Antonov AN124 Ruslan

[Simon Chaddock]

My 'racing drone' powered EDF Airbus A350 flies rather better than I dared hope but could the principle be expanded into a 4 jet?

A couple of months ago an AN124 flew several times into Manchester, and a smokey old thing it is, but it does has many characteristics that might work in its favour.

Compared to the size of its turbo fans it is a big plane with a larger wing area than say a 747.

With a high wing layout it can belly land on the fuselage rather than the engine nacelles as does the A350.

Its huge complex cross section fuselage is a negative both to build and for surface area drag but as a slow flying light weight the penalty is less severe than it might be.

Using the same Drone motors on 4s and 4 blade 5x3 'fans' it comes out with a 2.6 m span. Rather big considering it will be made largely from 2 mm Depron to stand much chance of being light enough to fly on the limited thrust available.

My first "experiment" was to examine the possibility of printing the complete nacelle and pylon. The A350 was also printed but used a planked Depron outer skin.

It would look something like this.

Like the A350 it is in 2 parts, the pylon and motor mount and the nacelle.

A bit disappointing as the body of the nacelle is rather delicate and it weighs 44.5 g which is 10 g more than the motor and prop. It also takes over 4 hours to print both parts.

Although not a project killer as I can always revert to the more complex multi part but lighter A350 type of nacelle construction.

The next "make or break" decision point is the wing or rather the inner section that carries the nacelles. It will be all to easy to end up with a total weight that would make the 10 g "excess" of each printed nacelle pale into insignificance!

Edited By Simon Chaddock on 15/09/2019 15:12:54

[Simon Chaddock]

Like my A350 the AN 124 will use a considerable number of printed parts probably rather more as it rather be bigger!

The wing will be in 3 pieces, a 1280 mm centre section with 'plug in' 700 mm outer panels.

I even managed to find a reasonable representation of the Tsagi 12% wing section.

The root wing chord is huge at 450 mm and far larger than my printer bed so many of the ribs will have to printed in pieces and glued together.

Ribs 1 to 3

The ribs use a "U" channel section with a material thickness of 0.2 mm.

There will be a single balsa/Depron/balsa spar. The 2 mm balsa spar flanges will be incorporated into the 2mm Depron skin.

The full set of 12 ribs for the RH inner panel out to the wing joint.

The wing join will use a 10 mm tapered glass fibre tube.

This will in effect be a test build. If it proves to be unsatisfactory I doubt I will proceed any further and even if I do it will most definitely not be a quick build.

Edited By Simon Chaddock on 17/09/2019 14:21:41

[paul d]

Following with interest Simon, as you know all this printing parts goes completely over my head but I do find it fascinating.

[Simon Chaddock]

The RH inner wing being assembled on the preformed lower wing skin which also incorporates the lower balsa spar flange.

Depron shear webs are added between each rib. The double shear web indicates where the outer wing panel joining tube plugs in.

The extra ribs ahead of the spar indicate the nacelle pylon positions.

Next the upper leading edge and the top spar flange are added.

This creates a very strong and stiff D box so the wing can be lifted from the board and safely handled.

The bag contains the 40 printed rib components required for the LH inner wing panel.

[desmo888sp]

awesome simon!

[Simon Chaddock]

Before starting on the other side of the wing it was rather important to complete a wing joint.

In comparison to the inner panel the outer section is alarmingly simple being little more than Depron skins with no spar and virtually no ribs!

The three Depron shear webs create the required wing section when the top skin in glued in place.

The two printed rib hold the joining tube. It slots into prepared holes into two ribs in the inner wing panel.

The tube has a very shallow taper, its part of a small fishing pole. This means it slides easily into the carefully reamed holes in the inner wing but becomes a 'snug' fit when fully home. There are short locating pins at the from and back of the joint to prevent rotation.

The aileron uses a 5g servo The larger hole in the 'joint' rib is to house the aileron servo connector.

Compared to the inner wing this panel is extremely light and hopefully just strong enough..

