Van's Air Force
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Postflight Inspection
- Thread starter n38139
- Start date
AX-O
Well Known Member
Looks like the aft bulkhead diameter is smaller than the spinner. Smaller than it should be. The metal looks to be under stress base on the deflection under the srews. I have also seen this happen on a fliberglass spinner for the same reason. I have also seen 2 different planes sling a #8 screw because of missmatched spinner/bulkheads. In both cases the screw came through the prop and damaged both blades.
It's not as close as the photo makes it look the rub marks were already on there from another prop/spinner I just haven't repainted it yet. My only intent was to show what happened not to point fingers. It is a Vans backing plate with an aftermarket spinner. The spinner manufacturer made this to work with the Van's backing plate and it was a pretty good fit. Going back to fiberglass.
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Taildrgr
Well Known Member
This post has me thinking about my spinner, too.
Mine might be the same brand aluminum spinner.
I added the aluminum plate below the prop like the fiberglass one would have which adds the additional screw to the flange. Also, my screw is closer to the edge of the prop opening.
My concern is that the flange on the other side of the prop blade still only has the one screw. Could this also be a point of failure?
Mine might be the same brand aluminum spinner.
I added the aluminum plate below the prop like the fiberglass one would have which adds the additional screw to the flange. Also, my screw is closer to the edge of the prop opening.
My concern is that the flange on the other side of the prop blade still only has the one screw. Could this also be a point of failure?
Looks like the ED for that last screw was pretty big to me as well. Having excess ED is much preferred than not enough on almost all structure, but in this case it may have been the cause of the crack due to centrifiugal force load on the unsupported edge of the propeller cut out.
That was my first thought when I saw it. The extra distance near the opening wasn't supported, it looks like about an inch or more long? The second installation photo shows the last screw very close to the edge of the opening, which gives better support, and the filler piece behind the blade will help support it as well.
Please tell me it's not a Cummins spinner. We just had a FG spinner by Jerry Herrold come apart, and we're replacing it with the Cummins. Cummins does direct that the first screw be placed 3/8" from the prop cutout. Hope it works. As you know, or soon will, it's a large PITA to go thru spinner replacement, especially as the debris from the old spinner scored the prop just a bit.
Good luck on the replacement.
Cheers,
Chip
vfrazier
Well Known Member
What Axel said seems most likely.
Use tape, if needed, to shim up any gaps in the fitment between the spinner and the spinner backplate. If the fit isn't NICE AND SNUG, you're doing it wrong. You should have to bump the spinner down into place with your hand when installing it.
Many use masking tape. I've used the green painter's tape that doesn't dry out like regular masking tape. Keep the tape evenly distributed all the way around the backplate with no lumps or gaps.
If it takes more than 2 or 3 layers of tape, maybe you should reconsider the fit.
Others please chime in if I've misspoke here!
YMMV!!!!
Use tape, if needed, to shim up any gaps in the fitment between the spinner and the spinner backplate. If the fit isn't NICE AND SNUG, you're doing it wrong. You should have to bump the spinner down into place with your hand when installing it.
Many use masking tape. I've used the green painter's tape that doesn't dry out like regular masking tape. Keep the tape evenly distributed all the way around the backplate with no lumps or gaps.
If it takes more than 2 or 3 layers of tape, maybe you should reconsider the fit.
Others please chime in if I've misspoke here!
YMMV!!!!
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KatieB
Well Known Member
Just a theory...
Not saying you have a Cummins spinner there, but here's my experience with aluminum spinners...
We use Cummins aluminum spinners on our Jabiru LSAs. Been using them since 2008 or so... probably close to 80 airplanes, plus Arion Lightnings. I've seen very few cracks, and the ones I have seen were small and attributed to over-tightening of the screws. I haven't seen anything catastrophic like the OP's picture. Of course, we fly with less horsepower and fewer Gs as well.
The reflection on the spinner in the OP's photo indicates a depression around the screws, which makes it appear that the screws are too tight. We recommend our customers to tighten them down just until snug with a hand screwdriver-- just until the plastic washers begin to compress, and almost zero distortion in the reflection around the screw.
Also, our cones and backplates are match drilled as a finished set at Cummins. If the Van's backplate has a slightly different angle to the flange than the spinner cone and you tighten it down that much, I could see it forming a stress riser and cracking over time--especially with the large distance between the prop cutout and the torn hole, which probably allowed the edge portion to vibrate excessively. But the spinner manufacturer would have more data about that.
Not saying you have a Cummins spinner there, but here's my experience with aluminum spinners...
We use Cummins aluminum spinners on our Jabiru LSAs. Been using them since 2008 or so... probably close to 80 airplanes, plus Arion Lightnings. I've seen very few cracks, and the ones I have seen were small and attributed to over-tightening of the screws. I haven't seen anything catastrophic like the OP's picture. Of course, we fly with less horsepower and fewer Gs as well.
The reflection on the spinner in the OP's photo indicates a depression around the screws, which makes it appear that the screws are too tight. We recommend our customers to tighten them down just until snug with a hand screwdriver-- just until the plastic washers begin to compress, and almost zero distortion in the reflection around the screw.
Also, our cones and backplates are match drilled as a finished set at Cummins. If the Van's backplate has a slightly different angle to the flange than the spinner cone and you tighten it down that much, I could see it forming a stress riser and cracking over time--especially with the large distance between the prop cutout and the torn hole, which probably allowed the edge portion to vibrate excessively. But the spinner manufacturer would have more data about that.
AX-O
Well Known Member
That's how we fixed them. We used plastic/vinyl tape.
