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C17 Globemaster III - 1/15th Scale for PSS

CAD to slope - 133" span

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Andy Meade11/01/2016 11:32:15
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c-17-globemaster-iii-a.jpg

Here we are then, another large PSS build. I had drawn up a large AC130 gunship for PSS a couple of years ago, but didn't as far as 3D CAD - just a few sizing sketches over some 3-views, but then someone else decided to make one!

Thus, the C17 idea was born. I watched those Discovery Channel episodes 10 or so years ago where they built one quickly, all in balsa with some mouldings here and there, for 4x turbine power. What a beast! So the C17 (or BGC - Big Grey Cloud) idea was niggling away at the back of my head, and with a build board full of other airframes requiring attention or finishing, it's obviously the ideal time to start something new and big! laugh

I started off with a quick internet search, and found a 60" C17 plan for depron, as a free plan. A good starting point, as the formers were all reasonably well shaped (apart from the undercarriage area), so I grabbed that, imported it into SolidWorks, and started work.

Firstly - what size? Well, the BGC is a big aircraft, and 60" would give something not very imposing in the air, and it would probably get bumped around a lot. Bigger then. I had always planned the AC130 to have a 400mm round fuselage, so this is where I started, giving me a 3.4m / 133" span.

Sketches were resized, some formers re-worked, and structure added to make this a two part fuselage, plug-in wings, and a removable tailplane.

The plan so far is to make the fuselage out of 4mm (cheap!) ply - a crutch with formers and a couple of (pine) stringers to keep everything square. This will then be blocked out in white foam, covered in brown paper & PVA, then probably glassed.

The wings, tailplane, and fin will be white foam, cut and veneered by me. Finish will probably be silver film straight on, then the whole model primed and sprayed. The engines will be 3D printed in 3 pieces, sanded and primed to match, and will have some facility to be knocked-off in long grass.

I intend to re-create the huge blown (but not blown) flaps from the full size, along with top-surface spoilerons / brakes. I will firstly use them as brakes when full flap is selected, but might also mix them to go up with the up-going aileron.

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The rest of the controls will be rudder, elevator (2 servos), and some scale lighting too I hope.

Overall fus structure :

progress05 former tweaks.jpg

progress07 former tweaks.jpg

Big(ish) :

progress04 scaling.jpg

progress08 engines and fin top.jpg

progress10 front view.jpg

Oh, and did I mention there will be two? I will get the first build moving quickly, then provide a kit of parts for Dave Gilder to create one too.

I want this flying this year, thus the "quick" construction and finishing method. Onwards!

Andy Meade11/01/2016 11:36:46
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Here is the plot of the side-view of the fuselage, along side my Futaba 10c :

20160107_221850.jpg

That'll do. Last night I started sticking former templates to wood - I should have the first formers complete this week.

Oh, I should also add - Dave is making his fin removable for transport, but as this will go into my trailer or camper van without too much hassle, mine will be one piece back there. The fuselage splits behind the TE of the wing - where pink changes to purple on the crutches in the above images.

David Gilder11/01/2016 11:59:52
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Looking Good there Andy.

Cant wait to see yours started and knowing there will be parts heading my way shortly after for me to get started.

I'm hoping to learn a lot about building big from you through this and the A10 build but will no doubt have lots of questions once underway!! (Like where is best to get the steel wing bar!)

Signed up and eager to get building myself!!

teeth 2thumbs up

Dave

Mark Kettle 111/01/2016 12:08:02
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Nice Andy, how exciting. crook Will you have to remove the landing wall to build the fin in 'situ' on the plan?

yes No joking aside keep up the good work.

Andy Meade11/01/2016 12:16:49
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Dave - if you have a "Homebase" nearby, go in and buy a 25mm square length of steel. Wall thickness is about 2.5 - 3mm if memory serves, and get the long one. 5 foot is all you need, but I think they do a 4 foot one. A cheap and wayyyy over-specced wing joiner - A10 technology carried over yes

 

Mark - thanks!  Hopefully will have this done for Lleyn, but we will see.

Edited By Andy Meade on 11/01/2016 12:17:34

Matt Jones11/01/2016 12:22:16
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Subscribed!

BTW, what's going on with that guy's thigh?

