Jocasta

[Jim Newberry - Nuviation Ltd.]

Hi Colin,

Thanks for bringing this to my attention - I must admit, I had thought that we had trapped all the gremlins by now. The good news is that you are not losing the plot - I have just compared my original CAD drawings with the published plan and there is a discrepancy - F3, F4, F5 and F6 are all 87mm across (excluding the tabs) on my CAD drawings but 95mm on the published plan. As you say, this prevents them being cut from 100mm wide balsa with full depth tabs. Your solution of cutting the tabs slightly shorter and filling the resulting hole will work fine - as a matter of fact I have started deliberately making tabs slightly less than full depth as it avoids end grain showing through on the other side which can sometimes cause minor surface irregularities after sanding. However, it does mean that the windscreen support will be a tiny bit undersize.The actual size difference will be lessened by the time the fuselage has been sanded smooth all over but there will most likely still be a small step. This can be sanded away but you're right - it is a nuisance that the niggle has crept in. As for F6A, its sole job is to give a bit of support to the rear of the wing and it would do this just as well if it were made from a single strip of 6mm balsa - it appears on the plan as a fat T shape but the vertical element of it is not essential. Nevertheless, the printing error is annoying so I'm sorry for the inconvenience you're suffering along the build! One thing I would suggest (which I am sure you have already worked out) is that if there are a couple of discrepancies between sizes on the plan, make sure that you cut parts like the undercarriage mounts, servo tray etc. to fit the parts that you have already built.

I would also be interested to know how people are getting on with the CNC packs in this regard - now that the formers are being cut from balsa, SLEC must also have discovered that they won't fit on a single sheet - I wonder if that could be part of the reason they were being produced from ply? I'll make enquiries of my own but in the meantime if anyone has a set of parts they could run a ruler over I'd be grateful.

Jim.

[John Taylor 14]

Hello Jim..my jocaster is coming along ok.it takes some time to cut all the parts by hand and make them fit !!. also THE SHED TEMPERATURE WAS DOWN TO 40 DEG TODAY WHEN I OPENED THE DOOR...just a quick question.i built the flat middle section on the wing and now they are all joined together please advise how to strengthen the two joints..on the out side with fiberglass do they need this???? or could i put two strips of thin ply over each joint..your advise would be most welcome..keep up the good work..will post some pictures if i get chance Regards John T

[Colin Anderson]

Hi Jim,

It's certainly good to know that I hadn't lost the plot or had a senior moment! I'm assuming that when you did the original drawings they weren't done as per the free plan? If this is so then I can only assume that the files for the formers somehow got resized slightly at the other end. It hasn't caused me any serious problems, just a bit of head scratching! It is kind of weird though that ,whatever the cause, it made the formers wider, but not deeper! Perhaps they were copied and pasted onto the plan and inadvertently transpormed. It's a mystery! If I find anything else as I progress, I'll post it here! 😊

[Michael Adams 3]

Hi All, it seems to me that you all have bought the kit for Jacasta, I tried the free plan, what a mess that was the supposed free plan in the magazine was the kit plan and not the build plan, I did report this to the editors but no sensible answer, so suggested that they sort out the plans properly and put the correct build plans into the magazines and leave the kit plans in the boxes.

Yours Mike.

[Michael Adams 3]

Hi Jim, just had a look at your build of the Jacasta, very nice, but the free plan in the magazine was not a build plan, it was a kit plan, I did manage to build from it but it was quite a problem at times, I have not had the chance to fly it yet but when I do I will try to get a photo for you, I did have a word with the editors about this but did not get a really satisfactory answer, I did tell them that they should check which plans to choose for the magazines, build ones in kit plans should stay in the boxes.

best regards Mike, Happy Xmas, A good flying new year.

[Robert Berger]

Yes, there are a lot of mistakes between the free plan and the build article. Another is the spars. The exploded picture in the magazine shows 3/8 x 1/4 hard balsa but the text is 1/4 x 1/4 cyparis. I got the balsa but found it to be too flexible. Because I had already cut out all of my ribs to 3/8 X 1/4 I then purchased 3/8 x 1/4 hardwood. The picture here shows my method for R1B angle. I glued the dihedral brace to the spar and then clamped "L" alloy to R1B and that gave me the correct angle of R1B to the wing. The next picture shows The use of my angle alloy to make sure that the ribs are at 90deg to the wing surface.

I have access to an air rifle range so I collected used led pellets and pp them into ziplock bags of various sizes. As you can see they sit over the ribs as they are flexible.

Here I have supported the lower skin with 1/16 strip and 1/4 x 3/8 balsa strip (found a use for the balsa spars) to lift the wing skin before trickling thin CA on the rib/skin joints.

masking tape over the ribs so that I know how close I can plane and sand too. When I scuff the tape we are there. Note that I have Permagrit sanding block. These are a must have. Also a balsa stripper a razor saw and Permagrit files and hole saws are really important tools. I forgot to put seervo lead holes in R3's so with the small Permagrit holesaw in my battery drill I could cut the hole on an angle between the ribs while in situe. The hole saws dont have teeth to rip your skin of the balsa.

