Alon Aircoupe Cabin Ventilation Kit
Background Info:
The cockpit of the Alon Aircoupe tends to get very hot in flight in the summer due to the great quantity of sunlight coming into the cabin through the windshield, the large sliding Plexiglas canopy and the rear windows. There is no structure to provide any shade in the cockpit.
The cockpit space of the Alon Aircoupe is ventilated by two existing, factory installed air intakes (on higher serial number airframes). One inlet is located on the front of the engine cowling below the spinner. This inlet is connected via a flexible aluminum duct to a fitting on the firewall, which allows air to flow through the firewall, through a damper assembly and through small diameter SCAT tubing to air outlets that are built into the plastic arm rest assemblies. The second factory installed air inlet is located on the leading edge of the fairing strip that covers the gap between the right hand wing stub and the right hand outboard wing assembly. This fairing strip has an opening in it with a flange attached to the back side of the fairing. A SCAT duct connects to the flange, and then passes rearward between the wing stub and the outboard wing assembly to a point aft of the right hand wing fuel tank and aft of the main center section spar. The duct then turns inboard and passes through the lightening holes in the wing center section and then enters the fuselage under the cockpit floor. The SCAT duct then runs up the right hand cockpit wall between the fuselage skin and the upholstery, forward of the passenger seat, where it connects to an adjustable air outlet assembly.
The cockpit of the Alon Aircoupe in general, and my airplane in particular, is very air-tight with no substantial means of exhausting the air that is ducted into the cabin by the above two inlet systems. So while there is a means provided to allow air into the cockpit, there is no positive means provided to exhaust that air. Therefore, the ventilation airflow is limited by the fact that it cannot easily exit the cockpit area.
A previous attempt at increasing airflow in the cabin by opening two vents between the aft baggage compartment wall and the tail cone of the aircraft resulted in no improvement whatsoever. In fact, in flight with the vents opened, no air flowed through the vents at all. This was verified by holding thin strips of tissue paper up to the vents and noting that the tissue paper didn't even wiggle.
Note that aftermarket air vents can be installed in the lower aft corners of the windshield Plexiglas, and these inlets reportedly do a good job of increasing cockpit ventilation. These vents do, however required holes to be cut in the windshield, and in my opinion, they don't look all that good on the airplane. Therefore another solution was desired.
Solution:
A simple kit was designed consisting of four 2-1/2 inch aluminum flanges, two pieces of 2-1/2 inch SCAT tubing, and two small aluminum air outlet vents to increase the airflow out of the cockpit. The idea behind the design is to suck air out of the cockpit area through the SCAT tubing and exhaust that air through the small vents that are mounted on two existing inspection plate covers under the right hand and left hand wing stubs. The high velocity airflow under the wing is used to create suction through the rear facing air outlets.
Design and Hardware:
The kit consists of the following parts:
4 ea 2-1/2 inch aluminum flanges Aircraft Spruce P/N 10350-10
2 ea 3 foot pieces of 2-1/2 inch SCAT Duct Aircraft Spruce P/N 05-29910
4 ea 2-1/2 inch Hose Clamps Aircraft Spruce P/N QS200-36H
2 ea Air Outlet Vents fabricated from 0.020 2024-T3 Aluminum
4 ea 3.5 inch diameter pieces of common vinyl window screen (to keep insects, etc, out of SCAT duct)
Miscellaneous No. 6 AN screws, washers and nuts for mounting the flanges
The total weight of these components as weighed on a digital scale is 2.1 lbs. The parts are centered near the CG of the aircraft at 43 inches aft of the datum (firewall). It is a simple matter to recalculate the empty weight and CG of the aircraft and prepare a new weight and balance form following the installation of the kit.
The outlet vents and outlet flanges are mounted on existing inspection plate covers that were installed earlier in compliance with a center section inspection AD. These inspection plate covers were part of a Univair kit, and are mounted to reinforced rings on the bottom skin of the wing center section stubs with three No. 8 screws and nutplates each. These inspection plates are firmly attached to the wing skin. They are well outboard of the centerline of the aircraft and are well outboard of the engine exhaust flow path. (The exhaust flow is not a factor anyhow, because these vents pull air out of the cockpit, not into the cockpit.)
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