Jemima Free Plan build

[Eifion Herbert]

Being completely unable to resist anything with vintage lines, and having nothing on the build board at the moment, I'm just going to have to build Jemima from the Feb magazine.

So here's a question for Jim Newberry the designer right away, as I've seen you've already kindly offered tips to some other Jemimaers, do you have an approximate materials list? The last plan build I did I just bought bits and bobs as I found I needed them and I'm sure ended up spending about a receiver's worth of money in postage, so I'm hoping to be a bit more organised this time round and order everything up front.

Also mods, is this OK to make a new thread? Or should I have piled in one of the existing ones, not quite sure of the netiquete with multiple people doing a build blog of the same model.

[Jim Newberry - Nuviation Ltd.]

Hi Eifion,

First of all, thanks for choosing to build Jemima, hope you enjoy it!

As far as materials go, I set out to design a model that needs as few different wood sizes as possible so you will find that four or five sheets of 1/4" x 4" x 36" medium to softish balsa plus a stripper will provide everything you need for all formers, tail surfaces, longerons and main spars. The wing ribs can be cut from four sheets of 3/32" balsa and for the sub spars you will just need half a dozen 1/8" square strips. Other than that you will only need a few small pieces of 1/16" or 1/32" ply, dowels for the wing bands, undercarriage wire, covering material and hardware. Part of the object of the exercise was to avoid having to buy lots of different wood thicknesses - this has led to some building oddities - eg the formers look excessively thick but it cuts down dramatically on waste.

Best wishes,

Jim.

[Eifion Herbert]

Hi Jim,

Thankyou so mcuh for that, that's incredibly handy, and such a quick response too. I can start putting my shopping list together. Starting to think about motors, I've got this:

http://www.e-fliterc.com/Products/Default.aspx?ProdID=EFLM1505

from an Eflite alpha 450. I wonder if it would have enough oomph for Jemima, the poor Alpha did have a heavy arrival, and although the airframe has been repaired and should be OK (haven't flight tested it yet) I wonder if I might be better off pressing the powertrain into service with Jemima and selling the Alpha as a bare model.

Can't wait to get started on this, there's some new techniques for me, those sub spars and webbing on the wings are new, as is the 3-d built up tailplane.

Thanks,

Eifion

[Ruprect Spode]

The Eflite motor you have is a 480 size 3530 equivalent motor theoretically capable of 275 watts of power with the correct battery and propellor combination. I should imagine even just 80 watts per lb would be sufficient for the Jemima.

[Eifion Herbert]

The build has commenced. Following Jim's build order from the mag seems like a good idea, so that's what I'm doing.

First job was tracing the tailplane onto greaseproof paper, flipping it over and aligning it to the plan, to make the 2nd half of the plan.

Next of course we have to start adding some wooden bits.

And that's it for tonight. Going to try to do a little and often on this build, not my usual technique of marathon sessions till I get tired and innacurate, then months of hiatus.

Now all I have to do is hope Mrs E doesn't stumble across this and recognise the pins from her sewing kit.

[Eifion Herbert]

Opted for yellow and silver as a classic vintagey colour scheme, but can't decide on yellow wings and silver fuse or the other way round.

[Eifion Herbert]

Next bit of progress, added the diaganol cross bracing, the spar and the upper ribs. Ten minutes in the garden with the trusty old permagrit sees the tailplane sanded to profile, to be put aside for the final assembly. Resisting the temptation to cover it now, as I like to have a photo of the completed airframe still naked.

First time I've done a 3d tail like this, it's almost like a mini wing in itself.

[Eifion Herbert]

Bit more progress, didn't document cutting out the elevators as they are a fairly simple shape cut out of sheet, so not much interesting going on there, though they may feature in a later update when it's time to cut the lightening holes and join them.

So let's make a rudder. First the outline is made:

Then add the horizontal members and diagonal cross bracing:

And when all was dry I transferred the outline from the plan to the wood with the aid of some tracing (greaseproof) paper, and here it is cut and roughly sanded to the outline.

