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  • Skylight 337 Progress Report

    A couple of you have shown interest in my version of the Taylorcraft skylight modification. I thought I'd report how the progress is going on the 337. The skylight itself is installed and being "test flown" under the careful supervision of my IA. I love it as much as I loved the last one I did. It makes the airplane more fun to fly and safer in crowded airspace. Another inch or two of headroon is nice too.

    An inspector working for our favorite government agency has seen the photos and description of the installation, spoken with my IA, and has indicated that he thinks there should be no problem with approving the 337. The paperwork is now "in progress" and should be a downhill battle from this point forward.

    The amount of time and effort for a really obvious and low-risk modification like this will seem ridiculous to old timers who used to be able to get something like this done in three days and a handshake up in Alaska, but to get a field approval done in California in 2006 is unfortunately a more significant achievement than it should be.

    I will make this 337 available for the benefit of the Taylorcraft community as soon as it is finished. My specific modification is to put in a skylight without cutting, welding, or changing any of the primary structure, so it can be returned to stock configuration at a later time. Basically it is a bunch of Adel clamps, upgraded wood side supports, an improved forward wood support beam (for pre-war airplanes that had the original support TAPED in place), and a new wood bulkhead over the rear cabin cross tube.

    I chose this path because I am not a welder and didn't want to screw around with anything permanent on a pre-war airplane. My version also uses plywood and Spruce for the skylight supports, because I figured that was how Taylorcraft would have done it in 1940.

    If you have a utility-class airplane and/or are not overly concerned about welding, then I believe there is an existing STC that allows you to replicate the F-21/F-22 factory installation, using welded steel tabs, and aluminum supports.

    After having done my version, I must say that it might have been easier to have a welder come in and stick 20 little tabs on the tubes and use the aluminum fairings. But mine can be un-done completely if someone ever wants to make a museum restoration out of this aircraft. If I were to own a post-war Taylorcraft in the future, I think I would bite the bullet and use the existing STC. There is probably no functional difference once it is all done.

    That being said, some people will want to save money and not buy an STC, or not want to weld, and so they can use my method when the 337 is approved. You can see several photos of my version in the gallery section.
    Taylorcraft : Making Better Aviators for 75 Years... and Counting

    Bill Berle
    TF#693

    http://www.ezflaphandle.com
    http://www.grantstar.net
    N26451 (1940 BL(C)-65) 1988-90
    N47DN (Auster Autocrat) 1992-93
    N96121 (1946 BC-12D-85) 1998-99
    N29544 (1940 BL(C)-85) 2005-08

  • #2
    Re: Skylight 337 Progress Report

    Bill, Good idea and thoughtful of you. We had a midair here in Alaska, about 2 weeks ago, in which two planes collided...flown by high time pilots...5 people lost. Clear day, out in the open. Our Taylorcrafts need more visibility. After you have flown one with a skylight, you will always feel like being in a box without one. Dick
    Dick Smith N5207M TF#159

    Comment


    • #3
      Re: Skylight 337 Progress Report

      How do I get to the gallery?
      MIKE CUSHWAY
      1938 BF50 NC20407
      1940 BC NC27599
      TF#733

      Comment


      • #4
        Re: Skylight 337 Progress Report

        Try this link...then work through the series of pix.

        Dick Smith N5207M TF#159

        Comment


        • #5
          Re: Skylight 337 Progress Report

          Yes! Go, Bill!

          Beautiful skylight. I'm already planing on using your design on my rebuild project.

          Bob
          Bob Gustafson
          NC43913
          TF#565

          Comment


          • #6
            Re: Skylight 337 Progress Report

            Bob, if you want to jump the gun just a little, you can start mking up some of the parts. I sincerely believe my 337 will be approved, so you will probably not be wasting your time.

            Assuming you have a post-war airplane that has the steel tabs welded on three sides of the upper cabin (tabs to mount the forward and side wood pieces), you can re-use the wooden upper windshield support if it's in good condition. I would highly recommend removing the old "blind nuts" or "T-nuts" and replacing them with 10-32 anchors or blind nuts.

            (On my pre-war plane, the original piece was very thin and held in place with cloth tape... not nearly secure enough in my opinion. And no steel mounting tabs. So I made a laminated beam that was held in place with Adel clamps. The forward support now has to support the front of the skylight and the top of the windshield, so a little more security is not a bad thing. On a post-war plane it will be an option.)

            Make sure the skylight is under the windshield so it is impossible for the airflow to get under it and try to peel it off in flight.

            You can also make up the new rear wood "bulkhead" that goes over the rear cabin cross tube, while you're waiting for my 337 to be approved. This is sort of a custom made piece that has to be shaped, notched, relieved and otherwised hand-worked to fit. On a post war plane you need to relieve it so it does not interfere with the trim cables in addition to everything else.

            It will help if you make up a "dummy" version out of cheap pine 2x6 or scrap wood first. Once you get it to where you know it fits around everything, then you can make up the real one out of Spruce using the dummy as a pattern. Of course if you are doing this before you cover the fuselage you will not have the hours of agony and sore muscles that I had working inside a covered fuselage!