[Robert Berger]

Opps forgot to add the masking tape picture. Here it is.

[Andjo]

Thank you all for the very usefull pictures.

Jim, what would you think about sheeting the fuselage instead of covering it?

André

[monty2]

Jim, as I was working diligently on my wing, I decided to have another quick look on the blog and saw your pictures of the wing and took [particular note of the shear web as I was about to start cutting some for my wing so I can dry fit everything, that way the memory box is overridden.

Then I spotted an issue, hope I'm wrong and you did something different. Your shear web is on the rear of the spars and outside the D box. So presumably the dihedral brace is on the front edge.

This implies that the spar cut outs are located further forward on ribs R1, and R1b. According to the published plan, the front of the spar hole is in the same location on all ribs, the shear web on the front of the spar and the brace on the rear.

Thought I would mention for those like me whose brain has addled a bit with age. Shows how things can change between original design and published material. Saw some of that in my original career in the motor industry. some of those needed national recall programmes on our cars. EXPENSIVE cos someone new better.

[Robert Berger]

I put my braces on the aft side of the spars (by mistake) but I can still shear web on them. They just stick out a bit off the spar line but wont be seen when the wing is covered,

[Jim Newberry - Nuviation Ltd.]

Well this is getting embarrassing - it seems there are quite a few mistakes and inaccuracies in the plan. Then, while trying to post a helpful picture in a bit of a hurry, I went and posted a picture of the Mk.1 wing (which had the shear webs aft of the spar - thanks Monty).

In view of the length of this thread now, and the number of corrections that people have spotted, I am thinking of starting an "Amendments" thread which will just list all the areas that need clarification or correction so that future builders will have all the information to hand rather than trying to wade through all the above posts here.

Apologies, again, for those of you who have been inconvenienced by the plan's shortcomings - I can at least assure you that it flies a treat once it's finished!

Jim.

[Colin Anderson]

Today, while adding the upper spine I found that F6 was either too short or I'd positioned it incorrectly! I'd fitted former F6 to fit between the fusalarge sides so that it was flush top and bottom; when in fact the top edge should have been 1/4" proud at the top to take the spine end. This would make the bottom end of F6 1/4" short; and, on looking this appears to be as it should be on the plan. It's not a big issue; I've simply added pieces along the top, with a gap in between for the spine.

I don't think you have anything to be embarrassed about Jim. I, for one, am grateful for people who design and share that expertise with the rest of us. It's a good plan and I'm sure it's going to be a great flier.

[monty2]

Seriously Jim I wasn't criticising, from your various comments, someone has done some changes either to fit the plan into a print box to fold for the Mag., or to fit bits onto wood for cutting. As I said in my former career we always had someone who new better (usually on the shop floor) than the designer. Sometimes they were right but more often they weren't

The important thing is if you make a change to the original, "check and check again" then make it yourself to prove what happens with your check incorporated.

Often its not the designers fault, he got it right. Cos he made it an it worked.

[Jim Newberry - Nuviation Ltd.]

Thanks for the last couple of posts chaps, I appreciate them a lot. Monty, I didn't take your comment as a criticism - I am genuinely grateful for people pointing out errors as it helps things get sorted. It's distinctly annoying that a basically good design (if I say so myself) has been marred by a number of inaccuracies either in my drawings, or in my written explanation of those drawings, or in the processes involved in getting those drawings into print and parts cut.

Something I am considering for the next model - which is on the workbench at the moment - is having a complete second set of plans and parts produced and getting another builder to produce the model. Sometimes I think designers are the worst people to check over a plan as we know what we intended by a particular sketch or comment and so don't come to it with the mindset of someone seeing it for the first time.

[kc]

I am amazed that the plans that are actually printed have not been checked BEFORE printing. I find it takes me about 10 minutes with a pair of calipers to find the main errors in the 'free' plans - it's very often former widths or spar slots too wide or small or in the wrong place. Almost always out by a round figure such as quarter inch , half inch or 1 centimetre, very rarely out by just a tiny amount.

[Levanter]

Jim

I'll volunteer to proof build for you. I like your designs very much.

[Jim Newberry - Nuviation Ltd.]

Here I must hold my hand up kc - RCM&E did send me a copy of the plan in PDF format and asked me to check it before sending it out. I viewed it on a computer screen and it all looked in order to me. What I now realise I should have done, but didn't, is print it off and check all the dimensions. The reason I didn't is that I had sent them the PDF of the plan from which I built the model and I assumed that the parts had simply been lifted directly from that file and moved around the paper to fit the format required for publication. That being so, I believed that the parts must be the correct size, as they had been when I printed my own plan. Of course, that doesn't explain the confusion over R4 and R2 - that was a case of me seeing what I expected to see, rather than what was written.

