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Dereck Woodward Bigga Bit

Scrap box build

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Nigel R02/01/2020 09:49:38
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Once upon a time this was a free pull out in RCME's sister publication RM.

bigga bit.jpg

A very conveniently sized 42" span. The fuselage is, from prop to tip of rudder, about 27".

It is in Dereck Woodward's typical style - everything simplified about as much as possible. Very little sanding and shaping to do. The simplest of radio installs. No cowling. Etc.

In the accompanying build article, Dereck recommended an OS 32. I'm electric in small sizes, so I'm going to use 4S 2200mAh lipo, of which I have a few, a Mega 22/30/2, again largely because I have it handy, and aim to prop it for about 500W.

For me, it's also a chance to try out a couple of building dodges and a bit of mixed style construction, using and abusing a couple of sheets of foamboard, rather than trad all balsa/ply that my recent sport sized builds have been.

Foamboard is called out for ribs, spar webs, control surfaces (edged with some actual balsa).

Nigel R02/01/2020 09:59:04
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I have made a start on the wing.

Already, I am deviating from the plan a little. I do not have the wide, flat, spruce spars that Dereck used. I like why he used them but I had no suitable stuff in the scrap box. My spars will just be the more usual square(ish) section hard balsa instead, of which I have some available.

Also, I used DevWing (as usual) to plot out a symmetrical section of the right size, so my airfoil is different. I don't think it matters much. The smaller bits used a regular NACA style airfoil, as did Dereck's predecessor design Bubbles (on which I imagine this is heavily based). Bigga Bit shows an airfoil with straight edges - presumably to make building flat on a board possible. I'll have to use a couple of jig strips. Dereck had stated online that many of these design parameters were not set in stone, the whole thing was just a 4:1 wing panel, plus tip and elevon. Airfoil? Something handy, providing it had no camber.

Thus far, I have cut the liteply template, and, cut out all the foamboard ribs. This did not take that long. About an hour, all told. Foamboard is slightly quicker to cut than 3/32 balsa, I guess. It is definitely cheaper.

I intend on using the liteply template as the centre rib of the wing, which can carry a peg to locate the wing. I'm going to do a bolt on wing instead of the underside hatch arrangement - I might well omit the U/C and make it a hand launcher.

Nigel R02/01/2020 10:00:24
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Oh, for reference:

Bigga Bit plan on Outerzone

Bob Cotsford02/01/2020 10:26:24
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Following with interest Nigel. I loved my Little Bit that started life with a Cox Golden Bee and ended it decades later with a 3S 1000mAh 100W setup. I gave mine a more contemporary swept back fin and later added a rudder, that had 'interesting' effects when applied at speed! Also 'interesting' was moving the balance point back a few mm too far, it has much more of an effect on a wing than it does on a conventional model with a tail.

Dickw02/01/2020 10:30:52
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Following with interest.

If it goes half as well as my 20 inch span Tiny Bit (also an Outerzone plan) you will have a lot of fun.

Dick

tiny bit.jpg

Nigel R02/01/2020 10:44:57
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Thanks gents.

CG is quite critical on a plank, as I understand it. I think this one is about 15% / 1-3/4" back from LE.

20" of Bit looks fun!

I am hoping this will be a quick build (and won't interrupt my longer project too much - I've broken my cardinal rule of "one project only" by starting this!) as it will be replacing several rather scraggy looking foamboard winter hacks that have racked up a fair few hours between them.

Nigel R04/01/2020 22:59:12
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3737 forum posts
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Nigel R04/01/2020 23:02:23
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3737 forum posts
585 photos

Some structure. Only a couple of hours work to get this far. I'm trying aliphatic to hold this lot together.

No leading edge yet. I ran out of pins. So that will need to wait until the spar and te joints have dried.

Martin Harris04/01/2020 23:53:33
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Posted by Nigel R on 02/01/2020 10:44:57:

20" of Bit looks fun!

Having flown it, I can certainly confirm Dick's statement that it's fun - what the picture doesn't really capture is the sheer lightness of the model - the battery is the size of a partly chewed pack of chewing gum and if I recall correctly, the fin is built from 1/32" balsa. It really belies the wisdom that lightweight models are only for calm conditions - I've seen Dick fly it on days when the birds are making excuses to stay in their nests.

Dickw05/01/2020 09:29:50
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Posted by Martin Harris on 04/01/2020 23:53:33:
Posted by Nigel R on 02/01/2020 10:44:57:

20" of Bit looks fun!