            Also, make up the new pieces to build up the side frames. The original thin plywood pieces can be re-used if they're in good shape, you just have to make two more identical ones, then make two "sandwich" panels using hardwood blocks. One change I would recommend from my installation is to put in blind nuts or anchors or self-lock nut plates in those wood blocks instead of wood screws. Considering the debate over T-88 epoxy glue, you might consider using Resorcinol or some other epoxy that does not lose strength with temperature. I used Devcon 15 minute epoxy, which has a history of holding my model airplanes together at high temperatures, but you cannot go wrong with an FAA approved glue. Aliphatic resin (yellow wood glue) may be approved and is cheaper than epoxy. Good old Titebond

            You can start collecting the hardware, Adel clamps, plexiglas or Lexan, etc. and start making up the center clamp piece that holds the skylight down to the upper cabin X. I used 1/8 plexiglas on the first one and 1/16 Lexan on this one to save weight. The Lexan is ore shatter resistant and crack resistant. But whichever you choose, drill all the holes about 1.5 times the diameter of the screw going through it.

            If I didn't put my skylight sketches in the Gallery I will do so now. But the sketches are not legally part of my 337, they're just entertainment literature. We kept the wording on the 337 to a minimum on purpose (thus far), with the hope that people would also have my sketches to fill in some blanks.

            If I ever "upgrade" this 337 to an STC then the sketches and my photos will become the official process and method. For now, common sense and AC 43.13 will supersede my methods if there is a conflict.

            Bill
            Taylorcraft : Making Better Aviators for 75 Years... and Counting

            Bill Berle
            TF#693

            http://www.ezflaphandle.com
            http://www.grantstar.net
            N26451 (1940 BL(C)-65) 1988-90
            N47DN (Auster Autocrat) 1992-93
            N96121 (1946 BC-12D-85) 1998-99
            N29544 (1940 BL(C)-85) 2005-08

            Comment


            • #7
              Re: Skylight 337 Progress Report



              I added some of my previous sketches from the first iteration of the skylight mod in 1999. I also added a photo of the outside of the center clamp and doubler. Note that more than one improvement was made between 1999 and 2006, most notably a strengthened side plate with better hold-downs for the sides of the skylight. Again, the rear wood bulkhead on a pre-war airplane is shaped slightly different from that on a post-war airplane because of the trim cable fairleads.
              Taylorcraft : Making Better Aviators for 75 Years... and Counting

              Bill Berle
              TF#693

              http://www.ezflaphandle.com
              http://www.grantstar.net
              N26451 (1940 BL(C)-65) 1988-90
              N47DN (Auster Autocrat) 1992-93
              N96121 (1946 BC-12D-85) 1998-99
              N29544 (1940 BL(C)-85) 2005-08

              Comment


              • #8
                Re: Skylight 337 Progress Report

                Bill:

                A couple questions:

                Why do you cut off the above-the-cabin stringers? Could they be left in place?

                You suggest using anchor nuts or blind nuts. I'm not sure I know what "blind nuts" are...and I think anchor nuts are riveted in...is there a metal structure to rivet the anchor nuts to? I agree the wood screws look a little iffy, but I can't see where machine screws could be used.

                It looks like the front bulkhead is flat or nearly flat while the aft bulkhead and the side fairings have a nice curve. Looking at the pictures it doesn't seem to be a problem, but logic indicates a compound curve. Does the lexan just lay down or is there some cursing involved?

                Bob
                Bob Gustafson
                NC43913
                TF#565

                Comment


                • #9
                  Re: Skylight 337 Progress Report

                  I thought the same thing...then I looked at the rest of Bill's Pictures HEREthis shows the installation of the blind nuts.

                  Comment


                  • #10
                    Re: Skylight 337 Progress Report

                    Originally posted by mulwyk
                    Does the lexan just lay down or is there some cursing involved?Bob
                    cursing, curving or both? - Mike
                    Mike Horowitz
                    Falls Church, Va
                    BC-12D, N5188M
                    TF - 14954

                    Comment


                    • #11
                      Re: Skylight 337 Progress Report

                      Originally posted by mulwyk
                      Bill:

                      Why do you cut off the above-the-cabin stringers? Could they be left in place?

                      You suggest using anchor nuts or blind nuts. I'm not sure I know what "blind nuts" are...and I think anchor nuts are riveted in...is there a metal structure to rivet the anchor nuts to? I agree the wood screws look a little iffy, but I can't see where machine screws could be used.

                      It looks like the front bulkhead is flat or nearly flat while the aft bulkhead and the side fairings have a nice curve. Does the lexan just lay down or is there some cursing involved?

                      Bob
                      Blind nuts are also called T-nuts. They have a large flange and pointed "teeth". Very common in the model airplane world, and can easily be found in the "Aircraft Parts" section of your local Ace Hardware You drill a slightly oversize hole and pound the nut in from the bottom, the teeth bite into the wood, and you have a threaded hole. Photo attached below.

                      I call "anchors" the little threaded inserts which are tubes with machine threads on the inside and coarse wood threads on the outside. You drill oversize and screw the anchor in, leaving a threaded hole.

