Scratch Build New Dog Plane From Coroplast
 

I have really enjoyed my LA Biplane, which was built from coroplast, and just finished 500 flights with it. The only issue I have with it is that it takes 12 bolts to put together at the field.

I'd like to have one that is easier to put together and is a good sturdy plane for sport flying and rough field use. I don't like having to turn a plane upside down to mount the wings, or have to build a cradle to carry it.

We have two planes at the field that are like that, I think they are Giant Ugly Sticks and have been around forever and have had several owners. They have been through several crashes and repairs and look pretty beat up. One is called the Big Dog and the other one is called the Old Dog.

I thought I'd make something similar and call it the New Dog.

I started on the design late last month.
https://cimg3.ibsrv.net/gimg/www.rcu...4fa4981ddf.jpg
Wings lock in place with 1/4" bolts in brass tubes inside plastic guides which will look like machine guns. They will be inserted through the front of the wings.
https://cimg4.ibsrv.net/gimg/www.rcu...2604dd2047.jpg
Started with 9 oz of bulkheads, saved 4 oz of weight.
https://cimg5.ibsrv.net/gimg/www.rcu...3604563ae0.jpg
Main wing spar from spruce and pine lattice wood.
https://cimg8.ibsrv.net/gimg/www.rcu...5c62dae288.jpg
The inspiration.

Some details.

Power will be a DLE 35ra. I have five of these engines and they have all been great.

The fuselage weight is 2 lbs at this stage, mostly due to the 1/4" ply sides. It will gain about 3/4 of a pound with the covering and rear spars. I'm using a design similar to the LA Bipe, it's easy to modify my bulkheads to go from a low wing to a mid-wing.

The wing spar weighs 2 lbs 8 oz and is 84 inches with an 18" cord. It will double in weight with the ribs, servos and covering.

I'm not worried about weight, this is not designed to be a 3-D plane. It should be around 13 lbs when finished.

https://cimg2.ibsrv.net/gimg/www.rcu...3d5c3812cd.jpg
Today I got to monkey around with the New Dog a little. I need to do an aerial assembly of the wing due to the way it mounts to the fuselage so it will fit. I don't have laser cut parts so the fits are not perfect. I'm using a precision building technique I learned in the Air Force, measure it with a micrometer, mark it with a piece of chalk, then cut it with an axe.

I have the wing almost ready to cover. Right now it's just tacked together, just need to put a half pound or so of glue on it to hold it together during those rough touch and goes.

The weight of all that wood and glue so far is 5 lbs 12 oz. The main landing gear will add another pound. The rest of the fuselage will be 1/4" sticks and the tail blocks and wheel so that won't add too much more weight.
https://cimg5.ibsrv.net/gimg/www.rcu...cc8e836697.jpg
Wing almost ready to cover
https://cimg6.ibsrv.net/gimg/www.rcu...1ab7ee74f9.jpg
Slides together easily.

The good thing is that it slides together easily and that was a real challenge.

Working on the rear of the fuselage. This takes a lot of time since I need to put in elevator and rudder servo plates, a tail wheel plate and the plug in mount for the rudder and stabilizer.
https://cimg9.ibsrv.net/gimg/www.rcu...d084e6b411.jpg

I almost forgot. The wing root construction is a little complicated due to the overlap of the wood spars.
https://cimg7.ibsrv.net/gimg/www.rcu...eb3fc9cca4.jpg
Middle root rib cutout.
https://cimg9.ibsrv.net/gimg/www.rcu...2291023380.jpg
Rear of root rib offset.

It's a good idea to get the tail feathers as straight as possible. Straight planes fly better.
https://cimg9.ibsrv.net/gimg/www.rcu...bba28e51bf.jpg

The fuselage is mostly finished except for adding the stab mount and Coroplast covering.
https://cimg0.ibsrv.net/gimg/www.rcu...5d2cda1b51.jpg

Corky is not going to be the pilot, he has no sense of responsibility.

I had a good question from a friend on another website, he asked "How do you know the weight ratio of engine placement to "pilot" placement ratio?" It's simple, I use TLAR.

It's an aeronautical engineering principle that has been used since the Wright Brothers designed their first plane. There are thousands of calculations involved with an aircraft to get the weight and balance just right to make a great flying plane.

The formula is quite complex and involves a lot of physics and moment arm calculations using known weights and distances. Many times the exact weights or distances are unknown during the design phase and things also change over time as the design progresses.

A lot of engineers use the complex 'system of equations' with unknown variables, that they learned in algebra, to give them an idea of the correct placement. Unfortunately for me, that takes a lot of time and math skills that I don't have.

I rely on the simple and time tested method, TLAR, that I use a lot since it has applications in many areas of science and life. TLAR is an acronym for That Looks About Right.

I've been doing some weighing of the various parts of the plane and so far, the weight is not too bad. I wanted to keep it around 14 or 15 lbs, which should give me great performance, for a sport plane, and not blow around in the wind like a feather. The max needs to be under 18 lbs.

I don't have the coroplast covering on anything yet.

The wing, with servos is 4 lbs 8 oz. Fuselage is 4 lbs, with servos, landing gear and wheels. The engine with ignition is 3 lbs.

The batteries, receiver, switches, and fuel tank, will add about a pound.

I don't have the weight for the stab and rudder yet.

It might come in a little over the 15 lb estimate.

