Jocasta

[Colin Anderson]

Jim, I'm new to R/C some I'm learning to fly. I previously built an IC Piper Cub, but this proved to be a little bit of a handful. I then tried an Wot4, but again it's a little on the fast side for me. I have no trouble flying either of these models, just landing them! Since then I've been leant a foam Wot4, which is a lot easier to fly, although I find it hard in any kind of wind or turbulence. Then I saw you Jocasta and this seems perfect for my needs.

As I plan on building this the old fashioned way, without CNC wood packs, I'd like to ask about wood selection. Could you give me a rough guide on which grades to use? Also, which servos did you use? I have some Futaba 3003s, but these seem much larger than the ones you've used.

Regarding the U/C mounts: the plan says cut four; why? Also, for the ply formers can I use ordinary ply, or is this too heavy?

[Jim Newberry - Nuviation Ltd.]

Hi Folks,

Sorry I've missed a couple of posts again so I'll try to catch up. Colin - You will find Jocasta very easy to fly and, if need be, very easy to repair, so I hope she will fill your requirements nicely. When it comes to wood selection, you are looking for wood that is light but not weak. If you pick a piece out of the model shop selection, give it a gentle squeeze at one end. If it can be easily squashed, it's too soft. If it hurts your fingers before it deforms, it is too hard (and heavy). Model shop owners don't like to see customers doing this so be a bit subtle, but on the other hand everyone does it!

As for servo choice, I used New Power 17g servos from 4-Max. They aren't the raciest servos out there, but they do the job just fine and are reasonably priced. Your Futaba 3003s are bigger and heavier but they will work fine. I googled them and found they are 37g each, so if you use four of them you will add 80 grammes. To be honest, I probably added more than that by painting my model with numerous excessively thick coats of paint, so you should be fine. Likewise, using birch ply rather than lite ply will add only a few grammes. The thing to remember though is that if you use larger servos AND heavier ply AND several thick layers of paint AND cheap heavy wheels AND heavy wood on the tail, requiring more lead in the nose.... Then overall you will have increased the weight of the model significantly. If you choose your covering carefully and take care to save weight wherever you can then you can get away with using your Futaba servos without adding much weight.

Now, why did I specify four undercarriage mount plates (to make two layers each of 3mm ply?) Well, a single layer is not enough thickness in my opinion and screwing the undercarriage into such a plate would be asking for it to rip out after a slightly ropey landing - 6mm is more appropriate. However, the point of the Jocasta design (and in fact all J-Class designs) was that it would not require builders to waste large amounts of wood so, rather than specifying 6mm ply for the undercarriage mounts, and thereby forcing builders to go out and buy a large chunk of 6mm ply just to use a tiny part of it, I recommended using two 3mm laminations that could be cut from offcuts. If you are building the model from scrap bin parts, you have the luxury of making your own choice. You could use a length of birch, thick ply, two laminations of thin ply or even a piece of aluminium - if it looks strong enough, it probably will be but if you're not sure, stick to the material specified and you can't go wrong!

I think I've answered all your questions, but if you have more please do ask, I'm always happy to help!

Michael - don't think that Jocasta is a difficult model - if any parts are unclear then that is my fault for failing to draw the plan properly, but I am always happy to help with clarification so please don't be afraid to ask! I think the picture you are referring to is just the general indication of things at the mid point of the wing. You can see the outline of the aileron servo, the rib is shown along with the solid lines showing the cap strips and leading edge sheeting. Don't get too hung up on the holes - you need a hole to thread the aileron servo lead along the wing to the receiver but the other holes were added originally to reduce weight (which they do but are not essential). If it is still unclear, let me know (by PM if you prefer) and I will be very happy to talk you through whatever you need.

Crunch1 - exactly!

Well I think I have caught up with all the questions asked but, as ever, I am here to answer any queries about the plan so please don't hesitate to ask!

Jim.

