Hi Mike and others!
It wasn't only Wil Schuemann who experimented with an air outlet.
About 25 years ago Dick Buttler worked with Schleicher to fit
an air extractor to his ASW 22. Martin Heide put an air outlet
(similar to the Mandl device) on the undercarriage door of his
ASH 25 prototype but was unable to measure a pressure difference in
the cockpit. This undercarriage door is currently in my
workshop in Adelaide.
The US Schleicher agent has developed an air extractor for the ASG 29
in close cooperation with Michael Greiner, the designer
of the aircraft. It feature a rather substantional funnel which is
designed to accelerate the cockpit air prior to entering the free
airstream. By doing so the turbulence around the air extractor is
reduced and the drag is supposed to be minimised.
The big question is whether the drag created by the turbulence around
the air extractor is less than the drag caused by the escape
of air around the canopy frame. In any case, a performance gain of
anywhere near four L/D points is totally unrealistic. If only half
true the LS10 would win every competition .......
I hasten to add that cockpit ventilation is likely to be improved as
the ventilation air can escape without finding its way through
the tail boom to the rear of the fuselage. That in itself is an
advantage - especially in a country like Australia.
Kind regards to all
Bernard
----- Original Message -----
From: "Discussion of issues relating to Soaring in Australia."
@lists.internode.on.net>
To:"Discussion of issues relating to Soaring in Australia."
Cc:
Sent:Tue, 05 Jun 2012 18:13:59 +1000
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 [1]
-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
@lists.internode.on.net>
Links:
------
[1] http://www.jonkersailplanes.co.za/index.php?pageid=36
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