I want to put a 3 oz spinner nut on my .15 Yellow Jacket engine for balance purpose. Will it be too much for the small egnine? Any adverse effect on the bearings etc etc? Appreciate expert advice.

Thanks.

-ZM

Zahid,


The spinner nut, or the spinner may be a lot heavier than the propeller.
But its dimensions are such that it has weight very close to the center of the prop shaft.

This means it would have very inertial effect on the engine; slowing its transition by a smaller amount than would an 8" glass filled nylon APC prop.

The use of these heavy spinner nuts is to balance tail-heavy models, by putting the balancing mass as far forward as possible. This heavy nut at the very front of the plane, has the greatest effect since it is furthest from the model's axis of rotation.
But in the case of the engine. it is closest to its axis of rotation.

You would need a very un-balanced nut, and/or bent crankshaft front end, and/or loose threads that allow the nut to cock, putting it out-of-line with the crankshaft center-line, to feel any effect.

That was a very quick response.

Thank you Dar.

-ZM

How about the gyroscopic precession stresses on the bearings and the motor mount during maneuvers?

George

George,


The force of the gyroscopic precession is also a function of the distance of the spinning mass from the center.

This is the reason gyroscope rotors (non-piezo) resemble bicycle wheels, with thin, light spokes and a massive annular weight.
The forces applied to the bearings by combustion and by the inescapable imbalance of a single cylinder engine, are exponentially larger than the forces of precession. Both of these 'naturally occurring' forces, affect both bearings (the front one through the crankshaft).

I have never seen a front bearing 'go south' even with a badly imbalanced prop.
It is not likely these relatively small forces of precession will do it.

As in real-estate, the 'reason d'etre' for the 'heavy hub' is its location, at the furthest front of the plane.

That weight on that size engine will definitely have some "flywheel effect" both on acceleration and decceleration. You'll find it will take a tiny bit longer to wind up from lower rpms, and when you back out of full throttle the rpms won't immediately drop as they do without the weight. It's true, it won't be as profound a difference as it would if the weight was further out from the hub, but you're not talking a lot of torque with a .15 engine. I think you'll notice a difference, but is it enough to hurt performance? You'll have to try it to see. It's not like it's a permanent thing, if it hurts performance, take it off and go to plan B for balancing the plane.

Khodges

Yes I had that fly wheel effect in mind. Performance will not matter since it is fitted to a powered glider 'Dynaflite Butterfly' and its job is only to launch the gider. The plane was balanced with 10 oz of lead behind the engine and I figured out that I can replace it with a 3 oz spinner nut and the engine moved a little forward.

Thanks.

-ZM

A fellow in our club has a Butterfly and has a .25 something or other on it. He made the wings almost straight-- took out most of the polyhedral, but kept the basic dihedral, and put a small set of wheels on it, flies it like a trainer. This past summer he flew it so high we lost sight of it unless the setting sun hit it just right, couldn't hear the engine at all. He'd finally close the throttle and glide back, total flight times in excess of 20 minutes. Nice plane.

Same with rotating radialengines in biplane to example Sopwith Camel, Fokker DR1..

Jens Eirik

Khodges

Can you pls ask the fellow member how much weight he needed to balance the plane.

-ZM