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Martyn's Ballerina @ 115%

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

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AVC04/01/2016 10:15:32
539 forum posts
147 photos


Is it any good??

Martyn K04/01/2016 10:20:14
5087 forum posts
3681 photos


I think a nomogram (remember those) with sq inches and sq dm on one axis and oz/gm on the other axis may be the way forward. Once you have made the visual relationship it should all fall into place.


Levanter04/01/2016 10:23:38
883 forum posts
437 photos

Martyn's builds and blogs are always extremely interesting. A great one to follow.

AVC04/01/2016 10:29:37
539 forum posts
147 photos

Thanks Martyn for the advice on the nomogram, I'll see if I can find something to help me on the conversion.

A very interesting building blog, btw, very detailed and well explained. I'll follow it with interest!

Martyn K04/01/2016 10:36:58
5087 forum posts
3681 photos

Many years ago - probably about 40 - I bought a copy of this:


and inside it has a wing loading nomogram...


I'll print a copy and paste it to my shed roof.


Edited By Martyn K on 04/01/2016 10:50:44

AVC04/01/2016 10:44:05
539 forum posts
147 photos

Great! I'll take a copy if that's ok with you.

Thanks a lot!!yes

Martyn K04/01/2016 10:48:36
5087 forum posts
3681 photos

I don't think either MAP or Ron Warring are still around although I think that MAP is now part of MHS I believe.

The book is long out of print - a great shame because it is perfect for this sort of thing although it was aimed at 1970's aeromodellers and some of the recommendations may not be totally representative in the 21st century.


McG 696904/01/2016 11:10:44
3309 forum posts
1257 photos


Regarding every possible conversion, I'm using this for years now.

It's a stand-alone (no install needed) converter for PC. It features 22 different categories (distance, mass, surface, density, etc.) Just make your choice of unit input (ex. kilowatt) and unit output (ex. pound-feet/minute), type in the digit to be calculated... et voila. You can even ad your own parameters/units if you feel it 'incomplete'.

Aviabox Converter

Anyone interested can PM me his mailaddress & I'll forward it with pleasure.

Happy calculating


Brussels, Belgium

AndyD04/01/2016 22:29:24
773 forum posts
553 photos

thx Martyn 6.4Ibs it is then,fingers crossed and some luck,trouble is im a heavy builder so i better cross my toes as well.

Clive Hall05/01/2016 17:39:04
93 forum posts
44 photos

Andy, I am planning a 62inch span Ballerina and I calculate that the weight should be 6lb 7oz for the same performance as Peter’s original. I based the figures on wing cube loading. This link explains it, it’s worth a look.

Peter Miller05/01/2016 18:10:38
11227 forum posts
1321 photos
10 articles
Posted by Clive Hall on 05/01/2016 17:39:04:

Andy, I am planning a 62inch span Ballerina and I calculate that the weight should be 6lb 7oz for the same performance as Peter’s original. I based the figures on wing cube loading. This link explains it, it’s worth a look.

I remember Dave Platt wrote about volumetric loadinga log time ago. He compared a full size Dakota wing.

AndyD05/01/2016 22:26:07
773 forum posts
553 photos

thx Clive,about the six/half pound seems the way to go give or take,if all fails i reprop it,my setups good for 1800w lol.

Martyn K06/01/2016 09:58:33
5087 forum posts
3681 photos

A bit of progress

The wing ribs have been completed. One thing I forgot to mention is that when I make my master template for the wing ribs, I make the spar slots just a little on the small size.dscn2669.jpg

Add some dummy spars and clamp the pack together and then a fine sanding to even out any variations. There will be some minor - maybe less than 0.5mm - and also sand the LE square.


I use a long permagrit block. If you don't have one I can guarantee that this will probably be your best investment in tools that you can make. Sand lengthways so the end ribs don't get stretched or rounded off.


All done. Those minor variations around the TE will get lost in the build.


I need to cut the holes for the aileron leads. My solution is a simple hole cutter made from a short length of discarded alloy heli boom and a brass tube tommy bar. My cutter was sharpened with a hand held countersink tool. When it gets hard work you will need to remove the cores from the inside of the cutter.


