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  #21  
Old 05-06-2014, 06:57 AM
f1rocket's Avatar
f1rocket f1rocket is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
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.
And that's exactly what happened to me yesterday. I spent many hours fiddling with the prop pitch only to find out that I had lost 10 knots at cruise and found it terribly easy to overspeed the engine. Today, I'll pull the spinner off multiple times until I can get the static RPM back down to the range of 4950.
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  #22  
Old 05-06-2014, 08:21 AM
roger lee roger lee is offline
 
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Location: Tucson, AZ
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Hi Scott,

"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."

I wasn't implying there are many different props on RV12's. I know for the most part they are all the same except for a small handful.

I was relaying for those that think one static rpm fits all isn't the case for all props. It was just an information and educational comment.
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  #23  
Old 05-06-2014, 11:51 AM
Peterk Peterk is offline
 
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Location: Texas
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I've been following Scott's guidance since I first flew my RV12 in '09. While he is not an official Van's RV12 advocate on here, he does work on their plane. He built it and rebuilt it and rebuilt it. He has always been very generous about passing on discoveries he makes about this aircraft when he runs across them.

Plus, he speaks his mind (don't we all!) when he's trying to be convincing. Regardless, I have been convinced over and over. He does know RV12's.
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  #24  
Old 05-06-2014, 04:33 PM
Dave12 Dave12 is offline
 
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Location: Elkton, Md.
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Quote:
Originally Posted by rvbuilder2002 View Post
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).
Scott hit nail on the head with this one. I find that .3 of a degree change in the Spring and Fall works well to maintain my static setting.
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  #25  
Old 05-07-2014, 12:03 AM
roger lee roger lee is offline
 
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If your prop pitch is set to achieve 5600-5700 then I wouldn't think messing with the prop each season would be necessary. .3 degree change should only be about 75 rpm +/-. Changing the pitch .3 degrees for the denser winter air may shouldn't be necessary because the plane and prop air foil is already benefiting from the cooler air.
I don't personally know of any one that changes that often. If you do that then bolt and nut replacement due from all that torquing and bolt stretch from going back and forth would be warranted.
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Last edited by roger lee : 05-07-2014 at 12:06 AM.
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  #26  
Old 05-07-2014, 11:17 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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There is no operational requirement to change propeller pitch with the change of seasons, and for many owners it probably isn't of much value. For others it can be of value if the summer density altitudes are extremely different from winter and they are looking for the ultimate overall performance (within the compromises that we have to make with a fixed pitch propeller).

The Sensenich propeller used on most RV-12's does not have any replaceable nuts (they are steel inserts pressed into the aft half of the propeller hub)for the bolts loosened when repitching the propeller, so replacing nuts is not an issue.

Replacement of the bolts would only need to be done on condition (damaged threads, etc.). Replacement just because they have been removed installed multiple time is in contrary with the Sensenich 2A0 Installation Manual and AC43.13.
In fact The Sensenich Manual specifies to full disassemble the propeller at each condition inspection (this would require removal of the bolts in question) but makes no mention of replacing the bolts after a specific interval.

If an owners does make a pitch adjustment a couple times per year, the only thing that might need replacement sooner would be the nordlock washers, and even that is on an on-condition basis.
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  #27  
Old 05-07-2014, 12:57 PM
roger lee roger lee is offline
 
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Nord washers are replacement items after a while (1-2 times no big deal, same for the bolts). Bolts that get torqued get stretched and if done more than a few times should be measured as per the Sensenich instructions and at the annual. That was confirmed by calling Sensenich. They are supposed to be automatically replaced at 2000 TBO. Personally I see no reason to remove bolts at an annual just to remove them. Sensenich says to measure all bolts and any that have stretched to be tossed. Torquing stretches bolts just some are more resistant than others. You can actually measure a new bolt with one that has gone though several torque cycles and it will be longer. Many bolts have stretch limits from an MFG especially in services with heating and cooling cycles and high vibration areas. The bolt torqued a few times is longer and there are guide lines for bolts under stress and torque cycles to get replaced. Each bolt has its own characteristics. Some stretch easier than others depending on service and its metal make-up.
Most prop Mfg's don't figure people for many duty cycles on bolts, washers and nuts.

These bolts are expensive so if you measure them and they have stretched then replacement is easy and finding them is usually a local event.

"Replacement of the bolts would only need to be done on condition (damaged threads, etc.)"
The excreta is your supposed to replace them if stretched which is determined by measuring and comparing to the others.

This came right from Sensenich.
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  #28  
Old 05-07-2014, 01:31 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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What the Sensenich documentation actually says -
"Remove the mounting bolts -- The bolts should be dimensionally checked against one another. Any bolts that exhibit stretching, corrosion or damage such as cracks or nicks are to be replaced."

It is not possible to measure the bolts individually for stretch because they are standard AN bolts (not close tolerance). Because of this, the lengths when new can very by quite a bit between one bolt and another (the length tolerance is pretty large on standard AN bolts). The only way they could be measured for stretch is if the were serialized and measurements recorded during the original installation.

In the past few weeks, we have been working extensively with Sensenich regarding the new version of the prop. hub they are now shipping. We have gone through many blade install / removal, and repitch processes... they have not sent replacements, nor suggested that the bolts be replaced...
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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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  #29  
Old 05-07-2014, 05:05 PM
roger lee roger lee is offline
 
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I have a Sensenich and it has no AN hardware on the prop or hub. They are allen head hardened bolts on the prop and hex head on the hub. You may be switching over to what I have now. Most of the Sensenich props I have seen in the shop on different LSA don't have AN hardware. I believe this may be a little older setup. Bolts don't need replacement every time, but if done repeatedly they should. I talked to Sensenich this afternoon and they agreeded that bolts need to be checked for stretch and replaced IF necessary. I did a big research project for them and when I was done my bolts needed replacing, but they had been torqued way more times than on any normal prop & plane.
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Last edited by roger lee : 05-07-2014 at 05:08 PM.
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  #30  
Old 05-07-2014, 05:17 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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We have sold nearly 400 of these props in the last few years and every one of them has been supplied from Sensenich with AN bolts.

I just worked with Sensenich testing the latest version (that uses the steel indexing pin tools to establish the prop. pitch), and that prop, along with the half dozen they just shipped to us for customer delivery, also have AN bolts.
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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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