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  #1  
Old 08-06-2016, 07:00 AM
Chrysopelea Chrysopelea is offline
 
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Location: santa rosa CA
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Default Prop Pitch

I got to fly a friend's RV12, and noticed it was a bit smoother.

I've been reading up here everything I can about prop pitch, and static and WOT RPM's. Static, I got 5000 RPM, haven't checked the WOT R's in the air, but the plane performs wonderfully.

After noticing my friend's plane being a tad smoother riding than mine, I got the necessary tools and checked my prop pitch.

I found one blade (pick a side) to be one degree off from the other.

From what I've read, this is enough to make a difference you can feel, so I plan to adjust my prop until both blades read exactly the same.

I'm hoping this will help make my plane run as smoothly as my friend's.

It's not like my plane shakes, although throughout the RPM range there are certain speeds that I can feel the engine doesn't like, but a quick twist on the Vernier solves that.

Any tips for when I tackle this?

I'm planning on matching the blade with more pitch (my meter reads 60 and 61 degrees, but I didn't level the pane, so those are just the degree numbers I got) so I hope to get 61/61.

The most important thing is to make sure both blades have the exact same pitch.

Even though I'm planning on only moving one blade, I should still loosen the entire hub evenly, so I can get a proper re-torque on the hub after I've made the adjustment, correc?.
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  #2  
Old 08-06-2016, 10:05 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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.2 degree difference is enough to be felt if the prop is otherwise well balanced, so 1 degree difference should be considered huge.

A good procedure is to always zero your digital level relative to the cockpit side rail. then it will never matter what surface the airplane is sitting on when you do an adjustment.... the number you read will always be relative to the longitudinal center line / water line of the airplane.
Measure each blade with them in the exact same rotational position. I.E., measure carefully from a point on the ground or use a level across the prop hub.
What are you using for a tool to repeatably attach a level / protractor to the prop blades. If you are using the tool sold by Van's on the back side (when the prop is horizontal) of the right side blade as most do, then increasing the pitch of a blade requires reducing the degree value. So if you want slightly more pitch you would make both read 60.
When I make adjustments I try and leave the center two bolts a little tighter than the outer four so that the blades aren't sloppy in the hub.
Sometimes as you are tightening the outboard bolts a blade rotates a minute amount and changes the value by .1. You can counter this by re-loosening the bolt slightly and tighten the opposite side most of the way, and then finish to final torque using the standard cross pattern. Not sure if that makes sense or not.

There is some variation in how smooth the Sensenich props run, even if the blades are pitched perfectly.
The only way to know for sure if it is really good is to have the dynamic balance checked once you have the pitch here you are happy with the pitch setting. Occasionally they are pretty good right out of the box but my experience is that most of the time it can be improved somewhat, and probably 50% of the time it can be improved an amount that is very noticeable. But don't spend $700 to have it done. You should be able to get it done for $150-$200. Finding someone that has previously done Rotax engines is a plus.
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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.

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Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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  #3  
Old 08-06-2016, 10:44 AM
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DaleB DaleB is offline
 
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Mike, I think I'm right behind you for a different reason. My blades are within .1 degree of each other, but I think I need a bit more pitch. On the trip to Oshkosh I was half an hour behind a friend flying at the same altitude and airspeed. I was at 7500', WOT turning just under 5400 RPM. He was at 7500', not quite WOT turning about 5100 RPM. My fuel burn is considerably higher as well, of course. When we landed at the same airport, I put in 15.7 gallons and he put in less than 12. Part of that difference would be his HACman mixture control, but not all of it. I need to check and see what my static RPM is, I haven't had it past about 4100 RPM on the ground since I bought it.
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Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)

Last edited by DaleB : 08-06-2016 at 11:30 AM. Reason: Typo... 15.7 gallons, not 17.5
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  #4  
Old 08-06-2016, 11:01 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by DaleB View Post
Mike, I think I'm right behind you for a different reason. My blades are within .1 degree of each other, but I think I need a bit more pitch. On the trip to Oshkosh I was half an hour behind a friend flying at the same altitude and airspeed. I was at 7500', WOT turning just under 5400 RPM. He was at 7500', not quite WOT turning about 5100 RPM. My fuel burn is considerably higher as well, of course. When we landed at the same airport, I put in 17.5 gallons and he put in less than 12. Part of that difference would be his HACman mixture control, but not all of it. I need to check and see what my static RPM is, I haven't had it past about 4100 RPM on the ground since I bought it.
My prediction is that you are actually slightly over pitched already, based on how I adjust RV-12's.

