Jocasta

[Jim Newberry - Nuviation Ltd.]

Hi Sean, glad to hear you are having a go at Jocasta, hopefully she will make a good first build project, feel free to ask any time you get stuck. When it comes to the wing, build the three sections separately, being sure to set the inner ribs of the two outer sections at the correct angle to accept the dihedral. Next, use a razor saw to cut through the upper and lower sheeting as well as the ribs to make room for the dihedral braces. Make several dry fits, without glue, propping up the outer panels to check that all fits and is square. When you feel ready, use slow setting aliphatic glue to join the wing panels with the dihedral braces and prop everything up to set overnight. While the glue is still wet, check, recheck and check again that the centre section is flat on the board with the two outer panels at the correct angle. Once everything is set solid, you will find you have gaps in the sheeting where you previously removed it to fit in the dihedral brace. Cut a sliver of sheet to fit this gap. Don't worry too much if you can't make a piece to fit exactly, you can always add a little filler later to close any gaps. Sand away any imperfections and add strips of glass fibre to the joint for strength. Let everything set solid, sand smooth and voila! Nothing difficult and you should have a straight, strong and smooth wing joint! Hope that helps.

Jim.

[Martyn K]

Hi all

Remember that this model has been selected as a 2015 Mass Build option so if you are planning on building one, why not start a build blog in the 2015 Mass Build Forum.

I am sure Jim and others will be more than happy to help with any queries you may have or advice that you may need.

Martyn

[Sean Zerafa]

I will keep this in mind when I start building it. Hopefully I'll start in 2 weeks as I'm very busy at the moment. Thanks for the help guys very much appreciated.

[Sean Zerafa]

I will keep this in mind when I start building it. Hopefully I'll start in 2 weeks as I'm very busy at the moment. Thanks for the help guys very much appreciated.

[WolstonFlyer]

I am just waiting for my Jocasta wood packs to arrive from MHS then I can get building. My back issue of the Oct magazine arrived in the post so now I have 2 copies of the plan just in case I spoil one. It is funny how the back copy of the magazine including the copy of the plan costs less than just buying the plan!

Edited By WolstonFlyer on 29/11/2014 17:02:37

[monty2]

To Jim Newberry, I have grown old and forgetful and need help copy of the Mag which gave the info I want.

? what size lee y motor and ESC do I need and also what size servos. If you can help by tomorrow cos I can get to my supplier on Monday. I haver a round trip of 80 miles to do and I need your help.

[Jim Newberry - Nuviation Ltd.]

Hi Monty, it's a 38mm outrunner, 900 kv and a 60 amp esc. If you look on the 4-Max home page and scroll down a bit you'll be able to see a picture of Jocasta which will take you to the exact spec. Sorry for the brief reply but I am literally about to walk out of the door to start a long night shift. Jim.

[WolstonFlyer]

The magazine also says:

PPO 3548-110 motor with 60A ESC and 3300mAh Li-Po

4 X 17g New Power servos and a 12x6 wooden prop.

Edited By WolstonFlyer on 29/11/2014 18:22:03

[Jim Newberry - Nuviation Ltd.]

Thanks WF, that's the one, not 38mm as I put - trying to type in a hurry on my phone!

[Colin Anderson]

Yesterday I started cutting out parts for Jocasta with the wood I had to hand; starting this way, I figure, will give me a better idea of how much additional wood I need to order.

I recently learnt to fly on a borrowed Wot4 and this got me thinking. The Wot4 doesn't have any dihedral. I'm guessing that this is because it's more of a sports trainer, rather than simply a trainer. I understand that dihedral is an aid to stability, which is desirable in a trainer. I'd like to ask, therefore, what might be a daft question. Given that I've got past the initial stages of a complete beginner, in so far that I can take off, fly basic circuits and actually land reasonably consistently, no longer needing the buddy lead; is dihedral vital for the Jocasta?

This is where I show my ignorance. Apart from stability, in what way does having dihedral effect manoeuvrability and performance? I'm not talking about knife edge or 3D here, just basic manoeuvres, such as loops and rolls.

[Jim Newberry - Nuviation Ltd.]

