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Constant Speed Prop: What You NEED to Know | Part 1

May 09, 2020
Hey guys,

what

's up John from www.fly8ma.com? Today we are going to cover in the shortest and simplest way possible

what

a

constant

speed

prop

eller is, what it does, why we have them and what you

need

to

know

for your CFI or commercial check trip Let's go ahead and first delve into what a

prop

eller is

constant

speed

. Well, a constant speed propeller is a propeller that has blades that rotate instead of staying fixed to the hub, so they actually change their angle of attack and change their pitch through control in the cockpit. Now what it looks like, we can easily tell by approaching any aircraft by simply looking at the center of the propeller, so when you look at something like an arrow or a 172 RG, it has a constant speed propeller. see these propeller blades that go into a hub and it's round at the base, the blades twist and twist through oil pressure, we'll talk more about that in a second here compared to these fixed pitch propellers we can see here how you would do it.
constant speed prop what you need to know part 1
Find a regular 172 or 152/172 where it will be a fixed pitch propeller where it's all one solid piece of metal and the blades don't turn at all based on the control in the cockpits, they have that natural turning built in. but they're not turning in the sense that we're talking about where they're actually changing their angle of attack, changing their stride relative to the center. Other tracks that you have when you walk towards New York Lane, have a constant speed propeller. Do you have a blue lever or an extra lever on the flight control so you have the throttle, the carburetor heats the mixture, but there's an extra lever there and it's very much like a mixture control, a lot of times where you can screw it on and off. finite adjustments which is often a propeller lever or propeller knob, many times it is blue and some of the older airplanes may be black or a different color, but any type of blue knob is a great indication that you have a constant speed propeller.
constant speed prop what you need to know part 1

More Interesting Facts About,

constant speed prop what you need to know part 1...

We are going to control and set the RPM, it is possible, however, on very new airplanes like some of the series or some other airplanes that have faded, they act like a DA 42 to have constants, be it propellers that change their pitch, change their angle, but that's all. computer controlled so you only have a single throttle lever instead of the throttle to control manifold pressure and you actually have a blue lever to control prop rpm. Now, what does a constant speed propeller do well? Changes its angle of attack, changes the pitch of the blades, they must maintain a constant rpm, therefore, the constant speed will be the speed of the engine, so, regardless of how much power the engine is generating or the speed of the air, Increasing or decreasing propeller rpm will remain the same, as you

know

from flying your Piper Arrow or Warrior. or Cherokee or your Cessna 152 or 172 when you accelerate or decelerate in airspeed you see changes in rpm because there is more or less resistance on the propeller in the case of a constant speed propeller airplane, that will not happen as you increase or you reduce the air. speed the RPM remains the same what will change is the turn of the blades on the propeller the angle of attack as they rotate to take in a greater amount of air as their speed increases while maintaining the same load in the inch of maintaining the same rpm of our engine for that given amount of power the engine is producing now, why do we have constant speed propellers on airplanes? why not just have regular fixed pitch propellers, like some of the basic training machines?
constant speed prop what you need to know part 1
Think carefully about riding a bike. Do you want to ride a bike? a single speed buys school and you have to go uphill and downhill or do you want to have a 28 or 24 speed bike where you can change the gears for when you pedal uphill, downhill or on flat ground because guess what our planes go up going uphill, it goes straight on level ground and they go downhill, they go downhill, so if you're trying to make the propeller more efficient for all those different speeds, well, it's very difficult to do that, that's always a compromise with a fixed pitch propeller. , while with a constant speed propeller.
constant speed prop what you need to know part 1
You can vary the gear, it's like changing gears in your car or changing gears on a bicycle to match the load on the engine with the speed at which airplanes travel, slower and the climb and cruise speeds faster. fast, makes the engine more efficient. go a little faster burn a little less fuel climb a little better all that kind of stuff, that's why we have it now, let's go ahead and dive into what you

