(2)
Impregnate each cloth patch with BMS 8-301, Class 3 prepared per BAC 5010, Type 113, or per manufacturer's instructions, and place between two pieces of PVA parting film.
NOTE: Weight of adhesive approximately equal to the weight of the dry fiberglass cloth is required to impregnate cloth.
E. Place repair patch.
(1)
Apply a coat of BMS 8-301, Class 3, adhesive mixture, prepared per BAC 5010, Type 113, or per manufacturer's instructions, over the repair area.
(2)
Remove parting film from one side of the smallest ply of the patch and place its exposed face against the repair area.
(3)
Use a squeegee over parting film that covers the patch to remove wrinkles and entrapped air. Do not remove too much adhesive by excessive pressure. This avoids producing a patch deficient in adhesive.
(4)
After removing parting film from the outer face place the next larger size ply of the impregnated patch over the ply on the repair area with at least 0.80 inch overlap all around.
(5)
Place succeeding plies of the patch as described in steps (3) and (4) above.
NOTE: On last two plies required, use a complete wrap around ram air duct prepared area as in step C. above. Use adhesive tape to secure last two plies during wrapping operation.
(6)
After placing the last ply, recover the entire lay-up with a piece of parting film extending about 0.50 inch over edges of the patch.
(7)
Sweep excess adhesive to edges of parting film thereby fairing the edges of the patch to the contour of the repair surface. All loose threads shall be embedded in resin.
(8)
Wipe off any excess adhesive that has been squeezed out at the edges of the parting film.
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21-52-101 Page 802 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 01/00
500 Ram Air Duct Repair
May 15/68 Figure 801 21-52-101
Page 803
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
F. Cure Impregnated Patch
(1)
Required curing time for BMS 8-301 adhesive mixture is about 6 days at 75°F or 1 hour at 165°F. A cured patch is hard and resounds when tapped lightly with a coin or other light metallic object.
(2)
Remove parting film from patch after curing.
(3)
The patch should be free from pits, blisters, starved areas, and excess resin deposit.
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21-52-101 Page 804 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 01/00
EQUIPMENT COOLING SYSTEM - DESCRIPTION AND OPERATION
1. General
A. The equipment cooling system cools the electrical and electronic equipment on the racks in the electronic compartment, some circuit breaker panels in the control cabin and the main instrument panel. Most of the equipment is cooled by "draw around" air. Equipment on shelves E3-1 and E3-3 is cooled by "draw through" air.
B. Cabin air is the cooling medium. It is drawn through and around the equipment into a system of ducts and manifolds. Some of the ducts and/or manifolds form the equipment mounting racks. The system leads to the blower inlet plenum (Fig. 1). Two blowers are connected to the inlet plenum. The blowers exhaust into an exhaust plenum. The exhaust plenum contains an automatic flow control valve, a check valve and an exhaust port. A condensate drain tube from the passenger cabin conditioned air distribution system is connected to the exhaust port. A drain port with orifice in the exhaust port allows moisture, which may have condensed in the distribution manifold duct assembly to be removed before it can get into the overhead distribution system. The blower inlet plenum is outboard of Rack E3. The exhaust plenum is outboard of Rack E3 and under the electronic compartment floor. When the airplane is on the ground or during low-altitude flight, one of the blowers draws the cooling air through the ducts and discharges it overboard through the automatic flow control valve and the exhaust port. During flight, the cabin-to-ambient pressure differential is adequate to close the flow control valve. The air that flows through the system is then discharged under the forward cargo compartment floor. The air circulates between the cargo compartment insulation and lining and thus heats the cargo compartment before it is discharged overboard through the forward outflow valve.
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