[hecilopter]

Glider was doing some maintenance on his RV-8 this weekend and noticed that 4 of the AN470 rivets that hold the spinner bulkhead and doubler together had the round heads popped off. It was interesting that it was the rivets closest to the mounting bolts that go thru the hub. Since we both have Superior XP-360 engines with Hartzell blended airfoil props, I thought I would check mine out of curiosity. Sure enough, 1 of mine has popped off. I have about 570 hrs on my plane and he has about 200 on his. Anyone else noticed this or is this just a coincidence? See pics below to see where the head has popped off (the shiny dot). My prop has been dynamically balanced and his has not. They both seem very smooth though.

 

[Bob Axsom]

Check the surface of the bulkhead

Check the surface of the bulkhead behind the trailing edge of the prop. At high pitch the prop will hit the bulkhead and leave a wear mark there. Adding spacers (washers) to move the bulkhead will eliminate the contact. Reprime the contact area so you can detect future contact and tell if the spacing is adequate to allow the pitch to change to coarse without contact. You may have to enlarge or elongate the spinner holes to accomodate the repositioning of the rear bulkhead

Bob Axsom

 

[hecilopter]

Spacers

Bob,

Thanks for the reply. There are spacers on the mounting bolts between the hub and the bulkhead. You can just see these in the first picture. I used the 2 wooden clamp technique already to rotate the prop to coarse pitch and check it and there is plenty of clearance there. Any other ideas?

 

[RV8N]

Glider was doing some maintenance on his RV-8 this weekend and noticed that 4 of the AN470 rivets that hold the spinner bulkhead and doubler together had the round heads popped off. QUOTE]

Yep, I had one do that also. Just a single rivet head and it was not near the blade like yours. It was almost equal distance from both blades. I have no idea what caused it but I drove a new rivet and documented it on my condition inspection checklist.

Karl

 

[Bob Axsom]

A couple of possibilities

Bob,

Thanks for the reply. There are spacers on the mounting bolts between the hub and the bulkhead. You can just see these in the first picture. I used the 2 wooden clamp technique already to rotate the prop to coarse pitch and check it and there is plenty of clearance there. Any other ideas?

Here are a couple of possibilities:

1 - Rivets over driven or over squeezed such that no yield is left in the fastener - possibly but not probably, even fractured

2 - The blades you have are 7496. Van and Hartell have now gone to a 7497. I have performance charts from Hartzell that show the 7497 efficiency drops off more than your 7496 at higher aircraft speed. The 7496 efficiency peaks at ~87.9% at ~185 KTAS and drops off only to slightly to ~87.8% at 200 KTAS. The new 7497 peaks at ~85.7% at 170 KTAS and drops to ~84.3% at 200 KTAS. I asked why about this and I was told that testing drove them to the thicker and additional mid-blade camber 7497 as a better fit for the higher horsepower applications and it provides additional stiffness. I asked about the availability of the 7496 because I am interested in speed and I was told that they may no longer be available (I haven't verified that). OK, so you may be experiencing difficulty with the rear bulkhead rivets because of the propeller you are using.

Bob Axsom

 

[Finley Atherton]

Rusty,
Thanks for the post. It happens in Australia also! One round rivet head missing near the prop blade. I can think of no reason why this happened except that the area is under more stress that anticipated and may need more rivets than called for? I don't know if it is a factor, but I have operated my prop full coarse at both idle power and with the engine dead a number of times (while doing simulated engine failures).

Fin
9A 0-320 with Hartzell.

 

[Jamie]

At first when I read this post I guessed it could be a bigger problem with the 'A' models because we frequently push on the spinners to push our planes back into hangars, etc. This appears to be happening to the butt scrapers too. Very interesting...I'll double-check mine this weekend.

 

[RV4man]

Too late

I am too late to save my bulkhead, fractured in two locations, may be able to repare it, we'll see. Looking for where I can buy a new bulkhead for my Hartzell.... it is the same as you indicate in prior posts.