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  #11  
Old 05-05-2014, 11:24 AM
roger lee roger lee is offline
 
Join Date: Sep 2013
Location: Tucson, AZ
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Tom, good job.


I have tried for 25 years to get some to understand how pitch can affect their planes and performance and it seems that with the introduction of SLSA that more people are taking a hard look at prop pitch and its effects. Because of our setup with the Rotax engine and its design we do well with a pitch to achieve between 5600-5700 rpm at WOT at our average cruise altitude. Some have special circumstances to consider, but the majority of us are in the same boat.

If we could use in flight adjustable props we could have the best of all worlds, but since we have only ground adjustable we should strive for a good balance between engine and aircraft.

Early on (pre June 2006) with the older Rotax crankcases those who chose to use WOT rpms down below 5300 for their WOT settings have cracked crankcases from stress. It happens on the top of the case. Over loading a prop also cause more engine temp and stress on the entire engine which was never designed to operate at WOT in this rpm range. You loose everything when over pitched. Under pitched just gets you a good climb, but you suffer loss at cruise and top end performance. I also think with today's engines and planes that using a fixed pitch (non adjustable) can limit your performance choices.
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  #12  
Old 05-05-2014, 11:45 AM
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f1rocket f1rocket is offline
 
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Location: Martinsville, IN
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This thread has caused me to go back and address prop pitch once again. When I put the digital angle finder on the blades, there is a difference of at least 5 degrees between them. I find that hard to believe. Is there a trick to measuring the angle? I've leveled the prop, and measured the angle the same distance from the hub on each blade? What am I missing?

I thought I'd ask before going any further. Thanks.
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Randy Pflanzer
Greenwood, IN

www.pflanzer-aviation.com
Paid through 2043!
Lund fishing Boat, 2017, GONE FISHING
RV-12 - Completed 2014, Sold
427 Shelby Cobra - Completed 2012, Sold
F1 EVO - partially completed, Sold
F1 Rocket - Completed 2005, Sold
RV-7A - Partially completed, Sold
RV-6 - Completed 2000, Sold
Long-EZ - Completed 1987, Sold

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  #13  
Old 05-05-2014, 12:09 PM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,667
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For the most part, all of the 300 + RV-12's now flying are built pretty close to the same, and they are flying with the exact same propeller blades / propeller, and engine.
With this being the case, and because of all of the data that has been acquired during extensive flight testing, using static RPM as a cross check has proven to be a very reliable way of setting propeller pitch.

All of the S-LSA RV-12's produced so far (~ 25) have had the prop pitch set to a specific pitch value (established by testing), and then cross checked using static RPM. They all perform nearly identical.

Density altitude condition at the time the static RPM check is done has some effect, but to a large degree it automatically compensates.
I.E., someone flying from a higher elevation airport (say 5000 ft) will be adjusting pitch to a slightly lower value to attain the proper static RPM, because of power loss with the higher altitude. This will automatically dial them in to a pitch that is better for the environment they are flying in. If someone is flying in a wide variety of density altitude conditions, they will probably want to adjust towards a slightly higher static RPM than nominal, if the are doing their checks and adjustments at a low density altitude.

A static RPM of only 4800 is not a best all around performance setting for an RV-12. In fact it is likely that the airplane is not any longer legal as an LSA because it will be able to easily exceed 120 Kts at zero density altitude and max continuous power (as already hinted at in a previous post made by the O.P. in this thread ). Also, at higher weights and density altitudes, it's takeoff and climb performance will be noticeably worse than most RV-12's

On an RV-12, a full throttle static RPM of about 4950, does provide a good all around performance pitch setting. The check needs to be done with no wind, the oil fully warmed to normal operating temp, and the density altitude on the ground, somewhere in the ball park similar to the conditions being flown in most often. If this process is used, doing the check at different times of the year will automatically compensate for major temp swings with the seasons (such as people in the mid west flying in the winter with temps in the teens and 20's, but in the 90's or higher in the summer).
After some experience, most owners learn a preferred pitch value for summer and winter, and then just switch back and forth between them. Here in the pacific north west, we don't have nearly that big of temp (density altitude swings so we pretty much use the same pitch all year round).
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Hubbard, Oregon
Van's Aircraft Engineering Prototype Shop Manager
FAA/DAR
RV-6A (aka "Junkyard Special ")
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  #14  
Old 05-05-2014, 01:47 PM
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Tony_T Tony_T is offline
 
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Location: Lacey, WA
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Quote:
Originally Posted by f1rocket View Post
This thread has caused me to go back and address prop pitch once again. When I put the digital angle finder on the blades, there is a difference of at least 5 degrees between them. I find that hard to believe. Is there a trick to measuring the angle? I've leveled the prop, and measured the angle the same distance from the hub on each blade? What am I missing?

I thought I'd ask before going any further. Thanks.
Randy
Hard to answer that question without seeing how and with what you are measuring the angle. There really is not a straight surface on the prop blade that you can rest a digital level against and be consistent. Some of us therefor made a fixture of sorts for the digital level that can be placed with consistency against the blade. Here is a picture of mine, a search will turn up others and many past posts about how to do this. Most of us can get the blades within about 0.1? of each other:


This fixture contacts the blade at three points and has a notch that lines up with the inner paint stripe. You have to be rather careful and take several reads and average them but 0.1? is possible.
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  #15  
Old 05-05-2014, 01:59 PM
roger lee roger lee is offline
 
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Location: Tucson, AZ
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Hi Randy,

No magic bullet here. I find more prop blade pitch unequal blades a little too often and it doesn't matter what MFG. After I found a few this way I check all my clients the first time I see them.

Here is an easy way to do your prop.
Since you already have a flying aircraft and pitch is in the proper area it should be an easy reset.


