ai4 ,,and ,,fig4 
#bj4    ,again1 in seeking for planes   
that offer the least resistance to the  
air1 one of the best that suggests      
itself is the ,t-shape 7,fig4 #ba71  and
 this may be improved by cutting off    
useless corners 7,fig4 #bb74 ,a  plane  
of this shape lends itself to great     
strength of construction  owing to its  
small extending parts4 ,it is compact1  
it gives an  entering edge half as long 
again as its span1 and gives a lift in  
proportion to that edge1 and it is in   

itself stable4 ,having thus  evolved a  
suitable plane for the front of the     
machine1 the best thing  to do is to    
base the back plane on the same design1 
and join the two  planes together to    
form the supporting surface of the      
machine1  allowing sufficient space     
between them to avoid any interference  
or  overlapping4 ,the design then stands
 thus 7,fig4 #bc71 when the back  plane 
is a slightly smaller copy of the front 
one4 ,the position of the  centre of    
gravity in this design would be         
coincident with the centre  of pressure 
longitudinally and laterally1 and would 
be situated about  at ,a4 ,a paper model
 on these lines with a low centre of    
gravity may be  easily constructed and  
will prove useful in illustrating the   
different  points here stated4 ,the     
paper should be cut out sufficiently    
wide to  allow of a central longitudinal
 fold 7,figs4 #bd and #be71 and a roll  
of  paper should be made for ballast and
 pushed through the fold as shown  in   

,fig4 #bf at the point marked ,a4       
,illustration3 ,,fig4 #ba4 ,,and ,,fig  
#bb4    ,illustration3 ,,fig4 #bc4      
,illustration3 ,,fig4 #bd4 ,,and ,,fig4 
#be4    ,illustration3 ,,fig4 #bf4      
,the writer1 when exhibiting at ,olympia
 this year1 distributed #ejj of  these  
paper models1 and the almost uncanny way
 in which they righted  themselves when 
started from all sorts of impossible    
positions  greatly interested the       
visitors4 ,in fact1 numbers of persons  
spent  considerable time and ingenuity  
in trying to force the little glider  to
 turn over or dive1 but quite without   
success4    ,in order to test the       
turning capacity of this design1 a      
rudder should  be fixed to the tail1 and
 the model launched at a moderate speed1
 when  it will be found that it turns   
quickly and without any pendulum        
motion1 and without any perceptible     
tilt4 ,and although the writer's        
experiments with the paper model and    
with many larger ones on the same  plan 

have run into thousands1 none of the    
models have ever been  induced to come  
down in any other position but on their 
feet4 ,the  largest model1 which        
measured #f ft4 #f in4 in length1 was   
launched both  upside down and with its 
head pointing vertically to earth from a
  height of #cj ft41 and in each case   
righted before it reached the  ground   
and landed on its skids4    ,as a       
further lifting surface1 a very simple  
expedient offers itself in  the shape of
 a duct built on the box-kite principle4
 ,the  diamond-shaped box has been      
proved over and over again to be a very 
efficient lifting device1 but it has not
 yet been tried on an  aeroplane 7,fig4 
#bg74 ,it is also a great stabilizer1   
since the air  entering into the        
diamond-shaped opening is collected and 
compressed  into the top angle there1   
and the whole box is thus practically   
suspended from its apex line in absolute
 stability4 ,the lifting  efficiency of 
such a box--or rather the top portion of

 the box1 for  the bottom part is not   
needed on our machine--is considerably  
greater than the value of the entering  
edge1 and if run the whole  length of   
the machine it forms a triangular girder
 of great strength1  giving rigidity to 
the whole structure4 ,the lifting       
efficiency is  doubled by allowing the  
centre third of the girder to be open1  
as the  dead air from the front part    
escapes1 and the back part forms a new  
entering edge4    ,illustration3 ,,fig4 
#bg4 ,,and ,,fig4 #bh4    ,there is also
 another lifting factor to be           
considered1 and this is the  car4 ,if   
the car is formed with a flat bottom1   
this at once becomes an  efficient      
lifting plane1 and if the car is        
suspended with an open  space between it
 and the under surface of the plane1 the
 loss caused  by the negative angle of  
the upper portion of the car front is   
compensated for by the lift given by the
 deflected air to the under  surface of 
the main plane 7see ,fig4 #bh74    ,it  

