Israeli Air Force A4 Skyhawk - Shalom

[Phil Cooke]

Wouldn't be needed (assuming the wing joiner is fitted securely of course) - like you say a huge chord and large area on the 1/8" root ribs. We wanted to avoid the use of a wrap around bandage as there is no fuselage fairing on the underside so it would ruin the looks of the model from beneath.

[Phil Cooke]

Pete, I've just double checked the drawing as I wasn't happy that we hadn't addressed this - I appreciate its hard to show in plan view - but the composite rib section DOES correctly show the additional 1/8" webbing in place behind the 1/16" webbing and on top of the bottom spar.

[Peter Garsden]

Like I have said, ooh errr missus...apologies

[Matt Jones]

Morning Peter, great progress here! On the wing you'll find a wing bandage isn't necessary, with such a short span the loads are small so a dihedral brace and accurate gluing together of the wing roots is sufficient.

With the brace I did cut all the way through the wing, made it slightly deeper than I needed, then sanded the excess flush with the wing surface after the epoxy had set. Doing it this way transfers the flight loads directly to the spars AND skins.

[Peter Garsden]

Thanks Matt, yes indeed, the wing is together now with a good join, and not cutting through of the skins, but I agree it would have been better to cut through, as the dihedral is not quite right and the structure a little under stress as I pinned the wing tips down to get the dihedral right. This is something which would not have been necessary if I had cut through the skins as you suggest.

So for future builders I would recommend do as I was told, not as I did - follow the designers as they know best - Messrs Cooke and Jones - or should it be Jones and Cooke?

[Phil Cooke]

That said, builders will have to make their own oversized 1/16" ply wing joiner as I've just noticed the one provided in the kit is sized to fit within the skins, certainly not 'tall' enough to enable protrusion top and bottom as we've described as ideal...

[Lorenz Mueller]

Despite advice to the contrary, and not having access to the build article in the magazine, I decided to do it slightly differently - lower wing skin in one piece. Until now all the required angles check out, and this way I could achieve a good fit and glue joint to the dihedral brace. Fillers to the upper spars are in by now, so top skins next, and then a decision: Ailerons as per plan or with horn balances as per scale? Any showstoppers there?

Lorenz

[Phil Cooke]

No show stoppers with running the ailerons or elevators out to the tip and adding the balance lands, I admit that looks much better and is true scale. The decision to omit both of them was in the quest for robustness on the slope, that's all - ailerons out to the tip don't last long with slope landings - the solid tip protects them nicely, that's all.

[Peter Garsden]

Such a surprise Lorenz to see a nearly completed model much further ahead than the rest of us all at once - how about a separate blog? Sounds interesting. As to the one piece wing, I presume you are going to split after construction to reglue with dihedral. The top sheeting of course runs diagnonally, really good idea as it fits so much easier, and adds strength.

[Chris Barlow]

The wing build looks very similar to the JP wing. Also your posts and Phil's reply clearly demonstrate the use of a 1/8 "filler" where the fillets fit. Thanks.

On my JP I cut through both skins to fit the brace too which didn't cause too much trouble except that I would have liked to see that there were no gaps against the spars (fillets) and a 100% glued area, which you can't with the wing skinned!

[Peter Garsden]

I rough fitted the ply front piece then drew round it and cut further before gluing with cryano in place. I then filed them back with my Permagrit files which are worth their weight in gold. Next purchase is a Proxxon Rotating Sanding Disc I think.

Next I pinned down the tailplane bits - be careful you get them the right way round as it is easy to make a mistake with them. The triangles only go one way. Pin to the plan as Phil suggests in his article.

There are those amazing Graupner pins again. I know I talk about product but every time I buy something I wonder how I did without it previously.

More apologies Phil. The diagram showing the 1/8 webbing is on plan page 2 - it was tucked under the fold which I couldn't fit on my working board. It is a shame really as normally I do a duplicate sheet by having them copied at Mail Box. This time I didn't bother. If I had done so I probably wouldn't have made the error I did.

Also I have managed to order about 3 duplicate sets of balsa longerons, so if anyone wants some for free let me know and I will bring some to the Bwlch on 21st May - trailing edge and leading edge of wing and 3/8 hard for the Fin Post. Can't see me using them again. I think the WIFI dropped as I was ordering. Such a pain.