Obviously a lot more sanding to go, but it was far to cold today do do any serious sanding, as my search for a suitable small, cheap vacuum to use in the workshop has come to nothing, and significant sanding is relegated to the garden.

So now I have a tailplane, elevators, fin and rudder, enough parts that when offered up together I'm starting to get an impression of the size and form of Jemima, and compared to my other models I think she's going to have quite an imposing size, should certainly have plenty of presence in the air.

Next update, fuselage sides. Might be a while, as tomorrow looks like a flying day rather than a building day.

Edited By Eifion Herbert on 20/02/2013 18:31:46

[Eifion Herbert]

Here we go for the fuse. Half of it at least. Hoping to get a 2nd half done this afternoon:

Yes there is half a fuse in there somewhere amongst the detritus.

Up until now I'd been using greaseproof paper to copy parts of the plan when I needed to use them as templates, then I remembered my printer does copying as well. A test showed that it copied the sizes faithfully so hopefully that will save me a bit of time, though the printer part is starting play up a little and now needs a little persuasion to pick up the paper.

I have a question for the more experienced balsa bashers, I'm finding that when cutting parts out of the thicker sheets my blade isn't staying dead vertical, leading to a slight chamfer on the part, usually it tends to end with the point wandering under the straightedge. Is there a trick or a nack to keeping that blade vertical, all the way through the cut or is just a matter of experience?

[Eifion Herbert]

Just ran the first fuselage side through the magic balsa coppier, and out pops the other side. Now I have two.

Building the second directly over the first proved very effective. They are absolutely identical, at least to within my ability to determine, anyway.

Tomorrow it's former time.

[Former Member]

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[Eifion Herbert]

I actually feel like I'm cheating a bit being a couple of steps behind you, and benefiting from your experience. Definitely going to wait till Jim gets back on your thread before trying to draw the fuse sides in. Still it means I've got no excuses for not getting it spot on!

[Eifion Herbert]

Formers made, checked for sqauredness, and duly glued to fuse side number one, checking with engineer's squares all the way. I must've spent 10 minutes staring at it in this state, checking and double checking and tripple checking that I could get the former in place without disturbing the squares and it was all still lined up. But there comes a point where no more checking helps, and you have to take a deep breath and commit wood to glue.

Once the first one's done the rest follow quite quickly:

Then the next tricky bit, glueing on side no. 2.

Did this by pinning the second side on, pulling the tail together and holding it in place with clothes pegs, and checking all was still square. After placing the model on a flat board, holding it down with weights and checking both sides were at 90 degrees to the board all the way along its length I finally glued the second side on.

It all seems straight so far. Phew. The rear of the fuse comes together quite easily without threatening to break anything. The front, I'm not so sure. Had a quick squeeze and I think it might be quite a challenge to get the front in to the required bend to reach F1. But that's something for another day.

[Eifion Herbert]

Did a bit more on Jemima today, added the rear formers and the diagonal top and bottom bracing. After adding the top bracing I feared I had built a banana as it didin't look straight at all, even though the midpoint of the formers lined up with the centreline on the plan. Turned out this must have been an optical illusion as the effect vanished when the bottom bracing was added.

Gave the front a bit of a squeeze, and at the moment I don't see any way the front section is going to bend enough to meet F1 without the entire thing going crack.

No pics on this post as the site doesn't seem to be playing ball

[Eifion Herbert]

Working again now so here's some photos!

[Jim Newberry - Nuviation Ltd.]

Hi Eifion,

If you're concerned about the bend at F1, you can cheat slightly by adding 1/4" doublers to the inside of both fuselage sides forward of F2 so that you don't need to pull them in as far. Later on you can plane and sand the outer faces of the fuselage to the correct profile. This will achieve the same shape but without the bending. Just make sure that the thickness of wood you use for the doublers leaves enough room to fit your battery in. That said, I had not problem bending the fuselage sides but then I used quite soft wood.

