dubs1946

3W 85XI.
There are not many posts about this engine, so i thought i would post some prop and rev. information with various props. that i tested today.
I am no great needle tweaker but just know the basics.
My engine has a tick over of about 1700-1800 rpm with good transition.
It is in a TA 152 100 inch 48Lb, i have run it for about 3 hours so i guess it not at its peak yet i run 40-1 synthetic oil. All the Props are carbon fiber, and its fitted with a rear Pitts style muffler.
With a Biela 26X10 5600 RPM this is quite a wide prop.
With a PT 26X10 6100 RPM
With a PT 26X12 5550 RPM
With a PT 27X10 5250 RPM

rcairflr

My Feedback: (44)

Your numbers seems very low. Not turning this into a brand war, but only posting this for reference only. My DA-85 turned the PT 26x10 at 6700RPM

dubs1946

Yes i thought it was low to but i don,t think i have leaned it out top end yet, today was the first real go at getting some figs.with different props but its good to know that your DA is turning 6700 with the same PT prop so i have some sought of comparison to go by.
How many hours has your engine run?what oil and what muffler?

Tired Old Man

My Feedback: (1)

The rpm counts is something many don't understand where most 3w engines are concerned. Even perfectly tuned a 3w will not usually have the same high rpm counts as some other engines. There are a couple of other engine manufacturers that experience similar situations.

However, though having a lower rpm count many engines have the ability to perform a lot more work than an engine providing higher rpm with the same prop. It's called torque. The high rpm engine can do it's work quickly up to a certain point but from there falls off quickly as well. The lower rpm engine (assuming it's propped correctly to remain inside it's best torque band) will do more work than the higher rpm engine. The better low rpm engines will continue pulling the same or more weight for considerably longer and not bog down in the process.

I've been telling people for years that using rpm counts to determine performance will often leave people selecting the wrong engine for their needs. The 3w 85 will out pull a DA 85 on even it's worst day. A 3w 140 is as strong or stronger than a DA 150. The 3w 110 is another engine that's seriously overlooked in favor of some other engines. MVVS is another brand that may not turn the highest rpm counts but they can handle more weight for longer periods than many other engines.

juanes1969

Dubs; I have the 3W-85 and your number are very, very low. Here are some number I got with mine. The engine has about 10 gallons thru it, running red line racing oil at 40:1
PT 27x8 = 7050 rpms
Mejzlik 27x10 Thin = 6900 rpms
Mejzlik 26x10 = 7250 rpms (too little prop)
Mejzlik 27x10 = 6800 rpms
Mejzlik 28x10 = 6200 rpms

The engine has been in two planes and I have writen all results with the different props to see what was that I needed for each aplication. This engine is a beast and very smooth.
Hope this helps,

John

T.O.M. sorry I didn´t see your post before posting, I did install the bigger props (27x10) because the plane performed a lot better with it. The other smaller props produced a lot of noise and in a 30 pound plane the lower rpms pulled it with more authority.

Tired Old Man

My Feedback: (1)

The one place where higher rpm counts are most useful are in determining speed. More rpm will generally produce more speed (not necessarily perform more "work"), but the values have to be determined in level flight. The reason for this comes from the pitch. A high pitched prop will not produce high rpm in a climb but if given the opportunity to achieve level flight unloading will generate relatively high rpm and move forward farther with each revolution. So a 14 pitch might turn the same rpm as a 10 pitch but the 14 would go faster.

Back to "static" rpm counts. They are of little real value since all propeller blades stall at a given point. To correctly grade a propeller and it's rpm capability requires the use of a wind tunnel. Grading propellers and engines gets real complicated, very quickly. Unfortunately rpm is not an accurate method of grading an engine.

dubs1946

I agree with T.O.M. on keeping an engine "inside it's best torque band" what i am trying to find out is what is the 3W85 best torque band, and also trying to find if i am within the ball park for the PT props i am using and it looks like i need to go on tweaking the needles.
I don't know if you can compare Mejzlik with PT props.

Tired Old Man

My Feedback: (1)

They are quite different in their performance. Neither has the best blade chord and design for what people need for sport or performance flying. The Mejzlik provides higher than average rpm numbers by letting an engine "unload" a bit more but fails to deliver more performance for the additional rpm. The PT is a fair to average prop with thrust and rpm change response.

pilot43

My Feedback: (3)

I am its engine until can adjust.

pilot43

My Feedback: (3)

On Your Engine what muffler is installed?