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Weighted Crush Plate?

Sully73

Active Member
Hello to my fellow RV-4 builders,
I have acquired a used Catto prop for my RV-4. This prop came with a 15 lb steel crush plate. I assume this was needed to move the C.G. forward.

Question:
Does anyone one else need this extra weight for weight and balance? Is this common?

I would rather move other components like the battery instead of adding extra weight.

Thanks in advance
 
Pretty common

Common issue with various RV tailgraggers as they were originally designed for heavier prop installations (CS and Sensenich metal FP). In my case (-7) the difference between the Catto and the sensenich FP metal prop was about 30 Lbs which moved the CG aft quite a bit. I added a landol ring and a heavy saber crush plate to compensate. Light weight battery and starter did not help either.
Figs
 
Common issue with various RV tailgraggers as they were originally designed for heavier prop installations (CS and Sensenich metal FP). In my case (-7) the difference between the Catto and the sensenich FP metal prop was about 30 Lbs which moved the CG aft quite a bit. I added a landol ring and a heavy saber crush plate to compensate. Light weight battery and starter did not help either.
Figs

The -4 is more the opposite of this - the design was for a lightweight wood prop and an O-320. This normally resulted in a middle empty CG. Unlike the side-by-sides though, in the tandem this greatly limited the usability of the back seat and baggage compartment as you’d shoot right through the rear CG limit before you could load to gross weight. The crush plate is just one way fixed pitch users moved the CG forward as there is only only so much weight you can remove from the back (the battery is already installed forward in most installations I’ve seen).

I myself used a 20# crush plate to bring my -4s CG forward. As far as ballast goes it’s the furthest forward station you can reasonably add weight to. If you want to put the plane on a diet you can switch to a lightweight battery and starter which will probably net you somewhere around a neutral CG change compared to the crush plate while still weighing a little less overall.
 
Question:
Does anyone one else need this extra weight for weight and balance? Is this common?

Yes, when I had a fixed pitched prop.

Yes.


Do the W&B with it on/off. Go fly it with someone in the back seat and with the back seat empty. it makes a big difference. It also helps with idle RPMs. Search for Catto prop testing on this site. I have done a lot of testing with different crush plates/props.
 
15# crush plate

I recently did this on my -7A. I have a lightweight Catto prop and was limited with baggage capacity, as well as being able to have only one person in the plane and stay in the aerobatic envelope. Added a 15# crush plate in front of the prop. Just finished the 5 hours of Phase 1 testing required by our AW certificate, and the only issue was running out of pitch trim with zero baggage weight. May need to put a few pounds in baggage. Also had the prop assembly balanced after the installation, and with the new Saber crush plate very little adjustment was needed.
 
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