|Nov 22, 2012, 01:38 PM|
Airbus A319-100 1:25th from own plans - half scratched ;)
a month ago i posted some pics of my A319 in Sergioīs fantastic build log. http://www.rcgroups.com/forums/showthread.php?t=1420129
He does a wonderful job and i got a lot of inspiration from that. So merci beaucoup mon ami
Our two builds are almost the same scale. His is in 1:22, mine is 1:25.
This leads to the following technical specifications:
wingspan: 1394 mm
length: 1326 mm
wing area: 25,46 dmē
horizontal stabilizer area: 5,05 dmē
I always design the planes in this size for a previously determined wing loading of 50g/dmē. With this the model can be operated safely and i feel comfortable flying it in normal flying weather with light to medium winds.
By multiplying the wing loading with the wing area (note: the elevator doesnīt count as its producing drag, not lift!) i get the design maximum takeoff weight.
MTOW= desired wing loading* wing area = 50g/dmē*25,46dmē = 1273g
Then time is right to chose the components for the model:
servos: 9g HXT900-ish, 5g HXT500-ish for each aileron
receiver: Corona RP6S1 6CH (as i am still flying 35MHz)
Now the interesting parts:
EDF: 2x 55mm AEO fan with ADH300 motor
ESC: 2x Mystery 30A blue series
Battery: 3S 2200mAh 25C
Every fan runs smoothly at about 25A (measurement=done) and the battery will juuuuust be able to handle the full current for takeoff and short passages. But this is an airliner so it should do the trick. The fans are said to produce around 500g each, so this should be sufficient as well.
For paved-runway-operations i am adding the micro pneumatic retract system HK is selling (i was kinda curious when buying )
Adding up all the weight of the components (900g) this leaves 500g just for the bare airframe. A manageable thing to do iīd say!
For the finish i am planning to glass the whole plane with 25 to 49g/mē glass. If the weight is already too high i will stick to paper and WBPU.
Now all the CAD work has to be done. I did just the fuse in detail because i originally planned to hot-wire cut the wings. Then afterwards i changed my mind and did the wing partly from scratch - thats why the title
|Nov 22, 2012, 01:52 PM|
Joined Oct 2012
Viele Grüße aus EDDT
|Nov 22, 2012, 03:42 PM|
Thanks you two
After i did all the computer stuff i printed the plan in DinA0. Normally i would convert the plan to pdf an print it tiled on A4, but this time i could print it in A0 for free
Then i had to transfer the templates for the spars to 6mm depron. I always use a ballpen and poke points through the paper. I then draw the rest between the points by hand. This works faster for me than glueing or other methods.
The hardest part was to cut all the pieces for the fuselage. Thats definitely one of the downsides of that building technique - the amount of parts that have to be accurate enough to snap into each other.
With all the parts joined it was time for the outer skin made out of 3mm depron. You can see in the pictures that i went from spar to spar which was really easy to do. The only tricky thing is to keep the "panel lines" as small as possible without deforming the skeleton.
After covering the upper half of the fuselage the stability greatly increased. Its impressive! Then the vertical and horizontal stabilizer were cut from 6mm depron and reinforced with a flat carbon profile and 4mm balsa profiles.
|Nov 22, 2012, 04:08 PM|
As soon as the tail was put together i drilled holes for the bowden tubes. The elevator has two Y-linked tubes operated by one HG 202 Carbon Gear servo i had left over. The servos were then located in the center wing box.
Since the opening for the wing will be the only opening of the fuselage every electronic system will be located there. I just hope to have calculated the CG right cause otherwise the battery may not be inserted...but thatīs to solve later on.
Then i installed the nose gear. approx. 85% of the weight and 100% of the landing shock will last onto the main wheels, so the nose gear mount can be made very light. The standard solution for turning the wheel is a pull-pull wire setup and i think iīm going to stick to that. Unfortunately i will have to use another servo then.
|Nov 22, 2012, 04:35 PM|
Yesterday i started with the wing. My favourite airfoil for model airplanes of that sort is the ClarkY. Its very easy to build and has just the right thickness (roughly 12%). Every single one of my self-built models uses the ClarkY and it just works, no matter if its windy or whatever...
Of course it isnīt scale but this is just a foamy airliner.
The other thing is the wing design. In this case i donīt want to add flaps or other fancy stuff so i like it simple. Just a main spar (4mm balsa), ribs and reinforcements for the main gear.
As a leading edge i used a stripe of 6mm depron as i am planning to glass the wing. When the upper skin is applied i just sand it.
The aileron servos are just glued in place and will be held in place by the upper and lower skin only.
When putting the wing and the fuse together it even starts looking like an Airbus
From now on the posts will take some more time as i am not in a hurry with this... maybe i will finish it for the next flying season, maybe not.
On question though: Is there a limit for uploading pictures? Like a personal webspace? Or can i just keep them coming?
Greetings to everyone
|Nov 24, 2012, 01:03 PM|
Today i managed to get the EDFs ready. Before i can continue with the wing the nacelles have to be ready so that the ESCs can be glued in place. The ESCs will be glued even with the underside of the wing, so that the cooling is more efficient than with an air duct as the air flows directly over the esc cooling pad.
My airbus will have the IAE engines, so the nacelle can be made more scale than when using the GE nacelles. They are also longer which means that the contact surface to the pylons is larger improving overall stability. And there will be more space for the cables.
Before i could make the thrust tubes the motor had to be transfered to the other EDF units. The plastic of the GWS EDF55 is a bit softer which absorbs noise and vibration. And they are coloured in a light grey, so painting of the EDF unit is not necessary.
After i transfered the motors i had to test them to full speed and see if the new housings work. Apart from medium vibrations at 50% throttle they are pulling nicely without rubbing too much.
An important goal before maiden will be the balancing of the fans and replacing the faulty motor ball bearings with high-quality ones. But this can be done later.
The nacelles will be made from two layers of 6mm depron which will be sanded in shape after glueing. To prevent the depron from distorting the edf housing it is pulled over the edge of a table parallel to grain direction to pre-bend it. After fitting it to the edf it is covered with tape and heated by a hair dryer for 15mins each. This helps keeping the right shape.
The second layer will be made the same way. Important is that they fit very tightly. Glueing will be done with polyurethane foam glue. After that they are sanded in shape and glassed.
Another important change is that the actual tubes are cylindrical, not tapered. This is to keep design simple and the increased speed will not be needed.
|Nov 25, 2012, 01:12 PM|
Alright...today i threw away the nacelles made yesterday. My double-layer 6mm Depron approach didnīt work. It was just too brittle and the material separated during sanding.
So i picked up my hot-wire foam cutter, made templates out of beaverboard and cut the halves of the new nacelles.
Since the A319 livery i would like to use comes with the GE engines i changed my plan and am now doing these.
After glueing the EDF in place i put the two halves together and began removing the foam with a razor sharp cutter. After that i began sanding with a sanding block. I had no plans for the GE nacelles, so i made them from scratch.
After filling all the holes and the glassing they could look quite alright...
Since this is my first build thread here and my english must sound awkward could you give me some feedback? What can i do better, what would you like to know?
Thanks in advance
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