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What all lies between DTFB and full balsa builds?

Tench745

Elite member
#22
Just one more comment or thought for you. The shape of the structure is what flies and the weight should only be adequate to maintaining the shape. You can build a plane out of almost anything but the real trick is to build the structure strong enough and light enough.

many people tend to be sort of stuck in a single technique or 2 and have their own material preferences. With the modern range of available materials the planes we fly should be engineering marvels but sadly they tend to be built full of compromises and often far too much material and hence weight.

Using the properties of the various materials and selecting the material, for each and every part, in relation to its strength and weight requirements would be the best approach. Balsa has great compression and tension resistance in one plane but is very weak in the other planes. FB has good tension properties but fails in compression. Plywood has great tension and compression properties in multiply directions but is really a little heavy as it often carries laminations that are set at angles, (by the construction), that are not load bearing and only provide a degree of support against deformation.

Other materials have better properties but tend to be rather brittle and lack resilience.

On other concern in material selection is the jointing or materials. Balsa tends to rip or splinter around its glue joints of even fail well away from the joint by splintering. Plywood not only breaks but its also tends to delaminate at the point of failure. FB crushes and tears whereas FGlass, CF, and 3D printed plastics seem to shatter. My current work into structures is to improve the security of the material joints, stress transfer from the joints and joint security under impact forces through material selection and design.

Simply put you can build out of anything! The best build will use a multitude of different materials each selected as best for purpose. (Purpose can include price, availability, and tooling requirements). There is NO superior material but rather each material should be seen as having advantages and disadvantages. You chose based upon maximizing the advantages and minimizing the disadvantages.

I still build using FB BUT by using many other materials I now build at about half the weight and with far greater strength/durability.

Just a few thoughts!

Have fun!
This very eloquently puts what the intent behind my "Plywood shouldn't be a primary building material" statement was. It is not the best choice of material for most structures in model aircraft. Full scale aircraft like the Falco use its properties well and have the size to carry that difference in weight.
 

Bricks

Master member
#24
Something many seem to forget is you are not building a plane to crash it or make it crash proof , you should be building to reveal the best flight characteristics of the design. The ARF`s are not built for crash resistance they are or at least should be built to fly the very best they can with the material they are built from. My 3D HobbyShop Demonstrater is built from plywood for rigidness and lightness, when looking at the design, if it was built out of balsa it would take much more wood to get the same stiffness which would be more weight to the overall plane..
 

Hai-Lee

Old and Bold RC PILOT
#26
I agree and disagree!
Manufactured retail product, (unless built for commercial usage, full sized aircraft, Man carrying), are built to a price. Just because a design is rendered in foam, balsa, Plywood, plastic, FGlass or even CF does not mean that it was built with the absolute best material. Sure plywood has great rigidity but also great brittleness combined with long term delamination issues.

As structural loads do not always act in the same direction throughout a model wing or fuselage and if the parts are cut via laser or similar there will be some areas that are not optimized for proper use of the material strengths and so extra material is normally used,

Personally I have FB, Foam, foamcore, Balsa, and plywood planes most factory built, (not the FB of course), and each has its own strengths and weaknesses. Additionally I repair models, (any model), for other club members who have problems in effecting their own repairs, construction materials not an issue!

Apart from the materials there is the construction methodology which can make or break the plane. I am sure that if you took a balsa design and cut the parts out of Ply then it would be way too heavy to fly well and conversely if you took a plywood design and built it out of Balsa it would be weak or even require serious amounts of additional material to make it fly properly. The design is the Key! Look at the plans for 2 identical planes made in different materials and the required differences and the different approaches will be very obvious.

There is no comparison of all ply Vs balsa Vs some other material you can build in whatever you like or choose. Just remember that each material has its place in a properly engineered Model.

Have fun!
 

Bricks

Master member
#27
I am wondering if your plywood delamination is coming from your local weather or quality of ply as I have several models going on 45 years with plywood in them and there is no delamination. I just sold a plane that was built in the early 60`s even the firewall was solid after all these years of glow fuel. It was a scratch build he even had the wings fold back pull a pin on each wing the ailerons would fold up as the wings would rotate to be on edge as they were swung back to the rudder. for carrier use it was an observation plane it was called the Fairchild.
 

Attachments

#28
I am wondering if your plywood delamination is coming from your local weather or quality of ply as I have several models going on 45 years with plywood in them and there is no delamination. I just sold a plane that was built in the early 60`s even the firewall was solid after all these years of glow fuel. It was a scratch build he even had the wings fold back pull a pin on each wing the ailerons would fold up as the wings would rotate to be on edge as they were swung back to the rudder. for carrier use it was an observation plane it was called the Fairchild.
Its definitely not the weather in my opinion, it's the quality of the wood, I purchased plywood from the DIY Warehouse called Bauhaus here in Germany and even looking at it for too long made it crumble.....the glue they used is an important part as well.
 

Hai-Lee

Old and Bold RC PILOT
#29
I am wondering if your plywood delamination is coming from your local weather or quality of ply as I have several models going on 45 years with plywood in them and there is no delamination. I just sold a plane that was built in the early 60`s even the firewall was solid after all these years of glow fuel. It was a scratch build he even had the wings fold back pull a pin on each wing the ailerons would fold up as the wings would rotate to be on edge as they were swung back to the rudder. for carrier use it was an observation plane it was called the Fairchild.
Firstly Plywood varies in so many ways that there are different grades and categories of plywood. The wood which is used in its construction can be from extremely softwood through to the best of rot resistant hardwoods. The glue used in the laminating process can likewise vary in properties.

Plywood can delaminate for a number of reasons including water damage, fuel contamination, solar degradation of the glue, unseen stress fractures in one or more of the laminations or even though external forces being applied that exceed the plywood's glue adhesive properties/strength.

Sure there are many surviving examples of old models having pristine plywood parts but similarly there are examples of modern kit planes having delamination problems from a very young age. Those that produce the kits nowadays, (China), use the cheapest material to keep their prices at rock bottom and so delamination is becoming a problem in its own right. You can do a few checks on a kit if you know what you are looking for but then I now seal the plywood areas/parts of planes I get in for build, rebuild or repair to improve their shelf life.

To improve structural strength and life span I try to use, aviation, marine or structural plywood but then cost and availability can be problematic. You can treat or seal substandard plywood's for strength and longevity but the life of the model and its initial costs need to be factored in.

Enough on this subject for now. For those really interested in the grades and variations in plywood should do their own internet research, the information is really eye opening!

Have fun!
 

FoamyDM

Building Fool-Flying Noob
#31
I've tried my first foray in this (I think). I took a Balsa Kit and cut it from Foam Board, when I build my Skinimoa. It is 1/4 the weight, and as it's a small plane, strength is less a concern. This skin is going to add most of the strength.

In most engineering, it it a trade off between functional effectiveness vs cost efficiency. it's why anything is done. Composites can be a spectacular tailored fit for your project but come at a cost of time and money, where in many spots, the free wood stir stick and $4 worth of Foam Board do the trick. Cost is durability and moisture sensitivity. This occurs frequently just like bridges lets say. they can be made from nearly ANY material. just some are WAY more $effective. and so they mostly boil down to steel and concrete. or some marriage of the two. but they have been made from CF, FG, Recycled plastics, trees/wood, laminated wood, aluminum. even how they get used as steel and concrete varies widely.
point is it is worth mixing and matching all these methods.