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A Depron and 3D printed Antonov AN2

quorneng

Well-known member
#1
This build came about via a rather disjointed route.
The AN2 makes an interesting model. A biplane with flaps on both wings and a huge radial driving a 4 blade prop.
CockpitView.jpg
There are no many 'electric' 4 blade props around but I found a nice 10x7.
At scale size this would give a wing span of 50" (1270 mm)
After 2 years of designing and printing lightweight structural components I wanted to make a scale 9 cylinder ASh 62 (a licence built P&W Cyclone) to go inside the cowling so that was the first task and only if practical would construction take place. Find the prop and then build a plane to match.
The basic 9 cylinder actually printed in silver and black PLA to avoid having to paint the very fine closely spaced cylinder fins.
ASh-62.JPG
A suitable motor to drive the 10x7 four blade from a 2200 mAh 3s would fit completely inside the crankcase.
It then followed on to print a mount that would support the motor and the 9 cylinder in the correct place directly from the scale firewall.
BunkHead2.JPG
The ASh-62 in the AN2 has a substantial exhaust collector ring.
ExhaustRing.JPG
It then seemed logical to print the cowling as well.
Cowl2.JPG

Only a single wall print so for rigidity it would have to be glued in position once the air frame was complete.
The engine is virtually a 'kit' as it is made up over 60 individual printed part glued together.:eek:
So far so good so now onto actually building something.
I found this highly detailed 3 view which included some fuselage cross sections.
3-viewB.jpg
With a bit of interpretation it was possible to create a suitable number of intermediate sections for the required 10 fuselage formers.
The AN2 fuselage is quite portly so should provide more than sufficient strength and stiffness from just its 3 mm Depron skin so why not simply 3D print the formers like this?
FormerC.JPG
Each former becomes a 'U' channel beam to support the skin. This section is light and easy to print with diagonal bracing to add stiffness.
The full set of 10 fuselage formers.
TenFormers.JPG
Although quite adequate for purpose 3D printing is not really a practical way of making a set of formers as the time to design and print is considerable. It would be much quicker to simply cut them out of 6 mm Depron unless of course you intended to build several identical AN2s.
Now finally actual building can start.
 

quorneng

Well-known member
#3
Quite a bit of the sides of the AN2 fuselage is flat so despite using 3 mm Depron and 3D printed formers its construction is actually quite conventional.
FirstForms.JPG

You can see the marks where the formers are to be placed.
With all the formers glued in a start can be made to form and plank the curved sections.
AllForms1.JPG

Although Depron is much more flexible than the same thickness in balsa it is still important to work equally on both sides and use lots of 'Mk 1 eyeball' to avoid producing a 'banana' fuselage. ;)
 

quorneng

Well-known member
#9
The spring units of the U/C of the AN2 are mounted on a stub centre section of the lower wing and reinforced by a strut to a fuselage former.
It seemed logical to include this strut in the former print.
UCmounting.JPG
At the same time the other U/C mountings were included in the fuselage.
Having used only 3D printing so far I wondered if the actual undercarriage struts and even the spring units themselves could be 3D printed too. Clearly not as strong as wire but if it broke off cleanly in a crash it would only take a metaphorical 'touch of a button' to print a replacement.
With the stub wing section added the undercarriage can be installed.
UClegs1.JPG
It took quite few attempts before the components actually fitted correctly. Note the use of printer filament for the hinge pins.
To test there would be adequate prop clearance wheels were added.
UCwheels.JPG

The hubs are also 3D printed with Depron 'tyres'. So far the only metal are the stub axles which are pressed into the undercarriage 'A' frames.
The spring units are soft with nearly 1" of travel which should reduce the shock loads on the undercarriage members.
If you have a 3D printer then this sort of thing is possible but it is not necessarily the easiest way of doing things. ;)
 

quorneng

Well-known member
#10
Moving on. The tail plane.
TailPlane1.JPG
A simple symmetrical section with 2 mm Depron top and bottom skins
The tail brace is Depron but with balsa leading and trailing edges for stiffness.
TailBrace.JPG
As the fin and rudder are quite large I decided to fix them to save the weight of a servo.
TailFin2.JPG
The AN2 will be flown bank and yank (AET)
Wings next.
 

quorneng

Well-known member
#12
This picture shows an AN2 with its wings removed.
AN2wingmnts.jpg

Note each wing has only two pin joints. this means there is no spar running across the top and bottom of the fuselage and that all the wing bending loads are carried by the wing bracing.
The AN2 has quite a thick wing section which suggested that each wing panel might be strong and stiff enough with using a spar as such and just relied on its top and bottom Depron skins to carry all the loads. As the fuselage had 3D printed formers why not all the wing ribs as well.
PrintRib1.JPG

There are no ailerons on the lower wing, just flaps.
The flaps are built up in Depron, top tape hinged amd driven by a small servo buried in the wing panel.
BotWingFlap.JPG

The complete cockpit 'glass house' will be built as a removable hatch for access to the battery.
 

quorneng

Well-known member
#13
I have to admit I cheated a bit on the top wing. Rather than fixed tot he fuselage as in the full size I simply made it sit on top as I had not incorporated the necessary fixings in the fuselage as I had with the low wing.
First the ribs with 3 different lengths although all the same section. Centre, inboard to allow for the flaps, outboard for the ailerons.
Ribs1.JPG

There are 4 servos (all micro 3.7g) in the top wing. 2 for the flaps 2 for ailerons.
The wing construction is the same as for the lower wing. Just Depron no spar as such.
WingsCmplt1.JPG

Of course in this state the wings have no strength at all and will rely entirely on the bracing. To make transport more difficult everything will be permanently fixed together so it will be a 'one piece' plane. :eek:
In the above picture you can see the motor wires sticking out of the bulkhead. The deep finned 30A ESC is mounted on the cockpit floor.
ESCfins.JPG

At least it now looks more like an AN2.
 

quorneng

Well-known member
#14
Moving on the wing struts (Depron and balsa) are simple glued on but exactly matching a wing rib.
WingStruts1.JPG

Testing the flaps and ailerons using a servo tester.
To secure the bracing wires small clear plastic plates are glued through the skin and onto the face of the rib underneath.
RigAnchor2.JPG

The wires are mono filament nylon fishing line with a breaking strain of 10 lbs. Although this type of line is considered 'stretchy' as each line can support 5 times the planes total weight the stretch is minimal in fact the Depron structure is capable of more flex than the lines.
 

quorneng

Well-known member
#15
Now structurally complete the fuselage is painted blue, the wings white and the control surfaces red. Finally the 3D printed radial engine with the motor inside and cowling is glued on as well as the trade mark big single exhaust pipe.
05Jan19a.JPG

To complete the detail a top carburettor intake and a dummy oil cooler underneath are added.
CarbIntake.JPG

With a 2200 mAh 3S it weighs 723 g. It will fly slowly and even slower with the flaps down.;)
 

The Hangar

Well-known member
#17
Now structurally complete the fuselage is painted blue, the wings white and the control surfaces red. Finally the 3D printed radial engine with the motor inside and cowling is glued on as well as the trade mark big single exhaust pipe.
View attachment 159929
To complete the detail a top carburettor intake and a dummy oil cooler underneath are added.
View attachment 159930
With a 2200 mAh 3S it weighs 723 g. It will fly slowly and even slower with the flaps down.;)
Man that turned out looking AWESOME! Great job!