Edited By Peter Garsden on 02/05/2016 13:43:25

[Phil Cooke]

Good progress Pete - like you, I've been making my tailplane up today, it's pinned to my board now. I'm not going to use the supplied 3/8" elevator 'block' as shown in your photo, preferring to use some pre-shaped elevator stock instead.

[Lorenz Mueller]

Posted by Peter Garsden on 02/05/2016 07:12:38:

Such a surprise Lorenz to see a nearly completed model much further ahead than the rest of us all at once - how about a separate blog? Sounds interesting. As to the one piece wing, I presume you are going to split after construction to reglue with dihedral. The top sheeting of course runs diagnonally, really good idea as it fits so much easier, and adds strength.

We'll see about the blog. It would not be telling much news as I thankfully had Phil and yourself to follow all the way. As to the wing - no I will not split it, don't have to. The wood block you can see under the right wing tip in the second picture gives me exactly 28mm (2x14mm) dihedral, so with the help of a few 5lb batteries to keep everything flat on the building board, the dihedral is in and correct from the beginning, and the dihedral brace well and truly glued. Next step will be the top skins, one at a time, taking care of the washout.

[Peter Garsden]

So to the fuselage - Look I know everyone has posted pictures of gluing formers in position, so I will follow the crowd.

As I had bought 3 inch wide 3mm balsa, I glued 2 pieces together rather than using 4 inch which requires 3 pieces, so in hindsight 3 inch is probably better.

Anyway, I used carbon paper to trace an outline of the fuselage, and the former positions as well as the triangular longerons. I then traced round one side to make the other and marked the positions of the longerons by joining up the lines from one side to the other.

And the formers if you please. This site has encouraged me to buy some engineer's squares which is a good thing and they have proved very useful

[Peter Garsden]

Here are some photos of the fuselage construction to date, frankly similar to others you have seen. I followed Phil's instructions, which turned out fine. I did manage, however to glue a slight twist into the fuselage because it was difficult to line up the second fuselage side accurately. With hindsight, it may have been better to use my SLEC jig that you can see in Chris Barlow's build blog. If, however, I had checked squareness with my engineer's square as shown in Phil's blog this could have been avoided.

Still, I think the twist has been corrected partially now the top 1/4 inch balsa is on behind the F4 to F7.

More tools recently purchased off ebay for £8.99 - engineer's squares - essential for checking squareness!

It was certainly true that quite a lot of pressure had to be applied with the clamps. Also important to line up and ensure a good dry fit and "fettle" as the instructions point out.

Had to use a lot of pins because this sheet of balsa arrived warped in a slight humped shape. I suppose I could have tested the vinegar idea before glueing it.

Edited By Peter Garsden on 06/05/2016 05:20:27

Edited By Peter Garsden on 06/05/2016 05:26:31

[Phil Cooke]

Good early start to the forum activity today Pete - like it!!

Yes the fus sides do take some bending, first in 2D onto F1 as you have done, then in the other axis as you pull the sides in around F2 and F3 - if you are not using ammonia then please take care not to crack the fuselage sides as you pull them in - they need some working - vinegar or ammonia should enable this no problems - its worth the smell!

[Peter Garsden]

Thanks Phil, yes I omitted to say that I have used vinegar, though it was malt vinegar which really stinks, as that is all we had in the cupboard. It's alright for chips but not so good on balsa. I also heated it up which made the smell worse.

The next pictures tell the story. When clamping the front down, even soaked in vinegar, there was a crack as the fuselage side glue bond broke, and had to be replaced with epoxy. Have left it to dry. When I get home, I hope the sides stay curved over the formers ready for some glue.

Question Phil - presumably the wood kit does not include F9 - couldn't find it anywhere? Or have a I thrown it away in error?

Another question Phil (I know you like answering my meaningless drivel) - on the plan it shows 3/8 balsa below the tailplane at the rear directly under the rudder. It then say make the jet exhaust out of rolled 1/16th sheet. What is that? I can't work out that part of the build. The wood pack only includes the fin above the tailplane which we are all remaking into an external ribbed rudder, so I was thinking of using the left over Fin3 is it for the below tailplane Fin part?