will be recognized that in the design   
here being gradually evolved1  the great
 lifting surfaces of the ordinary       
machine have not been  largely reduced1 
they have simply been broken up into    
several smaller  surfaces1 each of which
 retains its efficiency4 ,something of  
the same  nature happened in prehistoric
 days1 when our first navigators at last
  made up their minds to abandon the    
flat-bottomed raft with its huge        
supporting surface1 for the new-fangled 
and dangerously narrow boat4    ,when   
all the different surfaces here         
mentioned are taken into  consideration1
 it will be found that the lifting      
surface in a  monoplane machine of this 
design1 with a span of #bj feet1 is     
equal to  the lifting surface of an     
ordinary bi-plane with a span of #dj    
feet4  ,and as the head resistance is   
less than half that of the bi-plane the 
speed should be very much greater4 ,at  
the same time the increased  speed      
renders the planes more efficient1 area 

for area1 than the  planes of the slower
 machine4          ,,chapter ,v4        
,,variable ,,speed ,,and ,,the          
,,parachute ,,principle4      ,hitherto1
 on the score of efficiency and also of 
stability1 our  investigations have led 
us to seek for speed as the grand       
panacea4 ,but  there are usually two    
sides to a question1 and though1 while  
in the  air1 speed may be most          
desirable1 it becomes a source of       
considerable  difficulty at both        
starting and landing4 ,a machine built  
to fly at #hj  miles per hour would have
 to get up something like #fj miles per 
hour  before it could rise4 ,and this   
difficulty is nothing like the problem  
that presents itself when we consider   
how it is to land in safety from  a     
flight at such a speed4 ,it becomes     
evident that some provision must  be    
made for starting and landing at some   
more practicable rates2 we  must have a 
variable speed machine4    ,to convert a
 high speed machine into a low speed    

machine means either  variable surface  
area1 variable camber1 or variable angle
 of  incidence4 ,any of these is        
possible1 but the choice must be decided
 by  simplicity of action4 ,to spread   
extra wings when rising or landing is  a
 cumbersome suggestion full of pitfalls 
and liable to accidents  through the    
failure of mechanical devices1 which1   
experience shows1  always have a way of 
failing at inopportune moments4 ,to vary
 the  camber of the planes is easier1   
but having decided on using flat  planes
 it would be loss of strength to make   
these flexible1 and an  increase of     
mechanical complications to have to flex
 them4 ,it would be  easy to alter the  
angle of incidence by having the leading
 edge  capable of a rotary movement1 and
 machines have been constructed         
employing this principle4 ,but the      
easiest plan of all1 since it does  away
 with all moving parts whatever1 would  
be to alter not the planes  themselves1 
but the whole machine4 ,thus suppose the

 angle of  incidence1 in order to get an
 efficient lift1 to be #a in #f1 the    
lifting plane1 all in the same line1    
would be set on its chassis so  that it 
presented an angle of #a in #e4 ,the    
machine would then lift at a  much      
slower speed4 ,naturally1 the tail being
 the furthest from the  centre of       
gravity would lift first1 and as soon as
 the speed was  sufficient the pilot    
would alter the elevator1 send down the 
tail on  to the ground1 thereby raising 
the leading edge of the front plane1    
and the machine would rise4 ,as the     
speed increased the tail would  continue
 to rise1 till1 at the maximum speed1   
the plane would be at  the minimum angle
 with the horizontal1 i4e4 at its lowest
 angle of  incidence4    ,this solves   
the problem of starting and to some     
extent of landing1 but  we have not yet 
come to the end of our resources4 ,most 
landings are  effected by shutting off  
the engine and planing down4 ,all flying
  machines will glide if put at the     

proper angle1 and it is the  business of
 the pilot to attend to this when he    
stops the engine4 ,but  to glide with   
the same wing area as is used in flying1
 means to glide  at the same rate4 ,in  
order to descend slowly it is necessary 
to have  more area4 ,is it possible to  
increase the area used for descent      
without interfering with the area used  
for flight8 ,in the design we  are      
engaged in considering1 it is possible1 
and without any mechanical  devices4    
,there is a large space between the     
front plane and the back  plane which is
 at present unused4 ,it is of very      
little value in  flight1 being in       
apteroid aspect and having practically  
no entering  edge4 ,but if this space is
 covered in it gives no resistance in   
flight1 and in descent it becomes a very
 efficient parachute4 ,further  than    
this1 if openings be cut in this plane  
immediately under the  centre of the two
 box-kite ducts1 the air under the      
longitudinal  plane1 having offered its 