[Colin Anderson]

Thanks Jim. I believe you have pretty much answered all my questions. I plan on sourcing all my wood from the Balsa Cabin (their prices seem exceptionly good), hence my question on grades. From your answer it sounds like medium would be about right for most parts, with perhaps hard for the highly stressed parts.

Thanks for explaining the U/C mounts, it makes perfect sense now. No doubt it's on the plan and I probably hadn't read it properly. Regarding the servos: I'll probably go with the ones you used or similar. Being new to R/C and even newer to electric I'm not really clear on which servos are safe to use for which size or type of model. One thing that would help me is if you have any images/diagrams of how the wing servos are mounted. I'm sure I'll figure it out, but it's so much easier if someone shows you how; and you also have some reassurance that the servos will be secure. Anyway, thanks for designing an electric trainer at exactly the right time! There doesn't seem to be many trainer plans/kits about and, although I can see the benefits of a foam plane, I find them hard to get excited about. 😊

[Jim Newberry - Nuviation Ltd.]

Colin no problem at all, I'll get a detailed sketch up shortly. Might take a day or two as I'm working all weekend but sit tight and I'll get on it! Jim.

[Colin Anderson]

Thank you Jim. That is very much appreciated. Have a great weekend. 😊😊😊

[monty2]

To Michael, I to am 74 coming up 75 and have already built Jims Jemima, it flew well until my tranny developed a fault then it came home in bits, too many to repair except the wing which is in one piece and OK.

Like you I am new to modelling, well 2nd hand having done some in my youth. I found it easy to follow Jims design before and this one looks as easy. To me with an engineering background at least.

I intend flying the Jocasta fully assembled first and then trying it with the Jemima wing, should be fun

Enjoy yourself, we old timers are as able as them youngsters.

[Jim Newberry - Nuviation Ltd.]

So - wing servo installation. There are dozens of different ways of doing this and the method shown on the plan is certainly not the only way, but it's a method that works for me and results in a relatively neat installation and a slop free linkage. To expand on what is shown on the plan, here is a quick sketch I have knocked up in TurboCAD.

As you can see, there are three plates made up from 1.6mm - 1/16" ply. Parts A and B are glued together to form a shallow tray with a square recess in the middle. The servo is fitted on its side on part C with the arm poking through the slot. Fix the servo in place using servo tape - better yet, I have found black double sided tape at Halfords that is used for attaching number plates to cars - it is very strong and thinner than servo tape. Coat the inside face of part C with a layer of varnish, sanding sealer or epoxy to make it non-porous and therefore better able to adhere to the tape. Once you tape your servo in place you will not be able to remove or reposition it and you will not be able to fit or remove the arm, so carry out as many dry runs as you need to be 100% certain that you are ready to fix it in place! Make sure in particular, that the arm is free to travel its full distance without fouling the sides of the slot and also make sure that the arm is mounted such that it is slightly forward of 90 degrees to the axis of the servo. With the servo at its neutral position, fit the arm one spline forward on the servo output shaft. Doing this will pretty much take care of the aileron differential required. Part C, with servo in place, should now fit into the hole in the tray formed by parts A and B. The ribs shown on the plan on either side of the servo have rebates cut into their lower edges to accept this assembly, the edges of which can be reinforced with short strips of 6mm - 1/4" balsa left over from the fuselage longerons. A short pushrod from the servo arm to the aileron horn completes the process and a photograph of the finished article can be seen on page 69 of the magazine.

Now, this method brings certain disadvantages - it is almost impossible to adjust the position of the arm once the servo is stuck to part C, and overall it might be said to be unnecessarily complex and fiddly for a beginner's model. Also, the servo cannot be replaced without some hassle and so here is another sketch showing a simpler method...

