Rotor Head: Rigit or not

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Rotor Head: Rigit or not

Postby Wildbird22 » Sun Jan 15, 2012 3:03 pm

Question for you scale pros:
I'm building a 500 size MD500D, and I'm trying to understand and figure out the pros and cons between the RIGID 5 blade rotor head using weighted-tip scale blades, compared to the FLOATING (flexible) rotor head using fiberglass or the CF blades.

I haven't ordered the rotor head cause I'm not sure which one to use, cause I don't know the difference in the characteristics of the two.

Can any of you guys enlighten me?
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Re: Rotor Head: Rigit or not

Postby 1hander » Sun Jan 15, 2012 3:40 pm

if i remember correctly,

the flapping head allows each grip to move independently of things like wind gust that would upset a rigid head...the flapping head is supposed to have less of a tendency to baloon up in fast forwartd flight and not climb or drop in turns... its upposed to be an improvement from the rigid head... ive tried both and even though the flapping head seemed only be very slightly better than the rigid head, i found that you still had to work hard to get it to fly nice for you and still reqiuired an E stabilizer just the like rigid head
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Re: Rotor Head: Rigit or not

Postby Hank79 » Sun Jan 15, 2012 5:51 pm

There both rigid, one has more flexibility in the blade grips than the other, i presume both utilise a spindle shaft and thrust bearings. If it was a real semi rigid head that allowed genuine flapping it would have hinges in the vertical or horizontal plane for lead lag or horizontal movement with hydraulic or gas dampeners. I would use what ever flies the best:)
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Re: Rotor Head: Rigit or not

Postby bell222 » Sun Jan 15, 2012 7:49 pm

I have a feeling that you cant use electronic stabs with flapping hinge heads
not sure ,maybe someone else knows
i have flapping hinge on my Hirobo but no electronics
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Re: Rotor Head: Rigit or not

Postby Wildbird22 » Mon Jan 16, 2012 6:16 pm

Interesting....The only experience I have in this so far is my little 450 size MD500D with the HobbyKing 5 blades head. That head is rigid, and using the RC Aerodyne weighted tip blades, It flies pretty good with no e-stab in a 3mph wind. And I really don't want to spend more money on e-stab, cause I want to fly the helicopter.....not some electronic component.

I'll just keep doing more research, and asking more questions.
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Re: Rotor Head: Rigit or not

Postby toast » Mon Jan 16, 2012 7:08 pm

Not quite on the same topic, but has anyone seen these heads and whats going on with the 2 swash plates? I gather the lower one does the phasing?

Image

Image

This is from CNCHeli. Not a brand I would recommend as the last 2 heads that I know of brought from there have gone back due to issues. This head is not damped either but I would expect using more flexable blades will give the same effect as dampening.
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Re: Rotor Head: Rigit or not

Postby 1hander » Mon Jan 16, 2012 8:05 pm

the very lower one has the timing built into it by having the 3 links from the center ring going down to the lower in a manner that gives it the timing it needs , looks like they seperated into two halves what would normally 1 piece..kinda like and upside down swash plate.. , so the timing is done with the lower half of the swash by the connector links instead of by adjusting the upper ring with the driver. looks like its a clockwise timing. pretty cool actually, if they got the timing right, it looks like 90 degrees though

funny thing is on the cad drawings it shows an antirotation the very lower ring toi the center ring, but theres not one on the actual, the antiorotation pins role is being played by the the ways the links arew articulated.
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Re: Rotor Head: Rigit or not

Postby toast » Mon Jan 16, 2012 9:10 pm

Yer, thats one thing I have noticed about these guys, the drawings are different from their products! You have to wonder why, especially wit a name like CNC heli... :blink:

They do a scale MD500 head too. But I think I like the look of the one Ron at Justscale is offering better.
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Re: Rotor Head: Rigit or not

Postby 1hander » Mon Jan 16, 2012 9:19 pm

its really interesting how they got the timing into the lower swashplate, iyts like middle ring is binding to the proper direction because of the leverage point on the lower ring. the lower atms where the links are coming up from the servos are articulated
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Re: Rotor Head: Rigit or not

Postby bell222 » Mon Jan 16, 2012 9:28 pm

im sorry but i have had no luck with the cnc heads
bad quality metal
we had a multi blade tail come to bits in flight and also a 4 blade head develop blade tracking due to
bearings wearing badly in the blade grips
have you seen this one from them
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Re: Rotor Head: Rigit or not

Postby toast » Mon Jan 16, 2012 10:10 pm

Yep, saw that on there. Thats not the one that fell apart is it? Its just a variation on their UH-1 head with the reduction arms. Infact most of their heads seem to have those arms. Its a wonder they are still in business if they are selling crap that doesn't work.