Edited By Simon Chaddock on 20/09/2019 21:21:20

[Simon Chaddock]

Still slow going as the construction and build sequence is rather made up as I go along.

The RH outer panel fully skinned with the aileron cut out.

And just to see what it looks like the RH wing assembled.

Although only a transport with a fairly modest sweep this does rather highlight the substantial wing taper root to tip.

Having got this far it should be relatively problem free to make the other side of the wing.

[Colin Leighfield]

Talk about a challenge! The C17 Globemaster would be a similar project I imagine. Don’t think I will be trying to do it though! Following with the usual fascination.

[Simon Chaddock]

Colin

I did think of the similar size Lockheed Galaxy but I was put off by its T tail.

Not for any aerodynamic reasons, I am sure in full size their are advantages, but rather the structural and weight implications in the design of the fin.

[Simon Chaddock]

A bit of a long slog duplicating everything to make the left hand inner and outer wing panels but eventually the full span laid out on the dining table.

Rather dwarfs that 24" rule!

The next task is to create the inner and outer motor mounts with the correct shaped pylons to check they properly fit into the wing centre section.

[Stephen Jones]

Looking good so far Simon.

I do admire all the patience and skill you put into these models of yours.

Steve.

[Simon Chaddock]

Without detail drawings it required some trial and error testing to get the nacelle in the correct relative position.

First one of the test motor mounts was positioned next to a test rib section to ensure it matched the profile.

Then just the final shape pylons were printed to test for fit in the wing.

The inboard and outboard pylons are of course a slightly different shape.

Fitting the printed 'one piece' nacelle to give the 1 mm prop tip clearance proved almost impossible. A two part nacelle with a short first part just covering the props made life much easier. The bigger second part thus had no assembly issues.

The final 4 pylon motor mounts along with the short nacelle parts.

Each pylon and motor mount takes 2 hours to print so altogether the best part of 14 hours printing. For safety each part was printed individually as there is nothing worse than if for some reason a print fails halfway through a 6 hour print of a bed full of parts!

Rather than go any further with the wing the next task is to consider how to make the fuselage and in particular how the wing centre section will fit onto it.

It a complex shape, unlike a conventional 'tube' airline fuselage, and I only have limited cross sections to work from!

Edited By Simon Chaddock on 01/10/2019 15:57:09

[Simon Chaddock]

At the start of this blog I suggested the aN124 was likely my last big Depron build. The reason for that statement is nothing dramatic but simply the limited supply of 'big sheet' 2 & 3 mm Depron!

It was this limitation that drove me to print all the wing ribs to save what Depron I have for the load bearing wing skin.

Before going any further with the wing I need to design & build at least the centre part of the fuselage to make sure it will actually fit.

Now if wing ribs can use up quite a bit of sheet, cutting out fuselage formers is far worse so logically they will have to be printed as well.

At this size the AN124 fuselage is "big" and its cross greatly exceeds the bed size of my 3D printer so the inevitable result is they will have to printed in parts and glued together. like the ribs

Although a 3D printed former is likely to be a bit heavier than the equivalent made from Depron it can be much stronger so raises the possibility that the inside of the fuselage could be more or less scale as well!

So first a test design of a 3D printed fuselage former from a position just ahead of the wing.

If it works it would give the fuselage an unobstructed internal clearance of 240 x 170 x 1200 mm (9.5 x 6.75 x 48 inches)!

In theory the parts for each former could be squeezed onto the printer bed.

However in practice it will be easier for each former to be printed in 6 parts, although in design terms they are symmetrical about the centre line so only 3 are different.

Even so each former is going take about 45 minutes to print and 8 similar sized are required for just the fuselage centre section. This is all going to take some time!

The issue never far away is that this big air frame will be powered by just 4 small quad motors driving 5" props which makes me wonder if I should adopt Ron Moody's approach in Oliver and "...think it out again"!

[Colin Leighfield]

You certainly don’t walk away from a challenge Simon. I wouldn’t know where to start!

