KK Ajax - BritKit Build Off 2012 - Page 7 - RC Groups
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Jul 05, 2012, 03:39 PM
I like real wooden aeroplanes!
Sundancer's Avatar
Originally Posted by Colonel Blink
Because the lower longeron has quite a severe curve in it, I am still concerned that there may be some stresses built in, and I am still worried that when I lift it from the board it may go 'Sproingggg!!!!' and one half will have the nose half an inch lower than the other. I have painted copious water onto the wood whilst pinned to the plan three times to try and combat this. It'll be fingers crossed during the Grand Unpinning Ceremony tomorrow night...
If you wet it it should be OK Colonel, but the real answer is steam m'boy. Prepare the longerons to length and then five minutes with the kettle (and a pair of oven gloves to prevent third degree burns) whilst SWMBO is absent and you will have a set of gently curved fully de-stressed longerons. Don't worry about matching the bend exactly, just steam 'em free hand. Another answer for severely curved longerons is to laminate them - but I wouldn't wish the task with three strips of 3/32" x 1/32" on my worst enemy, let alone you Colonel!
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Jul 06, 2012, 06:42 AM
Registered User
I can't say that I had any trouble with any of my Ajaxes - the two pictured earlier are the third and fourth fuselages (one burst rubber motor, one had a heavy book dropped on it, ahem) - it never occurred to me that you had to steam the curve in them!
Jul 09, 2012, 03:50 PM
So I'M meant to be in control?
Colonel Blink's Avatar
Well folks, my fears were ungrounded - the side frames seemed to keep their shape when I removed the pins, and even when I unstuck the frames from the clingfilm over the plan.... I even found and used a razor blade to seperate the halves. Using such a sharp but flexible and unergonomic blade terrified me, I don't mind saying. My understanding is that all you...er....more mature moggelers would build whole models using a razor blade - but I think they were single edged ones, n'est-ce pas???

So with two frames as identical as my sausage figures and crossed eyes could make them, we came to the part that has been a bit of a bÍte noire for me throughout the build - joining the fuz sides. Started off by adding the two bulkheads as square as I could (I had found that the upright the front one abuts was either not glued in square, or the wood wasn't square). I elected to use CA - it was a payoff between the 'one hit which must be right' and the Titebond 'gives a bit of wiggle time but more chance of it going out of line when you've walked away'. That bit seemed to go OK. I then joined the tail end, which is where a problem I have began to make itself present. I have always had difficulty 'sighting' things for alignment. This may be because I have a very lazy eye (in fact its so lazy I can hear it snoring at times) and so I am effectively monocular; this can make depth perception interesting at times. Hence copious measurement is the order of the day.

Having measured so often that my 12" steel rule was glowing dull red, I decided to pin the fuz over Mr Hatfull's plan to assist with the joining of the nose. This is where I felt a little out of my depth - I'm sure it gets easier with practice, but trying to work in 3 dimensions in mid air was a challenge until I borrowed two of Mr Morrison's Finest Fuselage Setting Pieces from the kitchen cupboard - Lady Blink will never notice (as it wasn't the drinks cabinet), and I promised Cook an extra thruppence a month if she kept quiet. It looks reasonably straight to my skewed eyes. Over the next few sessions I added the rest of the crossbraces.

I now have a basic fuselage framework - not perfect, but I think passable. Still will need a few further furtling sessions.....
Jul 09, 2012, 04:01 PM
So I'M meant to be in control?
Colonel Blink's Avatar
Quick question - how are you chaps attaching your motors? Self tappers? Small BA screws and nuts? Hot glue? Currently the Ajax has a simple rectangle of 3/32" balsa at the nose. I would quite like some sort of 'weak link' that in a less than perfect arrival with Mother Earth would give way before the fuz itself. I was considering mounting the motor onto a piece of 1/32" ply with the screw heads behind it; I would then relieve the 3/32" balsa front to clear the screw heads and simply glue the ply to the balsa. The theory is that the screwheads should break through the ply rather than the fuz longerons breaking...
Jul 09, 2012, 04:54 PM
Visitor from Reality
Okay, if you ask five aeromodellers 'how to', chances are, you'll get about seven answers.

The first two to answer will have come up with other ways to do whatever by the time the rest have chimed in...