How hard can it bee to design and manufacture a head that works?
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Re: Rotor Head: Rigit or not

Postby bell222 » Mon Jan 16, 2012 10:33 pm

no Brett
it was a std 600 size 4 blade head and 3 blade tail
the customer was very lucky he managed to spin the heli down and land
just did some damage to the landing struts on the scalie
he wont trust there heads now
i am still waiting on the swash pin so that i can complete the new super scale head in the Blue Thunder
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Re: Rotor Head: Rigit or not

Postby Kananga » Tue Jan 17, 2012 2:30 am

toast wrote:Yer, thats one thing I have noticed about these guys, the drawings are different from their products! You have to wonder why, especially wit a name like CNC heli... :blink:

They do a scale MD500 head too. But I think I like the look of the one Ron at Justscale is offering better.


Maybe its intentional with the idea it stops people downloading the drawings and making their own.

A common misconception is the mention of cnc makes people think parts are more accurate or better quality which is not always the case.
Cnc is good for speed and repeatability it doesnt actually mean its any more accurite than a manually made part.
Companies often use a softer material so the machine can make it quicker with it being easier to get a reasonable surface finish. Often parts are then annodised not just for prettiness but to add a bit more hardness to the surface.

In my experiance mass produced cnc parts are no more accurate and its easily achievable to often get better results by manual methods. Cnc has its place in industry and works very well but dont kid yourself into thinking a cnc part is better than a hand made version.

Only my 2 cents.
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Re: Rotor Head: Rigit or not

Postby teamdavey » Tue Jan 17, 2012 6:28 am

In answer to the OP question. For what it is worth, my preference is for flapping or soft teeter with or without stabilization (stabilization works for both) for scale flying.

"Rigid" head but with flexible blades should also work well. Personally I find "rigid" heads and stiff blades do not "sit" well in the hover even with stabilization.
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Re: Rotor Head: Rigit or not

Postby AirBear24 » Sun Oct 14, 2012 3:18 pm

Well, I am a newbie here as far as scale helicopters, but I have thousands of hours piloting and giving instruction in full size helis, and both scale and full size have the same aerodynamic principles.
With a rigid system you basically have a fixed unit between the rotor head and rotor shaft (mast). The blades have some give (flex) but when the head moves, the mast does too, which in turn moves the fuselage, all as a single unit. With flapping blades in a multi-blade system each blade floats independantly of the others. This is usually called a fully articulated system. A flapping two-blade system is usually called a teetering or semi-articulated system, like a see-saw. When one blade goes up the other one goes down. These floating systems allow the mast to hang below the rotor head without forcing the mast (and fuselage) to tilt with the plane of the rotor.
With rigid rotor systems the mast/fuselage combination tilts in the direction the rotor head tilts. With flapping or articulated systems the mast tends to remain perpendicular to the earth and the tilting of the fuselage is caused by acceleration and deceleration (fore and aft) and by centrifugal force in turns (left and right banking).
If you bring a helicopter with a rigid rotor to a hover and then move the cyclic stick slowly to the left or right the rotor will tilt in the same direction but the fuselage will also tilt that way. If you make the same maneuver with a teetering or articulated head the plane of the rotor will tilt the same direction as the stick and the helicopter will begin to move in that direction but the fuselage will tend to remain perpendicular to the earth. It will only tilt from acceleration.
The biggie here is that the rigid rotor system limits the travel of the blades up and down (particularly down). This is essential in aerobatic maneuvers such as as inverted flight 3-D, etc. If you tried to fly inverted with a floating system the rotor blades most likely would cut off the tail boom. Almost all civilian helicopters use variations of articulated, semi-articulated and teetering rotors. In scale helis it should produce more realistic flight.
I am under the impression that most flybarless gyro systems work by sensing the tilt of the helicopter. Since a helicopter with a flapping blade rotor head tends to have much less fuselage tilt I am not sure how effective FBL gyros work with them. Maybe someone with experience using flybarless gyros with a flapping blade system can enlighten us.
I am probably making this post tedious to read, but there is another important consideration, that of Center of Gravity (CG). In most helicopters, the helicopter should balance perfectly level if you suspend it with a string from the center of the rotorhead. Lets say you have a helicopter with a rearward (aft) CG. If you come to a hover with a helicopter with flapping blades the helicopter will hover with the tail low and the center of lift will be in the center of the rotorhead. If you bring the same helicopter to a hover with a rigid rotor, the helicopter will tend to be more level since the rotorhead/mast combo is forcing the fuselage to follow it, but the center of lift will move rearward to some point along the trailing blade as it crosses the tail boom. This causes the rotor system to have an asymetrical lift pattern which can be very noticable in the controls. The helicopter is usually overly sensitive in certain areas.
I tried to keep it fairly simple and left out some other factors such as gyroscopic precession, etc.
Hope this wasn't too boring!

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Re: Rotor Head: Rigit or not

Postby toast » Sun Oct 14, 2012 3:31 pm

Good answer! This is why we tend to keep scale models with a forward CofG. Gives a lot "softer" feel when flying.
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