0TreeLemur Posted September 5, 2021 Report Share Posted September 5, 2021 Somebody ought to know this. According to the Type Cert, for a M20C, the original HC-C2YR-1 7666-2 propeller had weight of 53.75lbs and a moment arm of -30.16". Looking at the post install update to the W&B, my A&P listed the weight and moment arm of the HC-C2YR-1BFP/F7497 "Top Prop" as 58.1 lb and -35.5". Ok, I get that it is heavier. Why does it have almost 5" more moment arm? Looking at the Hartzell manual, I don't see this data. Must be in the Mooney STC. I can't seem to find that paperwork right now. Anybody have reference to this? Just checking my A&P's work. He's a genius mechanic, but I check his math. Thx. Quote Link to comment Share on other sites More sharing options...
RLCarter Posted September 6, 2021 Report Share Posted September 6, 2021 Checking math is always good, and/or question him as to how he came up with his figures Quote Link to comment Share on other sites More sharing options...
DXB Posted September 6, 2021 Report Share Posted September 6, 2021 13 hours ago, 0TreeLemur said: Somebody ought to know this. According to the Type Cert, for a M20C, the original HC-C2YR-1 7666-2 propeller had weight of 53.75lbs and a moment arm of -30.16". Looking at the post install update to the W&B, my A&P listed the weight and moment arm of the HC-C2YR-1BFP/F7497 "Top Prop" as 58.1 lb and -35.5". Ok, I get that it is heavier. Why does it have almost 5" more moment arm? Looking at the Hartzell manual, I don't see this data. Must be in the Mooney STC. I can't seem to find that paperwork right now. Anybody have reference to this? Just checking my A&P's work. He's a genius mechanic, but I check his math. Thx. I think it is a mistake. I don't see how the station could change by >5" on a different prop. I have the identical Top Prop on my C - here is the logged W&B data for it: Weight Arm Moment Propeller- Hartzell #HC-CZYR-1BFP/F497 4/2/2011 58.1 -30.16 -1752.3 Propeller Spinner assembly #835-58P 4/2/2011 3.1 -29.18 -90.458 1 Quote Link to comment Share on other sites More sharing options...
A64Pilot Posted September 6, 2021 Report Share Posted September 6, 2021 A inch maybe, but think how strange it would look being 5” more forward of the cowling. Doubt it’s right. Quote Link to comment Share on other sites More sharing options...
0TreeLemur Posted September 6, 2021 Author Report Share Posted September 6, 2021 Digging a bit more, I found this from the M20 STC. He seems to have taken the example moment arm literally. Instructions say to use the same moment arm as the prop replaced, which makes a lot more sense. 2 Quote Link to comment Share on other sites More sharing options...
OR75 Posted September 7, 2021 Report Share Posted September 7, 2021 The prop CG is not 5 in for the CG of the previous prop , you could tell if it was Quote Link to comment Share on other sites More sharing options...
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