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  #1  
Old 05-04-2014, 06:07 AM
todehnal todehnal is offline
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
Posts: 980
Default Prop Pitch

I need to make another attempt at getting the right prop setting. The first setting netted me a 5200 static RPM. In my clumsy effort to make an adjustment, I lost my starting point and just had to take another swag at it. When I tested, I was 4950 static. Wow, I was excited. Admittedly, there was a little breeze during the run up, but I thought that I was good to go. The flight test later, revealed a much longer ground roll. Another static test, in a no wind condition, revealed that I am only getting 4750 static. No wonder I have such a long ground run. Lesson learned. I didn't realize just how much effect a little wind can have on that test. Anyway, my plan is to be very careful, not to loose the current position, and to only do a small tweak. In the interest of trying to simplify the process, I thought I would ask if anyone has plotted there corrections, and could give me a heads up. My goal is to get as near to 4950 as I can. So, what is your best guess for the amount of pitch correction necessary; .1, .2, or .3 degrees?

Thanks for your thoughts and for sharing your experience............Tom
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2013- RV12, Kit #119. N123M First flight Nov21. It's a keeper!
1998- RV-9 tail kit, built and sold
1989- RV-6 tail kit, built and sold
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  #2  
Old 05-04-2014, 06:47 AM
Peterk Peterk is offline
 
Join Date: Mar 2008
Location: Texas
Posts: 1,378
Default

Tom. Mine is at 4930. If you use the setting marks on the hub, mine is just shy of number 4...not exactly on it but just enough that it doesn't look exact. As you are finding out, a hair-width can make a difference. Perhaps as important though is what Scott has mentioned; make sure the two blades are set at the same pitch (within 1 tenth of a degree). If not, you can guarantee yourself vibration. Both blades move when you change one but there is still room for a difference. As Scott said, put a "smart level" on the same inside flat portion of both blades and make them match. Don't use the tips...line up with most inboard stripe for instance. Put in on the identical location of the 2nd blade.

Before you fine-tune it, tighten the two middle clamping bolts by hand and then the outside bolts in a "star" until just before the blades won't move. While they will still move, get them to match...and stay on your setting mark. Like I said, mine is just a hair before "4".

You want 4930 because you climb great and still have enough throttle in cruise to make changes. Not that you want to, but you should be able to push it to 5800 if desired. Cruise nicely at 5300/5350 around 115 knots TAS.

Pete
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  #3  
Old 05-04-2014, 08:54 AM
roger lee roger lee is offline
 
Join Date: Sep 2013
Location: Tucson, AZ
Posts: 322
Default

Hi Tom,

You need to forget about static. It should only be used to get in the ball park to do a flight test for the first flight. You are already there. With a ground adjustable prop your real concern is the wide open throttle (WOT) at your average cruise altitude. Average cruise is a little important because if you live in Florida and never fly over 2K the prop should be set different than the guy who lives in Colorado and takes off at 7K and is always at 10K.
Set your WOT rpm to achieve around 5600-5650 (even 5700 depending on your use and where yo live). This will give you the best overall performance between cruise, climb and fuel economy. We have to average these out since we can't in flight adjust. Too course and too little pitch just cost you performance. Too course is absolutely the worst scenario.
Tweaking the prop after the first flight is easy and I can tell you about how many degrees +/- if I know what the WOT rpm was during the flight. The other reason you can not go by static is props are not created equal and static for one is not the same for the other. Also some props static rpm does not correlate to the same WOT rpm as others due to design. 2 blade props many times may have different static than a 3 blade. I did a research project about 1.5 years ago with 9 different props (different air foils, lengths and # of blades). Static was different on some. I got to do all the setup and fly 4 exact same planes side by side for real time testing. There was 1-2 better props, but for 95% of them the deciding factor which made all fairly equal was WOT rpm.


Read this and it may help.

http://www.rotax-owner.com/rotax-blo...djustable-prop


If you have any questions please call me. I have reset well over a hundred LSA props and not a single person has ever gone back.