[Jim Newberry - Nuviation Ltd.]

Thanks Levanter, I'll bear you in mind.

[WolstonFlyer]

Hi Jim, does this mean that my as yet unopened CNC and extra wood pack is wrong? It arrived 2 or 3 weeks ago and I have been 'saving' it for when I start my Christmas holidays at the end of the week.

Thanks, James

[Jim Newberry - Nuviation Ltd.]

Hi WF,

As I understand it, you may find that your formers are made from 6mm ply rather than the 4.5mm balsa I had intended. This will make your model very slightly heavier than it might be with formers made from balsa, but the difference will be only a few grammes at most. You will also find that the slots in the fuselage sides are too narrow to accept the tabs in the formers - if so, you can either open up the slots slightly with a file or simply remove the tabs from the formers - they add some strength to the glue joint but their main function is to aid accurate assembly (there's an irony). As we now know that the formers shown on the plan are very slightly wider than the formers used in my model, you will also find that your model is imperceptibly wider than mine but unless we put the two finished models next to each other and check them with callipers, the difference will not be noticeable.

As for the wing ribs, you will probably find that you have R4 ribs supplied for the outboard ribs when they should be R2 - you could either use an existing R2 rib to produce the correct shape from scrap or you could use the R4 ribs but add a small triangular piece to the rear edge, gluing it to the inside of the wing tip and shaping it in situ. Its sole purpose is to support the covering material around the wing tip.

You will probably find that you have 6mm spars while the ribs have 9mm slots. You can either replace your spars with 9mm x 6mm balsa (or cyparis) or attach a strip of 3mm x 6mm balsa (or cyparis) to the rear of your supplied spars so that they fit the cut outs.

I'm sorry about the hassle but they are at least all minor irritations rather than show stoppers and all easily overcome!

Edited By Jim Newberry on 15/12/2014 18:54:19

Edited By Jim Newberry on 15/12/2014 18:55:30

[WolstonFlyer]

Thanks Jim. I have printed that out to keep with my copy of the magazine and plan

[monty2]

Its me again with a query, the dihedral guide, looks to be very shallow and visually doesn't seem to match the brace.

I don't have a protractor at present, so before gluing g bits together could you let me know what the angle should be rather than a tip height, I think I can take the bits to an engineering company I know to check it out.

My maths are very rusty and I left my maths tables behind years ago so I can't calculate it, is it sine, cosine or what too far back in the memory.

[Jim Newberry - Nuviation Ltd.]

Hi Monty,

I have just checked my copy of the plan against my original CAD drawings and the shapes shown for both the dihedral brace and the jig for R1b are correct so you can trust them (phew!). If you want to know the angles, the measurements I have derived from the CAD drawings are 4.3 degrees from the horizontal for each wing panel and to achieve this, R1b must be set at an angle of 2.6 degrees from the vertical. I am sure that a few minutes' work with a calculator could define the angles with greater precision but I don't see the point of doing so when no-one could reasonably be expected to hand build a component to that degree of accuracy.

For the record, I don't design dihedral based on an overly complicated formula because I don't think it is either necessary or helpful to do so. Rather it is a case of setting the angle based on similar successful designs - in other words, what looks about right and has been known to work in the past.

Hope that helps,

Jim.

[monty2]

Ta

[Colin Anderson]

Felt a bit daft today and not a little frustrated. My Jocasta fusalarge is nearing completion and today I was fitting the tailwheel mounting plate, as well as the two rear side pieces with slots ( I assumed these glued directly to the sides, rather than inset?). I'd previously checked that both wing platform and tailplane platform were square and that the rear of the fusalarge was not banana shaped. All was well. However, what I hadn't checked (and should have, before I got so far) was check the angle of incidence of the flying surfaces (well, their platforms - I haven't built the wing yet) in relation to one another. I've no idea what the overall incidence is, but from the plan they are parallel to one another; only, to my frustration, mine weren't! My tailplane platform (and hence the tailplane, when fitted) would have a positive angle of incidence! Damn!

How had this happened? I think it was a combination of two things. Usually I'd build directly over the plan. However, in this case the entire lentgh of the fusalarge doesn't fit, so I copied it onto my computer, printed it out onto several A4 sheets and stuck them together. Clearly, when I copied them I'd made errors ('cause I had to fold the plan to go on the scanner) and then sticking the A4 sheets together I'd obviously not got things lined up as well as I thought. Error number two was not getting sufficient bend in the longerons where they meet the leading edge of the tailplane. I've remedied the error by adding tapered pieces (to bring the tailplane platform back to zero). Of course this now meant that the bottom edge of the fin no longer reached the bottom edge of the fusalarge so I've had to splice in a small piece at the bottom of this! I just hope I'm not adding too much weight to the tail!