Multiblade Scale head rotor phasing.

[Kiwi]

OK,

Here's a question I have not been able to find an answer to so far so I hope this is the place to go looking.

I will soon start machining my four blade rotor head to suit my Dragonus 450. Yes I can go and buy one but I don't want to as I would much rather learn more by manufacturing my own.

But here is my dilemma. Everyone tells me to fear multi blade heads because they have some serious side effects. Such as pitch changes in forward flight, they like to balloon and also roll. I can easily buy a heli mixer and two gyros to flatten that out but me being me ask why that is necessary as the real things don't use gyros and electronic mixing to achieve straight and level flight.

I sort of understand the principal of phasing on multi rotor heads. I think it has some relationship to gyroscopic effect and likely some others I don't know about. Now an electronic mixer can phase a rotor head to -45 degrees, 0 or +45. Depending on the rotation direction you set your mixer to the positive or negative setting. Conventional two blade Bell Hiller systems use 0.

OK back to me making my own multi blade head. Is that phasing achievable by offsetting the swash plate to blade grip linkage by 45 degrees. If the head rotates clockwise it would be +45. To achieve that all I need to do is drill the head Jesus bolt so it is 45 degrees more advanced than the swash plate and that will give me my phasing.

Am I on the right track here or am I totally out of the ball park. Guys this is a project and a learning experience for me so if you can help out please shoot first and ask questions later.

[CSpaced]

I wish I could offer an opinion, what I can say is that I can't wait to see the head you machine - post pics!

[DStJohn]

Kiwi,
Yes you are on the right track, you can do it by offsetting the blade grip linkages. Vario rotor heads can be offset by +/- 45 degrees by moving the anti-rotation pin on the swash (I can provide photos if you wish).
The biggest thing to be aware of is that the multiblade heads want to balloon in forward flight. I am flying the newer 2 blade bolt Vario multiblade heads (3 and 4 blade) and it does not have a real strong tendency, so I am able to mix it out in my 10X radio. It can be done without the Helitronix mixer and gyros, it just takes some work & experimentation, which if your making your own head, you are up to.

[Kiwi]

Dan,

Wow I was worried no one was going to get back to me on this one. Actually to machine a four blade rotor head is likely one of the easiest things to make. I have struggled on engine installations in gassers that are far more complex I think.

Ok I will get some photos as we go with this project as its one that has caught my imagination and I need to follow it through. What is the principal cause of the ballooning in forward flight. I have some very limited time in the real things and of course the brain and the bum are fantastic things to compute whats going on and thus do the mixing as the flying environment changes.

Its also interesting what you have to say about the two bolt blades having less of a ballooning effect so that makes me think the blades must lead and lag as they rotate into a non static airstream. That would be hell of a difficult to mix out as its airspeed related and nothing in any radio has the ability to changes mixes with speed.

Dan, can you post some pictures here of the Vario grips and the anti rotation pin. It would be very easy to make a totally adjustable swash plate so the phasing could be fine tuned.

But first off a glimpse of those two bolt grips to see whats up there and what can be done at home. I certainly do not intend to make my own grips. Thats way to complex at this stage of the game, not impossible of course but easier to buy them at this stage.