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Antonov AN124 Ruslan


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Erfolg

With a full continuous structural skin the fuselage is in effect a 'tube' which gives substantial bending and torsional rigidity so no further reinforcement is necessary. The only real concern is the thin section of the side wall part of the former to resist local compression resulting from handling but like most of my light weights it will require some care on the 'how and where' to just pick it up! smile o

My intention is for the fuselage and tail feathers to be all one piece as it will, I think, just fit in my car.

Repairs? I will cross that bridge when /if needed. sad

If the CofG position allows it I would like to place the battery(s) and rx in the wing so only the rudder and elevator servo connections have to be made when the wing is fixed on. It would leave the fuselage completely "scale" empty! wink 2

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As you know Simon the integrity of a tube and most monocoupes revolves around the uniformity of section. the stresses being pretty near uniform around the whole of the shape. Cut outs needing compensations, where as changes in section lead to stress concentrations. It is at these points where structural failure originate. The Ant is bound to have apertures and changes of section.

Full size practice has normally incorporated stringers, for structural purposes, even if perceived as there just for the joining of sheets.

But then again Colin Chapman was renowned for also being on the limit, even his street vehicles, the race cars just capable of getting to the finish line in many casessmiley

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The next task is to build the section of the fuselage up to the nose door quite a complex shape as it includes that 'cantilevered' cockpit.

I do not intend to make the nose hinged but simply 'removable' so you can at least see inside. wink 2

Although it looks like it might be just a straight continuation in fact the top section of the fuselage changes quite a bit leading up to the actual cockpit so the formers are different however by using 3 part glued together formers at least the bottom portions are all the same.

front2

This allows relatively large planks to be used in the lower area.

front1

The reminder is still slow going as it requires relatively narrow individually fitted planks.

So far the fuselage has used 72 printed parts, most of which are different! smile o

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The initial attempt at the cantilevered cockpit on the front section.

cockpit1.jpg

It took a few 'iterations' before it was something like the right shape so the front and mid sections could be joined.

2fusejoined

"Designing as you go along" makes progress agonisingly slow.

Next is the removable nose section.

Not exactly looking forward to this as its a complex shape and has to fit the fuselage accurately! smile o

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Colin

I don't know about the most challenging but probably the most likely not to fly properly.

I had similar doubts about my Bombardier Q400 with its long fuselage & small wing, but compared to the 'whale' like fuselage of the AN 124 its fuselage now seems modest and ever so streamlined. With two big props the big unknown was not one of thrust but of control.

With its generous control surfaces the AN 124 is likely to be the other way round! wink 2

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The nose plan.

nosefull

Quite a complex shape as it has a 'cutout' at the top around the cockpit and a step at the bottom.

As before built as a half shell over the plan.

noseplank1

But the complex shape and the extreme change in section over a relatively short distance makes the planking very tedious.

After all it is just a big 'fairing' that serves no structural purpose so it has to be kept as light as possible. wink 2

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  • 2 weeks later...

The ext is the rear fuselage between the wing and the tail plane.

Built in the same way as before.

rearfuse3

rearfuse2

On the full size this would incorporate the rear door ramp but will not be included to ensure adequate rear fuselage rigidity.

Once complete it does allow the four section built so far to be stacked together.

fusestack

Its getting rather big and there is still a tail section to do that will hold the tail plane.smile o

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The tail section that carries the tail plane and fin is the last bit of the fuselage.

Built as before.

fusetail1

The cut out is for the tail plane although the picture is upside down.

When complete it allows the full fuselage stack to be assembled.

fusefull1

It is 2.46 m long with just its 3 mm Depron skin holding it all together. smile o

I don't know if it will fly but it will definitely crash only once! wink 2

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With its bulk and weight rising I started to get even more nervous about the thrust that would be available so the first task was to check a finished nacelle would actually run on a 4s.

It certainly screams in a rather satisfactory manner and blows quite a bit of air about.

Next it needed a test stand to measure the thrust reasonably accurately.

teststand1

It will simply sit on a set of kitchen scales.

