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Airbus A350 for 50 mm EDFs

In Depron?

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onetenor29/10/2017 01:00:50
1366 forum posts

Talking about sanding POR glue . I made a trial fuz with 2mm depron . Circular section with seam underneath and POR glued. Not being ready to proceed further I kept it on the radiator near my chair. It was there for a couple of weeks.When I picked it up again there was a cracking sound and the joint opened. On examination the POR had gone crystal clear and brittle. Tony B must have seen this before as he advised I must sand the brittle glue off before attempting to re glue the seam again.Obviously the heat had accelerated the glue drying out like this but will it eventually happen over a period of time anyway? Time will tell if our Depron models fall apart I suppose.frown

Pete Collins29/10/2017 09:20:48
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60 forum posts
2 photos

Thanks Simon,

​I thought you'd come up with some magic method of printing it all in one piece!

Pete

Simon Chaddock29/10/2017 10:33:45
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5009 forum posts
2623 photos

OT

Yes POR does harden over time but my oldest 'stressed skin' wing (in other words it relies on the glued joints for its strength) is still flying after 6 years.

I found that Depron itself becomes considerably more brittle over such lengths of time.

What I try to avoid is relying on the glue to hold the Depron into shape as this in effect stressed the joint (or rather the delicate Depron immediately adjacent to the glue) before any 'flight' load is applied. I either preform the Depron (and use its grain where appropriate) or use many individual pieces (ie narrow planks) to keep down the load required to bend each one.

Simon Chaddock01/11/2017 15:52:23
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5009 forum posts
2623 photos

I am afraid the thread title is now a bit misleading as what it looks like it will definitely not be using 50 mm EDFs in fact it will not be using fans at all but ducted props, four blade 3x3.5 for a racing quad! smile o.

As the test fuselage has gone together well it will be used as the basis for a 62" (1570 mm) span Airbus A350 -1000.

First it is extended forward with a parallel section to the point where the fuselage starts to narrow towards the nose.

Fuse mid 1

Next it will be extended rearwards to the point where the fuselage narrows for the tail section.

In preparation the former 'set' for tapered rear fuselage has been 3D printed.

Rear formers

The resulting shape is rather complicated. It starts off round but then significantly narrows to a vertical ellipse in the area of the tail plane and returns to a true circle at the beginning of the 'tail cone' itself.

This continuously changing section will make it a bit of a nightmare to plank! wink 2

Simon Chaddock05/11/2017 22:56:35
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5009 forum posts
2623 photos

The nose and tail sections under construction.

Fuse nose 1

Fuse tail 1

The little printed cone is the APU exhaust that goes right on the end.

When each section id fully skinned (planked) the base former is carefully cut out so the ends of the skin can be carefully sanded to make sure it fits 'true and square' on the the preceding fuselage section.

Nose inside

To give more glue area on what would otherwise be a butt joint a 2x2 mm flange is glued to the former.

Flange 1

All five sections glued together.

FuseCmplt 1

61.5" (1560 mm) long and at 96 g it is just within my guesstimated target of 100 g.

Next is to start thinking about the wings although I really need the motors and fans (props) before I start building iti

Andrew Price 206/11/2017 15:14:04
796 forum posts

You just do not do easy do you Simon?

Andrew Price 206/11/2017 15:14:05
796 forum posts

You just do not do easy do you Simon?

Simon Chaddock08/11/2017 11:39:11
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5009 forum posts
2623 photos

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

Erfolg08/11/2017 18:59:59
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10584 forum posts
992 photos

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

Simon Chaddock08/11/2017 21:43:19
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5009 forum posts
2623 photos

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

Martian09/11/2017 12:16:43
1612 forum posts
773 photos

Loving your journey with these materials really excellent stuff for me though it would be like juggling with jelly

Simon Chaddock12/11/2017 17:34:22
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5009 forum posts
2623 photos

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

Simon Chaddock13/11/2017 17:45:20
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5009 forum posts
2623 photos

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

Callsign Tarnish14/11/2017 18:53:47
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6 forum posts
Simon, I'm very much of the old school, traditional builder, mentality but I have to say it's quite inspirational seeing what the more adventurous of us can achieve with new materials. Enjoying this.
Simon Chaddock15/11/2017 01:50:55
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5009 forum posts
2623 photos

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!

Simon Chaddock17/11/2017 13:59:16
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5009 forum posts
2623 photos

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

Erfolg17/11/2017 19:31:39
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10584 forum posts
992 photos

If it were my project or model, one of my concerns would be what will happen to the Nacelles and supports when the model lands?

Colin Leighfield17/11/2017 20:51:54
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5286 forum posts
2074 photos

I just know it’s going to work!

Simon Chaddock19/11/2017 00:01:26
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5009 forum posts
2623 photos

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

Stephen Jones19/11/2017 00:25:06
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2409 forum posts
1391 photos

Wow their is a big difference in size when seen side by side.

Steve

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