resistance to the vertical passage of   
that  plane1 will escape into the duct  
and again offer considerable  resistance
 to the descent of this closed-in       
surface before it escapes  finally out  
of the end of the duct4    ,a model made
 on these lines will not need putting at
 any angle4 ,it  will assume its proper 
angle when left to itself by reason of  
its  design and the way the weight is   
balanced between the supporting  planes1
 and it will descend by partly gliding  
and partly parachuting  at a steep angle
 but quite slowly4 ,while1 if the pilot 
so choose1 he  can1 by raising the tail1
 increase the speed to a glide1 which he
 can  turn into a parachute action at   
any moment4          ,,chapter ,,vi4    
,,the ,,design ,,which ,,fulfils ,,the  
,,conditions4      ,in constructing any 
sort of machine it is usual to first    
obtain the  most important device and   
then to build up the accompanying parts 
to  that4 ,we have now succeeded in     
evolving the thing we set out to look   

for1 i4e41 a plane which will fly and   
lift with the minimum of head           
resistance1 and which is absolutely     
stable laterally and  longitudinally by 
reason of its construction and without  
any  interference from the pilot or the 
employment of balancing devices of  any 
description4 ,we have now to fit the    
propelling apparatus1 car1 and  chassis 
on to this4    ,fortunately1 the design 
is one that lends itself easily to      
manipulation1 which is not always the   
case with models4 ,the short span  of   
the planes1 for instance1 with the      
dihedral angle1 at once suggests  girder
 construction 7see ,figs4 #bi1 #cj71    
which is1 perhaps1 the  strongest of all
 devices1 being an ,m strut girder1     
familiar to us in  numberless bridges4  
,illustration3 ,,fig4 #bi4 ,,and ,,fig4 
#cj4    ,the photo which forms the      
frontispiece of this book1 and which1 by
 the  way1 makes the car look much too  
large owing to its position nearest  the
 camera1 represents a #f-;foot model    

which was exhibited at the  ,olympia    
,show1 in order to show the construction
 of a full-sized  machine made to the   
design of the paper model4 ,this has    
since been  considerably simplified1    
though the broad lines have been        
retained1 by  doing away with the struts
 and supports at the rear4 ,the whole of
 the  back plane is now supported by two
 curved members1 which start from  the  
girder of the leading edge and curve    
down to the ,t-section  longitudinals   
which form the rigid part of the        
chassis4 ,these  longitudinals and the  
skids end at the leading edge of the    
back plane  and the laminated skids and 
wheels are placed there4 ,the machine is
  built without a wire and without a    
casting4 ,it was made entirely of  wood1
 but is so designed that it can be made 
entirely out of steel  tube by using the
 ordinary screw connexions4 ,if built of
 timber1 the  joints are made with      
strips of steel bolted and screwed on to
 the  wood4 ,the girders forming the    

leading edge of each plane have sockets 
formed in the upright struts of the ,m  
into which the ribs fit 7see  ,fig4     
#cj71 and these are solid pieces on edge
 tapering to the trailing  edge1 where  
they are clipped to a slight spar which 
holds them  together4 ,this             
construction1 while very strong1 is yet 
sufficiently  flexible to bend          
considerably before it reaches breaking 
point4  ,longitudinal rigidity is       
secured by means of the triangular duct 
which  forms a complete girder from end 
to end4 ,a sufficient number of         
uprights fill the space between the     
plane and the two ,t-section            
longitudinals which form the rigid      
bottom of the machine4 ,on these  latter
 the floor is placed and the car is     
built up1 enclosing all the             
obstructions and putting the pilot in a 
place of safety1 enclosed on  all sides 
in the middle of the strongest part of  
the machine1 with the  strongest portion
 of that part between him and the       

ground4 ,the centre  of gravity is      
situated behind the pilot in the back of
 the car1 near  the floor1 and here is  
space for the oil and petrol tanks4 ,the
 engine  is in front of the pilot1 who  
is thus able to control it and watch it1
  and at the same time is free from the 
danger of having it fall upon  him in   
case of an accident4 ,as the machine    
turns horizontally and  vertically on   
its centre of gravity1 the front part of
 the car forms a  sort of baffle or     
blinker for the rudder and elevator to  
act against4  ,both these are at the    
tail of the machine1 where they have the
 most  leverage1 and these two are      
controlled by the one lever1 which is   
pushed forward or pulled backward to    
raise or lower the elevator1 and  turned
 bicycle fashion to move the rudder4 ,as
 the machine balances  itself1 there is 
no need for any balancing device either 
automatic or  controlled4               
,illustration3 ,,fig4 #ca4     ,the     
propellers may be two or more1 and those

