[13brv3]

Greetings,

On Van's drawing, they show a 1/4" spacer, and a single washer between the C/S prop hub and the spinner backplate. I understand this is needed to make sure the prop doesn't hit the spinner backplate at full pitch rotation.

Can anyone verify that you actually need this 5/16" of spacing to clear the prop? In other words, would just the 1/4" spacer work? This is a 74" blended airfoil Hartzell.

Bottom line is that it looks like I've cut the cowl to spinner spacing pretty close, and will likely end up with 1/8" at most of gap. I'd ideally like more, just to make the cowl easier to get on and off, so I'm looking for any way possible to increase the gap.

Thanks,
Rusty

 

[RV7ator]

Rusty,

I left out the AN960 for the same reason - too small a gap. I twisted the blades into full coarse pitch, and it cleared the bulkhead. Operationally, you'd never use full coarse pitch. Also, the washer is Van's idea, not Hartzell's. I believe the washer is there to push the bulkhead back just enough to clear hub fillets radii without cutting away more metal than the plan's dimensions.

I gave Ken Krueger a note at the homecoming to correct a mistake in the instructions, which may have led you down the garden path. The suggested spacer should be 2 1/8, not the 2 1/4 in the instructions.

2 1/2 Hub-to-ring gear
( 1/4) Bushing
( 1/16) Washer
( 1/16) Bulkhead
___________
2 1/8 Spacer

If you use a 2 1/4 spacer, the gap you set shrinks 1/8 when you mount the for-real prop.

After falling into this trap, I sanded off the cowl face, which serendipitously squared it to the spinner, until it was just breaking through. Then I added lay-ups internally to beef the cowl back up.

John Siebold
Boise, ID

 

[13brv3]

Hi John,

Thanks for the comments. Van's has taught me to double check critical dimensions on the plans, so I caught the same error for the spacer dimensions. I actually ended up using a slightly longer spacer, and think I accounted for the difference OK. The problem came in my execution of the cowl fitting

I think I'll give Harzell a call today, and ask about the extra washer than Van's adds to the spacer. If I can leave it out, that will buy me 1/16". I'm also going to ask if I can put a 1/16" spacer between the crank drive hub, and the prop hub. The part of the rear spinner bulkhead that was removed with a flycutter would work perfectly for this. That would only leave about 1/16" of the drive lug shoulders exposed, and I have a feeling that Hartzell won't go for this.

If I get desperate, I might even remove 1/16" of the spinner flange. I'll know more once I get the prop and spinner bulkhead mounted, but I'll take all the space I can get. I'd probably be happy with about 3/8", just to be able to get the cowl off and on easier.

Thanks,
Rusty

 

[13brv3]

I talked to Hartzell, and they agreed that the extra washer can be left out. In other words, the 1/4" spacer is all that's needed between the prop hub, and spinner backplate.

I also asked about using a 1/16" spacer between the engine and prop hub, and they shot that down. They said it would cause problems later on, so I'll forget about doing that.

Cheers,
Rusty