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Antonov AN 2 in Depron with 3d printing.

Old 01-29-2020, 09:34 PM
  #1  
quorneng
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Default Antonov AN 2 in Depron with 3d printing.

When I first got my 3D printer I played around trying to create a fairly detailed 9 cylinder radial with a brushless out runner enclosed within the crankcase
Now after a couple of years learning how to do it better (and lighter) I wanted to try again but what single engine plane has a big semi exposed radial.
It had to be the AN2.
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It would make an interesting model. Virtually a STOL biplane with flaps on both wings and a fixed 'rough field' undercarriage.
The first problem was to find a 4 blade prop indeed the choice was so limited it rather set the size of the whole project. From the prop size the 'dummy' engine could be designed and 3D printed and then the air frame built to suit. Find the prop, build the plane!

The AN2 used an ASh-62 which was a licence built version of the P&W 9 cyl Cyclone so good detail pictures of the engine were readily available.
The 3D printed crankcase showing how the brushless motor fits inside.
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The final version of the complete ASh-62 printed in silver and black PLA so no paint required.
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The motor and dummy engine sits on a printed 'mounting' sized to position the motor and prop in the correct place relative to the scale bulkhead position.
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Although not visible when inside the cowling it has a pronounced exhaust collector ring.
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The 3D printed cowling and 4 blade prop.
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The brushless motor was sized to drive the 10x8.25 4 blade from a standard 2200 mAh 3s.
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It generates quite a bit of 'pull'.

Now its just a case of building an AN2 to match.

Last edited by quorneng; 01-31-2020 at 05:51 PM.
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Old 02-01-2020, 12:06 AM
  #2  
Don Sims
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Looks great!
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Old 02-01-2020, 11:39 AM
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Don
Thanks. The 9 cylinder is virtually a kit of printed parts. 7 bits make up each cylinder ending up with over 70 in all but it does give the lightest and finest detail end result.
The cowling in printed too as just a single wall.
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For rigidity it will have to be glued in place when the air frame is complete which is a bit of a pity as it will cover up all the engine detail but at least I know its there!

I found this 3 view which gave some fuselage cross sections making it relatively easy to 'guesstimate' any intermediate ones.
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It was then blown up and tile printed to give a size that matched the engine and cowl.
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It ended up with 10 3D printed fuselage formers.
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Each has U channel form which is easy to print yet stiff, light and pretty near how it was done in the full size.
The AN2 has quite a large area of flat side so construction is remarkably conventional, just using 3 mm Depron instead of balsa.
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Planking is used to complete the curved sections
Stiff, light and hollow! The view down the fuselage from the engine bulkhead.
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It makes you realise just how big the engine of the AN2 is!
One advantage of 3D printing like this and if you can think far enough ahead is it is possible to include attachment points and any necessary reinforcement in the original print.
For example the fuselage formers that pick up the undercarriage mountings have a significantly bigger cross section than those further down towards the tail.
Still a way to go.

Last edited by quorneng; 02-04-2020 at 01:27 AM.
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Old 02-08-2020, 12:22 AM
  #4  
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The AN 2 undercarriage is supported by a stub centre section of the lower wing which is braced by a strut to a specific fuselage former. It was obvious to simply include this in the former printing.
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I also decided to actually print all the undercarriage struts including the inner and outer parts of the spring units.
I was well aware of potential strength limitation but I judges it would be better for it to rip cleanly off in a hard landing. Just a touch of a button and cheap to print a replacement!.
With a lower wing centre section in place the undercarriage could be installed.
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Note the use of printer filament as hinge pins.
To ensure it would give the appropriate prop clearance wheels were added. Printed hubs with Depron tyres!
The printed 'firewall' former includes a locating ring that picks up the printed motor mount.
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The suspension is quite soft with nearly 1" (25 mm) of travel which should help reduce the shock loads on the undercarriage members.
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Old 02-17-2020, 11:35 PM
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The next stage is the fin and tail plane.
Simple symmetrical camber structures using 2 mm Depron skins.
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The tail plane brace is Depron but it has balsa leading and trailing edges for stiffness.
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Although built with a separate fin & rudder I decided that with such a boxy rear fuselage and short nose it would be possible to fix the fin, saving the weight of a servo and fly the AN2 AET or 'bank and yank'.
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So far so good but the next bit, the wings, is rather important as it is what the AN2 is all about.
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Old 02-24-2020, 09:24 PM
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As the wings are a constant chord I decided to use 3D printed ribs.
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Although the wing section is the same the ribs are cut off at different lengths to account for the flaps and ailerons
With a braced biplane the wings a lighted loaded in bending so with the fairly thick wing on the AN2 no conventional spar is necessary as the top and bottom Depron wing skins will provide sufficient strength and torsional rigidity.
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The bottom wing has no aileron but just a full span flap. A small 3.7 g servo is buried in each of the lower wings.
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Without the bracing the wing has no rigidity so is temporarily held in place with a bit of string until the glue sets.
The top wing is built the same way but as a single structure over the top of the fuselage.
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The top wing has 4 servos in it, 2 for ailerons, 2 for the flaps.
Next are the inter plane struts and the bracing.

Last edited by quorneng; 02-25-2020 at 12:28 AM.
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Old 03-01-2020, 12:23 PM
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10 lb Nylon mono filament line is used for the bracing wires.
This is normally considered 'stretchy' but as each line is capable of lifting 5 times the all up weight of the AN2 the degree of stretch under load is small and actually less than the 'give' in the Depron structure itself.
Each anchor consists of a piece of clear plastic that passes through the wing skin and is glued to the side face of the rib underneath.
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The AN2 has double wires on the leading flying wire, single everywhere else.
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Four cabin windows are let into the fuselage skin.
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For simplicity the cockpit canopy is a Depron box structure with the glazing bars cut from black 'sticky backed plastic' sheet.
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It is held down by the leading edge of the top wing at the rear and magnets at the front
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Old 03-02-2020, 05:16 PM
  #8  
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wow! it looks fabulous!
I'm just curious, what is the wingspan??



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Old 03-02-2020, 07:27 PM
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Hi
Its wing span is 50" (1270 mm).
And being a biplane it takes up rather a lot of room.
A rather poor video of its second ever flight.
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Old 03-02-2020, 07:38 PM
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Originally Posted by quorneng View Post
Hi
Its wing span is 50" (1270 mm).
And being a biplane it takes up rather a lot of room.
A rather poor video of its second ever flight.
https://www.youtube.com/watch?v=A_koMXdAwPg&t=30s
Wow that flies like a dream.
And it looks scale too. But I feel the painting could have been better. Apart from that, it looks like a fun plane to fly.
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Old 03-03-2020, 12:21 AM
  #11  
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That one flies great. Nice job on it.
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Old 03-03-2020, 10:14 AM
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My AN2 was really built to test the principles of combining 3D printing and thin Depron sheet into a scale structure that flies well rather than for looks.
Along the way I wanted to test if a full set of scale flaps was practical as well as. The slightly bigger and rather heavier Maxford AN2 kit only has flaps on its upper wing.
The down side of this is that although it has substantial power with an almost instant take off it flies so slowly even with no flap set it needs really gentle wind and turbulence conditions.

Just in case it damaged its nose in testing I designed a replacement highly detailed ASh-62 with an exhaust collector ring and carburettor. It also has a 'clip on' cowling so you can actually get to see it all!
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So far it has not been required!


.
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