Hi Colin,

You certainly could reduce the dihedral if you felt like it without suffering any drastic effects. The natural tendency of the model to self recover from an unintentional attitude upset would be slightly reduced but if you are confident in your flying skills then this might not be something you are concerned about. You will probably find that the recommended throws for aileron and rudder are a bit off - the ailerons in particular may become slightly over sensitive with reduced dihedral as the throws suggested on the plan need to ensure that the ailerons have enough authority to overcome the lateral stability of the dihedral. However, I would not recommend getting rid of the dihedral entirely. Not for reasons of advanced aerodynamics but for the sake of appearance - I think this model will look very odd indeed with a flat wing. Of course, beauty is in the eye of the beholder but I designed Jocasta to look like a vintage free flight model, and as such she should have plenty of dihedral. In the end though, it's your model so feel free to tinker as much as you like.

Jim.

[Colin Anderson]

Hi Jim,

Thanks for such a quick answer; I wasn't expecting such a quick answer! 😊

I'm quite happy with the dihedral as it is. As you say, it's a matter of ascetics. I've only just got to solo stage so I'd really only consider myself as a raw beginner. My take offs are fine and I'm pretty confident of my flying abilities (for the stage I'm at); however, it did take me considerable time to learn to land with reasonable consistently! The extra stability for landings will be of immense benifit! I was simply curious as to what way dihedral effects manoeuvrability and by how much. I guess what I'm asking is: will it make loops and rolls harder or is it just a question that the plane will be more recoverable from such manoeuvres? 😊

[Jim Newberry - Nuviation Ltd.]

Oh I'm stuck in a hotel room today with the iPad next to me listening to Radio 4 while building a park flyer type thingy on my portable building board, hence the quick reply! Funnily enough, I'm in Argentina and it has occurred to me that there is some irony in the fact that I have carted a stack of balsa halfway across the world to South America, not far from where it grows!

Back to the issue of Jocasta and her dihedral, she will loop and roll, although not as well as your Wot 4, but then this is a very different animal altogether. Whereas the Wot 4 can, in the right hands, do an impressive aerobatic display with axial rolls, knife edge flight and harriers, Jocasta was never designed to do anything of the sort and her rolls tend to be a bit more barrelly. Loops are easy enough but prolonged inverted flight is a no no. To be fair to the model, expecting her to do more than a few gentle and fairly basic aerobatics would be like trying to thrash the family hatchback around Silverstone and wondering why it won't keep up with everyone else.

[Colin Anderson]

Hmmm, stuck in Argentina! Lucky you! The wife an I were in South America (Ecuador, Peru and Bolivia) last year. I asked various guides if they could show me a balsa tree, but sadly I never got to see one. It would have been nice to have actually seen the tree that supplies our hobby.

On balance I think I'll stick with the dihedral as designed. Inverted and knife edge is a long way off for me at present; I've only got as far as loops and rolling off the top! I'm quite happy with that.

Enjoy yourself in Argentina 😊

[Robert Berger]

Hi Jim.

I am busily cutting all the parts out by scroll saw and I have finished all the formers F1 - F6 from 1/4 ply and have the fuselage sides cut out. I suddenly noticed that the dotted lines showing where the formers sit in the fuselage are only 3/16 apart. I don't see anywhere on the plans a mention of the former thickness but in the cutaway picture in the magazine it shows the formers as 1/4. I have this horrible feeling that I should be using 3/16 for the formers. Tell me I am wrong and 1/4 is fine.

[Jim Newberry - Nuviation Ltd.]

Hi Robert,

The thickness you use for the formers won't make a massive difference overall, but I'm surprised that you are making all the formers from ply. Only F1 needs to be ply to provide strength for the motor to bolt to it, the others can all be made from balsa to save weight.

If you have already made all the formers and don't want the hassle of remaking them from balsa, you should be able to get away with your ply ones but I would remove as much internal material as possible to reduce weight.

Jim.

[Colin Anderson]

I'm glad I read this post Jim. I too might very well have done the same as Robert. It does say on the cutaway drawing in the magazine that all forward formers are 1/4" ply. I did wonder about this, having built a 73" Cub that uses only 3 mm lite ply for its formers. The magazine cutaway drawing is obviously confusing several of us. 😊

[Jim Newberry - Nuviation Ltd.]