Getting closer to the completion.
The horizontal stab is finished.
Got to pick up another sheet of coroplast today and get started on the covering.https://cimg2.ibsrv.net/gimg/www.rcu...86483d190b.jpg

My method for getting the stab straight.

I fabricate two stands and use them to keep the rods level with respect to the fuselage.

I wallow out the holes a little with a step drill. Put the rods in and tack the washers in place with CA, then fill in the wallowed out holes with microballoons and CA.

When the left and right halves of the stab are slid onto the rods they will be lined up.
https://cimg9.ibsrv.net/gimg/www.rcu...ab7409cab5.jpg

Okay, close enough for government work.

That is really cool. I'm curious about the Coroplast, as mentioned in the thread title. Is it used only for sheeting?

There is extra satisfaction when you build a plane from a kit, and a ton of extra satisfaction when you actually design it yourself. When I build kits, I always modify the design, either to make something better, or to just customize it to my wants/needs. I love building kits as much as I love flying, and I actually designed and built a plane a long time ago.

I know what you mean about the TLAR. I was actually a mechanical engineer, and I used TLAR far more often in my career than actually calculating stuff. Truth be known, I only used calculus one time in my entire career, and that was only to save me from doing a couple of hours of algebra calculations, since the calculus method was really quick and simple. I couldn't tell you the first thing about calculus now, since I forgot every single thing that I learned 35 years ago.

I finished the rudder, it was quick. Just glued three pieces together and cut out one of the flutes to make the hinge.

The stab is a little harder. I decided to add some trailing edge balsa to give the coroplast something to bond to.

I cut a lot of flutes out to make it easy to bend around the ribs. I also cut out a flute to make the hinge. The elevator portion will be doubled over to make it rigid.

I'll also slide bamboo skewer material in the flutes where the control horns mount to keep them from collapsing.
https://cimg0.ibsrv.net/gimg/www.rcu...1147d965be.jpg
https://cimg1.ibsrv.net/gimg/www.rcu...f72ea06d0c.jpg
The rudder is locked into place by the rods for the stab.

Outrider6 - I mainly use the coroplast for the sheeting. Sometimes I use it to reinforce areas that may flex or need more strength. The neat thing about it is that it also makes the hinges with no air gaps. I used to worry about how long they would hold up, so far they are doing great on my biplane, it has over 80 hours of summer and winter flying time with no cracking of the hinges.

There are a lot of things I really love about the material. It is super strong, resistant to almost everything, cleans up with windex, it's easy to shape, except for compound curves, it cuts like butter, it's really cheap, 4'x8' sheets only cost $12, it comes in over 20 colors, no ironing or painting is required and it never wrinkles.

It is a little heavy, a 4x8 sheet weighs 5 lbs, 4 oz. Some of that weight can be used to make a structure stronger. I do that with the stab and wings.

I'm thinking about making another fuselage for this plane and shave off over a pound. It depends on how happy I am when I fly it.

Almost have the stab completed.

This part is not too bad. Even with CA the process is slow. The CA does not cure very fast on coroplast, it can take three days to reach full strength. I usually glue, clamp wait a few hours and glue some more.
https://cimg1.ibsrv.net/gimg/www.rcu...aef38d3c74.jpg
Getting the flutes cut for the bends.
https://cimg5.ibsrv.net/gimg/www.rcu...67d39e35ce.jpg
Trial fit before putting on the glue.

Slowly making progress. Got the tail feathers fitted on the fuselage this morning. Still need to do a little trimming and work on the stab.
https://cimg0.ibsrv.net/gimg/www.rcu...cff5a683b0.jpg

I have one heavy wing half almost done. Came in at 3 lbs, 8 oz. Just need to cut the aileron to make a flap and add some servos and controls.
https://cimg7.ibsrv.net/gimg/www.rcu...4fdbcb6b08.jpg

I was just looking at the weights of all the parts so far. Looks like it will be on the heavy side, not close to 15 lbs, but still around 10 oz under my max of 18 lbs, since I didn't do the normal lightning hole thing. It should still have good vertical performance, it just won't accelerate straight up.

Got both wing halves finished.

Working on getting the servos installed.

Then on to the fuselage covering. I'm saving that for last in case I need to do some chopping on the fuselage, or move some servos out of the tail to adjust the CG.

Getting the servos and control rods mounted. I don't like this part of the building process. Actually, I don't like any part of the building process. I'd rather be flying.

I like to set mechanical differential in the aileron control horns. It's easy to do and I can adjust it later electronically if needed.

The short bamboo sticks are put into the flutes under the control horns to prevent the coroplast from being crushed when the horns are bolted on.
https://cimg4.ibsrv.net/gimg/www.rcu...c2cbd4bf26.jpg

This is a great ignition setup that has a high reliability and redundancy built in.

I've found that the Tech Aero IBEC has been way more reliable than the Opto Kill circuits.
https://cimg4.ibsrv.net/gimg/www.rcu...a0e4f5eb27.jpg

I'm working on a New Dog II design. Just in case I'm not happy with the weight and performance of this one.

It will be lighter and simpler to build.

Getting ready to cover the fuselage with the green coroplast.
https://cimg4.ibsrv.net/gimg/www.rcu...d6079b2e0d.jpg

Poked a few more holes in it and shaved off 4 ounces.

Slow progress on the old New Dog plane build.
https://cimg3.ibsrv.net/gimg/www.rcu...06f14eae7e.jpg

Got the hard part of the fuselage covered. Coroplast only likes to bend one way. It also takes several hours for the CA glue to fully cure.