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Dehavilland DH-88 Comet Build and Review

unrauv

Active member
#1
Get complete plans here : http://rcfbaircraft.my-free.website/

I will start by posting pictures of my drawings and the plans. These are new and things may have to be adjusted.
Engine and retract Mount first.
Red = Cut out line.
Blue Dashed = Cut 50% and hollow out.
Green = Crease lines.
NewDH-88EnginePodOutterAndInnerSide.png

Folded out, I hope it works. I guess I should cut one out and test it.
NewDH-88EngineFoamCutOut.png

Note : The retract mounts are glued in place after the engine nacelles and wing are glues together.
 
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unrauv

Active member
#2
I cut it and tested the result, going it make a small change.
NewDH-88ChangetoBulkHead.png

Mirror the change vertically and its done.
NewDH-88MirrortheChange.png

Create the pdf tiles
NewDh-88Create8x10Tiles.png
 
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unrauv

Active member
#3
A few things you may want to get for the engine mounts, I use 3M blind nuts.
http://www.hobbyking.com/hobbyking/store/__17868__M3_Blind_Nuts_10pcs_bag_.html

I file the threads down to 3mm in width then drill and glue them in the back of the 1/8" plywood engine mount. If you don't want to do this then you will have to cut out the bulk heads after the glue is dry. I use PL Premium in the small black squeeze bottle to glue my models together. Blue masking tape to hold things in place while it drys.
 

unrauv

Active member
#8
Details, Material and Tools

Hi All

I guess I should add some details:

Wingspan = 1195 mm = 3.9'.
Length = 910 mm = 2.9'.
2 x 28x26 1200 - 1350 NTM Motors. http://www.hobbyking.com/hobbyking/..._28_26A_1200kv_286w_short_shaft_version_.html
2 x Plush 30A ESC. http://www.hobbyking.com/hobbyking/store/__2164__TURNIGY_Plush_30amp_Speed_Controller.html
2 x 9x6 Props 1 CW rotation, 1 CCW rotation. http://www.hobbyking.com/hobbyking/store/__22427__APC_Style_Propeller_9x6_Grey_CCW_2pcs_.html
http://www.hobbyking.com/hobbyking/store/__22969__APC_Style_Propeller_9x6_Grey_CW_2pcs_.html
2 x 2" Dubro Black Spinners.
6 x HTX 900 9 gram servos. http://www.hobbyking.com/hobbyking/store/__662__HXT900_9g_1_6kg_12sec_Micro_Servo.html
2 x 2 1/2" Foam wheels from Dubro

Materials and Tools
1/16" Hobby plywood. I use this to join the wings, it is very strong in shear.
1/8" plywood I use door skin or birch plywood from you local lumber store.
3/16" Elmers Encore Foam Board.
3/16" Elmer Encore Mighty Core Foam Board. (Optional)
Card Board
3/32" Music wire. (Optional)
Hot Glue Gun.
Dermel with assorted bits for sanding and cutting.

16Ga wire, you can order it from Hobby King or just use Automotive wire.
If you use copper you might get away with 18Ga. http://www.hobbyking.com/hobbyking/store/__9681__Turnigy_Pure_Silicone_Wire_16AWG_1m_Red_.html http://www.hobbyking.com/hobbyking/store/__9680__Turnigy_Pure_Silicone_Wire_16AWG_1m_Black_.html
Male and female 3.5mm ends for ESC's. http://www.hobbyking.com/hobbyking/store/__68__PolyMax_3_5mm_Gold_Connectors_10_PAIRS_20PC_.html

Servo wire. http://www.hobbyking.com/hobbyking/store/__5492__Flat_26AWG_servo_wire_1mtr_R_B_W_.html
JR servo ends. http://www.hobbyking.com/hobbyking/...rvo_Plug_Set_JR_Gold_Plated_10pairs_set_.html
Crimpers. http://www.hobbyking.com/hobbyking/..._Connector_Crimping_Tool.html?strSearch=Crimp
Medium foam safe Zap in the 1 oz bottle. http://www.hobbyking.com/hobbyking/...ld_Plus_Odorless_CA_Glue_1_oz_Foam_Safe_.html
Good Soldering high heat soldering gun for the heavy jobs, and a pencil soldering iron 20W for the serve wires.

I know this is a lot of stuff, but in the end you will be able to build all my models models.
 
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unrauv

Active member
#9
Building the wing and order of doing things

Top Wing

1) Cut out the wing and spars. Place blue tape around the edges to keep the paper template in place.
2) Cut out the Aileron and flap edges.
3) 50% cut the back edges of the aileron and flap, fold back the aileron and flap. Cut the bevels along the bottom sides. Apply 2 layers of transparent along the top side paper hinge.
4) You can now crease along the green lines on top wing. I use the end blunt of a 1/8" BBQ skewer and a framing square for my straight edge.

