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prop pitch blade to blade comparison

seagull

Well Known Member
My prop is the 2 blade Sensenich. I have created a jig to measure the pitch on each prop blade in comparison to each other.
I am not really interested in total pitch, the RPM range is fine and I have a good climb and speed. What I was trying to find out is if the blades are creating the same thrust.

I have checked the pitch 4 times on each blade rotating the prop 1/2 turn then checking. Each time and the measurements were exactly the same.

My question; is this much difference worth chasing?

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For the smoothest operation possible, I strive for the exact same reading to the tenth of a degree but will accept up to .1 degree difference if that is where it is once all of the bolts are torqued.

This may seem like overkill but in reality, even if both blades read 71.0 degrees, there is still the possibility of them already being nearly .1 degree different.
Depending on the measuring tool being used, the actual values could be 70.06 and 70.15, with the tool indicating 70.1 for both because the actual value hasn't crossed the threshold point for the tool to indicate the next tenth increment.
 
As has been suggested before, get a digital 10 to 12" magnetic base digital torpedo level and the Prop pitch measurement jig tool from Van's to get it fairly accurate.

Adjusting your pitch once or twice, fine tuning it, will make the process seem more simple and routine.

Find a way to lift the tail under the eyelet with your wheels chocked to get a dead level measurement on your longeron with your digital torpedo level first.

The rest of the procedure is pretty easy.

I like to put a piece of tape with a very fine inked line where the split in the front and back prop hub meet, for a reference mark, before you loosen up the bolts and start adjusting.

I also write down and measure the pitch indicated by the gauge on both props, BEFORE I loosen the prop hub bolts up, for a reference.

For reference, only:

Another RV-12 user with a 2011 observes the following performance flying 1000 ft over the ocean with temps around 72F. He has his pitch setting for cruising at 8500 to 12500 ft, he's 90 # under max gross with wife in the plane.

At 90 kts climb speed, 5200 rpm
at 85 kts climb speed, 5150 rpm
at 75 kts climb speed, 5090 rpm

N836BL likes and prefers a fast climbing plane. His pitch is set at what Van's recommends, and with both of us being right at 1320 with 12-14 gals in the tank, he sees the following.

At 75 kts, 5150 rpm to 5170 or 80 at 1000 ft ASL on takeoff. Usually 60 to 75 degrees F and density altitude at 1300 to 1900, sometimes as high as 2700 on a hot humid low pressure day, with onshore fog that's burned off finally. We almost always see a minimum of 800 fpm climb rate, usually 900 fpm. He likes his plane to climb fast. At 5200 rpm and 5000 ft, it will easily cruise at 112- 115kts TAS, no problem.

My plane is still pitched too course, at 75 kts and 5020 rpm. I'd like to see at least 5150 to 5200 rpm at 75 kts climb and hopefully 900 fpm or a little better, near max 1320. My plane will pull 5600 to 5650 full throttle in level flight at 3000 ft elevation. Right at 120 kts TAS. ;-)

Good luck and let us know how it turns out.
 
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NinerBikes,
Thanks for your input you may have mis-read my question. The topic of whether to pitch for power or speed is one that has been thrashed on the forum and I don't want to go down that road.

My question was how much difference is tolerable.

Thanks for the input Scott,
I have a digital level from HF, maybe not accurate / repeatable enough for this task. I found using bubble levels I could "read" more error. Since I am not worried about the actual pitch number, the plane flies great, I will only nudge one blade. Ill look for a better digital level.
 
Find a way to lift the tail under the eyelet with your wheels chocked to get a dead level measurement on your longeron with your digital torpedo level first.

NinerBikes - Jacking up the tail cone so the longeron is level is totally unnecessary and will not make any difference in the final outcome.

The beauty of using a digital level as Van's has suggested is Van's has given us the suggested prop angle based on the longeron being the reference point. All that is necessary is to place the digital level on the longeron, zero the level while it is on the longeron and you are good to go.

Using the longeron as a zero reference point, will yield the exact same results no matter what the angle is of your hangar floor, your mechanics or your friends floor ... assuming one is vigilant in making sure the prop hub is horizontally level when the desired blade angle is being established.
 
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NinerBikes - Jacking up the tail cone so the longeron is level is totally unnecessary and will not make any difference in the final outcome.

A number of us have told him that, and the instructions in the KAI are very specific (and don't say to level the airplane).

But if it works for him......

For everyone else... The pitch value recommended in the KAI is in relation to the longeron.
So if you first zero your level with it sitting on the longeron (and properly positioned directly fore and aft, you can then use the digital tool to set the pitch of the blades. Regardless of what the pitch attitude of the airplane is (the tail cone could be vertical with the spinner point straight down at the ground, and it would still work).
 
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Use a level with a tripod mount

Ill look for a better digital level.

Seagull - If you decide to purchase another digital level, consider purchasing one that has a threaded hole in the bottom for a tripod mount. Mine has a 1/4-20 threaded hole on the bottom (probably because it also has a built in laser) that I use to secure the level to the Van's prop tool .... just drill a hole in TOOL-00002 and mount the tool onto the level. No need to worry about having good magnets on the level or accidentally bumping the level causing it to fall off the tool. Below are a couple of links to photos.
https://2.bp.blogspot.com/-omZdN-nmEQg/V284dCsbqWI/AAAAAAAAMCk/JeHNmBuSnOcN8hJpll6p2EI-QLG6eszxACLcB/s1600/DSC02077.JPG
https://3.bp.blogspot.com/-v016ecjY4n0/V284sMF_OLI/AAAAAAAAMCw/0CDVSAAEZ1otMO-Tl6a7o7rFNSR3tQTJACLcB/s1600/DSC02075.JPG
 
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