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RV-6 Propeller Moment Arm?

C

cyrus

Well Known Member
Has anyone ever bothered to figure out the moment arm for their prop on an RV-6? Since the Datum starts at 0, and the spinner is around 10" long? (not in front of my plane) I'm guessing it's somewhere between 10" and 20" but curious if anyone ever actually calculated it :)

Thanks!!
Cyrus
 
cyrus said:
Has anyone ever bothered to figure out the moment arm for their prop on an RV-6? Since the Datum starts at 0, and the spinner is around 10" long? (not in front of my plane) I'm guessing it's somewhere between 10" and 20" but curious if anyone ever actually calculated it :)

Thanks!!
Cyrus
Click to expand...

A mesauring tape and this picture might help...

http://www.vansairforce.com/community/showpost.php?p=1200138&postcount=6

izB9I7.jpg


The datum is 60 inches ahead of the wing leading edge - https://www.vansaircraft.com/pdf/RV6Awb.pdf
 
Thanks Gil, good advice. Of course, I realize what I need to figure out after I leave the hangar! :)
 
12 inches

cyrus said:
Thanks Gil, good advice. Of course, I realize what I need to figure out after I leave the hangar! :)
Click to expand...

Well, I just had to go to my hangar...:)

Got my tape out - Firewall to center of a Sensenich prop w/2.25 inch spacer = 36 inches
= 48 inches to wing LE per my previous picture

So prop. moment = 12 inches from the 60 inch imaginary datum line :)
 
You?re the best! I even went so far as to scale the w&b drawing in photoshop so a 60 unit box fit from the leading edge of the drawing to the imaginary datum and then made another cube to check the distance to the center of the prop. I got 13 inches which is pretty close for a drawing :) I?ll use your 12 for my weight and balance calculations though. The point of this is to see if I can stay within the comfort zone if I replace my Sensenich FM72 with a ground adjustable prop that?s 20lbs lighter.

Thank you!!
 
cyrus said:
You’re the best! I even went so far as to scale the w&b drawing in photoshop so a 60 unit box fit from the leading edge of the drawing to the imaginary datum and then made another cube to check the distance to the center of the prop. I got 13 inches which is pretty close for a drawing :) I’ll use your 12 for my weight and balance calculations though. The point of this is to see if I can stay within the comfort zone if I replace my Sensenich FM72 with a ground adjustable prop that’s 20lbs lighter.

Thank you!!
Click to expand...

On my -6A it shifted the CG back about 0.75 inches in the fully loaded, but low fuel state.

No paint on mine yet, which would make it a bit worse.
 
My CG is 69.3in with the Sensenich 72FM and estimate it to become 70.36 with the GA composite prop. I?ll probably move my ELT forward but even as is, I?m comfortable that I can change props and be safe. Thank you again!
 
1" sounds about right. I remember getting right around 1" when I added the 20 lb crush plate to my 6A.

Larry
 
lr172 said:
1" sounds about right. I remember getting right around 1" when I added the 20 lb crush plate to my 6A.

Larry
Click to expand...

My previous numbers were for full loading - If I take the empty CG and subtract 20 lbs at the prop, it moves back 1.10 inches.

It all sounds consistent. :)
 
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