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Wing Tips: Cabin Door Hinges & Windlace Cords – Part V

In our last Wing Tips article, we worked through the challenges of getting the main cabin door to seal against water leaks. It must seem like I’m really trying to drag out this door seal thing, making it into more of an issue than it really is. But over the past 37 years, we have struggled more with door closure and water leak problems than any other area of interior renovation. However, I promise that we’re getting down to discussing the last of the issues related to door seals.

Water leak concerns take us back to the main cabin door and its hinges. By their very design, these hinges were born to leak. Unlike car doors, the door jamb of your Bonanza or Baron is cut out to allow for the flush door hinge to close into the airframe. Not such a great idea, as this gap in the jamb creates the very tedious problem of how to seal the hinge area from water leaks. Even Cessna and Piper recognized the potential problem and designed their hinges in such a way as to avoid this mess. Beech relied on two different rubber seals in an attempt to keep the water out. With proper maintenance and a good measure of patience, a reasonable level of leak control can be achieved. Actually, three things can be done to manage this situation.

The first step in getting these seals to keep out water is to remove the formed black rubber foam block that is stuffed into the pocket that forms the support for the door hinges. If this $300 piece of foam block is still relatively flexible, we usually rejuvenate it by bonding a ¼” or ½” thick piece of closed cell foam rubber to the back side of the block (we buy ours from Skandia Inc). The idea here is to overstuff the hinge box structure to try to prevent water from coming through from behind the door hinge when the door is closed. Sometimes this is all that is required to stop a hinge leak, but in the majority of cases one must proceed to a second step.

Step two is an attempt to create a seal between the outer hinge cover plate and the cabin skin. We recreate a thin U-shaped ⅛” thick neoprene rubber seal here that establishes relatively good closure between the edge of the door hinge plate and the outer cabin skin. To do this you need to drill out the three or four rivets that secure the hinge plate to the machined aluminum hinge. With the plate removed, we tap the holes with an 8/32 tap and reattach the hinge plate using countersunk stainless steel machine screws.

We sometimes find that either the hinge cover plate or the cabin skin around the hinge is damaged. The damage must be corrected for this thin rubber seal to work. If the hinge plate is damaged, we will fabricate a new one using .032” 2024T3 aluminum. We then cut the ⅛” neoprene rubber to a precise U-shape so that when bonded to the outer hinge plate the inner edge of the seal is sandwiched between the outer hinge plate and the door hinge when the outer plate is re-attached with the new 8/32 screws. We then bond a piece of the same thin black foam to the forward outer surface of the hinge plate. This piece of foam will establish a seal between the forward surface of the hinge plate and the back side of the outer cabin skin when the door is closed. The picture shows it all.

Be sure to trim the outer edge of the ⅛” seal to just touch the edge of the cabin skin when the cover plate is installed. All that’s needed is closure. If the seal is too large, it will soon begin to tear. Don’t be discouraged if you have to try this procedure more than once. We sometimes need a second attempt in order to get satisfactory results. Also, be prepared to replace these delicate seals every couple of years. Keep a template of the correctly shaped seal that works on your door hinges; you’ll be glad you did at replacement time.

Even with the effort of carefully executing these first two steps, it is likely that some seepage can still occur, which brings us to step three. Accepting that door hinge leaks are a fact of life, we create an exit path for any water that may still get past the hinge seals. We end all inside insulation about 3” short of the forward door frame to allow any errant water that makes its way past the door hinge to flow down and out the drain holes in the belly. As added insurance, we will sometimes locate an additional ⅛” drain hole in an appropriate location in the belly. We’vee had quite good success with these techniques. Remember, the whole idea is to keep the water from soaking into the hydroscopic cabin insulation and upholstery, which obviously results in a corrosion problem or unsightly water damage.

The rubber seal we’ve been discussing is designed to control water leaks only. Now let’s look at eliminating in-flight cabin door air leaks. Air leaks are controlled by the ¾” diameter vinyl- or leather-covered soft bead that goes around the entire door jamb, known in the industry as the windlace cord. When properly installed and adjusted, this windlace cord should rest snugly against the door frame when the door is in the closed and fully latched position. Any gapping and you’ve got an in-flight air leak. Position this cord too tightly against the door and, you guessed it, the door won’t close.

Adjusting these windlace cords is often time-consuming. This cord is held in place with 68 counter-sunk sheet metal screws that position it between a lip that forms the outer surface of the door jamb and the inner structural hat section of the door frame. Therefore, any adjustment requires the removal of some screws in the problem area and repositioning the seal until it closes against the closed door correctly. If the seal is too tight, remove some screws and pull the seal in, away from the jamb, then reinstall the screws. A word of caution: do this with a hand screwdriver only, and be careful not to strip the sheet metal screws.

If the windlace cord is too loose, you must remove the windlace cord in the problem area and remove some of the outer flange. Reinstall the cord so that it is positioned close enough to seat properly against the closed and latched door. For this job, we use a rotary file in a high speed router tool. Works great! The final check of the fit of the windlace cord is the business card. We like to adjust these windlace cords a little on the tight side so that after a few weeks in service they take a set that ensures that they seal completely and the door is relatively easy to close and latch.

Now for disclaimer time! These Beech cabin doors are unquestionably among the most tedious in the industry to adjust and seal. Success often comes in stages. Seals change with time, use, and temperature. A couple of days sitting closed and latched in the hot sun will often make a hard-to-close door much easier to latch. One of our biggest concerns when delivering an airplane back to a customer is unquestionably door-closing issues, particularly in winter. With all of the tricks we have learned in the past 37 years, it can still be a fight. We’ve been known to spend an entire day getting a door to properly close and seal. It’s important to remember that these doors and door jambs were hand-built and fit by skilled craftsmen, and some doors just fit better than others.

The end to door and window seals is in sight. Next time we’ll take care of the less tedious seals for center opening windows as well as baggage and cargo doors. ’Til then, fly safe.

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