What air ducts are required, if I want to replace all of the air ducts in my Sundowner, Sport, Super, or Musketeer?
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Technical Editor:
Below are all the part numbers and dimensions for the original ducts in all of the 1975 and later 19/23/24 airframes. The pre-1975 planes, and the Duchess twin, have many similarities, but also many differences. The IPC, and other FAQs, should be checked for specifics on earlier models (and the Duchess).
NOTE: If ducts are ordered from Custom Ducts, I recommend that you request molded cuffs that are one inch wide, rather than the standard 3/4″ cuffs called out in these part numbers.
111728-8B8-10 (1ea) This is the very short, single, 1.25” ID by 5” long duct, with a 3/4″ cuff on each end. It connects the splitting Tee to the inline Wye feeding the two center-pedestal Wemac outlets. It is located under the instrument panel, next to the co-pilot’s left foot.
111728-8B8-19 (1ea) This is the short, single, 1.25” ID by 9.5” long duct, with a 3/4″ cuff on each end. It connects the inline Wye to the RH center-pedestal Wemac outlet.
111728-8B8-46 (1ea) This is the moderate-length, single, 1.25” ID by 23” long duct, with a 3/4″ cuff on each end. It connects the inline Wye to the LH center-pedestal Wemac outlet.
111728-8B8-33 (2ea) This is the short 1.25” ID by 16.5” long duct, with a 3/4″ cuff on each end. It connects the cheek air box to the RH and LH Wemac in the corners of the instrument panel (two required).
NOTE: I recommend that these be ordered from Custom Ducts, with molded cuffs that are 1″ long and made slightly oversize; 1.31″ ID (1 and 5/16″, on both ends). This will make it much easier to install these ducts on the plastic fittings, without fitting damage.
Instrument panel corner Wemac outlet hint: The aft (outlet end) duct cuffs can be positioned properly (angled up) by placing a short length of 3/4″ heater hose under them, in the airframe channel. The Wemac air inlet will slip right into the cuff, as the trim is reinstalled; no clamp needed. The slight compression placed on the duct, as the trim is slid forward into position, will keep the duct well attached and sealed.
111728-8C8-14 (1ea) This is the very short, single, 1.5” ID by 7” long duct with a 3/4″ cuff on each end. It connects the firewall diverter outlet to the right-side splitting Tee, forward of the co-pilot’s left foot.
NOTE: If ordered from Custom Ducts, request that the cuff on one end of this duct (the diverter end) be molded 1/16″ oversize, for easier installation on the plastic diverter.
111728-8C8-264 (2ea) This is the long duct to the rear seat lower spar cover heating outlets (two ducts required); 1.5″ ID by 132″ long. You will have extreme difficulty getting the old duct out of the forward cabin area, and even more difficulty trying to get new 1.5” duct installed. I strongly recommend that you use 1.25” SCEET (red silicone) duct instead, for this particular application. It will go in far easier, and won’t cause as many interference and corrosion problems due to an overly-cramped installation. The smoother inner liner will flow as much or more air as the 1.5” CEET duct. You can use short lengths of the 1.5” duct to connect to fittings. The 1.25” duct is a fairly snug fit inside the 1.5” duct, and can also be sealed with red RTV compound. The SCEET will never absorb moisture, regardless of age.
NOTE: The preferred alternative is to order two special ducts from Custom Ducts. They will consist of 1.25” ducts, with bonded-on lengths of 1.5” turbo duct on both ends (to form the needed 1.5” diameter cuff/adapter).
111728-8D8-23 (2ea) This is the short 2.00” ID by 11.5” long duct which connects the cheek air box to the RH and LH air inlet boxes beneath the sides of the windshield (two required).
NOTE: I recommend that you order these from Custom Ducts. They should be 12″ long rather than 11.5″. Both ends should have 1″ long molded cuffs, molded to an oversize 2.125″ diameter (2 and 1/8″ ID). This will make these much easier to install on the plastic boxes at each end, without damage to the boxes.
Just use sturdy Ty-wraps for clamps; no metal clamps allowed (they crush the plastic parts).
Pedestal Wemac hint: Remove the Wemacs with trim. Make note of the Wemac trim orientation (vertical or horizontal rectangle); the Wemac outlet orientation (angled toward feet or knees), and rear air inlet plenum orientation (where the hose attaches). If these don’t go back in the same way, duct routing will be difficult. Let the cuffed end of a new duct stick out of the Wemac hole; attach it to the Wemac inlet adapter with a Ty-wrap; then push the duct and Wemac back into the hole, and attach the Wemac trim to the pedestal.
