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PSS A-4E 'Top Gun' Skyhawk


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F2 made, everything dry fitted and tweaked for alignment, then the nose assembly was all glued up.

nose section 5.jpg

Its important to get the nose profile at just the right angle, the datum line (copied off the plan) should be exactly 1" high above the building board as shown above.

You can then add F1 which saddles the ply nose profile. The battery box with F2 and F3 dry fitted can then be offered up - once everything is aligned and square it can all be glued up.

nose section 6.jpg

nose section 7.jpg

Note the small length of triangular section added between the front face of F3 and the fuselage floor to add a bit more support.

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Hi Chris, yes all quite simple so far, the build is not a complex one, by design!

Its best if you slide the tube through F2 and F3 such that it sits on the marked up tube dry - then once everything is squared up and tweaked into accurate alignment then you can add the glue. You'll find you may have to open out the tube holes in F2 and F3 top and bottom to allow the tube to sit at the dropped down angle required - the laser cutting is very accurate and assumes the box is fitted perpendicularly.

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Although the next stage for me should be to join the 2 fuselage halves together by setting the perpendicular formers F4-F7, I found myself thinking a step ahead yesterday to the assembly of the main fus to the nose section, and this led to a little fettling required which is worthy of note to other builders.

Dry fitting the parts together at F3 showed a little gap between F3 and the inner fuselage wall. The triangular section wasn't seating properly against the formers 45 degree shoulder. It's due to the tolerances involved in manufacture between the 1/2" triangular balsa strip I've used and the accurate laser cut formers which are meant to interact.

Sorry, no pictures of the 'before' state, but here's the amended dry assembly showing no gap - note you are looking for all 3 formers F3, F2 and F1 to rest up cleanly against the inside of the fuselage wall. Getting this right now will aid assembly later, as adjustment will be difficult when its all pinned down on the board.

triangular 1.jpg

From the inside, you should be able to see no gap between former and fuselage wall, the triangular section should nicely engage upto the laser cut formers at the base.

triangular 2.jpg

My fix was to lightly dress the triangular section locally where the formers meet - it just needed 1/32" removing as shown to enable a 1/16" gap to be closed up between former F3 and the fuselage side. Its worth checking all 6 joints (each side of formers F3, F2 and F1) before you commence the assembly later on the board. I found I had to fettle the triangular strip like this at F3 and F1 to ensure properly closed joints (all dry fitted)

triangular 3.jpg

Right, time to join my fuselage sides...

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In preparing to join the fuselage sides I've found my former F7 is a little short in the vertical and in need of some rework in the quest for better joints. Again I think this is a result of poor tolerancing on the 3/4" and 1/2" triangular strip I've used combined with the fact that the formers are accurately cut to suit a perpendicular alignment, when in reality the lower triangular strip is angled up from the rear of the wing to create the fuselage profile. If I placed the former in the correct position and mated it up against the 3/4" triangular stock at the top I was left with a ~3/32" gap at the bottom. This would mean the former wouldn't interface with the lower triangular stock nor the fuselage bottom sheeting to be added later.

f7 short.jpg

I added 3 strips of 3/32" balsa to the base of the laser cut former and sanded them to profile and width as shown. I then trial fitted the former, which was a little big now on the rear side, and the 45 degree shoulders needed fettling a little so they allowed for the angled 1/2" triangular strip. Another dry fit shows a much improved joint and corrected former height, ready for some glue.

f7 short 2.jpg

I used a little 5 minute epoxy to secure F6 and F7 together, ensuring they are square.

f7 short 3.jpg

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With the fuselage joined over the wing box formers it was time to add the nose section and pull the sides in over F3, F2 and F1. There's a bit of set up needed here to ensure you build a straight fuselage, it's well worth doing a couple of dry fits, understanding what area needs to be glued, what tools are needed etc, to ensure the assembly goes smoothly.

First job, pin the nose section down to the plan on the centreline, pin at the very front away from where the fuselage sides and triangular section will run, and further rear on the side wall of the 1/4" balsa floor. Push the pins right in so they don't protrude over the height of the 1/4" base, that way assembly will be eased when you offer the fuselage sides up. If the pins are left too high they may foul.

noseclamp 1.jpg

At the wing T/E position, pin a scrap piece of 1/8" balsa to the board, the fus needs to sit on this to elevate it properly at the front. Draw a centreline on the wood to enable accurate alignment of the fuselage at the rear. A centreline drawn on the rear face of F7 will help here too...

noseclamp 2.jpg

Have all your tools ready to hand, as once you've added glue to the many required areas of the fuselage you'll need all the help you can get to align this and pinch it up with some clamps. Don't clamp against the fuselage directly, use some blocks of balsa to clamp up to - it will spread the load over the joints and avoid surface damage to the model.

