Trials  of  Agricultural  Motors. 
18D 
As  each  of  the  tractors  completed  either  its  ploughing  trial  or 
its  reaping  trial,  it  took  its  place  in  driving  the  friction-brake 
dynamometer,  by  which  its  power  was  ascertained,  the  dynamo- 
meter taking  the  place  of,  or  representing  the  driving  of,  a 
threshing  machine  or  other  machinery. 
It  was  not  considered  necessary  by  the  judges  to  make 
indicator  experiments  with  the  engine,  although  mean  pressure 
observations  in  the  petrol  and  oil  engine  cylinders  were  taken. 
The  results  of  the  brake  dynamometer  trials  are  given  in  the 
table  already  referred  to,  from  which  it  will  be  seen  that  the 
15  to  16  B.H.P.  required  for  a threshing  machine  of  either  54  in. 
or  60  in.  drum  measurement  was  easily  given  off  by  the  steam 
engines,  and  the  power  of  the  McLaren  engine  was  far  in  excess 
of  the  requirements  for  this  part  of  the  work.  The  petrol  and 
oil  engines,  however,  in  all  cases  showed  themselves  to  be  of  con- 
siderably under  the  nominal  power  given  in  the  entry  list,  and 
in  some  cases  it  was  found  undesirable  to  pursue  this  test  for  the 
length  of  time  at  first  intended. 
There  were  none  of  them  capable  of  running  continuously 
on  paraffin  or  heavy  oil,  and  the  Ivel  engines  showed  themselves 
also  deficient  in  constructive  details,  as,  for  example,  in  the 
bearing  next  the  pulley  for  driving  threshing  or  other  machines, 
this  bearing  showing,  in  fact,  a disregard  of  the  power  it  would 
have  to  transmit. 
The  ploughing,  reaping,  and  machine  driving  trials  having 
been  completed,  the  road  trials  were  then  entered  upon,  the 
tractors  hauling  loads  varying  from  3 tons  by  the  Ivel  motors, 
to  8 tons  12  cwt.,  the  several  loads  being  given  in  Table  No.  5.  All 
passed  over  the  same  road,  which  is  shown  by  the  map,  Fig.  8. 
All  covered  this  route  twice,  hauling  their  loads  in  tractor  wagons 
lent  by  Messrs.  Aveling  and  Porter.  The  route  included  about 
eight  miles  of  fairly  level  roads,  including  the  Icknield  way,  which 
is  of  good  surface,  the  remaining  four  miles  consisting  of  roads 
of  varying  surface  and  narrow,  the  worst  of  which  was  on  the 
approach  to  Bygrave  from  the  Icknield  way,  on  which  is  a 
gradient  of  about  one  in  twenty. 
Two  arrows  on  the  map  give  the  course  followed  by  the 
tractors.  The  whole  of  the  tractors  went  through  these  trials, 
all  the  steam  vehicles  and  the  Ivel  vehicles  with  complete  success, 
but  some  little  difficulties  arose  with  the  Saunderson  25-30  h.p. 
vehicle,  apparently  resulting  from  the  hurried  completion  of  the 
engines. 
The  time  taken  in  making  these  journeys,  fuel  consumed,  and 
other  figures  relating  to  this  part  of  the  trial  will  be  found  in 
Table  No.  5 given  in  the  Consulting  Engineer’s  Report. 