Having flown it, I can certainly confirm Dick's statement that it's fun - what the picture doesn't really capture is the sheer lightness of the model - the battery is the size of a partly chewed pack of chewing gum and if I recall correctly, the fin is built from 1/32" balsa. It really belies the wisdom that lightweight models are only for calm conditions - I've seen Dick fly it on days when the birds are making excuses to stay in their nests.

Yes, fin is 1/32" balsa, battery is 2s 300mAh, all up weight rtf is 89gms (3 1/8 oz), and I have 5 mins of fully aerobatic flight.

Nigel - the CG on my Tiny Bit looks to be the same as shown on your plan and it works fine - but don't go mad with control throws as I find 3mm each way is more than adequate on the Tiny Bit.

Dick

Alan Gorham_05/01/2020 11:14:29
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1237 forum posts
139 photos

I built a Little Bit (28" span version) when I was at Uni 20-odd years ago. It was definitely a quick and well thought out build. Dereck was a Yorkshireman so nothing went in that wasn't needed.

Mine originally had an OS 10FP fitted so I could have a throttle. It flew like a hooligan but it was a bit nose heavy and too heavy generally to bother adding tail weight. I then swapped the OS for a Cox Black Widow. It shed so much weight that I actually got a performance boost, but it used to stretch my concentration a bit running at full pelt until the tank went dry.

I still have the model in the loft. Thanks for sparking some happy memories! I'll follow the rest of your build with interest.

Nigel R05/01/2020 11:16:16
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3737 forum posts
585 photos

3oz, wow!

I can believe it goes on windy days. My now rather ratty foamboard delta is 20" and will go nicely on gusty days. Bit more than 3oz total weight though, more like 12oz.

I will take note in the warning on control throws. Derecks build article says much the same thing. He calls out 1/4" for both aileron and elevator I think.

Nigel R05/01/2020 23:41:40
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3737 forum posts
585 photos

20200105_231227.jpg

Nigel R05/01/2020 23:42:07
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3737 forum posts
585 photos

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Nigel R05/01/2020 23:48:49
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3737 forum posts
585 photos

I added a central liteply rib to carry the wing peg.

I did not fit foamboard webs. I realised it was a bit late to fit them after the spars were both in, as the webs would have needed to go between them. I used some scrap 1/16 instead.

I've also got the first bit of D box sheeting in place, and the first bit of TE sheeting.

So far so good.

Bob Cotsford06/01/2020 09:32:57
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8386 forum posts
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Wing peg? Are you making it a two piece model then Nigel?

Nigel R06/01/2020 09:50:22
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3737 forum posts
585 photos

I am Bob. It probably sounds like unnecessary complexity, but, I figured I could either make a radio hatch on the underside, or drill a hole in F2 and add a couple of wing bolts and make the wing the hatch. Going with a removable wing means I can break the thing down for storage if needed. I don't expect it to take significantly longer than arranging for a hatch - less covering work this way, a touch more woodwork arranging the blocks for the bolts, six of one etc.

These here foamboard ribs.

* they're definitely very cheap

* they're a lot squishier than wood

* they warp something rotten

* they're not much of any quicker to cut out than a rib of 1/16 or 3/32 if you're just zipping around a template with a knife

* it's a bit more awkward to make sure all the edges are perfectly 90 degrees, vs a thin wood rib. They needed the edges tidying up after they were cut out

I think a better mousetrap would involve something a little more rigid at a few strategic points (tip, root, maybe around the servo mount).

I'm on the fence as to whether I want to use the stuff for elevons and rudder. I will probably cut elevons and see what I think after edging them. As a backup I can probably dig out a sheet of 3/16 from the stack of spare wood.

Ken Lighten06/01/2020 13:34:40
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258 forum posts
42 photos

A good few years ago I enlarged this up to 60” span and flew it with an O.S.40fp, flew superbly till I buried it into the grass flying inverted low and fast (up is down and down is up!!), even had a photo of me and it in the hallowed pages of the RCM&E. Such a simple airframe, just make sure the c of g is in the right place

Ken

Nigel R07/01/2020 22:25:07
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3737 forum posts
585 photos

Biggest bit ?

Sounds ace!

Nigel R07/01/2020 22:26:57
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3737 forum posts
585 photos

20200107_222034.jpg

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