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Airbus A350 - 900

Old 03-04-2018, 02:32 PM
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quorneng
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Default Airbus A350 - 900

The Airbus A350 has been called "The plane that Airbus did not want to make" but were in effect forced into it by the airlines and to some extent by competition from the advanced composite construction of the Boeing Dreamliner.
As it eventually turned out (and 2 years behind the Dreamliner) the A350 is very advanced, efficient and expensive! but on paper at least it does seem to cut across some of the existing Airbus model range which is presumably why Airbus were not keen to develop it in the first place.
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What set me thinking about building it was this picture of the A350's Trent although in this case it is mounted on the inboard pylon of the prototype A380.
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It is huge. The question was if I built an A350 in my usual lightweight Depron construction would it actually need an EDF or could it use a much simpler low power ducted prop although I would still have to find a way to build those fancy "sharklet" wingtips!
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It became a realistic option when I found on offer a pair of racing drone motors with 3x2 4 blade CW and CCW props. With 3" props in a scale Trent nacelle the A350 would come out at a quite reasonable 60" span.
Before going any further I had to determine how much, or little!, thrust each nacelle might give as this would determine the weight the A350 would have to be build down to!
I then considered 3D printing the nacelle. After some experiments the best strength to weight option appeared to be to fabricate it out of several printed sections.
The nacelle pylon and motor mount being the most highly stressed could be made in one piece so ensuring the motor would be exactly in the centre of the duct.
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The inner duct could be made up as a simple printed tube with 5 printed formers glued on to support the nacelle outer skin which is made of 2 mm Depron
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The completed Depron nacelle skin.
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The 4 blade prop.
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The motor after body more or less follows the Trent after body profile.
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On a 4s battery it gave about 7 oz thrust drawing 13A along with quite an impressive whine!
So if I could build the A350 for say 24 oz (680 g) (or less!) it stood a reasonable chance of flying.

My apologies for labouring this bit of the build but without an accurate thrust test of the ducted prop there would be little point in proceeding further.

Last edited by quorneng; 03-05-2018 at 12:09 AM.
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Old 03-04-2018, 03:23 PM
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solentlife
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You are a one of mate ... I bow my head to your creations.

Watching with great interest.

Nigel
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Old 03-05-2018, 06:26 PM
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quorneng
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Having satisfied myself there was sufficient(?) thrust the fuselage has to be next.
It is by far the biggest bit yet does little apart from keep the wings and tail in the right place so "weight saving" is the order of the day. To be constructed with 2 mm Depron planking over light weight formers.
Most of the fuselage is 140 mm diameter and there are quite a few similar formers. Could they be printed rather than cut from Depron?
After a bit of experimenting a thin wall (0.15 mm thick) "U" channel offered the best solution.
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Surprisingly rigid each former weighs just over 1 g and of course each would be exactly the same diameter.
I also discovered it was possible to make the 'cut down' formers required over the wing mounting by changing a single variable.
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Not having used such formers before I decided to build the bit of the fuselage over the wing just as a test.
Built vertically it was typically wobbly to start with but being a parallel tube the planking was relatively quick and easy.
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A novel view looking down inside the fuselage.
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As hoped it is light and strong and the printed formers give a greater finger crush strength than a similar Depron former of 2 or 3 times the depth.
In fact the test fuselage was so good that I decided to simply incorporate it into the finished article.
All I have to do is print lots of formers and build all 1500 mm of it!
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Old 03-05-2018, 07:07 PM
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solentlife
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I have also considered using 3D printed formers .... as well as my Laser printed stuff.

Very nice !

