In my usual fashion it has been 'modded'. I always found the original design of spinner to be a bit blunt looking compared to the rest of the aircraft, so this was my opportunity to change it's shape.
My boss loaned me an old spinner from his plane and I used that to make a 'splash mold' part off the front of it. I then combined that part with a replacement spinner that was kindly sent by Matthias.
The result is a sharper look - more Mark 9 Spitfire than the old rounded Mark 1 looking spinner.
The other modification is the addition of a front plate. This has added a great deal of rigidity and security to the attachment of the spinner, I feel quite confident it will not come off again!
The front plate is made using the same schedule as the back plate. A 3mm thick sheet of carbon is cut out and drilled to match the bolt holes in the crush plate. Then an angled flange of carbon is added to the edge, projecting forward, giving a large area of contact with the inner front of the spinner.
The spinner was fitted and aligned using a laser level before all the holes were drilled. Then nut plates were fitted to the inside of the front and back plate flanges. 12 on the back plate and 4 on the front plate. I've gone for metric anchor nuts this time round and button head Allen screws with fibre washers underneath for security as I found the Tinnermans with the sprung plate to be unreliable over time.
Everything runs very smoothly now. However I will still do a dynamic balance to see what the vibration levels are and if they can be improved at all.
Regarding the old spinner - the conclusion was that it was a substandard part.
It was not made by the factory but supplied to me by Hercules propellors using their own mold. They had not followed the same layup schedule as the factory spinner. They only put carbon on the back inch or so where the fasteners go for the backplate - the factory made spinners have carbon all the way up to and beyond the cut outs for the propellor. Therefore the old spinner was vulnerable to cracking in the prop cut out area.
I believe this is what must have happened, a crack formed and then quickly propagated on the fateful flight, the spinner ripping open once the high pressure air got inside and popped it off, wrenching the fasteners as it went. We will never know for sure exactly what happened as the spinner was disintegrated but the above seems to be the most likely cause. Please check your spinner if you believe it was made by Hercules as they are not fit for purpose.
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| Original and new shapes compared. |
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| Front plate for added security, micro on the edge was done to form fit to the inside of the spinner. |
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| Side view of front and back plates |
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| All done and looking good |
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| I think this shape of spinner suits the Twister better |
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| Button headed Allen screws with fibre washers underneath with a front plate. This is the same standard used on certified aerobatic aircraft |
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