Rob,
I've done enough 2 seat cross country flying to
realise the fun involved, I'm talking aerodynamics.
Harry,
There may be more wetted area and cross section
on the 2 seat fuselage but comparing a Discus2 B
to an Arcus (this necessarily approximate) I get
about 32% more cross section on the Arcus
fuselage and about 49% more wetted area. Shape is
similar so I'd expect similar drag coefficients.
The mass is 800 Kg vs 525 at gross which is 52%
greater so at any given sink rate the POWER is
52% greater. The wing area is 15.6 M^2 vs 10.16
M^2 so a ratio of 1.54 (rounded up).
No large differences (slightly worse at 750Kg)
and as the Arcus has flaps I'd expect it to
perform the same at mid range speeds and better
at high speeds where the Standard Class glider
starts to go out of the low drag region of the airfoil.
Span loading is different though (mass per unit
span) for the Arcus 800/20 =40, for the D2 525/15
35. Induced drag is dependent on the square of
the span loading - derived here
http://aerocrafty.blogspot.com.au/2013/06/span-loading.html
(weird website behaviour on my office PC but
works Ok in the iPad in Chrome) so yes, the two
seat Arcus and ASG32Mi likely will climb worse
than the 15M standard class glider even though
the Reynolds numbers on the Arcus wing are 15%
higher (lower profile drag coefficient). Why the
high speed performance is worse is a mystery.
I don't have any numbers on the height and width
of the ASG32 fuselage but if less than that of
the Arcus I'd expect an improvement.
I wouldn't draw any conclusion about the ASG32
performance from Finland except that it is
clearly not a terrible glider in performance
compared to the Arcus and looks nice.
Mike
At 10:33 PM 12/07/2014, you wrote:
Mike,
Itâs all about driving a large fuselage
through the air. The quite small size difference
between say, a Discus A and B fuselage makes an
appreciable difference in performance,
particularly at higher speeds. Compare the
massive size difference between an ASG 29 and a
two seater fuselage. I donât know what the
actual drag figures are but they must be a large
difference. Likewise the two seater ASH 25 and
Nimbus 3DMs and 4DMs are left far behind the
ballasted 18 metre gliders when the speeds get
up a bit. The actual Arcus fuselage is very
similar to the 20 year old Nimbus 3D fuselages
so I guess there was not much scope to improve
them much.The Jonkers JS fuselage is reputed to
be an exact copy of an earlier German glider.
Actually expected the new Schleicher 32
fuselage, being a new design, to have lesser
drag but the information from Finland is not
indicative of a substantial improvement. Time
will tell. Am sure you could give us some useful
information on drag calculations,
Harry Medlicott
From: <mailto:thebunyipboo...@gmail.com>Rob Izatt
Sent: Saturday, July 12, 2014 7:09 PM
To:
<mailto:aus-soaring@lists.internode.on.net>Discussion
of issues relating to Soaring in Australia.
Subject: Re: [Aus-soaring] 20M gliders
You can get two people in a two seater and share
the fun which is the wholepoint of said two
seaters. Without handicaps glider comps would be even less viable.
On 12 Jul 2014, at 5:59 pm, Mike Borgelt
<<mailto:mborg...@borgeltinstruments.com>mborg...@borgeltinstruments.com>
wrote:
From what has been written here over the last
few days, it is disappointing that a new
flapped 20M two seater doesn't have as good
performance as a 15M unflapped glider.
Mike
Borgelt Instruments - design & manufacture of
quality soaring instrumentation since 1978
www.borgeltinstruments.com
tel: 07 4635 5784 overseas: int+61-7-4635 5784
mob: 042835 5784 : int+61-42835 5784
P O Box 4607, Toowoomba East, QLD 4350, Australia
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Borgelt Instruments - design & manufacture of
quality soaring instrumentation since 1978
www.borgeltinstruments.com
tel: 07 4635 5784 overseas: int+61-7-4635 5784
mob: 042835 5784 : int+61-42835 5784
P O Box 4607, Toowoomba East, QLD 4350, Australia
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