There is no perfect world, but flight characteristic balance is key.
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Tucson, AZ

Last edited by roger lee : 05-04-2014 at 12:39 PM.
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  #4  
Old 05-04-2014, 12:24 PM
RFSchaller RFSchaller is online now
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 3,165
Default

Also consider your climb performance. Out here in Phoenix the density altitude can be a real factor especially in the high country to the north. My static WOT RPM is little over 5000 which means my cruise suffers, but even in the summer I usually get 800 FPM on climb out in the valley
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  #5  
Old 05-04-2014, 03:10 PM
todehnal todehnal is offline
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
Posts: 980
Default Getting a Better Starting Point

You guys have been great. I went ahead and re-pitched today, and went .4 degrees flatter. I did that to have a better starting point for my top speed test. I know that I did not like the take off, and climb performance that I had on the last flight, plus all I could get was about 5400 flat out, which netted me right at 120 kts., as I recall. Although my temps were all in the green, I felt that the manifold pressure seemed awfully high at a 4900 to 5000 RPM cruise. Hopefully this adjustment has gotten me close. With that small adjustment, I like the way it statics, and sounds. I will know much more after my morning flight, in smooth air, tomorrow.

Tom
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2013- RV12, Kit #119. N123M First flight Nov21. It's a keeper!
1998- RV-9 tail kit, built and sold
1989- RV-6 tail kit, built and sold
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  #6  
Old 05-04-2014, 04:28 PM
roger lee roger lee is offline
 
Join Date: Sep 2013
Location: Tucson, AZ
Posts: 322
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With only 5400 rpm WOT you could have flattened the pitch by about .75 degrees
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Tucson, AZ
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  #7  
Old 05-04-2014, 08:30 PM
Dave12 Dave12 is offline
 
Join Date: Oct 2010
Location: Elkton, Md.
Posts: 1,745
Default

Check your pm's.
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Wag Aero Sport Trainer built,sold and wrecked
N588DF RV12 #336 built, sold and alive and well in New York
N73DF RV12 #244 built, sold and alive and well in Florida
N91 RV RV9 I wish I could say I built this one! Mark Santoleri hit the ball out of the park on this gem.
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  #8  
Old 05-05-2014, 07:41 AM
todehnal todehnal is offline
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
Posts: 980
Default I Like It!

Okay, here are my prop "post re-pitch" results. By the way, I am flying out of a field with an elevation of 400 ft. My flight this morning was in very nice weather, with light winds, 68 degrees, 61% humidity, and clear skies. The take off roll displayed very good performance. Climb out at 75 to 80 was indicating 5050 rpm, which gave me right at 1000 fpm climb, at just under 1100 lbs gross weight. At 5000 rpm, I was indicating 119 kts tas, and full throttle netted 5700 rpm, with some impressive speeds. Also, I must have lucked out in getting a very precise match with both blade settings, as it feels much smoother than after the last change. After the flight, I did a static run-up and it seems a little low, at about 4800, but as Roger Lee pointed put, the static numbers don't tell the whole story. Basically, I am pretty happy with what I have. It remains to be seen as to what it will be like at the full 1320 lbs.

Thanks for everyone's help...........Tom
__________________
2013- RV12, Kit #119. N123M First flight Nov21. It's a keeper!
1998- RV-9 tail kit, built and sold
1989- RV-6 tail kit, built and sold

Last edited by todehnal : 05-05-2014 at 07:44 AM.
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  #9  
Old 05-05-2014, 08:22 AM
roger lee roger lee is offline
 
Join Date: Sep 2013
Location: Tucson, AZ
Posts: 322
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Hi Tom,

Sounds like a good place to be and now you can get the best all around performance from your plane.
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Roger Lee
Tucson, AZ
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  #10  
Old 05-05-2014, 11:08 AM
todehnal todehnal is offline
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
Posts: 980
Default Another Milestone Reached

Roger, Thank you so much for your help. I'm ecstatic with the results!! ...........Tom
__________________
2013- RV12, Kit #119. N123M First flight Nov21. It's a keeper!
1998- RV-9 tail kit, built and sold
1989- RV-6 tail kit, built and sold
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