Best of British!

Jim.

[Eifion Herbert]

Here's F1 made of 2 1/8th liteply laminates clamped and setting with 12-min expoxy (well it's quite old epoxy, so it's more like 30 min now)

Had another squeeze of the nose with a plywood offcut of the correct width serving as F1 and it seems my previous fears were unfounded as it bends in the required amount without too much trouble. However I've noticed that one side does bend easier than the other - even though the pieces were cut from the same sheet - go figure so I'm wondering what's the best way to make sure it comes out even, as if one side's bending more that the ohter it'll mess up the thrustlines.

Might it be a good idea to clamp it all up dry and leave overnight to allow some of the stresses to work their way out of the wood?

[Stuart Eggerton]

Hi Eifion, I must have have missed your thread when looking at latest posts. Your Jemima is looking great. , good accurate building by the looks of it.
I had a similar problem re the nose former. Clamps work well, as well as weights to keep the fuselage in place.

[Eifion Herbert]

Searched the the house for the clamp I know I have somewhere, but it succeeded in hiding from me, so off to my local hardware store this morning to get another one. I imagine the first clamp will turn up at some point, and there will allways be jobs that require two....

...Like this one. Found that one clamp didn't pull in the fuse front along the entirety of its height. Didn't fancy popping out again to buy a third, so made cunning use of some cord and a pen.

Both sides of F1 are the same distance from F2 so it's sqare in that respect, but the left fuse side is bendier than the right so the whole F1 is offset a little to the right. It's just a couple of mm in it, but measurable. I'm hoping I can go some way to fixing this but cutting the 1/2 and 1/4 inch sheet for the bottom of the fuse slightly off-square, pushing F1 a little back to the left.

Currently wating for my ageing 12-min epoxy to go off. Been 40 mins now and it's still a little soft, so will give it longer. Maybe I really should get some new!

[Former Member]

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[Eifion Herbert]

Here's the here's the fore ply undercariage mounting plate, and a few sections of quater inch sheet making up the lower front of the fuselage up to F1.

Sticking to my little and often mantra, that'll do for tonight. Can't do a huge amount more now until I choose and acquire a motor.

[Stuart Eggerton]

Looking good

[Eifion Herbert]

Power system has been acquired and tested:

Motor, a 35 amp 1000kv unit, 50 amp ESC turning a 11 x 5.5 inch prop.

This little lot draws 28 amps, producing just under 300 watts on a 3-cell lipo when bench tested so should be just right for Jemima, and the extra headroom on the ESC is just peace of mind.

No excuse now, time to crack on with the balsa bashing!

[Eifion Herbert]

Want to get the motor fixed before starting to build the cowl, I think it'll be easier to work out where everything should go, and to ensure I can extract the motor if needed. With that in mind I toddled off to modelfixings.co.uk to acquire some M3 countersunk head bolts and blind nuts with which to attach the motor.

So Jemima's current state is "waiting for postman"

[Eifion Herbert]

Bit more progress on the front end of Jemima.

F1 now boasts a motor, I'm sure that will come handy at some point during flight. And there's some decking for the windscreen to sit on.

Now we need somehting to cover up that motor. Here's the detail of how it's built up from the inside. Took me a lot of head-scratching before starting to make this part. For anyone else similarly head-scratching all I can say is just crack on and do it, it's much easier to work out and make adjustments when you've got parts in your hand, than trying to get it all clear in your mind first.

The other side is a little prettier.

Fits quite nicely on the body.

Now I'm wondering how to attach it. I'd like to make it removable so I can replace the motor if needed, and my go-to method would be little pegs made of cocktail sticks that fit into locating holes in F1, just to locate it, and a few magnets to hold the thing in place. However, do you think I can get the pegs and the holes properly lined up? Can I heck! Anyone have any thoughts on how to do this before I turn my F1 into swiss cheese through trial and error?

Lastly, just for fun, I will really need to clear my bench before I start on the wing!