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MYR
04-29-2009, 06:02 AM
The objective of this thread is to try to get ideas from the readers as to improve the cowlings cooling for air cooled engines.

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Could someone tell me why the NACA air inlet of Kitfox and Jabiru planes are placed point ahead ? Why are these air inlets not placed the point towards the rear ?

Bernouilli proved that when the air speed increases the pressure decreases.
With the point of the inlet ahead and the large width at the rear, the air speed dicreases and the pressure increases.
In my mind, if the pressure of the air flow increases, it prevents the warm air that is around the engine to go out towards the cowling air outlet.
I should have placed the point toward the rear as to decrease the air flow pressure and create a air suction like in a Venturi tube.


Please explain me if I am right or wrong ?
Is this idea of making a suction in the bottom of a cowling with a venturi effect is realistic or not ?

MYR
04-29-2009, 12:31 PM
http://www.hiboox.fr/go/espace-membre/albums/organiser_album.php?cle_album=b1e22866430694c1efe5 8f3568bd054c#Here is a plane with the point of the NACA air inlet ahead, and the large width towards the rear,

Mark
04-30-2009, 07:44 AM
In this application, the NACA duct is providing ram air into the liquid cooled radiator (as well as some oil cooler installations), postioned directly behind the duct.

MYR
04-30-2009, 07:51 AM
Someone just said it to me. In this case, of course the NACA duct is in the right direction.
So, are there special KitFox cowlings for Jabiru and other air cooled engines ?
How are they ?
Could someone send some pictures ? (from outside and from inside).

SkyPirate
05-03-2009, 12:36 PM
I'm thinking it may be because of the vacuum effect from the larger outlet,..just like if you have an area that you need to remove dirt or debri ..and you can not get a vacuum hose in the area..you take a garden hose ..cut to the desired length..about 3 inches from one end ..put a hole..now put an air blower chuck pointing toward the short end of the hose..dirrect the other end of the hose to the debri area..squeeze the air chuck ..it sucks the debri right out ,..like a vacuum cleaner,..the design of the lower vent looks to be of the same nature..so you could actually put the inlet holes any where you like (As long as it is not in an area that creates a vacuum itself) ..cosmetically it looks good in front,.. I could be wrong with my conception of it's function ..but ..it makes sense to me ..

in effect the larger outlet creating the vacuum ..with the smaller inlet ..it's like putting your thumb over that same garden hose with water coming out ..it's velocity is increased (ventury effect) ,..just like the air chuck when you squeeze the handle ..faster moving air is cooler,.. lower air pressure in the front doesn't really matter due to the prop wash because it is not forced into the front inlet ..it is sucked into it,..now on the ground ..taxiing ..the it's a different story,..idle prop speeds do not create enough velocity to sufficiently cool the motor on hot days due to low velocity passing by the outlet vent..,..less vacuum ..less airflow ..excessive idleing will result in over heating.