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  #1  
Old 09-27-2018, 03:05 PM
Jetmec Jetmec is offline
 
Join Date: Sep 2018
Location: Pine Bush NY
Posts: 11
Default Prop choises

I recently watched a video on someone flying their RV7 and they were asked why he didnít go with a constant speed prop. His answer was that the constant speed is only good for climbing and slowing down. Whatís everyone elseís thought on that?
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  #2  
Old 09-27-2018, 03:15 PM
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Raymo Raymo is online now
 
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Location: Richmond Hill, GA (KLHW)
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Default

Search and you'll find a bunch of threads on this topic. Other search engines work better than the built-in one using site specific lingo.

I have a 3 blade Catto. Why?
Answer1: My engine is an O360-A4M (solid crank)
Answer2: Very smooth
Answer3: $$$

Example:
site:vansairforce.com constant speed fixed pitch

Link to above search.
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RV-7A - Slider - N495KL - First flt 27 Jan 17
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Catto 3 blade NLE, FlightLines Interior, James cowl, plenum & intake, Anti-Splat -14 seat mod and nose gear support
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  #3  
Old 09-27-2018, 03:21 PM
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johnbright johnbright is offline
 
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Location: Newport News, Va
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http://www.vansairforce.net/articles/props.htm
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O-360, 8.5:1, vert sump, SDSEFI EM-5
Z-14 adapted for EFI, wiring and IP CAD files here
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  #4  
Old 09-27-2018, 03:23 PM
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airguy airguy is offline
 
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Location: Garden City, Tx
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A constant speed prop is more costly, more complex, more weight, and more maintenance than a fixed pitch prop. So why do people use them and love them?

Simply put - it's like having an infinitely variable transmission to hook horsepower up into the air. With a fixed pitch prop, it's like having a car with only one gear. You can choose that gear to be very good at one thing and one thing only - your friend obviously has chosen his to be good at cruising flight, which is very common. Others choose it for lower flight speeds (like banner towing or glider launches) or max climb, or a variety of other points.

One side effect of this is that the prop operates part of its time outside the ideal airspeed range. When the airspeed is too slow (at takeoff, for example), the prop has too much load for the engine and the engine can't make full rated RPM - which means you don't get full rated horsepower. At the very highest speed range, the prop doesn't have enough load to utilize all the engine horsepower and the engine will go overspeed, and you'll have to pull the throttle back to prevent that. Either way, you're not getting everything the engine has to offer converted to thrust.

With a constant speed prop, it will change the pitch of the prop as the airspeed and horsepower changes - it is essentially "changing gears" to allow you to set the engine at the best RPM to make the best power. I can turn the engine at 2700 rpm for full power at takeoff, and dial it back to 2400 for efficient cruise at high altitude, leaving the throttle wide open the whole time - something that no fixed pitch prop can do. It gives you large advantages in takeoff power, climb rate, descent rate (acts like an airbrake when you pull the power way back) and still gives very good cruise performance. It's a combination of operational advantages that makes it worth the cost, weight, complexity, and maintenance. Kind of like a girlfriend or wife.

The larger the range between stall and max cruise speed, the better a constant speed prop will perform on an airplane. In a Cessna 152 that range is very small and you won't ever see one with a constant speed - the advantage does not outweigh the cost. On RV's I suppose you could say it's a toss-up and people go either way. On faster airplanes constant speed is the standard.
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Last edited by airguy : 09-27-2018 at 03:26 PM.
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  #5  
Old 09-27-2018, 03:47 PM
Jetmec Jetmec is offline
 
Join Date: Sep 2018
Location: Pine Bush NY
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Thanks for the replyís, great info so far and Iím already exploring the other links provided. I will be building an RV-9, but not until sometime next year. Have my wedding in June and have to prepare basement for the build which Iím doing now. I think my future wife is more excited than I am about taking trips in the RV🤣
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  #6  
Old 09-27-2018, 04:18 PM
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Dugaru Dugaru is offline
 
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Default The CS prop question

You will absolutely LOVE traveling in the RV-9. It's a nearly perfect GA aircraft for two people to scoot around in. I can't get over how much I like mine. It's a freaking time machine, it's easy and fun to fly, and it's simple and inexpensive to operate and maintain.

By airplane standards.

I bought one with a Hartzell CS prop. I love it. But I haven't had to pay very much to maintain the prop so far.

The one thing I'll say is that with the -9's superb climb and cruise performance on a FP prop, I don't think a CS is anything close to being a NECESSITY, at least not here in the flatlands. If I had a limited budget and had to choose, I'd be sorely tempted to sink the extra cash into IFR avionics instead of a CS prop. I may be even more of that view when I really have to sink $$ into my CS prop.

But you really can't go far wrong either way.

Quote:
Originally Posted by Jetmec View Post
Thanks for the replyís, great info so far and Iím already exploring the other links provided. I will be building an RV-9, but not until sometime next year. Have my wedding in June and have to prepare basement for the build which Iím doing now. I think my future wife is more excited than I am about taking trips in the RV🤣
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  #7  
Old 09-27-2018, 04:38 PM
CJ in EP CJ in EP is offline
 
Join Date: Apr 2017
Location: Eden Prairie, MN
Posts: 27
Default Thank you!

Thanks, Greg,

Pretty sure that was the best explanation of a c/s prop that I've ever read. I too will soon have a flying 9A with a c/s prop (at recommended hp though) and the trick is that I've never flown a c/s prop in my meager 150ish hours. I clearly have some learnin' in front to me, and as I'm focusing all my time and energy into finishing this, it weighs on me that even when she gets her ticket, we wont be anywhere close to being able to go flying together.

I ask the community for suggestions on where/how to start putting together a training plan. I'm not current. I am an extremely inactive member of a flying club so easy access to an airplane and instructor isn't an issue. I'd like to think that the plane will be finished by next fall. Stein has very effectively separated me from as much of my cash as possible, and Classic Aero finished the job, so I'm looking for a thorough, yet cost effective plan which is executed at the right time.

Suggestions would really be appreciated. Thanks!
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  #8  
Old 09-27-2018, 04:57 PM
Jetmec Jetmec is offline
 
Join Date: Sep 2018
Location: Pine Bush NY
Posts: 11
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Thanks Dugaru, what Iíve researched so far has stated just what you have numerous times and I think when that time comes. I will more then likely go with a fixed pitch and spend my money on more glass, interior and paint.
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