Dornier DO 18 - (Perhaps another long story)

[bweaver]

I enjoy reading all the build and repair projects that club members have included in the TEMAC forum. I find the topics are entertaining, informative and helpful when it comes to motivating me to take on another project or keep working on a current project. The forum construction topics include many useful tips and techniques the model builder or repairer. I hope you may find this subject somewhat the same.  Please feel free to comment, make suggestions or inquiries as desired.

This stand-off scale model will be fashioned after a German 1930's era flying boat, known as a Dornier Do 18, which had both military and civilian versions.   I will be attempting to construct a reasonable facsimile of the civil aircraft version and finishing it in a Lufthansa airline colour scheme. 

I am using drawings of the Dornier DO 18K1 WW II version of the aircraft purchased from Flying Models (on line). The plans are for use in constructing a balsa model.  I am not using the plans for this purpose.  I am using the plans primarily for obtaining the aircraft's outline for guiding me in the construction of the the stand-off scale model. For my purposes "standoff scale" means, the farther you stand off from the model while viewing it, the more it resembles the original full-size aircraft.

The finished model will have a 66 inch wingspan while the fuselage is 59 inches long.  There are protruding sponsons affixed to the fuselage for water stability.

I am utilizing construction grade foam board as the primary construction material.  It will be fibre glassed and painted. It will have throttle, elevator, ruder, ailerons and flaps.

If you (the reader) can stand the pace of this project's progress, you are probably like me; where you can enjoy watching paint dry, grass grow, seasons and years advance from one to the next.  At times, the construction of this model may be delayed due to my procrastination or hesitation I experience involved in planning the next steps.  (Being lazy and having other things to do may also have something to do with construction delays.). If you can offer tips to help the project move along, they will be sincerely appreciated.

[bweaver]

I began the project earlier this year by purchasing the plans in February and started the construction of model early in the spring.   Once flying season came along, construction stopped.  I now plan on proceeding with its construction. (See what I meant by procrastination.)

The steps of construction up to this point in time have not been photographed, so the photo below reflects the model components in their current state.

The model is going to be powered by two inexpensive Racestar BR 3536 950 KV brushless motors and two 40 amp ESCs that will allow flexibility in using 3 or 4 cell batteries to power the model.

The photo below depicts the components I have fabricated to date, along with balsa elements that will be used for the trailing edges of the wing.  The control surfaces will also consist of balsa.

The wing has been hot wired in three pieces. (A center section and 2 outer portions.)  The finished wing will consist of three pieces with the center portion of the wing permanently affixed to the pylon with struts secured between the wing and sponsons. The outer portions of the wings will be removable for ease of transport.

The wing and the tandem motors (one push and one pull) will be mounted on a pylon above the fuselage.  This pylon/wing and motor arrangement creates some challenges in the construction and design for use with foam. 

At this point The fuselage consists of 1 piece of 2 inch blue foam board forming more than one half of the bottom of the fuselage hull.  The rear bottom tail portion of the fuselage and the sides consist of 1/2 inch pink foam board.  The vertical stabilizer and rudder is just resting there at this time.  It will be shaped and finished in the future.

NOTE: Lowes has been my usual source for blue construction grade foam for my projects.  For some time now Lowes hasn't been carrying blue foam board, hence the reason for the pink foam board, which I have now purchased from Home Depot.  I don't believe it will make much of a difference using the pink foam board, but time will tell.

The pylon has been designed for its structural ability to support the wing and tandem motors.  (The original balsa, ply construction shown on the plans wouldn't work for use with the foam.)

The primary structural elements of the pylon consist of a combination of 1/8th inch and 1/4 inch plywood.  The ply has been cut and drilled out to lighten the structure, but still retain its strength for supporting the wing and motors.  As construction proceeds, the pylon will have foam board attached to enhance its structural integrity be shaped to coincide with the desired shape of the pylon motor cowling enclosure.

The top portions of the fuselage have to be added and shaped.  It will involve more sculpturing of the model than building it.

I don't know how fast this project will proceed at, but I will attempt to have the model completed for flying this spring.

In the interim, due to the holiday season we are in, I wish everyone a happy holiday and New year.