Here, a simple plate is fixed between the ribs in the same position as before but with a rectangular cut out to accept the servo which now simply slides into place and is held by screws through the lugs. Again, the arm must be positioned slightly ahead of 90 degrees when the servo is at neutral but now the servo can be removed and replaced as often as desired once fitted. There are only two drawbacks to this method - the plane of rotation of the servo arm and control surface differ by 90 degrees and so a ball joint at one end of the pushrod would be desirable (though not essential) and of course the appearance is somewhat less tidy, however it is a method that has been successfully employed on Wot 4s (and many other models) for many years and works very well.

I hope all this helps, I must apologise for the rough and ready drawings, I'm a bit short of time at the moment but wanted to get back to you as soon as I could. Any more queries, please fire away.

Jim.

Edited By Jim Newberry on 09/11/2014 14:15:51

Edited By Jim Newberry on 09/11/2014 14:17:14

Edited By Jim Newberry on 09/11/2014 14:18:34

[Colin Anderson]

Thanks Jim. Exellent explanation and diagrams. I've now got an excellent idea on how to go about the installation. Your second method is the method I used to mount the servos in my Cub. I like the first method better, as its neater and appears to be mechanically better.

[Kevin Fairgrieve]

As the Jocasta seems to have been included in the mass build for next year, has any one done an I.C. conversion?

Kev

[monty2]

Hit a minor snag yesterday, all sorted with my trusty scalpel..

It was time to put fuselage halves together but the wood pack formers don't go in the slots. Why you may ask? A simple dimensional issue. The Formers are a cut from nominal 6mm thick ply but the slots are a nominal 5mm wide, actually 4.81mm.

Easy enough to overcome by increasing the slot width but important to check which side to ensure proper location of each former.

Just thought I would comment in case anyone else has found this snag.

[Martyn K]

Posted by Kevin Fairgrieve on 21/11/2014 20:10:48:

As the Jocasta seems to have been included in the mass build for next year, has any one done an I.C. conversion?

Kev

Hi Kev

You can be the first - I reckon its lightly loaded enough to be comfortable with a OS40LA or similar..

How does that sound?

M

[Colin Anderson]

Not as big a snag as I've hit Monty! I'm trying to figure out how I'm going to afford to even get started! I'm new to R/C and even newer to electric. I don't have any electric stuff, so I've got to start from scratch. Either using the wood packs or buying the balsa etc., I don't see me getting much change out of £100; all the electric stuff recommended from Power Max is around another £150! My only choice will be to tackle it in stages.

[Dave Hopkin]

Posted by Jim Newberry on 09/11/2014 14:15:16:

So - wing servo installation. There are dozens of different ways of doing this and the method shown on the plan is certainly not the only way, but it's a method that works for me and results in a relatively neat installation and a slop free linkage. To expand on what is shown on the plan, here is a quick sketch I have knocked up in TurboCAD.

'.......... Any more queries, please fire away.

Jim.

Edited By Jim Newberry on 09/11/2014 14:15:51

(Diagrams deleted for brevity....)

Jim a question; why not glue two small hardwood bearers across plate C (first method) to screw fix the servos rather than double sided tape? Any particular reason?

[Jim Newberry - Nuviation Ltd.]

That would work just as well Dave, the double sided tape method is just what I have used and found quick and simple to set up, provided the comments about the need for accurate alignment are noted.

Jim.

[Dave Hopkin]

Ok ta, I just wondered if there was a specific advantage to your method

[monty2]

To Colin, when I came back to flying after???????? years, I faced the same issue and after much thought and discussion with 'er indoors decided to maintain harmony by going electric. No mess or puddles of fuel..

But I get the impression, on this forum, others are asking about using I. C. engines. so perhaps Jim Newberry may come up with a mod to suit.

Or, with a bit of ingenuity. you may be able to work out a solution. It can't be difficult??? or can it.

Perhaps the answer, as increasingly, many sites are having noise issues with neighbours, is to bite the bullet and go electric?

[Jim Newberry - Nuviation Ltd.]

