This is one of the best videos I've seen on propellers. The pitch of propellers for model airplanes is usually measured 75% of the way from the hub to the tip. The blades are usually wider there and it's also where most of the thrust is generated. To calculate the angle of attack, divide the pitch by the diameter and then divide by 2.36 (this is ~75% of Pi). So, for a 69x58 prop, it would be 58/69/2.36=0.3562. This is the tangent of the angle. To find the angle in degrees, use the arc-tangent function which gives 19.6 degrees. Since this is greater than a typical stalling angle of 15 degrees, it's likely that the blades will be stalled at zero airspeed. But once the plane begins to accelerate, the relative wind will lower the angle of attack of the blades, and they will become more efficient. The pitch speed of a 69x58 prop at 2400 rpm is 2400x58/1056=131.8 mph. At 2400 rpm, the rotational speed at the 75% point of the blade is 2400*69*Pi*75%/1056=369.5 mph. If the plane is flying at an airspeed of 105 mph, the tangent of the angle of the relative wind is 105/369.5=0.2842 which results in an angle of 15.86 degrees. Subtracting the relative wind angle from the blade's fixed angle of attack gives a relative angle of attack of 19.6-15.86=3.74 degrees. Subtracting the airspeed from the pitch speed gives a slippage of 131.8-105=26.8 mph or 26.8/131.8*100=20.3 percent.
@@pccaviationscience6769 Good deal. Also, the speed of the relative wind is the square root of the sum of the two speeds squared; e.g., RW = Sqrt(105^2 + 369.5^2) = 384.129. It’s the length of the hypotenuse of the helix described by the 75% point of the blade through the air.
I made my first Rubber band model aircraft in year 1964 and learned a theory of propeller. Model airplane making learns more aerodynamics than hours in 747 cockpit.
I have always flown Piper single engine aircraft. There seems to be a difference between Piper & Cessna thoughts about the fixed Props that they use. The Piper Props seemed to have a longer diameter & be wider. What do you think about it.
The diameter and pitch depend on several factors, such as ground clearance, the torque the engine can produce, the RPM they intend to turn the engine at and the intended climb/cruise speeds. In general, all other things being equal, a bigger diameter prop will be more efficient because you are accelerating more mass/sec of air, so can afford to accelerate it less.
since it is a fixed pitch propeller, is it can only be used only on condition only? i mean when you want to climb use the climb propeller and when you to cruise use the cruise propeller. i have a thought on this.
With fixed pitch propellers, you have to make a compromise and pick a pitch that works well for all conditions. Of course, it has to be approved but he FAA for the aircraft, as well. Most props are a compromise that give just enough climb performance to handle normal climb requirements, and still give you decent cruise performance. "Climb props" shift the compromise towards the climb performance a little, but you may not be able to cruise as fast.
Nice explanation but i have doubt how to find the theoretical values for these force acting on a propeller? Is there any formulas could u tell me that😅
Good question, and it might be fun to try to actually calculate these. If you wanted to do that, I think you could probably apply some of the formulas from your basic physics class to approximate the centrifugal (centripetal, actually, but basic Newtonian physics as applied to a circle), thrust and torque forces. The twisting force is probably a bit more complicated to try and calculate. This class is aimed at understanding things from a pilot's perspective, though, so we don't go into the engineering considerations. For us, it is only important to understand that these forces exist, and that they are formidable, so that we can do our preflight inspection of the prop with an informed eye.
This is one of the best videos I've seen on propellers. The pitch of propellers for model airplanes is usually measured 75% of the way from the hub to the tip. The blades are usually wider there and it's also where most of the thrust is generated. To calculate the angle of attack, divide the pitch by the diameter and then divide by 2.36 (this is ~75% of Pi). So, for a 69x58 prop, it would be 58/69/2.36=0.3562. This is the tangent of the angle. To find the angle in degrees, use the arc-tangent function which gives 19.6 degrees. Since this is greater than a typical stalling angle of 15 degrees, it's likely that the blades will be stalled at zero airspeed. But once the plane begins to accelerate, the relative wind will lower the angle of attack of the blades, and they will become more efficient. The pitch speed of a 69x58 prop at 2400 rpm is 2400x58/1056=131.8 mph. At 2400 rpm, the rotational speed at the 75% point of the blade is 2400*69*Pi*75%/1056=369.5 mph. If the plane is flying at an airspeed of 105 mph, the tangent of the angle of the relative wind is 105/369.5=0.2842 which results in an angle of 15.86 degrees. Subtracting the relative wind angle from the blade's fixed angle of attack gives a relative angle of attack of 19.6-15.86=3.74 degrees. Subtracting the airspeed from the pitch speed gives a slippage of 131.8-105=26.8 mph or 26.8/131.8*100=20.3 percent.
This is really interesting! It's never occurred to me to try and arrive at an actual angle from this direction. Thanks!
@@pccaviationscience6769 Good deal. Also, the speed of the relative wind is the square root of the sum of the two speeds squared; e.g., RW = Sqrt(105^2 + 369.5^2) = 384.129. It’s the length of the hypotenuse of the helix described by the 75% point of the blade through the air.
All aeronautics is an educated guess.... taken to three decimal places. This video explains where we should start .....when guessing on propellers.
thanks for the video. very well explained, helped me a lot !
I made my first Rubber band model aircraft in year 1964 and learned a theory of propeller. Model airplane making learns more aerodynamics than hours in 747 cockpit.
Thanks, very complete.
This is what I'm searching for😊 thanku for ur explanation 👍
Most welcome 😊
great videos
Thank you sir!
Im just here to refresh my memories of yesteryear. Yep...
Making turbine blades. All the same concept... just in reverse.
I have always flown Piper single engine aircraft. There seems to be a difference between Piper & Cessna thoughts about the fixed Props that they use. The Piper Props seemed to have a longer diameter & be wider. What do you think about it.
The diameter and pitch depend on several factors, such as ground clearance, the torque the engine can produce, the RPM they intend to turn the engine at and the intended climb/cruise speeds. In general, all other things being equal, a bigger diameter prop will be more efficient because you are accelerating more mass/sec of air, so can afford to accelerate it less.
since it is a fixed pitch propeller, is it can only be used only on condition only? i mean when you want to climb use the climb propeller and when you to cruise use the cruise propeller. i have a thought on this.
With fixed pitch propellers, you have to make a compromise and pick a pitch that works well for all conditions. Of course, it has to be approved but he FAA for the aircraft, as well. Most props are a compromise that give just enough climb performance to handle normal climb requirements, and still give you decent cruise performance. "Climb props" shift the compromise towards the climb performance a little, but you may not be able to cruise as fast.
You should carry at least 2 propellers all the time and switch them as you need in mid flight😁😁😁
Best of both worlds. Carry three engines all synched as conditions require...
Need more diagrams go explain. I still don't understand pitch and RPM
Nice explanation but i have doubt how to find the theoretical values for these force acting on a propeller? Is there any formulas could u tell me that😅
Good question, and it might be fun to try to actually calculate these. If you wanted to do that, I think you could probably apply some of the formulas from your basic physics class to approximate the centrifugal (centripetal, actually, but basic Newtonian physics as applied to a circle), thrust and torque forces. The twisting force is probably a bit more complicated to try and calculate. This class is aimed at understanding things from a pilot's perspective, though, so we don't go into the engineering considerations. For us, it is only important to understand that these forces exist, and that they are formidable, so that we can do our preflight inspection of the prop with an informed eye.
great video thank you
Glad it was helpful!
Ur making it complicated