Static RPM should be 4870 to 4930?
 

Hi there,

I have a question about the static RPM at the Engine ground run. The WOT RPM should be 4870 to 4930. I am located at 3000 feet above sea level.
Is it the same RPM or higher and how much? Does anyone have experience with it?
Thanks a lot for feedback :)

Henry

I've always thought of 5100-5200 WOT as the target - that gives you good RPM in climb, and enough speed.

TODR

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!

Static RPM should be 4870 to 4930?
 

Thanks for the response,
I was not in the air until now, so I have to adjust the propeller pitch and RPM before my First Flight. I will try with 5100 - 5200.
Regards, Henry

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.

Since the note said he was looking for a value prior to first flight it seemed he was asking for static WOT.

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.

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.