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Apr 04, 2020, 02:03 AM
Foam is where the heart is
brett.c's Avatar
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Build Log

The Dream Machine in foam


Now that I am housebound for the next few weeks I thought I'd start another project.
The Dream Machine was designed by Jim Rice and published in RC Modeler back in 1983.

This plane caught my eye because it not only looks great, and hopefully flies great, but it is a fairly straight forward design and thus easy to build.
I'll be using the tried and true foam and paper method as I used with the El Gringo https://www.rcgroups.com/forums/show...Gringo-in-foam

Wingspan is 48" (1.2M) and AUW should be around 1400grams.

Due to the CV19 debacle parts are little hard to obtain ATM so I have sacrificed one of my fleet to act as a parts donor. It was a bitza that I made up from a wrecked 1.6M phoenix glider. It was fast and flew well but just looked a bit ugly, so no waste really.
Motor is a 3536 1250 kV spinning a 9x6 prop . Battery will be a 2200/4s with 50A ESC. This should provide plenty forward urge.

So far I have drawn up a fully scale drawing of the fuselage and laid out all the electronics to see how things will fit. All looks good thus far with plenty of battery room. She looks nice and sleek, a bit like an Italian WW2 fighter.
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Apr 04, 2020, 01:48 PM
Foam is my friend!!!
NewZee's Avatar
I took a look at your "El Gringo" Build log, and am interested in this kind of foam construction! I'll subscribe, and follow along! (BTW what kind of foam are you using?)? I'll likely be using either the "Blue" or "Pink" house insulating foam (Dow or Owens), that is readily available here in the US!!
Apr 04, 2020, 05:18 PM
Foam is where the heart is
brett.c's Avatar
Thread OP
I use Knauf XPS foam board from my local hardware chain store call Bunnings.
It isn't as user friendly as the blue Dow foam but it is more readily available here.
It tends to rip if sanded aggressively and I'm not sure if it the best for hotwire cutting over large areas.
I find the quickest and best way so sand it into shape is using a multitool with 120grit paper.
Apr 04, 2020, 08:08 PM
Foam is my friend!!!
NewZee's Avatar
Quote:
Originally Posted by brett.c
I use Knauf XPS foam board from my local hardware chain store call Bunnings.
It isn't as user friendly as the blue Dow foam but it is more readily available here.
It tends to rip if sanded aggressively and I'm not sure if it the best for hotwire cutting over large areas.
I find the quickest and best way so sand it into shape is using a multitool with 120grit paper.
I've mostly used the "pink" stuff and have experimented with PVA and brown paper! Have yet to refine my "technique! I've also covered foam shapes with traditional "monokote" type coverings, but that's expensive!!
Apr 05, 2020, 03:53 AM
Foam is where the heart is
brett.c's Avatar
Thread OP
Started on the fuselage today.

Pic 1. First step is to slice down the 30mm thick foam to make 2x 10mm thick pieces for the fuse sides. I use the outer skins for this and end up with a 7.5mm thick piece from the center which will be used to make the tail surfaces.
Pic 2. I lay the plan over one of foam pieces and mark out the datum points using pins.
Pic 3. Then it is a matter of joining the dots and cutting out the shape.
Pic 4. Formers are put in place for a dry test fit.
Pic 5. Then it is all glued and placed into my high tech, no expense spared, fuselage jig (patent pending).
Pic 6. Now ready for sanding.

Next: Motor and battery mounts.
Apr 05, 2020, 03:31 PM
Foam is my friend!!!
NewZee's Avatar
Watching with interest!!! When you cut the 10mm thickness's do you pass the foam under the wire (foam is moving , wire is fixed)? or does the wire pass over the foam? . I like your high tech fuselage alignment fixture!!
Apr 05, 2020, 05:35 PM
Foam is where the heart is
brett.c's Avatar
Thread OP
Quote:
Originally Posted by NewZee
When you cut the 10mm thickness's do you pass the foam under the wire (foam is moving , wire is fixed)? or does the wire pass over the foam? .
I built that table such that I would drag the bow over the foam. The aluminium sides can be adjusted to suit desired thickness.
All good in theory, however in practice I wasn't steady enough with the bow to get a good ripple free cut.
Now I hang the bow underneath to give tension on the wire and feed the foam into it. This works much better.
One day I will make a gravity fed slide from an old door or similar set at an incline.
Apr 06, 2020, 05:27 PM
Foam is where the heart is
brett.c's Avatar
Thread OP
Pic 1. I don't have no fancy lazer cutter so everything has to be cut by hand. I do have a little scroll saw which comes in handy for this kind of work. For the holes I find that a step drill works best as it chamfers the edges as it cuts. Lite ply is 2.5mm thick and is doubled up for the motor mount.

