Hi. Does anyone know where the designed center of lift or pressure is in level flight for the Mini Max? I know it's close to where your sitting. My Eros wants to oscillate in pitch when trimmed for level flight. I am constantly chasing the elevator in calm air. This is usually when the CG is too close to the center of lift. I'm in the flight envelope for my weight but a little to the rear at 27% so I'm thinking a little nose weight might help this. Has anybody else had this problem? Thanks Bill

The Gone Goose rubber powered model  showed this right on the drawing which I built as a teen and learned all the aerodynamics that need to be learned.It said if the goose stalls move the wing back and if it dives move it forwards.It was infact asking you to shift the position of centre of lift which also changes the CG which could be done on the goose.
with the max wing cant be moved but the cg can.looks like in this case cg/cp being too near are trading places.I wonder why the goose never mentioned tilting the wing or tail to adjust flight path but may be that was a complex excercise for fledgeling learners.
the goose drawings can be found on outerzone.co.uk.

Thanks. I found a old post that said the CP was 25%. If that is the case then my CG is behind the CP which accounts for (tail heavy, sensitive elevator) Team has said they fly best at 28 to 29%. That puts me out of the flight envelope for my weight. Every paper I've read said the CG needs to on or infront of CP. I'm retired and don't proclaim to have any aerodynamics knowledge except a little practical experience from flying RC models for 50 years and flying Team aircraft for 25 years and I've never had one that the nose hunts. I think moving my CG forward is my next step to see if it cures my oscillations. Bill

Interesting situation.

From the figures you mentioned, it looks like you are planning to move the cg forward by more than 2 % of chord, to get it ahead of CL.

Another point is about the Max design itself. If CL is at 25% chord, and acceptable CG location per flight manual is 21 to 30 % of chord, does that not mean the fore/aft location of CG relative to CL should not be that critical?  I don’t know the answer, just thinking out loud.

I guess the CL at 25 % is not a fixed location, and moves slightly fore and aft depending on the angle of attack ( moves forward at higher angles of attack/ lower speeds, and moves back at lower angles like in fast cruise.)

Also, 2 stroke rpm can keep wandering up and down marginally even at fixed throttle settings ( in my Kawasaki 340, rpm fluctuates by up to 200 either way at cruise setting of 5900-6000.) Wandering rpm can cause slight speed changes, in turn causing trim changes.

All of your points are excellent. I'm still not sure the CP is 25%. I read another paper that said the CP on small aircraft is 50% of the cord. I think this is in the design so i'm hoping someone will chime in on the Mini Max position.

The center of pressure changes with angle of attack. As angle of attack increases the cp moves forward.  Near the stall angle of attack the cp of the Minimax approaches about 31% chord.  At low angles of attack it moves aft.  At zero degrees the cp is at about 67%. At -2 degrees the cp is at 122%. At -4.4 degrees, the zero lift angle of attack, the cp is at infinity. The cp never moves into the designed cg range.  If it did the airplane wouldn't just wander, it would swap ends.

WOW I didn't realize the CP was at 67% at level flight. That explains a lot. Everything I have read has been wrong. Now i'm really confused about whats causing my oscillations. None of my other Team planes has done this. Thanks for your help Bob.

could thrustline be the culprit?As keith103 mentioned if the rpm fluctuates and an off thrustline has been balanced by elevator trim then theoretically the rpm fluctuation can cause imbalance in pitch.

Quoted from nitrobill

I didn't realize the CP was at 67% at level flight.

A level flight angle of attack is more like 6°, then the cp is at about 40% chord and the load is about evenly distributed between the front and rear spars.

Thanks for the help. Once I get trim set the RPM doesn't change until the pitch changes either up or down. I'm going to move the CG forward and that will take some of the sensitivity out of the elevator because 27% puts me right at the back of the flight envelope for my weight. Maybe that will tone it down a little. Thanks Bill