3-blade rotor

wulfefw190 said:
I would be interrested in some as well. Are there any builders that manufacture them?

I've never heard, even is is quite simple to design. take a look to Cierva head with 3 flapping pins on 120° and flapping stops for each blade.
Anyway, apart from replica reasons, I can't see any good reason to go on a 3 blade sistem which is more complex, more expensive only probably smoother, even if a good balanced 2 blade rotor with right undersling distance has no shake at all.
I forgot that 3 blade has also problem from hangar space point of view.
ciao
 
If I remember right Scott Malone (Soma) built one but getting in touch with him will take some work. 503-661-3266
 
6432R said:
Does anybody know where to get plans/drawings for a 3-blade rotor head? Thanks
I can not imagine why any gyronaut would want to go down this path, unless they are educated enough, and competent enough to do all the work themselves. If that was the case, this question wouldn't have had to be asked.
There is astounding simplicity and efficiency in the conventional two blade system that many gyronauts still do not comprehend. The increase in knowledge and engineering required to correctly develop a three blade system is way beyond most of us and I doubt that those that have successfully built a three blade system would ever sell even the plans to the masses.
The popular theory among the misinformed is just simply add another rotor, and you have half as much lift again.......Wrong on both counts!
 
Last edited:
Im not an engineer. What are your Idea's on why a 3rd blade is not worth it?
Im just starting to understand gyro's.
 
wulfefw190 said:
What are your Idea's on why a 3rd blade is not worth it?
For all the extra complexity and engineering involved, what do you gain in a conventional gyro? Unless you are an experienced gyronaut and understand the engineering involved, then all you will likely gain is a far more expensive rollover. There would be no difference in lift, and the difference in drag (efficiency) would depend on too many other factors to make a blanket statement.
If the blade loading was too high with two blades , I would rather go a few % longer than use an extra blade.
There are gains that can be made when collective pitch is a requirement.

I would liken the difference to making a see-saw work with a straight board pivoted in the middle, to making one work as well with three separate boards at 120 degrees apart. It can be done but there is far more engineering involved
 
Get out your file and hacksaw: Attached is a drawing of the Cierva C-30 3-blade rotorhead.

The hourglass shape of the hub forging results from the need to get the flap hinges as near to the center of rotation as possible.

Even so, without flap hinges on the exact center of rotation, control forces would have been horrendous in an age before power boosted controls became cheap and reliable.

I’m speaking of what Cierva called “direct control;” control by rotorhead tilt. With fixed rotorhead, feathering bearings and swashplate, offset flap hinges don’t affect control force and offer some advantages, i.e., increased control power, making the machine more controllable during periods of reduced rotor thrust.
 

Attachments

  • [RotaryForum.com] - 3-blade rotor
    Cierva direct control.webp
    42.3 KB · Views: 0
Last edited:
3 Bladed Rotors

3 Bladed Rotors

wulfefw190 said:
Im not an engineer. What are your Idea's on why a 3rd blade is not worth it?
Im just starting to understand gyro's.

After hearing Scott Tinnesand talk about the 18A, and seeing the videos at the website below, I think 3 blades are too scary for me. Call me a wimp.

Heather

https://www.rotaryforum.com/forum/showthread.php?t=961

brett s said:
There's a couple of videos of some ground resonance testing using a CH-47 at the following site, near the bottom of the page:
https://www.chinook-helicopter.com/video/video.html

In this case it was intentionally induced, pretty scary stuff. I can't remember ever seeing a case of this in a Chinook happening accidentally, it's not very susceptible but as the videos show not impossible.
 
Thanks for your input ,people ! Keep it coming. My main reason for wanting a 3-blade is to be able to fold the blades for ground travel so as to not have to remove the rotor. For lurkers, don't be afraid to try something! I had not built an airplane until I built my first one!
 
I can tell you from my limited experience that 3 blades must be right...all the time.
A little dirt in the exterior friction plates on the dampers on my J2 made it shake like a mother- looked like the tails were going to fall off.
I wouldn't want to ever get into a resonance issue.
Just think of the force on them if you try and stop them when they're only turning 20 RPMs
3 blades above you at 300-400 rpm deciding to go awry will kill you (and destroy anything close to you) in a heartbeat.
If there was a way I could go to two blades with pitch control I'd do it in a heartbeat.

-Easier to store
-Less maintenance
-Less to worry about- a hard landing can cause resonance- It's one thing to have a blade strike the ground, another when it will shake your machne to rubble
- Doesn't need a sophisticated suspension, I could go to a more fixed landing gear setup instead of the struts
 
Back
Top