Headland turns using the tractor’s “fifth wheel” steering device instead of front steering wheels

Krasimir Trendafilov1, Nedelcho Delchev2
1 Faculty of Technics and Technologies, Trakia University, 8600 Yambol, 38, Gr. Ignatiev Str.
2 Faculty of Agriculture, Trakia University, 6000 Stara Zagora


Trendafilov, K. & Delchev, N. (2018). Headland turns using the tractor’s “fifth wheel” steering device instead of front steering wheels. Bulgarian Journal of Agricultural Science, 24(6), 1137–1147

Performance of nonworking moves by farming units in headland is associated with some expenditure of time, which reduces their productivity, as well as soil compaction leading to yield reduction. Both the reduction of length and duration of nonworking moves and reduction of the headland width are subject of numerous studies. Many manufacturers achieve this through various systems to reduce the radius of the turn of tractors and increase the speed of the front axle in turns. Recently a turning device has appeared in practice representing a fifth wheel located on the front mounting system of the tractor by means of which the turning is performed. This type of turning is applicable to mounted machines only. The present study describes various options of making turns with the tractor’s fifth wheel and these are compared to the front wheel turns. The length of nonworking moves, the duration of their performance and the headland width have been determined. The results show the working widths of mounted machines where the use of a fifth wheel is effective.

Keywords: headland; turning device; type of turns; turning time; fifth wheel; length of nonworking moves; width of headland
B                  working width of the unit, m
p. O               center of the turn (Fig. 2 and Fig. 3)
R                  minimum radius of the unit, m
distance from the tractor’s rear axle to the outer board of the tractor’s fifth wheel mounted on the front mounting system, m (Fig. 2)
Lk                 longitudinal base of the tractor (distance between front and rear axle), m (Fig. 2)
kinematic length of the unit (distance from tractor’s rear axle to the last row of working units of the machine, m (Fig. 2) 
α                   central angle of a circle arc formed while the unit moves in the headland, degree
p. A                start of the nonworking move (Fig. 3) 
p. C               making a turn with a fifth wheel (Fig. 3)
p. F               the beginning of a turn with the front steering axle (Fig. 3)
p. D               end of the nonworking move (Fig. 3) 
AC, CF, CD     straight sections of the nonworking move
CD, DN arched sections of the nonworking move
OC, CS           straight lines relating to the geometric construction of the turn
l                   length of the nonworking turn in the headland, m
E                  minimum theoretical width of the headland, m
Er                 actual width of headland, m
k                   number of moves for cultivating the headland
M                 transverse width of the tractor, m
b, c, d             length of straight sections in the headland, m
Ω–turn            pear-shaped turn (Fig. 4a)
T–turn            fishtail turn (Fig. 4b)
Π-turn            sprawling turn (Fig. 4d)
tu                  time for tractor movement during nonworking move, s
to                  time for turn using the tractor’s fifth wheel, s
p                   number of turns using fifth wheel in nonworking move
ta                  time for acceleration or deceleration of the tractor, s
tcv                  time for tractor movement at constant speed, s
ts                  idle time of the tractor for turning the steering wheels from 0 to maximum turning angle, s 
n                   number of accelerating and decelerating moves of the tractor
m                  number of stops of the tractor for turning the steering wheels
v                  speed of tractor movement, km h-1
Δv                speed change in accelerating and decelerating tractor movement from 0 to v, km h-1
a                   acceleration, m s-2
la                  the distance covered by tractor in acceleration from 0 to v or deceleration from v to 0, m
time for accelerating and decelerating movement of the tractor when the constant speed set cannot be reached v (in short nonworking move), s
ta5                 time for accelerating or decelerating movement with fifth wheel, s
tovc                time for making a turn with a fifth wheel tractor and constant speed, s
tud                 time for raising and lowering the fifth wheel, s
v5                 speed of movement of the tractor fifth wheel, km h-1
Δv5               speed change in accelerating or decelerating movement of the tractor fifth wheel, km h-1
ld                  length of arc covered by the fifth wheel in making a tractor turn, m (see Fig. 1)
la5             part of arc length ld covered in accelerating from 0 to v5 or decelerating from v5 to 0, m

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