The draft refers to the force required to pull a machine or implement through the soil. It depends on soil conditions, the type of implement, and the depth and width of the operation.

Formula for Draft (D):

D=K×AD = K \times AD=K×A

Where:D = Draft (force) in Newtons (N) or pounds (lbs)

K = Draft coefficient (depending on soil type and implement)

A = Area of the implement in contact with the soil, typically the width of the tool multiplied by the depth of the soil worked (m² or ft²)

Example Draft Calculation:

If a plow has a width of 1.5 meters and works at a depth of 0.3 meters, and the draft coefficient KKK is 1.5 N/cm²:

• Area (AAA) = 1.5 m×0.3 m=0.45 m²1.5 \, \text{m} \times 0.3 \, \text{m} = 0.45 \, \text{m²}1.5m×0.3m=0.45m²
• Draft (DDD) = 1.5×0.45=0.675 N/cm²1.5 \times 0.45 = 0.675 \, \text{N/cm²}1.5×0.45=0.675N/cm²

Convert the draft into proper units based on the specific parameters.

Emmanuel Okon Wilson many thanks for your answer, i am just wondering how can we accurately detemine the drag coefficient, i believe there are various cariable which need to be taken into consideration while calculating draft force, it will be more clear if you try to calculate draft force required to pull a traierl

How to calculate agricultural machinery draft and power requirements? Calculating Agricultural Machinery Draft and Power Requirements depend on soil conditions, implement type, operating depth, and speed. The general formula for draft is;

D = Fc X W

Where

D = Draft Force (KN)

Fc = Specific draft (KN/m)

W = Implement width (m)

Power requirement formula is;

P = D X V/ 3.6

Where:

P = Power (kW)

D = Draft force (kN)

V = Speed (km/h)

3.6 = Conversion factor from km/h to m/s

Example 1: A chisel plow with working depth: 0.45m, working width: 3m, operation speed: 8km/hr, have a 13 tools with 8cm width end points, running a primary tillage operation in a loamy sand soil.

Solution 1: Draft and Power Requirement for Chisel Plow.

Given Data;

Working depth (d) = 0.45 m

Working width (W) = 3 m

Operating Speed (V) = 8 km/h

Numbers of Tools = 13

Tool width = 8 cm (Not necessary for draft calculation)

Soil Type = Loamy sand

Typical Draft Constant (k) for Chisel Plow in Loamy Sand = 35 – 50 kN/m²

Taking an average value of 42.5 kN/m²

Step 1: Calculate Draft

Using the equation:

D = k × W × d

D = 42.5 × 3 × 0.45

D = 57.38 kN

Step 2: Calculate Power Requirement

Using the power equation:

P = D X V/ 3.6

P = 57.38 X 8/3.6 = 127.51 KW

Assuming 80% efficiency in power transmission: Pactual = 127.52/0.8 = 159.39 KW

Thus, the minimum tractor power required is approximately 160 kW (215 hp).

Example 2: 16tons loading semi-trailer with tandem axles, weight transfer on tractor hitch is 15% of the loading capacity, working speed in sandy loam field: 10-15km/hr, and in roads: 20-25km/hr

Solution 2: Semi-Trailer Load Transfer and Power Requirement

Given Data:

• Semi-trailer load capacity = 16 tons (16,000 kg)
• Weight transfer to tractor hitch = 15%
• Working speed in sandy loam field = 10 – 15 km/h
• Speed on roads = 20 – 25 km/h

Step 1; Computing of Load on the Tractor Hitch

The weight transferred to the tractor hitch:

Hitch Load = 0.15×16,000 =2,400 kg =2.4 tons

Therefore, 2.4 tons is transferred to the tractor, and the remaining 13.6 tons is on the semi-trailer axles.

Step 2: Calculate Rolling Resistance Force (RR)

Rolling resistance depends on the terrain and tire type. Using standard values for rolling resistance coefficient (f):

· Sandy loam field: f = 0.08

· Paved road: f = 0.02

Rolling resistance force: (RR) = f × W

Where;

W = total weight (16,000 kg × 9.81 m/s² = 156,960 N).

· On field: RRfield ​= 0.08 ×156,960 = 12,557 N = 12.56 kN

· On road: RRroad= 0.02 × 156,960 = 3,139 N = 3.14 kN

Step 3: Calculate Power Requirement

Using;

P = RR X V/3.6

· On field (15 km/h max speed):

Pfield = 12.56 X 15/3.6 = 52.33 KW

· On road (25 km/h max speed):

Proad = 3.14 X 25/3.5 = 21.81 KW

Thus, the tractor needs:

• At least 55 kW (75 hp) for field operations.
• At least 25 kW (35 hp) for road transport.

However, additional power is needed for acceleration and gradient resistance. A tractor with at least 80-90 hp is recommended.