It was brought to my attention that I kind of left the discussion open ended and without a direction. So, I'm going to provide an update on what has been done and why it got quiet on my part. I have a lot of dialog in different arenas including full scale aircraft integration of powerplants and drive systems. When I first did the concept for the hinged propeller the reasoning was because I was looking to see if I could overcome the challenges of making a variable pitch propeller for models. The primary challenge of such a propeller are the bending loads at the root of the blades due to thrust and precession. This is particularly a concern to a control line model as the bending cycle is every revolution continuously which means several million cycles can readily be achieved. To eliminate those bending loads a hinge can be used. This is interesting and is not in use in the aviation community at large. Should a hinged propeller show that it would eliminate the stresses there is a very wide market for the application. So, I spent a non insignificant piece of money and did some patent research to which we eventually were on the verge of submission. Then the flaw happened.
I believe I talked about blow back in one of my videos. Blow back is a term used to describe what happens when air comes in to a rotor disk from the side. This causes a dissymmetry of lift that causes the rotor disk to tilt in a direction with the wind resulting in a thrust vector in the same direction. This is one of the reasons helicopters are difficult to hover in one place and it is also the reason a helicopter flies more or less the same as an airplane once flying. The term for that we use is velocity stable.
On the fateful day we had a wind coming across our local trees which are close to the circle. This means there was a wind shadow down low and a wind shear at about the tree height. To the airplane and propeller this created a sideward gust. To the propeller this side ward gust caused the aforementioned blow back to occur. The first time caught me by surprise but I had honestly been aware that such a thing could happen and knew to be watching for it. The other thing I was watching for on the list of potential negative side effects was any tendency to whirl. The yaw response on one level was a thing of beauty, nice clean near 90 degree instantaneous yaw. Crazy cool... But turned out to be a death cab for frankenlaser. After the first time inadvertently occurring, I decided to explore the repeatability of the event and get a better look at the response. I managed to get another 3 or 4 good shots at it before I dug a deeper hole than I could dig the airplane out of. The impact was spectacular and the parts scattered and shards drifted in wind like no tomorrow. The motor shaft made a satisfying chip in the cement. The ESC and Timer survived.
This is not a characteristic which is good. So, needles to say, for now the work has stopped. The patent efforts are on hold / done. I do have some ideas on how to limit or restrict impact of the blow back. Returning to this effort is still in the list of things to play with but I want to get on with building a few airplanes with the overbalanced offset hinge flaps fist. The propeller definitely eliminates or significantly improves the impact of precession but that is only a contributing factor to the yawing in the high maneuvers. The wind has as much and perhaps more impact up there than we give credit to. Go watch some of my tail cam videos, they can be very informative.
Topic: The Hinged Propeller and Precession, an update (Read 1182 times)