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Static RPM should be 4870 to 4930?
- Thread starter heiri_ch
- Start date
the_other_dougreeves
Well Known Member
I've always thought of 5100-5200 WOT as the target - that gives you good RPM in climb, and enough speed.
TODR
TODR
Jetguy
Well Known Member
Trailer & Error
Because you are at 3000 feet think about moving toward a Higher rpm for better climb performance.
Currently how does you plane climb now? If its ok stick with what you have. Think of it this way.
Better climb equals higher rpm on the ground. Faster top end cruise speed equals lower rpm on the ground.
However there is a limit to how low you can go on the ground and you are there at 4870.
Any lower and you will hurt your engine!
Because you are at 3000 feet think about moving toward a Higher rpm for better climb performance.
Currently how does you plane climb now? If its ok stick with what you have. Think of it this way.
Better climb equals higher rpm on the ground. Faster top end cruise speed equals lower rpm on the ground.
However there is a limit to how low you can go on the ground and you are there at 4870.
Any lower and you will hurt your engine!
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RFSchaller
Well Known Member
I agree the sweet spot for mine is about 5100. It's a good place to start anyway.
Don't get confused between WOT static rpm on the ground, and WOT in level flight.
Setting for 5100-5200 RPM, WOT in level flight will have you way over pitched in my opinion. Setting for 5100-5200 WOT on the ground will have you way under pitched.
Most RV-12 owners have found that setting up for about 4950 WOT static on the ground, gives good overall performance.
This will give you very good take-off performance and good cruise performance through a wide range of altitudes.
The wide range cruise performance comes because you will have a prop pitch that will require you to throttle back some in level flight at lower altitudes, but, you have more throttle to use as you climb, thus maintaining good cruise #'s.
Now if you want an airplane that operates more like the Piper or Cessna you have always flown, where the only way to over speed the engine was to point the nose straight down, then use a lower static RPM.
It will give you real good cruise #'s at lower altitudes (you will likely exceed the 120 Kt LSA speed limit).
The down side is that you will have poorer climb performance, poorer cruise performance if you ever cruise up high, the oil temps will tend to be higher, and you will be lugging the engine more in climb (Rotax specifies a minimum of 5200 RPM during high power operation (full throttle / high manifold pressure). That really isn't possible with most LSA because of the compromise induced by a fixed pitch prop, but using a static RPM of about 4950 gets us very close (climb RPM of 5100-5150).
Keep in mind that while the engine is breaking in, all of the RPMs will climb a bit (particularly the idle speed), so setting for a slightly lower RPM (50 or so) is not a bad idea.
Also keep in mind we are talking about very small pitch changes on the prop.
The difference between over pitched and under pitched is less than 2.0 degrees. When fine tuning, I am making changes of only about .2 degrees.
Setting for 5100-5200 RPM, WOT in level flight will have you way over pitched in my opinion. Setting for 5100-5200 WOT on the ground will have you way under pitched.
Most RV-12 owners have found that setting up for about 4950 WOT static on the ground, gives good overall performance.
This will give you very good take-off performance and good cruise performance through a wide range of altitudes.
The wide range cruise performance comes because you will have a prop pitch that will require you to throttle back some in level flight at lower altitudes, but, you have more throttle to use as you climb, thus maintaining good cruise #'s.
Now if you want an airplane that operates more like the Piper or Cessna you have always flown, where the only way to over speed the engine was to point the nose straight down, then use a lower static RPM.
It will give you real good cruise #'s at lower altitudes (you will likely exceed the 120 Kt LSA speed limit).
The down side is that you will have poorer climb performance, poorer cruise performance if you ever cruise up high, the oil temps will tend to be higher, and you will be lugging the engine more in climb (Rotax specifies a minimum of 5200 RPM during high power operation (full throttle / high manifold pressure). That really isn't possible with most LSA because of the compromise induced by a fixed pitch prop, but using a static RPM of about 4950 gets us very close (climb RPM of 5100-5150).
Keep in mind that while the engine is breaking in, all of the RPMs will climb a bit (particularly the idle speed), so setting for a slightly lower RPM (50 or so) is not a bad idea.
Also keep in mind we are talking about very small pitch changes on the prop.
The difference between over pitched and under pitched is less than 2.0 degrees. When fine tuning, I am making changes of only about .2 degrees.
RFSchaller
Well Known Member
Since the note said he was looking for a value prior to first flight it seemed he was asking for static WOT.
MartySantic
Well Known Member
Agree with Scott. Prior to the first flight, 4950 rpm is a perfect start value for WOT static on the ground. Mine eventually ended up near 5000 rpm.
