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I normally think of black boots on a prop as being for de-icing. However, the Extra 300 is not suitable for known-icing conditions, or even IMC flight. (It's AFM says "Only VFR flights at day are allowed").

Considering the Extra 300's aerobatic mission, the gyroscopic loads on the engine are fierce. The upshot is that the manufacturer would not include a single extra gram more than necessary here.

So why are they there/what do they do? It has the owner and I stumped.

enter image description here

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    $\begingroup$ Since you're in contact with the owner, they can touch and feel the black section -- does it feel like plastic/rubber, or paint? $\endgroup$ – Zeiss Ikon Apr 29 at 12:10
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    $\begingroup$ Interesting question. Doing a Google image search for extra 300 propelller shows that many (but not all) have the same thing. $\endgroup$ – CGCampbell Apr 29 at 13:54
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The inner portion of the blade is protected by a self-adhesive PU-strip, unless the blade is equipped with a de-ice boot.

The outboard edge as you can see in the very lower-right corner is protected with a stainless steel erosion sheath. Since the inboard section is slower (radial speed), its protection is a lighter polyurethane-strip/tape.

enter image description here

The Extra 300's service manual lists the 3-blade prop as one of two MTV-9 series (you can see the MT logo already in your photo). The above quote and illustration are from the MTV-9 series operation manual from mt-propeller.com. An example tape is the 3M 8663HS, which comes in black or transparent.

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