Andy Meade11/01/2016 12:24:00
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I have no idea I got a standard model from GrabCAD, and for some reason one thigh went a bit odd. I was too lazy to fix it I'm afraid surprise

David Gilder11/01/2016 12:38:31
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Posted by Andy Meade on 11/01/2016 12:16:49:

Dave - if you have a "Homebase" nearby, go in and buy a 25mm square length of steel. Wall thickness is about 2.5 - 3mm if memory serves, and get the long one. 5 foot is all you need, but I think they do a 4 foot one.

If I need 5ft and they do 4ft that leaves me a ft short!!!

I suspect flappy wing syndrome if this is the case!!!cheeky

Andy Meade11/01/2016 13:08:11
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Sorry, I should have said they do a 4 foot and a 6 foot. Get the 6 foot, cos all you need is 5. Let me double check that actually.

David Gilder11/01/2016 13:16:33
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Beginning to be scared now..... If this is how you measure things!! cheeky

Maybe I should wait for the plans and measure it myself!!! lol

5ft sounds about right for the 11ft wingspan!

Andy Meade11/01/2016 13:18:01
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I've sized up the wing boxes, just not actually measured anything in the model. The limiting factor is the monster anhedral the wing uses.

It's 5 foot.

 

Edited By Andy Meade on 11/01/2016 13:19:48

David Gilder11/01/2016 13:27:40
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Cool.

I will get it on the order list!!!

wink

Nothing to stop me cracking on with a relatively quick build when the parts arrive then!

Flyer11/01/2016 13:33:45
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Very nice Andy. Will follow this with interest. It will dwarf the AC130 ......... a mere 2.7m .

As a matter of interest, would a built up and glassed wing be much lighter than foam veneered?

(Looking at doing that myself).

keep up the good work

Ade

Andy Meade11/01/2016 13:37:31
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2605 forum posts
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Hi Ade,

I'd imagine the built up version to be not only lighter but stronger too. My main reason for going with a foam wing is that my built up wings are an embarrassment when it comes to straightness, and I can knock out a completed foam wing pretty quickly.

I really want to see the C17 and AC130 flying a tight formation on the slope!

Flyer11/01/2016 13:42:10
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Posted by Andy Meade on 11/01/2016 13:37:31:

I really want to see the C17 and AC130 flying a tight formation on the slope!

I'm not too sure that I can build a straight wing that big yet !!! , but I've a better chance that a foam wing. You may have to wait until next year to 'hopefully' see the C17 and AC130 fly together, as I will not be able to get on with the construction plans until February, due to work, but you never know.

Do you hollow the white foam infill blocks on the fuselage?

Cheers

Ade

Matt Jones11/01/2016 13:42:39
1186 forum posts
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Andy, built up wings are easy at this size, 1/8" - 1/4" ribs and 3/32" sheeting, it goes on much easier than the usual 1/16".

Dave, if you want to save weight I'd make the wing three piece with the dihedral build into the centre section, the joiners to the outer panels could then be short lengths or carbon tube, say in the region of 25-35mm dia rather than 5' of box steel. thumbs up

Andy Meade11/01/2016 13:43:38
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2605 forum posts
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Yes, where possible I will use a hot-wire to leave about a 2" wall on the fuselage. The rigidity should be supplied by the crutches and formers.

 

That's a good idea Matt - certainly possible. The centre section could then bolt into the fuselage with the normal large dowels + bolts, or maybe a ply tongue on the front like the Cocker B52. yes

The only problem with that is..where to split?  The flaps take up about 85% of the span, and you'd likely want not just plug-in tips.  Also storage - with that sweep, it becomes a big lump very quickly.  I'll let Dave decide what he wants to do with his laugh

Edited By Andy Meade on 11/01/2016 13:46:33

Edited By Andy Meade on 11/01/2016 13:53:37

David Gilder11/01/2016 13:54:04
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Interesting idea Matt.

Yes it would save in weight but with this being a very wide bodied aircraft, going light could lead to penetration issues resulting in a very non scale like flying characteristic!

I think the A10 would have had a lot less speed and penetration if it hadn't had the extra weight provided by the steel bar!

And to add also, Andy is very kindly cutting me a set of wings so its less to worry about and will aid a speedier build!

I will be doing a blog also when I start my build!

Phil May11/01/2016 14:05:38
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Subscribed and following with interest 👍

Andy Meade11/01/2016 14:06:32
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I can always cut another kit of parts Phil! wink

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