If you increase the pitch even more your take-off and climb performance will begin to suffer.
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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.

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Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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  #5  
Old 08-06-2016, 11:46 AM
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DaleB DaleB is offline
 
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That could be, I'll let you know what I find out what the static RPM is. I do know the previous owner was making efforts to see if he could get a little more speed out of it. He may have pitched the prop a little more aggressively, I don't know. However, I'm trying to figure out how that would cause me to run a couple of hundred RPM higher in cruise than my buddy with an RV-12 flying at the same speed.

I just looked again at a D180 screen shot from the trip. 7500', OAT 18C, DA 9690, 22.3" MAP. The TAS was 119 knots, 5380 RPM and burning close to 7 GPH. The EGT was 1152/1102. It sure looks to me like it could use a little more pitch and a leaner mixture, but I could well be wrong. Its happened before, just ask my wife.
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RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)
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  #6  
Old 08-06-2016, 01:20 PM
Sink Sink is offline
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Here is an article I copied and pasted from another website, but it has made its rounds. It's worth reading and may help you. Good general info.

"" Understanding the Ground Adjustable Prop
Keeping it simple and effective for the common setup.

Let's discuss prop pitch and how it affects flight characteristics. It can help flight characteristics or it can hinder. I'm often asked; What's the correct prop pitch for a specific plane? There is no single answer as many props are available to us today for Rotax engines and for different fuselages. There are, however, some commonalities and that is where we are headed in this article.
Certain principles do apply in either the 2 stroke or 4 stroke engines, although the numbers will be different as with most ground adjustable props. This article won't get into all the designs, blade twists, angles, thrusts, shaft powers, etc...etc. Whoa, just thinking about it puts my brain in a tail-spin. We are going to keep it simple and easy to follow. I am going to use the Rotax 912ULS as an example.
First let's pick a few numbers to keep in the back of our minds for later. We are going to shoot for certain idle rpm, so let's pick 1700 +/- rpm and 5600-5650 rpm for wide open throttle (WOT), flat and level at your average cruise altitude. It wouldn't make sense to set a prop for sea level when you are at 9,000' msl all the time. Why 5600- 5650 rpm as a target? Through a lot of testing this was found to be the BEST BALANCE point for climb, cruise, engine temps and fuel consumption. The "continuous run" rpm Rotax recommends for the Rotax 912ULS is 5500 and that rpm can be flown all the time if you chose to do so. Another good reason would be if you were to break a cable or had a throttle control failure. One carb would probably go wide open, as it's supposed to do and then you could advance your throttle and have the other carb go wide open. You could then fly to wherever you needed for a safe landing area; shut down and land. Anything over 5500 rpm (i.e. 5600-5800 rpm) would limit you to a 5 minute run time under normal flight situations for longevity of the engine, but in an emergency the engine can truly run for much longer times without fear of damage. A prop manufacturer will usually have some instructions for their prop and sometimes a suggested starting point for pitch depending on the engine. Another often asked question is “What should my static rpm be”? There is no specific or accurate answer for everyone's engine and prop. The static won't mean much if you only want to fine tune your existing setup. Static is more important for the first run owners or for new prop installation. The static rpm setting is just to get you in the ballpark and then you will need to fine tune it for your specific aircraft and needs while flying WOT at your average altitude. So in keeping it simple, you will want to set the pitch on most props to achieve a target with a beginning static (ground run) WOT rpm of around 4800-5000 rpm, but your static rpm may be slightly different depending on what you wanted for a final in flight WOT rpm outcome and different props can run different static rpms from one to another. The factors here are long vs shorter blades, two vs three blades and stiff vs flexible blades.
(Note: These next figures are general and yours may vary slightly) To do this properly, you will need to go fly at your average cruise altitude and fly flat and level at WOT for at least 1 minute. Now if your WOT rpm at this time is 5500 rpm and up to 5650 rpm you're probably set up fairly well for your engine, temperatures and fuel economy. If you are up at 5700+ rpm then you may want to land and add a little pitch (about .25-.75 degrees) back into the prop pitch, which will make it more coarse.
If you already have your prop setup is only turning 5200 rpm WOT flat and level you need to flatten or reduce the pitch approximately 1.5-2 degrees to achieve 5600-5650 rpm. Now you may have some special circumstance like a float equipped aircraft (heavy aircraft) that needs a little better climb, lots of high DA takeoffs or lots of tight short fields where better climb is more important so a climb pitch of 5650-5725 rpm WOT might be warranted. We need to tune our props for the type of flying that we do.

