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Martyn's Ballerina @ 115%

It's called Ballerina 115 - sounds more impressive than Ballerina 70

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Martyn K07/12/2015 21:05:40
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Place holder posting and official notification that I am taking part. I haven't missed a MB yet and I don't intend to start now..

My MB plan for 2016 is to scale Peter's Ballerina plan to 115% and fit an OS70FS. Why? Well 2 reasons

1. I like the look of the Ballerina, it's reminiscent of an Astro-Hog and if I wasn't building this then I may build another Astro-Hog. My other two are now flying in that great flying field in the sky.

2. I have a spare OS70FS and it seems a shame not to use it

3. (O.K. - I cant count), my eyesight is a bit dodge on dull days and bigger models are easier to see before I crash them.

First I had to do a quick sanity check to make sure everything fits:

So scan the plan (or bits of it) to A4, Print to PDF, Print from PDF increasing the size to 115% - seemples

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Side View. I intend to mount the engine inverted. Allowing for parallax,its actually a very good fit. There is about 10mm between the carb and the Firewall.

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Top view. Plenty of space which is very reassuring. I thought it would be too narrow

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Bottom view - I can offset the mount slightly to the left and add a little right thrust using shims. Plenty of space.

That's the prep and sanity check done, got enough balsa and ply in stock to make a decent start. The next build type post should be in January.

Looking forward to it

More to come

Martyn

FastFlyer Smyth07/12/2015 21:51:05
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Subscribed yes

Craig Thomas08/12/2015 10:32:32
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Looking forward to this one.
Peter Miller08/12/2015 11:26:38
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I shall be watching

Martyn K03/01/2016 22:22:11
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4295 forum posts
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Happy New Year party in case you are not following my Aurora Build

I made a start on the 1st January - cutting parts - no nailing of bits together yet (just kidding) and am starting to accumulate a reasonable kit.

My Ballerina is scaled up by 15% and will house an OS70 FS Surpass.

As this is a Mass Build and hopefully to encourage newbies to the building scene I'll add a little more detail than I usually do. I will describe the way I do things, they are not necessarily the best - in fact there are almost certainly better ways - but they suit me. Feel free to ask questions if its not clear why I am doing things the way I do.

As this is a scaled up version of Peters original, I will be making some structural changes - mainly because the model will be larger and have more mass, I'll explain where and why I have changed things as I make progress.

So making a start...

 

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I have scaled parts up by simply scanning 1:1 to A4, drop the colour depth to 2 channel (black and white), printed the result to PDF then from PDF printed at 115%. Great for small parts but wont work for a full wing..

All the formers and R2B have been printed in this way and need to be transferred onto the wood we will use.

For small parts, I tend to use pin prick technique. This involves pinning the artwork to the underlying wood and using a map pin or similar simply prick the outline and any inner holes etc that will need to be cut.

For larger parts like these formers I use Carbon Paper and then carefully draw around the curves freehand and use a pen and rule for straight edges. Where Centre lines are shown draw these as well - they are useful references.

The 4 ply formers (lite and birch) were marked out and cut out. I am fortunate, I use a Band Saw for the outside edge of birch ply parts and a fret saw for the inner holes (except F1 inner - use a hole saw).

Lite Ply formers are cut using a Stanley knife with a new blade. Dont try and go through in one go - it normally takes 4 to 6 cuts to cut through 3mm Lite Ply

dscn2659.jpg

Ready for cutting..

The balsa formers have the grain running transversely - across the width. 1/8" balsa is specified. These formers carry more load during construction (I think) - as the fuselage gets nearer completion the load is shared by more components. Balsa varies vastly in density, You need to select wood that is of a medium density for the formers and straight grained. No knots or stains.

Balsa Desity Table

Balsa at 10lbs/ft^3 can be tested by pressing with your thumb nail. There is a knack to it and experience is a wonderful thing but you should be able to mark it by pressing gently. You will see a nail nick in the wood but it should not be too deep. This is the density you are looking for - its better to weigh it using the above chart as a reference until you get more experience.

Most wood is 3" or 4" wide. You will need to make it wider for the formers so will need to glue 2 sheets together. Cut the balsa to the correct former width. Sand the edge to that 2 pieces but up to each other neatly. Join on one side using masking tape

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Flip over and glue the pieces together. Lay it down flat and weigh the balsa down until the glue dries

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I use PVA glue for (almost) all my wood to wood joints. I have tried Aliphatic but never really got on with it. Cyano has its uses, but I find the joints using Cyano can be a bit brittle.

Joining other materials - such as Plastic to wood etc, I use 24 hour Araldite and learn to be patient..

More to come

 

Martyn

Edited By Martyn K on 03/01/2016 22:31:09

Martyn K03/01/2016 22:22:47
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Wing Ribs

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This is a parallel chord wing which simplifies construction considerably. Rather than cutting out all the variants shown on the plan, I simply used R2B from which all the other wing ribs can be cut. My preference to cut wing ribs is to make a master

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Then simply cut round it. The wing rib is about 12" long and at first glance it looks like I will only get 6 ribs per sheet. However, by being careful, I managed to get 9 ribs per sheets. I am still cutting these out - I always cut a few spares just in case

dscn2664.jpg

To cut wing ribs out using this method (rather than the sandwich method that others will advocate), press down on the rib and with a new blade in your scalpel carefully cut around the rib. Cut the verticals for the spar slots and then remove the wood after the outline has been completed.

The cut thumb happened on the Aurora - however - it is very easy to slice the top of a finger so take care.

More to Come

Martyn

Edited By Martyn K on 03/01/2016 22:23:09

Biggles' Elder Brother - Moderator03/01/2016 22:52:00
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Great start Martin and excellent detailled blog. Following with interest!

