Wishing that all of you are safe and healthy.

Since my daughter is home now for the time being, she has suddenly shown an interest in control line flying. She picked Bill Osbornes Platter. Below is the picture of of what she has built and arranged the electrics with masking tape so it can be moved around neatly later. the question we both (both novice) have is where is the CG located as measured from the fire wall or from the bell crank pivot screw?

The control rod is exactly 8 inches long and the the lead out center 8 inches from the bottom as shown in the PDF. We decided to go with the 1.5 inch nose extension for beginners.

We have enough backyard space to maiden.

Thanks in advance for your input.



 

Thank you Dave.

So it looks like about half an inch ahead of the bellcrank front leadout, or about three inches from engine firewall? knowing it is a beginners learner plane, is the airplane that sensitive to CG?

Thank you Tim. Will follow your guide line .

Hence my question, is the CG at 3 inches from the engine mount? The drawing is not to scale. So is it 2.5 or 3.0 or 3.25 inches from the fire wall? Many here as seen in the search have enjoyed this plane. What I am looking for is to confirm the distance of CG from the firewall from their experience

Thank you all for your quick responses. Looks like the maiden will be perhaps tomorrow as they predict low winds.

Dave, thank you for going through the extra effort to confirm the CG). So went flying with the Platter balanced at 3 inches from the motor mount. Tim, we experinced your recommendation regarding the CG sensitivity, half inch is too much.

So here is what we experienced.  The Platter went straight up into a hover (reminding me of my 3D RC flying) . It was not leaning forward or to its back. Straight up. So we placed the battery at 2.5 CG that I had already marked. Now it went to a direct dive.  CG sensitive.

Thinking out loud (please help us think it through..), I think the CG at 3 inch behind the motor mount as you drew it is absolutely correct.

Next, trying to assure that the Platter is not so sensitive. The control rod is in the closest hole next to the pivot screw on the bell crank, the stab horn it is in the outer most hole away from stab, the line at the handle is about 2.5  inches apart. The stab deflection is 10 degrees up or down.  The bell crank is 2 inches wide, not the small one. I do think these are least sensitive positions that I can get.(?) The controls are free, no binding or hesitation.

The ready to fly Platter, weight is 5.8 ounces. The motor is Arrowing 2205- 22 that calls for a 7 by 5 prop or larger on 800mah, 30 C 2S battery. Moreover I have the motor set at zero , no down thrust, just a bit of right thrust with washers. We also tried at 3 inches CG and a smaller prop of 6 by 4 on the 2S battery but not enough punch to sustain flight.

At this time my gut feeling is to put a Cox Blackwidow with 6 by 3 prop and prove all is correct  and called for in the original design. However the school baseball field is very close to our housing development (our flying field is shut down) and these days all are home. Too much noise to even loose the baseball field too. 

So we are stuck with this motor, 2S battery and a 7 by 5 prop. Next will try, putting a single washers on the upper bolts to get a downthrust and try it at CG of 3 inches behind the motor mount. Option three, install a slower motor with a 6 by 3 prop.

Appreciate any other thoughts and recommendations. Thanks again.

Dave, we launch by hand. just straight out, just a bit nose up.  We make sure we feel the line tension and throw it tangent to the circle to maintain line pull.  Saw the youtube video several times to see how Mr. Bill launches before the maiden and try to replicate the process.
Is there a way to ROG?

Sports,

I have not flown an Osborne Platter, so everything I might suggest is simply a guess. However, if we set aside the uniqueness of the round wing and compare it to, let's say an OrangeCrate entry, which do not have the most optimal aerodynamic shapes or weights, a very neutral  elevator is needed and more of a level launch. I think the reason is that they don't attain flying speed instantly. The prop wash alone is not enough to generate adequate lift. Launching upward prevents it from gaining airspeed before it falls out of the sky. So while it seems wrong, starting level, and letting it settle while gaining speed seemed to be the winning combination. Cranking in up elevator to keep it off the ground only works if the thrust to weight ratio is well over one. Which I would expect to be the case with a Cox-powered platter, but perhaps not with yours? I'm thinking that your battery setup and roundwing would mean this same technique might be how to get through the first critical seconds and gain that flying speed.

I assume you have some type of flex attachment of the prop so that you can survive a few impacts?

Wishing you the best luck,

The Divot

PS--As to the ROG, if you could launch from the edge of a paved surface or use some carpet or cardboard overtop the grass that might work, too. Can you make a wheeled dolly like would be used on a speed plane? It would best be made using some wire and soldered together.

Sports,

That's waaay cool that you got it working. Awesome!

It might also be the perfect plane to learn to fly inverted with, too.

The Divot