Nigel
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Old 03-07-2018, 06:35 PM
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quorneng
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The fuselage nose and tail sections under construction.
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The advantage of building vertical like this is it is self supporting so the completed item is "empty" - just formers and the skin.
With the limited power available weight is a key factor in this build.
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Old 03-07-2018, 10:36 PM
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Interesting build Q. It's coming along nicely.
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Old 03-08-2018, 07:29 PM
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quorneng
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The nose section complete.
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To save a bit of weight there are no windows anywhere. In fact the A350 cockpit windows virtually follow the nose profile anyway to they can be painted on afterwards.
The 'test' fuselage with a constant chord 'plug' added to take it up to where the nose section starts.
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The tail section is a bit more complicated as the tail plane and fin have to be fixed to it although haven't worked out how best to do it.
One of the penalties of "design as you go along" type of building.
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Old 03-08-2018, 11:00 PM
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mclarkson
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Amazing! FWIW, the "sharklets" made me think of this post from another forum:
https://www.rcgroups.com/forums/show...postcount=3438



I just cut a curve in a piece of 1x4 board. Then both sides of that wood clamped the wing for glueing on the second layer of foam. I used the same wood for clamping the 3 layers of balsa strips (not yet attached to the wing). After removing the laminated balsa from the clamped wood, it sprung back slightly. I then used steam from a kettle to bend the curves equally on each wing, clamped it again and let it dry.

It was really quite easy. Each piece of foam and the laminated balsa were curved separately so, when all glued together, it had the proper curve and stayed like that. I'm hoping to use the same method again to make a 2-meter Radian clone from Model Plane Foam.
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Old 03-10-2018, 03:59 PM
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quorneng
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The basic fuselage joined together.
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As built each section ends with a former. As all the strength is provided by the skin I decided a simple butt joint would not be adequate so a Depron inner flange was added to the face of one former.
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The opposing former was then removed so when the two sections are glued together the flange not only provides support to the butt joint and significantly increases the glue area.
I also decided to assemble the tail plane and fin as one assembly and then fit it into the tail of the fuselage.
The tail plane under construction.
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Note the printed spar & dihedral brace. This dihedral also means that each elevator half will have to have its own 3.7 g micro servo.
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Old 03-13-2018, 08:24 PM
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The tail plane and fin assembly.
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The bespoke printed brackets to hold everything in their correct positions.
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With the servo added the fuselage is cut open to the appropriate points and the fin assembly glued in and the fuselage skin restored.
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Care is taken to ensure the Depron fuselage skin exactly mates with the tail assembly as that glue joint is the only thing taking the loads!

Wing next, It is both highly swept and highly tapered. It may be the 'bees knees' at mach 0.8 but could be a problem at 15 mph!

Last edited by quorneng; 03-14-2018 at 04:02 PM.
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Old 03-16-2018, 05:21 PM
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quorneng
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I decided to create the wing in four pieces. L&R centre sections out to the nacelles and L&R outer wing panels.
The centre section with the weight and thrust from the nacelles has to carry complex loads and has a rapidly changing section. By comparison the outer wing panels have a relatively simple constant section constant taper at least as far out as the "sharklet" wing tips!
The root wing section is both unusual (for a model) and surprisingly thick so I believed my usual Depron skin with balsa spar flanges would be adequate as it is only using drone motors/ducted props rather than much heavier EDFs.
The ribs in the centre section are printed. This is the root rib - it only just fits on the printer bed!
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Just for comparison I also printed out the wing section at the tip.
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Now that is what I call a wing taper!
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Old 03-17-2018, 02:26 AM
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That is one heck of a taper.
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Old 03-20-2018, 06:56 PM
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quorneng
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Although big and long the fuselage is basically made up of circles. The wing, particularly the section out to the nacelles, Changes both size and shape quite rapidly along it length.
The printed wing ribs of the inner section.
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The ribs held in place by the balsa spar flanges and the 3 mm Depron shear web panels between each rib.
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Note the trailing edge support to keep each rib at the correct angle.
In this state the wing is just rigid enough to start adding the 2 mm Depron skin. The Depron is sufficiently flexible not to distort the structure as it is applied.
The complete LH inner wing section with a slot to accommodate the nacelle pylon.
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The open frame work ribs should allow the motor and servo wires to be passed through them fairly easily.
The intention is to mount the ESCs in the U/C fairing under the wing. As the wing is highly swept it is possible the battery will go in there as well. If so then only two servo connections (elevator & rudder) will have to made to fit the wing.
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Old 03-24-2018, 12:00 AM
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Having completed the LH inner wing I decided to proceed to complete the LH wing befre even starting the RH one simple to make sure it could be done!
By comparison the outer wing panels have a simple forward constant taper in fact with a small area and not carrying the structural loads of the nacelles I decided they could be very simple.
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Just upper and lower skins in Depron with no ribs!
Next came the "sharklet" tips. Laminated from 4 layers of 2 mm Depron held around a suitable diameter tube.
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The complete tip sanded to shape and glued to the outer wing panel.
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The complete LH outer wing panel. The aileron is simply cut out from the wing.
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The aileron servo is let in from the under surface and servo wire easily fed down the ribless wing
The completed LH wing.
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The inner and outer panels have to be glued together up side down as only the top surface is flat.

