120 degree swash phasing

[ironcrosse]

So I was reading up on 90 degree swash phasing and how to establish it, and quite intriging it was, then I began wondering about the 120 degree setup, such as that on the Belt. How do you setup or ensure correct phasing on a 120 setup? And why even have a 120 design? Curiosity just got the best of me and I find it an interesting topic with more questions than answers.

[B2TheEYo]

By phasing, you mean "mirroring" your TX's controls mentally to control the model in other orientations, etc. - correct?

90 degree swash plates are for fixed pitch models. They don't change blade pitch, they just tilt the swashplate left/right/forwards/backwards to manipulate the flybars balance to in-effect give the model momentum to move in the desired direction.

120 degree swash plates operate the same way as a 90 degree swashplate, by tilting in the four directions to manipulate the flybars blance to generate directional-momentum. What we gain with the third servo is a balance (triangle) to support the primiter of the swashplate to allow it to be raised and lowered on the shaft to increase and lower blade pitch.

More or less look at a 90 degree swash plate, if you were to have both servos raise up at the same time to essentially duplicate increasing pitch on a 120 degree swashplate, what would happen? Because only two sides of the shape have support the unsupported remaining portion of the swashplate will lag behind and inevitably render the swashplate raising un-level, in addition while in fight the force being applied would amplify this problem. So in effect the third servo is just a "balance" to the issue.

The best way to study this is just get a swashplate and play with it on a uninstalled shaft.

[lankey]

Phasing/Timing/Advance.... something I don't know a vast amount about. I think it's all down to gyroscopic presession.

If for example, you put in an elevator command to perform a loop and you find that the aircraft is corkscrewing, this may be due to phasing. Basically it's the tendancy to give elevator when you input aileron or vise versa.

Some heads come with built in phasing. Some are mechanically adjustable. On non-adjustable heads, you can use p-mixes in your Tx to try and remove unwanted command reactions- for example aileron to elevator mixing.

If you have a stock belt cp with the stock radio, there's no way to adjust phasing.

I believe a 120 degree CCPM is a popular design choice due to it's simplicity over 90 degree?

[ironcrosse]

I was reading from a scale forum on multiblade and flybarless systems and cyclic gyros. Thats where i read they were using 90 degrees as theyre setup and was just curious as to why. Yes, gyroscopic precession and where the servo input is on the swash in relation to the flybar in the plane of rotation does determine overall flight movement, your correct on that. Does flybarless/multi blade really change things that much?

[lankey]

Well, as to why a 4 servo setup might be popular with the scale guys- god knows. As a rule of thumb, multiblade heads (being flybar abscent) usually run with a FBL stabilization system. Now, I have absolutely no experience with FBL systems- they'll take away mechanical complexity and replace it with electronic complexity.... within the system I suppose will be a phasing correction function, automatic or manual? Bottom line, you can tweak the hell out of it!

I'm sure someone more versed in FBL will chime in