[Erfolg]

Well Simon, this is a far cry from our days of poring pipe and welding concrete, for plant to last several hundred years, without maintenance!

You certainly are making that 3D printer work for its living.

Always a challenging subject and method of build.

Keep at it lad.

[Simon Chaddock]

Slow going having to work out how and what sequence to actually construct it!

The centre section plan and the first of the formers.

With all the formers printed the first 3 mm skin planks go on. An operation made easier as part of the side of the centre section fuselage has a flat area.

The inside is very empty!

Note the 6 mm Depron temporary 'jury' struts. These will be removed once the 'half shell' skin is complete, lifted from the board and the other half of the formers added.

Edited By Simon Chaddock on 09/10/2019 17:16:33

[Colin Leighfield]

This is certainly a very “technical” build and showing us things that might become a lot more commonplace soon. Real model aeroplane engineering.

[Simon Chaddock]

With the planking complete a "trial fit" of the wing on the half shell.

More for my own encouragement that an absolute necessity at this stage.

But it looks about right.

The fully planked  half shell is rigid enough to be lifted ready for the other side of the formers to be added.

Maybe unusual materials but the construction method is actually quite "old style".

 

Edited By Simon Chaddock on 14/10/2019 00:19:38

[cymaz]

What do you imagine the final weight will be? A kilo or two?

[Simon Chaddock]

cymaz

It had better end up around a kilo all up otherwise it won't fly on the meagre thrust of its 4 quad motors!

I am trusting that the benefits of a low wing loading, overall size and a fairly efficient air frame will enable flight on a 25% thrust to weight ratio.

Using printed wing ribs and fuselage formers to reduce the amount of scarce Depron used has a weight penalty so flight is likely to be even more marginal than it might otherwise be.

On this build weight is always the "elephant in the room".

[Stephen Jones]

Well Simon,

If it will not fly under power you could always find a hill to chuck it off .

Steve

[Erfolg]

I am not at all sure that the model is ideal for slope soaring. The wind speed, probably needs to be optimal. Perhaps more importantly, the model is probably not going to be robust for the rough and tumble that most sites impose.

Probably more thrust is what would be required. Even this is not necessarily the correct answer. More thrust often requires bigger or better motors and fans. Which implies for a similar duration a larger capacity lipo is needed, or a shorter flight is generally accepted. It could add up to a weight increase. Another issue could be, Simon is a Colin Chapman, the wiring to supply the current is often, to my mind marginal. It is all a fine balance in this area of construction.

[Stephen Jones]

I think it would still work in a gentle breeze.

Have you seen some of the light and delicate airframes that John Woodfield slopes.

Of coarse he would have to find a nice hill with a nice breeze in the right direction.

Steve.

[Simon Chaddock]

With the other side of the formers added, its terribly wobbly to start with, the long slow job of planking continues.

Slow because each plank has to sanded and formed to fit the formers and its neighbour along it whole length. It the plank has to be forced into shape their is every chance the fuselage will develop a twist as the planking progresses.

The small un planked area is for the substantial leading edge fuselage to leading edge fairing. To ensure a smooth contour this will be completed when the wing is in place.

The inside is very empty.

If it looks like it could stand the weight I might add a Depron floor.

The undercarriage housing 'bumps' are quite noticeable.

Eventually some reinforced finger holes will be added in this area in order to be able to hand launch it as the fuselage is much to wide to hold.

The exact position of the holes will have to be determined when the plane is more or less complete and the CofG set.

This of course is only a part of the fuselage. There are likely to be 4 more sections to complete it!

It is going to take some time.

[Erfolg]

Will there be some longitudinal stringers, to aid bending resistance, and a little torsional resistance?

I cannot see you slope soaring it though. Even Winters Hill was a +10 mile journey when available, Mam Tor is what +30 and always seems to have good blow, as to Teds Nose, is this still available, again a good distance, I have not heard of anyone flying at Disley for years, although I guess the BATS club would know.,

Will you be sectioning the fuz, using transfer bulkheads/rings, to help in both transport and in my case it would be repairs?