Bottom Wing
Now the bottom of the wing, order is important here because of all the cut out holes.
1) 50% cut the spar alignment holes.
2) Now crease the the bottom wing along the green lines.
3) Push the wing flat and cut out the engine nacelle alignment hole and landing gear holes.
4) Cut out servo holes to the edges not including the top gear.
5) On the right wing do the 50% cut along the center wing section and remove the paper and foam. I run the pointed end down the cut line and then remove the paper and foam. Use the blunt end to remove any of the left over foam.
6) Use the pointed end of the skewer and hollow out the spar alignment holes.
7) 50% Cut the leading edge, fold back and cut the bevels. I then put a small cut 1/8" inch back along the bevel side so I have an aiming line for the bevel cut.
8) Apply a single layer of transparent tape along the leading edge.

Dihedral Block for construction of wing.
51mm x 100mm View attachment DH-88Comet-RightWing1.pdf


Spars
1) Test place the foam spars, put the plywood spar in pace and mark the glue side on the wood and foam spars.
2) Now zap the spars together being careful to line them up.
3) Use a pen or pencil and mark the outer edges of the spars.

Repeat the above steps for the left wing.

Remove all the paper template and tape.

Check the the bottom side back edges with the aileron and flap and trim if required so the are nice and flush.

Spars
Glue the spars in place using your preferred method, I use a small bead PL Premium and let the spars fully dry, about 2 hours is good. Its lighter then hot glue.

Join the Wings
On a flat table put the bottom of the right wing flt on the table and prop up the left wing using the construction prop. Line everything up back edges and front leading edge. Use the foam joiners wit zap to get things lined up and ready for the wood joiners. Now Zap the wood joiners in place one the wood spars. See the picture below.

Cut out and place and zap in the plywood backing for the landing gear.

Wing Ribs
Place wing ribs at the engine nacelles mounting cut outs. Cut and test the width to ensure the back edge comes together.

Here is a picture of the ribs in place on the Dehavilland Mosquito.
20150421_143125.jpg

You are now ready for wiring the wing
Stay tuned for wiring.
 
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unrauv

Active member
#15
Wiring Diagram and notes

DH-88WiringDiagram1.png

DH-88WiringDiagram2.png

Note don't be too stingy with the wire , it is much easier to trim it off than add it.
Use tape to keep the servo wires in place. Just pull the wires out when you want to add the servo ends. You want about 3 inches out the bottom.

Mark the servo wires, I usually use a black permanent marker and put lines on the wire to indicate the channel. Two lines for Ailerons, 5 lines for Gear, 6 lines for Flaps. These wires will be soldered together and shrink wrapped once the win is closed in and glued together.
 
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unrauv

Active member
#16
I have now uploaded a complete set of drawings to the website. If you rush on ahead you are on your own.
 
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unrauv

Active member
#17
Closing in the Wings.

1) On a flat surface fold down the left wing first, then the right so the paper overlaps, make sure there isn't too much compression on the top surface as this can cause too much internal stress in the wing. In other words it can cause the wing to warp. Ensure all the wires are though on the top. Check all the servo wires are tapped in place. Check the areas where the wires pass over the spars to make sure there are no bulges on the top surface. Be patient at this stage because you only get to do this ONCE!!

There is a video that FT did that shows how to fold and glue a symmetrical wing. You may want to refresh yourself first.

Stay Tuned....
 
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unrauv

Active member
#18
Now that you are satisfied with the fit and are ready to close and glue the wings.

WingGluing.png

Use the PL Premium first, along the leading edge, top of the ribs and on the areas of the spars shown. Now use the hot glue on the areas shown, close in the with wing making sure the angle to the leading edges look the same. Apply pressure only on the spar area of the wing. Use you hands and flatten your wrists to apply pressure to as mush area along the wing as possible. Hold for 8 to 10 minutes.

Now do the right side with the paper overlap. To seal the back of the wing use a bead of medium foam safe ZAP and push the edges together. Use packing tape to the center join area.
 
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unrauv

Active member
#19
Building the Fuse

1) Cut out the fuse using the template.
2) Hollow out all the blue dashed areas.
3) Poke holes along the shown on the template.
4) Cut out and make the bulkhead rectangles. Make not of the number, mark them on the foam board later.
5) Cut out 75% of the wing holes. Leave them in place until everything is dry, then finish the cutting and pop them out.

Here is a 8x10 with the exact width, cut there out and place straight section between B4 and B6. It will help keep thing square. These should no be glued in, then are just for construction purposes.
View attachment DH-88Comet-FuseHelpers.pdf

6) On a flat surface glue and fold up and glue the sides, stick the tail out off the table.
 

unrauv

Active member
#20
Joining the Wing and Fuse.

First of all make yourself on of these, get a good firm paint stick and glue 150 Grit sandpaper to it. It is great for making adjustments on the width of the wing cut out. Make sure you apply even pressure on both sides of the fuse.

20151103_143243.jpg

You are going to have to cut wire pass through hole on one side, this is the side you will push the wing from.
WireAssessHole.png

Push in one side of the wing through the fuse feed the wire so the go through both holes. Now slowly start working the wing through the fuse, if it feels too tight pull the wing completely out, do a little sanding an try again. Take you time and don't make a mess of it.I use all cut the trailing edge of the win in the fuse so the wing is not as wide.

Once the wing is in place, center the wing as best as you can with the center of the fuse.
CenterWing.png
Measure from wing tip to tail, pivot the wing until both measurements are equal, draw a line on the Wing. Hot glue the wing in place.
 
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