need

to know for your commercial or CFI check trip, so Let's first enter the cabin here. and take a look at our basic controls, you're used to seeing a tachometer and we still have the tachometer, but we also have a manifold gauge.
The manifold gauge is power, it's how much you push the throttle forward, the tachometer is simply how fast the prop is running. When spinning, you could spin very fast and take in a small amount of air and it wouldn't really give you much thrust or much power to pull the plane forward in the air or you could spin at low revs, take in a lot of air. about going slow on your bike, you turn your feet very slowly but you turn the rear wheel very fast so you can go very fast. The same with the airplane, you could actually be at low revs, you take in a lot of air and develop more thrust, there will always be an unusual angle of attack on the propeller for a given speed and when I say it will attack on a propeller, It's exactly the same on a wing, however it's inverted 90 degrees, so instead of the air flowing to the sides while we're used to going straight from nose to tail across the wing, that's the angle attack for our wing, the angle attack for the propeller is in the vertical plane instead of the horizontal plane because those blades think they're just shearing up and down and they're moving. so fast that it doesn't actually move forward, I'll just think about cutting up and down and moving forward very slightly and we can look at this diagram here that shows us when the planes are parked on the runway ready to take off and you hold the brakes and you apply all the power and you have the blades tilted to say maybe an arbitrary number like an 8 degree angle of attack, so the propellers that take an eighth degree angle of attack bite into the air, they're taking that full eight degree bite now that The plane accelerates, the air begins to flow. the propeller in the horizontal plane and that causes a lower angle of attack, so suddenly now the propeller has a lower angle of attack, which has a little less drag than when you accelerate down the runway on your 152 or in your Piper.
Cherokee, you see the RPM increase slightly as the airspeed increases, our MP increases, but with the constant speed prop it constantly takes in a larger and larger mouth of air to maintain that set rpm and maintain that angle of attack established, the angle of attack that the The manufacturer designed it to be most efficient because any wing or propeller in a propeller is just a wing that rotates in the vertical plane, any wing or propeller has an optimal angle of attack for which it is designed and the more, the less it will be. more drag just like we know our maximum lift over drag speed in our airplane our best glide speed all come from a precise angle of attack we want to fly on the wing where the wing produces the most lift with the least amount of drag The same with the propeller there will be an RPM and a speed at which it produces the greatest lift or forward thrust, the thrust that pushes the plane forward or the power at which it can produce its greatest thrust by pushing it through the air for a certain rpm. at a given speed and finally give an angle of attack now to summarize this is the end of

part

1 so let me summarize it here in the simplest terms a constant speed propeller is simply a transmission or gear change on a bicycle or In your car you can have high or low rpm, you can have high or low power settings and you can vary the amount of power separately from the RPM, why is this so good?
Well we can go high rpm, high power for climbing, we can go high power at low revs for a cruise game as we accelerate, we have them for efficiency, they work off the engine oil pressure, that's how they control their angle and to control the amount of oil pressure that is supplied to them, we have a propeller governor that we are going to use. we'll talk about that in

part

two, that prop governor is what's connected to the blue lever in the cockpit, so there's a wire that goes from that blue lever to the prop governor, it senses the RPM of the engine and then varies the amount of oil pressure going to the propeller to control the angle of the blade controlling the RPM controlling the load so if the RPM needs to be high increasing the load reducing the RPM down makes a very good I work by modulating those rpm, that's the basics, that's what I really want you to do.
What you can take away from this video, part 2 has a lot more detail and a lot more examples of how to use one of these in the airplane to correlate what will happen to the manifold pressure rpm. Go ahead and check that part 2 is included. in our online commercial pilot ground school and fly myself, go to our home page, click on the commercial pilot training camp prep course that is guaranteed to help you pass your check trip along with all our other amazing online courses, Private Commercial Instrument Pilot, etc. Visit the entire website online at Flight Health Comm.
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