Gyroscopic rotor precession

[_Icarus]

Everywhere I've read on the subject, it says that helicopter rotors undergo maximum tilt 90 degrees after they are given maximum pitch.

I recently purchased an Esky Lama v4 and as I was examining it, I noticed that the swashplate and linkages are arranged so that the rotor is given maximum lift 135 degrees, rather than 90 degrees, before it achieves maximum tilt.

This is consistent this the top rotor setup where the stabilizer bar is mounted at a 45 degree angle to the rotor. Most model helicopter pictures that I've seen show the flybar mounted at 90 degrees to the rotor.

What would be the conditions in the Lama's design that would require this special arrangement?
Is it unique to the design of that model or is it something that is found in other models as well?

[HX3D014]

it is only for the top Uncontrolled Blade.
it gets its input or Stability Hold 45 Deg before (not 90 or 135)
the reason is because it is uncontrolled (The fly bar that is) and so, if the fly bar gets a nudge to tilt. it gets the reaction 90 deg later.

lets say we nudge/tilt the heli forward. the fly bar will now want to tilt right.
Same goes for the Uncontrolled Blade. so the balance between the two is usually 45. this is also only when the fly bar reaches max tilt. usually it dose not want to tilt. thus correcting the tilt via its input to the blades telling it to follow. Why 45. because it has to be uncontrolled.

the blades Center of pressure change works against the Fly bar. so as the blades CP moves forward. it wants to push the fly bar back.

Post a Picture of the Linkage system for both the upper and lower blades.

A real heli rotor tail has a Hinge system called Delta3 (http://www.google.com/patents?id=2zsNAAAAEBAJ&printsec=abstract&zoom=4&dq=delta-3+hinge#PPA3,M1). it is a system that keeps the dissymmetry of thrust caused by the advancing blade over the retreating blade at bay. it is more or less a hinge system near 45deg to the Feather axis.

I am a little green in this area. and would like a full explanation. or to find out more with you.

90deg Phase lag/Gyroscopic precision is only changed by one thing. that thing is not present on any CX helicopters I have seen(that thing/Condition is To complicated and Controversial to post here in this thread just now)

[_Icarus]

I'm glad to see that I am not the only one who is curious about this apparent violation of the laws of physiscs.
Seriously though I'm sure there is a rational explanation.

Here are the pictures. My camera is not very good and I had a hard time getting adequate focus & brightness. That's the best I could do.

Upper rotor
44029

lets say we nudge/tilt the heli forward. the fly bar will now want to tilt right
Actually when I hold up the heli with the rotors spinning and I nudge/tilt it forward, the stab wants to stay in the same rotation plane and hence finds itself tilted backwards with respect to the mast. Now in that condition, the blade which is 45 degree away from the front is the one that gets max pitch. Since this is designed to negate the forward tilt of the heli it follows that the upper rotor must be getting max lift 45 deg after it gets max pitch. (Apparent violation #1)

Lower rotor taken from the back of the heli.
The left horn controls pitch and the right horn controls roll.
It is important to note that there is no servo mixing, each one acts alone.
44028

I also posted a sketch of the swashplate arrangement earlier here:
http://www.wattflyer.com/forums/showpost.php?p=284891&postcount=17
(Apparent violation #2)

I looked at pictures of other coax models on the web and all those that are equipped with the same type of cambered blades seem to have the same upper rotor arrangement. You can't really see the swashplate arrangement on web pictures, but I'm guessing it's the same as well.

My guess is that this arrangement is dictated by the cambered blades.
I made a test to verify that this morning. I cut out some flat carboad blades and mounted them on the lower rotor. When I spun them up and moved the control stick, I could see that the rotor was no longer tilting in the pitch and roll axis as before. The tilt was occuring somewhere in between the two. It was hard to tell the exact angle of the tilt axis because the blades were not tracking wery well. But I think it shows that the blade camber could have something to do with this whole apparent variable precession issue.

I'm going to keep searching the web to try to find the explanation. I'll post if I find anything. I fyou find something please do the same.

Cheers

[HX3D014]

Looking at your second pic i would like to know if you can post a pic of the linkage from the upper swash section (The part that rotates) to the Lower blade.
I want to know now if it is 90deg there.
also include some portion of the blade or tell me which way the bottom blade spins. EG.
bottom blade spins clockwise while looking down on it from above.

Bryce.

[_Icarus]

I'm at work now so I can't post pictures.
The upper linkage in 180 degrees. There is one link on each side of the blade holder.
The lower rotor spins clockwise.

[_Icarus]

I found this link http://www.synchrolite.com/0940.html
It explains that the rotor lag is not entirely due to gyroscopic precession, there is also apparenlty an aerodynamic precession component. In other words, the rotor blade has to fly to the new position (flap angle?) and that takes some time. Obviously there are no flapping hinges on the little Lama rotor head but the blades are quite flexible, so I guess that you can sort of talk of flapping. So it seems that the aerodynamic precession could be the mechanism that introduces the extra 45 degrees.

[_Icarus]

i would like to know if you can post a pic of the linkage from the upper swash section (The part that rotates) to the Lower blade.
I want to know now if it is 90deg there.
also include some portion of the blade or tell me which way the bottom blade spins.

45019

[_Icarus]

I finally found a thread that discuses this 45 deg angle thing at lenght
http://www.rcgroups.com/forums/showthread.php?t=449319

[HX3D014]

Wow. That’s a long thread. Give me a month or two to get through it.

I purchased a Lama V3 today for my Brother. had a good look at it.

Make sense now. what you are asking. I think I kinda understand the answer. but I don't dare to explain just yet.

I will get through that thread first. then Do some more thinking and then get back to you.

PS. If I am not back in a month. Send some one looking for me.


Bryce.