Is there a dive prop?

SixPapaCharlie

SixPapaCharlie

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For the times when you are up their wishing you were down here?

Honestly, I don't understand how a prop can be a climb or cruise prop. It's pulling the same mass through the same medium. I don't really get how adding horsepower does anything when the RPM of the same blade is the same.

But if we can have those things, I want a dive prop that is most efficient when I am trying to go down.
 
Get your complex endorsement, you’ll learn more about how props work.
 
What’s the goal, more speed, less fuel, sound cool, better flight performance? :)
 
I pull the nose up and I have a climb prop, level off and it becomes a cruise prop, push the nose over and ...
 
equate it to bicycle gears.
Climb prop = Low gear power source turns fast but produces low speed , power source working easier (less torque)
Cruise prop = High Gear power sources turns slower but produces higher speed, power source working harder (more torque)

in Theory a climb prop is actually faster than a Cruise prop because the engine produces more horsepower at higher RPM, But a climb prop may be limited by the engine redline and you have to pull the prop back in cruise.

A cruise prop depends on what you want, for speed you may want it to turn near redline, for economy you may want it to turn slower.

A dive prop would likely just be a climb prop, because the flatter blade would work more like a brake in the dive allowing you to dive at a steeper angle.

Brian
CFIIG/ASEL
 
I think what you need is a hybrid aircraft propulsion system with integrated regenerative braking for descents. Then you could just look for massive updrafts to charge your batteries and then continue on your way.
 
Some planes have them, but they're rare because it's tough to pull out. So you need to install brakes:

 
SixPapaCharlie said:
I don't really get how adding horsepower does anything when the RPM of the same blade is the same.
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Funny, I’ve wondered that exact same thing. I still don’t understand how it works. Take for example a 150hp O320 and a 180hp O360. Both are turning the the prop the same RPM but one has a little more zippity doo-dah than the other… how? Maybe this is why I didn’t do well in physics class.
 
This from the mind that created the metal landing calculator
 
SixPapaCharlie said:
Honestly, I don't understand how a prop can be a climb or cruise prop. It's pulling the same mass through the same medium. I don't really get how adding horsepower does anything when the RPM of the same blade is the same.
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But they're not the same blade, that's the whole point.
 
SixPapaCharlie said:
For the times when you are up their wishing you were down here?

Honestly, I don't understand how a prop can be a climb or cruise prop. It's pulling the same mass through the same medium. I don't really get how adding horsepower does anything when the RPM of the same blade is the same.

But if we can have those things, I want a dive prop that is most efficient when I am trying to go down.
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Move the nut on a 1/4 - 20 thread bolt and compare it to moving the nut on a 1/4 -28. Now imagine the thread as the propeller pitch.

Or you can just try to pull out in traffic with a car equipped with standard transmission in 5th gear or cruise the highway in 1st gear to understand the effect.
 
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If I have a fixed pitch prop on a 150HP engine and a fixed pitch prop on a 180 hp engine, the plane should go the same speed at 2700 RPM.
 
SixPapaCharlie said:
If I have a fixed pitch prop on a 150HP engine and a fixed pitch prop on a 180 hp engine, the plane should go the same speed at 2700 RPM.
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Why? There is only one pitch of fixed pitch prop out there? If you think that then why did you start a thread about different prop pitches? :confused2:
 
SixPapaCharlie said:
For the times when you are up their wishing you were down here?

Honestly, I don't understand how a prop can be a climb or cruise prop. It's pulling the same mass through the same medium. I don't really get how adding horsepower does anything when the RPM of the same blade is the same.

But if we can have those things, I want a dive prop that is most efficient when I am trying to go down.
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Dive prop is of course absurd. So what's gonna help ya get down faster, a climb prop or a cruise prop? I think a climb prop. For the same reason it gives you a better climb when the engine is powering the prop, the mirror image, descending without power, will get ya down faster because of increased drag. This of course assumes you pull the power all the way back. Unless if, the plane doesn't have a Vne, and you point it straight down, like perpendicular to the earth, firewall the throttle, then the cruise props thing about giving you a faster airspeed will get you down faster. Just be careful about how far down you wanna get.
 
SixPapaCharlie said:
So if I have a Grumman Traveler with an O-320 and a Grumman Tiger with an O-360, they would have different pitches?
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Different props. This information is available in the Type Certificate Data Sheet (TCDS) if you do not have the POH's handy.

The Traveler has a McCauley 1C172/BTM7359 which is a 73" diameter prop with 59" pitch, while the Tiger has a 1A170/KFA7563 which is 75" diameter with 63" pitch. So the Tiger prop is not only coarser but also has a larger diameter.
 
