Hi Peter
My understanding is that balancing and vibration can be two separate issues.
All materials have a rotational frequency about which they vibrate. Even a
perfectly balanced engine can need a torsional damper to ensure that this
frequency is transferred to rev ranges outside the normal operating range of
the engine. Prop indexing assists in this and the rule of thumb we have
discussed recently on this and the Corvaircraft list (search the archives)
is that the prop blade should be mounted at 90 degrees to the nearest crank
throw. Sometimes balancing, dampers, sliding crank counterweights and
indexing are still not enough and in those cases we see tachos placarded
against certain rev ranges (eg., the Cutlass O-360).
Regards John
- Original Message -
From: "Peter Diffey" <pe...@heroic.co.uk>
To: <kr...@mylist.net>
Sent: Sunday, November 27, 2005 8:47 AM
Subject: KR> prop indexing - dunno what that is !
> Hi,
>
> I guess that indexing a prop is a US term, cos I have not heard it in
> UK, so I am guessing what is meant.
>
> I think in many cases it is a practical choice rather than an
> engineering decision.
>
> Assuming that the prop is well balanced, the orientation should not make
> any difference what way round it is, however in the case of props on
> hand swung VW engines, if you put the prop on 120 degrees out, it will
> be a pig to start, because you reach TDC with the prop at something like
> 300 true, or down by your boot laces.
>
> I know that there are blokes out there that like to try anything just to
> prove it can be done
>
> Ah, finally, *ugger, *ollocks and other anglo-saxon words are perfectly
> acceptable english when the prop kicks back and catches you across the
> knuckles.
>
> Pete Diffey
> St Albans, UK
>
>
>
>
>
>
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