T

todehnal

Well Known Member
More Prop Pitch (See Post 12 for actual measurements)

Installed my prop yesterday, to finish up with the nose cone. I was surprised at how little adjustment we have on pitch. I can only twist the blades about 1/8" travel at the hub. That can't be more that a couple of degrees of pitch. I think that I must have the wrong white plastic center core piece!! It will barely rotate. I need a little help from someone who has experience with the prop. Thanks.

Tom
 
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The amount of adjustment you see is still way more than you will use.
I would guess that the majority of RV-12's flying have the props set within probably .5 degrees of each other (If it has been adjusted properly).

Keep in mind, the prop was designed for a wide range of applications. From high drag, slower aircraft; to faster low drag (like the RV-12). Consequently, the RV-12 doesn't need to be able to use a large portion of the pitch range.

When you get to the point of fine tuning the prop pitch you will find that .2 degrees produces a very measurable RPM and performance difference.
 
You should be able to adjust both prop blades to within 0.1 degrees of each other. See the following thread for a simple tool that you can make.
It works rather well. As Scott says, you will be amazed how much a 0.1 or 0.2 deg of prop pitch will affect your static RPM. Your total adjustment should be on the order of +/- 2 degrees.

http://www.vansairforce.com/community/showthread.php?t=64568&highlight=prop+pitch+tool

Also search this forum using the following words

prop pitch
digital level
static RPM

Lots of info.
 
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Build the pitch gauge

Build the pitch gauge using a digital level shown in an earlier thread here. Be sure to fasten the level SECURELY to the gauge and leave it there-- otherwise your calibration will change every time to mount the level the the fitting. Ask me how I know!!!
As Scott says, 0.2 deg change will make a big difference in RPM-- also getting both blades within 0.1 deg of each other will make a big difference.
As I adjusted the prop I made a chart of blade angle vs. climb RPM and one of angle vs cruise speed at 5200 RPM. That way when I take the blades off for inspection I can put them back just as they were. I can also adjust the pitch for summer and winter flying-- density altitude DOES make a difference.

Wayne 120241/143WM
 
As everyone has said, a little goes a long ways! Our first setting gave a little overspeed, and I changed it a couple degrees, thinking I would be closer. It would hardly get off the ground! By the time you have yours right, you will have a new appreciation for the science of prop design. I sure did...

Bob
 
Thanks

Perhaps I panicked a bit too early. I will build the tool, and then I can determine if I have an issue. Thanks guys................Tom
 
Perfect timing

I am in the process of setting up my prop too and just did my first static WOT test and got 5260rpm. The PAP was looking for something around 4950 so I was going to mess with it. I have the digital level set-up and the article about "perfect pitch."

Thanks for the guidance about how little to change the pitch to make a difference.

I did email "support" and Gus felt leaving it would work however an over-rev condition could occur in flight at WOT so I need to be cautious. I am going to flying out of the Denver area at a field elevation of 5460 and am concerned about climb performance. Any comments or suggestions welcome.
 
High Altitude Operation

If I were in your shoes, I would leave it alone. We flew an old 170 B for many years. Typically you could expect 2350 with full power on takeoff. After lifting off, the routine was to lower the nose, wait for 2550, and then climb. You absolutely control rpm with attitude. Nothing has changed. you will do the same. I think that you will enjoy that little extra rpm on takeoff roll, and you will be very comfortable controlling your rpm with attitude. Go for it!!

Just my opinion..............Tom
 
funflying said:
I am in the process of setting up my prop too and just did my first static WOT test and got 5260rpm. The PAP was looking for something around 4950 so I was going to mess with it. I have the digital level set-up and the article about "perfect pitch."

Thanks for the guidance about how little to change the pitch to make a difference.

I did email "support" and Gus felt leaving it would work however an over-rev condition could occur in flight at WOT so I need to be cautious. I am going to flying out of the Denver area at a field elevation of 5460 and am concerned about climb performance. Any comments or suggestions welcome.
Click to expand...

By adjusting the prop for a static RPM at an altitude of 5460, you will already be compensating for flying from high elevations, so I think you should change it.

If you had that RPM at 1500 ft and were planning to immediately relocate the airplane to Denver, then I would suggest you leave it and see how close it is
 
For what it's worth mine has a static RPM of about 5050 with a density altitude of 2000 Ft. I see 5200 RPM in climb and true at 113 KTAS at 5000 MSL. I noted in another thread (as others have too) that the prop blades can have significantly different pitch if you rely on the hub mechanism to keep them equal. They really need to be checked individually.
 
I Think I have A Real Problem

I see that there are numbers stamped on the prop hub (1 thru 5), and marks on the white plastic core, to assist in setting the prop pitch. Mine settles on 4. If I take all of the play out in one direction, I can get to about 3.75. If I go the other direction, I can only get to about 4.25. I cannot even turn it far enough to get to the next stamped number, be it 3, or 5. Surely there is something wrong. I measured the slots in the back of the white plastic core. They are .500" I also measured the tabs on the plate that these engage with, and they are .450" That gives me just .050" play on the plastic core. Not near enough to effect any measurable prop pitch change. About all that is good for is to give you enough wiggle room to accurately match the two blades with each other. So, is it time to call Sensenich??

I can't believe this is correct!!............Tom
 
We have all been surprised at how little movement is allowed by the hub. I think you will find, however, that the seemingly small movement is enough to span the full range of performance for the 912 in the -12. Follow the instructions in the plans and PAP to adjust the prop. It is almost essential to use a protractor to get it accurate. There have been several good posts on how to make a protractor using a small digital level.

Keep the faith, Tom.

Tony
 
todehnal said:
I can't believe this is correct!!............Tom
Click to expand...
Yep, I thought the same thing. The best thing to do for now is just get them as close to even as possible and see what RPM you get when you run the engine. Also, I found that lightly "jiggling" the blades while applying the twisting force freed them up a bit. But it really is a very small range that you need - you're only adjusting within a band of a few hundred RPM out of 5,500 or so.
 
todehnal said:
Not near enough to effect any measurable prop pitch change.
I can't believe this is correct!!............Tom
Click to expand...

Tom,
Have you actually measured how much pitch change it provides?

There is nothing wrong with being a prove it to me type person ( I am often one myself). The proof is in the static RPM.
As has been written by many in this thread you started, adjust the prop for a full throttle ground run static RPM of 4950 -5000 (the adjustment range you have will allow you to do this) and go fly. It is highly likely that you will not change it after that, but if you do, there is a good chance you will be back here telling everyone how frustrating it is when trying to make a very small pitch adjustment (.1 - .2 degrees - NOTE: that's point 1, or point 2). The amount of pitch range you see is far more than you will use for getting proper adjustment.

Side note... Sensenich custom makes a special range limiter for the RV-12 props. Do you think they would supply them that way if it wouldn't work?
 
Building On

It just appeared to me, that .050" clearance over the limiter was way too small, and that it would be a lot easier to fix now, rather than later. I do qualify as a "prove it to me" sort of guy, and I am a bit away from actually running the engine. I have the last few sections of the builder's manual to complete first, but given all of the support that I have received, I will take heed, and as RVer's say, "build on". Thanks to everyone for all of your thoughts.

Tom
 
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I'd recommend setting the blades equal at the mid point of allowed movement and see what you get for static RPM. Until you do that you have no data to support your concerns. I think you'll be pleasantly surprised with the results.
 
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