Selection of airfoil and sizing of propeller

In summary, the author is looking for a propeller which is the most efficient at converting engine torque into thrust for his aircraft. He is considering the propeller's velocity, advance ratio, and efficiency. However, he is still facing some problems.
  • #1
shaft
8
0
Two problem to solve.
1) I have 4 propellers built with different airfoils. I have the graphs of coefficient of thrust and efficiency in function of advance ratio. There is a mathematical method to select which one is the best or the only way is just look at graphs
2)I know the maximum thrust necessary at my aircraft so I need to found the right dimension (diameter) and number of blade for a propellers .
I can calculate the thrust produced by the propeller but this change with the advance ratio and the pitch angle so really i don't know how to select the best diameter and number of blade.

I thank you in advance for the answers
 
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  • #2
shaft said:
Two problem to solve.
1) I have 4 propellers built with different airfoils. I have the graphs of coefficient of thrust and efficiency in function of advance ratio. There is a mathematical method to select which one is the best or the only way is just look at graphs
2)I know the maximum thrust necessary at my aircraft so I need to found the right dimension (diameter) and number of blade for a propellers .
I can calculate the thrust produced by the propeller but this change with the advance ratio and the pitch angle so really i don't know how to select the best diameter and number of blade.

I thank you in advance for the answers
A propeller is a device which converts torque from an engine into thrust. Selecting a propeller is more than just picking one which produces the right thrust. You also must consider the engine driving the propeller and what its torque characteristics are.
 
  • #3
SteamKing said:
A propeller is a device which converts torque from an engine into thrust. Selecting a propeller is more than just picking one which produces the right thrust. You also must consider the engine driving the propeller and what its torque characteristics are.
but in the ideal case that I can have always the best engine appropriate for the propeller ?
 
  • #4
shaft said:
but in the ideal case that I can have always the best engine appropriate for the propeller ?
That's not the point. You are selecting a real propeller driven by a real engine to add thrust for a real plane.

If the propeller can't absorb the torque output by the engine at its speed of revolution, then the propeller also won't produce the amount of thrust you think that it will.
 
  • #5
yes you have right, but in the case that I can select the engine after the selection of propeller, in this way it's the propeller that give the characteristics to the engine.
 
  • #6
shaft said:
yes you have right, but in the case that I can select the engine after the selection of propeller, in this way it's the propeller that give the characteristics to the engine.

Good luck with that approach then.
 
  • #7
SteamKing said:
Good luck with that approach then.

so if i don't know the characteristic of the engine I can't built a propeller ?
 
  • #8
shaft said:
so if i don't know the characteristic of the engine I can't built a propeller ?
You can build any number of propellers, but you want to build (or select) the propeller which is the most efficient at turning the available torque produced by your engine into thrust for your plane.

This article discusses the key topics in selecting the best propeller for your aircraft:

http://www.experimentalaircraft.info/articles/aircraft-propeller-selection.php
 
  • #9
the problem is that i have already small efficiency of the propeller because the velocity of fly is max 30m/s this mean a small advance ratio and a small efficiency and if i decrease the diameter of prop i don't have enough thrust .
It's a loop where I don't found a solution for this I am doing some semplification like I can have the best engine for the propeller and considering only the condition where it spend the major part of time.
 

1. How do you select the best airfoil for a specific aircraft?

The selection of an airfoil for an aircraft depends on several factors such as the desired flight characteristics, weight and size of the aircraft, and intended use. Wind tunnel tests and computational fluid dynamics (CFD) simulations are commonly used to evaluate the performance of different airfoils and determine the most suitable one.

2. What is the importance of airfoil shape in propeller design?

The shape of the airfoil plays a crucial role in determining the efficiency and performance of a propeller. A well-designed airfoil can generate more lift and reduce drag, resulting in better thrust and overall propulsion efficiency. Additionally, the shape of the airfoil also affects the distribution of forces on the propeller and its structural integrity.

3. How do you determine the size of a propeller for a given aircraft?

The size of a propeller is determined by several factors, including the aircraft's weight, engine power, airfoil design, and desired performance. Generally, a larger propeller diameter is preferred for aircraft with higher power requirements, while a smaller diameter may be more suitable for slower aircraft. Wind tunnel tests and CFD simulations are commonly used to optimize the propeller size for a given aircraft.

4. What are the key considerations in designing a propeller for different flight conditions?

When designing a propeller, it is essential to consider the expected flight conditions, such as cruising speed, altitude, and takeoff/landing requirements. Different flight conditions may require different propeller designs to achieve the desired performance. For example, a propeller designed for high-speed flight may not be suitable for a slow takeoff or landing.

5. How do you balance the trade-off between propeller efficiency and noise?

The design of a propeller involves a trade-off between efficiency and noise. A propeller with high efficiency may produce more noise, while a quieter propeller may have lower efficiency. To balance this trade-off, engineers use various techniques such as twist distribution, chord length, and blade shape optimization to achieve a propeller design that meets the desired performance and noise requirements.

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