                      You could leave the upper cabin stringers, but why? The object is visibility and the stringers are there only to support the fabric. You can easily splice new stringers back in, or even splice back the cutoff pieces later if needed.

                      The front piece is flat on mine out of convenience and the fact that the top of the windshield is not originally curved. You could use a curved piece but at greater effort. The Adel clamp attachment method stronlgy prefers a flat beam, which is also the shape of the windshield. On a post war airplane, or if you want to weld the little tabs, then you can make the front piece with a curve in it more easily. If you put a curve in it, the front view of the airplane would look strange.

                      The Lexan lays down easily, as does the plexiglas. Depending on where you fly and what you wear for a hat, you may want to apply an automotive window tint film to the inside of the skylight. I would recommend a 10 or 20% tint, with a chrome mirror finish outside. The mirror finish will make your airplane flash in reflected sunlight, a free anti-collision strobe. If your airplane is down in the mountains, it could also reflect sunlight to a rescue aircraft looking for you. The tint will help control the heat in the summer. It WILL get hotter under the skylight, but IMHO the benefits justify wearing a hat or putting in the tint film.

                      Photo of Blind Nut below:
                      Attached Files
                      Taylorcraft : Making Better Aviators for 75 Years... and Counting

                      Bill Berle
                      TF#693

                      http://www.ezflaphandle.com
                      http://www.grantstar.net
                      N26451 (1940 BL(C)-65) 1988-90
                      N47DN (Auster Autocrat) 1992-93
                      N96121 (1946 BC-12D-85) 1998-99
                      N29544 (1940 BL(C)-85) 2005-08

                      Comment


                      • #12
                        Re: Skylight 337 Progress Report

                        Bill:
                        I've actually seen those blind nuts in my local Ace Aerospace outlet. They are in the aeronautical furniture parts department.

                        More questions:
                        No headliner (that's a good thing), but what do you do behind the baggage area? Is that just open?

                        How do you seal the skylight to rainwater from seeping in? I see a foam weatherstrip (from Ace no doubt) but what about the screw heads?

                        Bob
                        Bob Gustafson
                        NC43913
                        TF#565

                        Comment


                        • #13
                          Re: Skylight 337 Progress Report

                          You're asking the right questions

                          The foam tape is actually closed cell very thin foam tape, 3M "Microfoam" medical tape. It's the same kind of stuff you wrap around a tennis racket for a squish grip. Model airplane "wing seating tape" will do it as well. Basically that stuff is a cushion under the plastic skylight. Not the primary seal.

                          The all important air and water seal is my old favorite 3M "Blenderm" surgical tape. It is appliedall around the perimeter of the skylight where it overlaps the fabric, and then another layer where the metal cover plates and strips overlap the skylight. THEN you poke the screws through that tape. This is a little bit of extra effort but you will not get water inside your airplane.

                          Thus far, the fuselage is open above the baggage compartment. I am happy enough to leave it that way, because you can look back and see everyting. But of course this means you can't have all your sh#t overflowing the baggage sack because it will fall out into the tailcone. Funny you asked about this, because it is exactly this thought process that led me to start sketching an improved baggage sack that zippers closed on top. Because I'm going to stay at 1280 pounds, short mount when I get my C-85, I won't have the giant wooden cave. But I also want to "repair" my microscopic baggage sack larger than it is. My sketches thus far are to basically split the differencne and make a bigger baggage compartment, but still a fabric material that is suspended from the structure rather than a rigid box.
                          Taylorcraft : Making Better Aviators for 75 Years... and Counting

                          Bill Berle
                          TF#693

                          http://www.ezflaphandle.com
                          http://www.grantstar.net
                          N26451 (1940 BL(C)-65) 1988-90
                          N47DN (Auster Autocrat) 1992-93
                          N96121 (1946 BC-12D-85) 1998-99
                          N29544 (1940 BL(C)-85) 2005-08

                          Comment


                          • #14
                            Re: Skylight 337 Progress Report

                            Blenderm tape is good stuff, Bill put me onto it last year. Ended up ordering a box of six or eight rolls from a medical supply. Not only do I use it for holding the door seal down, I found out I can apply it to the bars that run down along the seat area, (the ones you have to get over to sit down), to keep the paint rubbing off onto my upholstered door panels.
                            Cheers,
                            Marty


                            TF #596
                            1946 BC-12D N95258
                            Former owner of:
                            1946 BC-12D/N95275
                            1943 L-2B/N3113S

                            Comment


                            • #15
                              Re: Skylight 337 Progress Report

                              you can start mking up some of the parts. I sincerely believe my 337 will be approved, so you will probably not be wasting your time.

                              Previously approved 337s are acceptable data that your local FAA can (and has - trust me!) simply choose not to accept. Don't think you are going to get a field approval just because someone else has, without talking to your rep first.

                              I suspect many IAs would consider replacing a little opaque painted plastic with a little transparent unpainted plastic a minor alteration. Then again, maybe not, considering the location (skylight) in this case. I wonder how much of our difficulties with the FAA are a direct result of not exploring all options before seeking official approval for things that don't necessarily need such approval?

                              Comment

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