Question

In order to minimize the bounce of seeds in furrows, the seed tube is inclined rearward from the vertical at an angle of:

• A. 15$^{\circ}$-20$^{\circ}$
• B. 25$^{\circ}$-30$^{\circ}$
• C. 30$^{\circ}$-45$^{\circ}$
• D. 45$^{\circ}$-60$^{\circ}$

Hint:

To achieve precise seed placement, high-speed planters use active mechanical delivery belts instead of gravity drop tubes, maintaining near-zero relative velocity at discharge.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
In agricultural planting machines (seed drills and planters), the seed tube guides the metered seeds from the metering unit down into the furrow.
When a seed is dropped, it acquires a forward speed equal to the travel speed of the machine relative to the ground.
Upon impact with the soil, this relative horizontal velocity causes the seed to bounce or roll along the furrow, resulting in non-uniform seed spacing.

Step 2: Detailed Explanation:
To reduce seed bounce and rolling, the horizontal velocity of the seed relative to the ground at the moment of exit should ideally be zero.
This is achieved by launching the seed backwards relative to the machine at a speed equal to the planter's forward travel velocity.
Inclining the seed tube rearwards directs the seed path slightly backwards, neutralizing a portion of the machine's forward speed.
Extensive dynamic testing and design standards indicate that a rearward inclination of $15^{\circ}$ to $20^{\circ}$ from the vertical minimizes seed bouncing without causing blockages inside the tube.
Angles larger than $20^{\circ}$ increase the risk of seed clogging due to excessive friction against the tube walls.

Step 3: Final Answer:
The recommended rearward inclination angle of the seed tube from the vertical is $15^{\circ}$-$20^{\circ}$.