You will also need a slot cutter. Danny Fenton gets full credit for this. A short length of 1/4 spruce or obechi (in this case) with some sand paper glued to it. Align and clamp the ribs up and then use your new tool to open the spar slots and get the correct depth.


I have decided to make up a set of laminated spars - mainly because I cant find any decent hard 1/4" square balsa or spruce. Mine are made from 1/4 x 1/16 spruce caps with a medium soft 1/4 x 1/8 balsa core.

The laminations are clamped together and then clamped flat to the building board so they don't warp or bow. Its a typical last job of the session and can be left while I go back to work and things like that


A close up..

More to come...


Martyn K06/01/2016 09:58:43
5087 forum posts
3681 photos

With those bits out of the way, I can actually start to build. For some reason, I nearly always start with a tailplane and looking at the other Ballerina blogs here it looks like I am not the only one with this strange perversion.

The enlarged tailplane outline (half) just fits on a single sheet of A4 paper so a mini plan was produced and used as the template for pin pricking..

I am using a solid core centre with additional sheet ribs and spars on either side. This method was advocated back in the 1960's and 1970's by the late and great Eric Coates as a way of producing light warp free structures. As BEB has pointed out, we don't need to worry too much about weight, but I do prefer a proper symmetrical streamline surface for my tail components. This structure also fits in nicely with the style of wing construction and hopefully will harmonise the model.

One thing that I need to be careful of is maintaining structural integrity. I have had two tail planes fold in mid air - not a pleasant experience so I will be ensuring that my tailplane is well braced.

The core comprises of 2 laminations of 1/16" sheet balsa - the reason is that the hinge material that I use will be sandwiched between the 2 halves.

4 sheets of 1/16"x 4 balsa edge joined as I showed above.

I don't have big enough carbon paper so I need to pin prick the outline.


Pin pricks are about 3-5mm apart


Note that the centre line and elevator hinge is marked. Joined the dots using a pen for clarity


1/4 x 1/8 balsa to delimit the elevator - one piece each side of the hinge line butted up and a long rule used to ensure that they are straight.

I have also added a spar - cut from 3/16" sheet tapering from 3/8" in the centre to 1/4" wide at the tip. Again using a straight edge to make sure that it is straight and parallel with the elevator


Then weigh it all down while the glue dries. The batteries are invaluable - they came from an old Uninterruptable Power Supply. Not only do they provide weight but also a very good 90 degree reference when assembling fuselage formers.


When dry, we can add the 'ribs'. These have been cut from 1/8" sheet and are 3/16" wide. I use this little Master Airscrew Balsa Stripper - another invaluable tool. It has a vernier adjustment with, IIRC, one turn of the thumb wheel moves the blade 1/64".


The locations of the ribs - 50mm spacing marked out. Note that this is NOT the centre line but the inner edge and will be used to aligned the stick ribs. You cant see the centre line when the stick rib is on top of it!


And finally all the ribs in place. each pinned to hold it in place while the glue dries. I just need to make a matching sandwich half now.

More to come


AVC06/01/2016 10:11:20
539 forum posts
147 photos

Very nice work Martyn, a lot to learn in your blog!

I also have the Master Airscrew stripper, and I agree with your assessment. Before using it, it was impossible to make square stripes...

Masher06/01/2016 10:12:08
1107 forum posts
79 photos

A very informative blog as always Martyn, watching closely for the tips.

Biggles' Elder Brother - Moderator06/01/2016 12:05:01
15748 forum posts
1460 photos

Nice work Martyn - as always!

Another vote for the Master Airscrew balsa stripper - that's the one I use. I am also delighted to learn that I'm not the only one that can never remember the pitch of the thread on it! I just set it with a pair of venier calipers using however many turns are needed!


McG 696906/01/2016 12:52:52
3309 forum posts
1257 photos


Following with interest...


BRU -BE / CTR Martyn Control

john stones 106/01/2016 15:05:48
11604 forum posts
1517 photos

Looking good Martyn, yep have to agree symmetrical tail end adds to the overall look. yes


Ian Jones06/01/2016 19:15:19
3226 forum posts
1401 photos

Still watching how yer goin on with this, especially since I won'y be building one myself and I'm quite jealous. I'm 3 years behind on my mass builds!

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