noseclamp 3.jpg

I used PVA for the assembly, note on the formers we are only gluing the vertical part of their sidewalls at this point, so don't apply glue all the way up. Once the fuselage sides are 'sprung out' into position over F3, clamp at the base of F3 and again at F1, ensuring that the fuselage is correctly aligned at the rear - check the centreline on F7 over the plan. Double check alignment all round and that all the joints are closed without gaps - if everything is true walk away and let it dry - its time for a beer!

noseclamp 4.jpg

noseclamp 5.jpg

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With the nose pulled in onto F3, F2 and F1 the clamps could be removed - its best to keep the fuselage pinned down to the board whilst we pull the tail end in and do some nice curving of the fuselage sides over the top halves of the cockpit formers.

This all induces a bit of load into the structure, so before any of that is done, its a good idea to add the 1/4" top sheet between F4 and F7 now, which will significantly stiffen the assembly, helping to keep it straight over the wing box when we add the curves fore and aft.

mid top sheet 1.jpg

mid top sheet 2.jpg

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With the fuselage still pinned accurately to the board on the datums, its time to pull the tail end in and add F8.

tail pull 1.jpg

You have to bring the sides in quite a bit to achieve the correct shape, the clamps and blocks are essential again here to hold everything in place. Unlike the prototype build, where I must have used softer fuselage sides (?) I found I needed to apply a little ammonia to the fuselage and top triangular section just aft of F7 to enable the bend to be achieved without too much creaking... without this I fear I may have cracked the fuselage sides - maybe the stock I have chosen here is a little harder than medium!? Anyway, the ammonia did the trick.

Take your time to ensure you pull the sides in evenly around F8 - a centreline on the former aids alignment. We'll add the rear top sheeting next, still with the fuselage pinned down, which will help ensure everything stays true when we release the structure from the board.

tail pull 2.jpg

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The rear top 1/4" sheeting was added with the fuselage STILL pinned down to the board.

fus curve 1.jpg

Now, its time to get real smelly! That's right - Friday night is AMMONIA night! thumbs up

Before any glue is added to the tops of the formers F2 and F3, the fuselage sides have to be eased around the curves and to achieve this its best to use household ammonia to help soften the balsa to avoid cracking. You can see the wetted area clearly below, I rub the liquid into the balsa with a cloth and then leave it for 15 minutes or so to take action...

fus curve 2.jpg

Don't forget to wet out the front fuselage 1/4" doublers too as they will need to twist along their length during the curving process.

Once the balsa is soft, you can slowly roll the fuselage sides up and over the shoulders of F2 and F3. Take your time and work upto the final curves, minimising the risk of cracking. Once in place clamp the fuselage sides carefully into position ensuring the inner surface of the sides follow the contours of the formers. Don't over clamp as you can buckle the assembly. Again, use soft blocks to clamp up against, avoiding damage to the model surfaces.

fus curve 3.jpg

fus curv 4.jpg

Leave it clamped overnight, no glue for now, once the ammonia has fully dried we can remove the clamps and you will find the balsa stays 'locked' in this position, making gluing easy tomorrow. Time for a well earned beer - its been a long week! beer

Edited By Phil Cooke on 18/03/2016 23:36:42

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Excellent detailed instruction Mr Phil, particularly as I have not started yet.

As everyone is doing fuselage first, I think I will start on wings.

Got a JW60 to build first - for DS'ing up at Rushup Edge, - http://www.modelflying.co.uk/forums/postings.asp?th=115617  and the Jart  - http://www.modelflying.co.uk/forums/postings.asp?th=111654 to finally finish (see separate blogs)

I know Ammonia is good (at least I presume because I have not tried it) but thought I would put in a bid for vinegar in hot water about 50/50 or even hot vinegar neat, which stinks less. Also I have been told that cryano is the only glue you can use which is water resistant, so I will try to soak the outside first, leave it for 15 minutes, glue the formers with cryano, clamp, then leave. Don't know if it will work until I try, but certainly Phil's method does work, I am sure.

The difference I suppose is that it is quicker because you bend and glue all in one motion. I know Phil uses wordworking adhesive which definitely won't stick if it is wet hence the pre-soaking and bending.

Maybe, to avoid clamping one could use accelerator.

Anyway food for thought.

Just got back from skiing in the Dolomites, so back to modelling, and no injuries.

Looking forward to seeing you all on April 16th.

Edited By Peter Garsden on 19/03/2016 14:06:50

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Thanks Pete, welcome home, glad you've had a great weeks boarding and have come back in one piece!