As losing a motor in flight can ruin a good Sunday, I always go for bolting motors to a ply 'firewall' (or should that be 'electron shield' in our case?) using small bolts into 'T' nuts. With an ittybitty lightweight as you're building, a 'prop saver' widget, where the prop is held onto the prop driver with a rubber 'O' ring, will prevent embarassing fuselage destruction if you arrive too vertically.

This firewall would likely be 1/16" birch ply, or maybe 1/8" Liteply, fitted with many small holes from my collection of 'lightening holes', and drilled to take appropriately small bolts and T nuts. That would be 2-56 for me, as I build in US $$$ these days - no idea what that translates into whatever strange measuring system Yorkshire has adopted from closely adjacent furriners these days. I suspect 8BA is nearly as long gone as I am...

From my fuzzy childhood memories of the Ajax/Achilles, it looks like you did a great job of making it the shape its supposed to be.

Hope that helps

Who lived in Hull, until a determination to leave that less than glorious city overtook him...
Jul 10, 2012, 01:08 AM
I like real wooden aeroplanes!
Sundancer's Avatar
Funnily enough I reckon Dereck is pretty much right. On the similar Witch I used a 1/16" ply firewall with a second small 1/16" ply patch mounted on the front and the little 1811 fixed to it with small self tapping screws, the whole thing covered with a hollow version of the rubber model's nose block. As Dereck said, the prop saver will give some protection. Your scheme would work, but I would use 1/16" ply instead of 1/32".

Your fuselage looks fine to me, well done on not cutting yourself with the dreaded razor blade. And yes, we did use these for most of our modelling in days of yore, the trick is to snap them in two length wise and them snap a small angled piece off the end to form a point. And also yes, we did cut ourselves quite a lot!

When joining fuz sides like these, if you don't have a fuselage jig (I would expire without mine!) joining over the plan or a drawn centre-line is the ONLY way to get them straight.
Jul 10, 2012, 02:54 AM
Sic itur ad Astra
sparks59's Avatar
Good progress Colonel.

Fuselage alignment. I'm also a devotee of the Morrisons - Heinz method myself, works well and is infinately adjustable.

The latest Coupe fuse has a fabricated former with cut outs in each corner so, as long as the former is made square...and it fits flush with the fuselage sides, squareness is automatically achieved. I might use this method on other (non former models in the future as it makes things easy and adds strength near the c of g for little extra weight).

Motor mounts - On conversion jobs like this one, I do similar to George, make a ply former, 1/16" for something of this size and usually attach the motor flange with small metric 2mm (or 6 or 8BA whatever I have) nuts and set screws. I would have no hesitation to use self tappers but dont have any that are suitably sized.
The standard prop saver on an 1811 avoids the need for impact relief points on a light model like this.

Keep it going.

Jul 10, 2012, 04:21 AM
Registered User
kkphantom's Avatar
[QUOTE=Sundancer;22122022the trick is to snap them in two length wise and them snap a small angled piece off the end to form a point. And also yes, we did cut ourselves quite a lot!


This as a lot easier with the old Gillette Blue carbon blades which were brittle and easily snapped, unlike the modern stainless versions. The old ones keep their edge much longer too, still available from Mike Woodhouse. Very entertaining build Colonel, Keep it up!
Jul 10, 2012, 04:24 AM
I like real wooden aeroplanes!
Sundancer's Avatar
Quite right Gary, I forgot to say that stainless steel blades were to be avoided like the plague, they don't snap and soon lose their edge. Mind you, it wasn't a problem back in the day as stainless blades were only introduced after I discovered the scalpal!
Jul 10, 2012, 04:36 AM
Sic itur ad Astra
sparks59's Avatar
I still use 'half razor blades' for cutting / trimming film covering, they are easily the cheapest and most effective solution, especially if epoxied into a small handle made from hard balsa or a chopstick to get into those awkward places.
Last edited by sparks59; Jul 10, 2012 at 08:45 AM. Reason: typos!
Jul 10, 2012, 05:52 AM
I like real wooden aeroplanes!
Sundancer's Avatar
Here is a scan of the first page of my treasured tatty copy of the MAP book "Construction for Aeromodellers", published 1955:

Old it may be but this is still the book I would give to anyone attempting to build a "coventional" balsa built-up model for the first time, if you read and follow it there isn't too much else you need to learn.