Pic2. Cutting out is complete and the assembly is now dry fit against the plans to ensure all is ready for gluing.

Pic 3. I use PU glue for this kind of work as it fills gaps and bonds well. The jig is supplied by my sponsor, the Makedoo Engineering Company.

Pic 4. Motor and battery assembly is now in place.

Next: Tail servos and pushrods.
Apr 07, 2020, 02:45 AM
Foam is where the heart is
brett.c's Avatar
Thread OP
Worked on the tail servos today.
The sleeves are carbon fiber tubes from the Phoenix glider.
Being fairly rigid I had to get the angles right such that the pushrods aligned with the servo arms and approximate location of the control horns.
The sleeves are not yet glued in place. That is so that I can push them back into the fuselage for covering and painting. Once complete small slits will be made in the paper so that the sleeves can be then pushed back out again and glued.

Next: Top decking
Apr 08, 2020, 06:05 PM
Foam is my friend!!!
NewZee's Avatar

Good Progress


You're making good progress! and so far are using many of the same techniques, and tools that I use! In fact it's looking eerily similar to a fuselage I built (and flew with a Balsa wing) for a slow flying FPV platform! of course I stopped there, and didn't try any shaping etc.
Apr 09, 2020, 01:28 AM
Foam is where the heart is
brett.c's Avatar
Thread OP
Speaking of shaping...
I completed the rear deck today.

I've moved the cockpit 20mm rearwards to improve access to the servos. IMO it looks a bit better that way.

1. Shave it down first.
2. Roughly sand to shape with a multitool
3. Even up with a sanding file.
4. Sand smooth with 120 paper.

I could have hotwire cut this but to be honest setting it all out takes longer than just carving it.
Besides, I need the practice for the front section which has compound curves making hotwire cutting difficult.

And of course, use a dust mask and vacuum up as much as possible after. I even use a fan to blow the dust away while working.
Just watch that the wife doesn't have any washing on the line
Apr 09, 2020, 05:31 AM
Foam is my friend!!!
NewZee's Avatar
Now it's starting to look like an airplane!
Apr 09, 2020, 11:08 PM
Foam is where the heart is
brett.c's Avatar
Thread OP
Quote:
Originally Posted by NewZee
Now it's starting to look like an airplane!
And now a bit more so.

I decided to fatten up the nose a bit to make it a little less droopy and provide some form of air intake.
The cowl is now ready to be hollowed out and I have yet to come up with sort of attachment for it.

Next: the tail end.
Apr 11, 2020, 03:22 AM
Foam is where the heart is
brett.c's Avatar
Thread OP
I decided that I didn't like to look of the cowl with the intake above the spinner, so I mounted the motor 6mm higher and reshaped the cowl.
This time I got wise and made up 2x 1.6mm ply plates to act as guides. They are permanently glued in place and they made sanding a whole lot easier.

I also made up the tail surfaces and I went a little off plan by rounding off the horizontal stab and elevators similar to the fin. I think this gives the plane more of a pre war look. I may do something similar with the wing tips.

Next: Cowling attachment and mounting the tail wheel.
Apr 11, 2020, 10:39 AM
Foam is my friend!!!
NewZee's Avatar
Quote:
Originally Posted by brett.c
I decided that I didn't like to look of the cowl with the intake above the spinner.
I think this is a great improvement!! (I didn't want to say anything, but I'm glad you changed it! I thought the original looked upside down!! but the inlet would have looked good below the spinner!!) the new look looks much more streamlined!! I also like your take on the tailfeathers!!! it's really coming together!!


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