I really hope someone does put an ic engine in Jocasta - I had been planning on building an ic Jocasta for the mass build but it looks unlikely to happen now as I've sold my house (unexpectedly) and will be shed less for the first couple of months of 2015, thus severely curtailing my building opportunities! If I went ahead with the ic version I would probably use something like a .40 two stroke and move Jocasta's firewall to suit a nylon engine mount or fit a suitably shaped aluminium plate. Having said that, I am most definitely not the best person to ask - I haven't owned an ic engine for over twenty years so I can't really claim to know what I'm talking about where oily motors are concerned!

Jim.

[Colin Anderson]

Hi Monty,

There's no restriction on noise, within reason at our site, as its on private land. However, there is a preference at the site for electric. Fitting IC would be no real problem. I could pinch one out of my Cub (Irvine 40) or out of an IC Wot4 I was given (OS 55). I'd imagine it would fly with either of these engines (my Cub is 73" and uses the Irvine 40 on only half throttle). However, I've learnt to fly with a borrowed foam Wot4 and am now allowed to fly solo, but only with electric. Now I've graduated to solo I need my own electric plane. I could buy the Wot4 pretty cheap, but don't really wish to pursue this route; although it would mean I could fly while I build the Jocasta.

In essence the solution is simple. I need more money!

[Colin Anderson]

Jim,

Could you perhaps advise this newbie on possible alternative (cheaper) electric power trains for this model? IC engines are easy to understand, electric less so.

[Den Moran]

Hi everybody, and festive (nearly,anyway!) greetings!

Jim, I've fitted the motor on, and the 'down' angle as per plan looks very steep. Can you confirm that the plan angle is the correct one, or did you need local adjustment when you set it up initially?

Have got the fuselage to the ready-to-cover stage, and hope to complete the wings and all before the festnogs hit! Also found a great place to fly off water - but still looking for suitable float plans. Cheers,

Den

[Jim Newberry - Nuviation Ltd.]

Hi Den,
Glad to hear it's coming together! I found the downthrust shown on the plan worked well for me so I'd suggest using it as a starting point and adjusting if you need to after the first flights. That thick high wing needs a fair amount of down thrust to prevent a large pitch power couple. I arrived at the angle after a lot of flights with my Jemima model which needed a similar amount. If you modify the downthrust will you let me know how you get on please?

[kc]

Colin, nobody else has answered your motor query yet so i am going to suggest a Turnigy motor. Maybe the 3536/9 910 kv motor with a 4S Lipo. or the 3536/6 1200kv for a 3S Lipo. I have used the Turnigy 3536/9 with a Zippy 4S 3000 in a completely different model ( actually an Avicraft Moronic which is very aerobatic at 4lbs with this motor) and it has been fine for 180 flights so far.

My view is to build any model with enough room to take the largest Lipo you might need and when its built & covered see what Lipo would balance nicely and still be accessible. Then decide & buy the Lipo based on the stated weight . Turnigy or Zippy Lipos have proved OK so far for me and others, they are much cheaper than other brands. Lipos dont last forever so maybe they wont last as long as expensive brands but then again maybe they will.

[Colin Anderson]

Thanks KC I appreciate that. It'll help a lot. 😊

[Mowerman]

Just reading through this thread as SWMBO bought the Laser cut pack and extra wood pack for my birthday (75) and it arrived on the date last Wednesday Haven't started yet as I am in the middle of a couple of repair jobs but looking round to source various bits of hardware and making notes from this thread.

A thought from reading this thread -Is the model designed specially for OAPs?

[Sean Zerafa]

Hi guys. This will be my first ever build and looking very forward into starting it. I have been looking at the plans and I understood most of the things, however the one thing that I'm really confused about is the wing. Are the left, right and centre wing section build separately and then joined together or do they have to be built as one thing from the start?

Please provide me with all the info you can give as it is a bit confusing for me. If possible I would also like some photos of the process of building it.

Thanks in advance guys.

Sean.