BEB

PS happy New Year to you!

AndyD03/01/2016 22:54:05
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606 forum posts
433 photos

Martyn what sort of weight are you aiming for at 115%,im doing 120% electric and thinking about 7 pound wth mine,ive got to be careful as my motor batt setup a bit on the heavyside.

Martyn K03/01/2016 22:57:42
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4295 forum posts
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I am hoping for about 4.5 - 5lbs (dry - but I am fitting a 10oz tank) - must try and keep it off the Christmas leftovers.

7 lbs seems a bit heavy for this though - I would have thought an upper limit of 6lbs to keep the character would be about right for 120%

M

AndyD03/01/2016 23:15:45
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606 forum posts
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i shall try for 6ish but just my batt and motor weigh 2Ib 10oz,wait an see,im going to leave my batt hatch untill last possible as i think the hatch might be under the pilot.great build shall be watching with interest nicking all the good ideas.

Andrew Price 203/01/2016 23:33:22
790 forum posts

Following with interest, Martyn. Thank you for the extra detail, some useful stuff already.

john stones 103/01/2016 23:34:26
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8584 forum posts
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Always good blogs Martyns, loads of pictures and commentary yes

John

Edited By john stones 1 on 03/01/2016 23:34:46

McG 696904/01/2016 08:07:47
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1506 forum posts
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Hi Martin,

Subscribed & will be following with interest.

Please keep detailing as much as possible as I will be back nicking your ideas for the wings of my Bella Ballerina HD. blush

Peter & kc suggested to move the dowel hole in F2 upwards by 6mm (& doing the same to the R1 rib slot with a depth of 50mm) for increased strength. Are you not doing this on yours?

Happy cutting

Chris

Brussels, Belgium

McG 696904/01/2016 08:32:28
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1506 forum posts
666 photos

Martin,

Also, if I remember well the balsa former's grain was drawn wrongly on the published plan & should be vertical just like the ply formers.

I didn't wrote this down in my notes though since mine will be Depron anyway and of course my neurons could be flashed out by my extensive glues-testing...surprise

May I suggest you a quick check with Peter or kc about this?

Happy checking

Chris

Peter Miller04/01/2016 08:36:11
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8464 forum posts
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This has been mentioned. Grain should always run up the longest dimention

McG 696904/01/2016 08:44:35
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1506 forum posts
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Thank you Peter, for confirming me the 'normal' condition of my neurons (at least, at this point of the build) ... angel

Chris

Martyn K04/01/2016 09:30:51
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4295 forum posts
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For Formers I (now) prefer the grain running across the Fuselage. I already mentioned that I think the formers carry most load during construction. What I find was happening was that as you pull the fuselage sides together, the formers would bow. The result was that I needed to add additional cross pieces to prevent this happening. When I saw the plan I thought I had been doing it wrong on all those previous models.

When the formers are glued in place, the effect of the fuselage sides will add the vertical stiffness.

It may be 'wrong' but this is how I am going to build it

Chris - on your other point, I will be using 6mm dowel for the wing locating peg.

AndyD - Target weights

Trying to keep to the same wing loading, my Ballerina will have an area increase of 32%, which means to maintain the same wing loading, my target weight should be 93oz (5.8lbs)

Yours - with a +20% scaling will have an area increase of 44%, which means to maintain the same loading, the target weight should be 102oz (6.4lbs)

M

AVC04/01/2016 09:55:05
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464 forum posts
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Posted by Martyn K on 04/01/2016 09:30:51:

Trying to keep to the same wing loading, my Ballerina will have an area increase of 32%, which means to maintain the same wing loading, my target weight should be 93oz (5.8lbs)

M

Hi Martyn

The experts will correct me if I'm wrong, but as the surface and the size of the model increases, the wing loading can do it also (the so called "scale effect", so you can be more flexible on that target weight. Using an "extreme" example, a 1/6 scale Piper Cub has a wing loading of around 55-60 grams / square decimeter (sorry, I still measure this in the Continent money...) whereas the full size is around 900 - 1000 grs / sq decimeter, and it still flies deadly slow...

My rule of (cut...) thumb is something around:

- trainer / slow flyer up to 1.6 meters ws: 50-60 gr/sq dec

- sport same size: 60 - 75 gr/ sq dec

- scale same size: 70 - 80 gr/sq dec

Obviously these thresholds don't apply for bigger models, so when building a big scale, I try to search for advice from the designer, or opinions from people that have built and fly it before.

In any case, I always try to save weight in every step of the process, using PVA or aliphatic as much as possible, cleaning glue on all junctions before it cures, using epoxy only for critical parts, etc etc...

Martyn K04/01/2016 10:06:31
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4295 forum posts
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Thanks for that. yes - that is a very good point indeed.

I have to admit that I can think happily in linear metric measurements and weights and can visualise cubic metric measurements - 1000ml and square mm and cm etc - but I get very confused trying to visualise a square decimeter.

Even though I know that a decimeter is about 4" long. Just a mental block that I have.

M

AVC04/01/2016 10:12:41
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464 forum posts
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Posted by Martyn K on 04/01/2016 10:06:31:

Thanks for that. yes - that is a very good point indeed.

I have to admit that I can think happily in linear metric measurements and weights and can visualise cubic metric measurements - 1000ml and square mm and cm etc - but I get very confused trying to visualise a square decimeter.

Even though I know that a decimeter is about 4" long. Just a mental block that I have.

M

I fully understand Martyn, I can easy move from linear decimal to linear imperial, and cc/ml to cubic inches is easy, but surfaces is a different subject: I can't get my head around so far (although I'm trying my best...smiley)

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