[Gregor77]

Awesome!   Why use pink foam verses the blue?  I think Blue is lighter and more flexible?  I might be wrong.

[Michael]

Bruce's scratchbuilds have produced some really cool model airplanes. I'll follow this thread, and I look forward to seeing this new beauty skim right off the water next spring!

[sihinch]

Merry Christmas Bruce!  Thanks for this gift.....good luck with the build.

[Frank v B]

....but Bruce, how are you going to make the shape of the nacelles out of beer cans like you did on the Savoie?

These nacelles are pointy.

Happy building.

Frank

ps: the Dornier Do 18 can be seen http://www.aircraftaces.com/dornier-18.htm

[bweaver]

Thanks Guys,

Greg, there was a NOTE in my second post about my use of blue and pink foam board in this build. (If you were speed reading, it was easy to miss )

Frank, never rule out the use of a beer can in any of my builds.  (Half the enjoyment of using beer cans in this hobby is emptying them. )

[bweaver]

The next steps for further construction of the fuselage has moved along slowly... (but that's just me).

My technique for building the fuselage with foam board involves constructing it from the outside-in, rather than where the typical balsa wood built-up fuselage is constructed with pieces built from the inside out. Let me explain.

Normal balsa wood fuselage construction uses an internal framing system consisting of longitudinal beams, with longerons and cross formers or bulkheads with stringers and other external elements used for strength and to shape the exterior of the fuselage where it is covered finally with some type of outer skinning or film material.

I use foam board as a flying boat model construction material for its weight, buoyancy and for its strength.  Simply put I build boxes, then shape their exteriors to reveal the outer shape and surface of the fuselage that was hiding inside. 

To accommodate this technique, it was necessary to locate on the drawings of the fuselage the 'DATUM LINE'.  This datum line is then marked on each side of the fuselage. This line will be used for helping me shape the exterior of the fuselage.  (How so, you might ask?)

Each of the hull former/bulkhead outlines were traced onto paper using the drawings and the datum line point identified.  Then the exterior shapes of each of the bulkheads were transferred to a piece of cardboard. These cardboard pieces will be used as templates for shaping the outside of the fuselage.

Areas of the fuselage structure were strengthened with additional foam board in places where the shaping of the fuselage will result in a significant reduction in the thickness of the fuselage sides being reduced in order to obtain the desired shape.

Next steps will involve finishing the pylon including its fixing in place within the fuselage and reinforcing it, including installation of the motors, ESC's and wiring arrangement.

[bweaver]

I decided to delay installing the two motors, and the two ESCs for now in the pylon.

I have reinforced the pylon, cut out wiring openings through out it for the wiring to go from the motor compartment, through the wing and into the fuselage (hull) of the flying boat. Two flight batteries will be installed in the bottom of hull with one battery secured on each side of the pylon.     

The pylon must structurally strong because it will be the primary support for the wing (which is separate from the fuselage) and also absorb the forces of the two motors in tractor and pusher configuration mounted above the wing. 

While it may not look like much of a change, the photos below illustrate the installation of the pylon and the reinforcement pieces added, including the wiring openings. 

The second last photo provides the reader with an idea of how the wing will be secured in the pylon in the future with the motors and related equipment mounted above it.

(Not much progress, but necessary.)

[bweaver]

I forgot to mention in the last post that the wooden pylon components were made water resistant by applying a coat of polyurethane with stain.  The stain makes it easier to see when applying it. (Just kidding. It was the only polyurethane I had, so I used it for the job.)

Wing ditherings. (Just a little bit.)

As noted I had previously hot wired the 3 wing sections. (A center section that will be permanently mounted into the pylon with 2 outer removable wing sections, one for each side.). This wing/fuselage configuration will let me fit the plane in my car without having to break it, or fold it severely in an undesirable manner.

A female wing spar is going to be permanently glued into the center section.  Male corresponding spars are permanently glued into the outboard wing sections.  (The male spars slide into the female spar permitting the wing sections to be fixed in place for wing alignment and strength.)     

The spar channels were chipped out by slicing into the wing and then digging out the portion desired.   

The spars I am using were recovered from previous model aircraft that were no longer needing them.  I hope these perform better as a hole than in their predecessor.

