|Feb 09, 2014, 12:13 AM|
I've been posting snippets about this plane for over a year, as I've worked on it in stages.
This is old news, but a quick summary of the Angry Bird:
I really loved my Wizard Compact DSX which was destroyed in December 2012 when it broke up in mid air at Tekapo in New Zealand. I really wanted something to replace it … a really fast fun Dser that you can pull out no matter how strong the wind. Something very strong, capable of 350mph, good for DS aerobatics and with a wide ballasting range.
Since I’d learnt some basic composite model building with the Scratcho - http://www.rcgroups.com/forums/showthread.php?t=1660287 I thought I should have a crack at making a big ship of my own. I knew it would be a big job, but looking back, I don’t think I really had any idea how big the job really would be!
I love the way the Scratcho flies with its HN1038 airfoil, so I looked for a model to modify, with a HN1038 airfoil, 2.5m to 2.8m span, 3 piece wing which I could modify to make a dynamic soaring plane. After a lot of head scratching, I bought a Sting F3F from Soaring USA, and spent a vast amount of time in early 2013, modifying it to make plugs for the hybrid Dser.
My wife was hooked on playing Angry Birds on her phone at the time, and I grabbed the name. Matter of fact, I think that’s the best part of this plane: the name!
Some of the modifications I made:
* Cut the fuselage boom and drooped it down 25mm, so its axis is in line with the wing datum line.
* I socked the boom to make it thicker, and added layers of glass here and there to add thickness or to allow room for servo etc.
* The Sting is a V-tail but I converted it to a whole new X-tail using a similar system to the Wizard Compact. I cut up the V-tail to make the stab. I vac bagged a new fin with foils to match the required base width but fine at the top. Then after lots of head scratching and pencil marking I cut it to neatly split along the 0/0 incidence line at a height of 30mm above the wing datum line, and cut out the stab shape.
* The trickiest job was setting up the aluminium dowels in carbon tubes, so that it was all square and straight and the fin could push on and off perfectly. I had to work the rear thicker dowel position to give enough strength (distance between dowels) and allow room for the servo, but I couldn't go too far back, to allow the elevator pushrod to clear the internal dowel tubes.
* The standard joiners are tiny, so I hacked out 8cm of the original joiner box and fitted my own bigger ones which take 40mm x 12mm steel or aluminium flat bar. The original wing has double dihedral, but I'm using straight joiners so it removed the dihedral between the centre and tips. The joiner boxes in the final plane will be 500mm long each side, so they double as joiner boxes and ballast boxes.
* New thicker stiffer incidence pins.
*Pointier nose cone!
* I've set it up so the tip panels also join together with the same joiner and pin positions so you could make a smaller fun plane from the tips.
After finishing the plugs, I was worn out, and the thought of making the moulds freaked me out. I gave up, and shelved it for a while.
Later in the year I had another look and decided that the horizontal stabilizer I’d made from the Sting’s V-tail was way too big. I wanted something a bit smaller, but had no luck finding it.
Around that time, the whole CAD and CNC learning adventure started. As it got closer I decided that my first CNC “project” would be to make a new stab for the Angry Bird.
Late last year I got re-started and made the centre panel mould … but had a disaster when the heat of the mould layup expanded the hollow plug. The second half of the mould (the bottom) was a failure, with big depressions. I decided to give up, but of course I couldn’t leave it and finally attacked the plug and re-did the bottom mould half. It’s not great, but it’s OK.
By this time I had a good drawing of the new stab, and the CNC machine became part of the family - so just recently I cut my teeth making good CNC moulds of the new Angry Bird stab, and last week I turned out the first part … looking totally fantastic. As a result, I was able to fair it into the fuz/ fin join properly and it’s ready to mould.
But I am most scared of making the wings. I have only ever made hollow core wings. I love solid cores of foam or expanding epoxy. But after much consideration I realized I’d have to do the Angry Bird as a hollow structure.
I’ve decided to go for a very thick skin, rather than using a core. The skin is:
• 2K paint backed with primer.
• 100gm glass
• 300gm glass
• 400gm stitched biaxial biased carbon.
• 300gm glass
• 300gm unicarbon sheet
• 400gm unicarbon spar caps, 45mm wide (a bit wider than the joiner boxes).
The internal structure is going to be double thickness carbon socked foam spars.
I cut samples of my layup to look at it and measure the thickness, and thought hey, this really should be done by resin infusion! I’d done some infusion with some early Scratcho wings but generally my layup for the lighter planes was too thin … and the Scratcho moulds have leaks.
I did a 700mm x 220mm test patch of my layup and infused it with LC3600 resin. Too slow for comfort, but a great result.
