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Airbus A350 for 50 mm EDFs


Simon Chaddock
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The wing plan printed out to give an idea of how big, or not, it is going to be.

Wingplan 1

It gives a 66" (1980 mm) span but like all modern airliners it is very highly tapered. 14" (360 mm) root chord but only 2.5" (65 mm) at the point where the tip starts to 'curl up' by 90 degrees. That's a 6:1 taper which would normally be considered to give 'horrible' stall characteristics. I suspect at my flying speeds the outer bit of the wing won't do much apart from create drag!

Still it does have a reasonable area of just about 2 sq ft. Now whether the whole plane will come in anywhere near my target of 24 oz (680 g) is too early to say. wink 2

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Now this will be interesting Simon.

The tip chord is very small relative to the root. It is also so narrow, that I wonder how well the tip area will work.

At a personal level, i defiantly would have a good few degrees of washout. Probably so much that often the lift contribution would be near to zero. Being a mardy, I would be after some control near or at the stall. Again being me, I would also cheat at the wing tip, I would increase the chord. Yes, i am definitely chicken.

Considering the model, it really is not the sort you would normally loop, roll, fly inverted, stall turn (intentionally). Best suited visually to circuits, low passes, to avoid brown trousers.

That Russian aircraft really does look good.

It is a great pity that I will never see it fly in the Depron.crying 2

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Erfolg

My intention is to keep the wing exactly to scale as it is very much part of the design. I will just have to live with any 'undesirable' characteristics.

In my experience swept wings tend to have 'gentle' stall characteristics due in part to the outward airflow but also their flexibility giving 'automatic' washout. I will have to watch out that the same flexibility does not result in reduced aileron effectiveness!

On the plus side the long fuselage and substantial fin (required in the full size for single engine operation) should mean it will recover rapidly from any 'wing drop' situation provided of course there is sufficient height!

Aerobatics?

I doubt very much it will be able to roll effectively but I will be a bit disappointed if it can't loop!.wink 2

Edited By Simon Chaddock on 08/11/2017 22:30:41

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The next critical component is the motor and fan or rather the tiny (3x3!) prop.

They have been purchased through HK and are intended for racing drones. Obviously these are the latest 'thing' so are surprisingly cheap and were on offer too!

The Trent nacelle.

77Trent

At this early testing stage I decided to mount the prop as a pusher right at the back of the nacelle. I have used this layout on a previous ducted prop (as well as a couple of EDFs) on the basis that there is nothing in the high speed slip stream so it is likely to give the maximum static thrust..

Pusher 1

This layout also results in a compact & rigid unit ensuring the prop stays clear of the duct walls. wink 2

Pusher 2

I have tested it on a 3s and although it pushes quite hard I suspect it will need a 4s set up to deliver the thrust I would like.

In addition the pusher layout precludes using a scale Trent tail cone so the 'flight' version may revert to a tractor arrangement with the prop forward well inside the duct.

The next task is to build a test stand so I can accurately measure the thrust.

Edited By Simon Chaddock on 12/11/2017 17:36:09

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After a bit of consideration I actually printed a test stand 'mushroom' to fit directly onto the motor mount.

Test stalk 1

It is filled with plaster both to support the thin walls and to add a bit of mass.

Test stalk 2

Sitting on the kitchen scales it generates 121 g thrust with a fully charges 3s drawing 4.1 A.

Even with two this level of thrust is sufficient for a 680 g plane but on 4s hopefully it will be - assuming it all hold together! wink 2

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CT

Thanks for the kind words.

I have just noticed in my previous post I missed out a word! It should have read "..this level of thrust is not sufficient for a 680 g plane...."!

The internal diameter of the first test duct was set slightly 'generous' to ensure it cleared the prop.

As it turned out not only was the motor mount and duct quite rigid but the prop was also pretty accurately centred as well. To reduce the prop tip clearance and so hopefully improve the thrust I printed a thin narrow ring to be glued inside the duct.

Ring insert 1.The prop tip clearance is now about 0.5 mm.

Ring insert 2

And it worked! On the same fully charged 3s in generated a reliable 132 g of thrust.. Not a dramatic increase (about 9%) but it is virtually for 'free' as there was very little change in the current draw. wink 2

My best guess suggests the complete nacelle is likely to weight 75 g. A large part of this total is from the 'printed' parts as the motor and prop themselves only weighs 30 g.

I would like to get the weight of a 'bare' nacelle down to 30g by incorporating some improvements to the printing technique although it is likely to fill up my waste bin with more 'unsuccessful' prints!

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Still awaiting delivery of the 4s ESCs so in the mean time move on to designing the nacelle pylon.

To save weight the intention is to print the pylon in conjunction with the motor mount and as before include a 'channel' within it to carry the motor wires into the wing.

The light weight 'pusher' motor with an integrated pylon.

Motor pylon P 2

By reducing the print wall thickness and using a Depron external skin the motor mount ends up about 12 % lighter.

However due to the way the pylon and motor mount are designed it does not print well and lacks some rigidity. Unfortunaely I cannot see a way round it without adding additional weight.

The tractor prop version has a slightly different internal structure and does not have the same print issue so this layout will be the chosen development route.

Motor pylont T 1

There is a slight weight penalty but worth the extra rigidity gained.

As the motor now faces forward it allows a 'representation' of the Trent tail cone to be used.

