On Tuesday, October 17, 2017 at 1:12:58 PM UTC-4, Paul Agnew wrote:
The purpose of the extraction vent is to increase the available airflow to the cockpit. The ASW-19 has NACA vents under the wing roots to draw air in, but there is no clear path for it to exit. The extraction vent, and modification of the bulkhead to allow airflow, gives the air someplace to go and reportedly greatly increases the comfort level in the cockpit. Noise reduction is primarily due to being able to keep the canopy vent closed and a reduction of "pressurized" air leaking under the canopy seals.

Any performance benefits are a bonus in my book and not a serious consideration unless you are a hard-core performance tweaker looking for every .1% gain.

Paul A.

Some experience on this topic(about 80 sold for 9 types)leads me to comment..
1) Extractors can and do help ventilation(and removal of exhaled moisture). They are a big improvement in 19's and 20's, maybe a bit less so in ships with better ventilation to start with.
2)Sealing the cockpit area off from the aft fuselage has a meaningful effect on this extraction by increasing the pressure differential between the cockpit and ambient. Without sealing, the pressure reduction is limited by air coming from the rudder horn and hinge area that is low pressure, but not as low as the vent.
3) Canopies leak. It is better to have the leak be into the cockpit and not out over the wing root area. Commonly one of the noises heard is air being sucked in around the edges of the little vent window.
4) The extractor shown may well infringe on the patent applied for by JS or their resources.

FWIW- Hard core performance guy.
UH