Instrument panel corner Wemac outlet hint: The aft (outlet end) duct cuffs can be positioned properly (angled up) by placing a short length of 3/4″ heater hose under them, in the airframe channel. The Wemac air inlet will slip right into the cuff, as the trim is reinstalled; no clamp needed. The slight compression placed on the duct, as the trim is slid forward into position, will keep the duct well attached and sealed.
NOTE: Child’s seat installations in some Supers and Sierras have short duct extensions for heat and/or ventilation. Those items are not included in this listing, for a couple of reasons. Contact me if you need assistance with those ducts.
CAUTION: Take extra special care with the cheek air inlet boxes, under the forward fuselage just ahead of the LH and RH corners of the windshield. They are extremely fragile, and none can be found. They can be repaired using paper-thin fiberglass cloth with home-made white ABS cement. If you choose to use an epoxy resin with the cloth, rather than ABS cement, first make sure that it does not dissolve the plastic box. You can also use dabs of Super Glue, with a matching accelerator, to tack the fiberglass in place. It will probably take too much Super Glue, to use it exclusively as the reinforcing agent for the fiberglass. The same Super Glue and matching accelerator can be used to repair cracks in the other plastic duct parts, and to apply as a water sealer to the seam lines in the boxes. Particularly in the case of the LH and RH divider boxes, sealing the seams helps make sure that any water goes out the drains, rather than on the floor of the airplane. These matching glue products can be found at any real hobby shop, where model aircraft supplies are sold. This is NOT the same stuff as the cheap super glue from the Dollar Store or Wal-Mart. You can keep the high-quality glue and accelerator refrigerated, and it will keep for a long time.
SPECIAL NOTE! Many of the original ducts are fastened to the LH and RH under-panel air divider boxes by means of two tiny screws (on each duct). These screws often have badly rusted heads, and can be very difficult to see. The clamps and drains must be removed from these air boxes, and the boxes removed from the plane, in order to get off the old ducts and clean up the boxes. Any attempt to get the ducts off, with the boxes in the plane, will result in damaged boxes. Make sure that the box drain hole is clear, on each box. I also recommend reinstallation using new Tygon 3/8” drain line tubes, available from Aircraft Spruce at a modest cost. When these boxes are reinstalled, make sure that the retaining clamps have the box positioned so that the drain line exits at the lowest point.
ADDENDUM FOR 1975-1976 4-seat Models 19/23/24R
During these two years only, underfloor ducts were used to provide overhead ventilation to the two rear seats. Effective with 1977, overhead ventilation was provided to all seats via a molded plastic plenum system above the headliner. The molded system is fed air from a NACA duct located on the left side of the forward dorsal fin. There was an optional blower assembly that provided powered overhead ventilation for ground operation. This was the next best thing to actual air-conditioning.
The extra pair of 1.25″ underfloor ducts in the 1975-1976 4-seat planes poses a severe added corrosion risk. This is because they not only run underfloor; they exit the floor behind the door jambs, passing through three longeron structural members until they enter the headliner area. Corrosion rendering the plane unairworthy has been discovered in several aircraft. The part number for the long underfloor ducts is:
111728-8B8-350 This is the very long duct to the rear seat overhead ventilation Wemac outlets (two ducts required); 1.25″ ID by 175″ long.
NOTE 1: The preferred alternative is to order two special ducts from Custom Ducts. CD is probably the only source you will find for an unbroken length of 175” duct. Spruce states that their longest length is 120”. If you order from CD, request that one end of this duct (the forward end) be made with a molded cuff that is 1/16” oversize. This will make installation on the plastic air box much easier; and it will prevent damage to the box.
NOTE 2: Because of the length of this duct, and the tortuous routing, you might find it preferable to cut this duct at a convenient (accessible) point. It can then be pulled in from both directions, and a duct coupler Ty-wrapped to the duct. The coupler can be made of thinwall 1.25” by 3” aluminum tube, with a slight bead rolled into each end (for duct security). I can provide these couplers as needed. Their weight is less than an ounce.
ADDENDUM FOR 1966-1969 19/23/23-24
Below are the air ducts required for the 1966-1969 Models 19/23/23-24, all variants.
2ea. 111728-8D8-32 (2″ by 16″). These connect the cheek air inlet boxes to the main plenum boxes.
2ea. 111728-8B8-33 (1.25″ by 15.5″). These connect the main plenum boxes to the pilot/co-pilot air outlets at the LH and RH corners of the instrument panel.
2ea. 111728-8B8-248 (1.25” x 124”). These connect the main plenum boxes to the rear seat air outlets.
