Mark,
To make simple cyclic pitch control from existing folding prop hub - one more pivot point should be added. Perpendicular to the blade hinges, and perpendicular to the main shaft. And the stoppers, so hub will tilt only 4-5 degrees each way. It can be done as rotor hub of the fixed pitch helicopter with fly bar or flybarless .
Jerry
Jerry
This is, in essence where I began. My effort was to make a controllable pitch propeller. The problem is one of fatigue at the base of the propeller and hub. The primary source of the fatigue is the bending stresses resulting from pivoting the propeller disk during flight in a circle. Each blade undergoes a bending cycle for every rotation during flight which the number of cycles add up very quickly. My background in modeling includes flying the high powered F1C gas free models with the folding propellers. The engine on these airplanes used to turn 30,000 RPM and I have a modified Nelson .15 which topped out quite a bit more and produces 1.15 Hp. I also have flown RC helicopters since the mid 70's until just a few years ago when it became not so much fun as a result of the onboard stability augmentation.
So, my path to the controllable pitch propeller resulted in the idea of hinging the propeller blade to eliminate the fatigue. It wasn't intended to reduce or even address the effects of precession. That wasn't on my mind but it was a result of a bench test I did.
Here's the thing about angular momentum in this specific case. Because the hinged propeller is basically non rigid, precession like a gyroscope is almost non present. However the work is still being done within the system. What is not happening is that there is a significant change in phase of where the work is going. There still exists a moment from the input a torque which will always be there. The difference is that the change in angular moment remains in plane. You can't change the laws of physics that state energy is always conserved, the question is where did the work come from and where did it go?
So, the failures that have occurred by Igor and Wolfgang both involve plastic folding propellers. If you look at the root portion of the blade, you'll notice quite a bit of offset from the pin axis to the blade centerline. I would have flown one of these but I was afraid of the way the blade is constructed of plastic. If you do the math you'll soon figure out there is a huge bending load is apply along the "knee" at the root of the blade. The tension in the blade can be easily determined by measuring the thrust dividing that by two and then dividing that by the sine of 2 degrees. It's a big number probably on the order of 200 pounds or more.
As Igor pointed out, the blades see an in plane cyclic load as result of drag forces. Add this to the large tension force on the folding blade geometry and being made from plastic, in hind sight, it is easy to realize it was going to fail in the application. This was part of why I did the bench test. For the glider and free flight models the prop generally isn't going through wild gyrations. Therefore one good test will answer a thousand questions and I hammered that prop and it tracked the whole time, perfectly.
I've made dozens of carbon fiber props for my F1C models which an example of is the test subject in my video. The design of the prop is such that the tension forces stay in plane and all of the load is carried in tension by the fibers within the prop. I was very tempted to fly the plastic glider prop several times but better sense prevailed. Wear on the hub is another issue and that also can be addressed by reducing the stresses in the hub which means either materials or size. I've used a fairly large pin size in the blade and the hub is designed such that one side of the yoke can carry 150% of the load which should result in a good safety margin.
To date I have about 20 flights on one airplane with the hinged prop on it. I don't see any points of concern yet and all of the flight characteristics are good. This model has always been a good flying model and the difference between non hinged and hinged is subtle. I've had a few different pilots fly A-B tests and it 50/50 on makes a difference or not. On another model which isn't as well yaw damped, the difference is much more significant. The hinged prop does indeed make a noticeable change. One thing I can tell you is the propellers that I made are better performing that the APC that came on in terms of raw performance and battery drain.
Going forward, I have a 13x6 blade I working on to use on my SV11. I haven't yet done the loads analysis to begin working on a hub for it which I will do after I pull a blade out of the mold and weight it. I don't know how long that will take me as I'm currently working on a Smoothie which it's hinged propeller is waiting for completion. I do have intent on creating a three bladed version for the larger size airplanes. There's a lot to pack in under the spinner.
There is a question remaining and there are dialogs within this about doing something cyclic pitch wise in order to create a power steering and about doing "collective" pitch AKA controllable pitch propeller. I'm on design model version 6 and will pretty much scrap previous versions.
The question boils down to - "to what end?" which is to say, what is the mission statement and how does it improve on the current state of the art? Well, my notion is that a controllable pitch propeller should be better at regulating the speed of the model. To do that doesn't necessarily require very sophisticated controls. A propeller which can change it's pitch is actually just moving it's efficiency band around. This can be used in several ways for our models. It can help with climbing and diving by decreasing pitch. Going up it can make more power by flattening and speeding up and going down it can brake by also flattening and slowing down. Wolfgang had the same basic idea although I was unware of his idea when I began working on this idea.
Here's my experience fly with a Fiorroti timer. It works quite well. A controllable pitch propeller most likely could be made to work better. However that is a big leap in terms of cost. Again the question with which I intended this discussion initially to be is it worth the pursuit for other than intellectual curiosity? My guess is, maybe. Especially on that first corner of the outside square which is one place where a fixed pitch propeller looses. Doing a simple speed governor on the prop and pumping the power demand the way Fiorroti does would be kinda slick. There's a whole lot more that would be incorporated.
In regards to doing a cyclic pitch affair on the front of the airplane AKA V22 Osprey or XV-3. It's doable but to what end? Attaching a swashplate to the front of the airplane would add quite a bit of complexity and remember this one important detail, the swashplate stays where it is because there is a servo connected to it whether said servo is hydraulic, electric or meat which restrains it from moving. When a swashplate connected to a bellcrank connected to lines going to a handle held by the primary meat servo, looses tension it is free to move about at will. What then is the result? Scary thoughts go through my brain. Also, it takes torque to move the swashplate which will add to the control moments of the airplane. There's no free lunch.
So, I am on this road which includes some airplanes and the whole powerplant project is going to hold at this current state until I get a couple models done and a Citabria in the hangar started. Yeah, work. I gotta make some money. The current airplane is going to it's new owner and the next is in queue.