SEALS FOR YOUR 1-26A-B-C

By Charles Shaw (196) -- Nov. 14, 2000

INSPIRATION VS. PERSPIRATION

No matter how well you seal your 1-26, there is a very limited amount of performance to be gained. Most of THAT comes from sealing the wing/fuselage joints and the spoiler/dive brake top surface leaks. This article doesn’t treat those things. What it does deal with can be of considerable importance, however. NOISE is extremely tiring and distracting. When applied to the ears of a tense and perhaps overworked pilot over an extended period of time, it can severely limit his abilities to function as a SAFE and efficient aviator. Also, it has been said, “If you think your 1-26 flies better, then you will.”

An early-model 1-26 can be made to operate with a quiet office for its pilot--as quiet as (perhaps quieter than) a plastic plane. I’m sorry to say that this is not as true for a 1-26E because of the flat metal fuselage skins around the wing roots which act like the heads of kettledrums! But even those can be improved, and the ideas here will work for all the “Humility Machines”.

MATERIALS

• Small tube of contact cement: (ACE #12773 has a nice tube & applicator tip.) Resist using more permanent cements such as Pliobond or automotive weather strip cement. These are more permanent that what you are attaching. Further, removing them would likely require the use of a cold chisel and a 2-pound shop hammer! Contact cement requires only lighter fluid or gasoline.
  
• Hardware-store weather strip foam tapes: Buy the densest (heavy duty) you can get. The real heavy duty ones seem to be closed-cell foam. Put these on with the contact cement.
  

  1/2" x 3/4" -- For use along the right bottom of the canopy, in between the latch tubes. Also for the front of the canopy along the top of the instrument panel.
  

  1/2" x 1/4" -- For the turtle-deck/fuselage seal and for part of the canopy rear edge seal.
  

  1/2" x 3/8" -- For part of the rear edge of the canopy. (On the turtle-deck.)
  

  1/2" x 1/8" or 3/8" x 3/16" -- (Select for best fit.) This cements inside the front edge canopy sheet metal and compresses against the foam strip along the curve above the instrument panel.
  

Blocks of foam:

• For the rear corners of the canopy and along part of the right edge, I am using a dense, closed-cell foam which is cut from a seal made for closing the gaps in the square-corrugated sheet metal buildings. You might locate something handier. You will need two small blocks about 1"x1.5"x2" for each corner and two about 1x1.5x8" for the right side. The "closed-cell" is important for these. For the wheel box/brake hole and the release, you can use the common foam plastic like is sometimes sold for cushions, etc.; although closed cell would be good for this too--if it is not too stiff. Some flex is needed. For the wheel box the size is about 6x6x3(or3.5)" and for the release about 1.5"h x 2"w x 4"l.
  

TOOLS

• A tool which I find really good for cutting foam is a modeler's saw. It has a very thin blade about 1" by 6" with very fine teeth--plus a handle. [Sometimes I have heard people call this a jeweler's saw.] A very fine-toothed hacksaw blade will substitute.
  
• A single-edge razor blade is a necessity.
  
• A modelers knife helps, too.
  
• Large and small scissors.
  
• Metal straight-edge (ruler?).
  
• Ruler and dividers for measurements.
  

THE TURTLE-DECK

Thoroughly clean where the tape will be cemented. Along the front face of the curved fuselage former at the rear of the opening, mark with pencil a 1/2” wide place for the cement from one side longeron, around the top, to the other longeron. Placement of the foam tape should be about 3/8” inside the outer curve of the former. I used to guess at the placement of the cement, but found the pencil was needed for a good job. Apply a closed-spaced, thin, continuous “S” of the cement and wait a couple of minutes for it to partly dry. Don’t try to spread it around, and don’t get carried away and use a lot of cement. Peel the covering from the weather strip sticky side and mate the foam with the cement. Always allow the foam tape to recover from the “peel” process, and avoid stretching or compressing it lengthwise.

Similarly clean and mark each longeron, apply cement, let it dry, then apply the foam tape. I put it on as one long piece and two short pieces for each side. Trim a bit as needed to fit better around the turtle-deck locator/fasteners.

Install the turtle-deck to press the foam tape in place. You will have to work to get it on the first few times until the tape begins to take a set. A good seal here requires the tape to be compressed quite a bit. Nothing is left showing from the outside. You have eliminated the use of tape, the messy residue it leaves; and, over the length of time (several years) this installation will last, saved yourself a bunch of time. Besides, it lowers the cockpit noise level and thus relieves the pilot stress level!

CANOPY REAR EDGE

Two layers of foam tape are used here because I have not found any one tape that is thick enough and yet not too wide. They are 1/2” wide, although there is room for a 3/4” width on the turtle-deck. Usually, a 3/8” thickness with an overlaying 1/4” thickness will be what is needed. Clean completely first. Here, you can omit the pencil marking and just put the tape against the rear stop. Use the same technique as before. Go easy on the amount of cement. Leave about 1/8” of the tapes extending lengthwise from each side of the turtle-deck. This can be trimmed later if necessary. After the second layer of tape is applied, AVOID compressing it for several hours until the cement has set up well. Otherwise, the cement may bleed through the tape and cause it to become PERMANENTLY compressed.