To ensure a realistic reading the motors wires are the full length as required when mounted in the wing.

To my relief it develops a full 8 oz (226 g) thrust which times 4 makes flying a plane with an estimated weight of 40 oz (1.15 kg) rather more realistic.

This thrust was achieved with a motor tail cone giving a nozzle exactly that of the FSA.

tailcone

However some restriction to as little as 85% FSA has shown to improve the thrust.

Out of curiosity I wondered if a 'pear shaped' tail cone could be used to provide a degree of restriction without altering the outside profile of the nacelle.

tailcone95b

It would be a simple direct replacement of the earlier tail cone and reduce the nozzle to 95% FSA .

tailcone95

To my surprise it raised the static thrust to a repeatable 8.3 oz. Not huge increase but an additional 4% thrust for 'nothing' I will take any day. wink 2

Edited By Simon Chaddock on 19/11/2019 22:57:22

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  • 2 weeks later...

As i had built the test stand and the exhaust cones were simple to print and change I decided to test a full range sizes from no cone at all to one that restricted the nozzle to 80% FSA.

Nozzle FSA Thrust (oz)

80 % 7.9

85 % 8.3

90 % 8.3

95 % 8.2

100 % 8.1

100% but no cone 8.0

The inlet duct is a constant 116% of the FSA

Each result was duplicated and the battery we recharged to 'full' on the charger before each run.

It does appear that a restriction to 85% FSA does give the best result for this particular duct.

To test the structural integrity of the installation a pair were mounted on the LH wing.

It makes a quite nice noise, nothing broke and it even shut the door!

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Hi Simon, just started reading this build blog today, got to say I'm impressed with your tenacity and engineering skills, it's always interesting to see what technology is being utilised for non traditional balsa bashing. Now I've read so far and following, any chance of posting links to your other builds or is it in your profile.... Glyn

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Simon, I love the testing, I think it is great do do this sort of thing to understand what we are dealing with rather than just forging ahead blind. I did similar tests for a 55mm fan a few years ago with a similar stand on kitchen scales and got the result that 85% FSA gave the highest thrust. However, I also had the Wattmeter hooked up and a tacho reading the motor pulses for rpm. The reduction in FSA increases the back pressure on the fan, increasing the fan loading, reducing the rpm and increasing current draw. It is not something for nothing, it is in fact slightly less efficient in terms of grams of thrust generated per Watt of power. If you know fan laws, you can then back calculate an average efflux velocity to see how that increases as the FSA reduces. As I was not interested in high velocity flight with my plane, I stayed at 100% FSA. I think I have posted about this before.

_exhaust test 2.jpg

Test stand with open exhaustdsc01166.jpg

Reading recorded by photographdsc01127.jpg

Duct added to exhaustdsc01493.jpg

Edited By PeterF on 29/11/2019 09:32:49

Edited By PeterF on 29/11/2019 09:37:19

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The last big bit are the "tail feathers".

They are big, bigger than my complete EDF DH Venom.

bigtail.jpg

As they are relatively a long was back they are kept as light as possible so no spar or ribs just a 2 mm skin over Depron shear webs. lhservo

The 5 g servo just fits between the skins'.

The completed tail assembly.

tail&fin1

As the fin and rear fuselage are 'generous' it will have no rudder and be flown 'bank and yank' so saving the weight of a servo.

Having satisfied myself the motors both work and seem to provide adequate thrust the wing bolt mountings can be designed and printed. The wing will be held on by 4 nylon M4 bolts, two each at the wing leading and trailing edge.

wingboltsfront

The wing centre section in place.

wingbolton

It certainly feels like the more I complete the more there is to do!

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Erfolg

Its in the Electric Ducted Fan section. From there a search "A 'not so micro' Venom" will reveal the build thread.

With this search engine the search term has to very specific or it simply doesn't find it.

As I could not remember the thread title I had to go through most of the 293 pages of my posts to find a relevant one so I could identify the section and title. smile o

Moral of story on this site - Keep the thread titles short and very specific. wink 2

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