Drawing the PA-44 Prop Diagram

Summary

This video provides a detailed breakdown of the PA44 propeller system, focusing on key components such as the prop hub, oil sump, oil pump, and fly weights. The script explains how the pilot valve, fly weights, and speeder spring work together to regulate propeller RPM based on oil pressure. It covers both over-speed and under-speed conditions and demonstrates how the system adjusts oil flow to maintain the correct RPM. The unfeathering accumulator, which stores oil pressure for restarting a feathered prop, is also discussed. The video offers a comprehensive understanding of the PA44's propeller mechanics.

Takeaways

• 😀 The PA44 prop system diagram is based on several assumptions, including no explanation of fly weights or blade angle effects on RPM.
• 😀 The prop hub is central to the system, where oil flows from the sump to the hub to control the blade angle.
• 😀 The oil sump provides oil that is pumped to the prop hub, with a pump shown in light green for clarity.
• 😀 The spring in the system generates pressure that opposes the oil pressure, affecting prop RPM.
• 😀 Higher oil pressure leads to higher RPM, while lower oil pressure results in lower RPM.
• 😀 The pilot valve controls oil flow, dividing segments where oil can either flow into the hub or return to the sump.
• 😀 Flyweights are connected to the pilot valve and adjust its position based on RPM conditions.
• 😀 The speeder spring keeps the flyweights in position, pushing them inward if RPM is too low (under-speed condition).
• 😀 In an overspeed condition, the flyweights move outward, lifting the pilot valve and allowing oil to flow out, reducing RPM.
• 😀 The UN Feathering accumulator stores oil pressure to quickly restart the propeller when it is feathered, without needing the oil pump.
• 😀 The process of unfeathering involves releasing oil from the UN Feathering accumulator to kick-start the prop, after which the oil pump resumes normal function.

Q & A

What is the assumption made at the beginning of the script regarding the audience's knowledge?

The script assumes the audience understands two key concepts: the effect of changing the blade angle of the propeller on RPM and the role of flyweights in propeller speed control.

What are the main components of the propeller system that are discussed in the script?

The main components discussed are the prop hub, oil sump, pump, spring, pilot valve, flyweights, speeder spring, and UN feathering accumulator.

How does oil pressure affect the RPM of the propeller in the system?

In the system, increased oil pressure leads to higher RPM, while decreased oil pressure results in lower RPM.

What is the role of the pilot valve in the propeller system?

The pilot valve controls the flow of oil to and from the prop hub, regulating the propeller’s speed. It moves based on the position of the flyweights, allowing oil to either flow into or out of the hub to adjust the RPM.

What happens when the propeller is in an over-speed condition?

In an over-speed condition, the flyweights move outward, which lifts the pilot valve and allows oil to flow out of the hub, reducing the RPM.

How does the system respond in an under-speed condition?

In an under-speed condition, the flyweights are pushed inward by the speeder spring, allowing oil to flow into the hub, which increases the RPM.

What is the purpose of the speeder spring in the system?

The speeder spring helps control the flyweights' position, pushing them inward during under-speed conditions when centrifugal force is insufficient to do so.

What function does the UN feathering accumulator serve in the system?

The UN feathering accumulator stores oil pressure, which is used to restart the propeller after it has been feathered, providing a quick kick to get the propeller spinning again.

How does the oil return to the sump once it has flowed out of the hub?

When oil flows out of the hub, it travels through an oil return line and returns to the sump for reprocessing.

What is the relationship between the movement of the flyweights and the pilot valve?

The flyweights, driven by centrifugal force, move outward when RPM increases and inward when RPM decreases. This movement lifts or lowers the pilot valve, allowing oil to flow into or out of the hub, adjusting the propeller's speed.