BTW, after the introduction of balsa construction to the UK in the thirties, aeromodelling was often referred to a "razor blade carpentry", a not inappropriate nick name.
Jul 10, 2012, 08:54 AM
Registered User
>but I think they were single edged ones, n'est-ce pas???

Nope .... and I still have the scar tissue to prove it.

Double-edged blades are now quite hard to find here - and expensive when found. With the dreaded taxes imposed a 5-blade dispenser costs well over $6.00 At least, expensive to my penny-pinching mind but perhaps comparable to the price 'you' pay.
Jul 10, 2012, 09:03 AM
Sic itur ad Astra
sparks59's Avatar
Usually I complain about being unable to buy the things I need in Abu Dhabi, but thankfully, the old fashioned twin edged razor blades are still available here at almost any corner shop, and what's more, they are cheap as chips!
Jul 15, 2012, 03:32 PM
So I'M meant to be in control?
Colonel Blink's Avatar
Well, things have slowed down over the past week due to work and domestic pressures, but at least progress has still continued - albeit at an almost tectonic pace due to only being able to grab a few half hour 'modelling interludes'....

Having had the cognescenti comment about the fire/spark/buzz wall, I simply faced both sides of the 3/32" with 0.5mm ply, and will reply primarily on the propsaver (note to self - ask Italian gasket factory to send a couple of dozen O rings of the correct size as spares).

Other than this it has been general fuselage furtling, sheeting in the area for the elevator servo, adding the undercarriage mounting tubes (plastic from the Amerang kit - I seem to remember my original one had brass tubing). I will be adding the wing dowels in the same place as Froglube's, but as all the dowel I have is fairly thick, I'll be taking a whizz down the model railway shop at lunchtime tomorrow to see if I can get any more suitabubble. I also noticed that when complete and fitted, the fuz longerons will be pushing into some unsupported covering on the underside of the wing, so I added a subspar between the middle three ribs to support it and keep the wing at the designed incidence.

And finally I have begun the second task which I have been dreading - bending up the undercarriage. I am (at best) OK in two dimensions - but three foxes me completely. Hence the front legs came out OK and 'almost' matched. The brace incorporates a third dimension and has been a bit of a pain. I nailed together a sort of semijig to assist me, because trying to get the brace to line up with the main leg whilst everything was swinging about in space was quite simply hopeless. It has definitely helped, but the results (so far) I am rating as 'just possibly acceptable'. I'll wait until the second leg is complete before I pass final judgement!! Since taking up electric flight, my soldering has improved for electrical matters, and on piano wire it is better than it used to be. However I still decided to make use of one of Sundancer's many hints - that of the 'of course I can solder' heat shrink tubing over the join. First leg is complete, second leg is bent and the joint held with a blob of CA ready for soldering (hopefully tomorrow).

Still some more fuz furtling to be done (fitting motor mount, sheeting in of nose, wing dowels etc), and my mind is beginning to wander around the electrical system and the likely positioning for balancing the servos way back. Currently I am erring on the ESC and Rx being as far forward as poss (being on 35MHz means a lot of aerial wire to find a home for) and then if that gets us somewhere off 'ridiculously tail heavy' I can then fit the Lipo somewhere amidships to get the CG right. Whether that theory is away with the fairies or not remains to be seen.

The other thing I am thinking about is covering (which will be my first attempt at mylar & tissue) or to be more accurate, the colour scheme. I am thinking of predominantly white as it evokes either the prewar period when the Ajax was originally designed, and/or my younger days when you used what was in the kit. Having said that, I think it may well be done with a blue fuz and trim because I like the idea (and the KK Handbook b&w photo shows it with a dark coloured fuselage). Need to work out how many sheets of Esaki to get - though I do need to crawl deep into the eaves because I think I may still have some there....
Last edited by Colonel Blink; Jul 16, 2012 at 02:54 AM.
Jul 15, 2012, 03:43 PM
So I'M meant to be in control?
Colonel Blink's Avatar
Originally Posted by Sundancer
......my treasured tatty copy of the MAP book "Construction for Aeromodellers", published 1955.
For me, it is my 'Basic Aeromodelling' by R H Warring, published as late as 1976 (which sits three books away from 'Radio Control Thermal Soaring' written by some other rather knowledgeable chap )

Interestingly, I also have a Ron Warring book in my technical library at work - 'Seals & Packings'..... seems RHW was a sealing engineer the same as yours truly.

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