The above ducts apply to the following airframes, without the 5th-6th aft seats:
M0901-M1094 (Musketeer 1966-mid 1968)
MA001-MA363 (Musketeer Super (1966-1969)
MB001-MB480 (Musketeer Sport 1966-1969)
NOTE: The parts book does not say this, but I believe that the Musketeer serial number range, for this duct installation layout, actually extends 1966 through 1969, including serial numbers through M1284.
ADDENDUM FOR CABIN AIR EXHAUST DUCTS, ALL AIRFRAMES SO EQUIPPED
These ducts are all used behind the aft cabin bulkhead/compartment cover. They rarely cause corrosion problems, as they don’t normally contact aluminum; but are nonetheless long overdue for replacement due to age-hardening and deterioration.
Sample part number is 115167-EXX-12-088-4:
115167 is another prefix for ventilation ducting, both straight and flanged-end ducts.
E is the original material code; in this example, qualified to 550 degrees F. A D code was used in the pre-1978 applications (350 degrees F), but SCEET should be used for replacements, due to moisture and corrosion resistance.
XX means that the duct has straight cuffs on both ends. An XZ code would denote one flanged end; ZZ two flanged ends.
12 is the inner size of the duct, in quarter-inch increments; in this example, a 3” ID duct.
088 is the length of the duct in half-inch increments; in this example, 44” long.
4 is the end cuff length in quarter-inch increments; in this example, one-inch long cuffs.
115167-EXX-10-020-3 This is the 2.5” ID by 10” long duct which connects the Super’s air filter box exit flange to the injector servo air box inlet flange. It has ¾” cuffs. Only cuffed duct may be used in this application; no lined duct without cuffs. Note that on the five Supers built in 1970 (MA364-MA368), the parts book says a much longer (66″) duct is used. This sounds odd; but I cannot confirm or refute it, having never seen one of these five planes.
115167-EXX-12-088-4 This is the 3.00” ID by 22” long duct which connects the cabin air exit grille, center rear of the hat shelf, to the exit (rear-facing) scoop on the LH upper side of the fuselage (just aft of the cabin). Used on 1978 and later 23/24R/76. One inch long end cuffs, standard size.
115167-EXX-12-200-4 This is the 3.00” ID by 50” long duct which connects the cabin air exit grille, center rear of the hat shelf, to the exit (rear-facing) scoop on the LH upper side of the fuselage (just aft of the cabin). Used on 1978 and later Model 19 Sport, without the hat shelf option. One inch long end cuffs, standard size.
115167-EXX-12-160-4 This is the 3.00” ID by 40” long duct which connects the cabin air exit grille, center rear of the hat shelf, to the exit (rear-facing) scoop on the LH upper side of the fuselage (just aft of the cabin). Used on 1978 and later Model 19 Sport, with the hat shelf option. One inch long end cuffs, standard size.
NOTE: The above three ducts were also used on the pre-1978 19/23/24, with the only difference being a material code of D rather than E. This is irrelevant for the replacement, as SCEET should be used for all applications. If the aircraft in question does have the aft cabin exhaust grille and duct, the above numbers will apply with respect to the needed diameter and length in a replacement duct.
Sample part number is 111716-AZ-6-XX-58:
115167 is another prefix for ventilation ducting, both straight and flanged-end ducts.
AZ is the original material code; in this example, qualified to 550 degrees F.
6 is the inner size of the duct, in half-inch increments; in this example, a 3” ID duct.
XX means that the duct has straight cuffs on both ends. An XZ code would denote one flanged end; ZZ two.
58 is the length of the duct in half-inch increments; in this example, 29” long.
NOTE: Straight cuff length on the original 115167 ducts was drawn as 1.5” long. !” is actually adequate length.
111716-AZ-6-XX-58 This is the 3.00” ID by 29” long duct which connects the forward dorsal fin NACA inlet air box to the overhead ventilation system molded duct (no powered blower option). Used on 1977 and later 19/23/24/76. One inch long end cuffs, standard size.
111716-AZ-6-XX-36 This is the 3.00” ID by 18” long duct which connects the forward dorsal fin NACA inlet air box to the powered blower inlet (on aircraft having the powered blower option). Used on 1977 and later 19/23/24/76. One inch long end cuffs, standard size.
111716-AZ-6-XX-23 This is the 3.00” ID by 12” long duct which connects the powered blower discharge port to the overhead ventilation system molded duct (on aircraft having the powered blower option). Used on 1977 and later 19/23/24/76. One inch long end cuffs, standard size. The stock duct is 11.5” long; but the stronger SCEET will require an extra half-inch of length due to the greater bend radius.