1/16th inch plywood ribs are installed at the abutting ends of each wing section (total of 4) for the purpose of protecting the abutting foam ends of each section from physical damage.

[bweaver]

Before getting into new stuff, I would like to touch a little bit on my house keeping.  For those who don't know me, I don't have a separate workshop area in my home to conduct my modelling activities, which at times can create a bit of a mess.  I use a habitable space in my home for my model building and for undertaking repairs.

So what do I do to keep the work area clean and minimize the spread of dust throughout the house when I am cutting/sanding wood and foam?'

Most of the dust developed can readily be collected by using a small shop vac with the suction hose opening secured in the vicinity of the material being sanded.  (Ensure the shop vac is turned 'on' before sanding begins.  It makes the dust recovery process that much more effective.  I also wear ear protection to protect my hearing and minimize exposure to verbal criticisms about the noise.)  For those of you who are visual learners, refer to the photos.

Wing Ditherings (come to an end)

After the plywood ribs were glued onto the foam wing ends, wing spar openings were cut through each plywood rib by using a Dremel and Dura-grit hollow tip burr tool.

To finish the outer wing sections, two - 2 inch wing tips were cut out using the hot wire tool.  These were glued to the ends of the outer wing section and the ends were shaped using the Dura-grit coarse and fine grit hand sanding tools.  (Remember - keep that shop vac handy.)

Wing attachment anchors were made using 1/8th inch plywood and balsa blocks with 4 - 40 hex bolts and blind nuts. (These anchors keep each outer wing section secured to the center wing section.)

A balsa wood trailing edge was installed and shaped to match the trailing edge of the foam wing.

After a number of dry fits and some adjustments, the spars were permanently glued into place into each wing section.  Foam pieces were cut out, then glued into the remaining spar channel spaces above the spars.  These pieces were shaped using a knife and Dura-grit tools.  Dings and dips in the wing surfaces are filled with Lepage Polyfilla, (big hole repair spackling). This product is very light and easy to sand.

The wing ditherings I was experiencing are over now.  I'm going to put the wing aside before taking on the installation of the servos and flaps and ailerons. The flaps and ailerons configurations are not inline with the wing like a normal installation.  These are hinged below and away from the trailing edge of the wing.  This is a very distinctive part of the aircraft.

(Does anyone know what this arrangement is called and what is its purpose?)

One of the photos shows the hinging arrangement that I will be using.

[octagon]

Looking great Bruce. I keep the shop vac handy too and I have a dedicated work shop. I also wear a mask when I am sanding. Looking forward to seeing the build progress.

[bweaver]

After a little cutting, filing, digging and sanding I have found the top front portion of the fuselage/hull emerging from the foam outer box..

As previously mentioned, my foam model construction technique involves constructing the model from the outside-in.

Built up balsa models involve constructing the model from the inside-out.  Refer to the example photo of Michael's current construction as an example of what I mean. (By the way, excellent work Michael.)

I have applied the final top pieces of the foam board to the top front of the fuselage hull.  The first 4 exterior bulkhead templates were used to assist in finding the shape of the hull within the box like structure.  You can see some additional foam strips have been added inside the fuselage hull to strengthen the foam board joint areas where they will be shaved down to define the shape of the hull/fuselage. 

The tools being used include a utility knife, files, Dura-grit sanding tools/files and pens and fine tip sharpy marker.

I used the drawings to assist in locating the cockpit window locations on the box. The window locations were drawn on the box.

Using the utility knife and files, the shape of the top of the hull was brought out of the box.

(A little black-felt marker make-up was applied to highlight the cockpit windows.)

I am not shaping the bottom of hull at this time.  Shaping the bottom of the hull will be carried out after the remainder of the fuselage, tail control surfaces and servos etc. have been installed and shaped. 

I am encouraged by all the other fine construction topics that are being posted by other club members on the forum.  Keep it up.  It keeps me motivated.

[Michael]

Looks amazing!

[bweaver]

I noticed the link to the picture I was referring to about Michael's balsa build failed.  Try again.  https://temac.ca/smf/index.php?action=dlattach;topic=8220.0;attach=44976;image