[poll] Bmw Vs Infiniti
- Thread starter Bmw's_Finest
- Start date
Stitch said:
Can it be cloud (Not the black one!) or fog or some form of water contented phenomenon? [???1]
Or even the white "stuff" that produced, as seen in the gif below.![[idea]](/images/smilies/icon_smile_idea.gif "Idea! [idea]")
[fake]
Or even the white "stuff" that produced, as seen in the gif below.
[fake]
![[confused]](/images/smilies/confused.png "Confused [confused]")
Life Is A Learning Process
Life is a learning process.
My understanding of what a propeller is, is different from yours. Also doing all these experiments with the air tunnel and having experience sitting behind a pilot seeing the plane entering the clouds and the storms, it is a whole new way of looking at the same thing.
What is propulsion? The word is derived from two Latin words: pro meaning before or forwards and pellere meaning to drive. Propulsion means to push forward or drive an object forward. A propulsion system is a machine that produces thrust to push an object forward. On airplanes, thrust is usually generated through some application of Newton's third law of action and reaction.
Propellers as Airfoils
On this slide, we show pictures of a P-51 propeller-powered airplane from World War II and a propeller being tested in a NASA Glenn wind tunnel. The details of propeller propulsion are very complex, but we can learn some of the fundamentals by using a simple momentum theory. The details are complex because the propeller acts like a rotating wing creating a lift force by moving through the air. For a propeller-powered aircraft, the gas that is accelerated, or the working fluid, is the surrounding air that passes through the propeller. The air that is used for combustion in the engine provides very little thrust. Propellers can have from 2 to 6 blades. As shown in the wind tunnel picture, the blades are usually long and thin. A cut through the blade perpendicular to the long dimension will give an airfoil shape. Because the blades rotate, the tips moves faster than the hub. So to make the propeller efficient, the blades are usually twisted from hub to tip. The angle of attack of the airfoils at the tip is lower than at the hub.
Propeller Propulsion System
On the slide, we show a schematic of a propeller propulsion system at the top and some of the equations that define how a propeller produces thrust at the bottom. The details of propeller propulsion are very complex because the propeller is like a rotating wing. Propellers usually have between 2 and 6 blades. The blades are usually long and thin, and a cut through the blade perpendicular to the long dimension will give an airfoil shape. Because the blades rotate, the tip moves faster than the hub. So to make the propeller efficient, the blades are usually twisted. The angle of attack of the airfoils at the tip is lower than at the hub because it is moving at a higher velocity than the hub. Of course, these variations make analyzing the airflow through the propeller a very difficult task. Leaving the details to the aerodynamicists, let us assume that the spinning propeller acts like a disk through which the surrounding air passes (the yellow ellipse in the schematic).
The engine, shown in white, turns the propeller and does work on the airflow. So there is an abrupt change in pressure across the propeller disk. (Mathematicians denote a change by the Greek symbol "delta" ( ). Across the propeller plane, the pressure changes by "delta p" ( p). The propeller acts like a rotating wing. From airfoil theory, we know that the pressure over the top of a lifting wing is lower than the pressure below the wing. A spinning propeller sets up a pressure lower than free stream in front of the propeller and higher than free stream behind the propeller. Downstream of the disk the pressure eventually returns to free stream conditions. But at the exit, the velocity is greater than free stream because the propeller does work on the airflow. We can apply Bernoulli's equation to the air in front of the propeller and to the air behind the propeller.
THE ABOVE INFORMATION IS PROVIDED BY NASA.ORG
Life is a learning process.
My understanding of what a propeller is, is different from yours. Also doing all these experiments with the air tunnel and having experience sitting behind a pilot seeing the plane entering the clouds and the storms, it is a whole new way of looking at the same thing.
What is propulsion? The word is derived from two Latin words: pro meaning before or forwards and pellere meaning to drive. Propulsion means to push forward or drive an object forward. A propulsion system is a machine that produces thrust to push an object forward. On airplanes, thrust is usually generated through some application of Newton's third law of action and reaction.
Propellers as Airfoils
On this slide, we show pictures of a P-51 propeller-powered airplane from World War II and a propeller being tested in a NASA Glenn wind tunnel. The details of propeller propulsion are very complex, but we can learn some of the fundamentals by using a simple momentum theory. The details are complex because the propeller acts like a rotating wing creating a lift force by moving through the air. For a propeller-powered aircraft, the gas that is accelerated, or the working fluid, is the surrounding air that passes through the propeller. The air that is used for combustion in the engine provides very little thrust. Propellers can have from 2 to 6 blades. As shown in the wind tunnel picture, the blades are usually long and thin. A cut through the blade perpendicular to the long dimension will give an airfoil shape. Because the blades rotate, the tips moves faster than the hub. So to make the propeller efficient, the blades are usually twisted from hub to tip. The angle of attack of the airfoils at the tip is lower than at the hub.
Propeller Propulsion System
On the slide, we show a schematic of a propeller propulsion system at the top and some of the equations that define how a propeller produces thrust at the bottom. The details of propeller propulsion are very complex because the propeller is like a rotating wing. Propellers usually have between 2 and 6 blades. The blades are usually long and thin, and a cut through the blade perpendicular to the long dimension will give an airfoil shape. Because the blades rotate, the tip moves faster than the hub. So to make the propeller efficient, the blades are usually twisted. The angle of attack of the airfoils at the tip is lower than at the hub because it is moving at a higher velocity than the hub. Of course, these variations make analyzing the airflow through the propeller a very difficult task. Leaving the details to the aerodynamicists, let us assume that the spinning propeller acts like a disk through which the surrounding air passes (the yellow ellipse in the schematic).
The engine, shown in white, turns the propeller and does work on the airflow. So there is an abrupt change in pressure across the propeller disk. (Mathematicians denote a change by the Greek symbol "delta" ( ). Across the propeller plane, the pressure changes by "delta p" ( p). The propeller acts like a rotating wing. From airfoil theory, we know that the pressure over the top of a lifting wing is lower than the pressure below the wing. A spinning propeller sets up a pressure lower than free stream in front of the propeller and higher than free stream behind the propeller. Downstream of the disk the pressure eventually returns to free stream conditions. But at the exit, the velocity is greater than free stream because the propeller does work on the airflow. We can apply Bernoulli's equation to the air in front of the propeller and to the air behind the propeller.
THE ABOVE INFORMATION IS PROVIDED BY NASA.ORG
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PhatBimmer said:
[read] ![[clap]](/images/smilies/icon_smile_clap.gif "Clap [clap]")
[headbang] ![[thumb]](/images/smilies/icon_smile_thumb.gif "Thumbs Up [thumb]")
brahtw8 gets pissed of easily![[}:)]](/images/smilies/icon_smile_evil.gif "Evil [}:)]")
[headbang] brahtw8 gets pissed of easily
But that is fine. Life is too short to waste on forum arguments that result from misinterpretation of sarcasm (mine and others).
Nevertheless, the Roundel is what it is.
![[driving]](/images/smilies/icon_smile_driving.gif "Driving [driving]"){kind=icon}
[headbang]![[:p]](/images/smilies/tongue.png "Stick Out Tongue [:p]")