CANOPY FRONT EDGE

Above the instrument panel there is space for a 3/4” width of weather strip. I use tape which is 1/2” thick and cement it to the space provided on the fuselage . On most 1-26’s, this 1/2” is not thick enough all the way around the curve of the canopy. I have been adding a strip of thinner (3/16”) tape cemented to the inside of the canopy itself, but it is only used over the part of the curve where it is needed.

CANOPY LEFT EDGE

Because this is the hinge side, there is no way to place foam tape so that is will compress and seal well when the canopy is closed. I still use a strip of 1-1/4” Scotch Decorator tape to close this gap. On top of it at the hinges, I use an additional strip of 3/4” white electrical tape (because the Scotch cuts in the hinges). These tapes are available in quite a few other colors. This is the ONLY tape I use on #196 except that to close the inspection covers. Jo and I do not normally remove the forward canopy to trailer or rig #196.

CANOPY RIGHT EDGE

This is the most varied part, but with one exception it is not very difficult.

Between the two latch tubes, I use a single strip of 1/2” thick by 3/4” wide foam tape cemented down to the fuselage longeron.

I remove the two latch bolts from the canopy itself (unscrew the two latch handles from their larger side), remove their spring(s), clean everything fully, and lubricate the bearing parts of the latch bolts before reassembling. Before I put them back, I stuff the springs thoroughly with foam pieces as large as I can cram in. Then when it is all put back, the holes where the bolt handles slide in the canopy frame are largely filled by the foam in the springs.

At the front and back extremes of the latch bolt tubes, I use closed cell foam blocks which are carefully cut (sculptured?) and then cemented only along their bottom edges to the longeron. The three photos of the right-rear corner seal show part of one of these before it was reworked. This is tedious work which involves much measuring, cutting, and trying in many small steps. Keep in mind that a close fit is needed and not much compression of the foam block is possible or desired. The shape of the canopy frame at this point is quite variable and makes the task go slowly. Cut first; glue last. Another way of sealing here might be to use closed cell blocks to build up some of the open space and then fill in with weather strip foam tape and fit it so it will compress. I haven’t tried this.

THE TWO LOWER, REAR CORNERS OF THE CANOPY

On the whole 1-26, these are probably the most difficult problem spots to solve. They are very close to the lowest-pressure point on the wings, and they are at a complex spot where three different structures made up of several different shapes come together. They can be VERY noisy, and they are close to the pilots ears! The simplest way of dealing with them--which is very inelegant--is to have two smallish pieces of soft foam on the end of strings which keep them close. Each time you get in the glider, stuff the foam in the hole!

Keep in mind that the offending hole is in between the OUTER skin pieces of the three glider parts. (Fuselage, canopy, turtle deck.) It is not necessary to fill all the spaces nearby, just cover up (fill in) that small hole which can be seen from the outside of the glider. No doubt, part of the extra space will get filled in too; but although it doesn’t help, it doesn’t hurt anything either. I am using one-inch thick, closed-cell foam blocks sculptured to fit into that space and provide a pretty effective seal. I cut these blocks to fit so that the little hole is filled, and the foam that does it is FLUSH with the OUTSIDE of the 1-26. I don’t make allowance for more that a few millimeters of compression in any direction--none fore and aft. Just a VERY close fit into the hole. The material is easy to work.

These foam blocks require very complex shapes and will be different with each canopy combination. I hope that the photos will be of some help. Notice that the base of each block is square on the longeron (where it is cemented down) and the front edge makes a 90 degree angle with the longeron in order to accommodate the up and down motions of the canopy parts which it must fit closely. Also note that a thin slice is cut out so that the blocks “wrap around” a small part of the other longeron extension (that the turtle-deck mates with). The blocks are also cemented to the top of that thin longeron piece. The top surfaces of the block are cut to fit last so that the canopy parts barely compress them. Any extra compression will cause the shapes you have created to distort and the result is loss of the careful fit which you need.

Your biggest problem is that all the work is very time consuming: measure-cut-fit-measure-cut-fit-cut- fit-, etc.

THE WHEEL BOX/BRAKE HOLE

Use as large a block of foam as you can make fit in the available space. Don’t hesitate to leave parts extending into unoccupied nooks and crannies. Cut away just enough foam to assure unrestricted movement of the aileron bell crank and other moving parts. Hollow out the inside of the block to fit around the brake cable pulley, leaving as much sound/air dampening material as you can. Plan to cement this block to the forward face of the wheel cover box ONLY. With the flexibility of the foam and the limited cementing, there is no way you can cause a malfunction of any operating system. The block should wind up as a box which is complete except for part of its rear side which is supplied by the wheel cover and its lower side which is supplied by a snug fit of the foam to the glider bottom skin. There must be a slit for the brake cable to run in, but it isn’t necessary to actually remove any foam-- just slice it. This also allows the foam block to be installed without loosening or disconnecting any glider parts.

Here we are not trying to completely stop all air movement--just slow and dampen it sufficiently to thoroughly quiet it down. The landing gear drag is there permanently on a 1-26!

THE RELEASE MECHANISM

This is like the wheel box/brake solution except there is no need to hollow the block out. Put the 1.5" x 2" x 4" chunk of foam over the mechanism with vertical slices (U-shaped) in it to allow the release arm to fit through, and cement it at the bottom to the steel structures. The foam is without doubt soft and flexible enough to allow the mechanism to do its job without interference; mine has been working for nearly 20 years. To do this job, you will need to remove the nose cone.

GOOD LUCK

I hope this gives you a few usable ideas you can probably improve upon. Best regards to all.

Charles

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