Will be good to see you start on the wing as you are right, all the blogs to date are fuselage led, starting at the other end we will teach each other the ropes!

The ammonia method works fine, really well in fact, its so powerful, it just stinks for 5 mins whilst its being applied - even with a mask on in my garage it caught me a couple of times - don't worry - a pint of cool beer after the event sorted me out so no long term reaction wink

I've never tried the vinegar/water mix so look forward to seeing how you get on. Cyano as a grabber is a good call if you want to apply it whilst wet, but some of the assemblies here may need a little adjustment time so watch out you don't get it grabbing before you've got all sub assemblies correctly aligned.

I've not flown since October, so like you, I've got a little 'cabin fever' myself and can't wait to get up the Orme in April. Fingers crossed for some good South Westerlies, warm air and cool beer.

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With the shoulders pulled in over F2 and F3 shes finally beginning to look a little like a Skyhawk, that characteristic angled cockpit section now showing through!

top sheet 1.jpg

Time to add the 1/2" soft sheeting just behind the canopy, with the fuselage STILL pinned firm to the board.

I noticed that both F3 and F2 sit up a little proud of the fuselage sides, this is because the shape of the sides (when cut to the drawing) doesn't correctly allow for the curvature required around the shoulders of the formers. Its only a couple of mm out, and I'm going to sand my formers down to meet the fuselage, but for anyone who hasn't yet cut their fuselage sides who wants to avoid this minor issue, then you should leave an extra 1/8" on the top side of the fus profile from F3 to F2, feathering out this additional height by F1 (forward) and F4 (aft)

Heres the former pre-correction, a couple of mm proud..

top sheet 2.jpg

...and after a little sanding, the 1/2" sheet dry fitted here to show the former is sanded just right.

top sheet 3.jpg

Once happy with the fit, cut the 1/2" sheet to shape and glue in place.

top sheet 4.jpg

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More 1/2" soft sheet is needed from the front of the nose to a point just behind F2. Again, F2 is a little proud, due to the pronounced curvature of the fuselage sides, and this also means the top surfaces of the fuselage sides, onto which the 1/2" sheet should be glued, is angled, leaving very little surface area to glue to.

front top sheet 1.jpg

front top sheet 2.jpg

You can see the resultant angle of the 1/4" fuselage side doublers clearly here, looking rearward onto the front face of F2. This resultant 'void' when the 1/2" balsa is glued on top needs filling. The best way to do that is to glue a short length of 1/4" triangular section along the top face of the 1/4" doublers, then sand both sides back so it is flat on top, taking care not to sand the fuselage sides as that would alter the resultant profile.

front top sheet 3.jpg

Once glued you can sand the 1/4" triangular flat on top and the void is filled...

front top sheet 4.jpg

front top sheet 5.jpg

1/2" top sheeting then added and pinned.

Edited By Phil Cooke on 20/03/2016 16:20:21

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With the fuselage unpinned from the board I did a little dressing of the lower sheet with the razor plane and tidied up the fuselage side overhangs, dressing them back square to F1.

I then added a couple of pieces of 1/8" balsa for the cockpit floor, checking first there was nothing left inside the fuselage as this sheeting effectively seals it off for eternity!

cockpit sheet 1.jpg

cockpit sheet 2.jpg

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Posted by Phil Cooke on 20/03/2016 22:11:17:

...I then added a couple of pieces of 1/8" balsa for the cockpit floor, checking first there was nothing left inside the fuselage as this sheeting effectively seals it off for eternity!

So, how then are we supposed to know how to construct and install properly THE PILOT RELIEF TUBE APPARATUS and misc. related sundries?

nerd

A4 night shootjpeg

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Not got a lot done on the A-4 this past couple of days as minor jobs on other models have taken priority in preparation for the start of the new season... not long now chaps! thumbs up

All there is to show is the 4 x 1/2" balsa laminates have been made up for the nose block as the lite-ply spine profile was susceptible to damage without them - so these were blocked in and 2D rough sanded to profile.

nose block.jpg

The fuselage then took a place at the back of the building board as the Dutch Navy started to fit out its ultimate piston powered fighter with some mud-movers. Bombs Away!!!

bombs away!!.jpg

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Another A-4 delay. disgust

My Jet Provost repair got finished today following its moment of 'extreme mountaineering' last October on the Orme. The wing and fuselage are now all patched up and recovered good as new, but she's gained a couple of ounces and now sports a 'squeeky' aileron which won't quite recentre as the stick is relaxed.

This photo gives us a chance to compare the sizes of the 2016 Mass Build A-4 against the 2014 Mass Build JP.

jp takeover.jpg

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