Constant Speed Prop

AggieMike88

AggieMike88

Touchdown! Greaser!
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The original "I don't know it all" of aviation.
Somewhere on the net (AvWeb? Pelican Perch?) there is a good article that teaches the unwashed and unworthy the basics of operating an aircraft equipped with a CS Prop.

If you remember the link, can you post it here?

I understand how the system works. I just wish to start brushing up on how to make use of it since I'm paring down my search to aircraft equipped with such a system.
 
full forward for takeoff. back off a bit if you want to minimize noise after reaching a safe altitude. back off to cruise setting when you want to cruise. don't touch it until you throttle back to land, and then put it back full forward.
 
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AggieMike88 said:
Somewhere on the net (AvWeb? Pelican Perch?) there is a good article that teaches the unwashed and unworthy the basics of operating an aircraft equipped with a CS Prop.

If you remember the link, can you post it here?

I understand how the system works. I just wish to start brushing up on how to make use of it since I'm paring down my search to aircraft equipped with such a system.
Click to expand...

I don't remember the link but there was a thread about it in the POA Forum. The thread was about a 182, IIRC. It was in fact Pelican Perch in Av Web.
 
tonycondon said:
full forward for takeoff. back of a bit if you want to minimize noise after a safe altitude. back off to cruise setting when you want to cruise. don't touch it until you throttle back to land, and then put it back full forward.
Click to expand...


pretty much says it all..:yes:
 
I'm a long time automotive enthusiast and while I'm new to aviation, engines are something I understand well.

In the automotive world, we use what we call "engine vaccum" as an indication of engine load. While most cars don't have a vaccum gauge, they are used for diagnostics and engine vaccum played a big role in pre-computerized cars. They used vaccum-mechanical systems to determine ignition timing, decide when the automatic transmission should shift, etc.

I've read a few descriptions of how to use a constant speed prop and look at the manifold pressure and didn't quite get it. Just reading through the first of those links it suddenly all falls into place and makes sense now! Manifold pressure is basically the same thing as engine vaccum on a car and you're pretty much using it to figure out the same thing.
 
cowman said:
I'm a long time automotive enthusiast and while I'm new to aviation, engines are something I understand well.

In the automotive world, we use what we call "engine vaccum" as an indication of engine load. While most cars don't have a vaccum gauge, they are used for diagnostics and engine vaccum played a big role in pre-computerized cars. They used vaccum-mechanical systems to determine ignition timing, decide when the automatic transmission should shift, etc.

I've read a few descriptions of how to use a constant speed prop and look at the manifold pressure and didn't quite get it. Just reading through the first of those links it suddenly all falls into place and makes sense now! Manifold pressure is basically the same thing as engine vaccum on a car and you're pretty much using it to figure out the same thing.
Click to expand...

I have a vacuum gauge on my plane....


Ignore the fact it has an auto engine in it..:hairraise::eek:
 

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AggieMike88 said:
Thanks Mafoo?

(okay, now i'm curious to know the story behind the handle)
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I used to play a lot of online video games. Came across someone named Mafoo early on, and liked the name. So I use it everywhere :).

I think the actual definition is a Chinese stable boy.
 
cowman said:
I'm a long time automotive enthusiast and while I'm new to aviation, engines are something I understand well.

In the automotive world, we use what we call "engine vaccum" as an indication of engine load. While most cars don't have a vaccum gauge, they are used for diagnostics and engine vaccum played a big role in pre-computerized cars. They used vaccum-mechanical systems to determine ignition timing, decide when the automatic transmission should shift, etc.

I've read a few descriptions of how to use a constant speed prop and look at the manifold pressure and didn't quite get it. Just reading through the first of those links it suddenly all falls into place and makes sense now! Manifold pressure is basically the same thing as engine vaccum on a car and you're pretty much using it to figure out the same thing.
Click to expand...
The "vacuum" gauge is pretty much a MAP gauge that reads backwards but there is another difference. The automotive version reads the difference between ambient pressure and manifold pressure while the MAP gauge reads the difference between the manifold pressure and a near total vacuum (makes you wonder why the gauge that references vacuum is called a pressure gauge and the one that references pressure is called a vacuum gauge, eh?).
 
I wonder just how far that vacuum gauge analogy works.

In a car, you can use that for all kinds of things beyond just engine load. You can detect an ignition misfire or sticking valve by periodic motions. You can detect retarded timing by abnormally high pressure/low vacuum (at least 5 inches), or vacuum that doesn't go up from idle to middle-RPM. You can even detect excessive blow-by with the response to rapid changes in throttle position (particularly overshoot while the throttle is closed and RPM hasn't dropped yet). And there's more....

All this without removing a single thing from the aircraft.
 
MAKG1 said:
I wonder just how far that vacuum gauge analogy works.

In a car, you can use that for all kinds of things beyond just engine load. You can detect an ignition misfire or sticking valve by periodic motions. You can detect retarded timing by abnormally high pressure/low vacuum (at least 5 inches), or vacuum that doesn't go up from idle to middle-RPM. You can even detect excessive blow-by with the response to rapid changes in throttle position (particularly overshoot while the throttle is closed and RPM hasn't dropped yet). And there's more....

All this without removing a single thing from the aircraft.
Click to expand...

I use all those functions to monitor my motor,,, but the main reason I have a vacuum gauge is to detect carb ice.... Which , by the way seems to be not an issue in my application..:nono:
 
gismo said:
The "vacuum" gauge is pretty much a MAP gauge that reads backwards but there is another difference. The automotive version reads the difference between ambient pressure and manifold pressure while the MAP gauge reads the difference between the manifold pressure and a near total vacuum (makes you wonder why the gauge that references vacuum is called a pressure gauge and the one that references pressure is called a vacuum gauge, eh?).
Click to expand...

For the same reason we drive on the parkway and park in the driveway:redface:
 
I would also recommend reading John Deakins/Pelican's Perch articles on Turbos, and lean of peak.... Excellent explanation on how engines actually work.
 
Is the performance gain worth the cost? What is the performance gain range? I know what it is, I'm just still debating if the cost is worth the gain versus a fixed pitch.

Are there higher marginal gains attained in bigger engines versus sub-200hp applications, or are the marginal gains constant across the horsepower band?
 
hindsight2020 said:
Is the performance gain worth the cost? What is the performance gain range? I know what it is, I'm just still debating if the cost is worth the gain versus a fixed pitch.

Are there higher marginal gains attained in bigger engines versus sub-200hp applications, or are the marginal gains constant across the horsepower band?
Click to expand...

The gain depends on what you would have without the CS prop.

If you have a climb prop, the CS wont give you much better climb/low speed performance improvement but you will definitely see an improvement in cruise.

If you have a cruise prop, your climb and short field takeoff performance will show improvement but you may not realize ANY top speed increase.

Constant speed allows you to have the best of both worlds, and smooth transition between the two.
 
When you are bucking around in 1000fpm thermals constantly having to warble the propeller is a PITA. With a CS prop you set it and don't have to worry about it anymore.
 
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