So today, I laid up the wing using cloth sections cut with templates I’d made yesterday. It’s so nice to be able to fiddle around getting the various sections in position, without any sticky resin, and no time pressure at all!
It went well. Here are some pics. I got video too, but it’s too boring.
I’ll put up some photos of the rest of the Angry Bird plugs another time.
|Feb 09, 2014, 12:25 AM|
Greatest to go just solid lay up and not core that will be bullet proof strong.
Resin infusion makes for a easy lay up and process and no rushing one thing I have noticed is having a layer of perforated plastic between mesh and peel ply make it really easy to get the mesh off.
I have found on lighter lay up's the mesh full of resin is hard get remove on well seasoned mold.
|Feb 09, 2014, 01:28 AM|
Glad to see the infusion working well for you. Isn't it fantastic! The only way to do it
I am also embarking on a similar project this year from a thin hollow molded plug. Will hit you up about it at some point.
|Feb 09, 2014, 02:14 AM|
Nice one Andrew, cudos for going super heavy straight off the bat! That thing will be a DS brick!
Cant wait to see some more
|Feb 09, 2014, 02:44 AM|
Not at 2.8m span and big wing area. Should come out at ~6kg flying weight, depending how heavy it is made behind the TE. Andrews old Wizard DS @ 2.5m span would float out at about 6kg in 30mph winds.
This Angry Bird should be good for 20mph+ winds. I know once the CG and control set-up is sorted, it is going to be one fun model to fly!
|Feb 09, 2014, 02:55 AM|
I don't know, but I reckon that layup will be a lot heavier for a big model like that. The Scorcher that you have now has a 800gsm layup with less span and much less wing area and weighs all up 4kg (albeit with a lot of lead in the nose). This one is a 1600gsm layup, over much more surface area. But 3 pieces means the tips can be lighter if need be. Hey that could be a good ballast setup- just build heavy and light tips!
|Feb 09, 2014, 04:16 AM|
I think the unicarbon sheet I'm using is maybe 200gm. I dunno, it's an old stiff roll that someone gave me! Curled quite tight and I have to press it flat for a day or so before laying it down. Anyway, I think that makes the main layup 1300gsm, not 1600. The spar caps are additional to that but only along the spar/ joiner line.
The infusion test layup piece I made has the same layup plus a layer of the thicker type of Innegra. It feels pretty heavy - 365gm. But very strong! Innegra does add lots of durability, but soaks up a heap of resin and once I realized how thick the cured test piece was, I decided to lose the Innegra ... I think the skin will be strong enough without it.
Doing the maths, predicting that losing the Innegra will take off 20% of the weight of the test layup, ( 300gm over a 70 x 22cm piece) its weight by area is .195gm per sq cm. The centre panel top and bottom have an area of 5405 sq cm, so the skin alone should weigh around 1.05 kg. That's without the spar caps, spars, splooge, joiner boxes and so on. But I think the centre panel should come in around 1.5kg, which is perfect I reckon. It does need to be strong.
The DSX's lightest config was 4.5kg for 2.5m span. The Shockwave was 5.5kg for 3m span. Both flew beautifully in much lighter air than you'd think they need.
|Feb 09, 2014, 04:25 AM|
Here are some photos and explanations from way back at the start. Before you ask, yes a few guys have asked "why are you doing all this when you have the CNC now?" Very good question! Half of me would love to drop the Angry Bird project and make life a lot, lot simpler. I started this before any CNC plans. I shelved it repeatedly because to be honest the thought of tackling it again made me feel a bit sick! But after all the organizing and work I put in, my pride just can't let go of it! I feel that I need to get it done. I'm learning lots of stuff that I'll be able to put to good use in the future anyway.
|Feb 09, 2014, 05:24 AM|
The upload thing jammed at one stage.
Keeping going ...
|Feb 09, 2014, 05:53 AM|
That's seriously impressive, and such a lot of work there Andrew. Should be a great all-round, almost all condition toy when it's done.
Would you mind explaining the reasoning behind drooping the tail boom?
|Feb 09, 2014, 06:03 AM|
For some reason it was angled up quite significantly. I checked my other planes (Wizard, Shockwave etc) and their booms were pretty much aligned with the wing datum line. My thinking was that the Sting's boom angle might be OK for an F3F plane but at 300+ mph, there would be quite a lot of force exerted on the boom by not being aligned with the flight path.
|Feb 09, 2014, 11:04 AM|
very nice work.
I like your tail work ,
1000-1300 gr/m Layups are great on the wings dont worry. Just what i do on my Hannibal- all cfk though and aprox 2400 gr/m for spars. But then i do not have a joiner restricting my spar layup .
but since it has not been mentioned:
I do not use such heavy layups along the flaps/ails. I keep them comparetively light
aprox 400 gr/m.
I will be following with lots of intrest.
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