quorneng
Master member
In aero modelling it is not long before material strength to weight becomes significant both in tension and compression.
Why not use high strength materials to build an RC plane? You could but to keep the all up weight within bounds the material would have to be very thin indeed. Not a problem for the tension forces but very thin material simply buckles at a very low compression. It follows that one material all in the same form makes a poor light weight structural material.
As basic 3D printing can only produce the same material it suggests it is not a 'good' process to produce a complete plane. It will be hard to create a structure that even approaches equal properties in tension and compression. To withstand both tension and compression means the elements in compression will have to thicker & heavier than those in tension which means the weight penalty is going to be significant.
One way to improve the compression performance of a thin material is to support it in such a way to limit buckling. This can be done by creating an integrated "cell" structure using the same material. This is in effect what most printed planes use but it is complex to programme and slow to print which limits just how fine and structurally efficient the support element can be.
Indeed most printed planes are already a 'composite' structures using inserted carbon rod or tube reinforcing elements to handle much of the bending loads.
The end result is all printed plane that has sufficient strength but it is not using all the material efficiently and is thus heavier than it might otherwise be. It is worth noting that the power required to fly a plane is directly proportional to its weight.
Once I had used a 3D printer I decided that it would be best used where its strengths (accuracy and repeatability) would give the most benefit and any weight penalty would be acceptable. This view was particularly driven by the fact I tend to build 'lightweight' planes that used a lot of sheet foam!
My usual foam wing construction consisted of thin foam top and bottom skins over foam ribs with a balsa spar. Cutting a lot of ribs accurately can be a chore. A 3D printed rib looked promising, particularly as the process allowed a single rib design to be scaled down to allow a tapered wing.
Starting simple I used printed ribs on a 'plank' wing.
20 full ribs, 8 shorter to allow for the ailerons but all of otherwise identical section.
After quite a bit of trial and error each 3 mm thick rib is a warren brace but with a thin (0.2mm) 'web' overall on one side.
Each full rib weighed 1.5 g compared to 1g for the same in 3mm sheet foam but was considerably stiffer. Furthermore I did not have to cut them out, just watch the printer make them!
The completed wing.
Light, stiff and remarkably simple to make.
If ribs work how about fuselage formers, particularly for an airliner fuselage?
Same sort of structure but as a 'ring', a circular I beam.
In fact such a former of the same weight and strength would be hard to make in any other material!
Part of the completed fuselage.
Needs some novel techniques to build but the end result is incredibly light and stiff.
There are of course other areas where the strength required means a full printed structure is acceptable, particularly if more than one is required.
These are some examples of how I have used 3D printing to make parts to build RC planes.
I have printed a sub 250g RC plane that uses only 3D printed parts and tissue but that is another story.
Why not use high strength materials to build an RC plane? You could but to keep the all up weight within bounds the material would have to be very thin indeed. Not a problem for the tension forces but very thin material simply buckles at a very low compression. It follows that one material all in the same form makes a poor light weight structural material.
As basic 3D printing can only produce the same material it suggests it is not a 'good' process to produce a complete plane. It will be hard to create a structure that even approaches equal properties in tension and compression. To withstand both tension and compression means the elements in compression will have to thicker & heavier than those in tension which means the weight penalty is going to be significant.
One way to improve the compression performance of a thin material is to support it in such a way to limit buckling. This can be done by creating an integrated "cell" structure using the same material. This is in effect what most printed planes use but it is complex to programme and slow to print which limits just how fine and structurally efficient the support element can be.
Indeed most printed planes are already a 'composite' structures using inserted carbon rod or tube reinforcing elements to handle much of the bending loads.
The end result is all printed plane that has sufficient strength but it is not using all the material efficiently and is thus heavier than it might otherwise be. It is worth noting that the power required to fly a plane is directly proportional to its weight.
Once I had used a 3D printer I decided that it would be best used where its strengths (accuracy and repeatability) would give the most benefit and any weight penalty would be acceptable. This view was particularly driven by the fact I tend to build 'lightweight' planes that used a lot of sheet foam!
My usual foam wing construction consisted of thin foam top and bottom skins over foam ribs with a balsa spar. Cutting a lot of ribs accurately can be a chore. A 3D printed rib looked promising, particularly as the process allowed a single rib design to be scaled down to allow a tapered wing.
Starting simple I used printed ribs on a 'plank' wing.
20 full ribs, 8 shorter to allow for the ailerons but all of otherwise identical section.
After quite a bit of trial and error each 3 mm thick rib is a warren brace but with a thin (0.2mm) 'web' overall on one side.
Each full rib weighed 1.5 g compared to 1g for the same in 3mm sheet foam but was considerably stiffer. Furthermore I did not have to cut them out, just watch the printer make them!
The completed wing.
Light, stiff and remarkably simple to make.
If ribs work how about fuselage formers, particularly for an airliner fuselage?
Same sort of structure but as a 'ring', a circular I beam.
In fact such a former of the same weight and strength would be hard to make in any other material!
Part of the completed fuselage.
Needs some novel techniques to build but the end result is incredibly light and stiff.
There are of course other areas where the strength required means a full printed structure is acceptable, particularly if more than one is required.
These are some examples of how I have used 3D printing to make parts to build RC planes.
I have printed a sub 250g RC plane that uses only 3D printed parts and tissue but that is another story.