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davidjoyce(at)doctors.org
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 Posted: Sat Aug 25, 2012 3:20 am Post subject: Landing mishap/ prop twist |
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Duncan, As all Europa props are close to 1600mm it makes
very little difference. The actual maths are set out in
the article 'Does propeller twist matter?' in Europa Flyer
no 65 (available like all back numbers on the beautiful
new Europa Club website at
www.theeuropaclub.org/the-club/europa-flyer/ ). For a
1600mm prop, the amount of twist needed rises rapidly from
6 degrees at 20 kts to 24 at 100kts but then levels off to
just 29 degrees at 160 kts before coming down somewhat at
higher speeds. As the curve flattens out in the working
range an increase in diameter just moves you marginally
along this relatively flat segment. In practice 26
degrees is within 3 degrees of optimal for speeds between
90 odd kts and 200+ kts, whereas 12 degrees (your Warp
drive blade) is optimal for sitting stationary on the
ground with the throttle half open (this giving an airflow
of 40kts past the cock[pit!)
Regards, David
On Sat, 25 Aug 2012 10:12:17 +0100
"Duncan & Ami" <ami-mcfadyean(at)talktalk.net> wrote:
[quote]
<ami-mcfadyean(at)talktalk.net>
You'll also need to measure the diameter for any
meaningful comparison;
generally, as diameter increases, the required overall
prop twist along the
blade needs to be slightly less.
Then there's the fact that most manufactured blades in
our class of use
(e.g. Warp Drive, Arplast) start off as a larger
diameter prop (with a
better amount of twist) which is then cut down to the
required diameter.
This of course removes twist, usually to well below the
optimum!
Duncan McF.
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Duncan McFadyean
Joined: 18 Jan 2011
Posts: 224
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| Posted: Mon Aug 27, 2012 5:21 am Post subject: Landing mishap/ prop twist |
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<<.whereas 12 degrees (your Warp drive blade)>>
David the Warp has 19.5 degrees twist at 72" diameter, as measured to the
point that the undersurface no longer has a point that is flat. All other
incarnations of the Warp Drive come from the same mould and are cut down to
the required size.
Removing 5" from the tip of a Warp Drive takes off about 1.75 degree of
twist; I have some tips spare if you'd like one!
Whilst this twist is measured from the point adjacent to the root where the
underside still has a flat area; it could be argued that measuring from
closer to the root where there is at least a 3:1 symmetrical airfoil section
will indicate more twist.
Not forgetting that an asymmetrical aerofoil will need at least a few
degrees of negative incidence before it starts to generate 'reverse thrust'.
I agree that there's not enough!
The fixed pitch Arplast has more twist (about 22 degrees), and other
versions (the faster VP blade) more still.
Duncan McF.
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davidjoyce(at)doctors.org
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| Posted: Mon Aug 27, 2012 5:55 am Post subject: Landing mishap/ prop twist |
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Duncan, when I wrote my article I was not able to come by
any definition of twist so took the difference in pitch at
tip and 1/3 radius. If you are measuring somewhere else
then it isn't possible to make comparisons, but at the
time Europa Warp drive blades were around 12 degrees
measured thus.
Regards, David
On Mon, 27 Aug 2012 14:20:51 +0100
"Duncan & Ami" <ami-mcfadyean(at)talktalk.net> wrote:
[quote]
<ami-mcfadyean(at)talktalk.net>
<<.whereas 12 degrees (your Warp drive blade)>>
David the Warp has 19.5 degrees twist at 72" diameter,
as measured to the
point that the undersurface no longer has a point that
is flat. All other
incarnations of the Warp Drive come from the same mould
and are cut down to
the required size.
Removing 5" from the tip of a Warp Drive takes off about
1.75 degree of
twist; I have some tips spare if you'd like one!
Whilst this twist is measured from the point adjacent to
the root where the
underside still has a flat area; it could be argued that
measuring from
closer to the root where there is at least a 3:1
symmetrical airfoil section
will indicate more twist.
Not forgetting that an asymmetrical aerofoil will need
at least a few
degrees of negative incidence before it starts to
generate 'reverse thrust'.
I agree that there's not enough!
The fixed pitch Arplast has more twist (about 22
degrees), and other
versions (the faster VP blade) more still.
Duncan McF.
--
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