Avro 504 N/O 1/20th scale electric

[g_kandylakis]

Having caught a cold and now recovering, I do not feel like going to the workshop to build anything. Better to stay warm and comfortable.

So, to pass the time in a creative manner I thought I 'd repost the build thread of my Avro 504 N/O. The detailed and rather long thread is of course lost togethere with "HPA 2.0"

The model is 1/20 scale, giving it a wingspan of 549mm and a wing area of 7,3 dm2. Target weight was in the 75 gram range (more on that later...)

It was meant as a replacement for competition use of my de Havilland 9 from 2010. The model was started in 2020, after sufficient documentation was collected in order to arrive to a well detailed model. It was completed just in time for the 2023 IIFI meeting in Nijmegen.

[g_kandylakis]

The Hellenic Naval Service received 6 aircraft of the type in 1925, in an attempt to reorganize after many years of military adventures, the first World War and the Greek-Turkish war of 1921-23 that followed.

From the build start one goal was to make the model convertible as well, in land and hydro form. This added some complexity but was indeed fun to achieve.

Also, the model would be flown free flight for the corresponding competition use but also radio controlled, when flying in smaller halls for trimming or fun. Too risky to fly it otherwise.

The method of switch to and from ff/rc has been described in a short article in May 2025 Aeromodeller magazine.

[g_kandylakis]

I started with the tail, which was rather easy.

Wanting to achieve thin scale-like outlines, outline accuracy and stability, I chose the full balsa core method, as is mostly used in larger models.

Thin 0,5mm balsa sheet, cut to size and ribs glued on either side to simulate the scale structure.

[g_kandylakis]

the outline itself is a wider curved piece of balsa, to simulate the tubing of the original.

The complete rudder is then sanded to airfoil ahape, using thin plastic as guides to limit the amount of material to be removed.

[g_kandylakis]

The same process was used for the horizontal tail, the stabiliser and the two elevators.

The sticks glued on one side remain oversize until the second side is done, to help with alignment

[g_kandylakis]

with the second side done, everything is trimmed to the core outline and the actual outline is added

[g_kandylakis]

and the stabiliser

[g_kandylakis]

tail finished and sanded

[g_kandylakis]

next came the fuselage.

I wanted a scale like structure so prefered to use basswood over balsa for the longerons, as this allows thinner cross sections to be used without sacrifising strength. There may be a small weight penalty involved but overall it is much better looking, especially in the open cockpit areas.

Some uprights in high stress areas were also made of basswood, the rear ones of balsa.

As usual, one side over the other to ensure complete repetition

[g_kandylakis]

there is some internal diagonal bracing that will be visible from the cockpit holes, so this was to be added.

Bt first, to avoid any deformation, a temporary balsa sheet piece was glued to each side for strength.

[g_kandylakis]

Thin thread, fuzz-free, was used fir the rigging. IT was CAed at one end and then, using weights to get equal tension, it was secured on the other ends.

[g_kandylakis]

the extending edges were cut and the balsa temporary parts removed with thinner, so the fuselage sides were ready to glue into a box.

Nothing unusual here, a slow process to ensure everything is true and square.

[g_kandylakis]

then came the first difficult task, to cut the formers for the stringers on the top and sides.

First attempts proved a disaster as the very thin and narrow balsa formers broke very easily, so I changed my approach and extended the parts beyond their outline, so that I could cut them to size after they were glued to the fuselage.

Before starting to glue the stringers a thick balsa block was glued to the bottom side of the fuselage to keep everything square. It would be removed only after the sides were done as well.

Black arrows indicate where glue was applied, so that the thinner would be applied for taking the block out.

[g_kandylakis]

The stringers were again made of basswood, sanded thin enough, aprox 0,8x0,5mm using a very simple sanding jig. It took some time though to get them all done.

[g_kandylakis]

all side formers added