Now to build the other side and hopefully keep it aerodynamically exactly the same.
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Old 03-24-2018, 12:55 AM
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Very impressive.
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Old 03-26-2018, 12:53 PM
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quorneng
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The right hand wing goes through the same construction process except it uses a dummy centre line rib that is removed once the wing skin is complete.
The centre line rib on the LH wing is double width to provide extra glue area for the centre line joint
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The underside of the wing has a substantial fairing which contains the under carriage on the full size. The intent is to use the space to hold the ESCs (20A no BEC) and the separate UBEC.
Testing showed the ESC produce very little heat so given the likely limited flight endurance they can be simply 'built in'.
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There is space for the stab rx as well.
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The wing is attached to the fuselage with 3 nylon bolts. By using 3D printed mountings the bolts can be heavily recessed into the wing.

Initial CofG tests with the wing in place indicated that with a bit of modification the battery could also be held in the wing although it needed to be stick out a bit ahead of the wing leading edge.
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This was accommodated by creating a suitable hole in the fuselage.
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Done like this means only the elevator and rudder servos have to be connected when the wing is attached. Everything else is permanently in the wing.
Another benefit of the substantial under wing fairing is it gives something to hold onto for a hand launch and will be suitably reinforced to allow for this.

Now to consider the decoration.
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Old 03-29-2018, 11:43 AM
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quorneng
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I normally maiden a plane before spending time decorating it but the weather has been so bad any attempt at flying would likely end in disaster.
The Thai Airlines decoration as shown in my first post is suitable being largely white (Depron) and purple (a colour I already have) which just leaves the gold and pink bands.
Rather than buy paint which I am unlikely to use in quantity I decided to use "sticky back plastic"! A4 sheets were available in the more or less the correct colours at a very modest cost.
Never really intended to have a super finish, difficult when building super light in Depron without adding extra weight, but rather to have true scale shape and look about right.
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The multitude of passenger windows fall into the same category but the cockpit windows are very prominent so a little bit more stick back plastic.
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1475 mm (58") span and 1625 mm (64") long with a 1000 mAh 4s it weighs 595 g (21 oz).
The motors together draw 10A (measured) giving 151W which means 115W/lb. A very low figure for an EDF and still pretty modest for a swept wing plane driven by tiny 3 inch props!
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Old 04-02-2018, 01:18 AM
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quorneng
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Picking a day with relatively calm conditions a video of its actual maiden flight.
https://www.youtube.com/watch?v=b8ZGijxUhLc&t=6s
Being completely untested I kept fairly high so the images are rather small and I 'held off' for just a fraction of a second too long so the wing dropped for a rather untidy landing.

Last edited by Don Sims; 04-05-2018 at 12:58 AM.
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Old 04-02-2018, 10:20 PM
  #19  
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Fantastic!
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Old 04-04-2018, 03:03 PM
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quorneng
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With some more kind weather I was able to fly a bit closer to the camera and with the benefit of some sunshine!
A short video including only the bits where there is something to see.
https://www.youtube.com/watch?v=KU7cw_T9bxE
The grass is ever so rough!


Last edited by Don Sims; 04-05-2018 at 12:52 AM.
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Old 04-05-2018, 12:59 AM
  #21  
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Great looking plane.
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