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Workshop Build-Along — Douglas Skyraider Part 7 — Tailwheel

Workshop Build-Along — Douglas Skyraider Part 7 — Tailwheel

While I was sheeting the fuselage, I also was working out the installation of my scale Tail wheel unit (custom made by Earl Aune). This included installing the new plywood former and reinforcement side doublers while still having access to the parts in between the pieces of sheeting. The sheeting also helps keep the fuselage structure rigid during the work as I remove it from the supports.

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I start by simply laying the tailwheel unit over the plans and then I take measurements to zero in on the exact location for the new plywood former.

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I also check the retracted position of the gear to see if there is any modifications needed. In this case with the wheel retracting in the scale “forward” direction, I do have to trim away some of the F-10 former. Much easier now than when the gear is installed. The Ziroli plans shows the standard Robart tailwheel unit which retracts aft similar to a P-51 Mustang.
The first step is to rough cut the former from 1/8-inch A/C birch plywood and to draw a centerline to keep the tail wheel centered when the unit is finally installed. I did much of the design work with my CAD program and used it to locate the attachment holes for the mounting bolts and blind nuts.

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The drawing also shows the basic layout and parts of the scale tail wheel unit along with the mounting plate and the bolt hole locations.

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I was also able to determine measurements for various parts. I originally was going to add a scale tail wheel well, but this interfered with the steering cables so I did away with the idea. This also saves some weight.

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Here you see the unit bolted to the new former which has been glued in place along with lite-ply reinforcement doublers on either side of the former. Also you see that Former F-10 has been trimmed to allow the gear to swing forward when retracted.

(Below) Here is the gear in the down position. The pushrod “pushes” the gear to the down and locked position, and since it retracts forward, taxi and landing stress keeps the gear in the locked position which eliminates stress and shock forces from being transmitted to the servo.

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Here you see the Tail-hook mechanics are in place and the wheel-well framework has been installed along with the 1/32-inch belly sheeting to add some toughness to this section of the belly.

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Once the mechanics are in place, you can install your servos in the area above the wing saddle and then run your pushrod and control linkages for the tail wheel driver lever. For the tail wheel steering, I used Sullivan Products Kevlar pull-pull cord and clevises.

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This is a view of the retraction arm linkage. To eliminate slop in the setup, supports will be added to the red pushrod guide tube.

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You can see here that I used large loops to connect the Sullivan Kevlar cords to the tiller arm ends. This places the knots away from any hardware items where they might be chaffed and worn because of vibration.

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The cords travel through the center of the fuselage and to clear and chaffing areas in the structure I used a couple of guides (fairleads) to isolate them. The servo you see below the cords is the tail wheel retract servo.

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Here is my servos in their removable servo tray. The pull-pull cords are attached to a pair of tension springs that I attached between the cords and the pull-pull hardware connected to the the dual servo arm. This maintains tension on the cords so they don’t snag on the tail wheel while the gear is retracted. This does soften the steering a bit but helps prevent taxiing shock from being transmitted to the servo. As you can see, I am using heavy duty servos from HitecRCD.

Now that the servos and control linkages are in place, the rest of the fuselage sheeting can be applied.

Stay tuned for more updates to come.

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Updated: December 1, 2016 — 11:26 AM

10 Comments

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  1. Love the thinking and attention to detail. This is a craftsman thinking two steps ahead; smooth work!

    1. Thanks Frank, instead of a craftsman, I prefer to call myself a crafty model builder!
      Cheers
      GY

  2. This is fun, building along with somebody. The plane is different from mine, and I’m at a different stage of construction, but Gery’s logic is insightful and transfers welcome hints to many applications.

  3. question
    how do you remove the bolts that are in the top part of the retract?

    1. Hi Eduardo, thanks for your comment. Originally the tailwheel was bolted to the former and then the former is installed in the fuselage. To get to the bolts that are now above the unit, you can easily use an extended hex driver snaked into place from the Wing Saddle area. I made one from an old hex-ball driver that I epoxied into the end of a carbon fiber pushrod tube. I actually have lots of custom tools for working with my models. I have a similar extended socket set that is used to get to the nuts behind my Fokker Triplane’s firewall.
      Cheers
      Gerry

  4. this is an beautiful setup and well explained. I would like to ask if anybody can help me I am looking for the exact shape and sizes of the ribs (tail plane and wings) and the body formers of bud nosen 103 inch P51 mustang as I have the plans and would like to build it in .5 mm aluminium hoping somebody can help
    regards
    hans

  5. Hello Hans. Try this: http://www.rcscalebuilder.com/
    This is a great forum, I visit often, full of RC scale model builders. I am sure someone there can help you.
    GY

  6. Nice work! What CAD program do you use? I am using CompuFoil for my wings (great program) and pencil to vellum for the rest of my designs. There is something that feels good about drawing (like a nice rev-matched double clutch downshift), but I realize there is more that can be done with CAD.

    1. Hey Dennis, I have been using Ashlar programs for close to 20 years. Started with DrawingBoard, which has been upgraded countless times. At present, I am using their Graphite CAD program which is a turbo-charged version of the DB program I started with. Ashlar has a lot of programs and mine is a 2D CAD program with some 3D wire-frame features. Some of the 3D programs they offer are amazing.
      GY

  7. Gerry, I’m hooking up my tail wheel very similar to yours. What brand servo clevises are you using, and where can I find eye bolts that small ( 2-56 thread ) Thanks.

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