Question

The drawbar power output of a tractor is always less than the power take off output because

• A. Drive wheel slippage only
• B. Tractor rolling resistance only
• C. Friction losses and rolling resistance only
• D. Slippage, rolling resistance and friction losses

Hint:

Drawbar power is typically 70--85% of PTO power on concrete, and only 45--60% on tilled agricultural soils due to high slip and rolling resistance.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Power delivered by the tractor engine travels through distinct power transmission paths to the PTO shaft versus the drive wheels and drawbar.
Key Formula or Approach:
\[ P_{\text{Drawbar}} = P_{\text{PTO}} - P_{\text{transmission friction}} - P_{\text{rolling resistance}} - P_{\text{slip}} \]

Step 2: Detailed Explanation:
Power delivery losses between PTO and drawbar include:
1. Transmission Friction Losses: Mechanical gear, bearing, and hydraulic churning losses in the final drive and differential.
2. Rolling Resistance: Energy consumed in flexing the tire carcass and compacting/deforming the soil bed.
3. Wheel Slippage: Kinematic slip of the drive tires against the soil interface during pull generation.
Together, slippage, rolling resistance, and mechanical friction ensure drawbar power is always significantly lower than PTO power.

Step 3: Final Answer:
Therefore, the reduced drawbar output is due to slippage, rolling resistance and friction losses, matching option (D).