RFSchaller
Well Known Member
We're talking about 1-2% in RPM in our recommendations. I wonder what instrument accuracy is not to mention effects of density altitude between data points. Naval aviators used to put a lot of stock in TLAR (That Looks About Right). This is probably a good example of that concept! 
Actually the difference between 5200 and 4950 is about 5%.
It may not seem like much , but it makes a big difference.
I have set up the prop on about a half dozen RV-12's.
I have found that .2 - .3 degrees pitch change will produce a very measurable RPM and performance change.
It may not seem like much , but it makes a big difference.
I have set up the prop on about a half dozen RV-12's.
I have found that .2 - .3 degrees pitch change will produce a very measurable RPM and performance change.
RFSchaller
Well Known Member
It's an iterative process so arguing about the initial static RPM is a little like two freshman engineering students arguing about the value of Pi.
I don't see it as arguing, just trying to make a point (for everyone else I guess) that RV-12s are different from other models.
The big difference is that most of them are exactly alike.
I have used the pitch measurement taken from one RV-12, to adjust the prop pitch on another RV-12 and get nearly the exact same performance results... repeatedly.
So, speaking specifics is of value.
For others that prefer the TLAR approach, they are of course welcome to use that.
MartySantic
Well Known Member
Disagree.....the WOT throttle RPM is important so one does not exceed the 5800 Max during the first flight. The Dynon is quite accurate as it counts pulses (is a digital instrument) and is NOT an analog instrument where there may some variation.
Did you work at Palo Verde? Send me a PM.
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RFSchaller
Well Known Member
The point I as trying to make is that the first WOT static RPM value is just a starting point, and as long as it's somewhere near 5000 RPM it will suffice as a starting point to be tweaked in.
I agree with Scott that it is very sensitive to pitch, so very small adjustments are needed during the zeroing in process. I do think there is value in sharing our individual experience, on best RPM and to some extent it will be a matter of preference: climb or cruise performance.
Rich
I agree with Scott that it is very sensitive to pitch, so very small adjustments are needed during the zeroing in process. I do think there is value in sharing our individual experience, on best RPM and to some extent it will be a matter of preference: climb or cruise performance.
Rich
ScottSchmidt
Well Known Member
Still tweaking
I am still tweaking but have settled for a little while. Like Scott and others have said it is very sensitive. I have done exactly the .2 degree changes on each adjustment.
I am located at 4230 ft. with density altitudes much higher during the summer. I have a static RPM around 4950 - 5000 and in the summer I do not get above 5100 RPM's during the climb but have a great cruise. Full throttle will get me over 5500 but never to 5800 in level flight, usually run around 5300 and get about 114-116 kts TAS. In the cooler days it is right at 5200 on climb.
I think I would like .1-.2 degrees less pitch so we get 5200 RPM's on climb out on a 85 deg. day. We have never been to lower altitudes so I don't know how my settings would work.
I had mine set towards the bottom of the window for the first flight and the RPM was way too low on climb out. With one person it is no problem but I quickly adjusted it.
I would set it at the top of the window 4950 +- 25. You can adjust from there.
I am still tweaking but have settled for a little while. Like Scott and others have said it is very sensitive. I have done exactly the .2 degree changes on each adjustment.
I am located at 4230 ft. with density altitudes much higher during the summer. I have a static RPM around 4950 - 5000 and in the summer I do not get above 5100 RPM's during the climb but have a great cruise. Full throttle will get me over 5500 but never to 5800 in level flight, usually run around 5300 and get about 114-116 kts TAS. In the cooler days it is right at 5200 on climb.
I think I would like .1-.2 degrees less pitch so we get 5200 RPM's on climb out on a 85 deg. day. We have never been to lower altitudes so I don't know how my settings would work.
I had mine set towards the bottom of the window for the first flight and the RPM was way too low on climb out. With one person it is no problem but I quickly adjusted it.
I would set it at the top of the window 4950 +- 25. You can adjust from there.
This is entirely possible because engine power output is a factor of density altitude.
The airport altitudes are different, but if there were different barometric pressures, and outside air temps at the different airports when the checks were made, it is entirely possible to end up with static RPM's the same.
Your experience is a perfect demonstration of the compromise induced by a fixed pitch prop, and why one person will prefer one pitch setting (based on the ground elevation of the airports they are using the most) and another person will prefer something slightly different.
RFSchaller
Well Known Member
Scott Schmidt,
Your numbers are almost identical to mine. My suggestion is stick with whatever meets your typical flying and treat the suggested range as a starting point. It's why they are licensed EXPERIMENTAL.
Rich
Your numbers are almost identical to mine. My suggestion is stick with whatever meets your typical flying and treat the suggested range as a starting point. It's why they are licensed EXPERIMENTAL.
Rich