Well this is interesting! Only F1 needs to be made from ply to take the loads imposed by the motor. Even then, 1/8" ply is quite adequate for an electric set up. The other formers would be quite strong enough if they were made from 3/16" medium balsa as these formers do not carry much load. Does anyone know if the cnc packs are being supplied with formers cut from 1/4" ply, and if so, are they using birch ply or light ply? The model has plenty of wing area to spare and so a little extra weight in the form of thick ply formers is not going to have an adverse effect on the flying performance but 1/4" birch ply is way over the top!! If someone can let me know about the cnc packs I can see about getting future batches changed. In the meantime, if you have already cut and fitted 1/4" ply formers, don't go to the trouble of trying to remove them or rebuilding your fuselage, your model will still fly well but with a phenomenal amount of strength where it is not needed!

Jim.

[Andjo]

My Jocasta is coming along slowly but surely, it's a bit cold in the garage over here now for working outside.

I also had some problems with the CNC parts not all fitting properly but I still found this the best way to go for me. This is my first flat pack build and following the threads here has helped me quite a bit as well as being very interesting.

Jim, if you see this I would like some advice on the best E Flite motor for this please.

I know George @ 4 Max has everything and will happily post it all but the exchange rate is rather high at the moment and purchases from the UK cost a bomb+

Many thanks André

[Jim Newberry - Nuviation Ltd.]

Hi Andre,

I believe the Eflite Power 15 (900 kv) or the Power 25 (870 kv) would both be broadly similar to the motor suggested.

Hope that helps. Would you mind lettings know where you are from - I'm just interested to know how far afield Jocasta is being built!

Jim.

[Colin Anderson]

Hi Jim,

I've been cutting out the ribs today and I have another quick question: the plan shows the outer end rib marked as R4; yet it clearly spans the full cord. I'm assuming this should be a full R2 rib; is this correct? I had a look at the images that you posted, but the one where I could look at the wing tip didn't show ailerons! Also the plan does not show cut outs in the ribs (other than for servo leads); I'm guessing that whether or not to add them is a matter of strength or weight saving?

Also, you mentioned in the artical that you were going to modify the tailwheel. Did you do this eventually and, if so, how?

[Jim Newberry - Nuviation Ltd.]

Hi Colin,

Yep, you're right - yet another printing error that no-one had noticed until now! The end rib is indeed a full length R2 and not R4. Thanks for spotting the error.

On the subject of lightening holes in the ribs, I used to have holes cut in all my ribs at the laser cutting stage but a few months ago I did an experiment whereby I measured the area of all the lightening holes I had had cut, then cut a piece of balsa that had the same area as the total area of all the holes. The result was massively disappointing! I had only saved a few grammes, less than 0.5% of the total weight of the model! I am unable to find out exactly how much all those little circles add to the overall laser cutting cost but suffice to say I no longer bother with lightening holes in ribs!

As for the tailwheel, no I haven't yet changed mine, but I have used the spring loaded variety on other models - if you need a link to help you find one, let me know and I'll be happy to help. Of course, for true vintage style, it should have a skid rather than a steerable tailwheel - and this, being lighter than a steerable wheel, would reduce the weight at the tail end which will in turn reduce the amount of nose weight required, but then you wouldn't be able to steer the model on the ground!

Feel free to come back with any more questions and I'll be happy to help out.

Jim.

[Andjo]

Hi Jim,

I live in Ieper in Belgium, home of the Menin Gate! I regularly read RCME and yours was the first free plan that said to me YES, I want to build this.

Thanks for the motor info, maybe George will do black motor & esc day for me.

Happy building to all Jocastenaars.

Andre

[Colin Anderson]

Thanks Jim,

Like you I'm amazed at how small the percentage of weight saving was. I guess that it depends on the material that the ribs were made of and their thickness. Given such a small saving the strength of the structure is of more benifit. 😊

[monty2]

Jim, I sent a post a few days ago, I picked up on a sizing discrepancy on the formers, Firstly they are ply but I cant say what type, secondly they are appx 6mm thick and the slots in the sides are only 5mm appx.

I have got round that with my trusty scalpel, altered the slots to suit. I am now looking at adding some additional lightening holes but after reading the comments re. ribs may not bother.