Static RPM

[JohnF]

I think my guess was correct as to why I saw a reduction in rpm after a certain amount of throttle was input; the prop was overpitched and at the upper limit of the engine's ability to keep things spinning it just reduced rpm due to overloading the engine...anyway that is the way I see it.

I started over this morning..put the prop at finest pitch, ran it, keep reducing the pitch in small increments, and checking it. I finally settled on 5,100 rpm at max because I fly from a 7,500-ft airport, and density altitudes are typically 8 to 9 thousand and I feel a bit better starting out with what amounts to a 'climb' setting. I can refine it was I gain experience with this setting.

[RFSchaller]

I always use a digital tach when I first set up a prop and a new engine. They are cheap at Aircraft Spruce (about $50). Just don't forget to take the gearbox reduction into account.

[Stan Bahrns]

My max static is around 4135 rpm & mine acts the same I checked my blade angle with a prop protractor & the blades are pitched at 24 degrees. I am wondering if anyone has the ideal pitch angle in degrees. I think if I had the right degrees it might save me a lot of time. I would like to try thae degree method first if one of you could give me a starting degree.
Thanks in advance

RV12 waiting for the inspector
RV-7A 350 hrs

[MartySantic]

Because there are so many variables when taking the pitch measurement, supplying an angle is impossible. Hope you are using a digital level and not the plastic dial type prop protractor which is useless.

Use one of the mounts as shown in a number of previous posts for your digital level. Ensure the blade is parallel to the ground. Use a stick or piece of PVC, and put a mark on it to ensure when you rotate the blade, the opposite blade tip is the same distance from the ground. Place the digital level on the blade. Find the midpoint by rotating the blade pitch from stop to stop (max pitch to min pitch). Rotate the prop half a revolution and place the digital level in the same exact position on the opposite blade. Ensure each is pitched the same.

The midpoint is a good starting point. From there make tiny adjustments to both blades (0.2 deg) until you get a static RPM of 4950-5000.

[roger lee]

Here is an article I wrote a while back on ground adjustable props. It is on the Rotax website.

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

Marty is right. 4135 static is too low. I have tested many props 2&3 blade and the pitch angles all vary and even the static rpms. Set it up around 4850 +/- static at WOT on the ground. Static is for nothing more than to get you in the ballpark so using a specific angle from one plane to another is no better. The aircraft then needs to fly to get your prop fine tuned for your specific flying. Once you set the static go fly. Go to your average altitude and go WOT for 30-45 seconds. A fairly good WOT rpm is around 5600-5650. This can vary some depending on your own personal needs in the flight performance envelope.

[BigJohn]

Stan,
Do exactly as Marty and Roger suggest. Make miniscual changes between test runs. Use the digital level as a guide, but do not try to use it to obtain a specific angle. When you get close to the static RPM you are looking for, use the level to get the two blades as close to the same angle as possible, for smoothest operation.

One more tip. After you have the prop set up the way you want it, get a dynamic balance done. On my plane this made a huge difference in vibration level.

Let us know how it goes.

John

[roger lee]

Hi Stan,

Once you test fly it and get an rpm and if you let me know what it is I can give you a pretty good estimate of how may degrees to subtract to flatten the pitch and you may only have to make one adjustment. I have reset well over a hundred LSA and experimental prop pitch setups in the last few years mainly from MFG's because they tend to over pitch the prop and end up with a loss of over all performance and over stresses the engine. These guys with engines of June 2006 or earlier that have max WOT rpms less than 5500
(i.e. 5000-5300) are looking the crack cases. That's one of the reasons for that service bulletin years ago and why those cases can't qualify for the 2000 TBO. Over pitching can and does cause harm. The newer cases are a little stronger due to a design change. If one of the older cases crack it is usually right on top about mid engine just off the center line. Oil doesn't gush out, but does seep or ooze out.

If you need any help just give me a call. The RV12 is a really good performer with the proper rpm.

[AirHound]

Originally Posted by roger lee

Hi Stan,

Once you test fly it and get an rpm and if you let me know what it is I can give you a pretty good estimate of how may degrees to subtract to flatten the pitch and you may only have to make one adjustment. I have reset well over a hundred LSA and experimental prop pitch setups in the last few years mainly from MFG's because they tend to over pitch the prop and end up with a loss of over all performance and over stresses the engine. These guys with engines of June 2006 or earlier that have max WOT rpms less than 5500
(i.e. 5000-5300) are looking the crack cases. That's one of the reasons for that service bulletin years ago and why those cases can't qualify for the 2000 TBO. Over pitching can and does cause harm. The newer cases are a little stronger due to a design change. If one of the older cases crack it is usually right on top about mid engine just off the center line. Oil doesn't gush out, but does seep or ooze out.

If you need any help just give me a call. The RV12 is a really good performer with the proper rpm.

Roger for technique adjusting prop angle, can one use two 1x4? sticks taped together on the front and back of a blade to make those small prop angle changes easier/smoother with a little leverage?

Best,
Doug in IL
Former CTSW owner

[waterboy2110]

Originally Posted by roger lee

Hi Stan,

Once you test fly it and get an rpm and if you let me know what it is I can give you a pretty good estimate of how may degrees to subtract to flatten the pitch and you may only have to make one adjustment. I have reset well over a hundred LSA and experimental prop pitch setups in the last few years mainly from MFG's because they tend to over pitch the prop and end up with a loss of over all performance and over stresses the engine. These guys with engines of June 2006 or earlier that have max WOT rpms less than 5500
(i.e. 5000-5300) are looking the crack cases. That's one of the reasons for that service bulletin years ago and why those cases can't qualify for the 2000 TBO. Over pitching can and does cause harm. The newer cases are a little stronger due to a design change. If one of the older cases crack it is usually right on top about mid engine just off the center line. Oil doesn't gush out, but does seep or ooze out.

If you need any help just give me a call. The RV12 is a really good performer with the proper rpm.

I agree with Roger that many are over pitching their prop - Vans is no exception. There have been posts from the Vans folks in this forum that make the claim that the recommended pitch for the 12 won't harm the engine which is incorrect. WOT level flight of 5650 is optimum and SL912-016 describes the types of environments that can lead to engine failure. The 12 suffers from several precursors. Rotax developed these parameters from experience.

[AirHound]

Originally Posted by waterboy2110

I agree with Roger that many are over pitching their prop - Vans is no exception. There have been posts from the Vans folks in this forum that make the claim that the recommended pitch for the 12 won't harm the engine which is incorrect. WOT level flight of 5650 is optimum and SL912-016 describes the types of environments that can lead to engine failure. The 12 suffers from several precursors. Rotax developed these parameters from experience.

Sorry for sounding simple here. As an overthinker/underdoer, I find it real difficult to smoothly and consistently obtain the VANS desired prop pitch setting just by loosening bolts and hand twisting blades . My idea to gain leverage is to loosen bolts juuuust enough to barely move blades, then retighten/snug-up/torque bolts without effecting the desired blade angle......seems a little leverage is called for to achieve satisfactory results on a consistent basis. I haven't checked my own idea (tape a lever to the blade to more precisely adjust it within specs/tolerances). Just wanted to see what tips or tricks others in the forum may have learned to achieve best results....Any thoughts out there???