Help me understand the blue knob

A

Adamoh

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Adamoh
I am a first grader explain to me how a high performance engine works!
Please!
 
Flavius Renatus said:
Think of the blue knob like a gear shift.

All the way in is like 1st gear and you pull it out as you get in cruise.

Flav
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Except in a car the gears beyond 1st gear get you going faster and this does not help you go any faster. It will help you save fuel and get a smooth ride, but that's about it. Not a big deal at all. I remember when I was getting my HP and thought it was very confusing as well. It really is very simple.
 
Do a search on my user name. I started a thread a few months back that got a lot of responses and good info.
 
Adamoh said:
Well both. As in manifold pressure and rpm and how it's different from just having power and mixture.
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They don't go hand in hand. Manifold pressure and rpm are typically associated with constant speed propellers (what you seem to be talking about) which may or may not be high performance (defined as greater than 200HP).

My Waco has a high performance engine (225 HP), but a fixed pitch propeller and no manifold pressure gauge.
 
"The beginning of wisdom is to call things by their proper name."

And it helps avoid confusion, too...

Adamoh said:
I am a first grader explain to me how a high performance engine works!
Click to expand...
The term "high performance" is used in the regulations to refer to an airplane with an engine(s) which produces more than 200 HP. I think we know what you meant but the similar use of the term might confuse some who read it.

hook_dupin said:
Perhaps you mean controllable pitch prop (which is separate from engine power)?
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Constant-speed, not controllable pitch. A controllable pitch prop is a prop on which the pitch can be adjusted ON THE GROUND. ie. you can change it from a "climb prop" to a "cruise prop", etc. A constant-speed prop is one that is controlled by a governor in flight that is generally pilot adjustable. These two terms are often used interchangeably by those who don't know the difference but there is a very significant difference.
 
Adamoh said:
Well both. As in manifold pressure and rpm and how it's different from just having power and mixture.
Click to expand...
I think an very easy way to look at it is that with a constant-speed prop your prop can adjust itself (through the governor) so that it is always optimized for the current situation.

During high-power climb it can be adjusted to a finer pitch to maximize climb performance. During cruise the pitch increases so that it is a more efficient cruise prop, etc.

Most of this adjusting happens automatically as the governor adjusts the prop to maintain the commanded RPM (from the blue knob). The pilot is only involved occasionally and the prop control is only adjusted a few times during flight while the throttle is used for the majority of power adjustments.

Just don't get suckered into believing the "over-square" mantra... Look in your AFM for any applicable restrictions or limitations on MP/RPM combinations.
 
Larry in TN said:
Constant-speed, not controllable pitch. A controllable pitch prop is a prop on which the pitch can be adjusted ON THE GROUND. ie. you can change it from a "climb prop" to a "cruise prop", etc. A constant-speed prop is one that is controlled by a governor in flight that is generally pilot adjustable. These two terms are often used interchangeably by those who don't know the difference but there is a very significant difference.
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If we're all picking nits, there are in-air controllable variable pitch propellers. The Beech 215 on the early Bonanzas had this, with an electric motor to set blade angle, and a crude "auto" mode that mimicked a constant-speed operation, but wore the motor out rapidly. :)
 
Larry in TN said:
Constant-speed, not controllable pitch. A controllable pitch prop is a prop on which the pitch can be adjusted ON THE GROUND. ie. you can change it from a "climb prop" to a "cruise prop", etc.
Click to expand...

That is technically a ground-adjustable propeller (what I have on the Waco).

Constant speed propellers are indeed a type of controllable pitch propeller. They differ from most marine type controllable pitch propellers in that their pitch is adjusted by a governor vice the blue knob/lever having a direct control of pitch.
 
schmookeeg said:
If we're all picking nits, there are in-air controllable variable pitch propellers. The Beech 215 on the early Bonanzas had this, with an electric motor to set blade angle, and a crude "auto" mode that mimicked a constant-speed operation, but wore the motor out rapidly. :)
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There were also some controllable pitch Hartzell hydraulic conversions for the old Bonanzas, although I think most of the conversions were constant speed. :)
 
One thing that should be understood when dealing with an airplane that has an in flight controllable pitch prop is that your manifold pressure + engine speed settings equal your power setting. Down low you may have more than one combination that will get you the same power setting but as you go up in altitude in a non-turboed airplane the options to away.
 
schmookeeg said:
If we're all picking nits, there are in-air controllable variable pitch propellers. The Beech 215 on the early Bonanzas had this, with an electric motor to set blade angle, and a crude "auto" mode that mimicked a constant-speed operation, but wore the motor out rapidly. :)
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I wasn't aware of those. Thanks!
 
One thing. When you lean to lean side of peak, the prop governor will allow the rpms to fall a bit, just like a fixed pitch prop.
 
Pull it out rpms go down push it in rpms go up, governor maintains prop rpm for best engine performance.
 
Here's how I remembered the order of movement as a student pilot:
The passenger says "LETS GO FASTER", and begins pushing everything towards the firewall from his side of the plane. Mixture, then prop, then throttle.
The pilot says "NOT SO FAST, SON", and starts pulling everything back. Throttle, then prop, then (finally) mixture.
Helped me out, hopefully that helps somebody else out too!
 
The way I learned it on a 182 was to draw a 7, where the top is (carb heat) throttle, prop, and mixture, and the bottom is cowl flaps. Go up the 7 to raise power, down the 7 to lower it.
 
Chrisj13 said:
Here's how I remembered the order of movement as a student pilot:

The passenger says "LETS GO FASTER", and begins pushing everything towards the firewall from his side of the plane. Mixture, then prop, then throttle.

The pilot says "NOT SO FAST, SON", and starts pulling everything back. Throttle, then prop, then (finally) mixture.

Helped me out, hopefully that helps somebody else out too!
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Works....as long as you aren't flying a Beech.
 
MAKG1 said:
The way I learned it on a 182 was to draw a 7, where the top is (carb heat) throttle, prop, and mixture, and the bottom is cowl flaps. Go up the 7 to raise power, down the 7 to lower it.
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That's rather airplane-specific. My carb heat is below the throttle, and my cowl flaps are fixed.
 
Adamoh said:
I am a first grader explain to me how a high performance engine works!
Please!
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16 posts ... welcome?

High performance just means over 200H.P.... ;)

6dc0913cc599da31a47fe47a65e3adc4.jpg
.

Pull the black knob first when you want to slow down.

Push the blue knob first when you want to speed up before the black one.

First grade lesson over. :goofy:
 
schmookeeg said:
If we're all picking nits, there are in-air controllable variable pitch propellers. The Beech 215 on the early Bonanzas had this, with an electric motor to set blade angle, and a crude "auto" mode that mimicked a constant-speed operation, but wore the motor out rapidly. :)
Click to expand...

Actually it wore out the bearing. Most electric prop owners run in manual mode most of the time now. No knob, just a toggle switch..
 
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