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Nutball

Foam board quick build

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Don Fry12/01/2019 15:17:58
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3026 forum posts
38 photos

David, is the motor mount just plugged onto the carbon spine, with a (filled epoxy?) load spreading ( balsa?) cone?

David Mellor12/01/2019 16:26:30
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1188 forum posts
599 photos

Duplicate post...... phat phingers again......

Edited By David Mellor on 12/01/2019 16:34:34

David Mellor12/01/2019 16:33:12
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1188 forum posts
599 photos

Don, I use a small conical ply load spreader.

I should have said that I generally use rod for the spline, not tube. Tube is OK for a while, but there is a surprising amount of torsion from the motor and rough landings, and eventually pultruded tubes just split and have to be replaced. Rod is more durable, though a tad heavier.

For really big Nutballs (48" and upwards) I use 16mm roll-wrapped carbon fibre tube which is excellent at resisting torsional loads. Unfortunately it is very expensive.

On these 28" Nutballs I make the motor mount from a pair of 1/8" ply plates chamfered down opposing sides. When these are glued back-to-back it produces a nice groove which accepts 4mm carbon fibre L/G legs. These are stitched and glued into the grooves formed in the motor mount. It is very light and strong, and of course, it is physically impossible to put what little weigh is in the L/G any further forward than that!

In this photo you can see the two 1/8" back-to-back chamfered plates of the motor mount with the conical load spreader fitted and the carbon rod spline in place. The carbon rod L/G legs are glued into the grooves formed by the chamfers then stitched in place, the sticking being soaked in cyano.

I remove the motor/ESC and Rx from my planes when I store them in the shed. You can see why in this photo...... mice have eaten the foam tyre on the right hand wheel..........

p1010775.jpg

Dave

Don Fry12/01/2019 19:25:04
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3026 forum posts
38 photos

Thank you David, got the concept. Thank you for the carbon fibre website. I had lost the address, they are good, and they do epoxy colours, just the job for a epoxy skinned aircraft, to get a weight free base colour.

Query, if you stuff an epoxy coated balsa core, in a protruded tube, would that not improve rotational stability to stress fracture.

Edit, for a fee, my whippets like mice for breakfast. Small high speed bits of fun, the mice, not the whippets.

Edited By Don Fry on 12/01/2019 19:30:34

kc12/01/2019 19:40:02
5698 forum posts
164 photos

As usual David Mellor's somewhat different construction technique is worth studying and gives food for thought.

Some months ago David suggested the HK Donkey ST3511/810kv was a good buy so I bought several. I am tempted to make a Nutball after reading this thread. So what size Nutball would suit this motor David?

kc12/01/2019 19:49:42
5698 forum posts
164 photos

Many aeromodellers give their wife reasons why they need a new plane but saying mice have eaten the tyres is a new one!

Baiting a mousetrap with the remaining tyre might be worthwhile.............

David Mellor12/01/2019 21:05:02
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1188 forum posts
599 photos

Don, yes, it does improve resistance to splitting, though still not as good as a rod.

Sounds like I should borrow your whippets for a few days.....

kc - I'd recommend using the ST3511/810 in 40" Nutballs.

I make them from laminated Depron. I have used grey Depron (in the photos and videos below) and I have to say that the grey isn't really very good for laminating compared with the white Depron which is noticeably stiffer and better for Nutballs.

My 40" ST3511 Nutball vital statistics are:-

Wing Area = 8.73 Square Feet

AUW = 35.5 ounces

Conventional Wing Loading = 4.1 ounces per square foot

Cubic Wing Loading = 1.38 ounces per cubic foot

Motor = HK Donkey ST3511/810

Battery = 3S 2200 mAh (mounted underwing on velcro)

Prop = APC 15 x 4

Power-to-weight = 148 Watts per pound (measured)

(Static) Thrust-to-Weight = 2.05

Flight Duration (steady, not WOT) = 20 minutes

Spar cap material = 1/64" ply

If you'd prefer more "zip" out of the ST3511, then I'd recommend 4S and a smaller prop.

Here's one I made earlier:

p1040459.jpg

A glimpse of the underside shows the ST3511 and underslung battery a bit more clearly, as well as the detachable L/G and detachable skid.

thumb-p1040460.jpg

And the maiden flight was completely uneventful, with a loops and some bunts:-

David Mellor12/01/2019 21:13:25
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1188 forum posts
599 photos

Sorry, kc, that photo of the underside of the 40" ST3511 Nutbal wasn't very clear.

Here's a couple of better shots of the velcro-mounted carbon rod L/G and velcro-mounted wire skid (the wheels are 5" polystyrene balloon type):-

p1040475.jpg

p1040472.jpg

kc13/01/2019 12:19:34
5698 forum posts
164 photos

Thanks David - at 40 inches that's bigger than I expected for the ST3511 motor. Presumably the laminations are 3mm, 5mm and 3mm the same as the 28inch?

That carbon rod L/G looks just like a piano wire job with soldered joints - is it really carbon fibre?

I am wondering how the angled tips are done on all these Nutballs - are they partially severed from the main wing and bent up or are they separate material just glued on?

David Mellor13/01/2019 12:53:36
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1188 forum posts
599 photos

kc

There is some latitude on diameter - anywhere between 37" and 41" would be fine.

The laminations are indeed 3mm, 5mm, 3mm and you could lighten the inner core if you felt it worth the hassle (see photo in earlier post).

What looks like solder joints is strong sewing thread soaked in cyano. Look carefully... all the straight pieces are carbon, any bent piece is steel.

Angled tips made completely separately.

Edited By David Mellor on 13/01/2019 12:53:56

kc13/01/2019 13:52:29
5698 forum posts
164 photos

I see now - the 'spreader bar' seems to be the bit thats bent to go through the wheels rather than the 'legs' - very unusual to those of us brought up on David Boddington/ Vic Smeed/ Peter Miller designs!

But that's the interesting thing about David Mellor's models and also Nutball style designs -they don't take the traditional construction as the accepted way to build but innovate using any available materials not not just balsa and piano wire. I particularly like the use of 1/64 ply in small pieces as reinforcement.

David Mellor13/01/2019 13:57:43
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1188 forum posts
599 photos
Posted by kc on 13/01/2019 12:19:34:

Thanks David - at 40 inches that's bigger than I expected for the ST3511 motor.

Just a thought....... 40" Nutballs are quite easily powered by much smaller motors than the ST3511.

It all depends what you want in the way of performance.

I have made a 40" Nutball that flew using just a 24 gram 1300 kv Blue Wonder motor (max power about 90 Watts flat out). It was fine for just floating about, would eventually loop (if you waited long enough) - but hardly what you might call sparkling performance!

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