Think of pitch as gearing. First gear at 3000 rpm speed is much different than 5th gear at 3000 rpm, but you won’t be able to climb a mountain in 5th gear at 3000 rpm.
 
Salty said:
Think of pitch as gearing. First gear at 3000 rpm speed is much different than 5th gear at 3000 rpm, but you won’t be able to climb a mountain in 5th gear at 3000 rpm.
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Likewise, after you cross the mountain, you want to shift down into a lower gear. This forces the engine to run at higher rpm's for the same speed. Higher rpm's=more power absorbed by pumping air through the engine & friction. In the same way a "climb" prop would create the most drag with the engine at idle, also making it a "dive" prop.

When you get your comanche, pull the power to idle with the prop full forward (high rpm) and note the descent rate. Then pull it back (low rpm), and you'll notice your descent rate will decrease by a couple hundred feet/ minute.

That's why we have constant speed props... it's a climb prop on takeoff and a cruise prop in cruise. A fixed pitch is going to compromise one or the other, so you can pick which is more important to you.
 
The 3-bladed MT prop on a Husky is a dive prop. It’s the one thing it does best.
 
Jim K said:
Likewise, after you cross the mountain, you want to shift down into a lower gear. This forces the engine to run at higher rpm's for the same speed. Higher rpm's=more power absorbed by pumping air through the engine & friction. In the same way a "climb" prop would create the most drag with the engine at idle, also making it a "dive" prop.

When you get your comanche, pull the power to idle with the prop full forward (high rpm) and note the descent rate. Then pull it back (low rpm), and you'll notice your descent rate will decrease by a couple hundred feet/ minute.

That's why we have constant speed props... it's a climb prop on takeoff and a cruise prop in cruise. A fixed pitch is going to compromise one or the other, so you can pick which is more important to you.
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Another thing you can do to demonstrate it is during power off 180 spot landings. A little high? Prop forward. A little low? Prop back.
 
SixPapaCharlie said:
For the times when you are up their wishing you were down here?

Honestly, I don't understand how a prop can be a climb or cruise prop. It's pulling the same mass through the same medium. I don't really get how adding horsepower does anything when the RPM of the same blade is the same.

But if we can have those things, I want a dive prop that is most efficient when I am trying to go down.
Click to expand...
Your engine cannot likely spin a "cruise prop" at full RPM.
 
SixPapaCharlie said:
Honestly, I don't understand how a prop can be a climb or cruise prop. It's pulling the same mass through the same medium. I don't really get how adding horsepower does anything when the RPM of the same blade is the same.
Click to expand...
The RPM isn’t necessarily the same. Full throttle in, say, a 70-knot climb with a climb prop may put you at 2700 RPM, developing full power from the engine. A cruise prop under those same conditions may only turn 2300, so roughly 85% power.

A cruise prop, on the other hand, can run full throttle in cruise, but a climb prop will have to reduce manifold pressure to avoid overspeeding, so less power at the same RPM. And due to its higher pitch, the cruse prop will be pulling you more distance per revolution.
 
Try to find someone that worked for Stuka...They should know something about diving planes...
 
SixPapaCharlie said:
If I have a fixed pitch prop on a 150HP engine and a fixed pitch prop on a 180 hp engine, the plane should go the same speed at 2700 RPM.
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Same prop, same RPM, and same amount of drag, yes [theoretically speaking]. But the 180hp engine would have some throttle left over.
 
Tools said:
Beta on a turbo prop.
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:yeahthat:

Nothing slows down and goes down faster than a turbo prop at flat pitch, or if allowable in beta or reverse. One turbine twin I used to fly could easily exceed 2500 fpm down at flight idle.
 
midwestpa24 said:
:yeahthat:

Nothing slows down and goes down faster than a turbo prop at flat pitch, or if allowable in beta or reverse. One turbine twin I used to fly could easily exceed 2500 fpm down at flight idle.
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Most of the jets I’ve flown exceed that in a normal descent.
 
MauleSkinner said:
Most of the jets I’ve flown exceed that in a normal descent.
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Yeah, but you are also going forward at quite a clip too. 2,500 fpm at less than 200 kts is fairly steep. 2,500 fpm at 350 kts, not so much.
 
midwestpa24 said:
:yeahthat:

Nothing slows down and goes down faster than a turbo prop at flat pitch, or if allowable in beta or reverse. One turbine twin I used to fly could easily exceed 2500 fpm down at flight idle.
Click to expand...


Pc12 doing an emergency descent can do 8000+fpm
 
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