 in front find a very firm  fixing in   
the intersection of two strong struts1  
which join the  wingtips to the bottom  
of the car1 and the supports which run  
from the  centre of these to the strong 
joint formed by the intersection of the 
longitudinal and lateral girder4 ,at the
 back there may be two  propellers fixed
 as in the front1 or one large one at   
the rear of the  car4 ,they are all     
worked from the one engine and the      
thrust is  slightly above the centre of 
gravity4 ,each propeller is placed just 
under the leading edge of a plane1 ,fig4
 #ca1 the idea being that a  certain    
amount of air is always thrown out by   
centrifugal force all  round a revolving
 propeller1 and this air1 which1        
ordinarily1 is lost1  must1 when thrown 
upwards1 exert a lift on the under      
surface of the  plane4 ,also1 when      
thrown towards the car1 it must1 by     
impinging on the  slanting surface of   
the car1 tend to impel it forward1 ,fig4
 #cb4 ,where  four propellers are used1 

the back pair should be of greater pitch
  than the front pair1 as they must to a
 certain extent1 work in the  stream    
from the front pair4 ,there are several 
ways of coupling the  propellers to the 
engine1 but in the model they are shown 
coupled up  by belts1 which seems to be 
the most efficient and lightest device4 
,illustration3 ,,fig4 #cb4    ,in order 
to cool the engine and keep the air in  
the car clear1 a  ventilating pipe is   
led from the front of the car to the    
engine1 and  the air1 rushing through   
this at the speed of the machine1 plays 
over  the engine and is conducted out   
through a large opening and discharged  
at the back4    ,the whole of this part 
of the machine is rigid and braced      
together by  means of struts1 though    
whether made of steel tube or timber1   
there  must always1 from the nature of  
the construction1 be a certain amount   
of elasticity which makes for strength1 
a great advantage over a  construction  
braced rigidly by non-elastic wires1    

which snap instead  of giving to a      
sudden strain4    ,under the two rigid  
,t-section longitudinals there are a    
number of  elastic laminated wood       
springs set at an angle1 and the lower  
ends of  these are pivoted on to a long 
elastic skid4 ,this skid is made in     
laminations1 with alternate joints1 and 
starts from the point where  the two    
planes intersect in the front of the    
machine1 which is one of  the strongest 
joints in the whole construction4 ,from 
this point it  bends out in a semicircle
 to protect the propeller and the front 
of  the machine and car1 this portion of
 it being very elastic by reason  of the
 laminations having free play one upon  
the other4 ,at the bottom  of the       
semicircle the skid is joined to the    
slanting skids or springs  depending    
from the bottom of the machine1 and here
 the laminations are  bolted together   
making the skid stiffer4 ,the skid runs 
the whole  length of the machine like   
the runner of a sledge4 ,on this skid   

the  wheels are sprung with a steel     
spring lever arrangement1 ,fig4 #cc4    
,the  shock of landing is1 therefore1   
taken first on the wheels1 and should   
it be sufficiently heavy to cause the   
skids to touch the ground there  is     
still the series of laminated wood      
springs to absorb any vibrations  and   
prevent any possible shock to the car4  
,the car is so secure from  vibration by
 reason of these precautions that the   
whole lower half of  the front of it may
 be made of protected glass1 to enable  
the pilot to  get a clear view of his   
surroundings4    ,illustration3 ,,fig4  
#cc4    ,the dimensions of the          
full-sized machine are estimated to be  
as  follows3--        ,span             
#bj feet      ,length                   
#dc feet      ,parachuting area         
#ejj square feet      ,efficient lifting
 area       #cfj square feet            
,weight 7all up7              #hjj lb4  
,it will be understood that though only 
#cfj square feet is counted as          

efficient for lifting1 the whole #ejj   
square feet is efficient as  parachuting
 surface in descending4 ,the weight of  
the machine compares  very favourably   
with existing machines1 and the load    
#b-a_/d lbs4 per  square foot1 gives    
plenty of margin for passenger carrying4
    ,the chief advantages claimed for   
this machine are3--        7#a7 ,speed4 
7#b7 ,stability4      7#c7 ,strength of 
construction4      7#d7 ,shock absorbing
 capacity4    ,it is a practical        
impossibility for the machine to turn   
over or be  blown over1 and it will     
recover its balance if started at any   
angle4  ,if allowed to dive vertically1 
either tail first or head first1 it     
will recover its position in six times  
its own length1 purely by its  own      
balance1 without any effort of the      
pilot4      ,,london3 ,,printed ,,by    
,,william ,,clowes ,,and ,,sons1        
,,limited1    ,,great ,,windmill        
,,street1 ,w41 ,,and ,,duke ,,street1   
,,stamford ,,street1 ,s4,e4