What else does my prop pitch do for me?

Setting the prop pitch excessively coarse (i.e. 5000-5300 rpm WOT) causes excessive stress on engine components and gearbox which may necessitate early maintenance and has been known to crack crankcases. Having the pitch too coarse will cause higher engine (CHT, EGT) and oil temperatures, excessive fuel consumption, poor climb and decreased cruise speed. Your engine doesn't have the horse power and torque to turn an excessively pitched prop. All piston engines have their limits and the props all have limits, too. So if your engine temps are up and your WOT engine rpm is below 5500 rpm try unloading the engine by reducing the prop pitch. If you have a prop that is too flat then it may climb well, but have a loss in cruise speed and of course engine temps and fuel are affected again.
Your exact numbers may vary some, but you now have a general idea on what to look for and how it may affect your flying and engine. We'll keep this discussion on the root topic of ground adjustable props. Special circumstance rpm settings and in flight adjustable props will warrant discussion in a future article.
One last parting comment: If adjusting prop pitch sounds complicated, it isn't; it usually will only take 30-40 minutes, a couple of wrenches, a prop protractor and/or a level. So take the time to fine tune, your engine will say thank you in improved performance. ""


p.s.
A plane does not need to be leveled to set a prop pitch. Just put a level on the blade out to your right side and level it to the ground with a 12" torpedo level. Then measure in from the tip of a blade 8"-8.5" inward and put a mark on each blade so your protractor is in the same place for each blade. Then put the prop protractor on the back side of that blade and take a reading. Determine how much you want to add or reduce the pitch and then loosen the securing bolts on the hub and turn it to that setting. Repeat for each blade. This way will ensure you can get a minimum of .1 degree of accuracy and depending on the protractor may be better.
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  #7  
Old 08-06-2016, 02:30 PM
Driftdown Driftdown is offline
 
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Quote:
Originally Posted by Sink View Post
Here is an article I copied and pasted from another website, but it has made its rounds. It's worth reading and may help you. Good general info.

"" Understanding the Ground Adjustable Prop
Keeping it simple and effective for the common setup.

Let's discuss prop pitch and how it affects flight characteristics.
Excellent article, thanks for posting.
With Rotax 912 ULS and a Neuform 3-blade prop (standard day), .25 degrees pitch change equates to how many RPM (approximately)?
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  #8  
Old 08-06-2016, 03:17 PM
redbaron redbaron is offline
 
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Smile Plaincode clinomitor on cell phone

I have used this set my prop and it is easy to use and very accurate
I use it on my Samsung Ck it out.
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  #9  
Old 08-06-2016, 10:56 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Sink View Post
p.s.
A plane does not need to be leveled to set a prop pitch.
I agree, but there can be times when it is valuable to know what the blade pitch value is relative to some part of the airplane so that regardless of the pitch attitude of the airplane you can reset the propeller pitch to a specific value.
Such as if the propeller is removed for some reason, or if you seasonally re-pitch to different values. If you know the pitch value relative to the side rail of the airplane, you will not have to remember to check it before the propeller is removed, and the ground attitude of the airplane will never matter (variability from different tire pressures, empty vs full fuel tank, re-pitching during a trip with a lot of baggage in the airplane, etc.)

I keep it recorded in the airframe logbook and regardless what ever happens or where the airplane is located, it is easy to get back to the exact same pitch value.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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  #10  
Old 08-07-2016, 06:37 AM
todehnal todehnal is offline
 
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This is a sanity check for my personal, and slightly altered method of measuring prop pitch. The above article, as well as most all documentation that I have seen, use the rear flat surface of the prop blade on the right side. This surface is slanted forward at the bottom, and requires holding the level against the surface with a magnetic based level, or rubber bands. I have been using the left blade. The flat surface on the left blade slants "bottom to the rear" and makes it much easier to position the level with repeated accuracy. So. my question is, why do all documented procedures call for fitting the level to the right blade? Am I making a mistake by using the more convenient left blade?

Thanks....Tom
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