2 vs 3 blade props

[David Lockhart]

Wayne,

You've hit on a couple of the big factors - mixture and pipe length.  With a
2C , the prop that works best is often the prop that the engine is best
tuned for.  Same thing goes for the 4C - but the current 4Cs are pretty
tolerant of prop/mixture changes so long as the overall load of the prop is
similar.

In very general terms, given all other things equal (RPM, blade shape,
airfoil), a 3 blade (or 4 blade) that is equivalent to a 2 blade (3 blade
having a reduced diameter) will have a slower downline and less unload -
less unload is part of what makes the speed easier to manage.  It will also
be quieter (reduced tip speed) and not pull quite as hard in verticals (less
diameter is less efficient).

Regards,

Dave


----- Original Message -----
From: "Wayne Galligan" <wgalligan at goodsonacura.com>
To: <discussion at nsrca.org>
Sent: Wednesday, August 11, 2004 11:32 AM
Subject: 2 vs 3 blade props


> I  have recently been experimenting with 2 and 3 blade props on my OS 1.40
> in my Entropy.   I was trying to get this airplane to fly similar in speed
> to my Aries as the Aries is a wide body and there was too much difference
in
> the speeds between the two airplanes.  I have not had the chance to use
one
> of Dave Lockharts prop but this is what I am using.
>
> 3 blade 16x11  GSW c.fiber
> 3 blade 16.5x12 Bolly c.fiber
> 2 blade 17x12 reg APC
> 2 blade 17x13 reg APC
>
> 15% Cool Power and c.fiber proto-type pipe by AeroSlave.
>
> The 3b 16x11GSW gave good performance both top end(8350rpm) and on
downline
> braking.  It is 1 oz lighter then the APC so it would accelerate quicker
and
> had good vertical. I had balance issue using this prop as I was at the
back
> of my c.g. already.  I flew this prop at the Houston Contest with good
> results.
>
> The 3b 16.5x12 Bolly had similar performance to the GSW but was noisier
and
> sounds much different then the other props.  A sound that I didn't like.
It
> made kind of a burbling like noise but engine was running fine.  This prop
> has narrow blades and does not seem to have more pitch then the GSW even
> though it was a 12 vs 11 pitch.
>
> 2b 17x12  APC works good in windy conditions and most all around flying.
> This prop needs a little more throttle management as it will  unload more
> then the 3 blades or 17x13.
> and it was the right prop at Lubbock at altitude and after carb
adjustments.
>
> 2b 17x13 APC  seems to be close in comparison to the 3 blades in downline
> braking when the pipe and mixture is set right.  It is much quieter of all
> the props and is more linear in throttle response.  I liked this prop best
> on the Entropy that I am flying that is not as wide a body as some of the
> new planes and is a little faster then like my Aries.
>
> Pipe tuning is definitely an issue when switching props so best results
may
> not be seen unless you retune.   So far the APC 2 blade 17x13 has gotten
the
> nod from me until I get one of  Dave Lockharts 3 blades to try.
>
> Wayne Galligan
>
> .
>
>
>
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