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6A CG Issue? Metal Prop to Whirlwind GA weight reduction

dmat

Well Known Member
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Hey, has anyone had an issue with CG converting from a metal Sensenich to a composite prop?

I have the 72FM sensenich prop on my IO360 engine with a 4inch spacer. I am converting to the Whirlwind GA200L with a saber 4 inch spacer and want to know what I am getting myself into before the swap.

Thanks in advance,
D
 
Easy enough to calculate with modifying your W&B values.
I think the new combo will move your CofG back slightly, Which means pack lighter!
 
Definitely do the calculations - this not hard. Our RV-6 is decidedly tail heavy, even with the metal Hartzell up front. I was going to try a lightweight composite Hartzell I have here for testing on it, but decided the potential performance gain wasn’t worth the loss of baggage capability, so that test is now low priority.

(Don’t get me wrong - the Hartzell three-blade composite is a great prop - its just that the aft CG on the -6 makes it problematic...)
 
Steel Crush Plate Option

You may be able to compromise by adding a Steel crush plate to the prop instead of an aluminum one. Some of the weight loss would be lost, but weight out forward of the prop is going to be as helpful to aft CG issues as it can be. I think Sabre makes them.
 
Wood

In January I pulled the Warnke wood prop 12 lbs and existing 4” spacer and Landoll ring 12lbs. Replaced with GA200l @ 18 pounds and Saber 4” spacer , carbon spinner. I weighed all coming off and all going back on. I ended up about 6 lbs lighter on the nose. I’ve noticed no change I could attribute to the 6 lbs reduction, but nice change going to whirlwind prop. I fly 99% of the time solo. I load the empty seat up, other stuff by flap torque tube. I weigh just under 200lbs, always full tanks. Not answering your question, just sharing my recent change/data points. You’ll enjoy the prop....quite, and smooth, but super smooth after a dynamic balancing . Had mine painted up to match my old girls 28 year old paint. Enjoy your new prop!

Edit: I’m a 0320 d1a
 

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Thanks Butch, I am looking forward to the new prop.

Looks like I am losing 25lbs in the nose which brings my CG to 68.58 which I believe is within the limits of the 6A.


Thanks,
D
 
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The real cg concern is when you have a passenger, baggage, and are low on fuel. Run some scenarios under those conditions to make sure you stay inside the envelope. I can tell you that I flight plan for Oshkosh and the like and use every available 1/10 of an inch of cg range. If you don’t actively plan your load, it is easy to get out of limits.
 
totally true, I need to run a bunch of numbers to make sure I am good to go. I am also looking into a weighted spacer just in case.

D
 
added 15#

I just put a 15# Saber crush plate in front of my Catto prop to move the CG forward. Finished the 5 hours flight test and all is OK. Also had the prop assembly balanced, though little adjustment was needed.
 
I have a FP Catto on an O-360 and had to add a 20# crush plate to get the cg forward. Saber was super helpful and great to work with for the crush plate.
 
Personally, I think there is a market for custom weighted props. If you want to add 8 pounds to your nose, just order a composite Whirlwind prop with 8 pounds of steal, (or lead, or whatever) molded into the base were it will not have much moment of inertia. Adding weight that far forward is the best way to adjust CG with the lease weight added. I know that CG is the only reason I don't have a Whirlwind. This approach, while probably sacrilegious in an engineer's eyes, would turn a negative about composite props on 6's into a positive. I'm guessing other makes and models would have similar needs.
 
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