Hello Paul The reason why I had reservations entering the debate in the first place was concerns about a large number of e-mails that need answering. I will answer yours but ask for everyone's understanding that I can not continue to do so! You are right - the ventilation air needs to escape again and this needs to be managed. For this very reason there are several openings (call them air extractors if you like) at the tail end of a glider. Even a partial sealing of these openings causes a large reduction in ventilation airflow. But not only that - it is also detrimental in terms of performance as the air attempts to escape in other (less desirable) places. I trust this helps. Kind regards to all Bernard
_____ From: aus-soaring-boun...@lists.internode.on.net [mailto:aus-soaring-boun...@lists.internode.on.net] On Behalf Of Paul Bart Sent: Thursday, 24 February 2011 2:18 PM To: Discussion of issues relating to Soaring in Australia. Subject: Re: [Aus-soaring] Air vent Hi Bernard Firstly let me say that I have no credentials in glider design, so please take my comments on that basis. Clearly, with the vents open, there is a considerable inflow into the cockpit. That is only possible if an equal amount of air leaves the cockpit. So I am wondering, would it not be better if the outflow was managed? Perhaps it already is. Cheers Paul On 24 February 2011 13:35, Future Aviation <ec...@internode.on.net> wrote: Hello Gary, hello all I wasn't going to enter the debate but now I feel that it is about time to put the record straight. A) The "Mandl air extractor" is anything but new. Schleicher experimented with a similar device more than 20 years ago and so did Dick Buttler in the US. B) If my information is correct both parties have found that considerable drag is created where the (almost stationary) ventilation air is meeting the free airflow again. C) Statements such as "The size and geometry of the extractor lower the pressure level inside the cockpit to ambient levels and allow the ventilation air to seamlessly re-enter the external flow outside the fuselage." can only be regarded as an attempt to mislead the gliding public. No air extractor known to mankind can accelerate the ventilation air without causing severe turbulence and hence create considerable aerodynamic penalties. D) If I remember correctly onother manufacturer has claimed that his "air extractor" improves the performance of his glider by 3 or even 4%. Claims like these are utter nonsense! They were even privately disputed (laught at) by a member of his own design team. E) There are a number of disadvantages with another opening in the fuselage and the ingress of moisture is only one of them. I hope this brings the debate back to a rational level. Please let me appologise upfront if I have hurt someone or destroyed previously held beliefs. Kind regards to all! Bernard -----Original Message----- From: aus-soaring-boun...@lists.internode.on.net [ <mailto:aus-soaring-boun...@lists.internode.on.net> mailto:aus-soaring-boun...@lists.internode.on.net] On Behalf Of gstev...@bigpond.com Sent: Wednesday, 23 February 2011 9:18 PM To: Discussion of issues relating to Soaring in Australia. Subject: Re: [Aus-soaring] Air vent Mike, I am deleting old emails. I came across this one of yours. Re rain ingress - you are an inventive sort of person -do you have any suggestions? I note you did not suggest anything at the time. Is it a problem, other than if the glider is tied down outside? Have you further considered the matter? If so what did you conclude? Has anybody else given the matter any thought? Gary ----- Original Message ----- From: "Mike Borgelt" <mborg...@borgeltinstruments.com> To: "Discussion of issues relating to Soaring in Australia." <aus-soaring@lists.internode.on.net> Sent: Friday, July 30, 2010 6:14 PM Subject: Re: [Aus-soaring] Air vent > > > When we were discussing the DG Mandl extractor air vent some time > ago I think I mentioned that the best location would be on top of > the fuselage in the low pressure area. > > It seems either somebody saw that or had the same idea. Blending the > vent tangentially to the rear was always a good idea and is commonly > used in engine cooling. Nice touch to add the louvre. This looks far > better than the relatively crude DG vent. Might want to organise > something so rain doesn't get in though. > > <http://www.streckenflug.at/news/js_communication_2010_07.pdf> http://www.streckenflug.at/news/js_communication_2010_07.pdf > > Mike > Borgelt Instruments - manufacturers of quality soaring instruments since > 1978 > phone Int'l + 61 746 355784 > fax Int'l + 61 746 358796 > cellphone Int'l + 61 428 355784 > > email: mborg...@borgeltinstruments.com > website: www.borgeltinstruments.com > > _______________________________________________ > 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> http://lists.internode.on.net/mailman/listinfo/aus-soaring ---------------------------------------------------------------------------- ---- No virus found in this incoming message. 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