OK, I’ll bite. What exactly is it about the shape of the Arcus that you don’t like?
From: aus-soaring-boun...@lists.internode.on.net [mailto:aus-soaring-boun...@lists.internode.on.net] On Behalf Of Mike Borgelt Sent: Monday, 14 July 2014 12:00 PM To: Discussion of issues relating to Soaring in Australia. Subject: Re: [Aus-soaring] 20M gliders 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, It’s 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 don’t 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: Rob Izatt <mailto:thebunyipboo...@gmail.com> Sent: Saturday, July 12, 2014 7:09 PM To: Discussion of issues relating to Soaring in Australia. <mailto:aus-soaring@lists.internode.on.net> 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 < mborg...@borgeltinstruments.com <mailto: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 <http://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 _______________________________________________ Aus-soaring mailing list Aus-soaring@lists.internode.on.net To check or change subscription details, visit: http://lists.internode.on.net/mailman/listinfo/aus-soaring _____ _______________________________________________ Aus-soaring mailing list Aus-soaring@lists.internode.on.net To check or change subscription details, visit: http://lists.internode.on.net/mailman/listinfo/aus-soaring _______________________________________________ Aus-soaring mailing list Aus-soaring@lists.internode.on.net To check or change subscription details, visit: http://lists.internode.on.net/mailman/listinfo/aus-soaring Borgelt Instruments - design & manufacture of quality soaring instrumentation since 1978 www.borgeltinstruments.com <http://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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