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We briefly discussed prop balancing in this recent thread (http://vb.taylorcraft.org/showthread...-backing-Plate) I offered to post some pictures of my current experiment so here they are for review. Because there's only a skull cap spinner on my Taylorcraft there isn't an option to attach balance weights to the aft spinner bulkhead or perimeter as is typically done in my experience.
The weight attachment location and value is determined with the use of complex propeller balancing equipment. A sensor is bolted to a forward/upper cross-crankcase bolt that measures movement in inches per second. The engine is run at cruise rpm while stationary and the out of balance rotational inertia of the crankshaft, propeller, or other reciprocating parts might displace the engine in its mounts at some fixed point of the crank's 360* rotation. The analyzer box takes that info plus a locked image and data from a strobe to determine the clock angle of one prop blade, and then suggests what weight at what 360* location might offset the imbalance. The weight's attached at the suggested location and the experiment rerun until the later movement fall to acceptable levels noted in my second attachment below. At least that's how I understand it without reading the Owner's Manual for the gear.
On my plane it suggested 50g be added where you see the bent chromoly plate bolted to the prop. The weight of the plate exceeds 50g because a portion is inside the radius of the prop bolts and therefore that portion has less of a balancing effect than if it were further outboard. We also discussed just extending the plate towards the center of the hub and adding weight there with hardware, but decided to try this bent example first. In case you're wondering that prop bolt the weight is under is longer than the rest to maintain adequate grip in the crank flange and slightly adds to the overall weight at that station.
The prop is indexed to the crankshaft with marks, the dome bracket to the prop, and the dome to the bracket should they need to be removed for inspection. As I noted in the earlier thread the only change I felt was the elimination of a buzz in the rudder pedals. How much weight is added depends on the out of balance condition of the original configuration.
Edit:
Prop balance example: https://www.youtube.com/watch?v=RyNIPsF-7Jg
Better explanation then mine: http://www.expaircraft.com/PropBalance.htm
Comments welcome.
Gary
The weight attachment location and value is determined with the use of complex propeller balancing equipment. A sensor is bolted to a forward/upper cross-crankcase bolt that measures movement in inches per second. The engine is run at cruise rpm while stationary and the out of balance rotational inertia of the crankshaft, propeller, or other reciprocating parts might displace the engine in its mounts at some fixed point of the crank's 360* rotation. The analyzer box takes that info plus a locked image and data from a strobe to determine the clock angle of one prop blade, and then suggests what weight at what 360* location might offset the imbalance. The weight's attached at the suggested location and the experiment rerun until the later movement fall to acceptable levels noted in my second attachment below. At least that's how I understand it without reading the Owner's Manual for the gear.
On my plane it suggested 50g be added where you see the bent chromoly plate bolted to the prop. The weight of the plate exceeds 50g because a portion is inside the radius of the prop bolts and therefore that portion has less of a balancing effect than if it were further outboard. We also discussed just extending the plate towards the center of the hub and adding weight there with hardware, but decided to try this bent example first. In case you're wondering that prop bolt the weight is under is longer than the rest to maintain adequate grip in the crank flange and slightly adds to the overall weight at that station.
The prop is indexed to the crankshaft with marks, the dome bracket to the prop, and the dome to the bracket should they need to be removed for inspection. As I noted in the earlier thread the only change I felt was the elimination of a buzz in the rudder pedals. How much weight is added depends on the out of balance condition of the original configuration.
Edit:
Prop balance example: https://www.youtube.com/watch?v=RyNIPsF-7Jg
Better explanation then mine: http://www.expaircraft.com/PropBalance.htm
Comments welcome.
Gary
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