Edited By Pete B - Moderator on 07/05/2016 12:09:53

[Phil Cooke]

Pete, no the woodpack doesn't include F9, is not really a former, more of an end cap - it was left out for 2 reasons - one - as not everyone will sand the fuselage to exactly the same section, and 2 - not everyone will have a 42mm exhaust tube - so not kitting F9 allowed for a little licence at the back. Stick it on last once the fus is sheeted top and bottom and that sheeting is cut back to a single plane.

[Phil Cooke]

As for the question about the portion of fin below the rudder and the exhaust shrouding, this isn't so easy to explain - I would urge you to take a look at photos of the full size in this area to gain an understanding of the shapes we are trying to model. It's hard for me to explain, as due to leadtimes on the prototype build, these parts were never fitted - see the photos below!

The plan has the following wording...

FUSELAGE EXHAUST PANELLING MADE FROM ROLLED 1/16” BALSA SHEET

Take a look at the full size photos and you will see the shape we are trying to recreate. Our model is complicated due to the snake exit and the need for a clean, uncompromised elevator horn linkage as in the photo above.

This needs to be improved visually on the production model. The plan intent (although its not that clear, admittedly!) is for a rolled portion of 1/16th balsa to be glued to the top of the fuselage to fill the majority of the gap. This should not interfere with the snake run! - and could, in practice (although not true scale) be made to join up with the lower 1/8" tailplane doublers.

Rear of the snake, and taking into account the working 'arc' of the elevator horn and clevis (shown as +/- 45deg on the plan although in reality you use nothing like that amount) we need to add a little portion of 'false' fin trailing edge, to bridge the gap from the top of the rolled exhaust shroud to the base of the rudder (fitting through the gap between the 2 elevator halves)

Of course I cant show you photos from my prototype as I never completed this part of the build, in the rush to fly it before the end of last season!

Please take a look at some full size references, and I'm sure this will help build the image of what we are trying to achieve - its purely aesthetics - not structural or functional.

[Phil Cooke]

This is what we are trying to replicate. But in a manner that doesn't compromise the snake and clevis run.

[Peter Garsden]

Cheers Phil, as always a thorough and detailed explanation beyond the call of duty - what would I do without you in life? It would be anxious and bereft?

So, followed Phil's suggestion and made some fillets to level off the top of the fuselage between F1 and F2

Then fitted the top 1/2" sheet and the cockpit floor fill in - incidentally fit this cross grain as it is stronger being only 3mm.

Finally, I have recut the top of my Fin to accord with the version I am building with the hump - more angular and less round, so a new Fin4 part - plenty of spare left over from the Wood Pack supplied sheet.

[Peter Garsden]

I decided to make the scale rudder (what is happening to me?) with fiddly bits of 3mm slices and 3 layers of 3mm as per Phil's design - again. One has to make one's own piece of 3/8 piece of post - as I said I managed to order about 8 lengths from Balsa Cabin and have a load left over which I will bring to the Bwlch next week - free to a good home. Also wing trailing edge and leading edge.

Put the fin together and left it - not for long because Super Phatic dries in 10 minutes good and strong. I used this because Aliphatic is not sandable and leaves humps.

[Peter Garsden]

Few Tips for F9 - not included in the wood pack. I decided to cut it massively over size then trim down for 2 reasons:-

1. I need to cut a hole in it and it is difficult to know where so oversize means it will go in the right place.
2. I want to use the hole in the middle as a backdrop for some flame imitations which Phil produced for the Tornado. I will print them off on photo paper, stick them to the balsa circle and push into the jet outlet. I will then paint the inside fluorescent orange to give a glow effect - we will see how it turns out.

[Peter Garsden]

So - to the jet profiles, vinegar and bending. I decided the easiest way to do the profiles was to make a cardboard template - easier than trying to line up 1/8 inch sheet as the end edge is exactly 4 inches then cut out and draw round - much easier than trying to line up 2 with the carbon paper.

The malt vinegar stinks. I must get some white vinegar. I have left them bending as I do this and print out the exhausts.

Incidentally I have given up with the forum albums. The software is rubbish. I upload all mine to my Picassa Album - or Flickr, then copy and paste the image URL - so this looks at Picassa and displays the image - so much easier.

[Peter Garsden]

I found that the radius of my epoxy mixing pot was the right radius for A1, so soaked the balsa then wrapped sponge sanding cloths round it with rubber bands. Will leave it to dry and see what happens