Dornier Do 28 (oz12045)


Dornier Do 28 (oz12045) by Roy Day 1991 - plan thumbnail

About this Plan

Dornier Do 28. Radio control scale model electric twin.

Quote: "Dornier DO-28 Electric Twin, by Roy E Day.

Would you like to have a good flying sport scale twin that you can take along on your vacation and win the attention of the fellows at the flying field? Then build and fly this 70-inch wingspan Dornier Electric Twin.

OBJECTIVE OF THE PROJECT: When I began this project I had three principal objectives. They were to design a sport scale electric model with the following characteristics:

1. A twin using the popular 05 size elec-tric motors.
2. An easily transported model so it could be a 'vacation' airplane.
3. A sport scale model of an airplane with comfortable handling characteristics and moderate wing loading.

The airplane I selected was the Dornier DO-28, a 6-8 passenger twin engine high wing monoplane. The high aspect ratio wing promised good lift. The engines mounted on a subwing simplified the power installation and eliminated the problem of disconnecting the motors every time the wing was removed.

Almost everyone, the author included, is intrigued by twins but is fearful of the dreaded 'engine out emergency'. An electric twin with motors and controller in series with the battery virtually eliminates the possibility of an engine out.

DESIGN PARAMETERS: The model was designed for three controls, no ailerons, which simplified the two-piece wing necessary for easy transport. Also the tail assembly and the landing gear must be easily removable. The basic design ground rule for electrics is that the airframe plus radio should not weigh more than the power system, ie the motors plus the batteries. The sizing of the airplane proceeds as follows. The motors selected were the Astro geared 05 cobalts. The battery pack planned was 16 cells of 1200 mAH. The 16 cells give a little added power over the usual 14 (7 per motor) without any danger of harming the cobalt motors. In fact, the DO-28 only draws 20 amps static. Current levels as high as 30 amps can be tolerated by the Astro brushes without any damage.

Power System Weights: 2 geared 05 motors = 16 oz; 16 x 1200 mAH cells = 30 oz; Total = 46 oz. Therefore the all-up flying weight should be 2 x 46 = 92 oz. Now the total weight budget becomes: Power system 46 Actual, Radio 8 Actual Airframe w/LG 36 Estimated; Covering 2 Estimated; Design Flying Wt = 92 oz.

For ease of flying the wing loading is set at 20 oz/sq ft. Now the corresponding wing area is computed by dividing the design weight (oz. by the desired wing loading - in this case, 92 divided by 20 - which gives us a wing area of 662 sq in, rounded to 600 sq in. Based on the aspect ratio of the Dornier, the wing span came out at 70 inches.

So now we have all the basic sizing parameters, weight goals and scaling dimensions. The resulting design is shown in the plans and we can now begin construction.

CONSTRUCTION: Lightweight construction is particularly important for electrics and essential if we are to meet the ground rules stated. If the weight is not kept in control, we will have another of those overweight/underpowered electrics that stagger about the flying field like a wounded butterfly, provoking snickers. For this plane no epoxy is used, only thick and thin CA glue. Plywood and hardwood are used only in high load areas, such as landing gear mounts, motor mounts, and wing attachments. Increased strength is obtained in some areas by using thin ply doublers on balsa and the liberal use of gussets. Properly fitted gussets of 3/32 balsa can add tremen-dous strength and stiffness with minimum weight.

Fuselage: The fuselage is conventional built-up stick construction. The two sides are built over the plans, then joined with the cross members while pinned upright on the board. Use medium weight balsa for the longerons and members in the forward part of the airplane. Lightweight balsa is all you need for the aft structural members. Bend the longerons in carefully to meet F-1. Former F-1 is made from two pieces of medium 3/32 balsa cross-laminated. The result is as strong as lite-ply, but lighter.

When the basic structure has been com-pleted and while the fuselage is firmly pinned upright on the board, start the construction of the subwing and motor mounts. Sketch B shows how the spruce spars rest on the 1/4- inch square balsa cross pieces and tie into the fuselage uprights. The thrust line of the motors should be 0-0, along with the wing and horizontal tail. If it is necessary to adjust the thrust line later, it can be easily done by shimming the motors in their beam mounts. I found that no adjustments were necessary.

Install all the ribs in the subwing except the one next to the fuselage. Glue it in place after the sides of the fuselage are sheeted. Glue in the leading edge of the subwing, the landing gear, and motor mounts. Before sheeting the subwing, it is a good idea to run the wiring through the soda straw conduit out to the motor mounts..."

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Dornier Do 28 (oz12045) by Roy Day 1991 - model pic

  • (oz12045)
    Dornier Do 28
    by Roy Day
    from Model Builder (ref:1911)
    January 1991 
    70in span
    Scale Electric R/C Multi Civil
    clean :)
    all formers complete :)
    got article :)
  • Submitted: 28/03/2020
    Filesize: 825KB
    Format: • PDFbitmap
    Credit*: MB2020
    Downloads: 1268

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