For general info for those that have an issue.
(best to remove 1 spark plug from each cyl)
First measure back from the tips about 8-8.5 inches and place a mark on each blade. You will need at least a 12" digital protractor or a prop protractor or both. I use both, but it isn't required. These will make your reset easy. I'll explain this as if we only have the 12" digital level. Stand in front of the plane facing the blades. Rotate each blade around one at a time and place the level on top of the right side blade and level the blade. (accuracy here does not seem to matter as I have found being off 1 degree off level doesn't change the pitch reading, but I personally like level) Once the blade is level on your right side place the level on the back flat side of the blade and get that reading. Do this to all three blades. I like to pick one blade as the master blade that all must be equal to. Hopefully at least 2 blades are equal and your 5 degree blade is a loner.
Loosen the 6 large 8mm hub bolts, but only so you can rotate the bolt by hand. Making things too loose will affect your blade tightening accuracy. Now rotate the off pitch blade back to your right side and level it. Put the level on the back of the blade and see what the reading is. Now you may want to put a rubber band around the level to hold it in place for a hands off operation which is much easier. Now loosen the bolts on the blade hub and turn the blade to the exact degree setting as your other two. Then snug the bolts back up. Then run all three blades around one more time to check your accuracy. It should be within at least .1 degree from each other. If you pay attention to detail this can be done to this accuracy with a bubble level. Once all three blades are equal tighten the 6 main 8mm hub bolts first and torque in 2-3 stages to their proper torque. Then tighten the smaller prop hub bolts. The large through bolts are the first to be loosened and the first to be tightened because they can and will change the torque on the other smaller hub bolts.

p.s.
If the pitch is set up for a good (5600-5700) WOT rpm for your average cruise altitude (this is the key) then you usually don't have to worry about summer verses winter. You may loose a little rpm during the cold dense air winter, but if the pitch is in a good place it may be about 50-75 rpm which isn't worth messing with because you'll have better performance in the winter any way.

p.s.s. LOL
When I did all the prop research I did find static could vary. It could vary from 4750 to 5000 rpm depending on the prop pitch, stiffness, number of blades and length and my target rpm was 5600-5650 at that time.
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  #16  
Old 05-05-2014, 02:00 PM
roger lee roger lee is offline
 
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Hi Tony,

Nice little setup.
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  #17  
Old 05-05-2014, 02:04 PM
roger lee roger lee is offline
 
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Location: Tucson, AZ
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prop protractor

http://www.aircraftspruce.com/catalo...s/propprot.php
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Tucson, AZ
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  #18  
Old 05-05-2014, 02:14 PM
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Bill_H Bill_H is offline
 
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Location: Marshall TX (KASL)
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There is a good article in an old RVATOR about RV12 prop pitching. Don't have it handy. Use Tony's jig on a Sears digital level. Make a mark or notch on the jig and index it on the same point on the paint stripe. NOTE you must rotate the prop and measure each blade on the same side of the engine! Use something to make sure it is exactly the same position like a dowel on a sawhorse or something. I can get mine to agree to 0.1 degrees but it takes some doing!

A friend is finishing a new RV9 with a new type of ground adjustable sensenich that is easy, fast, repeatable, and precise. Uses a set of 6 pre-machined rods that you insert into the hub and twist the blades to bump against. Each rod produces a predefined different pitch. No measuring. Wish it was on the RV12!

Last edited by Bill_H : 05-05-2014 at 02:28 PM.
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  #19  
Old 05-05-2014, 04:33 PM
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f1rocket f1rocket is offline
 
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Quote:
Originally Posted by Bill_H View Post
NOTE you must rotate the prop and measure each blade on the same side of the engine! !
Bingo. That's what I was doing wrong. Once I rotated and re-leveled, the props where the same.

Thanks Scott. I'm going back to the static RPM test. I've run several flight tests with the prop changes and it's hard to find the sweet spot with so many variables.
__________________
Randy Pflanzer
Greenwood, IN

www.pflanzer-aviation.com
Paid through 2043!
Lund fishing Boat, 2017, GONE FISHING
RV-12 - Completed 2014, Sold
427 Shelby Cobra - Completed 2012, Sold
F1 EVO - partially completed, Sold
F1 Rocket - Completed 2005, Sold
RV-7A - Partially completed, Sold
RV-6 - Completed 2000, Sold
Long-EZ - Completed 1987, Sold

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  #20  
Old 05-05-2014, 05:13 PM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,667
Default My final comment...

This is the RV-12 forum on the Van's Airforce web site.
Because of that, everything I post is in the context of an RV-12, and I think anyone else doing so should also keep that in mind

Experience that someone has on multiple different Rotax 912 powered airplanes with different propellers, many different blade shapes and diameters, etc, is really only relevant for the 2% of the flying RV-12's that are not a mostly stock build. For those few, Rogers advice can be of a lot of value.
I do not think it is helpful for the other 98% that for all practical purposes are as identical as any other production line airplane would be. In fact, some of the advice I have seen will result in performance that has no chance in matching what is in the RV-12 POH, so consider the value of that info based on what propeller pitch you have chosen to use.


The majority of what I post is for the 90+ % of the viewers that never post here in the forum. I attempt to pass along information from the viewpoint of Van's Aircraft. It should not be considered the official word from the high up office (but a lot of that results from what I or someone else in engineering tells them when they come and ask).

Hundreds of RV-12 owners are now flying using the prop. pitch adjustment process prescribed by Van's, and they are happy with the result.

As always, the builder is the one with the responsibility of making the final decision of what they will do.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Hubbard, Oregon
Van's Aircraft Engineering Prototype Shop Manager
FAA/DAR
RV-6A (aka "Junkyard Special ")
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