Variable Pitch Prop?

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Mtns2Skies

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Mtns2Skies
As most of you know I train in the 152 and I'm currently on Vacation. Well as some of you know when I get back I will switch to the Piper Arrow which is a complex plane. Well I don't totally understand how a variable pitch prop works also when or how it should change. I don't understand the mechanics about how it changes it's bite/torque. Also when you change it for climb vs. cruise do you want more or less bite? When you pull the lever back does it increase or decrease the blade angle?

(stupid question sorry but I forgot over vacation, What is manifold pressure?)
 
Call it a constant speed prop, not a variable speed prop. Way back in the dark ages I flew a Bonanza with an electric prop...there was a rotary switch to adjust prop pitch for various situations; I never saw one, but there have been variable speed props that were ground-adjustable. Your Arrow will have a governor that controls RPM, so constant speed is the correct term.

You get the most bang for your buck at high RPM, so when the prop control is fully forward the blade pitch is low ("fine" for purists); if the Arrow's prop could go into feather you would get minimum thrust with a blade angle of 90 degrees, but of course it doesn't and you won't. What you will get is coarser blade pitch (lower RPM) as you pull the prop control back. That help?

Bob Gardner
Bob Gardner
 
bobmrg said:
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You get the most bang for your buck at high RPM, so when the prop control is fully forward the blade pitch is low ("fine" for purists); if the Arrow's prop could go into feather you would get minimum thrust with a blade angle of 90 degrees, but of course it doesn't and you won't. What you will get is coarser blade pitch (lower RPM) as you pull the prop control back. That help?

Bob Gardner
Bob Gardner
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Most bang in terms of most delivered horsepower, not reduced noise or "for your buck" economy.

You'll see that you keep the pitch control forward (high rpm/flattest pitch) for takeoff and move the knob forward to climb. Pull it back to reduce noise and *maybe* gain some efficiency in MPG at lower power settings (for that, see the POH).
 
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HawkEye007 said:
As most of you know I train in the 152 and I'm currently on Vacation. Well as some of you know when I get back I will switch to the Piper Arrow which is a complex plane.
Click to expand...

I've gotta start with... Why? Do you hate money that much? ;) :rofl: Switching to a complex plane will make your training take longer and be MUCH more expensive, and chances are you won't be allowed to solo it. If you want to build complex time, wait for your instrument training.

Well I don't totally understand how a variable pitch prop works also when or how it should change. I don't understand the mechanics about how it changes it's bite/torque. Also when you change it for climb vs. cruise do you want more or less bite?
Click to expand...

It's called a constant speed prop for a reason - As long as the engine is providing enough power to support the selected RPM at the flattest blade pitch, the engine will remain at the same RPM. When you push the throttle in (higher manifold pressure), the engine will develop more power and to keep the engine at the same speed, the prop will take a bigger bite of the air.

The other thing that will happen with the prop is when you climb or descend without changing power settings. When you climb without changing power in a fixed-pitch airplane, the RPM's will drop, right? It's harder for the prop to claw into the air when you slow down like that. With a constant-speed prop, if you climb without changing power settings, the prop will flatten out to maintain the engine RPM's. If you dive without changing power settings, the prop will take a bigger bite to compensate.

That's the pilot perspective. You'll also want to learn it all from a systems perspective.

When you pull the lever back does it increase or decrease the blade angle?
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When you pull the lever back, the RPM's go down. Would a bigger angle or a smaller angle make that happen?

(stupid question sorry but I forgot over vacation, What is manifold pressure?)
Click to expand...

Go to the link Ron posted, and right near the top of the article is a link to another excellent Deakin article called "Manifold pressure sucks!" That article is what made the subject really make sense to me several years ago.
 
flyingcheesehead said:
I've gotta start with... Why? Do you hate money that much? ;) :rofl: Switching to a complex plane will make your training take longer and be MUCH more expensive, and chances are you won't be allowed to solo it. If you want to build complex time, wait for your instrument training.
Click to expand...

*Ahem* I'm 13 so ive got a while. also Thanks a ton for the post Bob, and the links you guys posted
 
bobmrg said:
Call it a constant speed prop, not a variable speed prop. Way back in the dark ages I flew a Bonanza with an electric prop...there was a rotary switch to adjust prop pitch for various situations; I never saw one, but there have been variable speed props that were ground-adjustable. Your Arrow will have a governor that controls RPM, so constant speed is the correct term.

Bob Gardner
Bob Gardner
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Don't forget about the venerable Beech Roby prop, Bob ;)
 
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Think of it as a gearshift in a car. The fixed pitch prop is always in second gear. Not optimum for either climb or cruise. A fixed pitch cruise prop is pitched a little more toward high gear so doesn't get away from the stop light well ( take-off). The climb prop is pitched a little more toward low gear so doesn't cruise very economically. The constant speed prop is able to shift gears. You get a climb prop (high RPM at low speed) for take off and a cruise prop for cruise (lower RPM at high speed).
 
bobmrg said:
Call it a constant speed prop, not a variable speed prop. Way back in the dark ages I flew a Bonanza with an electric prop...there was a rotary switch to adjust prop pitch for various situations; I never saw one, but there have been variable speed props that were ground-adjustable. Your Arrow will have a governor that controls RPM, so constant speed is the correct term.
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Bob,

Why did the Electric variable Pitch Prop go out of favor? The motor is tiny and the system far simpler than a CS prop.
 
dmccormack said:
Bob,

Why did the Electric variable Pitch Prop go out of favor? The motor is tiny and the system far simpler than a CS prop.
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I haven't the faintest idea.

Bob
 
there was a bonanza in here recently with an electric prop. he mentioned that he had to absolutely BEG a prop shop to overhaul it. that could be one reason why they aren't seen anymore, just no shops out there to maintain them anymore?
 
tonycondon said:
there was a bonanza in here recently with an electric prop. he mentioned that he had to absolutely BEG a prop shop to overhaul it. that could be one reason why they aren't seen anymore, just no shops out there to maintain them anymore?
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Hmm...

Prop overhaul shouldn't be a problem -- though some of the early model 35s had a wooden prop -- maybe he needed a new pitch controller/driver?

You would think the simpler mechanism would require less maintenance?

The Bo owner could probably find the shop he needed through the American Bonanza Society.
 
yea it could've been an overhaul of the controlling motor. im not exactly sure.
 
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