Propeller Blade Angle
12-30-2005, 06:44 AM
#1
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Propeller Blade Angle
From Jeppesen Private Pilot Manual:
"If the angle of each section of a propeller were averaged, you could determine an overall blade angle. A propeller with a low blade angle, known as a climb propeller, provides the best performance for takeoff and climb, while one with a high blade angle, known as a cruise propeller, is more adapted to high speed cruise and high altitude flight."
Wouldn't you want a high blade angle for takeoff and climb, as this would give you a bigger bite of the air? Wouldn't you want a flatter propeller with a low blade angle for cruising flight? I asked a pilot about this, and he said a low blade angle means high pitch vice versa? Aren't propeller pitch and blade angle interchangeable terms?
"If the angle of each section of a propeller were averaged, you could determine an overall blade angle. A propeller with a low blade angle, known as a climb propeller, provides the best performance for takeoff and climb, while one with a high blade angle, known as a cruise propeller, is more adapted to high speed cruise and high altitude flight."
Wouldn't you want a high blade angle for takeoff and climb, as this would give you a bigger bite of the air? Wouldn't you want a flatter propeller with a low blade angle for cruising flight? I asked a pilot about this, and he said a low blade angle means high pitch vice versa? Aren't propeller pitch and blade angle interchangeable terms?
12-30-2005, 08:14 AM
#2
New boss = Old boss
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Position: Ca B737
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Think of bicycle gears. It is easier to peddle up hill in a lower gear (higher RPM) than a high gear. Then when you get to the top of the hill (Altitude) you shift to high gear and accelerate. It is all about balancing power and work.
12-30-2005, 12:20 PM
#3
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Position: HC-130H A/C
Posts: 78
You must be talking about a variable pitch propeller. A propeller you control blade angle the above is correct. At takeoff you also have dense air. If you had the high blade angle you would over torque the engine. As you get to altitude the air is less desne and requires a greater blade angle to maintain altitude and speed. In a constant speed prop, as the air gets less dense the prop wants to overspeed, hence increaseing blade angle to maintain the onspeed. Since you control the blade angle you actually increase the blasde angle at altitude to maintain the RPM (ie 100%).
12-31-2005, 07:47 AM
#5
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Cut and paste, it might help though....
The most common type of propeller in sport aviation is the fixed pitch propeller. Although cheap, this is one of the crudest propulsion devices you could use, and has been superseded by a variety of more advanced options, now readily available on the market. But, how do you know how each type of propeller operates and what advantages the different types offer? How are you going to choose between the different types available for your aircraft, especially considering that a more capable propeller is also more expensive?
There are four common families of propeller, which I will introduce to you. They are fixed pitch, ground adjustable, in flight adjustable and constant speed. The last two are both examples of variable pitch propellers.
In order to appreciate the advantages which are characteristic of the different families of propeller, we must first consider the most fundamental characteristic of a propeller – the pitch. Pitch is important, as it is the manner in which pitch is controlled that allows us to differentiate between one family of propeller and another.
A useful analogy when considering the affect of pitch is that of an automobile gearbox. By comparing a propeller's pitch to a gear ratio, and considering the function of a gearbox, we will gain an appreciation of the different families of propellers.
What is pitch?
Propeller theory includes a variety of concepts that may at times be called pitch. Pitch can refer to the blade angle with respect to a flat plane, the distance that a propeller will advance through the air for each rotation or the amount of "bite" that the blade has on the air. Essentially these concepts all describe the same thing. To use our automobile analogy, pitch is like the gear ratio of the gearbox. The important thing to note with pitch, is that it is available in a wide variety of degrees, or 'amounts', much like different gear ratios. To demonstrate, consider the following examples:
* A fine pitch propeller has a low blade angle, will try to move forward a small distance through the air with each rotation, and will take a 'small' bite of the air. It requires relatively low power to rotate, allowing high propeller speed to be developed, but achieving only limited airspeed. This is like having a low gear in your automobile.
* A coarse pitch propeller has a high blade angle, will try to advance a long distance through the air with each rotation, and will take a big 'bite' of the air. It requires greater power to rotate, limiting the propeller speed that can be developed, but achieving high airspeeds. This is like having a high gear in your automobile.
There are four common families of propeller, which I will introduce to you. They are fixed pitch, ground adjustable, in flight adjustable and constant speed. The last two are both examples of variable pitch propellers.
In order to appreciate the advantages which are characteristic of the different families of propeller, we must first consider the most fundamental characteristic of a propeller – the pitch. Pitch is important, as it is the manner in which pitch is controlled that allows us to differentiate between one family of propeller and another.
A useful analogy when considering the affect of pitch is that of an automobile gearbox. By comparing a propeller's pitch to a gear ratio, and considering the function of a gearbox, we will gain an appreciation of the different families of propellers.
What is pitch?
Propeller theory includes a variety of concepts that may at times be called pitch. Pitch can refer to the blade angle with respect to a flat plane, the distance that a propeller will advance through the air for each rotation or the amount of "bite" that the blade has on the air. Essentially these concepts all describe the same thing. To use our automobile analogy, pitch is like the gear ratio of the gearbox. The important thing to note with pitch, is that it is available in a wide variety of degrees, or 'amounts', much like different gear ratios. To demonstrate, consider the following examples:
* A fine pitch propeller has a low blade angle, will try to move forward a small distance through the air with each rotation, and will take a 'small' bite of the air. It requires relatively low power to rotate, allowing high propeller speed to be developed, but achieving only limited airspeed. This is like having a low gear in your automobile.
* A coarse pitch propeller has a high blade angle, will try to advance a long distance through the air with each rotation, and will take a big 'bite' of the air. It requires greater power to rotate, limiting the propeller speed that can be developed, but achieving high airspeeds. This is like having a high gear in your automobile.
01-02-2006, 04:34 PM
#7
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Joined APC: Sep 2005
Position: Retired 767 Captain
Posts: 548
Rich, another part of the equation,just to confuse you further, if you happen to be flying an aircraft with a big ol` recip (R 1820, R2800, R3350), a real danger is an overboost. These engines are equipped with a one or two stage supercharger. On takeoff if you didn`t push the prop(s) up (flat pitch), it would be possible..no for certain, you could apply too much power for the prop setting and damage the engine(s). Back in the dark ages, when I was a cadet going through Navy flight training,flying the North American T28B, the Navy, with it`s infinate wisdom, declared that an overboost would be an automatic "down" (in other words, a failure for that flight). Of course the cadets, on solo flights, if they happened to overboost an engine didn`t report it. The consequence was a rash of engine failures.Glad I switched to jets...less levers to push and pull.
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