The DG website has a thread dating back to 2010 on the (Clemans) Mandl
extractor.
Go to http://www.dg-flugzeugbau.de/mandl-absaugung-e.html#Zulassung then scroll
to the top of the loaded page for the start of the thread and some interesting
comments by Holger Back along with the device's background.
Best regards,
Brian DuRieu
________________________________
From: Anthony Smith <anthony.sm...@adelaide.on.net>
To: 'Discussion of issues relating to Soaring in Australia.'
<aus-soaring@lists.internode.on.net>
Sent: Tuesday, 5 June 2012 7:12 PM
Subject: Re: [Aus-soaring] Mandl extractor - Is it snake oil or is there
something to it?
Air into the cockpit must equal air out.
If you are ramming air into the cockpit and do not have a suitable exit, where
does it go? Predominantly out around the edges of the canopy and worse still
along through the wing roots and out the air brake box. In ‘very bad’ examples
it is the equivalent of having the airbrakes unlocked (but not open) which is
enough of a performance drop to be noticeable to the pilot.
The solution is to provide a ‘nice’ way of exiting the air without disturbing
the surface flow too much. The JS1 idea is very neat, but complex. The DG way
is relatively crude.
In older types , an air extractor is a way of getting your 34:1 Std Libelle (or
similar) a bit back towards the quoted 38:1.
Personally, I plan to have an extractor on the Bergfalke behind the (fixed)
main wheel. I can’t make the louvers like Jonkers, and detest the crudity of
the DG design, so I am playing with the concept of making a true reverse NACA
duct (which is NOT the same as having a NACA scoop facing backwards) behind the
fixed main wheel. The reason why? It is impossible to completely seal the nose
release in the Bergfalke. As I have air coming in continuously, I might as
well have somewhere to dump it and the air behind the main wheel is already
pretty disturbed (which may actually defeat the reverse NACA concept – the
original NACA inlet duct design was for laminar flow).
From:aus-soaring-boun...@lists.internode.on.net
[mailto:aus-soaring-boun...@lists.internode.on.net] On Behalf Of Mike Borgelt
Sent: Tuesday, 5 June 2012 5:44 PM
To: Discussion of issues relating to Soaring in Australia.
Subject: Re: [Aus-soaring] Mandl extractor - Is it snake oil or is there
something to it?
At 04:40 PM 5/06/2012, you wrote:
Not sure about independent, but Jonker does the same thing for their
JS1's, and I've heard of experimental ASW20 mods to add one.
http://www.jonkersailplanes.co.za/index.php?pageid=36
-Matthew
No the JS-1 vent is not the same as the Mandl extractor although both aim to
suck exit air out through a low pressure point. The Mandl device is on the
bottom of the fuselage and looks to be in around the trailing edge of the wing
location in the fore and aft sense. The JS-1 vent is on top of the fuselage not
far aft of the canopy and it has a little wing in it to get the air to flow
along the surface better. The JS-1 location is likely a lower pressure area
(top of wing and fat part of fuselage) than the lower fuselage lined up with
the wing TE where the pressure is about back to static pressure. Also the Mandl
extractor doesn't seem to try to flow the exit air parallel to the airstream.
Some tests with dye or tufts would be interesting as well as static pressure
measurements. Don't forget also if you manage to put the vent in a low pressure
area and close the inlet, cockpit pressure will be a fair bit lower than
outside - maybe up to 100 feet or so
altitude equivalent with consequent effects on the pressure altitude measured
by your logger.
This is by no means a new idea to have an exit vent. Wil Schumann used the back
of the gear doors as an extractor on his H301b Libelle. I had an exit vent on
my Mini Nimbus in 1978. Gliders are coming out with better cockpit ventilation
nowadays. It took long enpough. failure to provide adequate ventilation in the
cockpit is like failing to provide proper cooling for the engine in a powered
aircraft.
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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