Motor pylont T 2

The forward part of the nacelle is next.

Overall this is proving to be a rather protracted development process, I probably could have simply built a complete nacelle in Depron quicker, but by using printed major components I know the second nacelle will be much quicker to do and be exactly the same! wink 2

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Erfolg

Landing is a concern however:

1 The landing speed will be low.

2 Without flaps the landing will be markedly nose high

The nacelles are well ahead of the CofG so providing the grass is short the hope is it will '3 point' using the generous rounded underside of the nacelles as skids.

The 'bare' 77 mm nacelle with a planked Depron skin alongside the all printed 50 mm version.

77 nacelle 1

The 4 blade 3x3.5 mounted as a tractor within the nacelle.

77 nacelle 2 Complete with the pylon it weighs 70 g.

Edited By Simon Chaddock on 19/11/2017 00:03:22

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With the test nacelle finished the next issue is to design the bit it has to fit to - the inner wing panel.wink 2

Like all modern airlines the wing is broad and remarkably thick right at the root but rapidly tapers down to a thin  transonic section once beyond the engine nacelle.

I decided to use 'printed' wing ribs as each is of a very different size and section. By pure luck rather than intent the biggest root rib just fits on the printer bed!

Just fits

The rapidly changing set of ribs.

Wing ribs 1

The biggest asset doing it like this is all the ribs have been generated from a single master set of dimensions by changing just the rib length and depth. they are accurate to 1/100 of a mm and repeatable at the press of button.

To make life a bit harder the wing has to built upside down as only the top surface is truly flat.

The single balsa/Depron/balsa spar is full depth such that its balsa flanges are flush with the surface of the 2 mm Depron skin.

Wing root 1

Although light and stiff the big downside of such lightweight printed components is they are virtually non repairable and have to be completely replaced if damaged in any way. Not easy to do with a wing rib. wink 2.

Edited By Simon Chaddock on 23/11/2017 12:03:52

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The first inner wing panel complete.

LH cmplt

The nacelle pylon fits in the wing slot.

LH under 1

The complete wing and nacelle (including the motor and ducted prop) weighs 98 g.

As it all seems to fit together the 8 individual parts for the second nacelle are printed off.

2nd nacelle 1

This is where printing really excels. Although the above represents about 4 hours printing it only requires a touch of a button (well almost!) and all the prats fit together perfectly. wink 2

Just out of interest a comparison if the root and tip wing ribs.

Root Tip

It does show just how tapered the wing is and the curved up tip "winglet" is even smaller still!

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The outer wing panel is a remarkably simple affair. All 2 mm Depron with no ribs or spar just a pair of shear webs.

Outer panel 1

The 'curled up'wing tip is sanded from a pre-formed blank of 4 laminations of 2mm Depron glued together and held with rubber bands over a suitable diameter cardboard tube until dry..

Tip blank

The tape top hinged aileron is cut out from the wing. and a 3.7 g servo inserted through the wing bottom skin. At the inboard end of the aileron the wing is just thick enough to hold the servo which is simply glued between the top and bottom surfaces.

The linkage has considerable mechanical differential incorporated in the linkage.

The inner and outer panels glued together.

LH wing 1 This shot does rather highlight its extreme root to tip taper.

With no ribs in the outer panel and open braced inner wing ribs feeding the servo wire through is fiddly but no real problem.

The half wing and the nacelle, complete with motor and prop, weigh 140 g which suggests the target weight of 24 oz (680 g) is achievable.

Edited By Simon Chaddock on 01/12/2017 11:09:25

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To save weight the motor wires are extended using 16 AWG lacquered magnet wire.

A short test on a 2s to make sure the soldered connections are sound.

With the nacelles glued into the wing and all the wires brount through the wing down to the root the wing halves can be glued together.

Wing complete 1

The nacelle glued into the wing.

Wing complete 2

All complete it weighs 9 oz (255g)

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Thanks for the kind words gentlemen but things do go wrong!

The centre part of the fuselage was originally just a 'test' to prove the construction technique but it got incorporated into the working fuselage.

At that time I had not even considered the wing construction or its section so the bottom line is the wing does not fit properly onto the underside of the fuselage! sad

After a bit of thought the only solution was to reprofile the wing mount which required the fuselage underside to be cut open and I would then have a find a way to repair several un-repairable printed formers. smile o.

Cut out 1

Printing new cross beams and simply gluing them in proved relatively simple.

The wing will now fit 'snugly' and more important at the correct angle of incidence.wink 2

With the fuselage underside temporarily 'open' it will also make running the long rudder and elevator servo wires a great deal easier so the tail plane and fin are top priority!

Edited By Simon Chaddock on 06/12/2017 00:55:39

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The tail plane in progress. It is quite modest in area but by comparison the elevators are pretty generous.

Tailplane 1

There are no ribs, just a shear web and 2 mm Depron skins. A printed U channel spar supports the elevators. The elevators them selves have a hard balsa leading edge to provide the necessary torsional stiffness. The horn will be on the inner edge of each elevator as the micro servo can only contained within the tail plane at its root.

The fin will be built directly onto the tail plane. The rear of the fuselage will then be cut open and the whole tail assembly glued in place

Well that's the plan! wink 2.

Edited By Simon Chaddock on 08/12/2017 16:46:26

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