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Old Jan 03, 2009, 04:28 PM
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Cardboard 3D Scratch Build.

My winter project. Hope to have it built and ready to fly this spring.

The plan is to build a low wing 3D capable airplane using mostly cardboard utilizing simple slab techniques for the wing construction and box construction for the fuselage.

Target specs are :
AUW: < 1200g
Wingspan: 42" - 46"
Wing area: ??
Length: 40" - 45"

Power setup will be:
Motor: Turnigy C35-42 1100
ESC: CC Pheonix35 or Plush 45
Batteries: 4S1P 2100 LiPo

Radio: Spekrum DX6
Servos: unselected as yet ( would like to use HiTec HS65MG but they are pricey )


Attached photo's are of 2 other cardboard aircraft I built and subsequently crashed. Both flew quite well, the first one was overweight. Both ended up crashing in nose down dives that neither recovered from. I learned quite a bit from the builds of the first 2 That I will incorporate into this 3rd build.

Comments and questions are welcome.

jc
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Old Jan 04, 2009, 10:04 PM
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Started the wing prototype today. Using an "I" beam for the spar, constructed from 1/8" x 1" balsa with 1/16" x 1/4" basswood for the top and bottom of the beam. I also re-enforced the root on each side with a strip of 1/32" ply on each sde of the spar. The weight is 13g for a length of 22".

Wing is made from a single piece of cardboard folded in the center. with as much of the cardboard cut out as I think is reasonable.

At this point I am not planing on making the wings removable. I will be doing some basic load testing to make sure the spar can support the required load.

Anyone know what is a reasonable multiplier for wing loading on a 3D aircraft ?

For my testing I am planing on clamping the root of the spar in a vice and then loading the single wing with weights; I was thinking that each wing should be able to support at least 2 x AUW.

jc

jc
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Old Jan 05, 2009, 07:39 PM
Zor
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Quote:
Originally Posted by jonathanC
Started the wing prototype today. Using an "I" beam for the spar, ; I was thinking that each wing should be able to support at least 2 x AUW.

jc
Hi jc,

With all the openings cut in the wings cardboard you will have to cover with something glued on.

I wonder why not leave the cardboard full and finish with some paint.

Zor
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Old Jan 05, 2009, 09:20 PM
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Zor,

Cardboard is a relatively heavy material. My first cardboard airplane ( the yellow and black Yak pictured above ) did have solid cardboard on the wings and fuselage. and weighed in at 1200g +. This would be fine for a sport plane of the size I built but I was trying to get a more 3D capable aircraft. Using solid cardboard sheeting does simplify the build but ends up adding 20% or more to the weight. I found by cutting out some of the cardboard you can still keep it simple and reduce the weight.

The link below is for cardboard aircraft using the methods you suggest. The author Chuck Felton has built some truly remarkable models using that technique.

http://home.earthlink.net/~charlesfelton/
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Old Jan 05, 2009, 09:28 PM
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Waiting for the wing prototype glue to harden then I will load test it. The dark stains on the leading edge is from CA glue used to stiffen and strengthen the leading edge.
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Old Jan 05, 2009, 10:05 PM
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OK well the wing survived the basic load test. I clamped the root of the spar in a vice with rubber jaws and then placed a 2Kg bag of rice half way down the wing. It held up no problem with just some slight flexing ( in the rubber jaws ).

The wing specs: ( without Aileron )
Weight: 81g uncovered.
Length: 500mm
tip: 165mm
Root: 235mm

( As a comparison my Chermark YAK54 has a similar wing area and is made of balsa and comes in at ~100g with aileron and covering )

Next steps will be to cut out the aileron and then its on to the side template for the fuselage.

jc
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Old Jan 06, 2009, 10:08 AM
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Hi JC,
Chuck Felton here. Your 3D cardboard designs are very inovative. As you have demonstrated, the cutouts in the wing panels save significant weight. I have thought about doing this with my own designs, but they are sport flyers so I don't go to the trouble. But I think our cutout method could be used to make a viable CL stunt model as well as your 3D RC design. Even with the cutouts the wing is very strong due to the stiffening effect of the cardboard wing skin.

As you probably saw on my site, I use 1/8" B Flute with white paper facing on one side. This cardboard has a weight of 2 oz/sq ft or 59 grams/sq ft. I would be interested to know the thinkness and weight of the cardboard you use for your designs.

My latest model shown in the photos is a 60" CL Piper Pawnee with a 40 engine. The all-up-weight is 55 oz with a wing loading of 15 oz/sq ft, not too bad for cardboard with no wing cutouts. After 30 years I am still hooked on building with this inexpensive material. Keep up the good work.
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Old Jan 06, 2009, 02:22 PM
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Glad to see you taking an interest in this project Chuck. Your builds are truly impressive. Its always good to see people trying out alternate building techniques.

The cardboard I use in my builds comes from packing material. Unfortunately there is no stamp on the cardboard so I can't be sure of the type. But it looks like 1/8" fluted non recycled with a smooth finish on one side. I will weigh some tonight and let you know the weight. I am fortunate that I had a supply of 4' x 8' sheets used to pack some metal doors.

One thing that surprised me when I started using cardboard is how strong it is once its been cut and folded into shape. For additional strength I put a thin film of glue ( usually generic white glue ) in any cuts and folds. This is improtant if you want to maintain a curved surface without adding any ribs or spars.
This time around I'm using thin CA glue. It adds incredible strength and rigidity to the cardboard but as you can see it bleeds badly. I need to test to see if Monokote will stick to the CA soaked cardboard, if it doesn't this might be a problem when I come to cover it. Standard Monokote film sticks to the smooth side very well.

One problem I haven't worked out yet is how to use cardboard on tight bends that change in radius or rounded corners; such as canopies and the rear top of the fuselage. In the past I've used balsa or kept the frame square.

I would also like to make the wings removable. My plan is to use thin aluminium or carbon fiber tubing as the male and cardboard tubing as the female. Pretty much the same setup as in commercial ARF kits. As yet though I have not found a source for the cardboard tubing.
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Old Jan 06, 2009, 04:45 PM
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JonathanC, Super interesting! The first cardboard airplane I ever saw was crashed in a swamp. The flying field my first club owned was almost surrounded by swamp. Two guys had a a midair. A bunch of us went out to look for the pieces and came upon another lost airplane built from cardboard that had been out there for a month or so. The airplane had pretty much turned to mush (as would a balsa plane have, too). However, at the time I would never have considered the use of this material to build airplanes with. Thanks for posting this build, I will visit here often!
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Old Jan 06, 2009, 06:40 PM
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Swamp recovery doesn't sound like too much fun ModeOne. Hope you had hip waders on.

I weighed a 38" x 42" sheet of the cardboard I'm using and it came in at 1lb 5.25oz or ~600g. That's 55g/ft2
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Old Jan 06, 2009, 08:52 PM
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I have cut the prototype aileron from a single sheet of cardboard and removed some cardboard from the center, leaving a thicker center support soaked with a little CA glue for strength to attach the control horn to. See attached picture.

The wing dimensions including aileron are:
Root: 12.5" (315mm)
Tip: 8.5" (216mm)
Length: 19.5" (500mm)

This gives a total wing area of ~2.85sq ft. This should be enough area to keep the wing loading down to ~13oz/sq ft giving good performance for my power setup.

The attached shot shows my last side fuselage template, I need to rework this as I need it slightly longer from where the wing spar attaches to the tail. I also need the sides to be deeper to accommodate the 1 1/8th " spar depth.

Also not sure if I want to go with the square look of my second plane for the cockpit or use an off the shelf parkflyer cockpit. The second option gives it a better "scale " look but is harder to incorporate into the build.

jc
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Old Jan 06, 2009, 09:30 PM
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JC
Thanks for the weight info. You've got yourself some good model building cardboard at 55 gr/sq ft, even lighter than what I am currently using at 59 gr/sq ft. It doesn't get much lighter than that for 1/8" thickness. Good luck and I'll follow your progress also. Chuck Felton
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Old Jan 07, 2009, 08:33 PM
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Thanks Chuck.

I have cut out a second fuselage template. This one is longer than the first and will be more of a square box construction. The white cardboard on the fuselage in the picture will be EPP foam on the finished model. I am going to try using EPP foam so I can get a better shape to the rear top of the fuselage. The white tail is a rough tail template.
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Old Jan 11, 2009, 06:21 PM
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Not a lot to report. I did some test shaping of foam and gluing of sheet balsa to the foam so I can get the covering to stick. I think I have a technique that will work.

I have cut the fuselage side templates, I need to work on the second wing next, as the wings are tapered and I need both wings assembled in order to get the correct angle where the wings meet the fuselage.

I picked up some HiTec HS65MG and Karbonite servos for the tail, rudder and alerons. Along with the servos I picked up a canopy from a Mini Funtana. Might be a bit of a challenge to get the canopy to fit.

Will post more pictures when I get the second wing constructed.

jc
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Old Jan 13, 2009, 10:52 PM
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Both cardboard wing frames are built and the fuselage side frames are cut. Servo location holes have been cut in the wings. For this step I cut the hole to match the servo, place the servo and screw it lightly in place. Now remove the screws and servo and put a drop of thin CA in the screw holes and let harden. This provides a solid grip for the screw.

The pictures show how the side frame will taper back towards the tail at the correct angle while the wing spars are correctly aligned with each other.

As I increased the length of the body on this build compared to my previous plane, I am a bit concerned about getting the CG in the right spot. According to my calculation it should be 81mm back from the leading edge ( pretty much right under the wing spar ). I am hoping that using foam on the top rear of the fuselage and locating all the servos closer to the CG I will be alright. I'll have to wait until the build is a further along before I can check it out though.
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